JP2011003498A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery improved in the deteriorating characteristic thereof by restricting the generation of HF (hydrogen fluoride) in electrolyte when keeping the lithium ion secondary battery under a condition at a high temperature.SOLUTION: This lithium ion secondary battery includes: a positive electrode capable of absorbing/discharging lithium ion; a negative electrode capable of absorbing/discharging lithium ion; a separator arranged between the positive electrode and the negative electrode; and organic electrolyte. The organic electrolyte includes: a plurality of solvents; an additive; and electrolyte. As the additive, a compound represented by formula (1) is included. (In the formula (1), R, Rand Rare each any one of hydrogen, 1-3C alkyl group, fluorine, and 1-3C fluorinated alkyl group).

Description

  The present invention relates to a lithium ion secondary battery, and more particularly to a structure of a lithium ion secondary battery in which deterioration during storage at high temperature is suppressed.

  From the viewpoint of environmental protection and energy saving, a hybrid electric vehicle (HEV) that uses an engine and a motor as a power source has been developed and commercialized. In the future, a plug-in hybrid electric vehicle (PHEV) having a system capable of supplying electric power from an electric plug is being developed. A secondary battery capable of repeatedly charging and discharging electricity is used as an energy source of the hybrid vehicle.

  In particular, lithium ion secondary batteries are more powerful than other secondary batteries, including nickel-metal hydride batteries, because they have a higher operating voltage and are easier to obtain higher output, and will become increasingly important as power sources for hybrid vehicles in the future. It is thought that the nature increases.

A lithium-ion secondary battery for a hybrid vehicle power source is generally composed of a positive electrode made of a lithium-containing transition metal composite oxide such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO ₂ , a negative electrode made of graphite, and the like. And an electrolytic solution containing a solvent, an additive, and an electrolyte.

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.

However, when LiPF ₆ is used, a small amount of moisture present in or entering the battery reacts with LiPF ₆ during production or use of the secondary battery, and hydrogen fluoride (HF) is generated. 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. This HF dissolves and corrodes the metal material of the battery container and the current collector, and dissolves the positive electrode active material to elute the transition metal. Furthermore, it is known that an inactive film SEI (Solid Electrolyte Interface) layer containing a metal is formed on the surface of the negative electrode active material to inhibit the action of Li ⁺ ions and cause deterioration of the battery. Such deterioration of the battery characteristics occurs even when a slight thermal decomposition of LiPF ₆ occurs in the electrolyte, and occurs remarkably during long-term storage and continuous charge / discharge of the battery. Become. There are two modes of capacity deterioration of a lithium ion secondary battery: storage characteristic deterioration and continuous charge / discharge characteristic deterioration. The continuous charge / discharge characteristic deterioration is a capacity deterioration caused by repeating a charge / discharge cycle and depends on the number of cycles. The storage characteristic deterioration is a capacity deterioration generated in a battery in a charged state and depends on a charge amount. For this reason, the deterioration suppressing methods for continuous charge / discharge characteristic deterioration and storage characteristic deterioration are different. As described above, when LiPF ₆ is used as an electrolyte, there is a problem that side reactions that adversely affect the constituent materials in the battery are likely to occur in a high temperature environment.

Therefore, in a lithium ion secondary battery, in order to suppress deterioration due to HF generated during long-term storage and continuous charging / discharging of the battery, it has been attempted to add various additives to the electrolytic solution. For example, Patent Document 1 proposes to neutralize and remove HF produced by thermal decomposition of LiPF ₆ by adding 1,4,8,11-tetraazacyclotetradecane (TACTD) to the electrolyte. Yes. The relationship between the capacity of the battery and the number of charge / discharge cycles of the battery is shown. By adding an appropriate amount of TACTD, it is said that the capacity deterioration of the battery due to charge / discharge can be suppressed and the storage characteristics can be improved. In Patent Document 2, N-methyl-2-pyrrolidone (NMP) is added to a non-aqueous electrolyte to suppress the generation of gas generated during the thermal decomposition of the electrolyte and to suppress deterioration of battery characteristics due to high-temperature storage. I can do it. Non-Patent Document 1 examines the relationship between the electrolyte composition and storage characteristics. It is said that deterioration in a high temperature environment at 60 ° C. can be suppressed by adding 2 wt% of vinylene carbonate (VC) to an electrolytic solution composed of LiPF ₆ , EC, and DMC.

Japanese Patent Laid-Open No. 9-245832 JP 2003-297424 A

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

However, in the method of Patent Document 1, HF is generated again as long as moisture and PF ₅ generated by the dissociation of LiPF ₆ are present, and there is a concern that the amount of HF in the organic electrolyte increases again with time. .

  Moreover, in the secondary battery at the time of charging / discharging, the reducing action is very strong near the negative electrode surface, and the oxidizing action is very strong near one positive electrode surface. Therefore, the deterioration of the battery due to a deterioration reaction such as the decomposition of the electrolyte solution and the electrolyte on the electrode surface becomes a problem. The battery capacity is reduced due to the deterioration reaction, and there is a problem that the deterioration reaction is accelerated particularly in a high temperature environment. In the method of Patent Document 2, since NMP has low oxidation resistance, it causes a side reaction with the positive electrode, which raises the internal resistance of the battery and may cause deterioration.

  In Non-Patent Document 1, the additive as described above has greatly improved the battery life in a high temperature environment as compared with the conventional one, but the storage capacity of the battery capacity is insufficient.

  Under the background as described above, an object of the present invention is to provide a new lithium ion secondary battery that can solve the above-described problems. In particular, an object of the present invention is to provide a lithium ion secondary battery in which deterioration during storage at high temperature is suppressed.

In order to achieve the above object, the present invention provides a positive electrode capable of inserting and extracting lithium ions, a negative electrode capable of inserting and extracting lithium ions, a separator disposed between the positive electrode and the negative electrode, and an electrolytic solution In a lithium ion secondary battery having
The electrolytic solution includes a solvent, an additive, and an electrolyte,
As said additive, the phosphorus compound represented by (Formula 1)

(In the formula, R ₁ , R ₂ and R _{3 each} represent hydrogen, an alkyl group having 1 to 3 carbon atoms, fluorine, or a fluorinated alkyl group having 1 to 3 carbon atoms.)
A lithium ion secondary battery is provided.

In order to achieve the above object, the present invention includes the following embodiments in the lithium ion secondary battery according to the present invention.
The additive is tris (2,2,2-trifluoroethyl) phosphite (TTFP), tris (2,2,2-difluoroethyl) phosphite, tris (2,2,2-fluoroethyl) phosphite 1 or more selected from the group consisting of tris (2-fluoroethyl-2-difluoroethyl-2-trifluoroethyl) phosphite and ethyl phosphite.
The concentration of the additive is 0.01 to 5 wt% with respect to the total weight of the solution composed of the solvent and the electrolyte.
As said solvent, the cyclic carbonate represented by (Formula 2)

(Wherein R ₄ , R ₅ , R ₆ and R ₇ represent any one of hydrogen and an alkyl group having 1 to 3 carbon atoms);
Chain carbonate represented by Formula 3

(In the formula, R ₈ and R _{9 each} represent hydrogen and an alkyl group having 1 to 3 carbon atoms.)
including.
The electrolyte includes a lithium salt represented by lithium hexafluorophosphate (LiPF ₆ ).
The positive electrode _is, in _{LiMn x M1 y M2 z O 2} ( wherein, at least one M1 is Co, chosen from Ni, at least one M2 is Co, Ni, Al, B, Fe, Mg, selected from Cr, x + y + z = 1, 0.2 ≦ x ≦ 0.6, 0.2 ≦ y ≦ 0.6, 0.05 ≦ z ≦ 0.4).
The cyclic carbonate contains at least one of ethylene carbonate or propylene carbonate, and the chain carbonate contains at least one of dimethyl carbonate or ethyl methyl carbonate.
The cyclic carbonate is ethylene carbonate, and the chain carbonate is dimethyl carbonate and ethyl methyl carbonate.
The concentration of the electrolyte is 0.5 mol / l to 2 mol / l with respect to the total amount of the solvent and the additive.

According to the present invention, in a lithium ion secondary battery using an electrolyte in which a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ) is dissolved, the deterioration during high temperature storage caused by thermal decomposition of the lithium salt is suppressed, The life of the lithium ion secondary battery can be improved.

It is a one-side cross-section schematic diagram of the winding type lithium ion secondary battery to which the present invention is applied.

The inventors of the present invention are effective in trapping PF ₅ generated by thermal decomposition of LiPF ₆ by a phosphorus compound such as tris (2,2,2-trifluoroethyl) phosphite (TTFP) used as an additive. As a result, the present invention was completed. Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the embodiment taken up here.

  FIG. 1 shows one embodiment of a lithium ion secondary battery to which the present invention is applied, and shows a schematic cross-sectional side view of a wound lithium ion secondary battery.

  This secondary battery uses lithium as an electrode reactant. This secondary battery is a so-called cylindrical type, and is a winding in which a pair of strip-shaped positive electrode 3, strip-shaped negative electrode 6 and separator 7 are wound inside a substantially hollow cylindrical negative electrode battery can 13. It has an electrode group, the positive electrode 3 and the negative electrode 6 are arranged to face each other with a separator 7 interposed therebetween, and an electrolyte is injected.

  The negative electrode battery can 13 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. A pair of positive electrode insulating material 10 and negative electrode insulating material 11 are arranged inside the negative electrode battery can 13 so as to be perpendicular to the wound peripheral surface so as to sandwich the wound electrode group.

  A positive electrode battery lid 12 is attached to the open end of the negative electrode battery can 13 by caulking through a gasket 14, and the inside of the negative electrode battery can 13 is sealed. The positive battery lid 12 is made of the same material as the negative battery can 13, for example.

  A positive electrode lead 8 made of, for example, aluminum (Al) is connected to the positive electrode 3 of the wound electrode group, and a negative electrode lead 9 made of, for example, nickel (Ni) is connected to the negative electrode 6. The positive electrode lead 8 is electrically connected to the positive electrode battery lid 12, and the negative electrode lead 9 is welded and electrically connected to the negative electrode battery can 13.

Below, the positive electrode of a battery, a negative electrode, and electrolyte solution are demonstrated.
(Positive electrode)
First, the positive electrode will be described. A positive electrode paste containing a positive electrode active material, a conductive material, a binder, and the like can be applied to the surface of the positive electrode current collector 1.

  A positive electrode material paste is prepared using a positive electrode active material, a conductive material, graphite, and a binder in consideration of the solid weight during drying and using a solvent. After applying this positive electrode material paste to the aluminum foil used as the positive electrode current collector 1, it was dried at 80 ° C., pressed with a pressure roller, and dried at 120 ° C. to form the positive electrode layer 2 as the positive electrode current collector 1. To form.

The positive electrode material includes a composition formula LiMn _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, Cr) And at least one selected from x + y + z = 1, 0.2 ≦ x ≦ 0.6, 0.2 ≦ y ≦ 0.6, 0.05 ≦ z ≦ 0.4) is preferable. .
In particular,
LiMn _0.4 Ni _0.4 Co _0.2 O ₂ , LiMn _1/3 Ni _1/3 Co _1/3 O ₂ , LiMn _0.3 Ni _0.4 Co _0.3 O ₂ , LiMn _0.35 Ni _0.3 Co _0.3 Al _0.05 O ₂ , LiMn _0.35 Ni _0.3 Co _0.3 B _0.05 O ₂ , LiMn _0.35 Ni _0.3 Co _0.3 Fe _0.05 O ₂ , LiMn _0.35 Ni _0.3 Co _0.3 Mg _0.05 O ₂
Etc. can be used. In some cases, these are generally referred to as positive electrode active materials. In the composition, when Ni is increased, the capacity is increased, when Co is increased, the output at a low temperature is increased, and when Mn is increased, the material cost can be suppressed. In particular, LiMn _1/3 Ni _1/3 Co _1/3 O ₂ has high low-temperature characteristics and high cycle stability, and is suitable as a lithium battery material for hybrid vehicles (HEV). In addition, the additive element is effective in stabilizing the cycle characteristics. In addition, the general formula LiM _x PO ₄ (M: Fe or Mn, 0.01 ≦ x ≦ 0.4) or LiMn _1-x M _x PO ₄ (M: divalent cation other than Mn, 0.01 ≦ It may be an orthorhombic phosphate compound having symmetry of the space group Pnma where x ≦ 0.4).

  The positive electrode binder may be any material as long as the material constituting the positive electrode and the current collector for the positive electrode are in close contact with each other. For example, a homopolymer or copolymer such as vinylidene fluoride, tetrafluoroethylene, acrylonitrile, ethylene oxide, styrene- Examples thereof include butadiene rubber.

The conductive material is, for example, a carbon material such as carbon black, graphite, carbon fiber, and metal carbide, and each may be used alone or in combination.
(Negative electrode)
Subsequently, the negative electrode will be described. The negative electrode 6 can be obtained by applying a negative electrode paste obtained by mixing a negative electrode active material, a conductive material and a binder to the surface of the negative electrode current collector 4 and providing the negative electrode active electrode layer 5.

  Using a negative electrode material, a conductive material, and a binder, a solid content weight at the time of drying is taken into consideration, and a negative electrode material paste is prepared using a solvent. The negative electrode material paste is applied to the copper foil used as the negative electrode current collector 4, dried at 80 ° C., pressed with a pressure roller, and dried at 120 ° C. to form the negative electrode layer 5 on the negative electrode current collector 4. Form.

The negative electrode material may be natural graphite, a composite carbonaceous material in which a film formed by a dry CVD (Chemical Vapor Deposition) method or a wet spray method is formed on natural graphite, a resin raw material such as epoxy or phenol, or petroleum. And carbonaceous materials such as artificial graphite and amorphous carbon materials produced by firing from pitch-based materials obtained from coal and coal, or lithium metal that can occlude and release lithium by forming a compound with lithium, lithium and Silicon, an oxide or nitride of a Group 4 element such as germanium (Ge) or tin (Sn) that can occlude and release lithium by forming a compound and inserting it into the crystal gap can be used. In some cases, these are generally referred to as negative electrode active materials. In particular, the carbonaceous material is a material having high conductivity, and excellent in terms of low temperature characteristics and cycle stability. Among the carbonaceous materials, a material having a wide carbon network plane interval _d002 is excellent in rapid charge / discharge and low temperature characteristics, and is preferable. However, since a material with a wide d ₀₀₂ may have a reduced capacity and a low charge / discharge efficiency at the initial stage of charging, the d ₀₀₂ is preferably 0.39 nm or less. Such a carbonaceous material is sometimes referred to as pseudo-anisotropic carbon. Furthermore, a carbonaceous material having high conductivity such as graphite, amorphous, activated carbon or the like may be mixed to constitute the electrode.

  The negative electrode binder may be any material as long as the material constituting the negative electrode and the negative electrode current collector are in close contact with each other. For example, a homopolymer or copolymer such as vinylidene fluoride, tetrafluoroethylene, acrylonitrile, ethylene oxide, styrene- Examples thereof include butadiene rubber.

The conductive agent is, for example, a carbon material such as carbon black, graphite, carbon fiber, and metal carbide, and each may be used alone or in combination.
(Electrolyte)
Next, the electrolytic solution will be described. The electrolytic solution is composed of a solvent, an additive, and an electrolyte.

  The electrolytic solution of a lithium ion secondary battery that can be operated in a wide voltage range in principle is required to have a withstand voltage characteristic, and an organic electrolytic solution using an organic compound as a solvent is used. An electrolyte having a lithium salt as an electrolyte and carbonate as a solvent can be made highly conductive, and is widely used as an electrolyte for a lithium ion secondary battery in that it has a wide potential window.

  It is known that an electrolytic solution composed of a lithium salt and a carbonate solvent reacts on the negative electrode surface of a lithium ion secondary battery. In order to suppress these electrode reactions and make the battery highly resistant to long-term storage and continuous charge / discharge of the battery, an additive having a reduction reaction potential higher than that of the solvent is often added to the electrolyte. These additives themselves undergo reductive decomposition to form an inert film (SEI) on the electrode surface. And the film formed on the electrode surface suppresses the continued electrode reaction.

As an electrolyte, LiPF ₆ is preferable because of its high quality stability and high ion conductivity in a carbonate solvent. The concentration of the electrolyte is preferably 0.5 mol / l to 2 mol / l with respect to the total amount of the solvent and the additive. If this concentration is too low, the electrical conductivity of the organic electrolyte may be insufficient. If the concentration is too high, the electrical conductivity will decrease due to an increase in viscosity, and the lithium ion secondary using the organic electrolyte will be reduced. Battery performance may be reduced.

As the additive, a phosphorus compound represented by the formula (1) can be used. The phosphorus compound of the formula (1) has high reactivity because the phosphorus (P) atom has an unshared electron pair, and easily combines with components generated by the decomposition of LiPF ₆ . Specific examples of the phosphorus compound that traps PF ₅ generated by the dissociation of LiPF ₆ include tris (2,2,2-trifluoroethyl) phosphite (TTFP). In addition, tris (2,2,2-difluoroethyl) phosphite, tris (2,2,2-fluoroethyl) phosphite, tris (2-fluoroethyl-2-difluoroethyl-2-trifluoroethyl) phosphite Fight, ethyl phosphite, etc. can be used. The compound preferably has a composition ratio of 0.01 wt% to 5 wt% with respect to the solvent. More desirably, 0.1 wt% to 2 wt% is preferable. If the composition ratio is high, the resistance of the electrolytic solution may be increased.

  As the solvent, an aprotic organic solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC), or propylene carbonate, or a solvent of two or more mixed organic compounds is used. Lithium ion secondary batteries have good discharge characteristics during charge / discharge cycles, low temperature and high current discharge characteristics, long-term storage, and long-term high-temperature storage characteristics. Therefore, there is a demand for an organic electrolyte that satisfies these requirements. In order to satisfy the above various requirements, it is difficult to use a solvent composed of only one kind of compound, and it is necessary to mix two or more kinds of compounds and use them as a solvent.

  Specifically, the degree of dissociation of the lithium salt represented by (Formula 2) is improved and ion conductivity is improved, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like. Is mentioned. Of these, EC is preferred because it has the highest dielectric constant, can improve the dissociation degree of the lithium salt, and can provide a highly ionic conductive electrolyte. Further, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) and the like represented by (Formula 3) can be used.

  DMC is a highly compatible solvent and is suitable for use by mixing with EC or the like. DEC has a melting point lower than that of DMC, and is suitable for improving low temperature characteristics at −30 ° C. EMC is suitable for improving low-temperature characteristics because of its asymmetric molecular structure and low melting point. Among them, a mixed solvent of EC and DMC that can ensure battery characteristics in a wide temperature range is preferable.

In order to confirm the improvement of the high-temperature storage characteristics of the lithium ion secondary battery according to the present invention, the following experiment was conducted.
(Example 1)
The wound battery of FIG. 1 was produced as follows. First, LiMn _1/3 Ni _1/3 Co _1/3 O ₂ is used as the positive electrode active material, carbon black (CB1) and graphite (GF1) are used as the conductive material, and polyvinylidene fluoride (PVDF) is used as the binder. , Solid weight when dry,
Using positive electrode material using NMP (N-methylpyrrolidone) as a solvent so that the ratio of LiMn _1/3 Ni _1/3 Co _1/3 O ₂ : CB1: GF1: PVDF = 86: 9: 2: 3 A paste was prepared. The positive electrode material paste is applied to the aluminum foil used as the positive electrode current collector 1, dried at 80 ° C., pressed with a pressure roller, and dried at 120 ° C. to form the positive electrode layer 2 as the positive electrode current collector 1. Formed.

Next, non-graphitizable carbon with d ₀₀₂ of 0.387 nm is used as the negative electrode material, carbon black (CB2) is used as the conductive material, PVDF is used as the binder, and the solid content weight during drying is simulated anisotropic A negative electrode material paste was prepared using NMP as a solvent so as to have a ratio of carbon: CB1: PVDF = 88: 5: 7.

  The negative electrode material paste is applied to the copper foil used as the negative electrode current collector 4, dried at 80 ° C., pressed with a pressure roller, and dried at 120 ° C. to form the negative electrode layer 5 on the negative electrode current collector 4. Formed.

The separator 7 was sandwiched between the produced electrodes to form a wound group and inserted into the negative battery can 13. Further, an electrolytic solution was injected and crimped to produce a wound battery. In the electrolyte solution, a solution obtained by dissolving 1 mol / l of a lithium salt LiPF ₆ as an electrolyte in a mixed solvent mixed at a volume composition ratio of EC: DMC: EMC = 20: 40: 40, from the mixed solvent and the electrolyte salt. 0.8 wt% of tris (2,2,2-trifluoroethyl) phosphite (TTFP) was added to the total weight of the resulting solution.
(Comparative Example 1)
As a comparison with Example 1, a battery using no additive was produced. Other manufacturing conditions are the same as those in Example 1.
(Comparative Example 2)
As a comparison with Example 1, a battery was prepared by adding 0.8 wt% of vinylene carbonate (VC) as an additive. Other manufacturing conditions are the same as those in Example 1.

  Table 1 shows the HF content (μg / l) in each electrolytic solution when the electrolytic solutions prepared in Example 1, Comparative Example 1, and Comparative Example 2 were stored in an environment of 70 ° C. for 14 days. Show.

From Table 1, compared with the electrolyte solution of Comparative Examples 1 and 2 to which TTFP is not added, the electrolyte solution of Example 1 to which TTFP is added has a smaller increase in HF after storage. That is, it can be said that TTFP suppressed the HF production reaction. This demonstrates that the amount of HF produced can be suppressed by adding TTFP even when the electrolyte is stored for a long period of time in a high temperature environment. The reason why HF is generated is that the moisture in the battery reacts with PF ₅ generated by the dissociation of LiPF ₆ . In the battery manufacturing process, it is difficult to completely remove moisture from the inside of the battery. However, since TTFP traps PF ₅ generated by dissociation of LiPF ₆ , generation of HF even when moisture remains in the battery. Can be suppressed. Since the amount of HF produced can be suppressed, the deterioration reaction is suppressed at high temperatures, so that a lithium ion secondary battery having excellent high temperature characteristics is obtained.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode collector, 2 ... Positive electrode layer, 3 ... Positive electrode, 4 ... Negative electrode collector, 5 ... Negative electrode layer, 6 ... Negative electrode, 7 ... Separator, 8 ... Positive electrode lead, 9 ... Negative electrode lead, 10 ... Positive electrode insulating material, 11 ... negative electrode insulating material, 12 ... positive electrode battery lid, 13 ... negative electrode battery can, 14 ... gasket, 100 ... lithium ion secondary battery.

Claims (9)

In a lithium ion secondary battery having a positive electrode capable of inserting and extracting lithium ions, a negative electrode capable of inserting and extracting lithium ions, a separator disposed between the positive electrode and the negative electrode, and an electrolyte solution,
The electrolytic solution includes a solvent, an additive, and an electrolyte,
As said additive, the phosphorus compound represented by (Formula 1)

(In the formula, R ₁ , R ₂ and R _{3 each} represent hydrogen, an alkyl group having 1 to 3 carbon atoms, fluorine, or a fluorinated alkyl group having 1 to 3 carbon atoms.)
A lithium ion secondary battery comprising:   The additive is tris (2,2,2-trifluoroethyl) phosphite, tris (2,2,2-difluoroethyl) phosphite, tris (2,2,2-fluoroethyl) phosphite, tris ( 2. The lithium ion secondary battery according to claim 1, wherein the lithium ion secondary battery is at least one selected from the group consisting of (2-fluoroethyl-2-difluoroethyl-2-trifluoroethyl) phosphite and ethyl phosphite.   2. The lithium ion secondary battery according to claim 1, wherein a concentration of the additive is 0.01 to 5 wt% with respect to a total weight of the solution including the solvent and the electrolyte. As said solvent, the cyclic carbonate represented by (Formula 2)

(Wherein R ₄ , R ₅ , R ₆ and R ₇ represent any one of hydrogen and an alkyl group having 1 to 3 carbon atoms);
Chain carbonate represented by Formula 3

(In the formula, R ₈₈ and R _{9 each} represent hydrogen and an alkyl group having 1 to 3 carbon atoms.)
The lithium ion secondary battery according to claim 1, comprising: The lithium ion secondary battery according to claim 1, wherein the electrolyte contains a lithium salt represented by lithium hexafluorophosphate (LiPF ₆ ). The positive electrode is LiMn _x M1 _y M2 _z O ₂ (wherein M1 is at least one selected from Co and Ni, M2 is at least one selected from Co, Ni, Al, B, Fe, Mg, Cr, x + y + z = 1, 0.2 ≦ x ≦ 0.6, 0.2 ≦ y ≦ 0.6, 0.05 ≦ z ≦ 0.4). The lithium ion secondary battery according to claim 1.   The lithium ion secondary according to claim 4, wherein the cyclic carbonate contains at least one of ethylene carbonate and propylene carbonate, and the chain carbonate contains at least one of dimethyl carbonate and ethyl methyl carbonate. battery.   The lithium ion secondary battery according to claim 4, wherein the cyclic carbonate is ethylene carbonate, and the chain carbonate is dimethyl carbonate or ethyl methyl carbonate.   2. The lithium ion secondary battery according to claim 1, wherein a concentration of the electrolyte is 0.5 mol / l to 2 mol / l with respect to a total amount of the solvent and the additive.

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