WO2013069074A1 - Non-aqueous electrolyte secondary cell - Google Patents

Abstract

Provided is a non-aqueous electrolyte secondary cell which, when in an overcharged state during operation of a vehicle, reliably allows operation of a pressure-type current blocking device provided in said non-aqueous electrolyte secondary cell. In this lithium secondary cell (100), an electrode body (20) housed inside a battery case (10) comprises a positive electrode and a negative electrode laminated with an electrolyte-impregnated separator interposed therebetween, and the opening (12) of the case (10) is closed by means of a lid (14). Further, a positive electrode terminal (38) and a negative electrode terminal (48) are provided on the lid (14), and these are connected inside of the battery case (10) to an internal positive electrode terminal (37) and an internal negative electrode terminal (47). Preferably, the non-aqueous electrolyte used in this lithium secondary battery (100) contains biphenyl and/or biphenyl derivatives in a content ratio of 6.0 mmol/cc or greater relative to the pore volume of the positive electrode.

Description

Non-aqueous electrolyte secondary battery

The present invention relates to a non-aqueous electrolyte secondary battery for vehicle drive power supply.

Generally, a non-aqueous electrolyte secondary battery such as a lithium (ion) secondary battery is a current interrupting device (CID: Current) in order to prevent an increase in internal pressure due to gas generation due to electrolysis of the electrolyte in an overcharged state. Interrupt Device). As a mechanism for operating such a current interrupting device, in addition to the one that operates when the internal pressure itself increases (pressure type current interrupting device), in addition to that, it follows an excessive temperature increase (pressure / temperature) Type current interrupting device) is known.

For example, Patent Document 1 includes a sealing plate that is provided at an opening of a battery case and functions as a pressure-type current interrupting device having a predetermined current interrupting pressure. In addition, cyclohexylbenzene (CHB), biphenyl is included in the electrolyte. (BP) and at least one selected from the group consisting of diphenyl ether (DPE), preferably a non-aqueous electrolyte containing 0.05 to 8 parts by weight as an additive with respect to the total electrolyte A secondary battery is described.

JP 2006-324235 A

In the non-aqueous electrolyte secondary battery described in Patent Document 1, cyclohexylbenzene, biphenyl, and diphenyl ether are used as additives for suppressing thermal runaway that may occur when the secondary battery is overcharged. They decompose and generate gas in their own potential state. Therefore, cyclohexylbenzene, biphenyl, and diphenyl ether contained in the electrolytic solution function as a gas generating auxiliary agent for developing a current blocking function of a sealing plate that is a pressure type current blocking device.

However, using such a conventional non-aqueous electrolyte secondary battery as a vehicle driving power source, as disclosed in Patent Document 1, the inclusion in at least one electrolyte selected from the group consisting of cyclohexylbenzene, biphenyl, and diphenyl ether If the ratio is about the above-mentioned predetermined numerical value, there is a possibility that the sealing plate which is the pressure type current interrupting device cannot be operated properly.

In other words, during normal operation of a vehicle equipped with the non-aqueous electrolyte secondary battery, if there is a load fluctuation due to an accelerator ON / OFF switching operation, cyclohexylbenzene, biphenyl, and diphenyl ether contained in the electrolyte Tends to be decomposed and become gradually decomposed. Then, for example, when a sudden load change event occurs and an overcharge state occurs, and when it is necessary to interrupt the current, the additive as a gas generating aid has already been consumed. Can happen. As a result, even if an overcharged state occurs, it is no longer possible to secure the gas generated by the decomposition of the gas generating auxiliary agent, the sealing plate as a pressure type current interruption device does not operate, It becomes difficult to suppress the increase in internal pressure.

Therefore, the present invention has been made in view of such circumstances, and can generate a sufficient amount of gas for operating the pressure-type current interrupting device when an overcharged state occurs during vehicle operation. Thus, an object of the present invention is to provide a non-aqueous electrolyte secondary battery for a vehicle driving power source that can surely develop the current interruption function of the pressure type current interruption device.

In order to solve the above problems, a nonaqueous electrolyte secondary battery according to the present invention is mounted on a vehicle and used as a power source for driving the vehicle, and includes a positive electrode including a positive electrode active material, and a negative electrode A negative electrode containing an active material, a lithium salt in a non-aqueous solvent, and a non-aqueous electrolyte containing a gas generating aid that generates gas upon decomposition (decomposed), and a current blocking function that is sensitive to an increase in internal pressure The non-aqueous electrolyte contains biphenyl and / or a biphenyl derivative as a gas generating auxiliary, and the content of the gas generating auxiliary in the non-aqueous electrolytic solution is A gas generating aid (amount) that generates gas (amount) corresponding to the operating pressure of the pressure-type current interrupter is added to the gas generation aid (amount) that is decomposed during normal operation of the vehicle. The amount added.

In the non-aqueous electrolyte secondary battery configured as described above, when the voltage applied between the positive electrode and the negative electrode reaches a predetermined value (for example, 4.5 V) during normal operation of the vehicle, the non-aqueous electrolyte secondary battery is supplied. A part of the biphenyl and / or the biphenyl derivative contained in the non-aqueous electrolyte as a gas generating aid is electrolyzed by a part of the electric energy (electric power; charging current). As a result, although a part of the gas generating aid (biphenyl and / or biphenyl derivative) is consumed, the non-aqueous electrolyte contains an amount of the gas generating aid that can be decomposed in advance during normal operation. In addition, since an excessive amount of the gas generating auxiliary agent is added, it is possible to prevent the entire amount of the gas generating auxiliary agent in the non-aqueous electrolyte from being consumed during normal operation.

And as a surplus of the gas generating auxiliary agent, a gas generating auxiliary agent that generates an amount of gas corresponding to the operating pressure of the pressure type current interrupting device is added. Even in the overcharged state, the surplus gas generating aid is decomposed, so that a sufficient amount of gas can be generated to operate the pressure type current interrupting device.

More specifically, the content ratio of the gas generating aid in the non-aqueous electrolyte is preferably 6.0 mmol / cc or more, more preferably 7.0 mmol / cc or more with respect to the pore volume of the positive electrode. An embodiment is mentioned. In the present specification, the pore volume (cc / g) of the positive electrode means a value measured using a mercury porosimeter.

This is because, conceptually, the amount of biphenyl and / or biphenyl derivative decomposed during normal driving of the vehicle is about 5.0 mmol / cc with respect to the pore volume of the positive electrode, and the operating pressure of the pressure type current interrupting device The amount of biphenyl and / or biphenyl derivative capable of generating a gas corresponding to the amount of about 1.0 mmol / cc with respect to the vacancy volume of the positive electrode, It means that 6.0 mmol / cc or more of biphenyl and / or biphenyl derivative is contained in the non-aqueous electrolyte. As a result, even if a part of the gas generating aid is decomposed and consumed during normal operation of the vehicle, when the overcharged state occurs, the gas generating aid remaining without being decomposed is decomposed. Since a sufficient amount of gas can be generated, it becomes easy to reliably operate a general pressure type current interrupting device.

In addition, during overcharge, a large current exceeding a specified value (for example, specification value) flows through the non-aqueous electrolyte, resulting in a decrease in capacity due to precipitation of lithium contained in the non-aqueous electrolysis on the negative electrode. is there. Then, in particular, as the operation time of the vehicle increases, the capacity reduction of the nonaqueous electrolyte secondary battery proceeds, and the vehicle drive output and the power supply to the auxiliary equipment mounted on the vehicle excessively decrease. There is a fear (reduction of Li precipitation resistance).

In contrast, according to the knowledge of the present inventor, biphenyl and / or biphenyl derivatives are contained in the non-aqueous electrolyte at the above-mentioned ratio, so that the capacity maintenance rate of the non-aqueous electrolyte secondary battery is sufficiently long. It was confirmed that it can be kept high. This is because even when a large current flows between the positive electrode and the negative electrode, a large amount of lithium ions contained in the non-aqueous electrolyte move to the negative electrode and precipitate on the negative electrode due to such a content of biphenyl and / or biphenyl derivative. It is estimated that a part of the electric energy supplied to the non-aqueous electrolyte secondary battery is consumed to such an extent that it can be sufficiently prevented from occurring (however, the action is not limited to this). .)

In particular, out of the total amount of biphenyl and / or biphenyl derivative contained in the non-aqueous electrolyte as a gas generation aid, a considerable amount of biphenyl and / or biphenyl derivative that is decomposed during normal operation of the vehicle described above (positive electrode). It is presumed that about 5.0 mmol / cc with respect to the pore volume) mainly contributes to the improvement of Li precipitation resistance (the action is not limited to this).

Furthermore, as a preferred embodiment of the present invention, the nonaqueous electrolytic solution further contains cyclohexylbenzene and / or a cyclohexylbenzene derivative as a gas generating auxiliary, and the content ratio of the gas generating auxiliary in the nonaqueous electrolytic solution is , Biphenyl and / or biphenyl derivative is 5.0 mmol / cc or more with respect to the vacancy volume of the positive electrode, and cyclohexylbenzene and / or cyclohexylbenzene derivative is preferably 0. The structure which is 5 mmol / cc or more, More preferably, it is 1.0 mmol / cc or more can also be mentioned.

In this case, conceptually, the biphenyl and / or biphenyl derivative contained at a rate of about 5.0 mmol / cc with respect to the pore volume of the positive electrode is used as a gas generating aid that is decomposed during normal operation of the vehicle. Corresponding gas in which cyclohexylbenzene and / or cyclohexylbenzene derivative contained at a rate of about 0.5 mmol / cc with respect to the pore volume of the positive electrode generates an amount of gas corresponding to the operating pressure of the pressure type current interrupting device Corresponds to generation aid.

In this way, even if some of the gas generating aids containing biphenyl and / or biphenyl derivatives and cyclohexylbenzene and / or cyclohexylbenzene derivatives are decomposed and consumed during normal driving of the vehicle, an overcharged state occurs. In this case, the gas generating auxiliary agent remaining without being decomposed is decomposed. Therefore, even in such a configuration, a sufficient amount of gas is generated at the time of overcharging, so that the pressure-type current interrupting device can be reliably operated.

In this way, even in a mode in which cyclohexylbenzene and / or cyclohexylbenzene derivative is added to the non-aqueous electrolyte as a gas generating auxiliary agent in addition to biphenyl and / or biphenyl derivative, lithium deposition in the negative electrode is prevented. It was confirmed that the capacity maintenance rate of the non-aqueous electrolyte secondary battery can be kept high over a long period of time.

Even in this case, among the total amount of biphenyl and / or biphenyl derivatives and cyclohexylbenzene and / or cyclohexylbenzene derivatives contained in the non-aqueous electrolyte as a gas generation aid, the decomposition occurs during normal operation of the vehicle described above. It is presumed that a considerable amount of biphenyl and / or biphenyl derivative (approximately 5.0 mmol / cc with respect to the positive electrode void volume) contributes mainly to the improvement of Li precipitation resistance (the action is limited to this). Not.)

According to the present invention, the non-aqueous electrolyte provided in the non-aqueous electrolyte secondary battery includes biphenyl and / or a biphenyl derivative as a gas generating aid, and the content (initial amount) of the non-aqueous electrolyte is a normal amount of the vehicle. Since the amount of gas generating aid that can generate gas corresponding to the operating pressure of the pressure-type current interrupting device is added to the gas generating aid that is decomposed during operation, Even if a part of the gas generating aid is decomposed and consumed during normal operation, if an overcharged state occurs, the gas generating aid remaining without being decomposed decomposes and the pressure type current interrupting device Can be reliably operated.

It is a schematic diagram which shows the vehicle carrying the nonaqueous electrolyte secondary battery of one Embodiment. It is a perspective view which shows roughly the structure of the nonaqueous electrolyte secondary battery of one Embodiment. FIG. 3 is a sectional view taken along line III-III in FIG. 2. It is a graph which shows the measurement result (Examples 1 and 2 and comparative example 1) of a capacity maintenance rate. It is a graph which shows the measurement result (Example 3 and 4 and comparative example 1) of a capacity | capacitance maintenance factor.

Hereinafter, embodiments of the present invention will be described in detail. The positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios. Furthermore, the following embodiment is an illustration for explaining the present invention, and is not intended to limit the present invention only to the embodiment. Furthermore, the present invention can be variously modified without departing from the gist thereof.

[First Embodiment]
<Nonaqueous electrolyte secondary battery>
FIG. 1 is a schematic diagram showing a non-aqueous electrolyte secondary battery of this embodiment and a vehicle equipped with the same, and FIG. 2 schematically shows the configuration of the non-aqueous electrolyte secondary battery of this embodiment. FIG. 3 is a perspective view, and FIG. 3 is a sectional view taken along line III-III in FIG.

As shown in FIG. 1, a lithium secondary battery 100 (non-aqueous electrolyte secondary battery) is mounted on a vehicle 1 (for example, an automobile including an electric motor such as an automobile, particularly a hybrid automobile, an electric automobile, or a fuel cell automobile). 1 functions as a power source for driving 1. In addition, the lithium secondary battery 100 is provided with a pressure type current interrupting device or mechanism (not shown), and the type and configuration thereof are not particularly limited. For example, JP 2010-212034 A, JP 2010-157451 A For example, Japanese Patent Application Laid-Open No. 2008-66255, and the like can be used.

As shown in FIGS. 2 and 3, the lithium secondary battery 100 includes a battery case 10 having a substantially rectangular tube shape (cuboid shape), in which a positive electrode and a negative electrode are stacked via a separator impregnated with an electrolyte. An electrode body 20 such as a so-called wound electrode body is accommodated, and the opening 12 of the case 10 is closed by a lid body 14. Further, the lid body 14 is provided with a positive electrode terminal 38 and a negative electrode terminal 48 for external connection, and the positive electrode terminal 38 and the negative electrode terminal 48 are partly on the outer side of the lid body 14 from the surface of the lid body 14. The lower end of each of the illustrated portions is connected to the internal positive terminal 37 and the internal negative terminal 47 inside the battery case 10.

Furthermore, the electrode body 20 includes, for example, a positive electrode sheet 30 having a positive electrode active material layer 34 on the surface of a long positive electrode current collector 32, and a negative electrode active material layer 44 on the surface of a long negative electrode current collector 42. The negative electrode sheet | seat 40 which has this is laminated | stacked alternately via the separator 50 of the elongate sheet form. The electrode body 20 as the laminated body is formed into a flat shape by, for example, crushing a wound electrode body obtained by winding around a shaft core (not shown) in a cylindrical shape from the side surface direction. The opening ends 20 a and 20 a are arranged in the battery case 10 so as to face the side walls 16 and 16 of the battery case 10.

Further, the internal positive electrode terminal 37 and the internal negative electrode terminal 47 described above are respectively connected to the positive electrode active material layer non-forming part 36 of the positive electrode current collector 32 and the negative electrode active material layer non-forming part 46 of the negative electrode current collector 42. They are joined by an appropriate technique such as ultrasonic welding or resistance welding, and are thereby electrically connected to the positive electrode sheet 30 and the negative electrode sheet 40 of the electrode body 20.

The separator 50 is interposed between the positive electrode sheet 30 and the negative electrode sheet 40 so as to contact both the positive electrode active material layer 34 provided on the positive electrode sheet 30 and the negative electrode active material layer 44 provided on the negative electrode sheet 40. Is arranged. By impregnating the electrolyte (non-aqueous electrolyte) in the pores formed in the separator 50, a conductive path (conductive path) is defined between the positive electrode and the negative electrode. The separator 50 has a width larger than the width of the stacked portion of the positive electrode active material layer 32 and the negative electrode active material layer 44 and smaller than the width of the electrode body 20, and the positive electrode current collector 32 and the negative electrode The current collectors 42 are provided so as to be sandwiched between the stacked portions of the positive electrode active material layer 34 and the negative electrode active material layer 44 so as not to contact each other and cause an internal short circuit.

As the constituent material of the separator 50, those known in the art can be appropriately used, and are not particularly limited. For example, a porous sheet (a microporous resin sheet) made of a resin can be preferably used, and examples of the resin include polyolefin resins such as polypropylene and polyethylene, polystyrene, and the like. The separator 50 can be preferably used even if it is a single layer (single layer), two layers, or a laminate of three or more layers.

(Positive electrode sheet 30)
As a material for forming the positive electrode current collector 32 serving as a base material of the positive electrode sheet 30, a material known in the art can be appropriately used, and is not particularly limited. For example, the metal which is excellent in electroconductivity, such as aluminum, the alloy which has aluminum as a main component, or a composite metal, is mentioned.

The positive electrode active material layer 34 includes at least a positive electrode active material capable of inserting and extracting lithium ions serving as charge carriers. As this positive electrode active material, those known in the art can be used as appropriate, and are not particularly limited. For example, the positive electrode active material contains lithium (Li) and at least one transition metal element, and has a layered structure or a spinel structure. Examples include lithium transition metal composite oxides.

More specifically, for example, cobalt lithium composite oxide (LiCoO ₂ ), nickel lithium composite oxide (LiNiO ₂ ), manganese lithium composite oxide (LiMn ₂ O ₄ ), or nickel-cobalt-based LiNi _x Co _{1 -XO 2} (0 <x <1), cobalt / manganese-based LiCo _x Mn _1-x O ₂ (0 <x <1), nickel / manganese-based LiNi _x Mn _1-x O ₂ (0 <x <1) or LiNi _x Mn _2−x O ₄ (0 <x <2), so-called binary lithium transition metal composite oxide containing two kinds of transition metal elements, or 3 of transition metal elements Examples include ternary lithium transition metal composite oxides (eg, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) such as nickel-cobalt-manganese-based species. wear. These lithium transition metal composite oxides have a potential in the range of about 3.5 to 4.2 V (potential with respect to the lithium reference electrode).

In addition, the lithium transition metal composite oxide includes, for example, aluminum alloy (Al), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), titanium (Ti), zirconium as a minute constituent metal element. (Zr), niobium (Nb), molybdenum (Mo), tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lanthanum (La), and One or more selected from the group consisting of cerium (Ce) may be included.

As such a lithium transition metal oxide, for example, a lithium transition metal oxide powder prepared and provided by a conventionally known method can be used as it is, or any number of lithium transition metal oxides appropriately selected according to the atomic composition can be used. Such raw material compounds can also be prepared by mixing them at a predetermined molar ratio and firing them by an appropriate means. In addition, a granular lithium transition metal oxide substantially composed of secondary particles having a desired average particle size and / or particle size distribution by pulverizing, granulating, and classifying the fired product by appropriate means. It is also possible to obtain a powder.

Furthermore, the positive electrode active material layer 34 is a substance that decomposes as an additive by an oxidation reaction with an additive contained in a non-aqueous electrolyte described later with the discharge of the lithium secondary battery 100, and its oxidation reaction May contain a self-sacrificial auxiliary material that makes it possible to adjust the amount of film produced on the surface of the positive electrode active material.

As this self-sacrificial auxiliary material, those having a lower potential (potential with respect to the lithium reference electrode) than the potentials of the positive electrode active materials listed above (about 3.5 to 4.2 V) can be preferably used. For example, the olivine type represented by the general formula LiMPO ₄ (wherein M represents at least one or two or more transition metal elements selected from the group consisting of Co, Ni, Mn, and Fe). Examples include lithium-containing phosphates having a structure. Preferred examples of such olivine-type lithium-containing phosphates include lithium iron phosphate (LiFePO ₄ ), lithium manganese phosphate (LiMnPO ₄ ), etc. (with respect to lithium reference electrode potential of about 3.2 to 3.8 V). can do.

In the combination of the positive electrode active material and the self-sacrificial auxiliary material described above, the relationship between the positive electrode active material and the self-sacrificial auxiliary material (with respect to the lithium reference electrode potential) satisfies the positive electrode active material> the self-sacrificial auxiliary material. If it is, it will not be restrict | limited in particular. For example, a preferred example is a combination using LiNi _1/3 Co _1/3 Mn _1/3 O ₂ having a layered structure as a positive electrode active material and LiFePO ₄ having an olivine structure as a self-sacrificial auxiliary material. Alternatively, a lithium transition metal composite oxide having a layered structure may be used as a self-sacrificial auxiliary material, and LiMn ₂ O ₄ having a relatively high potential (about 4.2 V) is used as a positive electrode active material. And a combination using LiNiO ₂ having a layered structure with a low potential as a self-sacrificial auxiliary substance.

Moreover, the positive electrode active material layer 34 may contain other components (optional components) known in the art such as a conductive material and a binder as necessary. Examples of the conductive material include conductive powder materials such as carbon powder and carbon fiber. Specific examples of the carbon powder include various carbon blacks such as acetylene black, furnace black, ketjen black, and graphite powder. Moreover, you may contain conductive fibers, such as carbon fiber and a metal fiber, metal powders, such as copper and nickel, and organic electroconductive materials, such as a polyphenylene derivative, individually or as a mixture thereof.

In addition, as the binder, those known in the art can be appropriately used, and although not particularly limited, various polymer materials can be suitably used. Specifically, a polymer that is soluble or dispersible in a solvent used for manufacturing the positive electrode active material layer 34 can be selected and used. For example, when an aqueous solvent is used, carboxymethylcellulose (CMC), hydroxypropylmethylcellulose Cellulose polymers such as (HPMC); polyvinyl alcohol (PVA); fluorine resins such as polytetrafluoroethylene (PTFE) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP); vinyl acetate copolymer; styrene butadiene Water-soluble or water-dispersible polymers such as rubbers (SBR) and rubbers such as acrylic acid-modified SBR resin (SBR latex) can be preferably used. Moreover, when using a non-aqueous solvent, polymers, such as a polyvinylidene fluoride (PVDF) and a polyvinylidene chloride (PVDC), can be employ | adopted preferably. In addition, the various exemplified polymer materials may exhibit functions as a thickener and other additives in addition to the function as a binder.

(Negative electrode sheet 40)
As a material for forming the negative electrode current collector 42 serving as the base material of the negative electrode sheet 40, a material known in the art can be appropriately used, and is not particularly limited. Examples thereof include metals having excellent conductivity such as copper, copper-based alloys, and composite metals.

The negative electrode active material layer 44 includes at least a negative electrode active material capable of inserting and extracting lithium ions serving as charge carriers. This negative electrode active material is a substance that decomposes by a reduction reaction with an additive contained in a non-aqueous electrolyte described later when the lithium secondary battery is charged, and is a film formed on the surface of the negative electrode active material by the reduction reaction The amount of production can be adjusted, and those conventionally used in the art can be used without particular limitation. Specific examples of the negative electrode active material include a particulate carbon material (carbon particles) including a graphite structure (layered structure) at least partially. In addition, various carbon materials such as so-called graphite (graphite), non-graphitizable carbon (hard carbon), easily graphitized carbon (soft carbon), and a combination of these are used. It can be preferably used.

Among these, graphite particles such as graphite can be preferably used. Since graphite particles can suitably occlude lithium ions as charge carriers, they are excellent in conductivity and have a small particle size and a large surface area per unit volume, so that a negative electrode active material suitable for high-rate pulse charge / discharge This is advantageous in that it can be.

Furthermore, the negative electrode active material layer 44 is a substance that reduces and decomposes the additive as the additive is charged with the lithium secondary battery 100, and has a potential (potential with respect to the lithium reference electrode) higher than the potential of the negative electrode active material. ) May be a noble self-sacrificial auxiliary material.

Examples of this self-sacrificial auxiliary substance include oxides or sulfides of transition metals such as titanium-based oxides or sulfides. More specifically, lithium titanate, titanium oxide (TiO ₂ ), Examples thereof include titanium sulfide, tungsten oxide, molybdenum oxide, cobalt oxide, iron sulfide and the like, particularly preferably lithium titanate, and more preferably Li _{4 + x} Ti ₅ O ₁₂ (0 ≦ x ≦ 3) and Li _{2 + x} Ti ₃ O ₇ (0 ≦ x ≦ 3) and the like.

In addition, the negative electrode active material layer 44 may contain other components (optional components) known in the art such as a binder as necessary. As such a binder, a binder used for a negative electrode of a general lithium secondary battery can be appropriately employed. For example, the same as that used for the binder of the positive electrode active material layer 34 described above. Those can be appropriately selected and used.

(Nonaqueous electrolyte)
The non-aqueous electrolyte used in the lithium secondary battery 100 preferably includes a non-aqueous solvent, a lithium salt as a supporting electrolyte (supporting salt), and biphenyl and / or a biphenyl derivative as a gas generating auxiliary agent. Further includes an additive that forms a film on the surface of the positive electrode active material layer 34 and / or the negative electrode active material layer 44 described above. The “biphenyl derivative” refers to a compound in which a hydrogen atom bonded to a carbon atom of a biphenyl molecule is substituted with an appropriate substituent such as an alkyl group, an alkoxy group, a cyano group, or a hydroxyl group.

As the non-aqueous solvent, those known in the art can be appropriately used, and the kind thereof is not particularly limited. For example, various organic solvents, more preferably carbonates, esters, ethers, nitriles, sulfones are used. And aprotic solvents such as lactones can be used. Specifically, for example, carbonates such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and 1,2-dimethoxyethane. 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane , Γ-butyrolactone, etc., which can be generally used for the electrolyte of a lithium secondary battery can be used alone or in combination of two or more.

Here, in the lithium secondary battery 100, in general, the negative electrode active material functions as a strong reducing agent in a charged state, and the nonaqueous electrolytic solution is reduced and decomposed during the first charge, and a film (SEI: Solid Electrolite) is formed on the surface of the active material. Interface) is generated. This coating serves as a physical barrier that prevents the decomposition of the non-aqueous electrolyte, suppresses the reductive decomposition reaction on the negative electrode, and can contribute to the improvement of battery characteristics (for example, cycle characteristics or high-rate characteristics), while excessive amounts. When a film is produced, it may cause a decrease in battery capacity and a decrease in charging efficiency. Therefore, it is preferable that the non-aqueous electrolyte contains an additive for controlling such film formation.

Examples of such additives include vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, propyl ethylene carbonate, dimethyl vinylene carbonate, diethyl vinylene carbonate, dipropyl vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, and trifluoropropylene carbonate. , Phenylethylene carbonate, carbonate compounds having an ethylenically unsaturated bond such as erythritan carbonate, or lithium-containing alkali metal salt LiPF ₂ (C ₂ O ₄ ) ₂ (so-called LPFO), Li [(C ₂ O ₄ ) ₂ B], Li (C ₂ O ₄ ) BF _{2 and the} like can be mentioned, but not limited thereto. Among these, vinylene carbonate or LiPF ₂ (C ₂ O ₄ ) ₂ is particularly preferable.

Specific examples of the lithium salt as the supporting electrolyte (supporting salt) include, for example, LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO _3. , Various lithium salts known to be able to function as a supporting electrolyte in an electrolyte solution of a lithium secondary battery such as LiC ₄ F ₉ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiClO ₄ , It is not specifically limited to these. Lithium salts can be used alone or in combination of two or more. Of these, LiPF ₆ is particularly preferred. The concentration of the lithium salt as the supporting electrolyte in the nonaqueous electrolytic solution is not particularly limited, and can be set as appropriate according to the required performance, and is the same as the nonaqueous electrolytic solution used in the conventional lithium secondary battery Can be composed.

Further, the content ratio of the biphenyl and / or biphenyl derivative, which is a gas generating auxiliary agent, in the non-aqueous electrolyte is preferably 6.0 mmol / cc or more, more preferably 7.0 mmol / cc with respect to the pore volume of the positive electrode. It is said above. The breakdown of this content ratio is conceptually that the amount of biphenyl and / or biphenyl derivative decomposed during normal operation of the vehicle is about 5.0 mmol / cc with respect to the pore volume of the positive electrode, and the pressure type current interruption The amount of biphenyl and / or biphenyl derivative capable of generating a gas corresponding to the operating pressure of the apparatus is about 1.0 mmol / cc with respect to the pore volume of the positive electrode, Preferably, 6.0 mmol / cc or more of biphenyl and / or biphenyl derivative is contained in the non-aqueous electrolyte with respect to the volume.

In other words, the content of the gas generating auxiliary in the non-aqueous electrolyte corresponds to the operating pressure of the pressure-type current interrupting device in the amount of gas generating auxiliary that is decomposed during normal operation of the vehicle. It is the amount to which a gas generating auxiliary agent (amount) for generating a large amount of gas is added.

According to the lithium secondary battery 100 configured in this way, even if a part of biphenyl and / or a biphenyl derivative as a gas generating aid is decomposed and consumed during normal operation of the vehicle, the overcharged state is maintained. When generated, a sufficient amount of gas can be generated by decomposing the gas generating auxiliary agent remaining without being decomposed, so that the pressure-type current interrupting device can be operated reliably. it can.

That is, when the voltage applied between the positive electrode and the negative electrode reaches a predetermined value (for example, 4.5 V) during normal driving of the vehicle, a part of the electric power is consumed and one of the biphenyl and / or biphenyl derivatives is consumed. The part is electrolyzed. As a result, although a part of biphenyl and / or the biphenyl derivative contained in the non-aqueous electrolyte is consumed, a gas corresponding to the operating pressure of the pressure type current interrupting device is generated in the non-aqueous electrolyte in advance. Since the surplus of the biphenyl and / or biphenyl derivative to be added is added, the entire amount of the gas generating auxiliary in the non-aqueous electrolyte is prevented from being consumed during normal operation. And the biphenyl and / or the biphenyl derivative as the surplus can be decomposed when overcharged, thereby generating a sufficient amount of gas to operate the pressure type current interrupting device. .

Further, when the content ratio of the biphenyl and / or biphenyl derivative, which is a gas generating auxiliary agent, in the nonaqueous electrolytic solution is 6.0 mmol / cc or more as described above with respect to the pore volume of the positive electrode, the lithium deposition resistance is improved. When the capacity retention rate of the lithium secondary battery 100 can be maintained sufficiently high over a long period of time and is 7.0 mmol / cc or more with respect to the vacancy volume of the positive electrode, a longer time has passed. It was confirmed that the capacity maintenance rate of the was maintained sufficiently high.

[Second Embodiment]
In the present embodiment, in addition to the above-mentioned biphenyl and / or biphenyl derivative, cyclohexylbenzene and / or cyclohexylbenzene derivative is added to the non-aqueous electrolyte as a gas generating aid. The “cyclohexylbenzene derivative” refers to a compound in which a hydrogen atom bonded to a carbon atom of a cyclohexylbenzene molecule is substituted with an appropriate substituent such as an alkyl group, an alkoxy group, a cyano group, or a hydroxyl group.

In this case, the content ratio of the biphenyl and / or biphenyl derivative, which is a gas generation aid, in the nonaqueous electrolytic solution is 5.0 mmol / cc or more with respect to the pore volume of the positive electrode, and the gas generation aid. The content ratio of the cyclohexylbenzene and / or cyclohexylbenzene derivative in the non-aqueous electrolyte is 0.5 mmol / cc or more with respect to the pore volume of the positive electrode. Conceptually, biphenyl and / or a biphenyl derivative of about 5.0 mmol / cc with respect to the pore volume of the positive electrode corresponds to a gas generating aid that is decomposed during normal operation of the vehicle, as described above. A cyclohexylbenzene and / or cyclohexylbenzene derivative of about 0.5 mmol / cc with respect to the pore volume of the positive electrode corresponds to a gas generating aid that generates an amount of gas corresponding to the operating pressure of the pressure type current interrupting device. obtain.

Thus, cyclohexyl benzene and / or cyclohexyl benzene derivatives have more hydrogen atoms bonded to the carbocyclic skeleton of the molecule than biphenyl and / or biphenyl derivatives, and thus the equivalent amount of hydrogen gas generated by decomposition is also increased. Since it becomes relatively large, the content ratio may be relatively small.

Also in the lithium secondary battery 100 configured as described above, during the normal operation of the vehicle, a part of the gas generating auxiliary agent containing biphenyl and / or biphenyl derivative and cyclohexylbenzene and / or cyclohexylbenzene derivative is decomposed and consumed. Even when the overcharged state occurs, the gas generating aid remaining without being decomposed is decomposed. Therefore, since a sufficient amount of gas is generated during overcharge, the pressure-type current interrupting device can be reliably operated. Further, lithium deposition on the negative electrode is suppressed (improvement of lithium deposition resistance), and as a result, the capacity retention rate of the nonaqueous electrolyte secondary battery can be maintained high over a long period of time.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

(Comparative Example 1)
Comparative Example 1 has a configuration equivalent to that of the lithium secondary battery 100 shown in FIGS. 1 and 2 (with a pressure-type current interrupting device) and has a non-aqueous electrolyte that does not contain a gas generating auxiliary agent. Produced.

(Examples 1 and 2)
Instead of the non-aqueous electrolyte of Comparative Example 1, the same procedure as in Comparative Example 1 was used except that the non-aqueous electrolyte of Examples 1 and 2 in which a predetermined amount of biphenyl was added to the non-aqueous electrolyte of Comparative Example 1 was used. Thus, lithium secondary batteries 100 of Examples 1 and 2 were produced. The contents of biphenyl in the non-aqueous electrolytes of these examples were 6.0 mmol / cc (Example 1) and 7.0 mmol / cc (Example 2), respectively, with respect to the pore volume of the positive electrode. .

(Examples 3 and 4)
Instead of the non-aqueous electrolyte of Comparative Example 1, the same procedure as in Comparative Example 1 was used except that the non-aqueous electrolyte of Examples 3 and 4 in which a predetermined amount of biphenyl was added to the non-aqueous electrolyte of Comparative Example 1 was used. Thus, lithium secondary batteries 100 of Examples 3 and 4 were produced. In addition, the content rate of biphenyl in the non-aqueous electrolyte of these examples is 6.0 mmol / cc or more with respect to the pore volume of the positive electrode, and further, 6. 0 wt% (Example 3) and 7.0 wt% (Example 4).

(Examples 5 and 6)
Comparative Example 1 except that the nonaqueous electrolytic solution of Examples 5 and 6 in which a predetermined amount of biphenyl and cyclohexylbenzene was added to the nonaqueous electrolytic solution of Comparative Example 1 was used instead of the nonaqueous electrolytic solution of Comparative Example 1. In the same manner as described above, lithium secondary batteries 100 of Examples 5 and 6 were produced. The content ratios of biphenyl and cyclohexylbenzene in the non-aqueous electrolytes of these examples were 5.0 mmol / cc and 0.5 mmol / cc (Example 5) and 5 respectively, with respect to the pore volume of the positive electrode. 0.0 mmol / cc and 1.0 mmol / cc (Example 6).

(Examples 7 and 8)
Comparative Example 1 except that the nonaqueous electrolytic solution of Examples 7 and 8 in which a predetermined amount of biphenyl and cyclohexylbenzene was added to the nonaqueous electrolytic solution of Comparative Example 1 was used instead of the nonaqueous electrolytic solution of Comparative Example 1. In the same manner, lithium secondary batteries 100 of Examples 7 and 8 were produced. In addition, the content ratio of biphenyl and cyclohexylbenzene in the non-aqueous electrolyte of these examples is 5.0 mmol / cc or more and 0.5 mmol / cc or more with respect to the pore volume of the positive electrode. The total amount was 5.0 wt% and 0.5 wt% (Example 7), and 5.0 wt% and 1.0 wt% (Example 8), respectively.

(Evaluation Test 1)
A plurality of lithium secondary batteries of Examples 1 to 8 and Comparative Example 1 were mounted on a vehicle, and the vehicle was operated under the condition of accelerator ON / OFF frequency = 4000 cycles, and then an overcharged state was caused. In the lithium secondary batteries of Examples 1 to 8, it was confirmed that the pressure-type current interrupting device operated reliably and the increase in internal pressure was suppressed. On the other hand, in the lithium secondary battery of Comparative Example 1, it was recognized that the pressure type current interrupting device did not operate reliably.

(Evaluation test 2)
The lithium secondary batteries of Examples 1 to 8 and Comparative Example 1 were mounted on a vehicle, and the vehicle was operated under the accelerator ON / OFF frequency = 4000 cycle condition (capacity after operation / before operation). % Of the capacity) was measured. FIG. 4 and FIG. 5 are bar graphs showing the measurement results of capacity retention ratios for Examples 1 to 4 and Comparative Example 1. In the figure, reference numerals E1 to E4 indicate measurement data of Examples 1 to 4, respectively, and reference numeral R1 indicates measurement data of Comparative Example 1.

From these results, the lithium secondary battery of Comparative Example 1 had a capacity maintenance rate of less than 90%, whereas the lithium secondary batteries 100 of Examples 1 to 4 had a capacity maintenance rate of over 95%. It was confirmed that it was kept high. In addition, it was confirmed that the lithium secondary batteries 100 of Examples 5 to 8 can achieve the capacity retention rate equivalent to that of Examples 1 to 4, respectively.

As described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without changing the gist thereof. For example, the lithium secondary battery 100 may have a cylindrical shape instead of a rectangular tube shape.

As described above, according to the present invention, when the non-aqueous electrolyte secondary battery is overcharged during vehicle operation, the pressure-type current interrupting device provided therein can be reliably operated. As schematically shown in FIG. 1, the present invention can be widely and effectively used for a vehicle including a lithium secondary battery as a vehicle driving power source, and for manufacturing the same.

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Battery case 12 Opening part 14 Cover body 16 Side wall 20 Winding electrode body 20a Open end 30 Positive electrode sheet 32 Positive electrode collector 34 Positive electrode active material layer 36 Positive electrode active material layer non-formation part 37 Positive electrode current collection terminal 38 External positive electrode Current collector terminal 40 Negative electrode sheet 42 Negative electrode current collector 44 Negative electrode active material layer 46 Negative electrode active material layer non-forming portion 47 Negative electrode current collector terminal 48 External negative electrode current collector terminal 50 Separator 100 Lithium secondary battery (nonaqueous electrolyte secondary battery )

Claims (5)

A non-aqueous electrolyte secondary battery mounted on a vehicle and used as a power source for driving the vehicle,
A non-aqueous electrolyte containing a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a lithium salt in a non-aqueous solvent, and a gas generating aid that generates gas by decomposition;
A pressure-type current interrupting device having a current interrupting function sensitive to an increase in internal pressure of the non-aqueous electrolyte secondary battery;
With
The non-aqueous electrolyte contains biphenyl and / or a biphenyl derivative as the gas generation aid,
The content of the gas generating aid in the non-aqueous electrolyte causes the gas generating aid to be decomposed during normal operation of the vehicle to generate a gas corresponding to the operating pressure of the pressure type current interrupting device. This is the amount of gas generation aid added.
Non-aqueous electrolyte secondary battery. The content ratio of the gas generating aid in the non-aqueous electrolyte is 6.0 mmol / cc or more with respect to the pore volume of the positive electrode.
The nonaqueous electrolyte secondary battery according to claim 1. The content ratio of the gas generating aid in the non-aqueous electrolyte is 6.0 wt% or more.
The nonaqueous electrolyte secondary battery according to claim 1 or 2. The non-aqueous electrolyte further includes cyclohexylbenzene and / or a cyclohexylbenzene derivative as the gas generation aid.
The content ratio of the gas generating aid in the non-aqueous electrolyte is such that the biphenyl and / or the biphenyl derivative is 5.0 mmol / cc or more with respect to the pore volume of the positive electrode, and the cyclohexylbenzene. And / or the cyclohexylbenzene derivative is 0.5 mmol / cc or more based on the pore volume of the positive electrode,
The nonaqueous electrolyte secondary battery according to claim 1. The content ratio of the gas generating aid in the non-aqueous electrolyte is 5.0 wt% or more of the biphenyl and / or the biphenyl derivative, and the cyclohexylbenzene and / or the cyclohexylbenzene derivative is 0%. .5 wt% or more,
The nonaqueous electrolyte secondary battery according to claim 4.

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