JP2016085836A - Nonaqueous liquid electrolyte for lithium ion secondary batteries, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous liquid electrolyte for lithium ion secondary batteries and a lithium ion secondary battery which enable the achievement of a superior discharge capacity at a low temperature, and the enhancement in preservation characteristic at a high temperature.SOLUTION: A nonaqueous liquid electrolyte for lithium ion secondary batteries comprises: 2.1-6.0 wt% of an ethylene sulfate derivative expressed by the formula (1); and 0.0004-0.2 wt% of a vinylene carbonate derivative expressed by the formula (2). [R1 to R4 represent H or a hydrocarbon group with 1-5C.]SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-aqueous electrolyte for a lithium ion secondary battery and a lithium ion secondary battery.

  Lithium ion secondary batteries are lighter and have higher capacity than nickel cadmium batteries and nickel metal hydride batteries, and thus are widely applied as power sources for portable electronic devices. In addition, it has begun to be used as a power source mounted for hybrid vehicles and electric vehicles. In recent years, the miniaturization and high functionality of portable electronic devices have progressed, and in order to improve the mileage of electric vehicles and the like, further increase in capacity of lithium ion secondary batteries serving as these power sources is expected. ing.

  A lithium ion secondary battery is mainly composed of a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. Generally, a lithium metal composite oxide is used for the positive electrode, and a carbon material that can occlude and release lithium ions is used for the negative electrode. A liquid electrolyte in which a lithium salt is dissolved in an organic solvent that is liquid at room temperature is used as a non-aqueous electrolyte. However, a side reaction in which the organic solvent decomposes occurs on the surface of the carbon material of the negative electrode, which adversely affects the characteristics such as an expected discharge capacity cannot be obtained. For this reason, it becomes an important subject to form a film on the negative electrode surface and to control the state and properties of this film so that the negative electrode does not directly react with the organic solvent.

  In order to form and control the negative electrode surface coating, a special additive is added to the electrolytic solution. For example, as shown in Patent Documents 1 to 3, there is a description that cycle characteristics are improved by adding a vinylene carbonate derivative or a cyclic sulfate to a non-aqueous electrolyte of a lithium ion secondary battery containing a carbon material. In addition, studies on adding a plurality of additives simultaneously have been made energetically, and as shown in Patent Document 4, it has been reported that 2 wt% or less of glycol sulfate and 1 wt% or less of vinylene carbonate are added.

Japanese Patent Application Laid-Open No. 08-045545 JP 2004-303544 A JP-A-10-189042 JP 2003-197253 A

  However, the discharge capacity at a low temperature of −10 ° C. was reduced by adding appropriate amounts of vinylene carbonate derivatives and ethylene sulfate derivatives, respectively, as compared to the case of not adding them. In addition, the capacity deterioration is not small when stored at a high temperature of 60 ° C., and it is necessary to simultaneously improve the discharge capacity at a low temperature and the storage characteristics at a high temperature. Even when a certain amount of vinylene carbonate derivative or ethylene sulfate derivative is added in Patent Document 4, the capacity retention rate at high temperature storage at 60 ° C. cannot be said to be sufficient, and it is necessary to further improve the storage characteristics at high temperature. It was.

  The present invention has been made in view of the above problems, and provides a non-aqueous electrolyte for a lithium ion secondary battery and a lithium ion secondary battery that have excellent discharge capacity at low temperatures and further improve storage characteristics at high temperatures. The purpose is to provide.

〔式（１）中、Ｒ_１及びＲ_２は、それぞれ独立に水素原子及び炭素数１〜５の炭化水素基のいずれかを表す。〕

〔式（２）中、Ｒ_３及びＲ_４は、それぞれ独立に水素原子及び炭素数１〜５の炭化水素基のいずれかを表す。〕 In order to solve the above problems, a non-aqueous electrolyte for a lithium ion secondary battery according to the present invention includes a non-aqueous solvent and an electrolyte, and includes an ethylene sulfate derivative represented by the formula (1) in 2.1 to 6. It contains 0 wt% and 0.0004 to 0.2 wt% of a vinylene carbonate derivative represented by the formula (2).

[In Formula (1), R < ₁ > and R < ₂ > represents either a hydrogen atom and a C1-C5 hydrocarbon group each independently. ]

[In Formula (2), R < ₃ > and R < ₄ > represents either a hydrogen atom and a C1-C5 hydrocarbon group each independently. ]

  By adding an appropriate amount of the ethylene sulfate derivative and the vinylene carbonate derivative at the same time, it is possible to form a stronger film that is added alone, and to reduce capacity deterioration during storage at high temperatures. At the same time, the cell impedance can be lowered. In particular, at low temperatures, the impedance at the positive electrode or the positive electrode / electrolyte interface increases and the discharge capacity decreases. However, it is considered that the resistance does not increase.

  When the content of the ethylene sulfate derivative is 2.1% by weight or more, a strong coating is formed, so that capacity degradation during full charge storage at high temperatures can be reduced. Since the ethylene sulfate derivative is a compound that easily contains water, when it is usually contained in an amount of 2.1% by weight or more, the influence of the water may appear. By dehydrating before adding to the non-aqueous electrolyte, the effect can be minimized. On the other hand, if the content is 6.0% by weight or less, the coating does not become too thick, the impedance of the electrode can be kept small, and the discharge capacity at low temperature can be increased.

  When the content of the vinylene carbonate derivative is 0.0004% by weight or more, a stronger coating is formed, and thus capacity degradation during full charge storage at high temperatures can be reduced. On the other hand, when the content is 0.2% by weight or less, the effect of increasing the discharge capacity at a low temperature is exhibited particularly by keeping the impedance of the positive electrode or the positive electrode / electrolyte interface low.

The ethylene sulfate derivative is preferably 1,3,2-dioxathiolane-2,2-dioxide in which R ₁ and R ₂ are both hydrogen atoms in the formula (1).

It is presumed that the ethylene sulfate derivative can form the strongest film when both R ₁ and R ₂ are hydrogen atoms. The melting point of the ethylene sulfate derivative may be related to the strength of the formed film.

The vinylene carbonate derivative is preferably 4,5-dimethyl-1,3-dioxol-2-one in which R ₃ and R ₄ are both methyl groups in the formula (2).

In the formula (2), unlike vinylene carbonate in which R ₃ and R ₄ are both hydrogen atoms, 4,5-dimethyl-1,3-dioxol-2-one does not form a film even when added alone, Although there is almost no effect of improving the characteristics, it is possible to form a stronger film by adding it simultaneously with the ethylene sulfate derivative and greatly improve the storage characteristics at high temperatures.

The electrolyte preferably contains LiPF ₆ from the viewpoint of improving conductivity.

〔式（１）中、Ｒ_１及びＲ_２は、それぞれ独立に水素原子及び炭素数１〜５の炭化水素基のいずれかを表す。〕

〔式（２）中、Ｒ_３及びＲ_４は、それぞれ独立に水素原子及び炭素数１〜５の炭化水素基のいずれかを表す。〕 The lithium ion secondary battery according to the present invention includes a positive electrode, a negative electrode, a separator, and a nonaqueous electrolytic solution having a nonaqueous solvent and an electrolyte, and the ethylene sulfate represented by the formula (1) in the nonaqueous electrolytic solution. It contains 2.1 to 6.0% by weight of a derivative and 0.0004 to 0.2% by weight of a vinylene carbonate derivative represented by the formula (2).

[In Formula (1), R < ₁ > and R < ₂ > represents either a hydrogen atom and a C1-C5 hydrocarbon group each independently. ]

[In Formula (2), R < ₃ > and R < ₄ > represents either a hydrogen atom and a C1-C5 hydrocarbon group each independently. ]

  ADVANTAGE OF THE INVENTION According to this invention, the non-aqueous electrolyte for lithium ion secondary batteries and lithium ion secondary battery which are excellent in the discharge capacity in low temperature, and also improve the storage characteristic in high temperature can be provided.

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

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the non-aqueous electrolyte for lithium ion secondary batteries and the lithium ion secondary battery according to the present invention are 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 storage element 30, a case 50 that houses the power storage element 30 in a sealed state, and a pair of leads 60 and 62 connected to the power storage element 30.

  The power storage 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 a product in which a positive electrode active material layer 14 is provided on a positive electrode current collector 12. The negative electrode 20 is a product in which 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. A non-aqueous electrolyte is contained inside the positive electrode active material layer 14, the negative electrode active material layer 24, and the separator 18. 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.

(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.

  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, 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 particles of the negative electrode active material and the binder, and the penetration of the non-aqueous electrolyte into the negative electrode active material layer 24 is facilitated by the pores. Therefore, it is preferable.

  The binder is not particularly limited as long as it can bind the negative electrode active material particles and the conductive auxiliary particles. For example, fluororesins such as polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and the like can be given. Further, the binder contributes not only to the binding of the particles of the negative electrode active material material and the particles of the conductive additive but also the binding to the negative electrode current collector 22.

  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.

(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, ClO ₄ ⁻ ) 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), and composite metal oxides such as lithium vanadium compounds (LiVOPO ₄ ).

  Furthermore, each constituent element (conductive auxiliary agent and binder) other than the positive electrode active material can use the same substances as those used in the negative electrode 20. Therefore, the binder contained in the positive electrode 10 contributes not only to the binding between the particles of the positive electrode active material and the particles of the conductive auxiliary agent, but also to the binding to the positive electrode current collector 12. Yes.

  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.

(Separator)
As long as the separator 18 is formed of an insulating porous material, the material, the manufacturing method, and the like are not particularly limited, and a known separator used in the lithium ion secondary battery 100 can be used. For example, as the insulating porous material, a known polyolefin resin, specifically, a crystalline homopolymer or copolymer obtained by polymerizing polyethylene, polypropylene, 1-butene, 4-methyl-1-pentene, 1-hexene, or the like. A polymer is mentioned. These homopolymers or copolymers can be used alone or in combination of two or more. Further, it may be a single layer or a multilayer.

〔式（１）中、Ｒ_１及びＲ_２は、それぞれ独立に水素原子及び炭素数１〜５の炭化水素基のいずれかを表す。〕

〔式（２）中、Ｒ_３及びＲ_４は、それぞれ独立に水素原子及び炭素数１〜５の炭化水素基のいずれかを表す。〕 (Nonaqueous electrolyte)
The non-aqueous electrolyte is a non-aqueous solvent, 2.1 to 6.0% by weight of the electrolyte and the ethylene sulfate derivative represented by the formula (1), and the vinylene carbonate derivative represented by the formula (2) is 0.00. 0004 to 0.2% by weight.

[In Formula (1), R < ₁ > and R < ₂ > represents either a hydrogen atom and a C1-C5 hydrocarbon group each independently. ]

[In Formula (2), R < ₃ > and R < ₄ > represents either a hydrogen atom and a C1-C5 hydrocarbon group each independently. ]

  Although the mechanism of the effect expression by including an ethylene sulfate derivative and a vinylene carbonate derivative simultaneously is not clear, the present inventors consider as follows.

  The ethylene sulfate derivative and the vinylene carbonate derivative are considered to act when forming a film on the negative electrode active material and contribute to improvement of cycle characteristics and suppression of gas generation. In addition, the present inventors have the effect that the ethylene sulfate derivative or vinylene carbonate derivative acts when forming a film on the positive electrode active material to lower the impedance of the positive electrode / nonaqueous electrolyte interface. thinking. It may act more positively on the positive electrode, reducing the impedance of the positive electrode itself.

By simultaneously adding 6.0 wt% or less of the ethylene sulfate derivative and 0.2 wt% or less of the vinylene carbonate derivative, the coating film at the positive electrode / non-aqueous electrolyte interface has high lithium ion permeability. As a result, the impedance is kept low even at low temperatures, and the discharge capacity at low temperatures is increased. The ethylene sulfate derivative was 2.1 to 6.0% by weight, and the vinylene carbonate derivative was 0.0004 to 0.2% by weight.
As a result, the oxidation reaction of the non-aqueous electrolyte at the positive electrode / non-aqueous electrolyte interface can be further suppressed, and the capacity deterioration during high-temperature storage can be reduced.

  Examples of ethylene sulfate derivatives include 1,3,2-dioxathiolane-2,2-dioxide, 4-methyl-1,3,2-dioxathiolane-2,2-dioxide, 4-ethyl-1,3,2-dioxathiolane Examples include -2,2-dioxide, and 1,3,2-dioxathiolane-2,2-dioxide is preferable from the viewpoint of improving discharge capacity at low temperatures.

  Examples of vinylene carbonate derivatives include vinylene carbonate (1,3-dioxol-2-one), 4-methyl-1,3-dioxol-2-one, 4-ethyl-1,3-dioxol-2-one, 4, Examples include 5-dimethyl-1,3-dioxol-2-one, and 4,5-dimethyl-1,3-dioxol-2-one is preferable from the viewpoint of improving storage characteristics at high temperatures.

  The ethylene sulfate derivative is contained in the non-aqueous electrolyte at 2.1 to 6.0% by weight. Since the storage characteristics at a high temperature are further improved, it is preferably 2.9 to 6.0% by weight. Moreover, since the discharge capacity at low temperature becomes large, it is more preferably 2.9 to 4.5% by weight.

  The vinylene carbonate derivative is contained in the nonaqueous electrolytic solution in an amount of 0.0004 to 0.2% by weight. Since the storage characteristics at a high temperature are further improved, the content is preferably 0.004 to 0.2% by weight. Moreover, since the discharge capacity at low temperature also becomes large, More preferably, it is 0.004 to 0.08 weight%.

  The non-aqueous solvent preferably contains a cyclic carbonate and a low viscosity solvent. The cyclic carbonate refers to an organic solvent having a dielectric constant of 20 or more so as to promote dissociation of the lithium salt that is an electrolyte, and the low viscosity solvent is 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.

  In addition, as a low viscosity solvent, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, 1,2-dimethoxyethane, 1,2-diethoxyethane, etc. may be used. it can. In particular, it is preferable to contain diethyl carbonate from the viewpoint of improving high-temperature storage characteristics. Diethyl carbonate may be used by mixing with other low viscosity solvents.

  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 because the conductivity becomes high.

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.

The hydrogen fluoride or fluorine ion 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.

(Exterior body)
The case 50 may be made of any material as long as it can seal the power generation element 30 and the non-aqueous electrolyte therein.

  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 non-aqueous electrolyte for lithium ion secondary batteries and lithium ion secondary batteries of Examples 1 to 46 and Comparative Examples 1 to 10 were prepared and evaluated according to the following procedure.

Example 1
First, a negative electrode was produced. In the production of the negative electrode, artificial graphite (90% by weight) as a negative electrode active material, carbon black (2% by weight) as a conductive assistant, and polyvinylidene fluoride (PVDF) (8% by weight) as a binder are mixed. A slurry was obtained by dispersing in N-methyl-2-pyrrolidone (NMP) as a solvent. 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, 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 wt%) as the positive electrode active material, carbon black (6 wt%) as the conductive assistant, and PVDF (4 as the binder) % By weight) were 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 non-aqueous electrolyte 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. Further, after the first charge, 2% by weight of 1,3,2-dioxathiolane-2,2-dioxide and 0.04 of 4,5-dimethyl-1,3-dioxol-2-one were added to the whole non-aqueous electrolyte. It added so that it might become weight%, and the nonaqueous electrolyte solution was obtained.

  A laminated body (element body) was obtained by laminating a separator made of polyethylene between the obtained negative electrode and 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 2-46 and Comparative Examples 1-10)
Except that the combination of the nonaqueous solvent, LiPF ₆ concentration, the type and content of the ethylene sulfate derivative contained in the nonaqueous electrolyte, and the type and content of the vinylene carbonate derivative were changed as shown in Tables 1 to 3 In the same manner as in Example 1, lithium ion secondary batteries of Examples 2 to 46 and Comparative Examples 1 to 10 were produced. In Tables 1 to 3, “EC” of the non-aqueous solvent represents ethylene carbonate, “DEC” represents diethyl carbonate, “EMC” represents ethyl methyl carbonate, and “PC” represents propylene carbonate. The ethylene sulfate derivative “DTD” is 1,3,2-dioxathiolane-2,2-dioxide, “MDTD” is 4-methyl-1,3,2-dioxathiolane-2,2-dioxide, and “EDTD” is It represents 4-ethyl-1,3,2-dioxathiolane-2,2-dioxide. The vinylene carbonate derivative “VC” represents vinylene carbonate, “MDO” represents 4-methyl-1,3-dioxol-2-one, “EDO” represents 4-ethyl-1,3-dioxol-2-one, “DMDO” represents 4,5-dimethyl-1,3-dioxol-2-one.

(Discharge capacity evaluation test)
After the production of the lithium ion secondary battery, the first charge was performed in an environment set at 25 ° C. in a thermostatic bath, and the first discharge was performed immediately after that. The charging was performed at a constant current and constant voltage up to 4.2 V at 30 mA, and the discharging was performed at a constant current of 2.5 mA at 30 mA. The measured value of the discharge capacity (mAh) in the first discharge is shown as “initial discharge capacity (mAh)” in Tables 1 to 3.

(-10 ° C discharge capacity evaluation test)
After the discharge capacity evaluation test, the temperature of the thermostatic chamber containing the two batteries was set to −10 ° C., and after waiting for 2 hours, charging and discharging were performed at that temperature. The charging was performed at a constant current and constant voltage up to 4.2 V at 30 mA, and the discharging was performed at a constant current of 2.5 mA at 30 mA. In Tables 1-3, the value obtained by dividing the discharge capacity at −10 ° C. by the initial discharge capacity and multiplying by 100 is shown as “−10 ° C. discharge capacity (%)”.

(High temperature storage test at 60 ° C)
After the discharge capacity evaluation test, the battery was charged at a constant current and a constant voltage up to 4.2 V to be in a fully charged state. Then, the lead portion of the battery was covered with an insulating tape, and three batteries were put into a thermostat set at 60 ° C. It was left in that state, and after one month, it was taken out from the thermostatic chamber and discharged to 2.5 V at 30 mA. And it charged / discharged on the same conditions as the discharge capacity evaluation test, and measured the discharge capacity. A value obtained by dividing the capacity by the initial discharge capacity and multiplying by 100 is shown as “recovered capacity after storage at 60 ° C. (%)” in Tables 1-3.

(Examples 1 to 6 and Comparative Examples 1 and 2)
First, Table 1 shows the evaluation results when 1,3,2-dioxathiolane-2,2-dioxide is selected as the ethylene sulfate derivative and only the content after the initial charge is changed. The vinylene carbonate derivative is 4,5-dimethyl-1,3-dioxol-2-one, except for the content of 1,3,2-dioxathiolane-2,2-dioxide. Fixed and compared.

  In the initial discharge capacity, it was confirmed that all of the lithium ion secondary batteries of the examples had a sufficient discharge capacity.

  When the content of 1,3,2-dioxathiolane-2,2-dioxide was 6.0% by weight or less, the discharge capacity at −10 ° C. was 50% or more. In particular, when the content of 1,3,2-dioxathiolane-2,2-dioxide was 4.5% by weight or less, it was 60% or more, indicating a good value.

  In the recovery capacity after storage at 60 ° C., the comparative example is less than 80%, whereas the content of 1,3,2-dioxathiolane-2,2-dioxide is 2.1 to 6.0% by weight. In all cases, 80% or more. In particular, when the content of 1,3,2-dioxathiolane-2,2-dioxide was 2.9 to 5.2% by weight, it was 87% or more, indicating a good value.

  From the above, when the content of 1,3,2-dioxathiolane-2,2-dioxide is 2.1 to 6.0% by weight, the −10 ° C. discharge capacity is 50% or more and stored at 60 ° C. The post-recovery capacity became 80% or more. When the content of 1,3,2-dioxathiolane-2,2-dioxide is 2.9 to 5.2% by weight, the recovery capacity is further improved to 87% after storage at 60 ° C. In the case of 4.5% by weight, in addition to the recovery capacity after storage at 60 ° C., the discharge capacity at −10 ° C. was 60% or more, which was particularly good.

(Examples 7 to 14 and Comparative Examples 3 and 4)
Next, as the vinylene carbonate derivative, 4,5-dimethyl-1,3-dioxol-2-one is selected, and Table 2 shows the evaluation results when only the content after the initial charge is changed. The ethylene sulfate derivative is 1,3,2-dioxathiolane-2,2-dioxide, and is fixed in the configuration shown in Table 2 except for the content of 1,3,2-dioxathiolane-2,2-dioxide. Compared.

  In the initial discharge capacity, it was confirmed that all of the lithium ion secondary batteries of the examples had a sufficient discharge capacity.

  In the -10 ° C discharge capacity, when the content of 4,5-dimethyl-1,3-dioxol-2-one was 0.2% by weight or less, all became 50% or more. In particular, when the content of 4,5-dimethyl-1,3-dioxol-2-one was 0.08% by weight or less, it was 60% or more, indicating a good value.

  In the recovery capacity after storage at 60 ° C., the comparative example is less than 80%, whereas the content of 4,5-dimethyl-1,3-dioxol-2-one is 0.0004 to 0.2% by weight. All of the examples were 80% or more. In particular, when the content of 4,5-dimethyl-1,3-dioxol-2-one was 0.004 to 0.12% by weight, it was 87% or more, indicating a good value.

  From the above, when the content of 4,5-dimethyl-1,3-dioxol-2-one is 0.0004 to 0.2 wt%, the −10 ° C. discharge capacity is 50% or more, and 60 The recovery capacity after storage at ℃ was 80% or more. When the content of 4,5-dimethyl-1,3-dioxol-2-one is 0.004 to 0.12% by weight, the recovery capacity after storage at 60 ° C. is 87% or more, which is further improved. In the case of 0.004 to 0.08% by weight, in addition to the recovery capacity after storage at 60 ° C., the discharge capacity at −10 ° C. was also 60% or more, showing a particularly good value.

(Examples 15 to 46 and Comparative Examples 5 to 10)
Table 3 shows the combinations of non-aqueous solvents and LiPF ₆ content, the type of ethylene sulfate derivative and the content after the initial charge, the type and content of vinylene carbonate derivative, and each measurement was performed. .

  In the initial discharge capacity, it was confirmed that all of the lithium ion secondary batteries of the examples had a sufficient discharge capacity.

  The lithium ion secondary battery in which the content of the ethylene sulfate derivative is 6.0% by weight or less and the content of the vinylene carbonate derivative is 0.2% by weight or less at a discharge capacity of −10 ° C. is 50%. That's it. In particular, when the content of the ethylene sulfate derivative was 4.5% by weight or less and the content of the vinylene carbonate derivative was 0.08% by weight or less, it was 60% or more, indicating a good value.

  In particular, when the ethylene sulfate derivative was 1,3,2-dioxathiolane-2,2-dioxide, the -10 ° C discharge capacity tended to increase.

  In the recovery capacity after storage at 60 ° C., the comparative example is less than 80%, whereas the content of the ethylene sulfate derivative is 2 to 6% by weight, and the content of the vinylene carbonate derivative is 0.0004 to 0.2. All the lithium ion secondary batteries of Examples having a weight% were 80% or more. In particular, when the content of the ethylene sulfate derivative was 3 to 5% by weight and the content of the vinylene carbonate derivative was 0.004 to 0.12% by weight, it was 87% or more, indicating a good value.

  In particular, when the vinylene carbonate derivative was 4,5-dimethyl-1,3-dioxol-2-one, the recovery capacity after storage at 60 ° C. tended to increase.

  From the above, the content of 1,3,2-dioxathiolane-2,2-dioxide is 2.1 to 6.0% by weight, and 4,5-dimethyl-1,3-dioxol-2-one When the content was 0.0004 to 0.2% by weight, the -10 ° C discharge capacity was 50% or more, and the recovery capacity after storage at 60 ° C was 80% or more. The content of 1,3,2-dioxathiolane-2,2-dioxide is 2.9 to 5.0% by weight, and the content of 4,5-dimethyl-1,3-dioxol-2-one is 0.8. In the case of 004 to 0.12% by weight, the recovery capacity after storage at 60 ° C. shows 87% and a better value, and the content of 1,3,2-dioxathiolane-2,2-dioxide is 2.9 to When the content of 4.5% by weight and 4,5-dimethyl-1,3-dioxol-2-one is 0.004 to 0.08% by weight, in addition to the recovery capacity after storage at 60 ° C. The discharge capacity at −10 ° C. was 60% or more, which was a particularly good value.

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 ... electricity storage element, 50 ... case, 60, 62 ... lead, 100 ... lithium ion secondary battery

Claims (8)

Including non-aqueous solvent and electrolyte,
2.1 to 6.0% by weight of an ethylene sulfate derivative represented by the formula (1),
0.0004 to 0.2% by weight of vinylene carbonate derivative represented by the formula (2),
A nonaqueous electrolytic solution for a lithium ion secondary battery, comprising:

[In Formula (1), R < ₁ > and R < ₂ > represents either a hydrogen atom and a C1-C5 hydrocarbon group each independently. ]

[In Formula (2), R < ₃ > and R < ₄ > represents either a hydrogen atom and a C1-C5 hydrocarbon group each independently. ] _2. The lithium according to claim 1, wherein the ethylene sulfate derivative is 1,3,2-dioxathiolane-2,2-dioxide in which R ₁ and R ₂ are both hydrogen atoms in the formula (1). Non-aqueous electrolyte for ion secondary battery. The vinylene carbonate derivative is 4,5-dimethyl-1,3-dioxol-2-one in which R ₃ and R ₄ are both methyl groups in the formula (2). A non-aqueous electrolyte for a lithium ion secondary battery according to 1. Lithium ion secondary batteries for non-aqueous electrolyte according to claim 1, characterized in that it comprises a LiPF ₆ as the electrolyte. A positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte solution having a nonaqueous solvent and an electrolyte,
2.1 to 6.0% by weight of an ethylene sulfate derivative represented by the formula (1) in a non-aqueous electrolyte solution;
0.0004 to 0.2% by weight of vinylene carbonate derivative represented by the formula (2),
A lithium ion secondary battery comprising:

[In Formula (1), R < ₁ > and R < ₂ > represents either a hydrogen atom and a C1-C5 hydrocarbon group each independently. ]

[In Formula (2), R < ₃ > and R < ₄ > represents either a hydrogen atom and a C1-C5 hydrocarbon group each independently. ] 6. The lithium according to claim 5, wherein the ethylene sulfate derivative is 1,3,2-dioxathiolane-2,2-dioxide in which R ₁ and R ₂ are both hydrogen atoms in the formula (1). Ion secondary battery. The vinylene carbonate derivative is 4,5-dimethyl-1,3-dioxol-2-one in which R ₃ and R ₄ are both methyl groups in the formula (2). The lithium ion secondary battery described in 1. The lithium ion secondary battery according to claim 5, comprising LiPF ₆ as the electrolyte.

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