WO2020059874A1 - Secondary battery - Google Patents

Abstract

This secondary battery is provided with: a positive electrode which has a positive electrode active substance layer containing a fluorine-base binder with a melting point less than or equal to 166°C, the content of the fluorine-base binder in the positive electrode active substance layer being 0.7-2.8 mass%; a negative electrode which is provided opposite of the positive electrode; a separator which is provided between the positive electrode and the negative electrode; and a particle-containing layer which is provided between the positive electrode and the separator and which contains inorganic particles and a resin material, wherein the content of the resin material in the particle-containing layer is 10-50 mass%.

Description

Rechargeable battery

The present invention relates to a secondary battery.

In recent years, techniques for using a low-melting binder as a binder for electrodes have been studied in order to improve battery characteristics. For example, in Patent Literature 1, by using polyvinylidene fluoride (PVdF) having a melting point of 165 ° C. or less as a binder for a positive electrode, a coating layer having a stable porous structure while having a high porosity is obtained. Technologies to be realized have been proposed.

JP 2003-157829 A

In recent years, secondary batteries have been used as a power source for various electronic devices and electric vehicles, so that it is possible to improve safety in the event of an internal short circuit and to suppress a decrease in charge / discharge cycle characteristics. Is desired.

の An object of the present invention is to provide a secondary battery that can improve safety at the time of internal short circuit and can suppress a decrease in charge / discharge cycle characteristics.

In order to solve the above-mentioned problem, a positive electrode active material layer containing a fluorine-based binder having a melting point of 166 ° C. or less is provided, and the content of the fluorine-based binder in the positive electrode active material layer is 0.7% by mass or more. A positive electrode that is 8% by mass or less, a negative electrode provided to face the positive electrode, a separator provided between the positive electrode and the negative electrode, and a particle containing inorganic particles and a resin material provided between the positive electrode and the separator. And a resin material content in the particle-containing layer of 10% by mass or more and 50% by mass or less.

According to the present invention, safety at the time of an internal short circuit can be improved, and a decrease in charge / discharge cycle characteristics can be suppressed.

FIG. 1 is an exploded perspective view illustrating an example of a configuration of a nonaqueous electrolyte secondary battery according to a first embodiment of the present invention. FIG. 2 is a sectional view taken along the line II-II of FIG. 1. It is a graph which shows an example of a DSC curve of a fluorinated binder. FIG. 3 is a cross-sectional view illustrating a part of FIG. 2 in an enlarged manner. It is a block diagram showing an example of composition of electronic equipment concerning a 2nd embodiment of the present invention.

Embodiments of the present invention will be described in the following order.
1 First Embodiment (Example of Laminated Battery)
2 Second embodiment (example of electronic device)

<1 First embodiment>
[Configuration of Battery]
FIG. 1 shows an example of a configuration of a nonaqueous electrolyte secondary battery (hereinafter, simply referred to as “battery”) according to the first embodiment of the present invention. The battery is a so-called laminated battery, in which the electrode body 20 to which the positive electrode lead 11 and the negative electrode lead 12 are attached is housed inside the film-shaped exterior material 10, and can be reduced in size, weight, and thickness. It has become.

(4) The positive electrode lead 11 and the negative electrode lead 12 are respectively directed from the inside of the exterior material 10 to the outside, for example, in the same direction. Each of the positive electrode lead 11 and the negative electrode lead 12 is made of, for example, a metal material such as Al, Cu, Ni, or stainless steel, and has a thin plate shape or a mesh shape, respectively.

The outer package 10 is made of, for example, a rectangular aluminum laminate film in which a nylon film, an aluminum foil, and a polyethylene film are laminated in this order. The exterior material 10 is disposed, for example, such that the polyethylene film side and the electrode body 20 face each other, and the respective outer edges are adhered to each other by fusion bonding or an adhesive. An adhesive film 13 is inserted between the exterior material 10 and the positive electrode lead 11 and the negative electrode lead 12 to suppress invasion of outside air. The adhesive film 13 is made of a material having adhesiveness to the positive electrode lead 11 and the negative electrode lead 12, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene or modified polypropylene.

The packaging material 10 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film, instead of the above-described aluminum laminated film. Alternatively, it may be constituted by a laminate film in which a polymer film is laminated on one or both sides of an aluminum film as a core material.

FIG. 2 is a cross-sectional view of the electrode body 20 shown in FIG. 1 along the line II-II. The electrode body 20 is of a wound type, and has a configuration in which a long positive electrode 21 and a long negative electrode 22 are laminated via a long separator 23 and wound flat and spirally. The outermost peripheral portion is protected by a protective tape 24. An electrolytic solution as an electrolyte is injected into the exterior material 10 and impregnated in the positive electrode 21, the negative electrode 22, and the separator 23.

Hereinafter, the positive electrode 21, the negative electrode 22, the separator 23, and the electrolyte constituting the battery will be sequentially described.

(Positive electrode)
The positive electrode 21 includes, for example, a positive electrode current collector 21A and positive electrode active material layers 21B provided on both surfaces of the positive electrode current collector 21A. The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode current collector 21A may have a plate shape or a mesh shape. The cathode lead 11 may be configured by extending a part of the periphery of the cathode current collector 21A. The positive electrode active material layer 21B contains one or more positive electrode active materials capable of inserting and extracting lithium, and a binder. The positive electrode active material layer 21B may further include a conductive auxiliary as needed.

(Positive electrode active material)
As the positive electrode active material, for example, a lithium-containing compound such as lithium oxide, lithium phosphate, lithium sulfide, or an intercalation compound containing lithium is suitable, and a mixture of two or more of these may be used. To increase the energy density, a lithium-containing compound containing lithium, a transition metal element, and oxygen is preferable. As such a lithium-containing compound, for example, a lithium composite oxide having a layered rock salt type structure shown in the formula (A), a lithium composite phosphate having an olivine type structure shown in the formula (B), and the like are given. No. The lithium-containing compound is more preferably a compound containing at least one of the group consisting of Co, Ni, Mn and Fe as a transition metal element. Examples of such a lithium-containing compound include a lithium composite oxide having a layered rock salt type structure represented by the formula (C), (D) or (E), and a spinel type compound represented by the formula (F). Examples include a lithium composite oxide having a structure, a lithium composite phosphate having an olivine type structure represented by the formula (G), and specifically, LiNi _0.50 Co _0.20 Mn _0.30 O ₂ , LiCoO ₂ , and LiNiO. ₂ , LiNiaCo _1-a O ₂ (0 <a <1), LiMn ₂ O _4, LiFePO _{4 and the} like.

_{Li p Ni (1-qr)} Mn q M1 r O (2-y) X z ··· (A)
(However, in the formula (A), M1 represents at least one element selected from Group 2 to Group 15 excluding Ni and Mn. X represents at least one of Group 16 elements and Group 17 elements other than oxygen. P, q, y, and z are 0 ≦ p ≦ 1.5, 0 ≦ q ≦ 1.0, 0 ≦ r ≦ 1.0, −0.10 ≦ y ≦ 0.20, 0 ≦ It is a value within the range of z ≦ 0.2.)

Li _a M2 _b PO ₄ ... (B)
(However, in the formula (B), M2 represents at least one element selected from the group 2 to group 15. a and b are 0 ≦ a ≦ 2.0, 0.5 ≦ b ≦ 2.0 Value within the range of.)

Li _f Mn _(1-gh) Ni _g M3 _h O _(2-j) F _k ... (C)
(However, in the formula (C), M3 is at least one of the group consisting of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr and W. F, g, h, j and k are 0.8 ≦ f ≦ 1.2, 0 <g <0.5, 0 ≦ h ≦ 0.5, g + h <1, −0.1 ≦ j ≦ 0.2 and 0 ≦ k ≦ 0.1. Note that the composition of lithium differs depending on the state of charge and discharge, and the value of f represents a value in a completely discharged state.)

_{Li m Ni (1-n)} M4 n O (2-p) F q ··· (D)
(However, in the formula (D), M4 is at least one of the group consisting of Co, Mn, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Mo, Sn, Ca, Sr and W. M, n, p and q are 0.8 ≦ m ≦ 1.2, 0.005 ≦ n ≦ 0.5, −0.1 ≦ p ≦ 0.2, 0 ≦ q ≦ 0 The composition of lithium differs depending on the state of charge and discharge, and the value of m represents a value in a completely discharged state.)

Li _r Co _(1-s) M5 _s O _{(2-t) Fu} ... (E)
(However, in the formula (E), M5 is at least one of the group consisting of Ni, Mn, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Mo, Sn, Ca, Sr and W. R, s, t and u are 0.8 ≦ r ≦ 1.2, 0 ≦ s <0.5, −0.1 ≦ t ≦ 0.2, 0 ≦ u ≦ 0.1 The composition of lithium varies depending on the state of charge and discharge, and the value of r represents a value in a completely discharged state.)

_{Li v Mn 2-w M6 w} O x F y ··· (F)
(However, in the formula (F), M6 is at least one of the group consisting of Co, Ni, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Mo, Sn, Ca, Sr and W. V, w, x, and y are 0.9 ≦ v ≦ 1.1, 0 ≦ w ≦ 0.6, 3.7 ≦ x ≦ 4.1, and 0 ≦ y ≦ 0.1. (The composition of lithium varies depending on the state of charge and discharge, and the value of v represents a value in a completely discharged state.)

Li _z M7PO ₄ ... (G)
(However, in the formula (G), M7 is one of the group consisting of Co, Mg, Fe, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W and Zr. And z is a value in the range of 0.9 ≦ z ≦ 1.1. The composition of lithium differs depending on the state of charge and discharge, and the value of z is a value in a completely discharged state. Represents.)

As the positive electrode active material capable of inserting and extracting lithium, an inorganic compound not containing lithium, such as MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , NiS, and MoS, may be used. it can.

正極 The positive electrode active material capable of inserting and extracting lithium may be other than the above. Further, two or more of the above-described positive electrode active materials may be mixed in any combination.

(binder)
The binder includes a fluorine-based binder. The upper limit of the melting point of the fluorinated binder is 166 ° C or lower, preferably 160 ° C or lower, more preferably 155 ° C or lower. When the melting point of the fluorine-based binder is 166 ° C. or less, the binder is likely to flow when the positive electrode active material layer 21B is dried (heat treated) in the manufacturing process of the positive electrode 21, and the surface of the positive electrode active material particles can be broadly thinned. Since the film can be favorably covered with the film, the exposed surface of the positive electrode active material particles can be reduced. Therefore, the reaction between the positive electrode active material particles and the electrolytic solution can be reduced, and gas generation can be suppressed. In addition, a decrease in cycle characteristics can be suppressed. Although the lower limit of the melting point of the fluorine-based binder is not particularly limited, it is, for example, 152 ° C. or higher.

融 点 The melting point of the above-mentioned fluorine-based binder is measured as follows. First, the positive electrode 21 is taken out of the battery, washed and dried with dimethyl carbonate (DMC), then the positive electrode current collector 21A is removed, and heated and stirred in an appropriate dispersion medium (for example, N-methylpyrrolidone or the like). Then, the binder is dissolved in the dispersion medium. Thereafter, the positive electrode active material is removed by centrifugation, and the supernatant is filtered, and then the binder is removed by evaporation to dryness or reprecipitation in water.

Next, a sample of several to several tens mg was heated at a heating rate of 1 to 10 ° C./min by a differential scanning calorimeter (DSC, for example, Rigaku Thermoplus plus DSC 8230 manufactured by Rigaku Corporation), and then heated at 100 to 250 ° C. Of the endothermic peaks appearing in the temperature range up to (see FIG. 3), the temperature showing the maximum endothermic amount is defined as the melting point of the fluorine-based binder. In the present invention, a temperature at which a polymer becomes fluid by heating and heating is defined as a melting point.

It is preferable to use polyvinylidene fluoride (PVdF) as the fluorine-based binder from the viewpoint of improving the chemical stability and adhesion in the battery. As the polyvinylidene fluoride, it is preferable to use a homopolymer of vinylidene fluoride (VdF). As the polyvinylidene fluoride, a copolymer of vinylidene fluoride (VdF) and another monomer can be used. However, the polyvinylidene fluoride, which is a copolymer, swells and dissolves in the electrolytic solution. The characteristics of the positive electrode 21 may be deteriorated because the bonding is easy and the binding force is weak. As the polyvinylidene fluoride, one obtained by modifying a part of the terminal or the like with a carboxylic acid such as maleic acid may be used.

The content of the fluorine-based binder in the positive electrode active material layer 21B is 0.7% by mass to 2.8% by mass, preferably 1.0% by mass to 2.8% by mass, and more preferably 1.4% by mass. % To 2.8% by mass.

と If the content of the fluorine-based binder is less than 0.7% by mass, the amount of the binder present in the positive electrode active material layer 21B becomes insufficient, and the adhesiveness between the positive electrode active material layer 21B and the separator 23 decreases. Therefore, generation of a gap between the positive electrode active material layer 21B and the separator 23 cannot be suppressed. Therefore, a favorable lithium ion transfer path cannot be maintained, and the deterioration of cycle characteristics is reduced. Further, when the content of the fluorine-based binder is less than 0.7% by mass, the surface coverage of the cathode active material particles with the binder becomes insufficient, so that the reaction between the cathode active material particles and the electrolytic solution can be suppressed. become unable. Therefore, the safety of the battery is reduced. Further, when the content of the fluorine-based binder is less than 0.7% by mass, the binding between the positive electrode active material particles and the binding between the positive electrode active material particles and the positive electrode current collector 21A become insufficient. When the cathode 21 is wound flat, the cathode active material layer 21B falls off the cathode current collector 21A.

On the other hand, when the content of the binder exceeds 2.8% by mass, the binder excessively covers the surface of the positive electrode active material particles, and the binder excessively covers the surface of the positive electrode active material layer. Thereby, the occlusion and release of lithium ions with respect to the positive electrode active material particles are inhibited, and the movement of lithium ions at the interface between the separator and the positive electrode active material layer 21B is inhibited. Therefore, the migration resistance of lithium ions in the battery increases, and the cycle characteristics deteriorate. When the content of the binder exceeds 2.8% by mass, the flexibility of the positive electrode active material layer 21B decreases, and when the positive electrode 21 is wound flat, cracks occur in the positive electrode 21.

含有 The content of the above-mentioned fluorine-based binder is measured as follows. First, the cathode 21 is taken out of the battery, washed with DMC, and dried. Next, a sample of several to several tens of mg was subjected to a differential thermal balance (TG-DTA, for example, Rigaku Thermoplus TG8120 manufactured by Rigaku Corporation) at a temperature rising rate of 1 to 5 ° C./min in an air atmosphere at 600 ° C. C., and the content of the fluorine-based binder in the positive electrode active material layer 21B is determined from the weight loss at that time. The amount of weight loss due to the binder can be determined by isolating the binder as described in the method for measuring the melting point of the binder, performing TG-DTA measurement of the binder alone in an air atmosphere, Can be confirmed by examining how many times they burn.

(Conduction aid)
As the conductive additive, for example, at least one carbon material of graphite, carbon fiber, carbon black, acetylene black, Ketjen black, carbon nanotube, graphene, and the like can be used. Note that the conductive assistant may be any material having conductivity, and is not limited to a carbon material. For example, a metal material or a conductive polymer material may be used as the conductive assistant. Examples of the shape of the conductive additive include, but are not limited to, granules, scales, hollows, needles, and cylinders.

(Negative electrode)
The negative electrode 22 includes, for example, a negative electrode current collector 22A and negative electrode active material layers 22B provided on both surfaces of the negative electrode current collector 22A. The anode current collector 22A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. The negative electrode current collector 22A may have a plate shape or a mesh shape. The negative electrode lead 12 may be configured by extending a part of the peripheral edge of the negative electrode current collector 22A. The anode active material layer 22B includes one or more anode active materials capable of inserting and extracting lithium. The negative electrode active material layer 22B may further include at least one of a binder and a conductive additive as necessary.

In this battery, the electrochemical equivalent of the negative electrode 22 or the negative electrode active material is larger than the electrochemical equivalent of the positive electrode 21. In theory, lithium metal does not precipitate on the negative electrode 22 during charging. Is preferred.

(Negative electrode active material)
Examples of the negative electrode active material include carbon materials such as non-graphitizable carbon, easily graphitizable carbon, graphite, pyrolytic carbons, cokes, glassy carbons, organic polymer compound fired bodies, carbon fibers, and activated carbon. Is mentioned. Among them, the coke includes pitch coke, needle coke, petroleum coke and the like. An organic polymer compound fired body is obtained by firing a polymer material such as a phenol resin or a furan resin at an appropriate temperature and carbonizing the material, and a part thereof is hardly graphitizable carbon or easily graphitizable carbon. Some are classified as. These carbon materials are preferable because a change in crystal structure that occurs during charge and discharge is very small, a high charge and discharge capacity can be obtained, and good cycle characteristics can be obtained. Particularly, graphite is preferable because it has a large electrochemical equivalent and can obtain a high energy density. Further, non-graphitizable carbon is preferable because excellent cycle characteristics can be obtained. Furthermore, a material having a low charge / discharge potential, specifically, a material having a charge / discharge potential close to lithium metal is preferable because a high energy density of the battery can be easily realized.

Other examples of the negative electrode active material capable of increasing the capacity include a material containing at least one of a metal element and a metalloid element as a constituent element (for example, an alloy, a compound, or a mixture). If such a material is used, a high energy density can be obtained. In particular, when used together with a carbon material, high energy density can be obtained and excellent cycle characteristics can be obtained, which is more preferable. In the present invention, alloys include alloys containing one or more metal elements and one or more metalloid elements in addition to alloys composed of two or more metal elements. Further, a nonmetallic element may be included. The structure includes a solid solution, a eutectic (eutectic mixture), an intermetallic compound, and a structure in which two or more of them coexist.

As such a negative electrode active material, for example, a metal element or a metalloid element capable of forming an alloy with lithium is given. Specific examples include Mg, B, Al, Ti, Ga, In, Si, Ge, Sn, Pb, Bi, Cd, Ag, Zn, Hf, Zr, Y, Pd and Pt. These may be crystalline or amorphous.

As the negative electrode active material, a material containing a metal element or a metalloid element belonging to the group 4B in the short-periodic periodic table as a constituent element is preferable, and a material containing at least one of Si and Sn as a constituent element is more preferable. This is because Si and Sn have a large ability to insert and extract lithium and can obtain a high energy density. Examples of such a negative electrode active material include a simple substance, an alloy, or a compound of Si, a simple substance, an alloy, or a compound of Sn, and a material having at least one or more of them.

As an alloy of Si, for example, Sn, Ni, Cu, Fe, Co, Mn, Zn, In, Ag, Ti, Ge, Bi, Sb, Nb, Mo, Al, as second constituent elements other than Si, Examples include those containing at least one selected from the group consisting of P, Ga, and Cr. As an alloy of Sn, for example, as a second constituent element other than Sn, Si, Ni, Cu, Fe, Co, Mn, Zn, In, Ag, Ti, Ge, Bi, Sb, Nb, Mo, Al, Examples include those containing at least one selected from the group consisting of P, Ga, and Cr.

Examples of the compound of Sn or the compound of Si include those containing O or C as a constituent element. These compounds may contain the second constituent element described above.

Above all, it is preferable that the Sn-based negative electrode active material contains Co, Sn, and C as constituent elements and has a low crystallinity or an amorphous structure.

Other negative electrode active materials include, for example, metal oxides or polymer compounds capable of inserting and extracting lithium. Examples of the metal oxide include lithium titanium oxide containing Li and Ti, such as lithium titanate (Li ₄ Ti ₅ O ₁₂ ), iron oxide, ruthenium oxide, and molybdenum oxide. Examples of the polymer compound include polyacetylene, polyaniline, and polypyrrole.

(binder)
Examples of the binder include resin materials such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC), and these resin materials as main components. At least one selected from the group consisting of copolymers and the like is used.

(Conduction aid)
As the conductive auxiliary, the same as the positive electrode active material layer 21B can be used.

(Separator)
The separator 23 is an insulating porous film that separates the positive electrode 21 and the negative electrode 22, suppresses a short circuit due to contact between the two electrodes, and allows lithium ions to pass therethrough. Since the electrolyte is held in the pores of the separator 23, the separator 23 preferably has characteristics of high resistance to the electrolyte, low reactivity, and difficulty in expanding.

The separator 23 is made of, for example, a porous material made of polytetrafluoroethylene, polyolefin resin (such as polypropylene (PP) or polyethylene (PE)), acrylic resin, styrene resin, polyester resin, nylon resin, or a resin obtained by blending these resins. It may be formed of a porous film, and may have a structure in which two or more of these porous films are laminated.

Above all, a porous film made of polyolefin is preferable because it has an excellent short circuit prevention effect and can improve the safety of the battery by a shutdown effect. In particular, polyethylene is preferable as a material constituting the separator 23 because it can obtain a shutdown effect in the range of 100 ° C. or more and 160 ° C. or less and has excellent electrochemical stability. Among them, low-density polyethylene, high-density polyethylene, and linear polyethylene are suitably used because they have an appropriate melting temperature and are easily available. Alternatively, a material obtained by copolymerizing or blending a resin having chemical stability with polyethylene or polypropylene can be used. Alternatively, the porous membrane may have a structure of three or more layers in which a polypropylene layer, a polyethylene layer, and a polypropylene layer are sequentially laminated. The method for producing the separator 23 may be either a wet method or a dry method.

不 織布 A non-woven fabric may be used as the separator 23. Aramid fiber, glass fiber, polyolefin fiber, polyethylene terephthalate (PET) fiber, nylon fiber, or the like can be used as the fiber constituting the nonwoven fabric. Further, these two or more kinds of fibers may be mixed to form a nonwoven fabric.

(4) The heat shrinkage at 150 ° C. of the separator 23 provided with the resin layer 23A is preferably 40% or less. When the heat shrinkage of the separator 23 is 40% or less, the heat shrinkage at the time of short circuit can be suppressed.

FIG. 4 is a cross-sectional view in which a part of FIG. 2 is enlarged. Particle-containing layers 23A are provided on both surfaces of the separator 23. In the present embodiment, a configuration in which the particle-containing layer 23A is provided on both surfaces of the separator 23 will be described. However, the particle-containing layer 23A may be provided only on one surface facing the positive electrode 21. However, from the viewpoint of improving safety and the like, it is preferable that the particle-containing layers 23A are provided on both surfaces. Further, in the present embodiment, a configuration in which the particle-containing layer 23A is provided on the surface of the separator 23 will be described. However, the particle-containing layer 23A may be provided on the surfaces of the positive electrode active material layer 21B and the negative electrode active material layer 22B. Good.

The particle-containing layer 23A includes inorganic particles having insulating properties, and a resin material that binds the inorganic particles to the surface of the separator 23 and binds the inorganic particles. Since the separator 53 includes the particle-containing layer 23A, the adhesion between the positive electrode active material layer 21B containing a fluorine-based binder having a melting point of 166 ° C. or less and the separator 23 can be increased. Even if the electrode body 20 repeatedly expands and contracts, generation of a gap between the positive electrode 21 and the separator 23 can be suppressed. Therefore, it is possible to suppress a decrease in cycle characteristics and to prevent the battery 40 from swelling.

樹脂 The content of the resin material in the particle-containing layer 23A is 10% by mass or more and 50% by mass or less. When the content of the resin material is less than 10% by mass, the amount of the binder present in the particle-containing layer 23 becomes insufficient, and the adhesiveness between the positive electrode active material layer 21B and the particle-containing layer 23 decreases. Therefore, when the electrode body 20 repeatedly expands and contracts due to the charge / discharge cycle, generation of a gap between the positive electrode 21 and the separator 23 cannot be suppressed. Therefore, it is not possible to maintain a good lithium ion transfer path, and the cycle characteristics deteriorate. On the other hand, if the content of the resin material exceeds 50% by mass, the resin material contained in the particle-containing layer 23A is too large, and the resin material of the swollen particle-containing layer 23B and the resin material of the similarly swollen cathode active material layer 21B are contained. Since the binder is mixed at the interface between the separator 23 and the positive electrode active material layer 21B, the surface of the positive electrode active material layer 21B is excessively covered with the resin material and the binder. As a result, lithium ion migration at the interface between the separator 23 and the positive electrode active material layer 21B is hindered, and the cycle characteristics deteriorate.

樹脂 The content of the resin material in the particle-containing layer 23A is measured as follows. From the image of the cross section SEM of the separator 23, the area is calculated by image analysis. The weight is calculated from the specific gravity of the binder and the particles. Alternatively, the content is calculated from the difference between the weight obtained by peeling off the particle-containing layer 23A and the weight heated to 400 ° C.

The resin material contained in the particle-containing layer 23A may have, for example, a three-dimensional network structure in which fibrils are formed and fibrils are connected to each other continuously. By supporting the inorganic particles on the resin material having the three-dimensional network structure, the inorganic particles can maintain a dispersed state without being connected to each other. In addition, the resin material may bind the surface of the separator 23 and the inorganic particles without fibrillation. In this case, higher binding properties can be obtained. By providing the particle-containing layer 23A on one or both surfaces of the separator 23 as described above, oxidation resistance, heat resistance, and mechanical strength can be imparted to the separator 23.

The inorganic particles include, for example, at least one of a metal oxide, a metal nitride, a metal carbide, a metal sulfide, and the like. Metal oxides are aluminum oxide (alumina, Al ₂ O ₃ ), boehmite (hydrated aluminum oxide), magnesium oxide (magnesia, MgO), titanium oxide (titania, TiO ₂ ), zirconium oxide (zirconia, ZrO ₂ ) , Silicon oxide (silica, SiO ₂ ) and yttrium oxide (yttria, Y ₂ O ₃ ). The metal nitride preferably contains at least one of silicon nitride (Si ₃ N ₄ ), aluminum nitride (AlN), boron nitride (BN), titanium nitride (TiN), and the like. The metal carbide preferably contains at least one of silicon carbide (SiC) and boron carbide (B ₄ C). The metal sulfide preferably contains barium sulfate (BaSO ₄ ) or the like. Further, zeolite _{(M 2 / n O · Al} 2 O 3 · xSiO 2 · yH 2 O, M represents a metal element, x ≧ 2, y ≧ 0 ) porous aluminosilicates such as layered silicates, titanates At least one of minerals such as barium (BaTiO ₃ ) and strontium titanate (SrTiO ₃ ) may be included. Among them, it is preferable to include at least one of alumina, titania (particularly having a rutile structure), silica, magnesia, and the like, and more preferable to include alumina. The inorganic particles have oxidation resistance and heat resistance, and the particle-containing layer 23A on the side facing the positive electrode containing the inorganic particles has strong resistance to an oxidizing environment near the positive electrode during charging. The shape of the inorganic particles is not particularly limited, and any of a spherical shape, a plate shape, a fibrous shape, a cubic shape, and a random shape can be used.

Examples of the resin material constituting the particle-containing layer 23A include fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene, and fluorine-containing rubbers such as vinylidene fluoride-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer. Styrene-butadiene copolymer or hydride thereof, acrylonitrile-butadiene copolymer or hydride thereof, acrylonitrile-butadiene-styrene copolymer or hydride thereof, methacrylate-acrylate copolymer, styrene-acryl Acid ester copolymer, acrylonitrile-acrylate copolymer, ethylene propylene rubber, polyvinyl alcohol, rubber such as polyvinyl acetate, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, cal Cellulose derivatives such as xylmethylcellulose, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamide such as wholly aromatic polyamide (aramid), polyamideimide, polyacrylonitrile, polyvinyl alcohol, polyether, acrylic acid Examples of such resins include resins and polyesters having at least one of a melting point and a glass transition temperature of 180 ° C. or more and having high heat resistance. These resin materials may be used alone or as a mixture of two or more. Above all, from the viewpoint of oxidation resistance and flexibility, a fluororesin such as polyvinylidene fluoride is preferable, and from the viewpoint of heat resistance, it is preferable to contain aramid or polyamideimide.

粒径 The particle size of the inorganic particles is preferably in the range of 1 nm to 10 μm. If it is smaller than 1 nm, it is difficult to obtain, and even if it can be obtained, it is not worth the cost. On the other hand, if it is larger than 10 μm, the distance between the electrodes becomes large, and a sufficient amount of the active material cannot be obtained in a limited space, so that the battery capacity decreases. In addition, the above-mentioned inorganic particles may be contained in the separator 23 as a base material.

平均 The average thickness of the particle-containing layer 23A is preferably 1 μm or more and 5 μm or less. When the average thickness of the particle-containing layer 23A is 1 μm or more, fusion between the positive electrode 21 and the separator 23 and fusion between the negative electrode 22 and the separator 23 during high-temperature pressing are ensured, and expansion after a cycle is suppressed. be able to. On the other hand, when the average thickness of the particle-containing layer 23A is 5 μm or less, cycle characteristics can be improved.

平均 The average air permeability of the separator 23 provided with the particle-containing layer 23A is preferably 10 s / 100 ml or more and 100 s / 100 ml or less. When the average air permeability of the separator 23 provided with the particle-containing layer 23A is 10 s / 100 ml or more, it is possible to suppress heat shrinkage at the time of short circuit. On the other hand, when the average air permeability of the separator 23 provided with the particle-containing layer 23A is 100 s / 100 ml or less, the cycle characteristics can be improved.

(4) The peel strength between the positive electrode 21 and the separator 23 is preferably 5 mN / mm or more and 35 mN / mm or less. When the peel strength is 5 mN / mm or more, generation of a gap between the positive electrode active material layer 21B and the separator 23 can be suppressed. Therefore, a favorable lithium ion movement path can be maintained, and a decrease in cycle characteristics can be suppressed. On the other hand, when the peel strength is 35 mN / mm or less, the adhesion between the positive electrode 21 and the separator 23 becomes excessively high and the inhibition of lithium ion migration at the interface between the separator and the positive electrode active material layer 21B is suppressed. can do. Therefore, an increase in the migration resistance of lithium ions in the battery can be suppressed, and a decrease in cycle characteristics can be suppressed. The peel strength between the positive electrode 21 and the separator 23 is measured according to iso29862: 2007 (JIS Z0237).

(Electrolyte)
The electrolyte is a so-called non-aqueous electrolyte, and includes an organic solvent (non-aqueous solvent) and an electrolyte salt dissolved in the organic solvent. The electrolytic solution may contain a known additive in order to improve battery characteristics. Note that, instead of the electrolytic solution, an electrolytic layer containing the electrolytic solution and a polymer compound serving as a holder for holding the electrolytic solution may be used. In this case, the electrolyte layer may be in a gel state.

環状 As the organic solvent, a cyclic carbonate such as ethylene carbonate or propylene carbonate can be used, and it is preferable to use one of ethylene carbonate and propylene carbonate, particularly a mixture of both. This is because the cycle characteristics can be further improved.

As the organic solvent, it is preferable to use a mixture of chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and methylpropyl carbonate in addition to these cyclic carbonates. This is because high ionic conductivity can be obtained.

It is preferable that the organic solvent further contains 2,4-difluoroanisole or vinylene carbonate. This is because 2,4-difluoroanisole can further improve the discharge capacity, and vinylene carbonate can further improve the cycle characteristics. Therefore, it is preferable to use a mixture of these, because the discharge capacity and cycle characteristics can be further improved.

Besides these, organic solvents include butylene carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, and 4-methyl-1,3 -Dioxolan, methyl acetate, methyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropironitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N, N- Examples thereof include dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, dimethylsulfoxide, and trimethyl phosphate.

Note that compounds in which at least part of hydrogen in these organic solvents has been replaced with fluorine may be preferable because the reversibility of the electrode reaction can be improved depending on the type of electrode to be combined.

Examples of the electrolyte salt include a lithium salt, and one kind may be used alone, or two or more kinds may be used in combination. The lithium _{salt, LiPF 6, LiBF 4, LiAsF} 6, LiClO 4, LiB (C 6 H 5) 4, LiCH 3 SO 3, LiCF 3 SO 3, LiN (SO 2 CF 3) 2, LiC (SO 2 CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, lithium difluoro [oxolate-O, O ′] borate, lithium bisoxalate borate, or LiBr. Above all, LiPF ₆ is preferable because high ion conductivity can be obtained and cycle characteristics can be further improved.

[Battery operation]
In the battery having the above structure, when charged, for example, lithium ions are released from the positive electrode active material layer 21B and occluded in the negative electrode active material layer 22B via the electrolytic solution. Further, when discharging is performed, for example, lithium ions are released from the negative electrode active material layer 22B and occluded in the positive electrode active material layer 21B via the electrolytic solution.

[Battery manufacturing method]
Next, an example of the method for manufacturing the battery according to the first embodiment of the present invention will be described.

(Preparation process of positive electrode)
The positive electrode 21 is manufactured as follows. First, for example, a positive electrode mixture is prepared by mixing a positive electrode active material, a binder, and a conductive auxiliary, and the positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) to form a paste. A positive electrode mixture slurry is prepared. Next, the positive electrode mixture slurry is applied to the positive electrode current collector 21A, the solvent is dried, and compression molding is performed by a roll press or the like to form the positive electrode active material layer 21B, and the positive electrode 21 is obtained.

(Negative electrode fabrication process)
The negative electrode 22 is manufactured as follows. First, for example, a negative electrode mixture is prepared by mixing a negative electrode active material and a binder, and this negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to prepare a paste-like negative electrode mixture slurry. I do. Next, the negative electrode mixture slurry is applied to the negative electrode current collector 22A, the solvent is dried, and compression molding is performed by a roll press or the like to form the negative electrode active material layer 22B, and the negative electrode 22 is obtained.

(Preparation step of particle-containing layer)
The particle-containing layer 23A is manufactured as follows. First, a coating material for forming a particle-containing layer is prepared by adding a resin material and inorganic particles to a solvent and mixing them. Next, the paint is uniformly applied to both surfaces of the separator 23 and dried to form a particle-containing layer 23A. After applying the coating material on both surfaces of the separator 23, the resin material is passed through a poor solvent and solvent-friendly bath of the solvent to separate phases, and then dried to form the particle-containing layer 23A. You may.

(Production process of electrode body)
The wound electrode body 20 is manufactured as follows. First, the cathode lead 11 is attached to one end of the cathode current collector 21A by welding, and the anode lead 12 is attached to one end of the anode current collector 22A by welding. Next, the positive electrode 21 and the negative electrode 22 are wrapped around a flat core through a separator 23 having a particle-containing layer 23A formed on both surfaces, and wound many times in the longitudinal direction. Then, a protective tape 24 is adhered to the electrode body 20.

(Sealing process)
The exterior body 10 seals the electrode body 20 as follows. First, the electrode body 20 is sandwiched between the package members 10, and the outer peripheral edge portion excluding one side is heat-fused into a bag shape, and is housed inside the package member 10. At that time, an adhesive film 13 is inserted between the positive electrode lead 11 and the negative electrode lead 12 and the exterior material 10. Note that the adhesive film 13 may be attached to each of the positive electrode lead 11 and the negative electrode lead 12 in advance. Next, after injecting the electrolytic solution into the exterior material 10 from one side of the unfused part, one side of the unfused part is heat-sealed in a vacuum atmosphere to be sealed. Thus, the batteries shown in FIGS. 1 and 2 are obtained.

[effect]
In the battery according to the first embodiment, a positive electrode 21 having a positive electrode active material layer 21B containing a fluorine-based binder having a melting point of 166 ° C. or less, and a particle-containing layer 23A containing inorganic particles and a resin material are provided on both surfaces. The separator 23 is combined. Further, the content of the fluorine-based binder in the positive electrode active material layer 21B is 0.7% by mass or more and 2.8% by mass or less, and the content of the resin material in the particle containing layer 23A is 10% by mass or more and 50% by mass. It is as follows. Thereby, safety at the time of an internal short circuit can be improved, and a decrease in charge / discharge cycle characteristics can be suppressed. In addition, battery swelling during high-temperature storage can be suppressed.

<2 Second Embodiment>
In the second embodiment, an electronic device including the battery according to the first embodiment will be described.

FIG. 5 shows an example of the configuration of an electronic device 400 according to the second embodiment of the present invention. The electronic device 400 includes an electronic circuit 401 of the electronic device main body and the battery pack 300. Battery pack 300 is electrically connected to electronic circuit 401 via positive electrode terminal 331a and negative electrode terminal 331b. The electronic device 400 may have a configuration in which the battery pack 300 is detachable.

Examples of the electronic device 400 include a notebook personal computer, a tablet computer, a mobile phone (for example, a smartphone), a portable information terminal (Personal Digital Assistants: PDA), a display device (LCD (Liquid Crystal Display), and an EL (Electro Luminescence). A) Display, electronic paper, etc.), imaging device (eg, digital still camera, digital video camera, etc.), audio equipment (eg, portable audio player), game equipment, cordless phone handset, electronic book, electronic dictionary, radio, headphone, navigation System, memory card, pacemaker, hearing aid, power tool, electric shaver, refrigerator, air conditioner, TV, stereo, water heater, microwave oven, dishwasher, washing machine, dryer, lighting equipment, toy, medical equipment, robot Load conditioners, although traffic signals and the like, without such limited thereto.

(Electronic circuit)
The electronic circuit 401 includes, for example, a CPU (Central Processing Unit), a peripheral logic unit, an interface unit, a storage unit, and the like, and controls the entire electronic device 400.

(Battery pack)
The battery pack 300 includes an assembled battery 301 and a charge / discharge circuit 302. Battery pack 300 may further include an exterior material (not shown) that accommodates assembled battery 301 and charge / discharge circuit 302 as necessary.

The assembled battery 301 is configured by connecting a plurality of secondary batteries 301a in series and / or in parallel. The plurality of secondary batteries 301a are connected in, for example, n parallel and m series (n and m are positive integers). FIG. 5 shows an example in which six rechargeable batteries 301a are connected in two parallel and three series (2P3S). As the secondary battery 301a, the battery according to the above-described first embodiment is used.

Here, a case will be described where the battery pack 300 includes an assembled battery 301 including a plurality of secondary batteries 301a. However, the battery pack 300 includes a single secondary battery 301a instead of the assembled battery 301. May be adopted.

The charging / discharging circuit 302 is a control unit that controls charging / discharging of the battery pack 301. Specifically, at the time of charging, the charge / discharge circuit 302 controls charging of the battery pack 301. On the other hand, at the time of discharging (that is, at the time of using the electronic device 400), the charging / discharging circuit 302 controls discharging to the electronic device 400.

ケ ー ス As the exterior material, for example, a case made of a metal, a polymer resin, or a composite material thereof can be used. Examples of the composite material include a laminate in which a metal layer and a polymer resin layer are laminated.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.

融 点 The melting point of the fluorine-based binder (PVdF) in the following Examples and Comparative Examples was determined by the measurement method described in the first embodiment.

[Examples 1-1 to 1-3, Comparative Examples 1-1 and 1-2]
(Preparation process of positive electrode)
A positive electrode was produced as follows. 98.3% by mass of lithium cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material, 1.4% by mass of PVdF (homopolymer of VdF) having a melting point of 155 ° C. as a binder, and 0.3% by mass of carbon black as a conductive agent % To obtain a positive electrode mixture, and this positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) to obtain a paste-like positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry was applied to the positive electrode current collector (aluminum foil) using a coating device, and then dried to form a positive electrode active material layer. Finally, the positive electrode active material layer was compression-molded using a press until the mixture density reached 4.0 g / cm ³ .

(Negative electrode fabrication process)
A negative electrode was manufactured as follows. First, 96% by mass of artificial graphite powder as a negative electrode active material,
After mixing 1% by mass of styrene butadiene rubber (SBR) as a first binder, 2% by mass of PVdF as a second binder, and 1% by mass of carboxymethyl cellulose (CMC) as a thickener, a negative electrode mixture was obtained. This negative electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) to obtain a paste-like negative electrode mixture slurry. Subsequently, the negative electrode mixture slurry was applied to the negative electrode current collector (copper foil) using a coating device and then dried. Finally, the negative electrode active material layer was compression molded using a press.

(Step of preparing electrolyte solution)
An electrolyte was prepared as follows. First, a mixed solvent was prepared by mixing EC, PC, and ethyl formate in a volume ratio of 11: 9: 80. Subsequently, in this mixed solvent, lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt was dissolved at a concentration of 1 mol / l to prepare an electrolyte solution.

(Coating layer manufacturing process)
A coat layer (particle-containing layer) was prepared as follows. First, PVdF (a homopolymer of VdF) was dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) so as to be an 8% solution. Subsequently, alumina particles were mixed and dispersed in an 8% NMP solution so that the blending amount of PVdF to make the total amount of PVdF and alumina particles was 5 to 55% by mass, to obtain a mixed solution. Next, using a coating apparatus, the mixed solution was applied to both sides of a microporous polyethylene film as a separator, and dried to form a coat layer. In addition, it produced so that the thickness of a coat layer might be set to 3.0 micrometers.

(Production process of laminated battery)
A laminated battery was manufactured as follows. First, a positive electrode lead made of aluminum was welded to the positive electrode current collector, and a negative electrode lead made of copper was welded to the negative electrode current collector. Subsequently, the positive electrode and the negative electrode are adhered to each other via a polyethylene film having a coat layer formed on both surfaces, and then wound in the longitudinal direction, and a protective tape is attached to the outermost peripheral portion, thereby obtaining a flat-shaped winding. A round electrode body was produced. Next, this electrode body was loaded between the package members, and three sides of the package member were heat-sealed, and one side had an opening without heat-sealing. As the exterior material, a moisture-proof aluminum laminated film in which a nylon film having a thickness of 25 μm, an aluminum foil having a thickness of 40 μm, and a polypropylene film having a thickness of 30 μm were laminated in this order from the outermost layer was used.

(5) Thereafter, an electrolytic solution was injected from the opening of the packaging material, and the remaining one side of the packaging material was thermally fused under reduced pressure to seal the electrode body. Furthermore, compression molding was performed from both flat surfaces at a pressure of 10 kgf at 60 ° C. As a result, a desired laminated battery was obtained.

[Comparative Example 1-3]
A battery was obtained in the same manner as in Example 1-1, except that PVdF was dispersed in an organic solvent in the step of forming a coat layer, and then applied to both sides of a polyethylene film without mixing alumina particles.

[Examples 2-1 to 2-3, Comparative Examples 2-1 to 2-3]
In the production process of the positive electrode, the same procedures as in Examples 1-1 to 1-3 and Comparative examples 1-1 to 1-3 were performed except that PVdF (homopolymer of VdF) having a melting point of 166 ° C. was used as a binder. I got a battery.

[Comparative Examples 3-1 to 3-6]
Except that PVdF having a melting point of 172 ° C. (homopolymer of VdF)) was used as a binder in the process of producing the positive electrode, the same procedures as in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3 were performed. I got a battery.

[Comparative Examples 4-1 to 4-6]
99.3% by mass of lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material, 0.4% by mass of PVdF (homopolymer of VdF) having a melting point of 166 ° C. as a binder, and 0.3% by mass of carbon black as a conductive agent %, And batteries were obtained in the same manner as in Examples 1-1 to 1-3 and Comparative examples 1-1 to 1-3, except that they were mixed.

[Examples 5-1 to 5-3, Comparative Examples 5-1 to 5-3]
99.0% by mass of lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material, 0.7% by mass of PVdF (homopolymer of VdF) having a melting point of 166 ° C. as a binder, and 0.3% by mass of carbon black as a conductive agent %, And batteries were obtained in the same manner as in Examples 1-1 to 1-3 and Comparative examples 1-1 to 1-3, except that they were mixed.

[Examples 6-1 to 6-3, Comparative Examples 6-1 to 6-3]
96.9% by mass of lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material, 2.8% by mass of PVdF (homopolymer of VdF) having a melting point of 166 ° C. as a binder, and 0.3% by mass of carbon black as a conductive agent %, And batteries were obtained in the same manner as in Examples 1-1 to 1-3 and Comparative examples 1-1 to 1-3, except that they were mixed.

[Comparative Examples 7-1 to 7-6]
96.7% by mass of lithium cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material, 3.0% by mass of PVdF (homopolymer of VdF) having a melting point of 166 ° C. as a binder, and 0.3% by mass of carbon black as a conductive agent %, And batteries were obtained in the same manner as in Examples 1-1 to 1-3 and Comparative examples 1-1 to 1-3, except that they were mixed.

[Examples 8-1 to 8-5]
In the manufacturing process of the laminated battery, the peeling strength between the positive electrode and the separator is changed by adjusting the compression pressure in the range of 2 to 30 kgf when compressing the laminated battery in which the electrolyte is injected from both flat surfaces in the range of 2 to 30 kgf. A battery was obtained in the same manner as in Example 1-1, except that the above procedure was repeated.

[Examples 9-1 to 9-4]
A battery was obtained in the same manner as in Example 1-1, except that the thickness of the coat layer was changed by adjusting the applied thickness of the mixed solution in the process of forming the coat layer.

[Examples 10-1 to 10-4]
A battery was obtained in the same manner as in Example 1-1, except that a coat layer was formed on a microporous polyethylene film having different air permeability.

[Examples 11-1 to 11-4]
In the step of forming the coat layer, PVdF (a homopolymer of VdF) is dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) so as to be a 3 to 15% solution, whereby the separator on which the coat layer is formed is formed. A battery was obtained in the same manner as in Example 1-1, except that the heat shrinkage was changed.

[Evaluation]
The following evaluation was performed on the batteries obtained as described above and the positive electrodes used in those batteries.

(Nail penetration test)
After charging the batteries at different voltages (4.20 to 4.45 V), a nail of φ2.5 mm was pierced into the center of each battery at a piercing speed of 100 mm / sec in a 23 ° C. environment and penetrated, and the thermal runaway occurred. Was checked. The highest voltage without thermal runaway is shown in Tables 1 and 2.

(Drop off of the positive electrode active material layer)
At the stage of slitting the positive electrode, it was confirmed whether or not some positive electrode active material layers on the positive electrode current collector were peeled off from the positive electrode current collector.

(Positive electrode crack)
The completed battery was disassembled, and it was confirmed whether or not holes were formed in the positive electrode current collector at the innermost periphery.

(Cycle characteristics)
First, the battery is allowed to stand still in a 45 ° C. environment until the temperature of the battery is stabilized, and then charged to 4.4 V with a current of 1 C, and then discharged to 3.0 V with a current of 1 C to obtain 1 C of the first cycle. The discharge capacity was determined. Subsequently, the charge / discharge cycle was repeated under the same charge / discharge conditions as in the first cycle, whereby the 1C discharge capacity at the 600th cycle was determined. Next, the cycle characteristics were determined by the following equation. Note that the current of 1 C is a current value at which a battery can be charged or discharged in one hour.
Cycle characteristics (%) = [(1C discharge capacity at 600th cycle) / (1C discharge capacity at 1st cycle)] × 100

(High temperature storage blister rate)
After the battery was fully charged, it was stored for one month in a 60 ° C. environment, and the swelling change rate before storage was measured.

(4) The following evaluation was performed on the separator used in the above-described battery and provided with a coat layer on both sides (hereinafter, appropriately referred to as a “separator with a coat layer”).

(Peel strength of separator with coat layer)
The peel strength of the separator was measured based on iso29862: 2007 (JIS Z 0237). Note that a general-purpose double-sided adhesive tape G9000 manufactured by Dexerials was used as a peeling tape.

(Average thickness of coat layer)
After measuring the thickness of the coat layer (particle-containing layer) at 20 points using a contact thickness meter, the measured values were simply averaged (arithmetic average) to obtain the average thickness of the coat layer. The measurement with a contact thickness gauge was performed using a cemented carbide sphere measuring element φ9.5 mm under the condition of a weight of 0.01 N. In addition, 20 measurement points were randomly selected from the separator with a coat layer.

(Average air permeability of the separator with coat layer)
Using a Gurley air permeability meter having a circular hole with an outer diameter of 28.6 mm, the Gurley air permeability was measured at 10 positions in the width direction of the separator with a coat layer, and the measured values were simply averaged ( (Arithmetic average) to obtain the average air permeability of the separator with the coat layer. Gurley air permeability was measured according to JIS P8117.

(Thermal shrinkage of the separator with coat layer)
First, a test piece was prepared by cutting a separator having a coat layer into a size of 5 cm × 5 cm. Next, the test piece was sandwiched between two stainless steel plates fixed with clips, left in a thermostat at 150 ° C. for 30 minutes, taken out, and the length of the test piece was measured. Next, the reduction ratio of the length based on the length before the test was determined as a percentage, and this was defined as the heat shrinkage of the separator with a coat layer.

Table 1 shows the configurations and evaluation results of the batteries of Examples 1-1 to 2-3 and Comparative Examples 1-1 to 3-6.

Table 2 shows the configurations and evaluation results of the batteries of Examples 5-1 to 6-3 and Comparative examples 4-1 to 7-6.

Table 3 shows the configurations and evaluation results of the batteries of Examples 8-1 to 8-5, 9-1 to 9-4, 10-1 to 10-4, and 11-1 to 11-4.

Table 1 shows the following.
Examples 1-1 to 1-3, 2-1 to 2-3: Positive electrode active material layer containing PVdF having a melting point of 166 ° C. or less and content of PVdF (resin material) is 10 to 50% by mass. In a battery combined with a separator provided with a coat layer, safety at the time of an internal short circuit (a nail piercing test) can be improved, a decrease in cycle characteristics can be suppressed, and battery swelling during high-temperature storage ( Gas generation) can be suppressed.
It is considered that the suppression of the decrease in cycle characteristics and the suppression of battery swelling are due to the following reasons. That is, since the positive electrode active material layer contains PVdF having a melting point of 166 ° C. or less, the surface of the positive electrode active material particles is thinly and widely covered with PVdF. Further, since the coat layer contains 10 to 50% by mass of PVdF, swelling of the coat layer is suppressed, and the adhesiveness between the positive electrode active material layer and the coat layer is adjusted to an appropriate strength. As a result, a decrease in cycle characteristics can be suppressed, and swelling (gas generation) of the battery during high-temperature storage can be suppressed.

Comparative Examples 1-1 and 2-1: In a battery in which a positive electrode active material layer containing PVdF having a melting point of 166 ° C. or less and a separator provided with a coat layer having a PVdF content of less than 10% by mass were combined. Although the safety at the time of an internal short circuit (a nail penetration test) can be improved, the cycle characteristics are reduced and the battery swells during high-temperature storage.
This decrease in cycle characteristics is considered to be due to the following reasons. That is, when the content of PVdF in the coat layer is less than 10% by mass, the adhesiveness between the separator and the positive electrode and between the separator and the negative electrode is extremely weak, and when the electrode body repeatedly expands and contracts due to a charge and discharge cycle. Therefore, a gap is easily generated between the positive electrode and the negative electrode. Therefore, the movement path of lithium ions between the positive electrode and the negative electrode is easily broken. Therefore, the cycle characteristics deteriorate.
The increase in the high-temperature storage swelling ratio is considered to be due to the following reason. That is, when the content of PVdF in the coat layer is less than 10% by mass, the area of the swollen coat layer in which the PVdF covers the positive electrode active material layer becomes extremely small. Therefore, the reaction between the positive electrode active material layer and the electrolytic solution increases, and the battery swells during high-temperature storage.

Comparative Examples 1-2, 1-3, 2-2, and 2-3: A positive electrode active material layer containing PVdF having a melting point of 166 ° C. or less and a coat layer containing more than 50% by mass of PVdF were provided. In a battery combined with a separator, the cycle characteristics deteriorate.
This decrease in cycle characteristics is considered to be due to the following reasons. That is, since the PVdF contained in the coat layer is too large, the PVdF of the swollen coat layer and the low-melting PVdF of the similarly swollen cathode active material layer are mixed at the interface between the separator and the cathode active material layer, The surface of the positive electrode active material layer is excessively covered with PVdF. As a result, lithium ion migration at the interface between the separator and the positive electrode active material layer is hindered, and the cycle characteristics deteriorate.

Comparative Examples 3-1 to 3-6: When the melting point of PVdF contained in the positive electrode active material layer exceeds 166 ° C., the cycle characteristics deteriorate except when the content of PVdF in the coat layer is 100%. In addition, battery swelling during high-temperature storage increases.
This decrease in cycle characteristics and increase in battery swelling during high-temperature storage are considered to be due to the following reasons. That is, when the melting point of PVdF contained in the positive electrode active material layer exceeds 166 ° C., the surface coating of the positive electrode active material particles with PVdF becomes insufficient, so that the adhesiveness between the separator and the positive electrode becomes weak, and the charge-discharge cycle causes When the electrode body repeatedly expands and contracts, a gap is easily generated between the positive electrode and the negative electrode. Therefore, the movement path of lithium ions between the positive electrode and the negative electrode is easily broken. In addition, since the surface coating of the positive electrode active material particles becomes insufficient, the reaction between the positive electrode active material particles and the electrolyte cannot be suppressed.
When the content of PVdF in the coat layer is 100%, it is considered that battery swelling during high-temperature storage can be suppressed for the following reasons. That is, since the amount of the PVdF of the swollen coat layer mixed with the low-melting PVdF of the similarly swollen cathode active material layer is large, the reaction between the cathode active material particles and the electrolytic solution can be suppressed. Therefore, an increase in gas generation during high-temperature storage can be suppressed.
Further, when the content of PVdF in the coat layer exceeds 10%, the voltage of the piercing test becomes 4.25 V or less, and the safety at the time of an internal short circuit (a nail piercing test) decreases.
The decrease in safety at the time of the internal short circuit is because the surface coating of the positive electrode active material particles is insufficient, so that the reaction between the positive electrode active material particles and the electrolyte cannot be suppressed, and the content of the inorganic particles is 90%. It is considered that the heat resistance is reduced.

Table 2 shows the following.
In a battery in which a positive electrode active material layer containing PVdF having a melting point of 166 ° C. or less and a separator provided with a coat layer having a PVdF content of 10 to 50% by mass are combined, PVdF in the positive electrode active material layer When the content is out of the range of 0.7% by mass or more and 2.8% by mass or less, the cycle characteristics deteriorate.

If the content of PVdF in the positive electrode active material layer is less than 0.7% by mass, the positive electrode active material layer will fall off.
This dropping of the positive electrode active material layer is considered to be because the content of PVdF contained in the positive electrode active material layer is too small, and the adhesiveness (that is, peel strength) between the positive electrode current collector and the positive electrode active material layer is reduced. .

If the content of PVdF in the positive electrode active material layer exceeds 2.8% by mass, cracks occur in the positive electrode.
It is considered that the cracking of the positive electrode occurred because the content of PVdF contained in the positive electrode active material layer was excessively large, and the flexibility of the positive electrode active material layer was reduced.

Table 3 shows the following.
When the peel strength between the positive electrode and the separator is 5 mN / mm or more and 35 mN / mm or less, safety at the time of an internal short circuit (a nail penetration test) can be improved, deterioration of cycle characteristics is suppressed, and high-temperature storage is performed. In this case, the effect of suppressing battery swelling (gas generation) at the time (hereinafter, referred to as “effect of improving safety”) can be further improved.
When the average thickness of the particle-containing layer is 1 μm or more and 5 μm or less, effects such as improvement in safety can be further improved.
When the average air permeability of the separator provided with the particle-containing layer is 10 s / 100 ml or more and 100 s / 100 ml or less, effects such as improved safety can be further improved.
When the heat shrinkage at 150 ° C. of the separator provided with the particle-containing layer is 30% or less, safety at the time of an internal short circuit (a nail penetration test) can be further improved.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications based on the technical idea of the present invention are possible.

For example, the configurations, methods, steps, shapes, materials, numerical values, and the like mentioned in the above-described embodiments are merely examples, and if necessary, use different configurations, methods, steps, shapes, materials, numerical values, and the like. Is also good.

The configurations, methods, steps, shapes, materials, numerical values, and the like of the above-described embodiments can be combined with each other without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10 Outer packaging material 11 Positive electrode lead 12 Negative electrode lead 13 Adhesive film 20 Electrode body 21 Positive electrode 21A Positive electrode collector 21B Positive electrode active material layer 22 Negative electrode 22A Negative electrode collector 22B Negative electrode active material layer 23 Separator 23A Particle-containing layer 300 Battery pack 400 Electronics machine

Claims (5)

A positive electrode having a positive electrode active material layer containing a fluorine-based binder having a melting point of 166 ° C. or less, wherein the content of the fluorine-based binder in the positive electrode active material layer is 0.7% by mass or more and 2.8% by mass or less; When,
A negative electrode provided to face the positive electrode,
A separator provided between the positive electrode and the negative electrode,
A particle-containing layer provided between the positive electrode and the separator, the layer containing inorganic particles and a resin material;
A secondary battery in which the content of the resin material in the particle-containing layer is from 10% by mass to 50% by mass. The secondary battery according to claim 1, wherein the peel strength between the positive electrode and the separator is from 5 mN / mm to 35 mN / mm. The particle-containing layer is provided on a surface of the separator,
The average thickness of the particle-containing layer is 1 μm or more and 5 μm or less,
2. The secondary battery according to claim 1, wherein the separator provided with the particle-containing layer has an average air permeability of 10 s / 100 ml or more and 100 s / 100 ml or less. The particle-containing layer is provided on a surface of the separator,
The secondary battery according to claim 1, wherein a thermal shrinkage at 150 ° C. of the separator provided with the particle-containing layer is 40% or less. The secondary battery according to claim 1, wherein the positive electrode, the negative electrode, and the separator are wound.

Images