JP2014049294A - Nonaqueous electrolyte for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte which is large in discharge capacity at a low temperature, and which has small reduction of capacity in cycle test at a high temperature, and also to provide the lithium ion secondary battery.SOLUTION: A nonaqueous electrolyte for a lithium ion secondary battery contains a nonaqueous solvent, an electrolyte, 0.5 to 6 mass% of chain sulfone derivative expressed by the following general formula (1), and 0.05 to 4 mass% of fluoroethylene carbonate. [In the formula (1), Rand Rare individually and independently hydrogen or a 1-5C alkyl group, and a part of the hydrogen of the alkyl group may be replaced with a halogen atom.]

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. It is also a promising candidate as a power source for hybrid vehicles and electric vehicles. However, with the recent miniaturization and higher functionality of portable electronic devices, further increase in capacity is expected for lithium ion secondary batteries serving as these power sources.

  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 involving an organic solvent 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 is an important issue to form a film on the surface of the negative electrode and to control the state and properties of the 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, it has been clarified that the storage performance is improved by adding non-cyclic sulfone to the non-aqueous electrolyte (see Patent Documents 1 and 2). It has also been clarified that cycle characteristics are improved by adding fluoroethylene carbonate to the non-aqueous electrolyte (see Patent Document 3).

Japanese Patent Laid-Open No. 7-230824 Japanese Patent Laid-Open No. 7-230825 Japanese Patent Laid-Open No. 7-240232

  However, even when acyclic sulfone was added, the storage performance at room temperature was improved, but the effect was not obtained in the high-temperature cycle test at 45 ° C. Furthermore, it became clear by the present inventors that the discharge capacity is reduced by adding acyclic sulfone at a low temperature of −10 ° C. Similarly, in the case where fluoroethylene carbonate was added, the capacity drop markedly appeared in the high-temperature cycle test at 45 ° C., and cell swelling was also observed.

  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 can provide a sufficient discharge capacity even at a low temperature and have good cycle characteristics even at a high temperature. An object is to provide a battery.

〔式（１）中、Ｒ_１とＲ_２はそれぞれ独立で、水素または炭素数１〜５のアルキル基であり、アルキル基の水素がハロゲン原子で置換されていてもよい。〕 In order to solve the above problems, a non-aqueous electrolyte for a lithium ion secondary battery according to the present invention comprises a non-aqueous solvent, an electrolyte, and a chain sulfone derivative represented by the following formula (1) in an amount of 0.5 to And containing 0.05 to 4% by mass of fluoroethylene carbonate.

Wherein (1), in each of R ₁ and R ₂ are independently hydrogen or an alkyl group having 1 to 5 carbon atoms, hydrogen of the alkyl group may be substituted with a halogen atom. ]

  Both the chain sulfone derivative and fluoroethylene carbonate contribute to film formation at the interface between the negative electrode active material of the lithium ion secondary battery and the non-aqueous electrolyte. By including appropriate amounts of the chain sulfone derivative and fluoroethylene carbonate in the non-aqueous electrolyte, a lithium ion battery having a high conductivity and a sufficient capacity can be obtained even at a low temperature. Further, it is considered that this coating can realize excellent high temperature cycle characteristics by suppressing side reactions such as decomposition of non-aqueous solvent.

  The non-aqueous solvent preferably contains 5 to 50% by mass of propylene carbonate with respect to the non-aqueous electrolyte. Since propylene carbonate has a relatively low melting point and a relatively high conductivity, it is possible to obtain higher lithium ion conductivity even at a low temperature, and a sufficient discharge capacity can be obtained even at a low temperature. In addition, since the potential window of propylene carbonate is relatively wide, it is difficult to cause side reactions with the positive electrode or the negative electrode, and by reducing the change in the non-aqueous solvent, it is possible to suppress a decrease in capacity during a high-temperature cycle test. Become.

  The chain sulfone derivative is preferably any of dimethyl sulfone, ethyl methyl sulfone, and diethyl sulfone. By containing these chain sulfone derivatives, the melting point of the nonaqueous electrolytic solution is lowered, and the increase in viscosity at low temperatures can be reduced, so that a large discharge capacity can be obtained even at low temperatures. In addition, since these chain sulfone derivatives are chemically stable, the formed film is not easily decomposed, and even after repeated charge and discharge many times, the nonaqueous solvent and the negative electrode are prevented from coming into contact with each other. The capacity drop can be reduced even during the cycle test.

  Among these chain sulfone derivatives, dimethyl sulfone is more preferable. Thereby, it is expected that the high-temperature cycle characteristics are particularly good.

〔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の炭化水素基からなる群より選ばれる少なくとも一種を表す。〕 The nonaqueous electrolytic solution preferably further contains 4% by mass or less of an ethylene glycol sulfate derivative represented by the following formula (2).

[In Formula (2), R < ₃ > and R < ₄ > represent at least 1 type chosen from the group which consists of a hydrogen atom and a C1-C5 hydrocarbon group each independently. ]

  The ethylene glycol sulfate derivative, together with the chain sulfone derivative and fluoroethylene carbonate, contributes to film formation at the interface between the negative electrode active material of the lithium ion secondary battery and the non-aqueous electrolyte. The addition of the ethylene glycol sulfate derivative is expected to increase the lithium ion conductivity of the coating and further reduce the internal impedance of the lithium ion secondary battery. This is expected to increase the discharge capacity at low temperatures. Moreover, since the formed film becomes stronger, it is expected to further improve the high temperature cycle characteristics.

The ethylene glycol sulfate derivative of the above formula (2) is preferably an ethylene glycol sulfate in which R ₃ and R ₄ are both hydrogen. Thereby, it is expected that the coating on the negative electrode surface becomes stronger and the high-temperature cycle characteristics are further improved.

〔式（１）中、Ｒ_１とＲ_２はそれぞれ独立で、水素または炭素数１〜５のアルキル基であり、アルキル基の水素がハロゲン原子で置換されていてもよい。〕 The lithium ion secondary battery of the present invention has at least a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the non-aqueous electrolyte includes a non-aqueous solvent, an electrolyte, and the following formula (1): It is characterized by containing 0.5 to 6% by mass of a chain sulfone derivative represented by the formula, and 0.05 to 4% by mass of fluoroethylene carbonate.

Wherein (1), in each of R ₁ and R ₂ are independently hydrogen or an alkyl group having 1 to 5 carbon atoms, hydrogen of the alkyl group may be substituted with a halogen atom. ]

  According to the present invention, it is possible to provide a non-aqueous electrolyte for a lithium ion secondary battery and a lithium ion secondary battery that can obtain a sufficient discharge capacity even at a low temperature and have good cycle characteristics even at a high temperature.

It is a schematic diagram of a lithium ion battery.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. However, the non-aqueous electrolyte and the lithium ion secondary battery using the same 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 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 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. The positive electrode active material layer 14, the negative electrode active material layer 24, and the separator 18 contain a non-aqueous electrolyte for a lithium ion secondary battery (hereinafter referred to as “non-aqueous electrolyte”). 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, 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 particles of the negative electrode active material and the binder, and the negative electrode active material layer 21 can be easily penetrated into the negative electrode active material layer 21 by the pores. This is preferable.

  The binder is not particularly limited as long as it can bind the particles of the negative electrode active material and the particles of the conductive additive. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoro Examples thereof include fluorine resins such as ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF). Further, the binder contributes not only to the binding of the negative electrode active material material particles and the conductive auxiliary agent particles but also 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 32.

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 additive 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 body, the material, the manufacturing method, and the like are not particularly limited, and a known separator 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.

(Nonaqueous electrolyte)
The nonaqueous electrolytic solution is a nonaqueous solvent, an electrolyte, a chain sulfone derivative represented by the following formula (1) of 0.5 to 6% by mass, a fluoroethylene carbonate of 0.05 to 4% by mass, It is characterized by containing.

  Although the mechanism of the effect expression by containing a chain | strand-shaped sulfone derivative and fluoroethylene carbonate simultaneously in a non-aqueous electrolyte solution is not clear, the present inventors think as follows.

  By adding the chain sulfone derivative and fluoroethylene carbonate together to the non-aqueous solvent, the solvation energy for the lithium ions in the non-aqueous electrolyte is reduced, which is required when lithium ions are inserted into the positive electrode 10. It is thought that energy will decrease. Therefore, a large discharge capacity can be obtained even at a low temperature.

  In addition, it is already known that the chain sulfone derivative and fluoroethylene carbonate each form a good surface coating on the surface of the negative electrode active material. In particular, the coating with fluoroethylene carbonate has a capacity deterioration due to charge / discharge cycles. It is known to have the effect of making it smaller. In the charge / discharge cycle, the capacity tends to deteriorate greatly at the initial stage, but the initial deterioration can be suppressed by adding a chain sulfone derivative. This is because the chain sulfone derivative not only forms a surface film but also imparts oxidation resistance to the non-aqueous solvent and prevents the non-aqueous solvent from being decomposed in the vicinity of the positive electrode. Therefore, by adding together the chain sulfone derivative and fluoroethylene carbonate, it is possible to further prevent the capacity from being reduced due to the charge / discharge cycle without canceling the mutual effects.

  By including 0.5% by mass or more of the chain sulfone derivative, the effect of preventing the decomposition of the nonaqueous solvent in the vicinity of the positive electrode appears, and the initial capacity deterioration in the high-temperature cycle test at 45 ° C. can be suppressed. In addition, by making the chain sulfone derivative within 6% by mass, the lithium ion conductivity of the coating formed on the surface of the negative electrode active material can be secured, and a sufficient discharge capacity can be obtained even at a low temperature of −10 ° C. it can.

  The content of the chain sulfone derivative is preferably 1 to 4% by mass, and more preferably 1 to 3% by mass.

  If 0.05 mass% or more of fluoroethylene carbonate is contained in the non-aqueous electrolyte, a film is formed at the interface between the negative electrode active material of the lithium ion secondary battery and the non-aqueous electrolyte, and a high temperature of 45 ° C. Capacity reduction during the cycle test can be minimized. Moreover, since the coating film formed on the surface of the negative electrode active material material does not become too thick and the internal impedance of the lithium ion secondary battery can be kept low by setting the fluoroethylene carbonate to 4 mass% or less, −10 A sufficient discharge capacity can be obtained even at a low temperature of ° C.

  The content of fluoroethylene carbonate is preferably 1 to 2.5% by mass, and more preferably 1 to 2% by mass.

In particular, the content of the chain sulfone derivative is preferably 1 to 4% by mass and the content of the fluoroethylene carbonate is preferably 1 to 2.5% by mass, and the content of the chain sulfone derivative is 1 to 3% by mass. And it is still more preferable that content of fluoroethylene carbonate is 1-2 mass%.
The mixing ratio of the chain sulfone derivative and the fluoroethylene carbonate is preferably 4: 1 to 4: 3. By setting such a mixing ratio, a sufficient value can be obtained for both the discharge capacity at a low temperature and the discharge capacity after a cycle test at a high temperature.

  The chain sulfone derivative is preferably any of dimethyl sulfone, ethyl methyl sulfone, and diethyl sulfone. Thereby, sufficient discharge capacity at a low temperature can be obtained.

  In particular, the chain sulfone derivative is preferably dimethylsulfone, in addition to a discharge capacity at low temperature, which is more preferable, and a sufficient discharge capacity can be obtained even after a cycle test at high temperature.

〔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の炭化水素基からなる群より選ばれる少なくとも一種を表す。〕 The nonaqueous electrolytic solution preferably further contains 4% by mass or less of a glycol sulfate derivative represented by the following formula (2).

[In Formula (2), R < ₃ > and R < ₄ > represent at least 1 type chosen from the group which consists of a hydrogen atom and a C1-C5 hydrocarbon group each independently. ]

  Similarly to the chain sulfone derivative and fluoroethylene carbonate, the ethylene glycol sulfate derivative also forms a film on the surface of the negative electrode active material, and the film also has an effect of suppressing capacity reduction during a charge / discharge cycle at a high temperature. When an appropriate amount of an ethylene glycol sulfate derivative is added to the chain sulfone derivative and fluoroethylene carbonate, not only the capacity decrease during charge / discharge cycles at higher temperatures is suppressed, but also the lithium ion conductivity of the surface coating of the negative electrode active material increases. As a result, the internal impedance of the lithium ion secondary battery can be reduced, and the discharge capacity at a low temperature can be increased.

  When the content of the ethylene glycol sulfate derivative is within 4% by mass, the increase in internal impedance of the lithium ion secondary battery is suppressed, and when a lithium ion secondary battery is produced, a sufficient discharge capacity at a low temperature is obtained. Can do.

Examples of the ethylene glycol sulfate derivative include ethylene glycol sulfate in which R ₁ and R ₂ are hydrogen atoms, propane-1,2-cyclic sulfate in which one of R ₁ and R ₂ is a hydrogen atom and the other is a methyl group, R Examples thereof include butane-1,2-cyclic sulfate in which one of ₁ and R ₂ is a hydrogen atom and the other is an ethyl group, and ethylene glycol sulfate is preferable from the viewpoint of improving cycle characteristics.

  The non-aqueous solvent preferably contains a cyclic carbonate and a chain carbonate. The cyclic carbonate has a dielectric constant of 20 or more so as to promote dissociation of the lithium salt as an electrolyte, and the chain carbonate has 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, and among them, propylene carbonate is preferably included. Propylene carbonate may be mixed with ethylene carbonate or butylene carbonate.

  The content of propylene carbonate in the non-aqueous electrolyte is preferably 5 to 50% by mass. If 5 mass% or more of propylene carbonate is contained, high lithium ion conductivity can be obtained and the discharge capacity can be increased. On the other hand, by making propylene carbonate 50 mass% or less, the irreversible capacity at the time of initial charge becomes small, and sufficient initial discharge capacity can be obtained.

  As the chain carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate, diallyl carbonate, or the like can be used. In addition, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, etc. can be used and mixed with chain carbonate. May be.

  The ratio of the cyclic carbonate and the chain carbonate 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. Moreover, 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 another electrolyte, 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 case 50 seals the power generation element 30 and the non-aqueous electrolyte therein. The case 50 is not particularly limited as long as it can prevent leakage of the nonaqueous electrolyte solution to the outside and entry of moisture and 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 polymer 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.

  Non-aqueous electrolytes for lithium ion secondary batteries and lithium ion secondary batteries of Examples 1 to 39 and Comparative Examples 1 to 9 were prepared according to the following procedure.

Example 1
First, a negative electrode was produced. In the production of the negative electrode, artificial graphite (90% by mass) as a negative electrode active material, carbon black (2% by mass) as a conductive additive, and polyvinylidene fluoride (hereinafter referred to as “PVDF”) (8% by mass) as a binder. %) And dispersed in a solvent N-methyl-2-pyrrolidone (hereinafter referred to as “NMP”) 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, 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 non-aqueous electrolyte was prepared. LiPF ₆ was added at a rate of 1.0 mol / L to a solution in which ethylene carbonate, propylene carbonate, and diethyl carbonate were mixed at a volume ratio of 2: 1: 7. Furthermore, a nonaqueous electrolytic solution was obtained by adding 0.5% by mass of dimethylsulfone and 1% by mass of fluoroethylene carbonate as a chain sulfone to the entire nonaqueous electrolytic solution.

  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 was put in an aluminum laminate pack, a non-aqueous electrolyte was poured into the aluminum laminate pack, and then vacuum-sealed, and a lithium ion secondary battery (vertical: 60 mm, horizontal: 85 mm, thickness: 3 mm) 5 Individually produced.

(Examples 2-39 and Comparative Examples 1-9)
Table 1 shows the composition ratio and lithium ion concentration of the non-aqueous solvent, the type and content of the chain sulfone added to the non-aqueous electrolyte, the content of fluoroethylene carbonate, and the type and content of the ethylene glycol sulfate derivative. Except having changed, the lithium ion secondary battery of Examples 2-37 and Comparative Examples 1-9 was produced like Example 1. FIG. In Table 1, “EC” in the non-aqueous solvent represents ethylene carbonate, “PC” represents propylene carbonate, “DEC” represents diethyl carbonate, and “EMC” represents ethyl methyl carbonate. In Table 1, “FEC content” represents the content of fluoroethylene carbonate, “EGS derivative” represents the ethylene glycol sulfate derivative, and “EGS content” represents the content of the ethylene glycol sulfate derivative. As the chain sulfone, “DMS” represents dimethyl sulfone, “EMS” represents ethyl methyl sulfone, “DES” represents diethyl sulfone, EGS derivatives, “EGS” represents ethylene glycol sulfate, “PCS” represents propane 1 , 2-cyclic sulfate, “BCS” represents butane 1,2-cyclic sulfate.

(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 the initial discharge capacity (mAh) in Table 1.

  While the initial discharge capacity of the comparative example was less than 140 mAh, the initial discharge capacity of the example was 140 mAh or more, and it was confirmed that both had sufficient initial discharge capacity. In particular, when propylene carbonate was included as a non-aqueous solvent, the initial discharge capacity tended to be larger than when it was not included.

(Low temperature discharge capacity evaluation test)
After the discharge capacity evaluation test, the temperature of the thermostatic chamber containing the battery 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. Table 1 shows a value obtained by dividing the discharge capacity at −10 ° C. by the initial discharge capacity and multiplying by 100 times as “−10 ° C. discharge capacity”.

  While the -10 ° C. discharge capacity of the comparative examples is less than 60%, the chain sulfone content is 0.5 to 6% by mass and the fluoroethylene carbonate content is 0.05 to 4% by mass. The -10 ° C. discharge capacities of the examples which are% showed values exceeding 60%. In particular, when the content of chain sulfone is 1 to 4% by mass and the content of fluoroethylene carbonate is 1 to 2.5% by mass, the −10 ° C. discharge capacity exceeds 70%. When the sulfone content is 1 to 3% by mass and the fluoroethylene carbonate content is 1 to 2% by mass, the −10 ° C. discharge capacity exceeds 77%, and the discharge is excellent even at a low temperature of −10 ° C. Showed capacity.

  In particular, when the chain sulfone was dimethyl sulfone, an excellent discharge capacity of −10 ° C. was obtained as compared with the case of ethyl methyl sulfone or diethyl sulfone.

(High temperature cycle test)
After the discharge capacity evaluation test, the battery was transferred to a thermostat set to 45 ° C., and a charge / discharge cycle test was started. In this cycle test, charging was performed up to 4.2 V in a constant current constant voltage charging mode of 150 mA, and discharging was performed up to 2.5 V in a constant current discharging mode of 150 mA, and this cycle was continuously performed 500 times. The pause time between charging and discharging and between discharging and charging was 10 minutes. Then, after 500 cycles, constant current and constant voltage charging to 4.2 V at 30 mA and constant current discharging to 2.5 V at 30 mA were performed. A value obtained by dividing the discharge capacity by the initial discharge capacity is shown as “capacity after 45 ° C. cycle” in Table 1.

  The capacities after 45 ° C. cycle of the comparative examples are all less than 85%, whereas the content of chain sulfone is 0.5 to 6% by mass, and the content of fluoroethylene carbonate is 0.05 to 4% by mass. The capacities after cycling at 45 ° C. of the examples which are% showed values exceeding 85%. In particular, when the content of chain sulfone is 1 to 4% by mass and the content of fluoroethylene carbonate is 1 to 2.5% by mass, the capacity after cycling at 45 ° C. exceeds 90%. When the sulfone content was 1 to 3% by mass and the fluoroethylene carbonate content was 1 to 2% by mass, the capacity after 45 ° C. cycle exceeded 92%, indicating excellent 45 ° C. cycle characteristics.

  In particular, when the chain sulfone was dimethyl sulfone, excellent 45 ° C. cycle characteristics were obtained as compared with the case of ethyl methyl sulfone or diethyl sulfone. In addition, when the ethylene glycol sulfate derivative is contained at a concentration of 4% by mass or less, the capacity after 45 ° C. cycle increases, and in the case of ethylene glycol sulfate, the capacity after 45 ° C. cycle tends to increase most. It was.

  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, 60, 62 ... lead, 100 ... lithium ion secondary battery

Claims (13)

A non-aqueous solvent;
Electrolyte,
0.5 to 6% by mass of a chain sulfone derivative represented by the following formula (1),
A non-aqueous electrolyte for a lithium ion secondary battery comprising 0.05 to 4% by mass of fluoroethylene carbonate.

Wherein (1), in each of R ₁ and R ₂ are independently hydrogen or an alkyl group having 1 to 5 carbon atoms, hydrogen of the alkyl group may be substituted with a halogen atom. ]   The said non-aqueous solvent contains 5-50 mass% of propylene carbonate with respect to a non-aqueous electrolyte, The non-aqueous electrolyte for lithium ion secondary batteries of Claim 1 characterized by the above-mentioned.   The non-aqueous electrolyte for a lithium ion secondary battery according to claim 1, wherein the chain sulfone derivative is any one of dimethyl sulfone, ethyl methyl sulfone, and diethyl sulfone.   The non-aqueous electrolyte for a lithium ion secondary battery according to claim 1, wherein the chain sulfone derivative is dimethyl sulfone. The non-aqueous electrolyte for a lithium ion secondary battery according to any one of claims 1 to 4, comprising an ethylene glycol sulfate derivative represented by the following formula (2) in an amount of 4% by mass or less.

[In Formula (2), R ₃ and R ₄ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms, and a part of hydrogen of the alkyl group may be substituted with a halogen atom. ] 6. The non-aqueous electrolyte for a lithium ion secondary battery according to claim 5, wherein in the ethylene glycol sulfate derivative of the formula (2), R ₃ and R ₄ are both hydrogen. A positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte,
The non-aqueous electrolyte solution includes a non-aqueous solvent, an electrolyte, a chain sulfone derivative represented by the following formula (1) of 0.5 to 6% by mass, and fluoroethylene carbonate of 0.05 to 4% by mass. A lithium ion secondary battery comprising:

[In Formula (1), R ₁ and R ₂ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms, and a part of hydrogen of the alkyl group may be substituted with a halogen atom. ]   The lithium ion secondary battery according to claim 7, wherein the nonaqueous solvent contains 5 to 50 mass% of propylene carbonate with respect to the nonaqueous electrolytic solution.   The lithium ion secondary battery according to claim 7 or 8, wherein the chain sulfone derivative is any one of dimethyl sulfone, ethyl methyl sulfone, and diethyl sulfone.   The lithium ion secondary battery according to claim 7, wherein the chain sulfone derivative is dimethyl sulfone.   The lithium ion secondary battery according to any one of claims 7 to 10, wherein the negative electrode mainly contains a carbon material. The lithium ion secondary battery according to any one of claims 7 to 11, wherein the nonaqueous electrolytic solution contains 4% by mass or less of an ethylene glycol sulfate derivative represented by the following formula (2).

[In Formula (2), R ₃ and R ₄ are each independently hydrogen or an alkyl group having 1 to 5 carbon atoms, and a part of hydrogen of the alkyl group may be substituted with a halogen atom. ] The lithium ion secondary battery according to claim 12, wherein in the ethylene glycol sulfate derivative of the formula (2), R ₃ and R ₄ are both hydrogen.

Images