JPWO2013018212A1 - Electrolyte for lithium ion secondary battery and lithium ion secondary battery using the same - Google Patents

Abstract

It is an object of the present invention to provide an electrolytic solution for a lithium ion secondary battery and a lithium ion secondary battery using the same, which can improve the storage life in a high temperature environment while suppressing a short circuit of the lithium ion secondary battery. In order to solve this problem, an electrolytic solution containing, as additives, a substance that suppresses generation of hydrofluoric acid in the electrolytic solution and a substance that suppresses precipitation of transition metal ions in the electrolytic solution is used.

Description

  The present invention relates to an electrolytic solution for a lithium ion secondary battery, a lithium ion secondary battery using the same, and a lithium ion secondary battery module.

  Lithium ion secondary batteries have high energy density and output density compared to secondary batteries such as lead batteries and nickel metal hydride batteries, and are therefore widely used in mobile phones and notebook computers. In recent years, lithium ion secondary batteries have been used not only for small mobile batteries but also for large batteries for hybrid electric vehicles (HEV) and electric vehicles (EV). This is because reduction of carbon dioxide emissions is desired for the purpose of environmental protection and suppression of global warming, and the demand for HEVs and EVs as environment-friendly vehicles is expanding. Furthermore, a large-sized lithium ion secondary battery is expected as a secondary battery for suppressing output fluctuations of electric power generated by natural energy. For applications with large capacity, it is often used as a module in which a plurality of lithium ion secondary batteries are connected in series or in parallel depending on the purpose. When used as a module, if even one of the batteries that make up the module changes its characteristics, the load on the specific battery will be concentrated during charging / discharging, which will deteriorate the characteristics and life of the entire module. . Therefore, in a large-sized lithium ion secondary battery and a battery module using the same, the life is more important than a conventional small battery. Moreover, since the energy to store becomes large, higher safety is required.

  First, regarding the life of a lithium ion secondary battery, the storage life in a high temperature environment is an issue. Specifically, there is a concern that the lifespan deteriorates due to decomposition or alteration of the constituent materials at high temperatures.

A lithium ion secondary battery includes a positive electrode composed of a positive electrode mixture layer containing a lithium-containing transition metal composite oxide such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO ₂ and a positive electrode current collector such as an aluminum foil, graphite And the like, a negative electrode composed of a negative electrode mixture layer containing copper and a negative electrode current collector such as copper, a separator disposed between the positive electrode and the negative electrode, and an electrolyte containing a solvent, an electrolyte, and an additive. As an electrolyte for a lithium ion secondary battery, a lithium salt such as lithium tetrafluoroborate (LiBF ₄ ) or lithium hexafluorophosphate (LiPF ₆ ) is used. Of these, LiPF ₆ having high electrical conductivity is often the main component of the electrolyte.

When LiPF ₆ is used, a small amount of moisture present in or entering the battery during the production or use of the secondary battery reacts with LiPF ₆ to generate hydrogen fluoride (HF). . Specifically, LiPF ₆ is dissociated by heat (LiPF ₆ → LiF + PF ₅ ), and PF ₅ generated at that time reacts with water to generate HF. In addition to LiPF ₆ , fluorine-containing compounds such as polyvinylidene fluoride (PVDF) that are widely used as binders can be decomposed to cause generation of HF. The HF dissolves and corrodes the battery container and the metal mixed as a foreign substance, and dissolves the positive electrode active material to elute the transition metal. Furthermore, an inactive film SEI (Solid Electrolyte Interface) layer containing metal is formed on the surface of the negative electrode active material, which inhibits the movement of Li ⁺ ions and causes battery deterioration.

  Since the above phenomenon progresses quickly in a high temperature environment, it becomes a problem particularly in a large-sized lithium ion secondary battery in which the inside of the battery is likely to become high temperature due to charge / discharge.

  Next, with respect to the safety of lithium ion secondary batteries, suppression of internal short circuits has become a problem. In a lithium ion secondary battery, there is a possibility that the battery may generate heat or fire due to an internal short circuit. Even if heat generation does not occur, the presence of a minute internal short circuit causes variations in battery characteristics due to self-discharge or the like.

The main cause of the internal short circuit of the lithium ion secondary battery is considered to be that the metal foreign matter contained in the raw material or mixed in the manufacturing process exists in the battery. If foreign metal is present in the battery, the foreign metal may break through the separator and penetrate, or the foreign metal may be dissolved and re-deposited in the electrolyte, causing an internal short circuit. As described above, when HF generated from LiPF ₆ or the like is present in the electrolytic solution, the amount of dissolved metal increases, and there is a problem that an internal short circuit is likely to occur with a decrease in life and safety is lowered. .

  As described above, there has been a problem that in a high-temperature environment, side reactions that adversely affect the constituent materials in the battery occur to deteriorate the battery, and further, safety is reduced due to a short circuit. Several solutions have been proposed for these problems.

  Specifically, a method of adding various additives to an electrolytic solution is known in order to suppress deterioration without deteriorating the storage life of the lithium ion secondary battery in a high temperature environment.

  (Patent Document 1) proposes a method for improving high-temperature storage characteristics by adding dimethallyl carbonate to an electrolytic solution.

  (Patent Document 2) includes a crosslinked polymer electrolyte composition composed of a polyether multi-polymer, an aprotic organic solvent, an additive composed of a phosphorus-containing compound, and an electrolyte compound composed of a lithium salt compound. A method for improving high-temperature storage characteristics using a lithium ion secondary battery has been proposed.

(Non-Patent Document 1) examines the relationship between the composition of the electrolyte and the storage characteristics. It is shown that by adding 2% by weight of vinylene carbonate (VC) to an electrolyte composed of LiPF ₆ , ethylene carbonate (EC) and dimethyl carbonate (DMC), deterioration under a high temperature environment at 60 ° C. can be suppressed. ing.

  In (Patent Document 3), at least one of a positive electrode plate, a negative electrode plate, a separator, and a nonaqueous electrolytic solution is an organic and / or inorganic Cu corrosion inhibitor, or an organic and / or inorganic Cu trapping agent. A method of adding an inhibitor is proposed. Inhibitors include 1,2,3-benzotriazole, or derivatives and analogs thereof such as 4 or 5-methyl-1H-benzotriazole, toltriazole, benzimidazole, 2-benzimidazole, and 2-mercaptobenzimidazole. 2-benzoxazole, 2-methylbenzothiazole, indole, 2-mercaptothiazoline, 2-mercaptobenzothiazole and the like.

  In addition, the following methods are known in order to suppress a short circuit due to metallic foreign matter in the battery.

  (Patent Document 4) proposes a method in which a non-aqueous electrolyte contains a leveling agent that suppresses concentrated precipitation of metal ions on an electrode plate. Examples of such leveling agents include 1,5-naphthalene-sodium disulfonate, 1,3,6-naphthalene-sodium trisulfonate, saccharin, aldehyde, gelatin, 2-butyne-1,4-diol, quinaldine, and pyridium. Compounds, ethylene cyanohydrin, azo dyes, potassium thiocyanate, potassium pyrophosphate and the like are mentioned.

  (Patent Document 5) proposes a method of containing a chelating agent that does not react with lithium ions or form a coordination bond but forms a complex with a transition metal ion in the battery. Examples of the chelating agent include EDTA, NTA, DCTA, DTPA, EGTA and the like.

JP 2010-232118 A JP 2006-024440 A JP 2001-273927 A JP 2001-357874 A Special table 2009-517836 gazette

Journal of The Electrochemical Society, 151 (10) A1659-A1669 (2004)

  However, the methods of (Patent Document 1), (Patent Document 2), and (Non-Patent Document 1) can suppress deterioration during high-temperature storage, but are not sufficient for suppressing internal short circuits. Moreover, although the method of (patent document 4) and (patent document 5) can reduce an internal short circuit, it is not enough about maintenance of a shelf life and deterioration suppression in a high temperature environment.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide an electrolytic solution for a lithium ion secondary battery that can improve a storage life in a high temperature environment while suppressing a short circuit of the lithium ion secondary battery. And a lithium ion secondary battery using the same.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention each contain a specific compound as a substance that suppresses the generation of hydrofluoric acid and a substance that suppresses the precipitation of transition metal in the electrolyte. As a result, it has been found that the improvement of the storage life under high temperature environment and the suppression of short circuit can be achieved at the same time, and the present invention has been completed.

  The electrolyte for a lithium ion secondary battery of the present invention and the lithium ion secondary battery using the same can suppress a short circuit while suppressing deterioration of the battery due to HF. As a result, the lithium ion secondary battery Can improve the service life and safety. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is a fragmentary sectional view showing one embodiment of the lithium ion secondary battery of the present invention.

  The electrolytic solution for a lithium ion secondary battery of the present invention uses a substance that suppresses the generation of HF in the electrolytic solution in order to suppress deterioration of the battery due to HF generation during high-temperature storage, and at the same time, transition in the electrolytic solution The main feature is to use a substance that suppresses metal deposition. When transition metal foreign matter is present inside the battery and the amount of HF generated increases, dissolution of the transition metal is promoted. Therefore, in a state where the HF concentration in the electrolytic solution is high, short-circuiting due to precipitation of dissolved transition metal ions at the negative electrode is likely to occur. Therefore, in order to suppress a short circuit during high temperature storage, it is necessary to suppress the precipitation of transition metal after the HF concentration is set to a sufficiently low state. Hereinafter, an electrolytic solution for a lithium ion secondary battery according to an embodiment of the present invention, a lithium ion secondary battery using the same, and a manufacturing method thereof will be described with reference to the drawings.

(Structure of lithium ion secondary battery)
The lithium ion secondary battery of the present invention may be any of a cylindrical type, a laminated type, a coin type, a card type, and the like, and is not particularly limited. As an example, the structure of a wound type lithium ion secondary battery will be described below. . FIG. 1 is a partial cross-sectional view of a wound lithium ion secondary battery.

  A wound type lithium ion secondary battery has a positive electrode and a negative electrode laminated via a separator, the laminated electrode is wound in a spiral shape to produce an electrode body, the electrode body is loaded into a battery container, and an electrolyte solution Obtained by sealing the battery container. In FIG. 1, 9 is a negative electrode lead, 10 is a positive electrode lead, 11 is a positive electrode insulator, 12 is a negative electrode insulator, 13 is a negative electrode battery can, 14 is a gasket, and 15 is a positive electrode battery lid. In addition, the following materials can be used for the lithium ion secondary battery according to the present invention.

(Electrolyte)
The electrolytic solution is composed of a solvent, an additive, and an electrolyte salt. Generally, an organic solvent-based nonaqueous electrolytic solution in which a lithium salt is dissolved as an electrolyte salt in an organic solvent is used.

（式中、Ｒ_１３、Ｒ_１４、Ｒ_１５及びＲ_１６は、独立して水素、フッ素、塩素、炭素数１〜３のアルキル基、炭素数１〜３のアルケニル基、又は１以上の水素がフッ素で置換された炭素数１〜３のアルキル基である）と、
（式７）で表される鎖状カーボネート

（式中、Ｒ_１７及びＲ_１８は、独立して水素、フッ素、塩素、炭素数１〜３のアルキル基、又は１以上の水素がフッ素で置換されたアルキル基である）との混合物を用いることができる。Examples of the solvent include cyclic carbonates represented by (Formula 6).

(Wherein R ₁₃ , R ₁₄ , R ₁₅ and R ₁₆ are independently hydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, an alkenyl group having 1 to 3 carbon atoms, or one or more hydrogen atoms. A C 1-3 alkyl group substituted with fluorine),
Chain carbonate represented by (Formula 7)

(Wherein R ₁₇ and R ₁₈ are independently hydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, or an alkyl group in which one or more hydrogens are substituted with fluorine). be able to.

  Examples of the cyclic carbonate represented by Formula 6 include ethylene carbonate (EC), trifluoropropylene carbonate (TFPC), chloroethylene carbonate (ClEC), fluoroethylene carbonate (FEC), trifluoroethylene carbonate (TFEC), and difluoro. Ethylene carbonate (DFEC), vinyl ethylene carbonate (VEC), or the like can be used. In particular, it is preferable to use EC from the viewpoint of film formation on the negative electrode.

  As the chain carbonate represented by (Formula 7), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), trifluoromethyl Ethyl carbonate (TFMEC), 1,1,1-trifluoroethyl methyl carbonate (TFEMC), or the like can be used. DMC is a highly compatible solvent and is suitable for use in a mixture with EC or the like. DEC has a lower melting point than DMC and is excellent in low temperature (−30 ° C.) characteristics. EMC is excellent in low temperature characteristics because of its asymmetric molecular structure and low melting point. Since EPC and TFMEC have propylene side chains and an asymmetric molecular structure, they are suitable as adjusting solvents for low temperature characteristics. TFEMC is suitable for maintaining the dissociation property of lithium salt at a low temperature because it fluorinates a part of the molecule and has a large dipole moment, and has excellent low temperature characteristics. The ratio (capacity ratio) of the cyclic carbonate represented by (Formula 6) and the chain carbonate represented by (Formula 7) in the electrolytic solution is preferably 1: 4 to 1: 2. .

（式中、Ｒ_１、Ｒ_２及びＲ_３は、独立してフッ素、又は１以上の水素がフッ素で置換された炭素数１〜３のアルキル基である）
及び（式２）で表される化合物

（式中、Ｒ_４、Ｒ_５及びＲ_６は、独立して水素、フッ素、塩素、炭素数１〜３のアルキル基、又は１以上の水素がフッ素で置換されたアルキル基である）
から選択される少なくとも１種類が添加される。The electrolytic solution of the present invention includes a compound represented by (formula 1) as a substance that suppresses the generation of hydrofluoric acid in the electrolytic solution and prevents deterioration during high-temperature storage.

(Wherein R ₁ , R ₂ and R ₃ are each independently fluorine or an alkyl group having 1 to 3 carbon atoms in which one or more hydrogens are substituted with fluorine)
And a compound represented by (formula 2)

(Wherein R ₄ , R _5, and R ₆ are independently hydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, or an alkyl group in which one or more hydrogens are substituted with fluorine)
At least one selected from is added.

（式中、Ｒ_９及びＲ_１０は、独立して水素、フッ素、塩素、炭素数１〜３のアルキル基、又は１以上の水素がフッ素で置換された炭素数１〜３のアルキル基である）
及び（式５）で表される化合物

（式中、Ｒ_１１及びＲ_１２は、独立してアリル基、メタリル基、エタリル基、ビニル基、アクリル基、又はメタクリル基である）
から選択される少なくとも１種類を添加することができる。これらの（式４）及び（式５）の化合物は、上記（式１）及び（式２）の化合物と組み合わせることによって、フッ酸の発生をより効果的に低減することができる。Moreover, in addition to the compound represented by the above (Formula 1) and the compound represented by (Formula 2) as needed, the compound represented by (Formula 4)

(In the formula, R ₉ and R ₁₀ are independently hydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, or an alkyl group having 1 to 3 carbon atoms in which one or more hydrogens are substituted with fluorine. )
And a compound represented by (formula 5)

(Wherein R ₁₁ and R ₁₂ are each independently an allyl group, a methallyl group, an etharyl group, a vinyl group, an acrylic group, or a methacryl group)
At least one selected from the above can be added. By combining these compounds of (Formula 4) and (Formula 5) with the compounds of (Formula 1) and (Formula 2), generation of hydrofluoric acid can be more effectively reduced.

  Examples of the compound represented by the formula (1) include tris (2,2,2-trifluoroethyl) phosphite, tris (2,2,2-difluoroethyl) phosphite, tris (2,2,2-fluoro). Ethyl) phosphite, tris (2-fluoroethyl-2-difluoroethyl-2-trifluoroethyl) phosphite and the like can be used. Although content of the compound represented by (Formula 1) in electrolyte solution is not specifically limited, 0.01 weight%-5 with respect to the total weight of a cyclic carbonate, a chain carbonate, and electrolyte salt It is preferable to set it as weight%. More desirably, the content is 0.1% by weight to 2% by weight.

  As the compound represented by (Formula 2), formamide, acetamide, N-methylformamide, N, N-dimethylformamide, N, N-diethylformamide, N-methylacetamide, N, N-dimethylacetamide (DMA), N-methylpropionamide and the like can be used. Although content of the compound represented by (Formula 2) in electrolyte solution is not specifically limited, 0.1 weight%-2 with respect to the total weight of a cyclic carbonate, a chain carbonate, and electrolyte salt It is preferable to set it to 0.0% by weight. When the content is higher than 2.0% by weight, the internal resistance of the battery is increased, and the output of the battery is decreased.

  As the compound represented by (Formula 4), vinylene carbonate (VC), methyl vinylene carbonate (MVC), dimethyl vinylene carbonate (DMVC), ethyl vinylene carbonate (EVC), diethyl vinylene carbonate (DEVC), or the like may be used. it can. VC has a low molecular weight and is considered to form a dense electrode film. MVC, DMVC, EVC, DEVC, etc., in which the hydrogen atom of VC is substituted with an alkyl group, is considered to form a lower density electrode coating according to the size of the alkyl chain, and effectively acts to improve low temperature characteristics it is conceivable that. Although content of the compound represented by (Formula 4) in electrolyte solution is not specifically limited, 0.1 weight%-2 with respect to the total weight of a cyclic carbonate, a chain carbonate, and electrolyte salt It is preferably 0.0% by weight. When the content is higher than 2.0% by weight, the internal resistance of the battery is increased, and the output of the battery is decreased.

  As the compound represented by (Formula 5), diallyl carbonate, dimethallyl carbonate (DMAC), dietalyl carbonate, allyl methallyl carbonate, allyl etalyl carbonate and the like can be used. Although content of the compound represented by (Formula 5) in electrolyte solution is not specifically limited, 0.1 weight%-2 with respect to the total weight of a cyclic carbonate, a chain carbonate, and electrolyte salt It is preferably 0.0% by weight. When the content is higher than 2.0% by weight, the internal resistance of the battery is increased, and the output of the battery is decreased.

（式中、Ｒ_７及びＲ_８は、独立して水素、フッ素、塩素、臭素、炭素数１〜３のアルキル基、１以上の水素がフッ素で置換された炭素数１〜３のアルキル基、ヒドロキシル基、ニトロ基、又はアミノ基である）、スルホニル基を有する化合物、ポリエチレングリコール（ＰＥＧ）、ポリエチレンオキシド、ポリプロピレングリコール及びポリプロピレンオキシドから選択される少なくとも１種類が添加される。In addition, the electrolytic solution of the present invention includes a nitrogen-containing cyclic compound represented by (Formula 3) as a substance for suppressing transition metal precipitation and preventing internal short circuit.

(Wherein R ₇ and R ₈ are independently hydrogen, fluorine, chlorine, bromine, an alkyl group having 1 to 3 carbon atoms, an alkyl group having 1 to 3 carbon atoms in which one or more hydrogen atoms are substituted with fluorine, At least one selected from a compound having a sulfonyl group, polyethylene glycol (PEG), polyethylene oxide, polypropylene glycol and polypropylene oxide (which is a hydroxyl group, a nitro group or an amino group).

  Examples of the nitrogen-containing cyclic compound represented by (Formula 3) include triazole and triazole derivatives. Specifically, 1,2,3-benzotriazole (BTA), 1,2,4-triazole, 5- Methyl-1H-benzotriazole (TTA), 3-amino-1,2,4-triazole, pyrazole, imidazole and the like can be used. The content of the nitrogen-containing cyclic compound is not particularly limited, but is 0.01 wt% to 5 wt%, preferably 0.05 wt%, based on the total weight of the cyclic carbonate, chain carbonate and electrolyte salt. % To 1% by weight.

  As the compound having a sulfonyl group, sulfolane, 1,3-propane sultone (PS), 1,4-butane sultone, hydroxypropane sultone, or the like can be used. Although content of the compound which has a sulfonyl group is not specifically limited, It is preferable that it is 0.01 weight%-10 weight% with respect to the total weight of a cyclic carbonate, a chain carbonate, and electrolyte salt. If it is less than 0.01% by weight, the effect is small, and if it is more than 10% by weight, not only does not dissolve, but the viscosity of the electrolyte may increase, which is not preferable. More desirably, it is in the range of 0.1 wt% to 5 wt%.

  Polyethylene glycol, polyethylene oxide, polypropylene glycol and polypropylene oxide have a mean molecular weight of 2,000 to 2,000,000 because the effect is small when the molecular weight is small, and the molecular weight becomes too small to dissolve in the solvent. The content of these compounds is not particularly limited, but is preferably 0.1% by weight to 2.0% by weight with respect to the total weight of the cyclic carbonate, the chain carbonate, and the electrolyte salt.

As the electrolyte salt is not particularly limited, inorganic lithium _{salt, LiPF 6, LiBF 4, LiClO} 4, LiI, LiCl, LiBr , etc., and as organic lithium _{salt, LiB [OCOCF 3] 4,} LiB [OCOCF 2 CF _{3] 4, LiPF 4 (CF} 3) 2, LiN (SO 2 CF 3) 2, LiN (SO 2 CF 2 CF 3) may be used ₂ or the like. In particular, LiPF ₆ is preferable because of its excellent quality stability and high ion conductivity in a carbonate solvent. The concentration of the electrolyte salt is preferably 0.5 mol / l to 2 mol / l with respect to the total amount of cyclic carbonate and chain carbonate. If this concentration is too low, the electrical conductivity of the electrolyte solution may be insufficient. If the concentration is too high, the viscosity will increase and the electrical conductivity will decrease, and a lithium ion secondary battery using the electrolyte solution Performance may be degraded.

(Positive electrode)
The positive electrode is formed by applying a positive electrode mixture containing a positive electrode active material, a binder, and a conductive agent on a current collector such as an aluminum foil.

A lithium composite oxide can be used as the positive electrode active material. The lithium composite oxide has a composition formula Li _α Mn _x M1 _y M2 _z O ₂ (wherein M1 is at least one selected from Co and Ni, and M2 is Co, Ni, Al, B, Fe, Mg) And at least one selected from Cr, x + y + z = 1, 0.2 <α <1.2, 0.2 ≦ x ≦ 0.9, 0.05 ≦ y ≦ 0.5, 0.05 ≦ z ≦ 0.5) is preferred. Among these, it is more preferable that M1 is Ni or Co and M2 is Co or Ni. In the composition, if Ni is increased, the battery capacity can be increased, if Co is increased, the output at a low temperature is improved, and if Mn is increased, the material cost can be suppressed. In addition, the general formula LiM _x PO ₄ (M: Fe or Mn, 0.01 ≦ x ≦ 0.4) and LiMn _1-x M _x PO ₄ (M: divalent cation other than Mn, 0.01 ≦ x An orthorhombic phosphate compound having symmetry of the space group Pmnb represented by ≦ 0.4) may be used.

  Examples of the binder used for producing the positive electrode include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, polyimide resin, styrene butadiene rubber (SBR), and the like.

  Examples of the conductive agent include graphite, acetylene black, carbon black, ketjen black, carbon nanotubes and derivatives thereof, carbon fibers, metal powder, and metal fibers.

(Negative electrode)
The negative electrode is formed by applying a negative electrode mixture containing a negative electrode active material, a binder, and a conductive agent on a current collector such as a copper foil.

  As the negative electrode active material, a carbonaceous material, a compound alloyed with lithium, lithium metal, or the like can be used. Carbonaceous materials include natural graphite, composite carbonaceous materials in which a film is formed on natural graphite by a dry CVD method or a wet spray method, resin materials such as epoxy and phenol, or pitch materials obtained from petroleum or coal. And artificial graphite obtained by firing, amorphous carbon materials, and the like. Examples of the compound that forms an alloy with lithium include oxides or nitrides of Group 4 elements such as silicon, germanium, and tin.

  Examples of the binder used for producing the negative electrode include PVDF, PTFE, polyacrylic acid, polyimide resin, SBR, and the like.

  Examples of the conductive agent include graphite, acetylene black, carbon black, ketjen black, carbon nanotubes and derivatives thereof, carbon fibers, metal powder, and metal fibers.

(Separator)
As a separator, the well-known separator currently used for the conventional lithium ion secondary battery can be used. Examples thereof include microporous films made of polyolefin such as polyethylene and polypropylene, and nonwoven fabrics. From the viewpoint of increasing the capacity of the battery, the thickness of the separator is preferably thin, and is preferably 20 μm or less. On the other hand, if the separator is made too thin, the handleability becomes difficult, or the separation between the positive and negative electrodes is insufficient, and a short circuit is likely to occur. Therefore, the lower limit of the thickness is preferably 10 μm.

(Battery container)
As the battery container, those used in conventional lithium ion secondary batteries can be appropriately used. For example, an aluminum or stainless steel container having a battery lid that is laser-welded to the battery container or sealed with a crimp seal through a packing can be used. The positive electrode and the negative electrode are isolated from the container by a glass or resin insulator in the battery container.

(Method for producing lithium ion secondary battery)
As an example, a method for manufacturing a wound lithium ion secondary battery will be described below.

  A conductive material such as graphite, acetylene black, or carbon black was added to and mixed with the lithium composite oxide particles as the positive electrode active material, and then further dissolved in a solvent such as N-methyl-2-pyrrolidinone (NMP). A binder such as PVDF is added and kneaded to obtain a slurry-like positive electrode mixture. Next, after apply | coating this slurry on aluminum foil, it dries and produces a positive electrode.

  Conductive materials such as carbon black, acetylene black and carbon fiber are added to graphite carbon or soft carbon, which is the negative electrode active material, and mixed. To this, PVDF dissolved in NMP as a binder or SBR that is a rubber-based binder is added and then kneaded to obtain a slurry-like negative electrode mixture. Next, after apply | coating this slurry on copper foil, it dries and produces a negative electrode.

  The positive electrode and the negative electrode are dried after the mixture is applied to both sides of the current collector. Further, it is densified by rolling and cut into a desired shape to produce an electrode. Next, lead pieces for passing a current through these electrodes are formed. And the separator which consists of a porous insulating material is inserted | pinched between these positive electrodes and negative electrodes, and this is wound. The wound electrode is inserted into a battery container (battery can) made of stainless steel or aluminum. Next, after connecting the lead piece and the battery can, the electrolytic solution is injected, and finally the battery can is sealed to obtain a lithium ion secondary battery.

(Lithium ion secondary battery module)
As a form using the said lithium ion secondary battery, the lithium ion secondary battery module which connected the some lithium ion secondary battery in series or in parallel is mentioned.

  The present invention will be described in more detail using examples and comparative examples.

(Example 1)
The wound type lithium ion secondary battery of FIG. 1 was produced as follows. LiMn _1/3 Ni _1/3 Co _1/3 O ₂ as the positive electrode active material, carbon black (CB2) and graphite (GF2) as the conductive material, PVDF as the binder, solid weight during drying Paste paste positive electrode mixture using NMP as a solvent so that the ratio of LiMn _1/3 Ni _1/3 Co _1/3 O ₂ : CB 2: GF 2: PVDF = 86: 2: 9: 3 Prepared.

  This positive electrode mixture is applied onto an aluminum foil as the positive electrode current collector 1, dried at 80 ° C., then pressed with a pressure roller and dried at 120 ° C., whereby the positive electrode mixture layer 2 is collected into the positive electrode collector. It was formed on the electric body 1. The ratio of the pore volume of the positive electrode mixture layer to the total volume of the positive electrode mixture layer was 30 vol%.

  Using pseudo-anisotropic carbon, which is amorphous carbon, as the negative electrode active material, using carbon black (CB1) as the conductive material, using PVDF as the binder, the solid content weight at the time of drying is determined as pseudo-anisotropic carbon: A paste-like negative electrode mixture was prepared using NMP as a solvent so as to have a ratio of CB1: PVDF = 88: 5: 7.

  This negative electrode mixture is applied onto a copper foil as the negative electrode current collector 3 and dried at 80 ° C., and then pressed with a pressure roller and dried at 120 ° C. to thereby form the negative electrode mixture layer 4 in the negative electrode collector. It was formed on the electric body 3. The ratio of the pore volume in the negative electrode mixture layer to the total volume of the negative electrode mixture layer was 35 vol%.

  A separator 7 was sandwiched between the produced electrodes to form a wound body. Thereafter, this wound body was inserted into the negative electrode battery can 13 and an electrolytic solution was injected.

The electrolyte solution was prepared by dissolving 1 mol / l of a lithium salt LiPF ₆ as an electrolyte salt in a mixed solvent mixed at a volume composition ratio of EC: DMC: EMC = 20: 40: 40. It was prepared by adding 1.0 wt% VC, 1.0 wt% DMA, and 1.0 wt% BTA as additives based on the total weight.

(Example 2)
The wound lithium ion secondary is the same as Example 1 except that 1.5 wt% VC, 1.5 wt% DMA, and 1.0 wt% TTA are used as additives. A battery was produced.

Example 3
The wound lithium ion secondary is the same as in Example 1 except that 2.5 wt% VC, 1.0 wt% DMA, and 2.0 wt% PS are used as additives. A battery was produced.

Example 4
The wound lithium ion secondary is the same as Example 1 except that 1.0 wt% VC, 1.0 wt% DMA, and 1.5 wt% PEG2000 were used as additives. A battery was produced.

(Example 5)
The wound lithium ion secondary is the same as Example 1 except that 1.0 wt% VC, 1.0 wt% TTFP, and 1.0 wt% BTA are used as additives. A battery was produced.

(Example 6)
The wound lithium ion secondary is the same as Example 1 except that 1.0 wt% DMAC, 2.0 wt% TTFP, and 0.5 wt% TTA are used as additives. A battery was produced.

(Example 7)
The wound lithium ion secondary is the same as Example 1 except that 1.0 wt% VC, 1.0 wt% DMA, and 0.01 wt% BTA are used as additives. A battery was produced.

(Example 8)
The wound lithium ion secondary is the same as Example 1 except that 1.0 wt% VC, 1.0 wt% DMA, and 5.0 wt% BTA are used as additives. A battery was produced.

Example 9
The wound lithium ion secondary is the same as Example 1 except that 1.5 wt% VC, 1.5 wt% DMA, and 0.01 wt% TTA are used as additives. A battery was produced.

(Example 10)
The wound lithium ion secondary is the same as in Example 1 except that 1.5 wt% VC, 1.5 wt% DMA, and 5.0 wt% TTA are used as additives. A battery was produced.

(Example 11)
A wound lithium ion secondary battery was fabricated in the same manner as in Example 1 except that 1.5% by weight of DMA and 1.0% by weight of BTA were used as additives.

(Comparative Example 1)
A wound lithium ion secondary battery was fabricated in the same manner as in Example 1 except that only 1.0 wt% VC was used as the additive.

(Comparative Example 2)
A wound lithium ion secondary battery was produced in the same manner as in Example 1 except that only 1.5% by weight of DMA was used as an additive.

(Comparative Example 3)
A wound lithium ion secondary battery was produced in the same manner as in Example 1 except that only 1.0% by weight of BTA was used as an additive.

(Comparative Example 4)
A wound lithium ion secondary battery was produced in the same manner as in Example 1 except that only 0.5 wt% TTA was used as an additive.

(Comparative Example 5)
A wound lithium ion secondary battery was produced in the same manner as in Example 1 except that 1.0 wt% VC and 1.5 wt% DMA were used as additives.

(Comparative Example 6)
A wound lithium ion secondary battery was produced in the same manner as in Example 1 except that 1.0 wt% VC and 1.0 wt% BTA were used as additives.

<Evaluation method>
(Voltage drop rate)
Changes in the battery voltage at 25 ° C. of the wound lithium ion secondary batteries produced in each Example and Comparative Example were evaluated. Each battery was charged at 0.3 C with an upper limit voltage of 4.2 V and a constant current and constant voltage charge for 5 hours, and then initialized by repeating charging and discharging up to the lower limit voltage of 2.7 V three times. After the initialization, the battery was left to stand, and the voltage drop rate from the second to third weeks was divided by 7 to obtain the voltage drop rate per day.

(Capacity maintenance rate)
Changes in the discharge capacity at 25 ° C. of the wound lithium ion secondary batteries produced in each Example and Comparative Example were evaluated. The capacity retention rate was evaluated by evaluating the rate of change in capacity after storage at 70 ° C. for 30 days, assuming that the discharge capacity after initialization was 100%. The discharge capacity of the battery was measured by charging the battery at 0.3 C to an upper limit voltage of 4.2 V and then discharging to a lower limit voltage of 2.7 V.

Table 1 shows the measurement results of the voltage drop rate and the capacity retention rate.

  From the results shown in Table 1, by using a substance that suppresses the generation of HF in the electrolytic solution and a substance that suppresses the precipitation of transition metal, the capacity retention rate during high-temperature storage is improved, and at the same time, a voltage drop due to a short circuit can be suppressed. I understood.

  Compared to conventional lithium ion secondary batteries, the lithium ion secondary battery of the present invention does not impair capacity even when used in a high temperature environment, and the voltage drop is small. Therefore, the lithium ion secondary battery of the present invention can be widely used as a power source for a hybrid vehicle, a power source for an electric control system of a vehicle, or a backup power source. Also suitable.

  In addition, this invention is not limited to above-described embodiment, Various modifications are included. For example, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. In addition, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 Positive electrode collector 2 Positive electrode mixture layer 3 Negative electrode collector 4 Negative electrode mixture layer 7 Separator 9 Negative electrode lead 10 Positive electrode lead 11 Positive electrode insulator 12 Negative electrode insulator 13 Negative electrode battery can 14 Gasket 15 Positive electrode battery lid It quoted by this specification All publications, patents and patent applications are incorporated herein by reference in their entirety.

Claims (5)

As a substance that suppresses the generation of hydrofluoric acid in the electrolyte, a compound represented by (formula 1)

(Wherein R ₁ , R ₂ and R ₃ are each independently fluorine or an alkyl group having 1 to 3 carbon atoms in which one or more hydrogens are substituted with fluorine)
And a compound represented by (formula 2)

(Wherein R ₄ , R _5, and R ₆ are independently hydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, or an alkyl group in which one or more hydrogens are substituted with fluorine)
At least one selected from:
Nitrogen-containing cyclic compound represented by (Formula 3) as a substance that suppresses the precipitation of transition metals in the electrolyte

(Wherein R ₇ and R ₈ are independently hydrogen, fluorine, chlorine, bromine, an alkyl group having 1 to 3 carbon atoms, an alkyl group having 1 to 3 carbon atoms in which one or more hydrogen atoms are substituted with fluorine, A hydroxyl group, a nitro group or an amino group), a compound having a sulfonyl group, at least one selected from polyethylene glycol, polyethylene oxide, polypropylene glycol and polypropylene oxide;
An electrolyte for a lithium ion secondary battery. As a substance that suppresses the generation of hydrofluoric acid in the electrolyte, a compound represented by (formula 4)

(In the formula, R ₉ and R ₁₀ are independently hydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, or an alkyl group having 1 to 3 carbon atoms in which one or more hydrogens are substituted with fluorine. )
And a compound represented by (formula 5)

(Wherein R ₁₁ and R ₁₂ are each independently an allyl group, a methallyl group, an etharyl group, a vinyl group, an acrylic group, or a methacryl group)
The electrolyte solution for lithium ion secondary batteries of Claim 1 which further contains at least 1 sort (s) selected from these.   The substance that suppresses the generation of hydrofluoric acid in the electrolyte is selected from at least one selected from tris (2,2,2-trifluoroethyl) phosphite and dimethylacetamide, and vinylene carbonate and dimethallyl carbonate. And at least one selected from benzotriazole, tolyltriazole, propane sultone, polyethylene glycol, and polypropylene glycol as a substance that suppresses precipitation of transition metal ions in the electrolyte. The electrolyte solution for lithium ion secondary batteries as described in 2.   The lithium ion secondary battery using the electrolyte solution for lithium ion secondary batteries in any one of Claims 1-3.   The lithium ion secondary battery module which connected two or more of the lithium ion secondary batteries of Claim 4 in series or in parallel.

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