WO2024195302A1 - Secondary battery - Google Patents

Abstract

Provided is a secondary battery with which it is possible to obtain excellent battery characteristics. This secondary battery comprises a positive electrode, a negative electrode, and an electrolytic solution. In a positive electrode active material of the positive electrode, the lithium carbonate content is 0.2–0.7 wt% inclusive, and the lithium hydroxide content is 0.2–0.7 wt% inclusive. A positive electrode coating film contains nitrogen and boron as constituent elements, an N1s spectrum derived from the nitrogen and a B1s spectrum derived from the boron are obtained by surface analysis of the positive electrode using X-ray photoelectron spectroscopy, a peak position of the N1s spectrum is 395–405 eV inclusive, and a peak position of the B1s spectrum is 188–198 eV inclusive. The electrolyte solution contains an electrolyte salt, and the electrolyte salt contains an anion that is expressed by formula (1).　Formula (1): B (R1) (R2) (R3) CN -

Description

Secondary battery

This technology relates to secondary batteries.

　With the widespread use of a wide variety of electronic devices such as mobile phones, secondary batteries are being developed as a power source that is small, lightweight, and has a high energy density. These secondary batteries contain a liquid electrolyte (electrolytic solution) along with a positive and negative electrode, and various studies are being conducted on the configuration of these secondary batteries.

Specifically, a gel electrolyte containing an electrolytic solution and a polymer compound is used (see, for example, Patent Document 1).

JP 2013-131394 A

Various studies have been conducted on the configuration of secondary batteries, but the battery characteristics of these batteries are still insufficient, leaving room for improvement.

There is a demand for secondary batteries that can provide excellent battery characteristics.

A secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode active material layer including a positive electrode active material, and a positive electrode coating covering the surface of the positive electrode active material layer. The positive electrode active material includes a lithium-containing compound, lithium carbonate, and lithium hydroxide, and the content of lithium carbonate in the positive electrode active material is 0.2% by weight or more and 0.7% by weight or less, and the content of lithium hydroxide in the positive electrode active material is 0.2% by weight or more and 0.7% by weight or less. The positive electrode coating includes nitrogen and boron as constituent elements, and a N1s spectrum derived from nitrogen and a B1s spectrum derived from boron are detected by surface analysis of the positive electrode using X-ray photoelectron spectroscopy, and the peak position of the N1s spectrum is 395 eV or more and 405 eV or less, and the peak position of the B1s spectrum is 188 eV or more and 198 eV or less. The electrolyte solution contains an electrolyte salt, and the electrolyte salt contains an anion represented by formula (1).

B(R1)(R2)(R3)CN ^-... (1)
(R1, R2, and R3 are each any one of a fluorine group, a cyano group, an alkyl group, a fluorinated alkyl group, a fluorinated ester group, and a fluorinated alkoxy group. However, among R1, R2, and R3, At least one of is any one of a fluorine group, a fluorinated alkyl group, a fluorinated ester group, and a fluorinated alkoxy group.

The above-mentioned "lithium-containing compound" is a general term for compounds that contain lithium as a constituent element. Details of lithium-containing compounds will be described later.

The "peak position of the N1s spectrum" mentioned above is the position where the spectral intensity of the N1s spectrum is maximum, and this position is expressed in terms of binding energy (eV). The "peak position of the B1s spectrum" is the position where the spectral intensity of the B1s spectrum is maximum, and this position is expressed in terms of binding energy (eV). Details of the peak positions of the N1s spectrum and the B1s spectrum will be described later.

In a secondary battery according to one embodiment of the present technology, the positive electrode includes a positive electrode active material and a positive electrode coating, the electrolyte includes an electrolyte salt, the positive electrode active material includes a lithium-containing compound, lithium carbonate, and lithium hydroxide, the lithium carbonate content in the positive electrode active material is 0.2% by weight or more and 0.7% by weight or less, the lithium hydroxide content in the positive electrode active material is 0.2% by weight or more and 0.7% by weight or less, the peak position of the N1s spectrum is 395 eV or more and 405 eV or less and the peak position of the B1s spectrum is 188 eV or more and 198 eV or less in a surface analysis of the positive electrode using X-ray photoelectron spectroscopy, and the electrolyte salt includes the anion shown in formula (1), so that excellent battery characteristics can be obtained.

Note that the effects of this technology are not necessarily limited to the effects described here, but may be any of a series of effects related to this technology described below.

FIG. 1 is a perspective view illustrating a configuration of a secondary battery according to an embodiment of the present technology. FIG. 2 is a cross-sectional view showing the configuration of the battery element shown in FIG. FIG. 3 is a plan view showing the configuration of each of the positive electrode and the negative electrode shown in FIG. FIG. 4 is a block diagram showing a configuration of an application example of a secondary battery.

Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The description will be given in the following order.

1. Secondary battery 1-1. Configuration 1-2. Physical properties 1-3. Operation 1-4. Manufacturing method 1-5. Actions and effects 2. Modifications 3. Uses of secondary batteries

<1. Secondary battery>
First, a secondary battery according to an embodiment of the present technology will be described.

The secondary battery described here is a secondary battery that obtains battery capacity by utilizing the absorption and release of electrode reactants, and is equipped with a positive electrode, a negative electrode, and an electrolyte.

The charge capacity of the negative electrode is preferably greater than the discharge capacity of the positive electrode. In other words, the electrochemical capacity per unit area of the negative electrode is preferably greater than the electrochemical capacity per unit area of the positive electrode. This is to prevent electrode reactants from depositing on the surface of the negative electrode during charging.

The type of electrode reactant is not particularly limited, but specifically includes light metals such as alkali metals and alkaline earth metals. Specific examples of alkali metals include lithium, sodium, and potassium, while specific examples of alkaline earth metals include beryllium, magnesium, and calcium.

Below, we will use an example where the electrode reactant is lithium. A secondary battery that obtains battery capacity by utilizing the absorption and release of lithium is known as a lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is absorbed and released in an ionic state.

<1-1. Configuration>
Fig. 1 shows a perspective view of a secondary battery. Fig. 2 shows a cross-sectional view of a battery element 20 shown in Fig. 1. Fig. 3 shows a plan view of each of a positive electrode 21 and a negative electrode 22 shown in Fig. 2.

However, FIG. 1 shows the exterior film 10 and the battery element 20 in a state where they are separated from each other, and the cross section of the battery element 20 along the XZ plane is shown by a dashed line. FIG. 2 shows only a part of the battery element 20. FIG. 3 shows the state where the positive electrode 21 and the negative electrode 22 are not wound.

As shown in Figures 1 and 2, this secondary battery includes an exterior film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and 42.

As described above, the secondary battery described here uses a flexible or pliable exterior film 10 as an exterior member for housing the battery element 20 inside. Therefore, the secondary battery shown in Figures 1 and 2 is a so-called laminate film type secondary battery.

[Exterior film]
1, the exterior film 10 has a bag-like structure that is sealed with the battery element 20 housed therein. As a result, the exterior film 10 houses a positive electrode 21, a negative electrode 22, and a separator 23, which will be described later.

Here, the exterior film 10 is a single film-like member that is folded in the folding direction F. This exterior film 10 is provided with a recessed portion 10U (a so-called deep drawn portion) for accommodating the battery element 20.

Specifically, the exterior film 10 is a three-layer laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside, and when the exterior film 10 is folded, the outer peripheral edges of the opposing fusion layers are fused to each other. The fusion layer contains a polymer compound such as polypropylene. The metal layer contains a metallic material such as aluminum. The surface protection layer contains a polymer compound such as nylon.

However, the configuration (number of layers) of the exterior film 10 is not particularly limited, so it may be one or two layers, or four or more layers.

[Battery element]
The battery element 20 is housed inside the exterior film 10. The battery element 20 is a so-called power generating element, and includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown), as shown in Figures 1 and 2 .

Here, the battery element 20 is a so-called wound electrode body, so that the positive electrode 21 and the negative electrode 22 are wound around the winding axis P while facing each other via the separator 23. This winding axis P is a virtual axis extending in the Y-axis direction, as shown in FIG. 1.

The three-dimensional shape of the battery element 20 is not particularly limited. Here, the battery element 20 has a flat three-dimensional shape, so that the shape of the cross section (cross section along the XZ plane) of the battery element 20 intersecting the winding axis P is a flat shape defined by the major axis J1 and the minor axis J2.

The long axis J1 is an imaginary axis extending in the X-axis direction and has a length greater than that of the short axis J2. The short axis J2 is an imaginary axis extending in the Z-axis direction intersecting the X-axis direction and has a length less than that of the long axis J1. Here, the three-dimensional shape of the battery element 20 is a flattened cylinder, and therefore the cross-sectional shape of the battery element 20 is a flattened, approximately elliptical shape.

(Positive electrode)
As shown in FIG. 2, the positive electrode 21 includes a positive electrode current collector 21A, a positive electrode active material layer 21B, and a positive electrode coating 21C.

The positive electrode collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is provided. This positive electrode collector 21A contains a conductive material such as a metal material, and a specific example of the conductive material is aluminum.

The positive electrode active material layer 21B contains one or more types of positive electrode active materials that absorb and release lithium. However, the positive electrode active material layer 21B may further contain one or more types of other materials such as a positive electrode binder and a positive electrode conductor. The method of forming the positive electrode active material layer 21B is not particularly limited, but specifically includes a coating method.

Here, the positive electrode active material layer 21B is provided on both sides of the positive electrode collector 21A. However, the positive electrode active material layer 21B may be provided on only one side of the positive electrode collector 21A on the side where the positive electrode 21 faces the negative electrode 22.

The positive electrode active materials include lithium-containing compounds, lithium _carbonate ( _Li2CO3 ) and lithium hydroxide (LiOH).

As mentioned above, lithium-containing compounds are a general term for compounds that contain lithium as a constituent element, and absorb and release lithium. There may be only one type of lithium-containing compound, or two or more types. There is no particular limit to the average particle size (median diameter) of the lithium-containing compound, and it can be set as desired.

Lithium carbonate and lithium hydroxide are components that are formed unintentionally during the manufacturing process of lithium-containing compounds and therefore remain in the lithium-containing compounds. Hereinafter, lithium carbonate and lithium hydroxide will be collectively referred to as "residual lithium components." These residual lithium components are unnecessary components that end up in lithium-containing compounds due to reasons related to the manufacturing process, and are a factor in degrading the battery characteristics of secondary batteries.

For this reason, the content (remaining amount) of the residual lithium component is set to be sufficiently small within a range that can guarantee the battery characteristics of the secondary battery. Specifically, the content of lithium carbonate in the positive electrode active material is 0.2% to 0.7% by weight, and the content of lithium hydroxide in the positive electrode active material is 0.2% to 0.7% by weight.

The content of the residual lithium component is within the above range because the surface state of the positive electrode active material, i.e., the element distribution on the surface of the lithium-containing compound, is optimized. Specifically, on the surface of the lithium-containing compound, the occupancy ratio of the constituent elements of the lithium-containing compound becomes sufficiently large relative to the occupancy ratio of the constituent elements of the residual lithium component. This makes it easier for lithium ions to be input and output in the lithium-containing compound while suppressing the generation of gas due to the presence of the residual lithium component, and makes it difficult for the electrolyte to decompose on the surface of the lithium-containing compound. In this case, the above-mentioned advantages can be stably obtained even when the secondary battery is used (charged and discharged) or stored in harsh environments such as high-temperature or low-temperature environments.

The residual lithium content can be measured using the Warder method according to the procedure described below.

First, a predetermined amount (Sg) of the positive electrode active material is weighed, and then the positive electrode active material is placed in a sample bottle. Here, S=10 (g). Next, ultrapure water (50 ml=50 cm ³ ) is put into the sample bottle together with a stirring bar, and then the ultrapure water is stirred (stirring time=1 hour) using a stirrer. Next, the ultrapure water after stirring is allowed to stand (standing time=1 hour), and the supernatant of the ultrapure water is collected using a syringe with a filter, and then the supernatant is filtered. Next, the supernatant after filtration (10 ml=10 cm ³ ) is collected using a volumetric pipette, and then the supernatant is placed in a stoppered Erlenmeyer flask.

Next, one drop of phenolphthalein solution is added to the supernatant, and while stirring the supernatant with a stirrer, titration is performed using a titration solution (hydrochloric acid (HCl) having a concentration M) until the color of the liquid (red) disappears, and the amount of hydrochloric acid added (A ml = A cm ³ ) is read. Here, the concentration M = 0.02 mol/l (= 0.02 mol/dm ³ ). Next, two drops of bromophenol blue solution are added to the supernatant, and while stirring the supernatant with a stirrer, titration is performed using the titration solution described above until the color of the liquid changes from blue to yellow-green (the blue color disappears), and the amount of hydrochloric acid added (B ml = B cm ³ ) is read. As the titration device, an automatic titration device COM-1600 manufactured by Hiranuma Sangyo Co., Ltd. can be used.

Finally, the lithium carbonate content (wt%) is calculated using the calculation formula represented by formula (11), and the lithium hydroxide content (wt%) is calculated using the calculation formula represented by formula (12).

Lithium carbonate content (wt%)=[(M×2B×(f/1000)×0.5×73.892×5)/S]×100 (11)
(S is the weight (g) of the positive electrode active material. B is the amount of dropping (ml = cm ³ ) from the end point of the first drop using the phenolphthalein solution to the end point of the second drop using the bromophenol blue solution. f is a factor that depends on the concentration of the titration solution. M is the concentration of the titration solution (mol/l = mol/dm ³ ).)

Lithium hydroxide content (wt%)=[(M×(A−B)×(f/1000)×23.941×5)/S]×100 (12)
(S is the weight (g) of the positive electrode active material. A is the amount (ml = cm ³ ) of the first drop to the end point using the phenolphthalein solution. B is the amount (ml = cm ³ ) of the second drop from the end point using the phenolphthalein solution to the end point using the bromophenol blue solution. f is a factor that depends on the concentration of the titration solution. M is the concentration of the titration solution (mol/l = mol/dm ³ ).)

Specifically, a lithium-containing compound is a compound that contains lithium as well as one or more transition metal elements as constituent elements, and may further contain one or more other elements as constituent elements. There are no particular limitations on the type of other element, so long as it is an element other than lithium and a transition metal element, but specifically, it is an element belonging to Groups 2 to 15 of the long period periodic table.

Among them, it is preferable that the lithium-containing compound contains one or both of the first lithium composite oxide represented by formula (2) and the second lithium composite oxide represented by formula (3). This is because a high voltage can be obtained.

Li _x Ni _1-y M1 _y O _2-a X1 _b ...(2)
(M1 is Co, Mn, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta and rare earth elements. X1 is at least one of F, Cl, Cr, I, P, S and Si. x, y, a and b are in the range of 0.9≦x≦1 .1, 0.005≦y≦0.5, -0.1≦a≦0.2, and 0≦b≦0.1 are satisfied.)

Li _x Mn _1-xyz Ni _y M2 _z O _2-a X2 _b ...(3)
(M2 is selected from Co, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta and rare earth elements. X2 is at least one of F, Cl, Cr, I, P, S and Si. x, y, a and b are each 0<x≦0.3, 0 .3≦y≦0.9, 0≦z≦0.5, -0.1≦a≦0.2, and 0≦b≦0.1 are satisfied.)

As is clear from formula (2), the first lithium composite oxide is a two-element composite oxide that _{may contain} two or more major elements (Ni and M1) as constituent elements _together with lithium. A specific example of the first lithium composite oxide is _{LiNi0.82Co0.14Al0.04O2} .

As is clear from formula (3), the second lithium composite oxide is a three-element _composite oxide _that may contain lithium as well as three or more major elements _{( Mn} , _Ni , and M2 ₎ as constituent elements. Specific examples of the _second lithium _composite oxide _{include LiMn0.30Ni0.50Co0.20O2} , _{LiMn0.33Ni0.33Co0.33Al0.01O2} , _{and LiMn0.04Ni0.87Co0.08Al0.01O2 .}

The positive electrode active material may further contain one or more of the other lithium-containing compounds. The type of the other lithium-containing compound is not particularly limited, but specific examples include oxides, phosphate compounds, silicate compounds, and borate compounds. However, the first lithium composite oxide and the second lithium composite oxide described above are excluded from the oxides described here.

Specific examples of oxides include _LiNiO2 , _{LiCoO2 , and LiMn2O4} . Specific examples of phosphate compounds include _LiFePO4 , _{LiMnPO4 , LiFe0.5Mn0.5PO4 ,} and _{LiFe0.3Mn0.7PO4 .}

The positive electrode binder contains one or more of the following materials: synthetic rubber, polymeric compound, etc. Specific examples of synthetic rubber include styrene butadiene rubber, fluororubber, and ethylene propylene diene. Specific examples of polymeric compounds include polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

The positive electrode conductive agent contains one or more conductive materials such as carbon materials, metal materials, and conductive polymer compounds. Specific examples of carbon materials include graphite, carbon black, acetylene black, and ketjen black.

The positive electrode coating 21C is provided on the surface of the positive electrode active material layer 21B, and therefore covers the surface of the positive electrode active material layer 21B.

Here, the positive electrode coating 21C covers the entire surface of the positive electrode active material layer 21B. However, the positive electrode coating 21C may cover only a portion of the surface of the positive electrode active material layer 21B. In this case, multiple positive electrode coatings 21C spaced apart from each other may cover the surface of the positive electrode active material layer 21B.

This positive electrode coating 21C is formed on the surface of the positive electrode active material layer 21B using a stabilization process for the secondary battery after assembly, and contains nitrogen and boron as constituent elements. The composition of the positive electrode coating 21C is not particularly limited as long as it contains nitrogen and boron as constituent elements.

As described below, the electrolyte contains boron-nitrogen-containing lithium as an electrolyte salt. As a result, during the stabilization process of the secondary battery after assembly, the boron-nitrogen-containing lithium contained in the electrolyte decomposes and reacts, forming a positive electrode coating 21C on the surface of the positive electrode active material layer 21B.

Therefore, the positive electrode coating 21C contains nitrogen and boron derived from the nitrogen-boron-containing lithium as constituent elements. In other words, the nitrogen-boron-containing lithium is the source of the nitrogen and boron contained as constituent elements in the positive electrode coating 21C, and details of the nitrogen-boron-containing lithium will be described later.

In this secondary battery, certain conditions are met regarding the physical properties of the positive electrode 21 (positive electrode coating 21C). Details of the physical properties of the positive electrode 21 will be described later.

Here, as shown in FIG. 3, the positive electrode active material layer 21B is provided on a portion of the surface of the positive electrode collector 21A, and more specifically, it is provided in the central region in the longitudinal direction (left-right direction in FIG. 3) of the positive electrode collector 21A. As a result, when the positive electrode 21 includes a positive electrode coating 21C, the positive electrode coating 21C is provided in the central region in the longitudinal direction of the positive electrode collector 21A, similar to the positive electrode active material layer 21B. Note that in FIG. 3, the positive electrode active material layer 21B and the positive electrode coating 21C are shaded.

(Negative electrode)
As shown in FIG. 2, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B.

The negative electrode current collector 22A has a pair of surfaces on which the negative electrode active material layer 22B is provided. This negative electrode current collector 22A contains a conductive material such as a metal material, and a specific example of the conductive material is copper.

The negative electrode active material layer 22B contains one or more types of negative electrode active materials that absorb and release lithium. However, the negative electrode active material layer 22B may further contain one or more types of other materials such as a negative electrode binder and a negative electrode conductor. The method of forming the negative electrode active material layer 22B is not particularly limited, but specifically includes one or more types of a coating method, a gas phase method, a liquid phase method, a thermal spraying method, and a firing method (sintering method).

Here, the negative electrode active material layer 22B is provided on both sides of the negative electrode collector 22A. However, the negative electrode active material layer 22B may be provided on only one side of the negative electrode collector 22A on the side where the negative electrode 22 faces the positive electrode 21.

The type of negative electrode active material is not particularly limited, but specific examples include carbon materials and metal-based materials, because they provide high energy density.

Specific examples of carbon materials include graphitizable carbon, non-graphitizable carbon, and graphite. The graphite may be natural graphite or artificial graphite.

Metallic materials are a general term for materials that contain one or more of metallic elements and semi-metallic elements that can form an alloy with lithium as constituent elements, and specific examples of the metallic elements and semi-metallic elements include silicon and tin. The metallic materials may be a single element, an alloy, a compound, a mixture of two or more of these, or a material that contains two or more of these phases. Specific examples of metallic materials include _TiSi2 and _SiOx (0<x≦2 or 0.2<x<1.4).

Details regarding the negative electrode binder are the same as those regarding the positive electrode binder, and details regarding the negative electrode conductor are the same as those regarding the positive electrode conductor.

The negative electrode 22 may further include a negative electrode coating 22C. This negative electrode coating 22C is provided on the surface of the negative electrode active material layer 22B, and therefore covers the surface of the negative electrode active material layer 22B. Figure 2 shows the case where the negative electrode 22 includes the negative electrode coating 22C.

Here, the anode coating 22C covers the entire surface of the anode active material layer 22B. However, the anode coating 22C may cover only a portion of the surface of the anode active material layer 22B. In this case, a plurality of anode coatings 22C spaced apart from one another may cover the surface of the anode active material layer 22B.

This negative electrode coating 22C, like the positive electrode coating 21C, is formed on the surface of the negative electrode active material layer 22B using a stabilization treatment for the secondary battery after assembly, and contains nitrogen and boron as constituent elements. Note that the composition of the negative electrode coating 22C is not particularly limited as long as it contains nitrogen and boron as constituent elements.

As described below, the electrolyte contains boron-nitrogen-containing lithium as an electrolyte salt, and the details regarding the boron-nitrogen-containing lithium are as described above. As a result, during the stabilization process of the secondary battery after assembly, the boron-nitrogen-containing lithium contained in the electrolyte decomposes and reacts, forming a negative electrode coating 22C on the surface of the negative electrode active material layer 22B.

Therefore, the negative electrode coating 22C, like the positive electrode coating 21C, contains nitrogen and boron derived from the nitrogen-boron-containing lithium as constituent elements. In other words, the nitrogen-boron-containing lithium is the source of the nitrogen and boron contained as constituent elements in the negative electrode coating 22C, and details of the nitrogen-boron-containing lithium will be described later.

In this secondary battery, it is preferable that the physical properties of the negative electrode 22 (negative electrode coating 22C) satisfy certain conditions. The physical properties of the negative electrode 22 will be described in detail later.

Here, as shown in FIG. 3, the negative electrode active material layer 22B is provided on the entire surface of the negative electrode collector 22A, more specifically, on the entire area in the longitudinal direction (left-right direction in FIG. 3) of the negative electrode collector 22A. As a result, the negative electrode coating 22C, like the negative electrode active material layer 22B, is provided on the entire area in the longitudinal direction of the negative electrode collector 22A. Note that in FIG. 3, the negative electrode active material layer 22B and the negative electrode coating 22C are shaded.

The negative electrode 22 therefore includes one facing portion R1 and two non-facing portions R2. The facing portion R1 is a portion involved in the charge/discharge reaction because the negative electrode active material layer 22B faces the positive electrode active material layer 21B. In contrast, the non-facing portion R2 is a portion that is not substantially involved in the charge/discharge reaction because the negative electrode active material layer 22B does not face the positive electrode active material layer 21B. Here, the facing portion R1 is disposed between the two non-facing portions R2.

(Separator)
2, the separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, and allows lithium to pass through in an ion state while preventing the occurrence of a short circuit due to contact between the positive electrode 21 and the negative electrode 22. This separator 23 contains a polymer compound such as polyethylene.

(Electrolyte)
The electrolyte is a liquid electrolyte. The electrolyte is impregnated into each of the positive electrode 21, the negative electrode 22, and the separator 23, and contains an electrolyte salt. Here, the electrolyte further contains a solvent that disperses (ionizes) the electrolyte salt.

Electrolyte salts are compounds that ionize in a solvent and contain anions and cations.

Specifically, the electrolyte salt contains one or more of the anions represented by formula (1). Hereinafter, the anion shown in formula (1) is referred to as a nitrogen-boron-containing anion. In other words, the electrolyte salt contains a nitrogen-boron-containing anion as the anion.

B(R1)(R2)(R3)CN ^-... (1)
(R1, R2, and R3 are each any one of a fluorine group, a cyano group, an alkyl group, a fluorinated alkyl group, a fluorinated ester group, and a fluorinated alkoxy group. However, among R1, R2, and R3, At least one of is any one of a fluorine group, a fluorinated alkyl group, a fluorinated ester group, and a fluorinated alkoxy group.

The nitrogen-boron-containing anion is an anion that contains nitrogen and boron as constituent elements. The reason why the electrolyte salt contains the nitrogen-boron-containing anion is as follows. First, the electrolyte salt serves as a source of nitrogen and boron during the stabilization process of the secondary battery after assembly, which makes it easier to form the positive electrode coating 21C that contains the nitrogen and boron as constituent elements. This suppresses the decomposition reaction of the electrolyte (particularly the solvent). Second, the positive electrode coating 21C is used to improve the migration speed of cations near the surface of the positive electrode 21. Third, the migration speed of cations is improved even in the electrolyte solution.

If the negative electrode 22 includes the negative electrode coating 22C, the negative electrode coating 22C is also easily formed, providing the same advantages as those described for the positive electrode coating 21C.

As described above, each of R1, R2, and R3 is not particularly limited as long as it is any one of a fluorine group, a cyano group, an alkyl group, a fluorinated alkyl group, a fluorinated ester group, and a fluorinated alkoxy group. However, one or more of R1, R2, and R3 is a group containing fluorine as a constituent element, and more specifically, any one of a fluorine group, a fluorinated alkyl group, a fluorinated ester group, and a fluorinated alkoxy group.

The number of carbon atoms in the alkyl group is not particularly limited, and specific examples of the alkyl group include methyl, ethyl, propyl, and butyl groups. However, the alkyl group may be either linear or branched.

A fluorinated alkyl group is an alkyl group in which one or more hydrogen groups have been replaced by a fluorine group. Specific examples of fluorinated alkyl groups include perfluoromethyl group ( _-CF3 ), _{perfluoroethyl} group ( _{-C2F5 )} , perfluoropropyl group ( _-C3F7 ) and _{perfluorobutyl} group ( _-C4F9 ).

The fluorinated ester group is a group represented by formula (4). Details regarding the fluorinated alkyl group are as described above. Specific examples of the fluorinated aryl group include a perfluorophenyl group (-C ₆ F ₅ ) and a perfluoronaphthyl group (-C ₁₀ F ₇ ).

-C(=O)-O-R4...(4)
(R4 is either a fluorinated alkyl group or a fluorinated aryl group.)

Specific examples of fluorinated ester groups include -C(=O)-O-CF ₃ , -C(=O)-O-C ₂ F ₅ and -C(=O)-O-C ₆ F ₅ .

The fluorinated alkoxy group is a group represented by formula (5). Details of the alkyl group, fluorinated alkyl group, and fluorinated aryl group are as described above. Specific examples of the aryl group include a phenyl group ( _{-C6H5 )} and a naphthyl group ( _{-C10H7 )} .

-OC(R5)(R6)(R7)...(5)
(Each of R5, R6 and R7 is any one of a hydrogen group, an alkyl group, an aryl group, a fluorinated alkyl group and a fluorinated aryl group. However, at least one of R5, R6 and R7 is , a fluorinated alkyl group, or a fluorinated aryl group.

As described above, R5, R6 and R7 are not particularly limited as long as they are any of a hydrogen group, an alkyl group, an aryl group, a fluorinated alkyl group and a fluorinated aryl group. However, one or more of R5, R6 and R7 are groups containing fluorine as a constituent element, and more specifically, are any of a fluorinated alkoxy group and a fluorinated aryl group.

Specific examples of fluorinated alkoxy groups include, -O- _CH2 ( _CF3 ), -O- _CH2 ( _C2F5 ), -O-CH( _CF3 ) ₂ , -O-CH( _C2F5 ) ₂ , -O _- C( _CF3 ) ₃ , -O-C _{( C2F5} ) ₃ , -O-C( _CH3 )( _CF3 ) ₂ , -O _- C( _CH3 ) _{( C2F5} )2, -O-C( _C6H5 )( _CF3 ) ₂ and -O _- C _{( C6H5 ) (C2F5 ) 2} .

Specific examples of nitrogen ^- containing boron anions are _BF3CN- , BF2( _CH3 ⁾ CN-, _BF2 ( _CF3 ) ^CN- , _BF2 ⁽ CN) _2- ^, _BF (CF3) _2CN- , BF( _C2F5 ⁾ _2CN- , BF(CN) _3- , BF( _CF3 ⁾ (CN) _2- , BF( _C2F5 )( _CN ⁾ _2- , B( ^{CF3)3CN-, B(CF3)2(CN)2- ,} _{B ( C2F5 )} ^3CN- _{, B(C2F5)2 (} ^CN _{) 2- ,} ^B _{( CF3 ) ( CN} ) _{. 3} ^- , B (CF ₃ ) ₂ (CN) ₂ ^-
, B( _{C2F5 )} (CN) _3- and B( _{C2F5 ) 2} ( ^{CN )} _2- .

Although not specifically listed here, specific examples of nitrogen-boron-containing anions may be anions in which one or more of R1, R2, and R3 are fluorinated ester groups, or anions in which one or more of R1, R2, and R3 are fluorinated alkoxy groups.

The type of cation is not particularly limited. Specifically, the cation contains one or more types of light metal ions. In other words, the electrolyte salt contains light metal ions as cations. This is because a high voltage can be obtained.

The type of light metal ion is not particularly limited, but specific examples include alkali metal ions and alkaline earth metal ions. Specific examples of alkali metal ions include lithium ions, sodium ions, and potassium ions. Specific examples of alkaline earth metal ions include beryllium ions, magnesium ions, and calcium ions. In addition, the light metal ion may be an aluminum ion, etc.

As mentioned above, it is preferable that the light metal ions contain lithium ions, since this allows a sufficiently high voltage to be obtained.

In the following, an electrolyte salt that contains lithium ions as cations and nitrogen-boron-containing anions as anions is referred to as nitrogen-boron-containing lithium.

The content of the electrolyte salt in the electrolyte solution is not particularly limited, but it is preferably 0.5 mol/kg to 2 mol/kg relative to the solvent. This is because high ionic conductivity can be obtained.

The solvent contains one or more types of non-aqueous solvents (organic solvents), and an electrolyte containing such a non-aqueous solvent is a so-called non-aqueous electrolyte. This is because it improves the dissociation of the electrolyte salt and the mobility of the ions.

This non-aqueous solvent contains esters and ethers, and more specifically, contains one or more of carbonate ester compounds, carboxylate ester compounds, and lactone compounds.

The carbonate ester compounds include cyclic carbonate esters and chain carbonate esters. Specific examples of cyclic carbonate esters include ethylene carbonate and propylene carbonate. Specific examples of chain carbonate esters include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The carboxylate ester compounds include chain carboxylate esters, and specific examples of chain carboxylate esters include ethyl acetate, ethyl propionate, propyl propionate, and ethyl trimethylacetate. The lactone compounds include lactones, and specific examples of lactones include γ-butyrolactone and γ-valerolactone. The ethers may be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane.

The electrolyte may further contain one or more of the other solvents. Specific examples of the other solvents include unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonic acid esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfates, nitrile compounds, and isocyanate compounds. This is because the electrochemical stability of the electrolyte is improved.

Unsaturated cyclic carbonates are cyclic carbonates that contain unsaturated carbon bonds (carbon-carbon double bonds). The number of unsaturated carbon bonds is not particularly limited, and may be one or two or more. Specific examples of unsaturated cyclic carbonates include vinylene carbonate, vinylethylene carbonate, and methyleneethylene carbonate.

Fluorinated cyclic carbonates are cyclic carbonates that contain fluorine as a constituent element. In other words, fluorinated cyclic carbonates are compounds in which one or more hydrogen groups of a cyclic carbonate are replaced with fluorine groups. Specific examples of fluorinated cyclic carbonates include monofluoroethylene carbonate and difluoroethylene carbonate.

Sulfonic acid esters include cyclic monosulfonic acid esters, cyclic disulfonic acid esters, linear monosulfonic acid esters, and linear disulfonic acid esters. Specific examples of cyclic monosulfonic acid esters include 1,3-propane sultone, 1-propene-1,3-sultone, 1,4-butane sultone, 2,4-butane sultone, and methanesulfonic acid propargyl ester. Specific examples of cyclic disulfonic acid esters include cyclodisone.

Specific examples of dicarboxylic acid anhydrides include succinic anhydride, glutaric anhydride, and maleic anhydride.

Specific examples of disulfonic anhydrides include ethanedisulfonic anhydride and propanedisulfonic anhydride.

Specific examples of sulfate esters include ethylene sulfate (1,3,2-dioxathiolane 2,2-dioxide).

A nitrile compound is a compound that contains one or more cyano groups (-CN). Specific examples of nitrile compounds include octanenitrile, benzonitrile, phthalonitrile, succinonitrile, glutaronitrile, adiponitrile, sebaconitrile, 1,3,6-hexanetricarbonitrile, 3,3'-oxydipropionitrile, 3-butoxypropionitrile, ethylene glycol bispropionitrile ether, 1,2,2,3-tetracyanopropane, tetracyanopropane, fumaronitrile, 7,7,8,8-tetracyanoquinodimethane, cyclopentanecarbonitrile, 1,3,5-cyclohexanetricarbonitrile, and 1,3-bis(dicyanomethylidene)indane.

An isocyanate compound is a compound that contains one or more isocyanate groups (-NCO). A specific example of an isocyanate compound is hexamethylene diisocyanate.

The electrolyte may further contain one or more of other electrolyte salts. Specific examples of other electrolyte salts include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bis(fluorosulfonyl)imide (LiN(FSO ₂ ) ₂ ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF ₃ SO ₂ ) ₂ ), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF ₃ SO ₂ ) ₃ ), lithium bis(oxalato)borate (LiB(C ₂ O ₄ ) ₂ ), lithium monofluorophosphate (Li ₂ PFO ₃ ), and lithium difluorophosphate (LiPF ₂ O ₂ ). This is because a high battery capacity can be obtained.

Among them, it is preferable that the other electrolyte salt contains one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, and lithium difluorophosphate. This is because the migration speed of cations is sufficiently improved near the surfaces of the positive electrode 21 and the negative electrode 22, and the migration speed of cations is also sufficiently improved in the electrolyte solution.

The method for analyzing the electrolyte is not particularly limited, but specifically includes one or more of the following: inductively coupled plasma (ICP) optical emission spectroscopy, nuclear magnetic resonance spectroscopy (NMR), and gas chromatography-mass spectrometry (GC-MS).

When analyzing the electrolyte, the secondary battery is disassembled to recover the electrolyte, which is then analyzed. This identifies the type of electrolyte salt and the amount of electrolyte salt contained in the electrolyte. In addition, the type of solvent is identified and the amount of solvent contained in the electrolyte is also identified.

[Positive lead]
1 and 2, the positive electrode lead 31 is a positive electrode wiring connected to the positive electrode current collector 21A of the positive electrode 21, and is led out of the exterior film 10. The positive electrode lead 31 contains a conductive material such as a metal material, and a specific example of the conductive material is aluminum. The shape of the positive electrode lead 31 is either a thin plate shape or a mesh shape.

[Negative lead]
As shown in Fig. 1 and Fig. 2, the negative electrode lead 32 is a negative electrode wiring connected to the negative electrode current collector 22A of the negative electrode 22, and is led out to the outside of the exterior film 10. Here, the lead-out direction of the negative electrode lead 32 is the same as the lead-out direction of the positive electrode lead 31. This negative electrode lead 32 contains a conductive material such as a metal material, and a specific example of the conductive material is copper. The details of the shape of the negative electrode lead 32 are the same as the details of the shape of the positive electrode lead 31.

[Sealing film]
The sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

The sealing film 41 is a sealing member that prevents outside air and the like from entering the inside of the exterior film 10. This sealing film 41 contains a polymer compound such as polyolefin that has adhesion to the positive electrode lead 31, and a specific example of the polymer compound is polypropylene.

The configuration of the sealing film 42 is the same as that of the sealing film 41, except that the sealing film 42 is a sealing member that has adhesion to the negative electrode lead 32. In other words, the sealing film 42 contains a polymer compound such as polyolefin that has adhesion to the negative electrode lead 32.

<1-2. Physical properties>
As described above, in this secondary battery, the positive electrode 21 (positive electrode coating 21C) satisfies predetermined conditions (physical property conditions) regarding the physical properties thereof.

[Physical properties]
Specifically, as described above, the positive electrode 21 includes the positive electrode coating 21C that coats the surface of the positive electrode active material layer 21B, and the positive electrode coating 21C includes nitrogen and boron as constituent elements. Therefore, when the surface of the positive electrode 21 (positive electrode coating 21C) is analyzed (elemental analysis) using X-ray photoelectron spectroscopy (XPS), a photoelectron spectrum (horizontal axis is binding energy (eV) and vertical axis is spectrum intensity) is obtained. This photoelectron spectrum includes two types of photoelectron spectra derived from the constituent elements of the positive electrode coating 21C, and the two types of photoelectron spectra are an N1s spectrum derived from nitrogen and a B1s spectrum derived from boron.

In this case, the physical properties of the positive electrode 21 satisfy the physical property conditions as described above. Specifically, the peak position N of the N1s spectrum is between 395 eV and 405 eV, and the peak position B of the B1s spectrum is between 188 eV and 198 eV.

Here, as described above, the "peak position N of the N1s spectrum" is the position where the spectral intensity of the N1s spectrum is maximum, and this position is expressed in terms of binding energy (eV). Therefore, "peak position N is 395 eV to 405 eV" means that the spectral intensity of the N1s spectrum is maximum within the range of binding energies from 395 eV to 405 eV.

Similarly, as described above, "peak position B of the B1s spectrum" is the position where the spectral intensity of the B1s spectrum is maximum, and this position is expressed in terms of binding energy (eV). Therefore, "peak position B is 188 eV to 198 eV" means that the spectral intensity of the B1s spectrum is maximum within the binding energy range of 188 eV to 198 eV.

The physical properties of the positive electrode 21 satisfy the physical property conditions because the electrochemical state of the positive electrode coating 21C is optimized, thereby suppressing deterioration of the battery characteristics.

In more detail, the positive electrode active material layer 21B contains a highly reactive positive electrode active material, and when the positive electrode active material is activated during charging and discharging, the positive electrode active material is more likely to react with the electrolyte. When the positive electrode active material reacts with the electrolyte, the decomposition reaction of the electrolyte is accelerated, and the battery characteristics are more likely to deteriorate.

However, when the positive electrode coating 21C is provided on the surface of the positive electrode active material layer 21B and the physical property conditions for the positive electrode 21 (positive electrode coating 21C) are satisfied, the electrochemical state of the positive electrode coating 21C is optimized. As a result, the surface of the positive electrode active material layer 21B is protected using the electrochemically stable positive electrode coating 21C, and the decomposition reaction of the electrolyte caused by the reaction between the positive electrode active material and the electrolyte is suppressed. Moreover, even if the positive electrode coating 21C is provided on the surface of the positive electrode active material layer 21B, smooth occlusion and release of cations in the positive electrode active material layer 21B (positive electrode active material) is guaranteed. Therefore, the decomposition reaction of the electrolyte is suppressed while smooth occlusion and release of cations in the positive electrode active material layer 21B is guaranteed, and deterioration of the battery characteristics is suppressed.

In addition, when the negative electrode 22 includes the negative electrode coating 22C, the above physical property conditions may be satisfied for the physical properties of the negative electrode 22 (negative electrode coating 22C) as well. That is, in the surface analysis of the negative electrode 22 (negative electrode coating 22C) using XPS, it is preferable that the peak position N of the N1s spectrum is 395 eV to 405 eV and the peak position B of the B1s spectrum is 188 eV to 198 eV. This optimizes the electrochemical state of the negative electrode coating 22C, thereby ensuring smooth occlusion and release of cations in the negative electrode active material layer 221B and suppressing the decomposition reaction of the electrolyte. Therefore, deterioration of the battery characteristics is suppressed.

[Analysis Procedure]
When performing a surface analysis of the positive electrode 21, first, the secondary battery is discharged until the voltage reaches 2.5 V, and then the secondary battery is disassembled inside a glove box (in an inert atmosphere) to recover the positive electrode 21. The type of inert atmosphere is not particularly limited, but specifically, it is an atmosphere using an inert gas such as argon gas. Next, the positive electrode 21 is washed using an organic solvent, and then the washed positive electrode 21 is introduced into an analysis device (XPS device) without being exposed to the air. The type of organic solvent is not particularly limited, but specifically, it is dimethyl carbonate, etc. Finally, the positive electrode 21 is analyzed using an XPS device.

As an XPS device, an X-ray photoelectron spectrometer Quantera SXM manufactured by ULVAC-PHI, Inc. can be used. The analysis conditions are as follows: incident X-ray = monochromated AlKα ray (1486.6 eV), analysis area (beam size) = 100 μmφ, analysis depth = several nm.

In this case, the F1s spectrum derived from fluorine is used to perform energy correction of the photoelectron spectrum. Specifically, waveform analysis is performed using commercially available software to determine the position (binding energy) of the main peak located on the lowest binding energy side of the F1s spectrum to be 685.1 eV.

To identify the peak position N, a photoelectron spectrum (N1s spectrum) is obtained, and then the binding energy at the position where the spectral intensity of the N1s spectrum is maximum is examined.

To identify peak position B, a photoelectron spectrum (B1s spectrum) is obtained, and then the binding energy at the position where the spectral intensity of the B1s spectrum is maximum is examined.

The procedure for performing the surface analysis of the negative electrode 22 is similar to the procedure for performing the surface analysis of the positive electrode 21 described above, except that the negative electrode 22 is recovered from the secondary battery instead of the positive electrode 21.

When checking whether the physical property conditions are satisfied for the negative electrode 22, it is preferable to analyze the non-facing portion R2 of the negative electrode 22 as shown in FIG. 3. As described above, the non-facing portion R2 is a portion that is not substantially involved in the charge/discharge reaction, and therefore it is possible to accurately and reproducibly check whether the physical property conditions are satisfied, regardless of the charge/discharge history (presence or absence of charge/discharge and the number of times, etc.).

<1-3. Operation>
This secondary battery operates in the battery element 20 as follows.

When charging, lithium is released from the positive electrode 21 and is absorbed into the negative electrode 22 via the electrolyte. When discharging, lithium is released from the negative electrode 22 and is absorbed into the positive electrode 21 via the electrolyte. When discharging and charging, lithium is absorbed and released in an ionic state.

<1-4. Manufacturing method＞
When manufacturing a secondary battery, the secondary battery is assembled according to the procedure described below as an example, and then a stabilization process is performed on the assembled secondary battery.

[Preparation of Positive Electrode]
First, a positive electrode active material containing a lithium-containing compound, a positive electrode binder, and a positive electrode conductive agent are mixed together to prepare a positive electrode mixture. As described above, this positive electrode active material contains lithium carbonate and lithium hydroxide together with the lithium-containing compound due to the manufacturing reasons of the lithium-containing compound. Then, the positive electrode mixture is put into a solvent to prepare a paste-like positive electrode mixture slurry. This solvent may be an aqueous solvent or an organic solvent.

Then, the cathode mixture slurry is applied to both sides of the cathode current collector 21A to form the cathode active material layer 21B. After this, the cathode active material layer 21B may be compression molded using a roll press or the like. In this case, the cathode active material layer 21B may be heated, or the compression molding of the cathode active material layer 21B may be repeated multiple times. Finally, as described below, after assembling the secondary battery, a stabilization process is performed using the assembled secondary battery. As a result, a cathode coating 21C is formed on the surface of the cathode active material layer 21B, and the cathode 21 is produced.

[Preparation of negative electrode]
The negative electrode 22 is formed by the same procedure as the procedure for preparing the positive electrode 21 described above. Specifically, first, a mixture (negative electrode mixture) in which the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent are mixed together is put into a solvent to prepare a paste-like negative electrode mixture slurry. Details regarding the solvent are as described above. Next, the negative electrode mixture slurry is applied to both sides of the negative electrode current collector 22A to form the negative electrode active material layer 22B. After this, the negative electrode active material layer 22B may be compression molded. Finally, after assembling the secondary battery, a stabilization process is performed using the assembled secondary battery. As a result, the negative electrode coating 22C is formed on the surface of the negative electrode active material layer 22B, and the negative electrode 22 is prepared.

[Preparation of electrolyte solution]
An electrolyte salt containing nitrogen-boron-containing anions is added to a solvent. In this case, other solvents may be added to the solvent, or other electrolyte salts may be added to the solvent. This causes the electrolyte salt to be dispersed or dissolved in the solvent, thereby preparing an electrolyte solution.

[Assembly of secondary battery]
First, the positive electrode lead 31 is connected to the positive electrode collector 21A of the positive electrode 21 using a joining method such as welding, and the negative electrode lead 32 is connected to the negative electrode collector 22A of the negative electrode 22 using a joining method such as welding.

Then, the positive electrode collector 21A on which the positive electrode active material layer 21B is formed and the negative electrode collector 22A on which the negative electrode active material layer 22B is formed are stacked together with the separator 23 interposed therebetween to form a laminate (not shown). The laminate is then wound to produce a wound body (not shown), and the wound body is then pressed using a press or the like to form the wound body into a flat shape. The wound body after this formation has a configuration similar to that of the battery element 20, except that it does not include the positive electrode coating 21C and the negative electrode coating 22C, and is not impregnated with an electrolyte.

Then, after the roll is placed inside the recess 10U, the exterior film 10 (adhesive layer/metal layer/surface protection layer) is folded so that the exterior films 10 face each other. Next, the outer edges of two of the opposing adhesive layers are joined to each other using an adhesive method such as heat fusion, thereby placing the roll inside the bag-shaped exterior film 10.

Finally, after injecting the electrolyte into the bag-shaped exterior film 10, the outer edges of the remaining sides of the opposing fusion layers are joined together using an adhesive method such as heat fusion. In this case, a sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32.

As a result, the wound body is impregnated with the electrolyte and is enclosed inside the bag-shaped exterior film 10, thus assembling the secondary battery.

[Stabilization treatment of secondary battery after assembly]
The assembled secondary battery is charged and discharged. Stabilization conditions such as the environmental temperature, the number of charge/discharge cycles (number of charge/discharge conditions), and the like can be set arbitrarily.

As a result, a positive electrode coating 21C is formed on the surface of the positive electrode active material layer 21B, thereby producing the positive electrode 21, and a negative electrode coating 22C is formed on the surface of the negative electrode active material layer 22B, thereby producing the negative electrode 22. Thus, the battery element 20 is produced, and the battery element 20 is sealed inside the bag-shaped exterior film 10, thereby completing the secondary battery.

<1-5. Actions and Effects>
According to this secondary battery, the positive electrode 21 includes a positive electrode coating 21C, and the electrolyte includes an electrolyte salt. The positive electrode active material includes a lithium-containing compound, lithium carbonate, and lithium hydroxide, and the content of lithium carbonate in the positive electrode active material is 0.2% by weight to 0.7% by weight, and the content of lithium hydroxide in the positive electrode active material is 0.2% by weight to 0.7% by weight. In a surface analysis of the positive electrode 21 (positive electrode coating 21C) using XPS, the peak position N of the N1s spectrum is 395 eV to 405 eV, and the peak position B of the B1s spectrum is 188 eV to 198 eV. Furthermore, the electrolyte salt of the electrolyte includes a nitrogen-boron-containing anion.

In this case, as described above, the series of actions described below are obtained.

First, the content of residual lithium components (lithium carbonate and lithium hydroxide) in the positive electrode active material is optimized, so that the element distribution on the surface of the positive electrode active material is optimized. This makes it easier for lithium ions to be input and output in the lithium-containing compound while suppressing the generation of gas due to the presence of residual lithium components, and also makes it difficult for the electrolyte to decompose on the surface of the lithium-containing compound.

Secondly, because the physical property conditions (peak position N and peak position B) of the positive electrode coating 21C are satisfied, the electrochemical state of the positive electrode coating 21C is optimized. This ensures smooth occlusion and release of cations in the positive electrode active material layer 21B while suppressing the decomposition reaction of the electrolyte.

Thirdly, because the electrolyte salt contains nitrogen-boron-containing anions, the positive electrode coating 21C is easily formed. This further suppresses the decomposition reaction of the electrolyte on the surface of the positive electrode 21. In addition, the migration speed of cations is improved near the surface of the positive electrode 21, and the migration speed of cations is also improved in the electrolyte.

As a result, excellent battery characteristics can be obtained.

In particular, if the lithium-containing compound contains one or both of the first lithium composite oxide and the second lithium composite oxide, a high voltage can be obtained, and therefore a greater effect can be obtained.

In addition, if the negative electrode 22 includes the negative electrode coating 22C and the physical properties of the negative electrode coating 22C also satisfy the physical property conditions, the decomposition reaction of the electrolyte is further suppressed while smooth occlusion and release of cations in the negative electrode active material layer 22B is ensured, and a greater effect can be obtained.

Furthermore, if the electrolyte salt contains light metal ions as cations, a higher voltage can be obtained, and therefore a greater effect can be achieved. In this case, if the light metal ions contain lithium ions, a higher voltage can be obtained, and therefore an even greater effect can be achieved.

In addition, if the content of electrolyte salt in the electrolyte solution is 0.5 mol/kg to 2 mol/kg relative to the solvent, high ionic conductivity can be obtained, resulting in even greater effects.

In addition, if the electrolyte further contains one or more of the following electrolyte salts as other electrolyte salts: lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, and lithium difluorophosphate, the lithium ion migration speed is further improved, and thus a greater effect can be obtained.

In addition, if the electrolyte further contains one or more of the following solvents as other solvents: unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonic acid esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfate esters, nitrile compounds, and isocyanate compounds, the decomposition reaction of the electrolyte is suppressed, and thus a greater effect can be obtained.

In addition, if the secondary battery is a lithium-ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the absorption and release of lithium, resulting in even greater effects.

2. Modified Examples
The configuration of the secondary battery can be modified as appropriate, as described below, although the series of modifications described below may be combined with each other.

[Modification 1]
As noted above, the electrolyte may contain other electrolyte salts along with the electrolyte salt containing the nitrogen-boron-containing anion.

In particular, it is preferable that the electrolyte solution contains lithium hexafluorophosphate as another electrolyte salt, and that the content of the electrolyte salt in the electrolyte solution is optimized in relation to the content of the other electrolyte salt in the electrolyte solution.

Specifically, the electrolyte salt contains a cation and a nitrogen-boron-containing anion. The hexafluorophosphate ion contains a lithium ion and a hexafluorophosphate ion.

In this case, the sum T (mol/kg) of the cation content C1 in the electrolyte and the lithium ion content C2 in the electrolyte is preferably 0.7 mol/kg to 2.7 mol/kg. This is because the migration speeds of the cations and lithium ions near the surfaces of the positive electrode 21 and the negative electrode 22 are sufficiently improved, and the migration speeds of the cations and lithium ions are also sufficiently improved in the electrolyte.

The "content of cations in the electrolyte" described here is the content of electrolyte salt of cations relative to the solvent, and the "content of lithium ions in the electrolyte" is the content of lithium ions relative to the solvent. The sum T is calculated based on the formula T = C1 + C2.

When calculating the sum T, the secondary battery is disassembled to recover the electrolyte, which is then analyzed using ICP atomic emission spectrometry. This allows the contents C1 and C2 to be determined, and the sum T can be calculated.

In this case, the electrolyte solution contains electrolyte salt, and therefore the same effect can be obtained. In this case, particularly when the electrolyte salt is used in combination with another electrolyte salt (lithium hexafluorophosphate), the total amount of both (sum T) is optimized. This further improves the migration speeds of cations and lithium ions near the surfaces of the positive electrode 21 and the negative electrode 22, and also further improves the migration speeds of cations and lithium ions in the electrolyte solution. Therefore, a greater effect can be obtained.

[Modification 2]
In the first modification, the electrolyte solution contains lithium hexafluorophosphate as another electrolyte salt. However, the electrolyte solution may contain lithium bis(fluorosulfonyl)imide as another electrolyte salt instead of lithium hexafluorophosphate. Even in this case, it is preferable that the content of the electrolyte salt in the electrolyte solution is optimized in relation to the content of the other electrolyte salt in the electrolyte solution.

Specifically, lithium bis(fluorosulfonyl)imide contains lithium ions and bis(fluorosulfonyl)imide ions. In this case, the sum T (mol/kg) of the cation content C1 in the electrolyte and the lithium ion content C2 in the electrolyte is preferably 0.7 mol/kg to 2.7 mol/kg. This is because the migration speeds of the cations and lithium ions near the surfaces of the positive electrode 21 and the negative electrode 22 are sufficiently improved, and the migration speeds of the cations and lithium ions are also sufficiently improved in the electrolyte.

As mentioned above, the sum T is calculated based on the formula T = C1 + C2.

In this case, the electrolyte solution contains an electrolyte salt, and therefore the same effect can be obtained. In this case, particularly when the electrolyte salt is used in combination with another electrolyte salt (lithium bis(fluorosulfonyl)imide), the total amount (sum T) of the two is optimized. This further improves the migration speeds of the cations and lithium ions near the surfaces of the positive electrode 21 and the negative electrode 22, and also further improves the migration speeds of the cations and lithium ions in the electrolyte solution. Therefore, a greater effect can be obtained.

[Modification 3]
A porous membrane separator 23 was used. However, although not specifically shown here, a laminated separator including a polymer compound layer may be used instead of the porous membrane separator 23.

Specifically, the laminated separator includes a porous membrane having a pair of surfaces, and a polymer compound layer provided on one or both surfaces of the porous membrane. This is because the adhesion of the separator to each of the positive electrode 21 and the negative electrode 22 is improved, thereby suppressing misalignment of the battery element 20. This suppresses miswinding of the positive electrode 21, the negative electrode 22, and the separator, thereby suppressing swelling of the secondary battery even if a decomposition reaction of the electrolyte occurs. The polymer compound layer includes polyvinylidene fluoride, etc. This is because polyvinylidene fluoride has excellent physical strength and is electrochemically stable.

In addition, one or both of the porous film and the polymer compound layer may contain one or more types of insulating particles. This is because the insulating particles dissipate heat when the secondary battery generates heat, improving the safety (heat resistance) of the secondary battery. The insulating particles contain one or more types of insulating materials such as inorganic materials and resin materials. Specific examples of inorganic materials include aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of resin materials include acrylic resin and styrene resin.

When making a laminated separator, a precursor solution containing a polymer compound and an organic solvent is prepared, and then the precursor solution is applied to one or both sides of a porous film. In this case, the precursor solution may contain multiple insulating particles.

Even when this laminated separator is used, the lithium can move in an ionic state between the positive electrode 21 and the negative electrode 22, so the same effect can be obtained. In this case, as described above, swelling of the secondary battery is further suppressed, so a greater effect can be obtained.

[Modification 4]
An electrolyte solution that is a liquid electrolyte is used, but an electrolyte layer that is a gel electrolyte may also be used, although this is not specifically shown.

In a battery element 20 using an electrolyte layer, a positive electrode 21 and a negative electrode 22 are wound facing each other with a separator 23 and an electrolyte layer interposed between them. The electrolyte layer is interposed between the positive electrode 21 and the separator 23, and also between the negative electrode 22 and the separator 23.

Specifically, the electrolyte layer contains a polymer compound together with an electrolyte solution, and the electrolyte solution is held by the polymer compound. This is because leakage of the electrolyte solution is prevented. The composition of the electrolyte solution is as described above. The polymer compound contains polyvinylidene fluoride and the like. When forming the electrolyte layer, a precursor solution containing an electrolyte solution, a polymer compound, a solvent, and the like is prepared, and then the precursor solution is applied to one or both sides of each of the positive electrode 21 and the negative electrode 22.

Even when this electrolyte layer is used, the lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer, so the same effect can be obtained. In this case, leakage of the electrolyte is particularly prevented as described above, so a greater effect can be obtained.

<3. Uses of secondary batteries>
Finally, uses (application examples) of the secondary battery will be described.

The use of the secondary battery is not particularly limited. A secondary battery used as a power source may be a main power source or an auxiliary power source in electronic devices and electric vehicles. A main power source is a power source that is used preferentially regardless of the presence or absence of other power sources. An auxiliary power source may be a power source used in place of the main power source or a power source that can be switched from the main power source.

Specific examples of applications of secondary batteries are as follows: Electronic devices such as video cameras, digital still cameras, mobile phones, notebook computers, headphone stereos, portable radios, and portable information terminals; Storage devices such as backup power sources and memory cards; Power tools such as power drills and power saws; Battery packs mounted on electronic devices; Medical electronic devices such as pacemakers and hearing aids; Electric vehicles such as electric cars (including hybrid cars); Power storage systems such as home or industrial battery systems that store power in preparation for emergencies, etc. In these applications, one secondary battery may be used, or multiple secondary batteries may be used.

The battery pack may include a single cell or a battery pack. The electric vehicle is a vehicle that runs on a secondary battery as a driving power source, and may be a hybrid vehicle that also includes a driving source other than the secondary battery. In a home power storage system, it is possible to use home electrical appliances and the like by utilizing the power stored in the secondary battery, which is a power storage source.

Here, we will specifically explain an example of a use of a secondary battery. The configuration described below is merely an example and can be modified as appropriate.

Figure 4 shows the block diagram of a battery pack, which is an example of an application of a secondary battery. The battery pack described here is a battery pack (a so-called soft pack) that uses one secondary battery, and is installed in electronic devices such as smartphones.

As shown in FIG. 4, this battery pack includes a power source 51 and a circuit board 52. This circuit board 52 is connected to the power source 51 and includes a positive terminal 53, a negative terminal 54, and a temperature detection terminal 55.

The power source 51 includes one secondary battery. In this secondary battery, the positive electrode lead is connected to the positive electrode terminal 53, and the negative electrode lead is connected to the negative electrode terminal 54. This power source 51 is connected to the outside via the positive electrode terminal 53 and the negative electrode terminal 54, and is therefore capable of charging and discharging. The circuit board 52 includes a control unit 56, a switch 57, a PTC element 58 which is a thermosensitive resistor, and a temperature detection unit 59. However, the PTC element 58 may be omitted.

The control unit 56 includes a central processing unit (CPU) and memory, and controls the operation of the entire battery pack. This control unit 56 detects and controls the usage status of the power source 51.

When the voltage of the power source 51 (secondary battery) reaches the overcharge detection voltage or overdischarge detection voltage, the control unit 56 turns off the switch 57 to prevent charging current from flowing through the current path of the power source 51. The overcharge detection voltage is not particularly limited, but is specifically 4.20V±0.05V, and the overdischarge detection voltage is not particularly limited, but is specifically 2.40V±0.10V.

Switch 57 includes a charge control switch, a discharge control switch, a charge diode, and a discharge diode, and switches between the presence and absence of a connection between power source 51 and an external device in response to an instruction from control unit 56. Switch 57 includes a field effect transistor (MOSFET) that uses a metal oxide semiconductor, and the charge current and discharge current are each detected based on the ON resistance of switch 57.

Temperature detection unit 59 includes a temperature detection element such as a thermistor. Temperature detection unit 59 measures the temperature of power supply 51 using temperature detection terminal 55 and outputs the temperature measurement result to control unit 56. The temperature measurement result measured by temperature detection unit 59 is used when control unit 56 performs charge/discharge control in the event of abnormal heat generation and when control unit 56 performs correction processing when calculating remaining capacity.

We will explain an example of this technology.

In Tables 1 to 18 described below, for convenience, examples are indicated as "Example" and comparative examples are indicated as "Comparative." More specifically, for example, to simplify the notation, Example 1 is indicated as "Example 1" and Comparative Example 1 is indicated as "Comparative 1."

<Examples 1 to 50 and Comparative Examples 1 to 34>
As described below, after the secondary batteries were manufactured, the battery characteristics of the secondary batteries were evaluated.

[Preparation of secondary battery]
The laminate film type secondary battery (lithium ion secondary battery) shown in FIGS. 1 to 3 was fabricated by the following procedure.

(Preparation of Positive Electrode)
First, 91 parts by mass of a positive electrode active material (lithium-containing compound), 3 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 6 parts by mass of a positive electrode conductive agent (carbon black) were mixed together to prepare a positive electrode mixture.

The lithium _- containing compounds used were _{LiNi0.82Co0.14Al0.04O2} (LNCA ₎ as the first lithium composite _oxide and _{LiMn0.30Ni0.50Co0.20O2} (LMNC ₎ as the _second lithium composite oxide. The average particle sizes (median diameters ( _μm )) of the lithium-containing compounds are as shown in Tables 1 to 10.

In addition, when the content of residual lithium components in the positive electrode active material was examined using the procedure described above, the content (weight %) of lithium _carbonate ( _Li2CO3 ) and the content (weight %) of lithium hydroxide (LiOH) were as shown in Tables 1 to 10.

Then, the positive electrode mixture was added to a solvent (organic solvent N-methyl-2-pyrrolidone), and the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. The positive electrode mixture slurry was then applied to both sides of the positive electrode current collector 21A (strip-shaped aluminum foil with a thickness of 12 μm) using a coating device, and the positive electrode mixture slurry was then dried to form the positive electrode active material layer 21B. The positive electrode active material layer 21B was then compression molded using a roll press machine.

Finally, as described below, the secondary battery was assembled and then a stabilization process was performed using the assembled secondary battery. As a result, a positive electrode coating 21C was formed on the surface of the positive electrode active material layer 21B, and thus the positive electrode 21 was produced.

(Preparation of negative electrode)
First, 93 parts by mass of a negative electrode active material (artificial graphite, which is a carbon material) and 7 parts by mass of a negative electrode binder (polyvinylidene fluoride) were mixed together to prepare a negative electrode mixture. Next, the negative electrode mixture was added to a solvent (N-methyl-2-pyrrolidone, which is an organic solvent), and the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry.

Then, the negative electrode mixture slurry was applied to both sides of the negative electrode current collector 22A (strip-shaped copper foil with a thickness of 15 μm) using a coating device, and the negative electrode mixture slurry was then dried to form the negative electrode active material layer 22B. The negative electrode active material layer 22B was then compression molded using a roll press machine.

Finally, as described below, the secondary battery was assembled, and then a stabilization process was performed using the assembled secondary battery. As a result, the negative electrode coating 22C was formed on the surface of the negative electrode active material layer 22B, and the negative electrode 22 was produced.

(Preparation of Electrolyte)
The electrolyte salt (lithium containing boron nitrogen) was added to the solvent, and the solvent was stirred to prepare an electrolyte solution.

The mixture described below was used as the solvent.

First, a mixture of ethylene carbonate (EC), a cyclic carbonate ester, and gamma-butyrolactone (GBL), a lactone, was used. In this case, the mixing ratio (weight ratio) of the solvents was ethylene carbonate:gamma-butyrolactone = 30:70.

Second, mixtures with similar compositions were used, except that the lactones were replaced with the linear carbonates dimethyl carbonate (DMC) or diethyl carbonate (DEC).

Thirdly, a mixture with a similar composition was used, except that the lactone was replaced with the linear carboxylic acid esters propyl propionate (PrPr) or ethyl propionate (PrEt).

The types of boron-nitrogen-containing lithium are as shown in Tables 1 to 10. In this case, the amount of electrolyte salt added was changed to vary the electrolyte salt content (mol/kg) in the electrolyte solution.

For comparison, an electrolyte solution was prepared in the same manner except that other compounds were used as the electrolyte salt instead of the boron-nitrogen-containing lithium, including lithium hexafluorophosphate (LiPF ₆ ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF ₄ ), and lithium trifluoro(trifluoromethyl)borate (LiBF ₃ (CF ₃ )).

(Assembly of secondary batteries)
First, the positive electrode lead 31 (aluminum foil) was welded to the positive electrode current collector 21 A of the positive electrode 21 , and the negative electrode lead 32 (copper foil) was welded to the negative electrode current collector 22 A of the negative electrode 22 .

Then, the positive electrode collector 21A on which the positive electrode active material layer 21B is formed and the negative electrode collector 22A on which the negative electrode active material layer 22B is formed were laminated together with a separator 23 (a microporous polyethylene film having a thickness of 25 μm) in between to produce a laminate. The laminate was then wound to produce a wound body, which was then pressed using a press machine to form the wound body into a flat shape.

Then, the exterior film 10 (adhesive layer/metal layer/surface protection layer) was folded so as to sandwich the roll housed in the recess 10U, and the outer peripheral edges of two sides of the adhesive layer were heat-sealed to each other to house the roll inside the bag-shaped exterior film 10. The exterior film 10 used was an aluminum laminate film in which the adhesive layer (polypropylene film with a thickness of 30 μm), the metal layer (aluminum foil with a thickness of 40 μm), and the surface protection layer (nylon film with a thickness of 25 μm) were laminated in this order from the inside.

Finally, electrolyte was injected into the bag-shaped exterior film 10, and the outer edges of the remaining side of the fusion layer were heat-sealed to each other in a reduced pressure environment. In this case, a sealing film 41 (a polypropylene film with a thickness of 5 μm) was inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 (a polypropylene film with a thickness of 5 μm) was inserted between the exterior film 10 and the negative electrode lead 32. This allowed the wound body to be impregnated with electrolyte.

As a result, the wound body was enclosed inside the exterior film 10, and the secondary battery was assembled.

(Stabilization of secondary batteries after assembly)
The assembled secondary battery was charged and discharged for one cycle in a room temperature environment (temperature = 23 ° C.). During charging, the battery was charged at a constant current of 0.1 C until the voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current reached 0.05 C. During discharging, the battery was discharged at a constant current of 0.1 C until the voltage reached 2.5 V. 0.1 C is the current value at which the battery capacity (theoretical capacity) is fully discharged in 10 hours, and 0.05 C is the current value at which the battery capacity is fully discharged in 20 hours.

As a result, a positive electrode coating 21C was formed on the surface of the positive electrode active material layer 21B, thereby producing a positive electrode 21, and a negative electrode coating 22C was formed on the surface of the negative electrode active material layer 22B, thereby producing a negative electrode 22. Thus, an electrochemically stabilized battery element 20 was produced, and the battery element 20 was sealed inside the exterior film 10, thereby completing a secondary battery.

[Evaluation of Battery Characteristics]
The battery characteristics (cycle characteristics, storage characteristics, and load characteristics) were evaluated according to the procedures described below, and the results shown in Tables 1 to 10 were obtained.

(Cycle characteristics)
First, the discharge capacity (discharge capacity at the first cycle) was measured by charging and discharging the secondary battery in a high-temperature environment (temperature = 60 ° C.) The charge and discharge conditions were the same as those in the stabilization treatment of the secondary battery described above.

　Then, in the same environment, the secondary battery was repeatedly charged and discharged until the total number of cycles reached 100, and the discharge capacity (discharge capacity at the 100th cycle) was measured. The charge and discharge conditions were the same as those during the stabilization treatment of the secondary battery described above.

Finally, the cycle retention rate, which is an index for evaluating cycle characteristics, was calculated based on the formula: cycle retention rate (%) = (discharge capacity at 100th cycle/discharge capacity at 1st cycle) x 100.

(Storage characteristics)
First, the discharge capacity (discharge capacity before storage) was measured by charging and discharging the secondary battery one cycle in a room temperature environment (temperature = 23 ° C.) The charge and discharge conditions were the same as the charge and discharge conditions during the stabilization treatment of the secondary battery described above.

Subsequently, the secondary battery was charged in the same environment, and the charged secondary battery was stored (storage time = 10 days) in a high-temperature environment (temperature = 80°C), and then the secondary battery was discharged in a room-temperature environment to measure the discharge capacity (discharge capacity after storage). The charge and discharge conditions were the same as those during the stabilization treatment of the secondary battery described above.

Finally, the storage retention rate, which is an index for evaluating storage characteristics, was calculated based on the formula: storage retention rate (%) = (discharge capacity after storage/discharge capacity before storage) x 100.

(Load characteristics)
First, the discharge capacity (discharge capacity at the first cycle) was measured by charging and discharging the secondary battery one cycle in a room temperature environment (temperature = 23 ° C.) The charge and discharge conditions were the same as the charge and discharge conditions during the stabilization treatment of the secondary battery described above.

　Then, the secondary battery was repeatedly charged and discharged in a low-temperature environment (temperature = -10°C) until the total number of cycles reached 100, and the discharge capacity (discharge capacity at the 100th cycle) was measured. The charge and discharge conditions were the same as those during the stabilization process of the secondary battery described above, except that the current during discharge was changed to 1C. 1C is the current value at which the battery capacity is fully discharged in 1 hour.

Finally, the load retention rate, which is an index for evaluating load characteristics, was calculated based on the formula: Load retention rate (%) = (discharge capacity at 100th cycle/discharge capacity at 1st cycle) x 100.

[Discussion]
As shown in Tables 1 to 10, the cycle retention rate, storage retention rate and load retention rate each varied greatly depending on the configuration of the secondary battery.

Specifically, the secondary batteries using the first lithium composite oxide as the lithium-containing compound (Tables 1 to 5) exhibited the trends described below.

Even if the lithium carbonate content was 0.2% to 0.7% by weight and the lithium hydroxide content was 0.2% to 0.7% by weight, when the electrolyte salt did not contain a nitrogen-boron-containing anion (Comparative Examples 1 to 17), the physical property conditions of the positive electrode 21 (positive electrode coating 21C) that the peak position N was 395 eV to 405 eV and the peak position B was 188 eV to 198 eV were not met, and the cycle retention rate, storage retention rate, and load retention rate all decreased.

In contrast, when the lithium carbonate content was 0.2% to 0.7% by weight and the lithium hydroxide content was 0.2% to 0.7% by weight, and the electrolyte salt contained a nitrogen-boron-containing anion (Examples 1 to 25), the above-mentioned physical property conditions were satisfied for the physical properties of the positive electrode 21 (positive electrode coating 21C), and the cycle retention rate, storage retention rate, and load retention rate all increased.

Similar trends were also observed in the secondary batteries (Tables 6 to 10) that used a second lithium composite oxide as the lithium-containing compound.

Even if the lithium carbonate content was 0.2 wt% to 0.7 wt% and the lithium hydroxide content was 0.2 wt% to 0.7 wt%, when the electrolyte salt did not contain imide anions (Comparative Examples 18 to 34), the above physical property conditions were not met, and the cycle retention rate, storage retention rate, and load retention rate all decreased.

In contrast, when the lithium carbonate content was 0.2% to 0.7% by weight and the lithium hydroxide content was 0.2% to 0.7% by weight, and the electrolyte salt contained a nitrogen-boron-containing anion (Examples 26 to 50), the above physical property conditions were met, and the cycle retention rate, storage retention rate, and load retention rate all increased.

In particular, when the electrolyte salt contained a nitrogen-boron-containing anion (Examples 1 to 50), the trends described below were observed.

First, the cycle retention rate, storage retention rate, and load retention rate were each sufficiently high, regardless of the type and median diameter of the lithium-containing compound. Second, the cycle retention rate, storage retention rate, and load retention rate were each sufficiently high, regardless of the type of nitrogen-boron-containing anion. Third, when the electrolyte salt contained a light metal ion (lithium ion) as a cation, the cycle retention rate, storage retention rate, and load retention rate were each sufficiently high. Fourth, when the content of the electrolyte salt in the electrolyte solution was 0.5 mol/kg to 2 mol/kg relative to the solvent, the cycle retention rate, storage retention rate, and load retention rate each increased further. Fifth, even when the composition of the solvent was changed, a high cycle retention rate, high storage retention rate, and high load retention rate were obtained. Sixth, when the above-mentioned physical property conditions were also satisfied for the negative electrode 22 (negative electrode coating 22C), a high cycle retention rate, high storage retention rate, and high load retention rate were obtained.

<Examples 51 to 68>
Secondary batteries were produced and their battery characteristics were evaluated in the same manner as in Example 3, except that other solvents or other electrolyte salts were added to the electrolyte solution as shown in Tables 11 and 12. In this case, the other solvents or other electrolyte salts were added to the electrolyte solution, and then the electrolyte solution was stirred.

Details of other solvents are as follows. As unsaturated cyclic carbonates, vinylene carbonate (VC), vinylethylene carbonate (VEC), and methyleneethylene carbonate (MEC) were used. As fluorinated cyclic carbonates, monofluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC) were used. As sulfonates, cyclic monosulfonates, propane sultone (PS) and propene sultone (PRS), and cyclic disulfonates, cyclodisone (CD), were used. As dicarboxylic anhydrides, succinic anhydride (SA) was used. As disulfonic anhydrides, propane disulfonic anhydride (PSAH) was used. As sulfates, ethylene sulfate (DTD) was used. As nitrile compounds, succinonitrile (SN) was used. As isocyanate compounds, hexamethylene diisocyanate (HMI) was used.

Other electrolyte salts used were lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB) and lithium difluorophosphate (LiPF ₂ O ₂ ).

The contents (wt%) of other solvents in the electrolyte and the contents (wt%) of other electrolyte salts in the electrolyte were as shown in Tables 11 and 12.

As shown in Table 11, when the electrolyte contained other solvents (Examples 51 to 63), two or more of the cycle retention rate, storage retention rate, and load retention rate were increased more than when the electrolyte did not contain other solvents (Example 3).

Also, as shown in Table 12, when the electrolyte solution contained other electrolyte salts (Examples 64 to 68), two or more of the cycle retention rate, storage retention rate, and load retention rate were increased more than when the electrolyte solution did not contain other electrolyte salts (Example 3).

<Examples 69 to 110 and Comparative Examples 35 to 56>
As shown in Tables 13 to 18, secondary batteries were prepared in a manner similar to that of Example 3, except that the electrolyte solution contained lithium hexafluorophosphate (LiPF ₆ ) or lithium bis(fluorosulfonyl)imide (LiFSI) as another electrolyte salt, and the battery characteristics were then evaluated.

In this case, the electrolyte salt was added to the solvent along with the other electrolyte salt, and the solvent was then stirred. The electrolyte salt content (mol/kg) in the electrolyte solution, the other electrolyte salt content (mol/kg) in the electrolyte solution, and the sum T (mol/kg) were as shown in Tables 13 to 18.

When lithium hexafluorophosphate was used as another electrolyte salt, the results shown in Tables 13 to 15 were obtained. That is, when the condition that the sum T is 0.7 mol/kg to 2.7 mol/kg was not met (Examples 69, 70, and 89 and Comparative Examples 35 to 45), the cycle retention rate, storage retention rate, and load retention rate each decreased due to the above-mentioned physical property conditions not being met, or the cycle retention rate, storage retention rate, and load retention rate each decreased even when the above-mentioned appropriate physical property conditions were met.

In contrast, when the appropriate physical property conditions were met and the condition that the sum T was 0.7 mol/kg to 2.7 mol/kg was also met (Examples 71 to 88), the cycle retention rate, storage retention rate, and load retention rate all increased.

The trends in superiority and inferiority described here were also observed when lithium bis(fluorosulfonyl)imide was used as another electrolyte salt (Examples 90-110 and Comparative Examples 46-55), as shown in Tables 16-18.

[summary]
From the results shown in Tables 1 to 18, when the positive electrode 21 contains a positive electrode active material and a positive electrode coating 21C, the electrolyte contains an electrolyte salt, the positive electrode active material of the positive electrode 21 contains a lithium-containing compound, lithium carbonate and lithium hydroxide, the content of lithium carbonate in the positive electrode active material is 0.2% by weight to 0.7% by weight, the content of lithium hydroxide in the positive electrode active material is 0.2% by weight to 0.7% by weight, the peak position N is 395 eV to 405 eV and the peak position B is 188 eV to 198 eV in the surface analysis of the positive electrode 21 (positive electrode coating 21C) using XPS, and the electrolyte salt contains a nitrogen-boron-containing anion, a high cycle retention rate, a high storage retention rate and a high load retention rate were obtained. Therefore, since each of the cycle characteristics, storage characteristics and load characteristics was improved, excellent battery characteristics were obtained in the secondary battery.

The present technology has been described above with reference to one embodiment and examples, but the configuration of the present technology is not limited to the configuration described in the embodiment and examples, and can be modified in various ways.

Specifically, the battery structure of the secondary battery has been described as being of a laminate film type. However, the battery structure of the secondary battery is not particularly limited, and may be of a cylindrical type, a square type, a coin type, a button type, etc.

Also, the battery element has been described as having a wound structure. However, the structure of the battery element is not particularly limited, and may be a stacked type or a zigzag type. In the stacked type, the positive and negative electrodes are alternately stacked with a separator between them, while in the zigzag type, the positive and negative electrodes are folded in a zigzag pattern while facing each other with the separator between them.

Although the electrode reactant is lithium in the above description, the electrode reactant is not particularly limited. Specifically, as described above, the electrode reactant may be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reactant may be other light metals such as aluminum.

The effects described in this specification are merely examples, and the effects of this technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to this technology.

The present technology can also be configured as follows.

＜1＞
A positive electrode, a negative electrode, and an electrolyte solution are provided,
The positive electrode is
a positive electrode active material layer including a positive electrode active material;
a positive electrode coating that coats a surface of the positive electrode active material layer,
The positive electrode active material includes a lithium-containing compound, lithium carbonate, and lithium hydroxide,
The content of the lithium carbonate in the positive electrode active material is 0.2% by weight or more and 0.7% by weight or less,
The content of the lithium hydroxide in the positive electrode active material is 0.2% by weight or more and 0.7% by weight or less,
The positive electrode coating contains nitrogen and boron as constituent elements,
A surface analysis of the positive electrode using X-ray photoelectron spectroscopy detects an N1s spectrum derived from the nitrogen and a B1s spectrum derived from the boron,
The peak position of the N1s spectrum is 395 eV or more and 405 eV or less,
The peak position of the B1s spectrum is 188 eV or more and 198 eV or less.
The electrolyte solution contains an electrolyte salt,
The electrolyte salt comprises an anion represented by formula (1):
Secondary battery.
B(R1)(R2)(R3)CN ^-... (1)
(Each of R1, R2, and R3 is any one of a fluorine group, a cyano group, an alkyl group, a fluorinated alkyl group, a fluorinated ester group, and a fluorinated alkoxy group. However, at least one of R1, R2, and R3 is any one of a fluorine group, a fluorinated alkyl group, a fluorinated ester group, and a fluorinated alkoxy group.)
＜2＞
The lithium-containing compound includes at least one of a first lithium composite oxide represented by formula (2) and a second lithium composite oxide represented by formula (3).
The secondary battery according to <1>.
Li _x Ni _1-y M1 _y O _2-a X1 _b ...(2)
(M1 is at least one of Co, Mn, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta, and rare earth elements. X1 is at least one of F, Cl, Cr, I, P, S, and Si. x, y, a, and b satisfy 0.9≦x≦1.1, 0.005≦y≦0.5, -0.1≦a≦0.2, and 0≦b≦0.1.)
Li _x Mn _1-xyz Ni _y M2 _z O _2-a X2 _b ...(3)
(M2 is at least one of Co, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta, and rare earth elements. X2 is at least one of F, Cl, Cr, I, P, S, and Si. x, y, a, and b satisfy 0<x≦0.3, 0.3≦y≦0.9, 0≦z≦0.5, -0.1≦a≦0.2, and 0≦b≦0.1.)
＜3＞
The negative electrode is
A negative electrode active material layer;
a negative electrode coating that coats a surface of the negative electrode active material layer,
The negative electrode coating contains nitrogen and boron as constituent elements,
A surface analysis of the negative electrode using X-ray photoelectron spectroscopy detects an N1s spectrum derived from the nitrogen and a B1s spectrum derived from the boron,
The peak position of the N1s spectrum is 395 eV or more and 405 eV or less,
The peak position of the B1s spectrum is 188 eV or more and 198 eV or less.
The secondary battery according to <1> or <2>.
＜4＞
The electrolyte contains light metal ions as cations.
The secondary battery according to any one of <1> to <3>.
＜5＞
The light metal ions include lithium ions.
The secondary battery according to <4>.
＜6＞
The electrolyte further comprises a solvent,
The content of the electrolyte salt in the electrolytic solution is 0.5 mol/kg or more and 2 mol/kg or less with respect to the solvent.
<5> The secondary battery according to any one of <1> to <5>.
＜７＞
The electrolyte solution further contains at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, and lithium difluorophosphate;
The secondary battery according to <6>.
＜8＞
The electrolyte solution further contains lithium hexafluorophosphate or lithium bis(fluorosulfonyl)imide,
The electrolyte salt includes a cation and the anion,
The lithium hexafluorophosphate contains lithium ions and hexafluorophosphate ions,
The lithium bis(fluorosulfonyl)imide contains a lithium ion and a bis(fluorosulfonyl)imide ion,
The sum of the content of the cation in the electrolyte solution and the content of the lithium ion in the electrolyte solution is 0.7 mol/kg or more and 2.7 mol/kg or less.
<5> The secondary battery according to any one of <1> to <5>.
＜9＞
The electrolytic solution further contains at least one of an unsaturated cyclic carbonate, a fluorinated cyclic carbonate, a sulfonic acid ester, a dicarboxylic acid anhydride, a disulfonic acid anhydride, a sulfuric acid ester, a nitrile compound, and an isocyanate compound.
<8> The secondary battery according to any one of <1> to <8>.
＜10＞
It is a lithium-ion secondary battery.
<1> The secondary battery according to any one of <1> to <9>.

Claims (10)

A positive electrode, a negative electrode, and an electrolyte solution are provided,
The positive electrode is
a positive electrode active material layer including a positive electrode active material;
a positive electrode coating that coats a surface of the positive electrode active material layer,
The positive electrode active material includes a lithium-containing compound, lithium carbonate, and lithium hydroxide,
The content of the lithium carbonate in the positive electrode active material is 0.2% by weight or more and 0.7% by weight or less,
The content of the lithium hydroxide in the positive electrode active material is 0.2% by weight or more and 0.7% by weight or less,
The positive electrode coating contains nitrogen and boron as constituent elements,
A surface analysis of the positive electrode using X-ray photoelectron spectroscopy detects an N1s spectrum derived from the nitrogen and a B1s spectrum derived from the boron,
The peak position of the N1s spectrum is 395 eV or more and 405 eV or less,
The peak position of the B1s spectrum is 188 eV or more and 198 eV or less.
The electrolyte solution contains an electrolyte salt,
The electrolyte salt comprises an anion represented by formula (1):
Secondary battery.
B(R1)(R2)(R3)CN ^-... (1)
(Each of R1, R2, and R3 is any one of a fluorine group, a cyano group, an alkyl group, a fluorinated alkyl group, a fluorinated ester group, and a fluorinated alkoxy group. However, at least one of R1, R2, and R3 is any one of a fluorine group, a fluorinated alkyl group, a fluorinated ester group, and a fluorinated alkoxy group.) The lithium-containing compound includes at least one of a first lithium composite oxide represented by formula (2) and a second lithium composite oxide represented by formula (3).
The secondary battery according to claim 1 .
Li _x Ni _1-y M1 _y O _2-a X _1b ...(2)
(M1 is at least one of Co, Mn, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta, and rare earth elements. X1 is at least one of F, Cl, Cr, I, P, S, and Si. x, y, a, and b satisfy 0.9≦x≦1.1, 0.005≦y≦0.5, -0.1≦a≦0.2, and 0≦b≦0.1.)
Li _x Mn _1-xyz Ni _y M _2z O _2-a X _2b ...(3)
(M2 is at least one of Co, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta, and rare earth elements. X2 is at least one of F, Cl, Cr, I, P, S, and Si. x, y, a, and b satisfy 0<x≦0.3, 0.3≦y≦0.9, 0≦z≦0.5, -0.1≦a≦0.2, and 0≦b≦0.1.) The negative electrode is
A negative electrode active material layer;
a negative electrode coating that coats a surface of the negative electrode active material layer,
The negative electrode coating contains nitrogen and boron as constituent elements,
A surface analysis of the negative electrode using X-ray photoelectron spectroscopy detects an N1s spectrum derived from the nitrogen and a B1s spectrum derived from the boron,
The peak position of the N1s spectrum is 395 eV or more and 405 eV or less,
The peak position of the B1s spectrum is 188 eV or more and 198 eV or less.
The secondary battery according to claim 1 or 2. The electrolyte contains light metal ions as cations.
The secondary battery according to claim 1 . The light metal ions include lithium ions.
The secondary battery according to claim 4 . The electrolyte further comprises a solvent,
The content of the electrolyte salt in the electrolytic solution is 0.5 mol/kg or more and 2 mol/kg or less with respect to the solvent.
The secondary battery according to claim 1 . The electrolyte solution further contains at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, and lithium difluorophosphate;
The secondary battery according to claim 6. The electrolyte solution further contains lithium hexafluorophosphate or lithium bis(fluorosulfonyl)imide,
The electrolyte salt includes a cation and the anion,
The lithium hexafluorophosphate contains lithium ions and hexafluorophosphate ions,
The lithium bis(fluorosulfonyl)imide contains a lithium ion and a bis(fluorosulfonyl)imide ion,
The sum of the content of the cation in the electrolyte solution and the content of the lithium ion in the electrolyte solution is 0.7 mol/kg or more and 2.7 mol/kg or less.
The secondary battery according to claim 1 . The electrolytic solution further contains at least one of an unsaturated cyclic carbonate, a fluorinated cyclic carbonate, a sulfonic acid ester, a dicarboxylic acid anhydride, a disulfonic acid anhydride, a sulfuric acid ester, a nitrile compound, and an isocyanate compound.
The secondary battery according to claim 1 . It is a lithium-ion secondary battery.
The secondary battery according to claim 1 .

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