JP2015125950A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery excellent in voltage resistance and low temperature characteristics, by enhancing the oxidation resistance of a separator.SOLUTION: In a lithium ion secondary battery having a positive electrode, a negative electrode, a separator and an electrolyte, material of the separator is polyolefin, and the electrolyte contains a compound represented by chemical formula (1). (In the formula (1), R1, R2, R3, R5, R6 and R7 represent an alkyl group of 1-4C, and R4 represents an alkylene group of 1-4C).

Description

The present invention relates to a lithium ion secondary battery.

  With the development and popularization of portable information devices such as mobile phones, notebook personal computers, and video cameras in recent years, the demand for secondary batteries that are small, lightweight, and have high energy density has greatly increased. Considering higher performance. In the future, the use of large batteries for automobiles is expected to expand. As such a secondary battery, a lithium ion secondary battery is particularly attracting attention.

  The general structure of a lithium ion secondary battery is that a positive electrode active material layer made of a positive electrode active material powder such as lithium-cobalt composite oxide, a conductive powder, and a binder is formed on the surface of a positive electrode current collector made of aluminum foil. A negative electrode formed by forming a negative electrode active material layer made of a copper foil and a negative electrode active material layer made of a copper foil on a surface of a negative electrode current collector made of a porous film. The power generation element is impregnated with an electrolytic solution.

  As separators, polyolefin porous membranes are widely used, and have basic characteristics such as excellent electronic insulation, ion permeability by electrolyte impregnation, excellent resistance to electrolytes, and moderate strength. In addition, it has a hole clogging effect that cuts off the current and suppresses excessive temperature rise at a temperature of about 120 to 150 ° C. at the time of abnormal battery temperature rise, and it is considered that these are preferably used.

  However, in recent years, the working voltage has been increased (about 4.3-4.5V) for high capacity and high output such as in automobiles. However, the separator due to the oxidation reaction in the vicinity of the positive electrode due to this high voltage. Deterioration of the surface has emerged as a major problem, and a solution is sought. The deterioration of the separator decreases the ion permeability, electrolyte resistance, and safety. Patent Document 1 discloses a base material made of a porous film, and a separator made of a crosslinked polymer supported on the base material and an inorganic particle layer. As a similar configuration, Patent Document 2 discloses a laminate separator including a polyolefin layer and a heat-resistant insulating layer containing a heat-resistant resin and oxidation-resistant ceramic particles.

  However, in any of the prior arts, a layer having oxidation resistance is imparted to the film as a base material, so that the ion permeability is hindered, and in particular, low temperature characteristics (0 to −20 ° C. that are easily influenced by the movement of ions). There was a problem of reducing the degree).

JP 2010-67377 A JP 2009-87889 A

  The present invention has been made in view of the above problems, and an object thereof is to provide a lithium secondary battery that improves the oxidation resistance of a separator and is excellent in voltage resistance and low-temperature characteristics.

  A lithium ion secondary battery according to the present invention includes a positive electrode, a negative electrode, a separator, and an electrolytic solution, wherein the separator is made of polyolefin, and the electrolytic solution includes a compound represented by the chemical formula (1). .

〔化学式（１）において、Ｒ１、Ｒ２、Ｒ３、Ｒ５、Ｒ６およびＲ７は炭素数１〜４のアルキル基を表し、Ｒ４は炭素数１〜４のアルキレン基を表す。〕

[In the chemical formula (1), R1, R2, R3, R5, R6 and R7 represent an alkyl group having 1 to 4 carbon atoms, and R4 represents an alkylene group having 1 to 4 carbon atoms. ]

  When fully charged at 4.3 to 4.5 V, the separator surface near the positive electrode is exposed to a strong oxidation state. The compound approaches there and causes a chemical reaction with the polyolefin, which is the material of the separator, and is immobilized on the separator surface (hereinafter referred to as an immobilization layer). Since this immobilization layer has an oxidation potential higher than that of polyolefin, it functions as an oxidation-resistant protective layer for the separator. In addition, since this immobilization layer is very thin and does not inhibit ion permeability, it is presumed that the low temperature characteristics are not deteriorated.

  The lithium ion secondary battery according to the present invention is characterized in that the compound is contained in an amount of 0.1 to 10% by mass in the electrolytic solution.

  By setting the addition amount in the above range, it is possible to more effectively improve the voltage resistance and low temperature characteristics.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery excellent in withstand voltage property and low-temperature characteristic can be provided.

It is a schematic cross section of a lithium ion secondary battery.

  Hereinafter, preferred embodiments of the present embodiment will be described with reference to the drawings. However, the lithium ion secondary battery according to the present invention is not limited to the following embodiments. In addition, the dimensional ratio of drawing is not restricted to the ratio of illustration.

(Lithium ion secondary battery)
Next, the electrode and the lithium ion secondary battery according to this embodiment will be briefly described with reference to FIG.

  The lithium ion secondary battery 100 mainly includes a power generation element 30, a case 50 that houses the power generation element 30 in a sealed state, and a pair of leads 60 and 62 connected to the power generation element 30.

  The power generation element 30 is configured such that a pair of electrodes 10 and 20 are disposed to face each other with the separator 18 interposed therebetween. The positive electrode 10 is obtained by providing a positive electrode active material layer 14 on a positive electrode current collector 12. In the negative electrode 20, a negative electrode active material layer 24 is provided on a negative electrode current collector 22. The positive electrode active material layer 14 and the negative electrode active material layer 24 are in contact with both sides of the separator 18. The positive electrode active material layer 14, the negative electrode active material layer 24, and the separator 18 contain an electrolyte solution. Leads 60 and 62 are connected to the end portions of the positive electrode current collector 12 and the negative electrode current collector 22, respectively, and the end portions of the leads 60 and 62 extend to the outside of the case 50.

(Separator)
The separator 18 separates the positive electrode 10 and the negative electrode 20 and allows lithium ions to pass through while preventing a short circuit of current due to contact between both electrodes, and is made of porous polyolefin. For example, it is a porous film made of a resin such as polyethylene, polypropylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and not only a homopolymer but also α- such as propylene, butene, hexene, etc. It may be a copolymer of olefin and ethylene.

  The thickness of the separator 18 is preferably in the range of 3 to 100 μm. When the thickness is smaller than 3 μm, it is difficult to obtain sufficient strength, and therefore, the positive and negative electrodes may contact each other and cause an internal short circuit. On the other hand, when the thickness of the porous film exceeds 100 μm, the membrane resistance of the separator 18 increases, which may cause a decrease in low-temperature characteristics.

  The separator 18 has pores having an average pore diameter of 0.01 to 5 μm, and a film having a porosity in the range of 20 to 95 vol% can be used. A film having a porosity in the range of 30 to 90 vol%, more preferably in the range of 40 to 85 vol% is preferably used.

  When a porous film having a porosity that is too low is used for the separator 18, the ion conduction path is reduced, and sufficient battery characteristics may not be obtained. In addition, when a porous film having a too high porosity is used for the separator 18, the strength may be insufficient. If the strength is insufficient, a thick porous film must be used to obtain the required strength, which is not preferable because the internal resistance of the battery increases. Therefore, it is desirable to select a porous film whose porosity satisfies the above range.

(Electrolyte)
The electrolytic solution includes a solvent, an electrolyte, and a compound represented by the chemical formula (1) as an additive compound.

〔化学式（１）において、Ｒ１、Ｒ２、Ｒ３、Ｒ５、Ｒ６およびＲ７は炭素数１〜４のアルキル基を表し、Ｒ４は炭素数１〜４のアルキレン基を表す。〕

[In the chemical formula (1), R1, R2, R3, R5, R6 and R7 represent an alkyl group having 1 to 4 carbon atoms, and R4 represents an alkylene group having 1 to 4 carbon atoms. ]

  Although the mechanism of the effect expression by containing the compound represented by the chemical formula (1) is not clear, the present inventors consider as follows.

  When the battery is fully charged at 4.3 to 4.5 V, the surface of the separator 18 in the vicinity of the positive electrode 10 is exposed to a strong oxidation state. The compound represented by the chemical formula (1) approaches there and causes a chemical reaction with the polyolefin, which is the material of the separator, and is immobilized on the surface of the separator 18 (hereinafter referred to as an immobilization layer). Since this immobilization layer has an oxidation potential higher than that of polyolefin, it functions as an oxidation-resistant protective layer for the separator 18. In addition, since this immobilization layer is very thin and does not impair ion permeability, the low temperature characteristics are not deteriorated.

  The compound is relatively stable even in the electrolytic solution, and the decomposition reaction on the electrode surface hardly occurs. The reason for this is that all of the bonding types of Si atoms are C atoms, and two Si atoms in the molecule are bonded by an alkyl group, and this “Si-alkyl group-Si” structure is a stable molecule. It is estimated that it contributes to When the fully charged state of 4.3 to 4.5 V is reached, it can selectively react with the surface of the separator 18, and no other chemical reaction occurs at a potential lower than this.

  On the other hand, in the case of a compound in which the bond type of the Si atom is an O atom, an N atom, or a compound having a “Si—O—Si” structure in the molecule, It decomposes by reacting with moisture, or is easily decomposed or polymerized on the electrode surface, making it difficult to form an immobilization layer on the surface of the separator 18 like the compound of this embodiment. In the case of a compound containing a halogen atom in the molecule, the probability of being attracted to the electrode surface due to the occurrence of polarization in the molecule due to the electron withdrawing property of the halogen atom increases, and an immobilization layer is formed on the separator 18 surface. It will be difficult to do. In the case of a compound containing an aromatic group or an unsaturated bond in the molecule, the probability of being attracted to the electrode surface due to the influence of the π bond that forms the aromatic group or the unsaturated bond increases, and the surface of the separator 18 It is difficult to form a fixed layer.

  The content of the compound represented by the chemical formula (1) is preferably 0.1 to 10% by mass.

  By setting the addition amount in the above range, it is possible to more effectively improve the voltage resistance and low temperature characteristics.

  It is preferable that the solvent contains a cyclic carbonate and a low viscosity solvent. The cyclic carbonate has a dielectric constant of 20 or more so as to promote dissociation of the lithium salt as an electrolyte. A low viscosity solvent refers to an organic solvent having a viscosity of 1.0 cP or less so as to improve the mobility of lithium ions.

  As the cyclic carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, and the like can be used. Among them, ethylene carbonate is preferably included. You may mix and use ethylene carbonate with propylene carbonate and butylene carbonate.

  Further, as a low viscosity solvent, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2- Diethoxyethane or the like can be used, and two or more of these low-viscosity solvents may be mixed and used.

  The ratio of the cyclic carbonate and the low viscosity solvent in the non-aqueous solvent is preferably 1: 9 to 1: 1 by volume.

The electrolytes include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiPOF ₂ , LiAsF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN. (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) _{2 and the} like may be mentioned, and two or more kinds may be mixed and used. Good. In particular, it is preferable to include LiPF ₆ that has high conductivity even at a low temperature.

When LiPF ₆ is dissolved in a non-aqueous solvent, the concentration of the electrolyte in the non-aqueous electrolyte is preferably adjusted to 0.5 to 2.0 mol / L. When the concentration of the electrolyte is 0.5 mol / L or more, the conductivity of the nonaqueous electrolytic solution can be sufficiently secured, and a sufficient capacity can be easily obtained during charging and discharging. In addition, by suppressing the electrolyte concentration to within 2.0 mol / L, it is possible to suppress an increase in the viscosity of the non-aqueous electrolyte, to sufficiently secure the mobility of lithium ions, and to obtain a sufficient capacity during charging and discharging. It becomes easy.

Even when LiPF ₆ is mixed with other electrolytes, the lithium ion concentration in the non-aqueous electrolyte is preferably adjusted to 0.5 to 2.0 mol / L, and the lithium ion concentration from LiPF ₆ is 50 mol%. More preferably, it is contained.

Hydrogen fluoride or fluorine ions produced by the reaction of LiPF ₆ with moisture is preferably 50 ppm or less, more preferably 30 ppm or less in the non-aqueous electrolyte. Therefore, the water content in the non-aqueous electrolyte is preferably 50 ppm or less, and more preferably 30 ppm or less.

(Positive electrode)
The positive electrode 10 includes a positive electrode active material layer 14 on both surfaces of a positive electrode current collector 12. Furthermore, the positive electrode active material layer 14 is formed by applying a paint containing a positive electrode active material, a conductive additive, and a binder to the positive electrode current collector 12.

The positive electrode active material is composed of lithium ion occlusion and release, lithium ion desorption and insertion (intercalation), or doping and dedoping of a lithium ion and a counter anion (for example, PF ₆ ⁻ ) of the lithium ion. Is not particularly limited as long as it can reversibly proceed, and a known electrode active material can be used. For example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), general formula: LiNi _x Co _y Mn _z O ₂ (x + y + z = 1) or Li _a Ni _x Co _y Al _1-xy O ₂ (0.98 <a <1.2, 0 <x, y <1) A composite metal oxide, olivine-type LiMPO ₄ (where M is Co, Ni , Mn, Fe, or V)).

  The conductive auxiliary agent is not particularly limited, and a known conductive auxiliary agent can be used. Examples thereof include carbon materials such as pyrolytic carbon such as carbon black, cokes, glassy carbons, organic polymer compound fired materials, carbon fibers, and activated carbon. Moreover, you may add negative electrode active material materials, such as non-graphitizable carbon, easily graphitizable carbon, and graphite, changing a shape.

  As carbon black, acetylene black, ketjen black and the like are particularly preferable, and ketjen black is particularly preferable. By including an electron conductive porous body, pores can be formed at the interface between the positive electrode active material material particles and the binder, and the penetration of the electrolyte into the positive electrode active material layer 14 is facilitated by the pores. preferable.

  The binder is not particularly limited as long as it can bind the particles of the positive electrode active material and the particles of the conductive additive. For example, a fluororesin such as polyvinylidene fluoride (PVDF) can be used. In addition, the binder contributes not only to the binding of the particles of the positive electrode active material and the particles of the conductive additive, but also to the binding to the positive electrode current collector 12.

  As the positive electrode current collector 12, various known metal foils used in current collectors for lithium ion secondary batteries can be used. Specifically, it is preferable to use an aluminum foil.

(Negative electrode)
The negative electrode 20 includes a negative electrode active material layer 24 on both sides of a negative electrode current collector 22. Furthermore, the negative electrode active material layer 24 is formed by applying a paint containing a negative electrode active material, a conductive additive, and a binder to the negative electrode current collector 22.

The negative electrode active material includes at least one selected from carbon materials such as natural graphite, artificial graphite (non-graphitizable carbon, graphitizable carbon, low-temperature calcined carbon, etc.), MCF (mesocarbon fiber), and the like. Among these, artificial graphite is preferable because it exhibits a favorable negative electrode capacity and cycle characteristics, and from the viewpoint of improving electrode density, it is more preferable to use artificial graphite mixed with natural graphite. In addition, for example, a metal capable of forming a compound with lithium such as Al, Si and Sn, an amorphous compound mainly composed of an oxide such as SiO ₂ and SnO ₂ , lithium titanate (Li ₄ Ti ₅ O _A known negative electrode active material such as ₁₂ ) may be mixed with a carbon material.

  Furthermore, the same material as that used for the positive electrode 10 can be used for each component (conductive aid, binder) other than the negative electrode active material. Therefore, the binder contained in the negative electrode 20 contributes not only to the binding of the particles of the positive electrode active material and the particles of the conductive additive, but also to the binding to the negative electrode current collector 22. Yes.

  As the negative electrode current collector 22, various known metal foils used for current collectors for lithium ion secondary batteries can be used. Specifically, it is preferable to use a copper foil.

  The case 50 seals the power generation element 30 and the electrolyte solution therein. The case 50 is not particularly limited as long as it can suppress leakage of the electrolyte solution to the outside and entry of moisture or the like into the lithium ion secondary battery 100 from the outside. For example, as the case 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with a polymer film 54 from both sides can be used. For example, an aluminum foil can be used as the metal foil 52, and a film such as polypropylene can be used as the synthetic resin film 54. For example, the material of the outer polymer film 54 is preferably a polymer having a high melting point such as polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is preferably polyethylene or polypropylene.

  The leads 60 and 62 are made of a conductive material such as aluminum or nickel.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not limited to these Examples at all.

  The lithium ion secondary batteries of Examples 1 to 15, Comparative Examples 1 to 6, and Reference Example 1 were prepared and evaluated according to the following procedure.

Example 1
First, a positive electrode was produced. Also in the production of the positive electrode, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (90% by mass) as the positive electrode active material, carbon black (6% by mass) as the conductive additive, and PVDF (4 as the binder) (Mass%) was mixed and dispersed in NMP to obtain a slurry. The obtained slurry was applied to an aluminum foil as a current collector, dried, rolled, and a positive electrode was obtained.

  Next, a negative electrode was produced. In the production of the negative electrode, first, artificial graphite (90% by mass) as a negative electrode active material, carbon black (2% by mass) as a conductive auxiliary, and polyvinylidene fluoride (hereinafter referred to as PVDF) (8% by mass) as a binder. %) Was mixed and dispersed in N-methyl-2-pyrrolidone (hereinafter referred to as NMP) as a solvent to obtain a slurry. The obtained slurry was applied to an electrolytic copper foil as a current collector by a doctor blade method and dried at 110 ° C. After drying, rolling was performed to obtain a negative electrode.

Next, an electrolytic solution was prepared. LiPF ₆ was added at a rate of 1.0 mol / L in a solution in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7. In the whole electrolyte solution, as a compound represented by the chemical formula (1), a compound in which R1, R2, R3, R5, R6 and R7 are CH ₃ groups and R4 is a CH ₂ group is added as an additive compound. It added so that it might be contained by mass%, and obtained electrolyte solution.

〔化学式（１）において、Ｒ１、Ｒ２、Ｒ３、Ｒ５、Ｒ６およびＲ７はＣＨ_３基を表し、Ｒ４はＣＨ_２基を表す。〕

In [Formula (1), R1, R2, R3, R5, R6 and R7 represent a CH ₃ group, R4 represents a CH ₂ group. ]

  A laminated body (element body) was obtained by sandwiching a separator made of polyethylene having a thickness of 15 μm, an average pore diameter of 1.0 μm, and a porosity of 50 vol% between the obtained negative electrode and the positive electrode. The obtained laminate is placed in an aluminum laminate pack, a non-aqueous electrolyte is injected into the aluminum laminate pack, and then vacuum-sealed to produce a lithium ion secondary battery (length: 60 mm, width: 85 mm, thickness: 3 mm). did.

(Examples 2-12 and Comparative Examples 1-6)
As in Example 1, except that R1 to R7 of the compound represented by the chemical formula (1) as the additive compound contained in the electrolytic solution were changed as shown in Table 1 and the addition amount was changed as shown in Table 1. The lithium ion secondary battery of Examples 2-12 was produced. Further, a lithium ion secondary battery of Comparative Example 1 was produced in the same manner as Example 1 except that no additive compound was added. Lithium ion secondary batteries of Comparative Examples 2 to 6 were produced in the same manner as in Example 1 except that the compounds of chemical formulas (2) to (6) were used as additive compounds and the addition amount was set to 4.0% by weight. .

(Example 13)
A lithium ion secondary battery of Example 13 was fabricated in the same manner as Example 4 except that a separator made of polypropylene having a thickness of 14 μm, an average pore diameter of 1.2 μm, and a porosity of 50 vol% was used.

(Example 14)
The lithium ion secondary battery of Example 13 was used in the same manner as in Example 4 except that a separator made of 4-methyl-1-pentene having a thickness of 16 μm, an average pore diameter of 1.0 μm, and a porosity of 45 vol% was used. A secondary battery was produced.

(Example 15)
The lithium ion secondary battery of Example 13 was used in the same manner as in Example 4 except that a separator made of a copolymer of propylene and ethylene having a thickness of 13 μm, an average pore diameter of 0.9 μm, and a porosity of 45 vol% was used. Was made.

(Reference Example 1)
As the separator, a separator made of polyethylene used in Example 1 and a crosslinked polymer layer (film thickness of 0.3 μm) made of crosslinked (meth) acrylate copolymer: silica particles = 30: 70 (mass ratio) was used. A lithium ion secondary battery of Reference Example 1 was produced in the same manner as in Example 1 except that no additive compound was added.

(Initial charge / discharge)
The lithium ion secondary batteries obtained in Examples 1 to 15, Comparative Examples 1 to 6 and Reference Example 1 were charged for the first time in an environment set to 25 ° C. in a thermostatic bath, and immediately after that, the first discharge was performed. Went. In addition, charge performed constant current constant voltage charge to 4.4V at 30mA, and discharge performed constant current discharge to 2.5V at 30mA.

(Withstand voltage evaluation)
As evaluation of withstand voltage, the storage characteristics in a fully charged state of 4.4V were evaluated. After the initial charging / discharging, the battery was charged at a constant current and a constant voltage up to 4.4 V at 25 ° C. to obtain a fully charged state. And the lead part of this battery was covered with the insulating tape, and it put into the thermostat set to 25 degreeC. The product was left in that state, taken out of the thermostat after 60 days, and the discharge capacity was measured. The value obtained by dividing the discharge capacity by the initial discharge capacity and multiplying by 100 is shown in Tables 1-2 as “Capacity after storage at 25 ° C. for 60 days (%)”.

(Low temperature characteristics evaluation)
After the above storage test, the temperature of the thermostatic chamber containing the battery was set to −20 ° C., and after waiting for 2 hours, charging and discharging were performed at that temperature. In addition, charge performed constant current constant voltage charge to 4.4V at 30mA, and discharge performed constant current discharge to 2.5V at 30mA. Tables 1 and 2 show values obtained by dividing the discharge capacity by the discharge capacity at 25 ° C. at the time of initial charge / discharge described above and multiplying by 100 times as “discharge capacity ratio (%) at −20 ° C. to 25 ° C.” .

(Evaluation of changes in separator after test)
After the above-described evaluation of the low temperature characteristics, the battery was disassembled and visually evaluated for changes in the separator. When there was no discoloration due to the oxidation of the separator, it was marked with ◯, and when there was discoloration, it was marked with ×. The results are shown in Tables 1-2.

  From comparison between Examples 1-12 and Comparative Examples 1-6, the electrolyte contained the compound represented by the chemical formula (1), so that oxidation of the polyethylene separator was prevented even under a high voltage of 4.4V. It was confirmed that the voltage resistance and low temperature characteristics were excellent.

  Further, from Examples 1 to 6, it is possible to obtain better voltage resistance and low temperature characteristics by setting the addition amount of the compound represented by the formula (1) to 0.1 mass% to 10 mass%. It could be confirmed.

  Further, from Examples 13 to 15, even when a separator other than polyethylene was used, the electrolyte contained a compound represented by the chemical formula (1), thereby preventing oxidation of the separator under a high voltage of 4.4V. It was confirmed that it was excellent in voltage resistance and low temperature characteristics.

  Moreover, from the reference example 1, when the separator which provided the crosslinked polymer layer was used, although it was excellent in withstand voltage property, it was confirmed that a low temperature characteristic is inferior.

  DESCRIPTION OF SYMBOLS 10 ... Positive electrode, 20 ... Negative electrode, 12 ... Positive electrode collector, 14 ... Positive electrode active material layer, 18 ... Separator, 22 ... Negative electrode collector, 24 ... Negative electrode Active material layer, 30 ... power generation element, 50 ... case, 52 ... metal foil, 54 ... polymer film, 60, 62 ... lead, 100 ... lithium ion secondary battery

Claims (2)

A lithium ion secondary battery having a positive electrode, a negative electrode, a separator, and an electrolytic solution, wherein the separator is made of polyolefin, and the electrolytic solution contains a compound represented by Chemical Formula 1 .

[In the chemical formula (1), R1, R2, R3, R5, R6 and R7 represent an alkyl group having 1 to 4 carbon atoms, and R4 represents an alkylene group having 1 to 4 carbon atoms. ]   The lithium ion secondary battery according to claim 1, wherein the compound is contained in the electrolytic solution in an amount of 0.1 to 10% by mass.

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