JP6825311B2 - Lithium ion secondary battery - Google Patents

Description

The present invention relates to a lithium ion secondary battery.

Generally, a lithium ion secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution as main components. Then, an appropriate electrolyte is added to the electrolytic solution in an appropriate concentration range. For example, lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , CF ₃ SO ₃ Li, and (CF ₃ SO ₂ ) ₂ NLi are added to the electrolyte of a lithium ion secondary battery as an electrolyte. Is common, and here, the concentration of the lithium salt in the electrolytic solution is generally set to about 1 mol / L.

Further, as the organic solvent used in the electrolytic solution, an organic solvent having a high relative permittivity such as ethylene carbonate or propylene carbonate and a high dipole moment is mixed in an amount of about 30% by volume or more in order to preferably dissolve the electrolyte. Is common.

In fact, Patent Document 1 discloses a lithium ion secondary battery using a mixed organic solvent containing 33% by volume of ethylene carbonate and using an electrolytic solution containing LiPF ₆ at a concentration of 1 mol / L.

Recently, Patent Document 2 and Patent Document 3 have reported an electrolytic solution containing a metal salt as an electrolyte at a high concentration and a lithium ion secondary battery including the electrolytic solution.

Patent Document 2 describes an electrolytic solution containing (FSO ₂ ) ₂ NLi as a metal salt and dimethyl carbonate as an organic solvent at a molar ratio of dimethyl carbonate to (FSO ₂ ) ₂ NLi of 2 or 3, and a negative electrode active material. A lithium ion secondary battery comprising graphite as a base material is specifically described (see Examples P and Q), and the lithium ion secondary battery is specifically described as having an excellent capacity retention rate. It is described together with the test results (see Table 19, etc.).

Patent Document 3 describes that an electrolytic solution having a molar ratio of a specific organic solvent to a specific metal salt of 3 to 5 is excellent in physical properties, and further, the electrolytic solution and graphite as a negative electrode active material are described. The provided lithium ion secondary battery is specifically described (see Example I, Example II, etc.). Then, in the same document, it is described that the lithium ion secondary battery has an excellent capacity retention rate together with specific test results (see Table 11 and the like).

Further, as a negative electrode active material other than graphite, a negative electrode active material containing Si having a high lithium ion occlusion ability is known.

For example, Patent Document 4 and Patent Document 5 describe a lithium ion secondary battery in which the negative electrode active material is silicon. Patent Document 6 and Patent Document 7 describe a lithium ion secondary battery in which the negative electrode active material is SiO.

In Patent Document 8, a layered silicon compound containing a layered polysilane as a main component, in which CaSi ₂ is reacted with an acid to remove Ca, is synthesized, and the layered silicon compound is heated at 300 ° C. or higher to release hydrogen. It describes the manufacture of the material and the lithium ion secondary battery containing the silicon material as the negative electrode active material.

Japanese Unexamined Patent Publication No. 2013-149477 International Publication No. 2015/045389 International Publication No. 2016/063468 Japanese Unexamined Patent Publication No. 2014-203595 JP 2015-57767 JP-A-2015-185509 JP-A-2015-179625 International Publication No. 2014/08608

When the present inventor actually manufactured a lithium ion secondary battery containing a Si-containing negative electrode active material and an electrolytic solution within the range described in Patent Document 3, and conducted a charge / discharge test, a certain number of times were performed. It was found that the capacity retention rate of the secondary battery drops sharply after charging and discharging.

As a result of diligent studies, the present inventor has found that a lithium ion secondary battery provided with a Si-containing negative electrode active material maintains a suitable capacity by using an electrolytic solution containing a fluorine-containing cyclic carbonate. However, the present inventor has newly found that the above-mentioned lithium ion secondary battery does not always have an excellent capacity retention rate in a low temperature environment.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a lithium ion secondary battery provided with a Si-containing negative electrode active material capable of more preferably maintaining a capacity in a low temperature environment. ..

As a result of diligent studies, by using an unsaturated cyclic carbonate additionally added to the electrolytic solution within the range described in Patent Document 3, the lithium ion secondary battery provided with the Si-containing negative electrode active material has a suitable capacity. The inventor has found that it is maintained. Based on such findings, the present inventor has completed the present invention.

The lithium ion secondary battery of the present invention
Si-containing negative electrode active material and
(FSO ₂ ) ₂ NLi, a chain carbonate represented by the following general formula (A), a fluorine-containing cyclic carbonate, and an unsaturated cyclic carbonate, and the above-mentioned chain carbonate with respect to (FSO ₂ ) ₂ NLi. An electrolytic solution having a molar ratio in the range of 2 to 6 and
It is characterized by having.
R ¹ OCOOR ² General formula (A)
^(R 1, ^{R 2} are each independently a linear alkyl _{C n H a F b Cl c} Br d I e, _{or, C m H f F g Cl} h Br i contains a cyclic alkyl in the chemical structure It is selected from any of _j. N is an integer of 1 or more, m is an integer of 3 or more, and a, b, c, d, e, f, g, h, i, and j are independently integers of 0 or more. 2n + 1 = a + b + c + d + e, 2m-1 = f + g + h + i + j.)

The lithium ion secondary battery of the present invention exhibits a suitable capacity retention rate in a low temperature environment.

Hereinafter, embodiments for carrying out the present invention will be described. Unless otherwise specified, the numerical range "a to b" described in the present specification includes the lower limit a and the upper limit b in the range. Then, a numerical range can be constructed by arbitrarily combining these upper and lower limit values and the numerical values listed in the examples. Further, a numerical value arbitrarily selected from these numerical values can be used as a new upper limit or lower limit numerical value.

The lithium ion secondary battery of the present invention
Si-containing negative electrode active material and
(FSO ₂ ) ₂ NLi, a chain carbonate represented by the following general formula (A), a fluorine-containing cyclic carbonate, and an unsaturated cyclic carbonate, and the above-mentioned chain carbonate with respect to (FSO ₂ ) ₂ NLi. An electrolytic solution having a molar ratio in the range of 2 to 6 (hereinafter, may be referred to as an electrolytic solution of the present invention) and
It is characterized by having.
R ¹ OCOOR ² General formula (A)
^(R 1, ^{R 2} are each independently a linear alkyl _{C n H a F b Cl c} Br d I e, _{or, C m H f F g Cl} h Br i contains a cyclic alkyl in the chemical structure It is selected from any of _j. N is an integer of 1 or more, m is an integer of 3 or more, and a, b, c, d, e, f, g, h, i, and j are independently integers of 0 or more. 2n + 1 = a + b + c + d + e, 2m-1 = f + g + h + i + j.)

The Si-containing negative electrode active material may be any material that contains Si and functions as a negative electrode active material. Specific examples of the Si-containing negative electrode active material include elemental silicon, SiOx (0.3 ≦ x ≦ 1.6), alloys of Si with other metals, and the silicon material described in Patent Document 8. The Si-containing negative electrode active material may be coated with carbon. The Si-containing negative electrode active material coated with carbon has excellent conductivity.

The particle size distribution of the Si-containing negative electrode active material preferably has a D50 of 0.6 to 30 μm, more preferably 1 to 20 μm, when measured with a general laser diffraction type particle size distribution measuring device. The range of 2 to 10 μm is more preferable, and the range of 3 to 8 μm is particularly preferable.

The silicon material described in Patent Document 8 (hereinafter, may be simply referred to as “silicon material”) will be described in detail. The silicon material undergoes, for example, a step of reacting CaSi ₂ with an acid to synthesize a layered silicon compound containing polysilane as a main component, and a step of heating the layered silicon compound at 300 ° C. or higher to release hydrogen. It is manufactured.

The method for producing a silicon material described in Patent Document 8 is shown below by an ideal reaction formula when hydrogen chloride is used as an acid.
3CaSi ₂ + 6HCl → Si ₆ H ₆ + 3CaCl _{2
Si 6 H 6 → 6Si + 3H} 2 ↑

However, in the upper reaction for synthesizing Si ₆ H ₆ which is polysilane, water is usually used as the reaction solvent from the viewpoint of removing by-products and impurities. Since Si ₆ H ₆ can react with water, in the step of synthesizing the layered silicon compound including the reaction in the upper stage, the layered silicon compound is rarely produced as containing only Si ₆ H ₆ , and is layered. Silicon compounds are represented by Si ₆ H _s (OH) _t X _u (X is an element or group derived from an acid anion, s + t + u = 6, 0 <s <6, 0 <t <6, 0 <u <6). Manufactured as a compound. In the above chemical formula, unavoidable impurities such as Ca that may remain are not considered. The silicon material obtained by heating the layered silicon compound also contains an element derived from an anion of oxygen or acid.

The silicon material has a structure in which a plurality of plate-shaped silicon bodies are laminated in the thickness direction. In order for a charge carrier such as lithium ion to efficiently occlude and release, the plate-shaped silicon body preferably has a thickness in the range of 10 nm to 100 nm, and more preferably in the range of 20 nm to 50 nm. The length of the plate-shaped silicon body in the longitudinal direction is preferably in the range of 0.1 μm to 50 μm. Further, the plate-shaped silicon body preferably has (length in the longitudinal direction) / (thickness) in the range of 2 to 1000. The laminated structure of the plate-shaped silicon body can be confirmed by observation with a scanning electron microscope or the like. Further, this laminated structure is considered to be a remnant of the Si layer in the raw material CaSi ₂ .

The silicon material preferably contains amorphous silicon and / or silicon crystallites. In particular, in the plate-shaped silicon body, it is preferable that amorphous silicon is used as a matrix and silicon crystallites are scattered in the matrix. The size of the silicon crystallite is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, further preferably in the range of 1 nm to 50 nm, and particularly preferably in the range of 1 nm to 10 nm. The size of the silicon crystallite is calculated from the Scheller's equation using the half width of the diffraction peak on the Si (111) plane of the obtained X-ray diffraction chart obtained by performing X-ray diffraction measurement on the silicon material. ..

The abundance and size of the plate-shaped silicon body, amorphous silicon, and silicon crystallites contained in the silicon material mainly depend on the heating temperature and heating time. The heating temperature is preferably in the range of 350 ° C. to 950 ° C., more preferably in the range of 400 ° C. to 900 ° C.

Next, the electrolytic solution of the present invention will be described. The electrolyte of the present invention contains (FSO ₂ ) ₂ NLi as the electrolyte.

The electrolytic solution of the present _{invention, (FSO 2)} other than 2 NLi, may include other electrolytes can be used in the electrolyte of lithium ion secondary battery. The electrolytic solution of the present invention preferably contains (FSO ₂ ) ₂ NLi in an amount of 50% by mass or more, more preferably 70% by mass or more, based on the total electrolyte contained in the electrolytic solution of the present invention. , 90% by mass or more is more preferable. All the electrolytes contained in the electrolytic solution of the present invention may be (FSO ₂ ) ₂ NLi.

Other electrolytes include LiPF ₆ , LiBF ₄ , LiAsF ₆ , Li ₂ SiF ₆ , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, FSO ₂ (CF ₃ SO ₂ ) NLi, ( SO ₂ CF ₂ CF ₂ SO ₂ ) NLi, (SO ₂ CF ₂ CF ₂ CF ₂ SO ₂ ) NLi, FSO ₂ (CH ₃ SO ₂ ) NLi, FSO ₂ (C ₂ F ₅ SO ₂ ) NLi, or FSO ₂ Examples thereof include (C ₂ H ₅ SO ₂ ) NLi, (OCOCO ₂ ) ₂ BLi, and (OCOCO ₂ ) BF ₂ Li.

The electrolytic solution of the present invention contains a chain carbonate represented by the general formula (A) as an organic solvent (hereinafter, may be simply referred to as “chain carbonate”).

In the chain carbonate represented by the general formula (A), n is preferably an integer of 1 to 6, more preferably an integer of 1 to 4, and particularly preferably an integer of 1 to 2. m is preferably an integer of 3 to 8, more preferably an integer of 4 to 7, and particularly preferably an integer of 5 to 6.

Of the chain carbonates, those represented by the following general formula (A-1) are particularly preferable.

R ³ OCOOR ⁴ general formula (A-1)
^(R 3, ^{R 4} are each independently a linear alkyl _C n _H a _{F b,} or, .n are selected from any of _C m _H f _{F g} including cyclic alkyl chemical structure 1 The above integer, m is an integer of 3 or more, and a, b, f, and g are independently integers of 0 or more, satisfying 2n + 1 = a + b, 2m-1 = f + g.)

In the chain carbonate represented by the general formula (A-1), n is preferably an integer of 1 to 6, more preferably an integer of 1 to 4, and particularly preferably an integer of 1 to 2. m is preferably an integer of 3 to 8, more preferably an integer of 4 to 7, and particularly preferably an integer of 5 to 6.

Among the chain carbonates, dimethyl carbonate (hereinafter, may be referred to as "DMC"), diethyl carbonate (hereinafter, may be referred to as "DEC"), ethyl methyl carbonate (hereinafter, may be referred to as "EMC") may be used. ), Fluoromethylmethyl carbonate, difluoromethylmethylcarbonate, trifluoromethylmethylcarbonate, bis (fluoromethyl) carbonate, bis (difluoromethyl) carbonate, bis (trifluoromethyl) carbonate, fluoromethyldifluoromethylcarbonate, 2,2 2-Trifluoroethyl methyl carbonate, pentafluoroethyl methyl carbonate, ethyl trifluoromethyl carbonate, and bis (2,2,2-trifluoroethyl) carbonate are particularly preferred.

One type of chain carbonate may be used as the electrolytic solution, or a plurality of types may be used in combination. For example, when DEC having a relatively low polarity and relative permittivity and a relatively small number of moles per unit volume is used alone, it can be expected that elution of metals such as aluminum from the electrode is suppressed. Further, by using a plurality of chain carbonates in combination, it is possible to suitably secure the low temperature fluidity of the electrolytic solution and the lithium ion transportability at low temperature. Examples of the combined use of the chain carbonate include two or three kinds selected from DMC, DEC and EMC. In combination with DMC and DEC or EMC, these molar ratios are preferably in the range DMC: DEC or EMC = 80: 20-95: 5.

The electrolytic solution of the present invention preferably contains the above-mentioned chain carbonate in an amount of 60% by volume, 60% by mass or more, or 60 mol% or more, based on 70 volumes, based on the total organic solvent contained in the electrolytic solution of the present invention. It is more preferably contained in%, 70% by mass or more or 70 mol% or more, further preferably contained in 80% by volume, 80% by mass or more or 80 mol% or more, and 90% by volume, 90% by mass or more or 90. It is particularly preferable that it is contained in an amount of mol% or more.

In the electrolytic solution of the present invention, the chain carbonate is contained in a molar ratio of 2 to 6 with respect to (FSO ₂ ) ₂ NLi. From the technical contents disclosed in Patent Document 3, it can be said that the molar ratio is preferably in the range of 3 to 5. As discussed in detail in Patent Document 3, if the molar ratio is too low or too high, the capacity retention rate of the lithium ion secondary battery may decrease. Further, from the viewpoint of satisfying both ionic conductivity and low temperature stability in a well-balanced manner, the molar ratio in the electrolytic solution of the present invention is preferably in the range of 3 to 6.

Examples of the concentration of (FSO ₂ ) ₂ NLi in the electrolytic solution of the present invention can be in the range of 1.5 to 3.5 mol / L and 2.0 to 3.0 mol / L.

The electrolytic solution of the present invention contains a fluorine-containing cyclic carbonate. The fluorine-containing cyclic carbonate means a cyclic carbonate having fluorine in the molecule. The amount of the fluorine-containing cyclic carbonate with respect to the entire electrolytic solution is preferably in the range of more than 0 to 40% by mass, more preferably in the range of 0.1 to 30% by mass, and further preferably in the range of 1 to 20% by mass. The range of 3 to 10% by mass is particularly preferable.

Specific examples of the fluorine-containing cyclic carbonate include a compound represented by the following general formula (B).

(R ¹ and R ² are independently hydrogen, alkyl group, halogen-substituted alkyl group or halogen. However, at least one of each R ¹ and each R ² contains F.)

When the fluorine-containing cyclic carbonate represented by the general formula (B) is represented by a specific compound name, fluoroethylene carbonate, 4- (trifluoromethyl) -1,3-dioxolane-2-one, 4,4-difluoro -1,3-Dioxolane-2-one, 4-fluoro-4-methyl-1,3-dioxolan-2-one, 4- (fluoromethyl) -1,3-dioxolan-2-one, 4,5- Difluoro-1,3-dioxolan-2-one, 4-fluoro-5-methyl-1,3-dioxolan-2-one, 4,5-difluoro-4,5-dimethyl-1,3-dioxolan-2-one On can be mentioned, with fluoroethylene carbonate being preferred.

The relationship between the Si-containing negative electrode active material and the electrolytic solution of the present invention will be described.

First, in a lithium ion secondary battery containing an electrolytic solution containing (FSO ₂ ) ₂ NLi and a chain carbonate, which does not contain fluorine-containing cyclic carbonate, and a Si-containing negative electrode active material, a part of the lithium ion secondary battery is charged and discharged. (FSO ₂ ) ₂ NLi decomposes to form a film on the surface of the Si-containing negative electrode active material. It is presumed that the coating contains an SO ₂ structure derived from (FSO ₂ ) ₂ NLi. Therefore, the Si-containing negative electrode active material and the SO ₂ structure are in direct contact with each other. Here, since the SO ₂ structure has an oxidizing ability, the oxidation of Si proceeds with time, and as a result, the Si-containing negative electrode active material deteriorates.

However, the electrolytic solution of the present invention contains a fluorine-containing cyclic carbonate. Fluorine-containing cyclic carbonate has excellent oxidation resistance, but easily decomposes under reducing conditions. Therefore, the fluorine-containing cyclic carbonate preferentially decomposes at the interface between the negative electrode and the electrolytic solution under the charge / discharge conditions of the lithium ion secondary battery of the present invention. As a result, a film derived from the decomposition product of the fluorine-containing cyclic carbonate is formed on the surface of the Si-containing negative electrode active material. After that, even if (FSO ₂ ) ₂ NLi is decomposed to form an SO ₂ structure, the Si-containing negative electrode active material and the SO ₂ structure are formed due to the presence of a film derived from the decomposition product of the fluorine-containing cyclic carbonate. Since direct contact can be prevented, deterioration of the Si-containing negative electrode active material can be suppressed.

Further, since the fluorine-containing cyclic carbonate is an organic solvent having a relatively high polarity, it is considered to be excellent in affinity with lithium ions and conductivity of lithium ions. Then, it is presumed that the electrolytic solution of the present invention containing the fluorine-containing cyclic carbonate can smoothly transfer lithium ions generated between the electrolytic solution and the positive electrode active material and / or the negative electrode active material.
Further, the electrolytic solution of the present invention contains (FSO ₂ ) ₂ NLi in a relatively high concentration, and therefore contains abundant lithium ions. Then, it can be said that the electrolytic solution of the present invention can immediately supply lithium ions to the electrodes during charging and discharging.
In addition, it is assumed that lithium fluoride and lithium carbonate are present in the film derived from the decomposition product of the fluorine-containing cyclic carbonate formed on the surface of the negative electrode active material. That is, many lithium ions are present near the negative electrode.

The electrolytic solution of the present invention contains an unsaturated cyclic carbonate. The unsaturated cyclic carbonate means a cyclic carbonate having a carbon-carbon double bond in the molecule. The presence of the unsaturated cyclic carbonate improves the capacity retention rate of the lithium ion secondary battery including the electrolytic solution of the present invention in a low temperature environment.

The unsaturated cyclic carbonate is preferably contained in an amount of more than 0 to 5% by mass, more preferably more than 0 to less than 2.5% by mass, and 0.1 to 1.5% by mass with respect to the entire electrolytic solution. It is more preferably contained in, and particularly preferably in an amount of 0.3 to 1% by mass. If the amount of unsaturated cyclic carbonate is excessive, the resistance of the lithium ion secondary battery may increase excessively.

Specific examples of the unsaturated cyclic carbonate include a compound represented by the following general formula (C).

(R ¹ and R ² are independently hydrogen, alkyl group, halogen-substituted alkyl group or halogen, respectively.)

When the unsaturated cyclic carbonate represented by the general formula (C) is represented by a specific compound name, vinylene carbonate, fluorovinylene carbonate, methylvinylene carbonate, fluoromethylvinylene carbonate, ethylvinylene carbonate, propylvinylene carbonate, butylvinylene carbonate. , Dimethyl vinylene carbonate, diethyl vinylene carbonate, dipropyl vinylene carbonate, trifluoromethyl vinylene carbonate, and among them, vinylene carbonate is preferable.

Further, as another specific example of the unsaturated cyclic carbonate, a compound having a carbon-carbon double bond of the general formula (C) outside the ring can be mentioned, and a vinyl ethylene carbonate can be mentioned as a specific compound name thereof. Can be done.

It is presumed that the unsaturated cyclic carbonate decomposes during charging and / or discharging of the lithium ion secondary battery to form a carbon-containing film on the negative electrode active material and / or the positive electrode active material. It is considered that the presence of such a carbon-containing coating suppresses excessive decomposition of the electrolytic solution and extends the life of the lithium ion secondary battery. It is also conceivable that the unsaturated cyclic carbonate forms a protective film on the surface of the Si-containing negative electrode active material together with the above-mentioned decomposition product of the fluorine-containing cyclic carbonate.

The electrolytic solution of the present invention may contain another organic solvent that can be used in the electrolytic solution of the lithium ion secondary battery (hereinafter, may be simply referred to as “another organic solvent”).

The electrolytic solution of the present invention containing another organic solvent may have an increased viscosity or a decreased ionic conductivity as compared with the electrolytic solution of the present invention containing no other organic solvent. Further, the reaction resistance of the secondary battery using the electrolytic solution of the present invention containing another organic solvent may increase.

Specific examples of other organic solvents include nitriles such as acetonitrile, propionitrile, acrylonitrile, and malononitrile, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 1, Does not contain ethers such as 3-dioxane, 1,4-dioxane, 2,2-dimethyl-1,3-dioxolane, 2-methyltetrahydropyran, 2-methyltetraxocyanate and crown ether, and fluorine-free such as ethylene carbonate and propylene carbonate. Cyclic carbonates, formamides, N, N-dimethylformamides, N, N-dimethylacetamides, amides such as N-methylpyrrolidone, isocyanates such as isopropylisocyanate, n-propylisocyanate, chloromethylisocyanate, methyl acetate, ethyl acetate , Butyl acetate, propyl acetate, methyl propionate, methyl isocyanate, ethyl isocyanate, vinyl acetate, methyl acrylate, methyl methacrylate and other esters, glycidyl methyl ether, epoxybutane, 2-ethyloxylan and other epoxys, oxazole, 2- Oxazoles such as ethyloxazole, oxazoline and 2-methyl-2-oxazoline, ketones such as acetone, methylethylketone and methylisobutylketone, acid anhydrides such as acetic anhydride and propionic anhydride, and sulfones such as dimethylsulfone and sulfolane. Sulfoxides such as dimethylsulfoxide, nitros such as 1-nitropropane and 2-nitropropane, furans such as furan and furfural, cyclic esters such as γ-butyrolactone, γ-valerolactone and δ-valerolactone, thiophene, Examples thereof include aromatic heterocycles such as pyridine, heterocycles such as tetrahydro-4-pyrone, 1-methylpyrrolidin, and N-methylmorpholin, and phosphate esters such as trimethyl phosphate and triethyl phosphate.

The electrolytic solution of the present invention may contain an organic solvent composed of hydrocarbons. The electrolytic solution of the present invention containing an organic solvent composed of hydrocarbons can be expected to have an effect of lowering its viscosity.

Specific examples of the organic solvent composed of hydrocarbons include benzene, toluene, ethylbenzene, o-xylene, m-xylene, p-xylene, 1-methylnaphthalene, hexane, heptane, and cyclohexane.

In addition, a flame-retardant solvent can be added to the electrolytic solution of the present invention. By adding a flame-retardant solvent to the electrolytic solution of the present invention, the safety of the electrolytic solution of the present invention can be further enhanced. Examples of the flame-retardant solvent include halogen-based solvents such as carbon tetrachloride, tetrachloroethane and hydrofluoroether, and phosphoric acid derivatives such as trimethyl phosphate and triethyl phosphate.

When the electrolytic solution of the present invention is mixed with a polymer or an inorganic filler to form a mixture, the mixture contains the electrolytic solution and becomes a pseudo solid electrolyte. By using the pseudo solid electrolyte as the electrolytic solution of the battery, it is possible to suppress the leakage of the electrolytic solution in the battery.

As the polymer, a polymer used for a battery such as a lithium ion secondary battery or a general chemically crosslinked polymer can be adopted. In particular, polymers capable of absorbing an electrolytic solution and gelling, such as polyvinylidene fluoride and polyhexafluoropropylene, and polymers in which an ionic conductive group is introduced into a polymer such as polyethylene oxide are preferable.

Specific polymers include polymethyl acrylate, polymethyl methacrylate, polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, polyglycidol, polytetrafluoroethylene, and polyhexafluoropropylene. Polycarboxylic acids such as polysiloxane, polyvinylacetate, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polyitaconic acid, polyfumaric acid, polycrotonic acid, polyangelica acid, carboxymethyl cellulose, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene , Polyester, unsaturated polyester copolymerized with maleic anhydride and glycols, polyethylene oxide derivative having a substituent, and copolymer of vinylidene fluoride and hexafluoropropylene can be exemplified. Further, as the polymer, a copolymer obtained by copolymerizing two or more kinds of monomers constituting the specific polymer may be selected.

Polysaccharides are also suitable as the polymer. Specific examples of the polysaccharide include glycogen, cellulose, chitin, agarose, carrageenan, heparin, hyaluronic acid, pectin, amylopectin, xyloglucan, and amylose. Further, a material containing these polysaccharides may be adopted as the polymer, and as the material, agar containing a polysaccharide such as agarose can be exemplified.

As the inorganic filler, inorganic ceramics such as oxides and nitrides are preferable.

Inorganic ceramics have hydrophilic and hydrophobic functional groups on their surface. Therefore, the functional group attracts the electrolytic solution, so that a conductive passage can be formed in the inorganic ceramics. Further, the inorganic ceramics dispersed in the electrolytic solution can play a role of containing the electrolytic solution by forming a network between the inorganic ceramics by the functional groups. Due to such a function of the inorganic ceramics, leakage of the electrolytic solution in the battery can be more preferably suppressed. In order to preferably exert the above-mentioned functions of the inorganic ceramics, the inorganic ceramics are preferably in the form of particles, and particularly preferably in the nano-level particle size.

Examples of the type of inorganic ceramics include general alumina, silica, titania, zirconia, lithium phosphate and the like. Further, the inorganic ceramics themselves may have lithium conductivity, and specifically, Li ₃ N, LiI, LiI-Li ₃ N-LiOH, LiI-Li ₂ SP ₂ O ₅ , LiI-Li ₂ S. -P ₂ S ₅ , LiI-Li ₂ SB ₂ S ₃ , Li ₂ O-B ₂ S ₃ , Li ₂ O-V ₂ O ₃ -SiO ₂ , Li ₂ O-B ₂ O ₃ -P ₂ O _{5, Li 2 O-B 2} O 3 -ZnO, Li 2 O-Al 2 O 3 -TiO 2 -SiO 2 -P 2 O 5, LiTi 2 (PO 4) 3, Li-βAl 2 O 3, LiTaO 3 Can be exemplified.

Glass ceramics may be used as the inorganic filler. Since glass ceramics can contain an ionic liquid, the same effect can be expected for the electrolytic solution of the present invention. Glass ceramics include a compound represented by xLi ₂ S- (1-x) P ₂ S ₅ (however, 0 <x <1), and a compound in which a part of S of the compound is replaced with another element. , And a compound in which a part of P of the compound is replaced with germanium can be exemplified.

Further, a known additive may be added to the electrolytic solution of the present invention as long as the gist of the present invention is not deviated. As an example of known additives, carbonate compounds typified by phenylethylene carbonate and erythritan carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic acid anhydride , Cyclohexanedicarboxylic acid anhydride, cyclopentanetetracarboxylic acid dianhydride, carboxylic acid anhydride typified by phenylsuccinic anhydride; γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ- Caprolactone, lactone represented by ε-caprolactone; cyclic ether represented by 1,4-dioxane; ethylenesulfite, 1,3-propanesulton, 1,4-butanesulton, methyl methanesulfonate, busalphan, sulfolane, sulfolene , Dimethylsulfone, sulfur-containing compounds typified by tetramethylthiuram monosulfide; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazole Nitrogen-containing compounds typified by lydinone and N-methylsuccinimide; phosphates typified by monofluorophosphate and difluorophosphate; saturated hydrocarbon compounds typified by heptane, octane and cycloheptane; biphenyl, Examples thereof include alkylbiphenyl, terphenyl, a partially hydride of terphenyl, and unsaturated hydrocarbon compounds typified by cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran.

Specific embodiments of the lithium ion secondary battery of the present invention include a negative electrode having a Si-containing negative electrode active material, a positive electrode having a positive electrode active material capable of occluding and releasing lithium ions, and an electrolytic solution of the present invention.

As the negative electrode active material in the negative electrode, only the Si-containing negative electrode active material may be used, or a known negative electrode active material such as graphite and a Si-containing negative electrode active material may be used in combination.

The negative electrode has a current collector and a negative electrode active material layer bonded to the surface of the current collector.

A current collector is a chemically inactive electron conductor that keeps current flowing through the electrodes during the discharge or charging of a lithium ion secondary battery. Collectors include at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel. Metallic materials can be exemplified. The current collector may be covered with a known protective layer. A current collector whose surface is treated by a known method may be used as the current collector.

The current collector can take the form of foil, sheet, film, linear, rod, mesh or the like. Therefore, as the current collector, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, or a stainless steel foil can be preferably used. When the current collector is in the form of a foil, a sheet, or a film, the thickness thereof is preferably in the range of 1 μm to 100 μm.

The negative electrode active material layer contains a negative electrode active material and, if necessary, a binder and / or a conductive auxiliary agent.

The binder plays a role of binding the active material, the conductive auxiliary agent, etc. to the surface of the current collector.

Examples of the binder include fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins and styrene butadiene. A known material such as rubber may be used.

Further, a polymer having a hydrophilic group may be adopted as the binder. The lithium ion secondary battery of the present invention containing a polymer having a hydrophilic group as a binder can more preferably maintain the capacity. Examples of the hydrophilic group of the polymer having a hydrophilic group include a phosphate group such as a carboxyl group, a sulfo group, a silanol group, an amino group, a hydroxyl group and a phosphoric acid group. Of these, polymers containing a carboxyl group in the molecule such as polyacrylic acid, carboxymethyl cellulose, and polymethacrylic acid, or polymers containing a sulfo group such as poly (p-styrene sulfonic acid) are preferable.

Polymers rich in carboxyl and / or sulfo groups, such as polyacrylic acid or copolymers of acrylic acid and vinyl sulfonic acid, are water soluble. The polymer having a hydrophilic group is preferably a water-soluble polymer, and in terms of chemical structure, a polymer containing a plurality of carboxyl groups and / or sulfo groups in one molecule is preferable.

The polymer containing a carboxyl group in the molecule can be produced, for example, by a method of polymerizing an acid monomer, a method of imparting a carboxyl group to the polymer, or the like. Acid monomers include acrylic acid, methacrylic acid, vinyl benzoic acid, crotonic acid, pentenic acid, angelic acid, tigric acid and other acid monomers having one carboxyl group in the molecule, itaconic acid, mesaconic acid, citraconic acid and fumaric acid. , Maleic acid, 2-pentenedioic acid, methylene succinic acid, allylmalonic acid, isopropyridene succinic acid, 2,4-hexadienedioic acid, acetylenedicarboxylic acid and other acid monomers having two or more carboxyl groups in the molecule. Will be done.

A copolymerized polymer obtained by polymerizing two or more kinds of acid monomers selected from the above acid monomers may be used as a binder.

Further, for example, a polymer containing an acid anhydride group formed by condensing the carboxyl groups of a copolymer of acrylic acid and itaconic acid, as described in Japanese Patent Application Laid-Open No. 2013-0654993, in the molecule. Is also preferably used as a binder. When the binder has a structure derived from a highly acidic monomer having two or more carboxyl groups in one molecule, it becomes easier for the binder to trap lithium ions and the like before the electrolyte decomposition reaction occurs during charging. It is considered. Further, since the polymer has more carboxyl groups per monomer than polyacrylic acid or polymethacrylic acid, the acidity is increased, but the acidity is increased because a predetermined amount of carboxyl groups are changed to acid anhydride groups. Does not rise too much. Therefore, a secondary battery having a negative electrode using the polymer as a binder has improved initial efficiency and improved input / output characteristics.

Further, a crosslinked polymer obtained by cross-linking a carboxyl group-containing polymer such as polyacrylic acid or polymethacrylic acid with a polyamine such as diamine may be used as a binder.

Examples of the diamine used in the crosslinked polymer include alkylenediamines such as ethylenediamine, propylenediamine and hexamethylenediamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, isophoronediamine and bis (4-aminocyclohexyl) methane. Saturated carbocyclic diamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, bis (4-aminophenyl) sulfone, benzidine, o-trizine, 2,4- Examples thereof include aromatic diamines such as tolylene diamine, 2,6-tolylene diamine, xylylene diamine and naphthalene diamine.

Further, a mixture or reactant of a carboxyl group-containing polymer such as polyacrylic acid or polymethacrylic acid and polyamide-imide may be used as a binder.

Polyamide-imide means a compound having two or more amide bonds and two or more imide bonds in the molecule. Polyamideimide is produced by reacting an acid component that becomes a carbonyl moiety in an amide bond and an imide bond with a diamine component or a diisocyanate component that becomes a nitrogen moiety in an amide bond and an imide bond. In order to obtain a polyamide-imide, it may be produced by the method, or a commercially available polyamide-imide may be purchased.

The acid components used in the production of polyamideimide include trimellitic acid, pyromellitic acid, biphenyltetracarboxylic acid, diphenylsulfonetetracarboxylic acid, benzophenonetetracarboxylic acid, diphenylethertetracarboxylic acid, oxalic acid, adipic acid, and malonic acid. Sebatic acid, azelaic acid, dodecanedicarboxylic acid, dicarboxypolybutadiene, dicarboxypoly (acrylonitrile-butadiene), dicarboxypoly (styrene-butadiene), cyclohexane-1,4-dicarboxylic acid, cyclohexane-1,3-dicarboxylic acid, Dicyclohexylmethane-4,4'-dicarboxylic acid, terephthalic acid, isophthalic acid, bis (carboxyphenyl) sulfone, bis (carboxyphenyl) ether, naphthalenedicarboxylic acid, and anhydrides, acid halides, and derivatives thereof. Can be done. As the acid component, the above compounds may be used alone or in combination of two or more. However, from the viewpoint of forming an imide bond, the acid component in which the carboxyl group is present in the adjacent carbon of the carbon to which the carboxyl group is bonded or The equivalent is essential. As the acid component, trimellitic anhydride is preferable from the viewpoint of reactivity, heat resistance and the like. In addition to trimellitic acid anhydride, pyromellitic acid anhydride, benzophenone tetracarboxylic acid anhydride, and biphenyltetra acid anhydride are used as part of the acid component in terms of tensile strength, tensile elasticity, and electrolyte resistance of polyamideimide. It is preferable to use a carboxylic acid anhydride.

As the diamine component used in the production of the polyamide-imide, the diamine used in the above-mentioned crosslinked polymer may be adopted. From the viewpoint of heat resistance and solubility, 4,4'-diaminodiphenylmethane, 2,4-tolylene diamine, o-trizine, naphthalene diamine, and isophorone diamine are preferable. From the viewpoint of tensile strength and tensile elastic modulus of polyamide-imide, o-trizine and naphthalenediamine are preferable.

Examples of the diisocyanate component used in the production of polyamide-imide include those in which the amine of the diamine component is replaced with isocyanate.

The mixing ratio of the binder in the negative electrode active material layer is preferably, in terms of mass ratio, negative electrode active material: binder = 1: 0.005 to 1: 0.3. This is because if the amount of the binder is too small, the moldability of the electrode is lowered, and if the amount of the binder is too large, the energy density of the electrode is lowered.

The conductive auxiliary agent is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be arbitrarily added when the conductivity of the electrode is insufficient, and may not be added when the conductivity of the electrode is sufficiently excellent. The conductive auxiliary agent may be a chemically inert electron high conductor, and examples thereof include carbon black, which are carbonaceous fine particles, graphite, Vapor Grown Carbon Fiber, and various metal particles. To. Examples of carbon black include acetylene black, Ketjen black (registered trademark), furnace black, and channel black. These conductive auxiliary agents can be added to the active material layer alone or in combination of two or more. The mixing ratio of the conductive auxiliary agent in the negative electrode active material layer is preferably, in terms of mass ratio, negative electrode active material: conductive auxiliary agent = 1: 0.01 to 1: 0.5. This is because if the amount of the conductive auxiliary agent is too small, an efficient conductive path cannot be formed, and if the amount of the conductive auxiliary agent is too large, the moldability of the negative electrode active material layer is deteriorated and the energy density of the electrode is lowered.

The positive electrode used in the lithium ion secondary battery of the present invention has a positive electrode active material capable of occluding and releasing lithium ions. The positive electrode has a current collector and a positive electrode active material layer bonded to the surface of the current collector. The positive electrode active material layer contains a positive electrode active material and, if necessary, a binder and / or a conductive auxiliary agent. The positive current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material used. For example, silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, and tin. , At least one selected from indium, titanium, ruthenium, tantalum, chromium, molybdenum, and metal materials such as stainless steel can be exemplified.

When the potential of the positive electrode is 4 V or more based on lithium, it is preferable to use aluminum as the current collector.

Specifically, it is preferable to use a current collector for the positive electrode made of aluminum or an aluminum alloy. Here, aluminum refers to pure aluminum, and aluminum having a purity of 99.0% or higher is referred to as pure aluminum. An alloy obtained by adding various elements to pure aluminum is called an aluminum alloy. Examples of the aluminum alloy include Al—Cu, Al—Mn, Al—Fe, Al—Si, Al—Mg, Al—Mg—Si, and Al—Zn—Mg.

Further, as aluminum or an aluminum alloy, specifically, for example, A1000 series alloys such as JIS A1085 and A1N30 (pure aluminum series), A3000 series alloys such as JIS A3003 and A3004 (Al-Mn series), JIS A8079, A8021 and the like. A8000 series alloy (Al—Fe series) can be mentioned.

The current collector may be covered with a known protective layer. A current collector whose surface is treated by a known method may be used as the current collector.

The current collector can take the form of foil, sheet, film, linear, rod, mesh or the like. Therefore, as the current collector, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, or a stainless steel foil can be preferably used. When the current collector is in the form of a foil, a sheet, or a film, the thickness thereof is preferably in the range of 1 μm to 100 μm.

As the binder for the positive electrode and the conductive auxiliary agent, those described for the negative electrode may be used in the same blending ratio.

As the positive electrode active material, the general formula of the layered rock salt _{structure: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 2, b + c + d + e = 1,0 ≦ e <1, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, Rh, Fe, Ge, Zn, Ru, Li ₂ MnO, a lithium composite metal oxide represented by 1.7 ≦ f ≦ 3), which is at least one element selected from Sc, Sn, In, Y, Bi, S, Si, Na, K, P, and V. ₃ can be mentioned. Further, as the positive electrode active material, a metal oxide having a spinel structure such as LiMn ₂ O ₄ , a solid solution composed of a mixture of a metal oxide having a spinel structure and a layered compound, LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (in the formula). M is selected from at least one of Co, Ni, Mn, and Fe) and the like. Furthermore, as the positive electrode active material, tavorite compound (the M a transition metal) LiMPO ₄ F, such as LiFePO ₄ F represented by, Limbo ₃ such LiFeBO ₃ (M is a transition metal) include borate-based compound represented by be able to. Any metal oxide used as the positive electrode active material may have the above composition formula as the basic composition, and those in which the metal element contained in the basic composition is replaced with another metal element can also be used. Further, as the positive electrode active material, a material containing no lithium may be used. For example, elemental sulfur, compounds complexed with sulfur and carbon, metal sulfides such as TiS _2, oxides such as V 2 _{O 5,} MnO _2, polyaniline and anthraquinone and compounds containing these aromatic in chemical structure, conjugated double Conjugated materials such as acetic acid-based organic substances and other known materials can also be used. Further, a compound having a stable radical such as nitroxide, nitronylnitroxide, galbinoxyl, and phenoxyl may be adopted as the positive electrode active material. When a lithium-free positive electrode active material is used, it is necessary to add lithium to the positive electrode and / or the negative electrode in advance by a known method. Lithium may be added in an ionic state or may be added in a nonionic state such as a metal. For example, the lithium foil may be attached to the positive electrode and / or the negative electrode to integrate them.

From the viewpoint of excellent and high capacity, and durability, as the positive electrode active material, the general formula of the layered rock salt _{structure: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 2, b + c + d + e = 1,0 ≦ e <1, D are W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, It is represented by at least one element selected from Rh, Fe, Ge, Zn, Ru, Sc, Sn, In, Y, Bi, S, Si, Na, K, P, and V, 1.7 ≦ f ≦ 3). It is preferable to use a lithium composite metal oxide.

In the above general formula, the values of b, c, and d are not particularly limited as long as they satisfy the above conditions, but those having 0 <b <1, 0 <c <1, 0 <d <1 are used. It is good, and at least one of b, c, and d is in the range of 10/100 <b <90/100, 10/100 <c <90/100, 5/100 <d <70/100. More preferably, the range is 20/100 <b <80/100, 12/100 <c <70/100, 10/100 <d <60/100, 30/100 <b <70/100, More preferably, the range is 15/100 <c <50/100, 12/100 <d <50/100.

The values of a, e, and f may be values within the range specified by the above general formula, and preferably 0.5 ≦ a ≦ 1.5, 0 ≦ e <0.2, 1.8 ≦ f ≦ 2. 5.5, more preferably 0.8 ≦ a ≦ 1.3, 0 ≦ e <0.1, 1.9 ≦ f ≦ 2.1 can be exemplified, respectively.

As a specific positive electrode active material, at least one selected from Li _x A _y Mn _2-y O ₄ (A is Ca, Mg, S, Si, Na, K, Al, P, Ga, Ge) having a spinel structure. Examples thereof include at least one metal element selected from the element and the transition metal element, 0 <x ≦ 2.2, 0 ≦ y ≦ 1). More specifically, LiMn ₂ O ₄ and LiNi _0.5 Mn _1.5 O ₄ can be exemplified.

Specific examples of the positive electrode active material include LiFePO ₄ , Li ₂ FeSiO ₄ , LiCoPO ₄ , Li ₂ CoPO ₄ , Li ₂ MnPO ₄ , Li ₂ MnSiO ₄ , and Li ₂ CoPO ₄ F. As another specific positive electrode active material, Li ₂ MnO _3- LiCoO ₂ can be exemplified.

One type of positive electrode active material may be used, or a plurality of types may be used in combination. As combination examples of the positive electrode active material, the general formula of the layered rock salt _{structure: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 2, b + c + d + e = 1,0 ≦ e <1, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, Rh, Fe, Ge, Zn, At least one element selected from Ru, Sc, Sn, In, Y, Bi, S, Si, Na, K, P, and V, and a lithium composite metal oxide represented by 1.7 ≦ f ≦ 3). Examples thereof include combined use with a polyanionic compound represented by LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (M in the formula is selected from at least one of Co, Ni, Mn and Fe). In the combined use of the lithium composite metal oxide and the polyanionic compound, the mass ratio of these is preferably in the range of lithium composite metal oxide: polyanionic compound = 90: 10 to 50:50, and 80:20 to 60:40. The range of is more preferable. Further, the positive electrode active material may be coated with carbon.

In order to form an active material layer on the surface of the current collector, a conventionally known method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method is used to collect electricity. The active material may be applied to the surface of the body. Specifically, the active material, the solvent, and if necessary, the binder and the conductive auxiliary agent are mixed to form a slurry, and then the slurry is applied to the surface of the current collector and then dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the dried one may be compressed.

A separator is used in the lithium ion secondary battery of the present invention as needed. The separator separates the positive electrode and the negative electrode, and allows lithium ions to pass through while preventing a short circuit due to contact between the two electrodes. As the separator, a known one may be adopted, and synthetic resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polyamide), polyester and polyacrylonitrile, polysaccharides such as cellulose and amylose, and fibroin , Natural polymers such as keratin, lignin, and suberin, and porous materials using one or more electrically insulating materials such as ceramics, non-woven fabrics, and woven fabrics. Further, the separator may have a multi-layer structure.

A specific method for manufacturing the lithium ion secondary battery of the present invention will be described.
A separator is sandwiched between the positive electrode and the negative electrode as needed to form an electrode body. The electrode body may be a laminated type in which a positive electrode, a separator and a negative electrode are stacked, or a wound type in which a positive electrode, a separator and a negative electrode are wound. After connecting the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal leading to the outside using a current collecting lead or the like, the electrolytic solution of the present invention is added to the electrode body to form lithium ions. It is good to use a secondary battery. Further, the lithium ion secondary battery of the present invention may be charged and discharged in a voltage range suitable for the type of active material contained in the electrode.

The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical type, a square type, a coin type, and a laminated type can be adopted.

The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a lithium ion secondary battery for all or part of its power source, and may be, for example, an electric vehicle or a hybrid vehicle. When a lithium-ion secondary battery is mounted on a vehicle, a plurality of lithium-ion secondary batteries may be connected in series to form an assembled battery. In addition to vehicles, devices equipped with lithium-ion secondary batteries include various battery-powered home appliances such as personal computers and mobile communication devices, office devices, and industrial devices. Further, the lithium ion secondary battery of the present invention includes wind power generation, solar power generation, hydraulic power generation and other power storage devices and power smoothing devices for electric power systems, power supply sources for power and / or auxiliary machinery such as ships, aircraft, and aircraft. Power supply sources for spacecraft and / or auxiliary equipment, auxiliary power sources for vehicles that do not use electricity as power sources, power sources for mobile household robots, power sources for system backup, power sources for non-disruptive power supply devices, It may be used as a power storage device that temporarily stores the electric power required for charging in a charging station for an electric vehicle or the like.

Although the embodiment of the electrolytic solution of the present invention has been described above, the present invention is not limited to the above embodiment. It can be carried out in various forms with modifications, improvements, etc. that can be made by those skilled in the art, without departing from the gist of the present invention.

Hereinafter, the present invention will be specifically described with reference to Examples, Comparative Examples, and Reference Examples. The present invention is not limited to these examples.

(Example 1)
(FSO ₂ ) ₂ NLi is added to and dissolved in diethyl carbonate, which is a chain carbonate, and fluoroethylene carbonate, which is a fluorine-containing cyclic carbonate, and vinylene carbonate, which is an unsaturated cyclic carbonate, are added and dissolved to dissolve the fluoroethylene carbonate. The electrolytic solution of Example 1 containing 3% by mass and 0.5% by mass of vinylene carbonate was produced. In the electrolytic solution of Example 1, the molar ratio of chain carbonate to (FSO ₂ ) ₂ NLi is 4. The concentration of (FSO ₂ ) ₂ NLi in the electrolytic solution of Example 1 is 2 mol / L.

Using the electrolytic solution of Example 1, the lithium ion secondary battery of Example 1 was produced as follows.

69 parts by mass of Li _1.1 Ni _5/10 Co _3/10 Mn _2/10 O ₂ as the positive electrode active material, 25 parts by mass of carbon-coated LiFePO ₄ as the positive electrode active material, and 3 parts by mass of acetylene black as the conductive auxiliary agent. , And 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a mixture. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. An aluminum foil was prepared as a current collector for the positive electrode. The slurry was applied to the surface of the aluminum foil using a doctor blade so as to form a film. N-Methyl-2-pyrrolidone was removed by drying the aluminum foil coated with the slurry. Then, the aluminum foil was pressed to obtain a joint. The obtained bonded product was heated and dried in a vacuum dryer to produce a positive electrode made of an aluminum foil on which a positive electrode active material layer was formed.

72.5 parts by mass of carbon-coated silicon material as a negative electrode active material, 13.5 parts by mass of acetylene black as a conductive auxiliary agent, and 14 parts by mass of a crosslinked polymer obtained by cross-linking polyacrylic acid with diamine as a binder are mixed. It was made into a mixture. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. A copper foil was prepared as a current collector for the negative electrode. The slurry was applied in a film form on the surface of the copper foil using a doctor blade. The copper foil coated with the slurry was dried to remove N-methyl-2-pyrrolidone, and then the copper foil was pressed to obtain a bonded product. The obtained joint was heated and dried in a vacuum dryer to produce a negative electrode made of copper foil on which a negative electrode active material layer was formed.

As a separator, a polyethylene porous membrane having a ceramic layer on one side was prepared. A separator was sandwiched between the positive electrode and the negative electrode to form a group of electrode plates. This group of electrode plates was covered with a set of two laminated films, three sides were sealed, and then the electrolytic solution of Example 1 was injected into the bag-shaped laminated film. Then, by sealing the remaining one side, the four sides were hermetically sealed, and the electrode plate group and the electrolytic solution were sealed to produce the lithium ion secondary battery of Example 1.

(Comparative Example 1)
An electrolytic solution of Comparative Example 1 containing fluoroethylene carbonate in an amount of 3% by mass was produced in the same manner as in Example 1 except that vinylene carbonate was not used. In the electrolytic solution of Comparative Example 1, the molar ratio of the chain carbonate to (FSO ₂ ) ₂ NLi is 4. The concentration of (FSO ₂ ) ₂ NLi in the electrolytic solution of Comparative Example 1 is 2 mol / L.
Then, the lithium ion secondary battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the electrolytic solution of Comparative Example 1 was used.

(Evaluation example 1)
The lithium ion secondary batteries of Example 1 and Comparative Example 1 are charged to 4.24 V and discharged to 3.05 V at a constant current of 0.5 C rate under the condition of 0 ° C. 4.24 V-3. A charge / discharge cycle of 0.05 V was performed 250 cycles. The capacity retention rate (%) was calculated by the following formula.
Capacity retention rate (%) = (250 cycle discharge capacity / first cycle discharge capacity) x 100

The capacity retention rate of the lithium ion secondary battery of Example 1 was 87.3%, whereas the capacity retention rate of the lithium ion secondary battery of Comparative Example 1 was 45.2%. The initial capacities of the lithium ion secondary batteries of Example 1 and Comparative Example 1 were the same. It can be said that due to the presence of vinylene carbonate, the capacity retention rate under the condition of 0 ° C. was remarkably optimized.

(Reference example 1)
(FSO ₂ ) ₂ NLi was added and dissolved in a mixed solvent in which dimethyl carbonate and ethyl methyl carbonate, which are chain carbonates, were mixed at a molar ratio of 9: 1, and fluoroethylene carbonate, which is a fluorine-containing cyclic carbonate, was further added. , The electrolytic solution of Reference Example 1 containing fluoroethylene carbonate in an amount of 10% by mass was produced. In the electrolytic solution of Reference Example 1, the molar ratio of the chain carbonate to (FSO ₂ ) ₂ NLi is 4.

Using the electrolytic solution of Reference Example 1, the lithium ion secondary battery of Reference Example 1 was manufactured as follows.

69 parts by mass of Li _1.1 Ni _5/10 Co _3/10 Mn _2/10 O ₂ as the positive electrode active material, 25 parts by mass of carbon-coated LiFePO ₄ as the positive electrode active material, and 3 parts by mass of acetylene black as the conductive auxiliary agent. , And 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a mixture. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. An aluminum foil was prepared as a current collector for the positive electrode. The slurry was applied to the surface of the aluminum foil using a doctor blade so as to form a film. N-Methyl-2-pyrrolidone was removed by drying the aluminum foil coated with the slurry. Then, the aluminum foil was pressed to obtain a joint. The obtained bonded product was heated and dried in a vacuum dryer to produce a positive electrode made of an aluminum foil on which a positive electrode active material layer was formed.

72.5 parts by mass of carbon-coated silicon material as a negative electrode active material, 13.5 parts by mass of acetylene black as a conductive auxiliary agent, and 14 parts by mass of a crosslinked polymer obtained by cross-linking polyacrylic acid with diamine as a binder are mixed. It was made into a mixture. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. A copper foil was prepared as a current collector for the negative electrode. The slurry was applied in a film form on the surface of the copper foil using a doctor blade. The copper foil coated with the slurry was dried to remove N-methyl-2-pyrrolidone, and then the copper foil was pressed to obtain a bonded product. The obtained joint was heated and dried in a vacuum dryer to produce a negative electrode made of copper foil on which a negative electrode active material layer was formed.

As a separator, a polyethylene porous membrane having a ceramic layer on one side was prepared. A separator was sandwiched between the positive electrode and the negative electrode to form a group of electrode plates. This group of plates was covered with a set of two laminated films, three sides were sealed, and then the electrolytic solution of Reference Example 1 was injected into the bag-shaped laminated film. Then, by sealing the remaining one side, the four sides were hermetically sealed, and the electrode plate group and the electrolytic solution were sealed to produce the lithium ion secondary battery of Reference Example 1.

(Reference example 2)
The electrolytic solution of Reference Example 2 was produced in the same manner as in Reference Example 1 except that the amount of fluoroethylene carbonate added was increased so as to contain fluoroethylene carbonate in an amount of 20% by mass. Also in the electrolytic solution of Reference Example 2, the molar ratio of the chain carbonate to (FSO ₂ ) ₂ NLi is 4.
Hereinafter, the lithium ion secondary battery of Reference Example 2 was manufactured in the same manner as in Reference Example 1 except that the electrolytic solution of Reference Example 2 was used.

(Reference example 3)
The electrolytic solution of Reference Example 3 was produced in the same manner as in Reference Example 1 except that the amount of fluoroethylene carbonate added was increased so as to contain fluoroethylene carbonate in an amount of 30% by mass. Also in the electrolytic solution of Reference Example 3, the molar ratio of the chain carbonate to (FSO ₂ ) ₂ NLi is 4.
Hereinafter, the lithium ion secondary battery of Reference Example 3 was produced in the same manner as in Reference Example 1 except that the electrolytic solution of Reference Example 3 was used.

(Reference comparison example 1)
The electrolytic solution of Reference Comparative Example 1 was produced in the same manner as in Reference Example 1 except that fluoroethylene carbonate was not added. In the electrolytic solution of Reference Comparative Example 1, the molar ratio of the chain carbonate to (FSO ₂ ) ₂ NLi is 4.
Hereinafter, the lithium ion secondary battery of Reference Comparative Example 1 was produced in the same manner as in Reference Example 1 except that the electrolytic solution of Reference Comparative Example 1 was used.

(Reference comparison example 2)
LiPF ₆ is added to a mixed solvent in which fluoroethylene carbonate, which is a fluorine-containing cyclic carbonate, ethylene carbonate, which is a cyclic carbonate, ethylmethyl carbonate, which is a chain carbonate, and dimethyl carbonate are mixed at a volume ratio of 15:15:30:40. In addition, it was dissolved to produce the electrolytic solution of Reference Comparative Example 2. In the electrolytic solution of Reference Comparative Example 2, the concentration of LiPF ₆ is 1 mol / L. Further, the electrolytic solution of Reference Comparative Example 2 contains fluoroethylene carbonate in an amount of 19% by mass.
Hereinafter, the lithium ion secondary battery of Reference Comparative Example 2 was manufactured in the same manner as in Reference Example 1 except that the electrolytic solution of Reference Comparative Example 2 was used.

(Reference evaluation example 1)
Each lithium ion secondary battery of Reference Example 1 to Reference Example 3 and Reference Comparative Example 1 to Reference Comparative Example 2 is charged to 4.24 V and discharged to 2.8 V at a constant current at a temperature of 25 ° C. and 1 C rate. The charging / discharging cycle of 4.24V-2.8V was repeated. The capacity retention rate (%) of the lithium ion secondary battery after a predetermined cycle was calculated by the following formula. Table 1 shows the capacity retention rate (%) at 200 cycles and 500 cycles.
Capacity maintenance rate (%) = (B / A) x 100
A: Discharge capacity in the first charge / discharge cycle B: Discharge capacity in a predetermined cycle

The meanings of the abbreviations in Table 1 and the following tables are as follows.
LiFSA: (FSO ₂ ) ₂ NLi
FEC: Fluorethylene carbonate

From Table 1, it can be seen that the capacity retention rate of the lithium ion secondary batteries of Reference Examples 1 to 3 is significantly superior to that of the lithium ion secondary battery of Reference Comparative Example 1. Further, the lithium ion secondary battery of Reference Comparative Example 2 is a lithium ion secondary battery including a general electrolytic solution having a LiPF ₆ concentration of 1 mol / L, but contains a considerable amount of fluorine-containing cyclic carbonate. Despite this, the capacity retention rate did not reach that of the lithium ion secondary batteries of Reference Examples 1 to 3. The electrolytic solution of the lithium ion secondary battery including the Si-containing negative electrode active material contains (FSO ₂ ) ₂ NLi, a chain carbonate and a fluorine-containing cyclic carbonate, and is a molar of the chain carbonate with respect to (FSO ₂ ) ₂ NLi. It can be said that an electrolytic solution having a ratio in the range of 2 to 6 is suitable.

(Reference example 4)
(FSO ₂ ) ₂ NLi was added and dissolved in a mixed solvent in which dimethyl carbonate and ethyl methyl carbonate, which are chain carbonates, were mixed at a molar ratio of 9: 1, and fluoroethylene carbonate, which is a fluorine-containing cyclic carbonate, was further added. , The electrolytic solution of Reference Example 4 containing fluoroethylene carbonate in an amount of 3% by mass was produced. In the electrolytic solution of Reference Example 4, the molar ratio of the chain carbonate to (FSO ₂ ) ₂ NLi is 4.

Using the electrolytic solution of Reference Example 4, the lithium ion secondary battery of Reference Example 4 was manufactured as follows.

A mixture of 93 parts by mass of Li _1.1 Ni _5/10 Co _3/10 Mn _2/10 O ₂ as a positive electrode active material, 4 parts by mass of acetylene black as a conductive auxiliary agent, and 3 parts by mass of polyvinylidene fluoride as a binder. To make a mixture. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. An aluminum foil was prepared as a current collector for the positive electrode. The slurry was applied to the surface of the aluminum foil using a doctor blade so as to form a film. N-Methyl-2-pyrrolidone was removed by drying the aluminum foil coated with the slurry. Then, the aluminum foil was pressed to obtain a joint. The obtained bonded product was heated and dried in a vacuum dryer to produce a positive electrode made of an aluminum foil on which a positive electrode active material layer was formed.

A mixture was obtained by mixing 70 parts by mass of a carbon-coated silicon material as a negative electrode active material, 15 parts by mass of acetylene black as a conductive auxiliary agent, and 15 parts by mass of a crosslinked polymer obtained by cross-linking polyacrylic acid with a diamine as a binder. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. A copper foil was prepared as a current collector for the negative electrode. The slurry was applied in a film form on the surface of the copper foil using a doctor blade. The copper foil coated with the slurry was dried to remove N-methyl-2-pyrrolidone, and then the copper foil was pressed to obtain a bonded product. The obtained joint was heated and dried in a vacuum dryer to produce a negative electrode made of copper foil on which a negative electrode active material layer was formed.

As a separator, a polyethylene porous membrane having a ceramic layer on one side was prepared. A separator was sandwiched between the positive electrode and the negative electrode to form a group of electrode plates. This group of plates was covered with a set of two laminated films, three sides were sealed, and then the electrolytic solution of Reference Example 4 was injected into the bag-shaped laminated film. Then, by sealing the remaining one side, the four sides were hermetically sealed, and the lithium ion secondary battery of Reference Example 4 in which the electrode plate group and the electrolytic solution were sealed was manufactured.

(Reference comparison example 3)
The electrolytic solution of Reference Comparative Example 3 was produced in the same manner as in Reference Example 4 except that fluoroethylene carbonate was not added. In the electrolytic solution of Reference Comparative Example 3, the molar ratio of the chain carbonate to (FSO ₂ ) ₂ NLi is 4.
Hereinafter, the lithium ion secondary battery of Reference Comparative Example 3 was produced in the same manner as in Reference Example 4 except that the electrolytic solution of Reference Comparative Example 3 was used.

(Reference Comparative Example 4)
LiPF ₆ is added to a mixed solvent in which fluoroethylene carbonate, which is a fluorine-containing cyclic carbonate, ethylene carbonate, which is a cyclic carbonate, ethylmethyl carbonate, which is a chain carbonate, and dimethyl carbonate are mixed at a volume ratio of 15:15:30:40. In addition, it was dissolved to produce the electrolytic solution of Reference Comparative Example 4. In the electrolytic solution of Reference Comparative Example 4, the concentration of LiPF ₆ is 1 mol / L. Further, the electrolytic solution of Reference Comparative Example 4 contains fluoroethylene carbonate in an amount of 19% by mass.
The lithium ion secondary battery of Reference Comparative Example 4 was produced in the same manner as in Reference Example 4 except that the electrolytic solution of Reference Comparative Example 4 was used.

(Reference Comparative Example 5)
LiPF ₆ was added to a mixed solvent in which ethylene carbonate, which is a cyclic carbonate, and ethylmethyl carbonate and dimethyl carbonate, which are chain carbonates, were mixed at a volume ratio of 30:30:40 to dissolve them, and the electrolysis of Reference Comparative Example 5 was carried out. The liquid was produced. In the electrolytic solution of Reference Comparative Example 5, the concentration of LiPF ₆ is 1 mol / L.
The lithium ion secondary battery of Reference Comparative Example 5 was produced in the same manner as in Reference Example 4 except that the electrolytic solution of Reference Comparative Example 5 was used.

(Reference evaluation example 2)
Each lithium ion secondary battery of Reference Example 4 and Reference Comparative Example 3 to Reference Comparative Example 5 adjusted to a voltage of 3.05 V was discharged at a constant current of 25 ° C. and 1 C rate for 10 seconds. The DC resistance during discharge was calculated from Ohm's law from the amount of voltage change and current value before and after discharge. The results are shown in Table 2.

From Table 2, it can be seen that the DC resistance of the lithium ion secondary battery of Reference Example 4 at the time of discharge is lower than the DC resistance of the lithium ion secondary batteries of Reference Comparative Examples 3 to 5. Lithium ion 2 containing an electrolytic solution containing (FSO ₂ ) ₂ NLi, a chain carbonate and a fluorine-containing cyclic carbonate, and having a molar ratio of the chain carbonate to (FSO ₂ ) ₂ NLi in the range of 2 to 6. It can be said that the next battery can release lithium ions from the Si-containing negative electrode active material with low resistance.

(Reference evaluation example 3)
Each lithium ion secondary battery of Reference Example 4 and Reference Comparative Example 3 to Reference Comparative Example 5 is charged to 4.1 V at a constant current of 0.3 C rate under the condition of a temperature of 25 ° C., and then up to 2.5 V. It was discharged and the discharge capacity was measured. These discharge capacities were used as the initial capacities.

Next, each lithium ion secondary battery is charged to 4.05V at a constant current of 2C rate under the condition of a temperature of 60 ° C. and discharged to 3.15V in a charge / discharge cycle of 4.05V-3.15V. 250 cycles were performed. The discharge capacity of each lithium ion secondary battery after 250 cycles of charging and discharging was measured under the same conditions as the initial capacity measurement. These discharge capacities were defined as post-cycle capacities. The capacity retention rate (%) was calculated by the following formula. The results are shown in Table 3.
Capacity retention rate (%) = (capacity after cycle / initial capacity) x 100

From Table 3, it can be seen that the capacity retention rate of the lithium ion secondary battery of Reference Example 4 is significantly superior to the capacity retention rate of the lithium ion secondary batteries of Reference Comparative Examples 3 to 5.

(Reference evaluation example 4)
After the test of Reference Evaluation Example 3, the negative electrode active materials in both the lithium ion secondary batteries of Reference Example 4 and Reference Comparative Example 3 were analyzed as follows.

Both negative electrode active materials after the test of Reference Evaluation Example 3 were subjected to an X-ray photoelectron spectroscopic analyzer for analysis. Specifically, the carbon coating existing on the surface of the negative electrode active material and the coating derived from the decomposition product of the electrolytic solution were removed by etching using Ar ions. Then, the surface of the negative electrode active material in which Si appeared was analyzed for Si. As a result, a peak indicating the binding energy between Si and Si and a peak indicating the binding energy of Si—O were observed from both negative electrode active materials. Here, the peak showing the bond energy between Si and Si is larger in the negative electrode active material in the lithium ion secondary battery of Reference Example 4, while the peak showing the bond energy of Si—O is in Reference Comparative Example 3. The negative electrode active material in the lithium ion secondary battery was larger.

In addition, the cross sections of both negative electrode active materials after the test of Reference Evaluation Example 3 were observed with a scanning electron microscope. As a result, it was found that the deterioration of the negative electrode active material in the lithium ion secondary battery of Reference Comparative Example 3 was remarkably advanced as compared with the negative electrode active material in the lithium ion secondary battery of Reference Example 4.

From the results of X-ray photoelectron spectroscopy analysis and the observation results with a scanning electron microscope, in the lithium ion secondary battery of Reference Example 4, due to the presence of the fluorine-containing cyclic carbonate, the oxidation of Si in the Si-containing negative electrode active material It can be said that the progress is suppressed. Here, Patent Document 3 describes that (FSO ₂ ) ₂ NLi in the electrolytic solution is decomposed at the time of charging / discharging to form a film containing S and O on the surface of the negative electrode. In Reference Comparative Example 3, the oxidation of Si in the Si-containing negative electrode active material proceeded because a film containing S and O, which are decomposition products of (FSO ₂ ) ₂ NLi, was formed directly on the surface of the Si-containing negative electrode active material. Probably because of it. On the other hand, in Reference Example 4, the oxidation of Si in the Si-containing negative electrode active material was suppressed because the fluorine-containing cyclic carbonate was preferentially decomposed to form a film on the surface of the negative electrode active material (FSO ₂ ) ₂ NLi. It is considered that this is because the direct contact between the decomposition product of Si and Si was suppressed.

Claims (5)

Si-containing negative electrode active material and
_{(FSO 2)} 2 NLi, chain carbonates represented by the following general formula (A), the fluorine-containing cyclic carbonate, and includes unsaturated cyclic carbonate, the _{(FSO 2)} the molar ratio of the chain carbonate for 2 NLi There Ri der range of 2 to 6, and said _{(FSO 2)} the molar concentration of 2 NLi is Ru der range of 2.0~3.5mol / L electrolyte solution,
A lithium ion secondary battery ( excluding those containing LiNO ₃ in the electrolytic solution ) .
R ¹ OCOOR ² General formula (A)
^(R 1, ^{R 2} are each independently a linear alkyl _{C n H a F b Cl c} Br d I e, _{or, C m H f F g Cl} h Br i contains a cyclic alkyl in the chemical structure It is selected from any of _j. N is an integer of 1 or more, m is an integer of 3 or more, and a, b, c, d, e, f, g, h, i, and j are independently integers of 0 or more. 2n + 1 = a + b + c + d + e, 2m-1 = f + g + h + i + j.) The lithium ion secondary battery according to claim 1, wherein the fluorine-containing cyclic carbonate is contained in an amount of more than 0 to 40% by mass based on the entire electrolytic solution. The lithium ion secondary battery according to claim 1 or 2, wherein the unsaturated cyclic carbonate is contained in an amount of more than 0 to 5% by mass based on the entire electrolytic solution. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the Si-containing negative electrode active material has a structure in which a plurality of plate-shaped silicon bodies are laminated in the thickness direction. The lithium ion secondary battery according to any one of claims 1 to 4, wherein the electrolytic solution contains 80% by mass or more of the chain carbonate with respect to the total organic solvent.