WO2016143295A1 - Lithium ion secondary battery - Google Patents

Abstract

A lithium ion secondary battery which is characterized by being provided with: an electrolyte solution which contains a hetero element-containing organic solvent and a metal salt at a molar ratio of 3-5, said hetero element-containing organic solvent containing a specific organic solvent that has a relative dielectric constant of 10 or less and/or a dipole moment of 5D or less, and said metal salt containing lithium as cations, while containing, as anions, a chemical structure represented by general formula (1); and a lithium metal composite oxide having a layered rock salt structure, which satisfies 1.10 ≤ (integrated intensity I(003) of peak ascribed to (003) plane)/(integrated intensity I(104) of peak ascribed to (104) plane) < 2.0 in a powder X-ray diffraction measurement, or which is represented by general formula Li_a(Ni_xCo_yM_z)O_b (wherein 1.05 ≤ a ≤ 1.20, 0.15 ≤ x ≤ 0.55, 0.25 ≤ y ≤ 0.75, 0.01 ≤ z ≤ 0.29, x + y + z = 1, 1.7 ≤ b ≤ 2.3, and M represents at least one element selected from among Mn, Zr, Mg, Ti, Al, W, Si, Mo, Fe, B, Zn and Cu). (R¹X¹)(R²SO₂)N General formula (1)

Description

Lithium ion secondary battery

The present invention relates to a lithium ion secondary battery.

In general, a power storage device such as a secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution as main components. An appropriate electrolyte is added to the electrolytic solution in an appropriate concentration range. For example, a lithium salt such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , CF ₃ SO ₃ Li, or (CF ₃ SO ₂ ) ₂ NLi is added as an electrolyte to the electrolyte solution of a lithium ion secondary battery. Here, the concentration of the lithium salt in the electrolytic solution is generally about 1 mol / L.

In addition, in order to dissolve the electrolyte suitably, an organic solvent having a high relative dielectric constant and dipole moment, such as ethylene carbonate and propylene carbonate, is mixed and used at about 30% by volume or more for the organic solvent used in the electrolytic solution. It is common.

Actually, 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. Patent Document 2 discloses a lithium ion solution using a mixed organic solvent containing 66% by volume of ethylene carbonate and propylene carbonate, and using an electrolytic solution containing (CF ₃ SO ₂ ) ₂ NLi at a concentration of 1 mol / L. A secondary battery is disclosed.

Also, for the purpose of improving the performance of the secondary battery, researches for adding various additives to the electrolytic solution containing lithium salt are being actively conducted.

For example, Patent Document 3 discloses an electrolysis in which a mixed organic solvent containing 30% by volume of ethylene carbonate is used, and a specific additive is added in a small amount to an electrolytic solution containing LiPF ₆ at a concentration of 1 mol / L. A lithium ion secondary battery using this electrolytic solution is disclosed. Patent Document 4 also discloses an electrolytic solution in which a small amount of phenylglycidyl ether is added to an electrolytic solution containing a mixed organic solvent containing 30% by volume of ethylene carbonate and containing LiPF ₆ at a concentration of 1 mol / L. And a lithium ion secondary battery using this electrolytic solution is disclosed.

JP 2013-149477 A JP 2013-134922 A JP 2013-145724 A JP 2013-137873 A

As described in Patent Documents 1 to 4, conventionally, in an electrolytic solution used for a lithium ion secondary battery, an organic solvent having a high relative dielectric constant and dipole moment such as ethylene carbonate and propylene carbonate is about 30% by volume or more. It has become common technical knowledge to use a mixed organic solvent and to contain a lithium salt at a concentration of approximately 1 mol / L. As described in Patent Documents 3 to 4, the improvement of the electrolytic solution is generally performed by paying attention to an additive separate from the lithium salt.

Unlike the conventional points of interest of those skilled in the art, the present inventors combine a metal salt composed of a specific electrolyte with a heteroelement-containing organic solvent containing an organic solvent exclusively having a low relative dielectric constant and / or low dipole moment. And a new electrolyte solution focusing on their molar ratio.

Now, it is generally known that resistance is generated during operation of a lithium ion secondary battery, and that the capacity of the lithium ion secondary battery decreases when charging and discharging are repeated. The lithium ion secondary battery having the above-described new electrolyte solution is no exception, and resistance is generated during operation, and the capacity is reduced when charging and discharging are repeated.

The present invention has been made in view of such circumstances, and an object thereof is to provide a lithium ion secondary battery in which resistance is suppressed to a certain extent and capacity is suitably maintained.

The present inventor has intensively studied through many trials and errors. As a result, the present inventor is able to suppress the resistance to a certain extent and provide a capacity if the lithium ion secondary battery includes a lithium metal composite oxide having a specific layered rock salt structure and the above-described new electrolytic solution. Has been found to be suitably maintained. Based on this knowledge, the present inventor has completed the present invention.

The lithium ion secondary battery of the present invention is
Heteroelement-containing organic solvent containing a specific organic solvent having a dielectric constant of 10 or less and / or a dipole moment of 5D or less, and a metal salt having lithium as a cation and a chemical structure represented by the following general formula (1) as an anion An electrolyte solution in a molar ratio of 3 to 5,
And
In powder X-ray diffraction measurement, 1.10 ≦ (integral intensity of peak derived from (003) plane I (003)) / (integrated intensity of peak derived from (104) plane I (104)) <2.0 Satisfied or general formula Li _a (Ni _x Co _y M _z ) O _b (1.05 ≦ a ≦ 1.20, 0.15 ≦ x ≦ 0.55, 0.25 ≦ y ≦ 0.75, 0.01 ≦ z ≦ 0.29, x + y + z = 1, 1.7 ≦ b ≦ 2.3, M is Mn, Zr, Mg, Ti, Al, W, Si, Mo, Fe, B, Zn, Cu A lithium-metal composite oxide having a layered rock salt structure represented by at least one of them.

(R ¹ X ¹ ) (R ² SO ₂ ) N General formula (1)
(R ¹ is hydrogen, halogen, an alkyl group which may be substituted with a substituent, a cycloalkyl group which may be substituted with a substituent, an unsaturated alkyl group which may be substituted with a substituent, or a substituent. An unsaturated cycloalkyl group which may be substituted with, an aromatic group which may be substituted with a substituent, a heterocyclic group which may be substituted with a substituent, or an alkoxy group which may be substituted with a substituent , An unsaturated alkoxy group that may be substituted with a substituent, a thioalkoxy group that may be substituted with a substituent, an unsaturated thioalkoxy group that may be substituted with a substituent, CN, SCN, or OCN Is done.
R ² represents hydrogen, halogen, an alkyl group which may be substituted with a substituent, a cycloalkyl group which may be substituted with a substituent, an unsaturated alkyl group which may be substituted with a substituent, or a substituent. An unsaturated cycloalkyl group which may be substituted, an aromatic group which may be substituted with a substituent, a heterocyclic group which may be substituted with a substituent, an alkoxy group which may be substituted with a substituent, Selected from an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, CN, SCN, OCN The
R ¹ and R ² may be bonded to each other to form a ring.
X ¹ is selected from SO ₂ , C = O, C = S, R ^a P = O, R ^b P = S, S = O, Si = O.
R ^a and R ^b are each independently hydrogen, halogen, an alkyl group that may be substituted with a substituent, a cycloalkyl group that may be substituted with a substituent, or a group that may be substituted with a substituent. A saturated alkyl group, an unsaturated cycloalkyl group that may be substituted with a substituent, an aromatic group that may be substituted with a substituent, a heterocyclic group that may be substituted with a substituent, and a substituent An alkoxy group which may be substituted, an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, OH , SH, CN, SCN, and OCN.
R ^a and R ^b may combine with R ¹ or R ² to form a ring. )

In the lithium ion secondary battery of the present invention, the resistance is suppressed to a certain extent and the capacity is suitably maintained.

It is a graph of the relationship between the molar ratio of a specific organic solvent and metal salt, and the ionic conductivity of the electrolyte solution whose metal salt is LiFSA and a specific organic solvent is DMC. 6 is a graph showing the relationship between the potential (3.0 to 4.5 V) and the response current with respect to the half cell of Example A. 6 is a graph showing a relationship between a potential (3.0 to 5.0 V) and a response current with respect to the half cell of Example A. 6 is a graph showing the relationship between the potential (3.0 to 4.5 V) and the response current with respect to the half cell of Comparative Example A. 6 is a graph showing a relationship between a potential (3.0 to 5.0 V) and a response current with respect to the half cell of Comparative Example A. It is a complex impedance plane plot of the battery in the reference evaluation example I. It is a X-ray photoelectron spectroscopic analysis chart about a sulfur element in reference evaluation example III. It is a X-ray photoelectron spectroscopic analysis chart about an oxygen element in reference evaluation example III. 2 is an X-ray diffraction chart of a lithium metal composite oxide of Production Example 1. 2 is an X-ray diffraction chart of a lithium metal composite oxide of Comparative Production Example 1.

Hereinafter, modes for carrying out the present invention will be described. Unless otherwise specified, the numerical range “a to b” described in this specification includes the lower limit “a” and the upper limit “b”. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.

The lithium ion secondary battery of the present invention is
Heteroelement-containing organic solvent containing a specific organic solvent having a dielectric constant of 10 or less and / or a dipole moment of 5D or less, and a metal salt having lithium as a cation and a chemical structure represented by the following general formula (1) as an anion In a molar ratio of 3 to 5 (hereinafter sometimes referred to as the electrolytic solution of the present invention),
And
In powder X-ray diffraction measurement, 1.10 ≦ (integral intensity of peak derived from (003) plane I (003)) / (integrated intensity of peak derived from (104) plane I (104)) <2.0 Satisfied or general formula Li _a (Ni _x Co _y M _z ) O _b (1.05 ≦ a ≦ 1.20, 0.15 ≦ x ≦ 0.55, 0.25 ≦ y ≦ 0.75, 0.01 ≦ z ≦ 0.29, x + y + z = 1, 1.7 ≦ b ≦ 2.3, M is Mn, Zr, Mg, Ti, Al, W, Si, Mo, Fe, B, Zn, Cu A lithium-metal composite oxide having a layered rock salt structure represented by at least one of them.

(R ¹ X ¹ ) (R ² SO ₂ ) N General formula (1)
(R ¹ is hydrogen, halogen, an alkyl group which may be substituted with a substituent, a cycloalkyl group which may be substituted with a substituent, an unsaturated alkyl group which may be substituted with a substituent, or a substituent. An unsaturated cycloalkyl group which may be substituted with, an aromatic group which may be substituted with a substituent, a heterocyclic group which may be substituted with a substituent, or an alkoxy group which may be substituted with a substituent , An unsaturated alkoxy group that may be substituted with a substituent, a thioalkoxy group that may be substituted with a substituent, an unsaturated thioalkoxy group that may be substituted with a substituent, CN, SCN, or OCN Is done.
R ² represents hydrogen, halogen, an alkyl group which may be substituted with a substituent, a cycloalkyl group which may be substituted with a substituent, an unsaturated alkyl group which may be substituted with a substituent, or a substituent. An unsaturated cycloalkyl group which may be substituted, an aromatic group which may be substituted with a substituent, a heterocyclic group which may be substituted with a substituent, an alkoxy group which may be substituted with a substituent, Selected from an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, CN, SCN, OCN The
R ¹ and R ² may be bonded to each other to form a ring.
X ¹ is selected from SO ₂ , C = O, C = S, R ^a P = O, R ^b P = S, S = O, Si = O.
R ^a and R ^b are each independently hydrogen, halogen, an alkyl group that may be substituted with a substituent, a cycloalkyl group that may be substituted with a substituent, or a group that may be substituted with a substituent. A saturated alkyl group, an unsaturated cycloalkyl group that may be substituted with a substituent, an aromatic group that may be substituted with a substituent, a heterocyclic group that may be substituted with a substituent, and a substituent An alkoxy group which may be substituted, an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, OH , SH, CN, SCN, and OCN.
R ^a and R ^b may combine with R ¹ or R ² to form a ring. )

First, the electrolytic solution of the present invention will be described.

The term “may be substituted with a substituent” in the chemical structure represented by the general formula (1) will be described. For example, in the case of “an alkyl group that may be substituted with a substituent”, an alkyl group in which one or more of the hydrogens of the alkyl group are substituted with a substituent, or an alkyl group that does not have a particular substituent Means.

Examples of the substituent in the phrase “may be substituted with a substituent” include an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an unsaturated cycloalkyl group, an aromatic group, a heterocyclic group, a halogen, and OH. SH, CN, SCN, OCN, nitro group, alkoxy group, unsaturated alkoxy group, amino group, alkylamino group, dialkylamino group, aryloxy group, acyl group, alkoxycarbonyl group, acyloxy group, aryloxycarbonyl group, Acylamino group, alkoxycarbonylamino group, aryloxycarbonylamino group, sulfonylamino group, sulfamoyl group, carbamoyl group, alkylthio group, arylthio group, sulfonyl group, sulfinyl group, ureido group, phosphoric acid amide group, sulfo group, carboxyl group, Hydroxamic acid group Sulfino group, a hydrazino group, an imino group, and a silyl group. These substituents may be further substituted. When there are two or more substituents, the substituents may be the same or different.

The chemical structure of the anion of the metal salt is preferably a chemical structure represented by the following general formula (1-1).

(R ³ X ² ) (R ⁴ SO ₂ ) N Formula (1-1)
(R ³ and R ⁴ are each independently C _n H _a F _b Cl _c Br _d I _e (CN) _f (SCN) _g (OCN) _h .
n, a, b, c, d, e, f, g, and h are each independently an integer of 0 or more, and satisfy 2n + 1 = a + b + c + d + e + f + g + h.
R ³ and R ⁴ may combine with each other to form a ring, in which case 2n = a + b + c + d + e + f + g + h is satisfied.
X ^{2 _{is, SO 2, C = O,}} C = S, R c P = O, R d P = S, S = O, is selected from Si = O.
R ^c and R ^d are each independently hydrogen, halogen, an alkyl group that may be substituted with a substituent, a cycloalkyl group that may be substituted with a substituent, or a group that may be substituted with a substituent. A saturated alkyl group, an unsaturated cycloalkyl group that may be substituted with a substituent, an aromatic group that may be substituted with a substituent, a heterocyclic group that may be substituted with a substituent, and a substituent An alkoxy group which may be substituted, an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, OH , SH, CN, SCN, and OCN.
R ^c and R ^d may combine with R ³ or R ⁴ to form a ring. )

In the chemical structure represented by the general formula (1-1), the meaning of the phrase “may be substituted with a substituent” is the same as described in the general formula (1).

In the chemical structure represented by the general formula (1-1), n is preferably an integer of 0 to 6, more preferably an integer of 0 to 4, and particularly preferably an integer of 0 to 2. In the case where R ³ and R ^{4 of the} chemical structure represented by the general formula (1-1) are combined to form a ring, n is preferably an integer of 1 to 8, preferably 1 to 7. An integer of 1 is more preferable, and an integer of 1 to 3 is particularly preferable.

The chemical structure of the anion of the metal salt is more preferably represented by the following general formula (1-2).

(R ⁵ SO ₂ ) (R ⁶ SO ₂ ) N Formula (1-2)
(R ⁵ and R ⁶ are each independently C _n H _a F _b Cl _c Br _d I _e .
n, a, b, c, d, and e are each independently an integer of 0 or more, and satisfy 2n + 1 = a + b + c + d + e.
R ⁵ and R ⁶ may combine with each other to form a ring, in which case 2n = a + b + c + d + e is satisfied. )

In the chemical structure represented by the general formula (1-2), n is preferably an integer of 0 to 6, more preferably an integer of 0 to 4, and particularly preferably an integer of 0 to 2. In the chemical structure represented by the general formula (1-2), when R ⁵ and R ⁶ are combined to form a ring, n is preferably an integer of 1 to 8, preferably 1 to 7. An integer of 1 is more preferable, and an integer of 1 to 3 is particularly preferable.

In the chemical structure represented by the general formula (1-2), those in which a, c, d and e are 0 are preferable.

The metal salt is (CF ₃ SO ₂ ) ₂ NLi (hereinafter sometimes referred to as “LiTFSA”), (FSO ₂ ) ₂ NLi (hereinafter sometimes referred to as “LiFSA”), (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 (C ₂ H ₅ SO ₂ ) NLi is particularly preferred.

The metal salt may be a combination of lithium and the anion described above. One kind of metal salt in the electrolytic solution of the present invention may be used, or a plurality of kinds may be used in combination.

The electrolyte solution of the present invention may contain other electrolytes that can be used for the electrolyte solution of the power storage device in addition to the metal salt. In the electrolytic solution of the present invention, the metal salt is preferably contained 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, and 90% by mass. More preferably, it is contained in% or more.

The electrolytic solution of the present invention includes a hetero element-containing organic solvent, and the hetero element-containing organic solvent includes a specific organic solvent having a relative dielectric constant of 10 or less and / or a dipole moment of 5 D or less. As the hetero-element-containing organic solvent, any organic solvent that can be used in the electrolytic solution of the power storage device may be used as long as it contains a hetero-element. The specific organic solvent may be a heteroelement-containing organic solvent having a relative dielectric constant of 10 or less and / or a dipole moment of 5D or less.

Since the hetero element-containing organic solvent or the specific organic solvent has a hetero element, the metal salt can be suitably dissolved at a certain concentration. On the other hand, the above metal salt cannot be suitably dissolved in an organic solvent composed of a hydrocarbon having no hetero element.

As the hetero element-containing organic solvent or the specific organic solvent, an organic solvent in which the hetero element is at least one selected from nitrogen, oxygen, sulfur and halogen is preferable, and an organic solvent in which the hetero element is oxygen is more preferable. Further, the hetero element-containing organic solvent or the specific organic solvent is preferably an aprotic solvent having no proton donating group such as NH group, NH ₂ group, OH group, and SH group.

Specific examples of the hetero element-containing organic solvent include nitriles such as acetonitrile, propionitrile, acrylonitrile, and malononitrile, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 1 , 3-dioxane, 1,4-dioxane, 2,2-dimethyl-1,3-dioxolane, 2-methyltetrahydropyran, 2-methyltetrahydrofuran, ethers such as crown ether, ethylene carbonate, propylene carbonate, dimethyl carbonate, Carbonates such as diethyl carbonate and ethyl methyl carbonate, amides such as formamide, N, N-dimethylformamide, N, N-dimethylacetamide and N-methylpyrrolidone, isopropyl isocyanate, n- Isocyanates such as propyl isocyanate, chloromethyl isocyanate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, methyl formate, ethyl formate, vinyl acetate, methyl acrylate, methyl methacrylate, esters, glycidyl methyl ether Epoxies such as epoxybutane and 2-ethyloxirane, oxazoles such as oxazole, 2-ethyloxazole, oxazoline and 2-methyl-2-oxazoline, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, acetic anhydride, anhydrous Acid anhydrides such as propionic acid, sulfones such as dimethyl sulfone and sulfolane, sulfoxides such as dimethyl sulfoxide, nitros such as 1-nitropropane and 2-nitropropane, furan, full Furans such as Lar, cyclic esters such as γ-butyrolactone, γ-valerolactone and δ-valerolactone, aromatic heterocycles such as thiophene and pyridine, tetrahydro-4-pyrone, 1-methylpyrrolidine, N-methyl Examples include heterocyclic rings such as morpholine, and phosphate esters such as trimethyl phosphate and triethyl phosphate.

The specific organic solvent is compared with a heteroelement-containing organic solvent having a relative dielectric constant of more than 10 and / or a dipole moment of more than 5D (hereinafter sometimes referred to as “other heteroorganic solvent”) other than the specific organic solvent. And the polarity is low. Therefore, it is considered that the affinity between the specific organic solvent and the metal ion is inferior to the affinity between the other hetero organic solvent and the metal ion. Then, when the electrolytic solution of the present invention is used as an electrolytic solution for a secondary battery, it is difficult for the aluminum and transition metal constituting the electrode of the secondary battery to dissolve as ions in the electrolytic solution of the present invention. It can be said that there is.

Here, in a secondary battery using a general electrolytic solution, aluminum and transition metal constituting the positive electrode are in a highly oxidized state particularly in a high voltage charging environment, and are dissolved in the electrolytic solution as metal ions that are cations. (Anode elution), and metal ions eluted in the electrolyte are attracted to the electron-rich negative electrode due to electrostatic attraction, and are reduced by bonding with electrons on the negative electrode, and may be deposited as metal. It is known. It is known that when such a reaction occurs, the capacity of the positive electrode may be reduced or the electrolytic solution may be decomposed on the negative electrode. However, since the electrolytic solution of the present invention has the characteristics described in the previous paragraph, elution of metal ions from the positive electrode and metal deposition on the negative electrode are suppressed in the lithium ion secondary battery of the present invention.

The relative dielectric constant of the specific organic solvent is preferably 10 or less, more preferably 7 or less, and even more preferably 5 or less. The lower limit of the relative dielectric constant of the specific organic solvent is not particularly limited, but can be exemplified by 1 or more, 2 or more, and 2.5 or more.

The dipole moment of the specific organic solvent is preferably 5D or less, more preferably 2.5D or less, and even more preferably 1D or less. Although the minimum of the dipole moment of a specific organic solvent is not specifically limited, If it dares to mention, 0.05D or more, 0.1D or more, 0.2D or more can be illustrated.

The specific organic solvent preferably contains carbonate in the chemical structure. More preferable specific organic solvents include chain carbonates represented by the following general formula (2).

R ²⁰ OCOOR ²¹ general formula (2)
(R ²⁰ and R ²¹ each independently represent C _n H _a F _b Cl _c Br _d I _e which is a chain alkyl, or C _m H _f F _g Cl _h Br _i I containing a cyclic alkyl in the chemical structure. selected from _j , n is an integer of 1 or more, m is an integer of 3 or more, a, b, c, d, e, f, g, h, i, j are each independently an integer of 0 or more 2n + 1 = a + b + c + d + e, 2m = f + g + h + i + j is satisfied.)

In the chain carbonate represented by the general formula (2), 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 represented by the general formula (2), those represented by the following general formula (2-1) are particularly preferable.

R ²² OCOOR ²³ general formula (2-1)
(R ²² and R ²³ are each independently selected from either C _n H _a F _b which is a chain alkyl or C _m H _f F _g containing a cyclic alkyl in the chemical structure. N, a , B, m, f, and g are each independently an integer of 0 or more, and satisfy 2n + 1 = a + b and 2m = f + g.)

In the chain carbonate represented by the general formula (2-1), 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 represented by the general formula (2-1), dimethyl carbonate (hereinafter sometimes referred to as “DMC”), diethyl carbonate (hereinafter sometimes referred to as “DEC”), ethyl methyl Carbonate (hereinafter sometimes referred to as "EMC"), fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate, bis (fluoromethyl) carbonate, bis (difluoro) methyl carbonate, bis (trifluoromethyl) Carbonate, fluoromethyldifluoromethyl carbonate, 2,2,2-trifluoroethyl methyl carbonate, pentafluoroethyl methyl carbonate, ethyl trifluoromethyl carbonate, bis (2,2,2-trifluoroethyl) Le) carbonate is particularly preferred.

Further, from the disclosure of this specification, a hetero element-containing organic solvent containing a chain carbonate represented by the above general formula (2), and lithium as a cation, the chemical structure represented by the above general formula (1) is represented by an anion. It is possible to ascertain an electrolytic solution containing a metal salt as a molar ratio of 3 to 5. Note that the description of the “electrolytic solution of the present invention” in this specification can be applied to this electrolytic solution within a reasonable range.

In the electrolytic solution of the present invention using a suitable specific organic solvent, the concentration of the metal salt exhibiting suitable ion conductivity is relatively high. Furthermore, in the electrolytic solution of the present invention using the chain carbonate represented by the above general formula (2) as the specific organic solvent, the variation in ionic conductivity is small with respect to some variation in metal salt concentration, It has the advantage of being excellent in robustness. Moreover, the chain carbonate represented by the general formula (2) is excellent in stability against oxidation and reduction. In addition, the chain carbonate represented by the general formula (2) has many free-rotatable bonds and has a flexible chemical structure. Therefore, the electrolytic solution of the present invention using the chain carbonate has a high concentration. Even in the case of containing a metal salt at a concentration, a significant increase in the viscosity can be suppressed and high ionic conductivity can be obtained.

The specific organic solvents described above may be used alone in the electrolyte solution, or a plurality of them may be used in combination.

For reference, Table 1 lists the dielectric constants and dipole moments of various organic solvents.

The electrolytic solution of the present invention contains a heteroelement-containing organic solvent and the metal salt in a molar ratio of 3 to 5. In the present specification, the molar ratio is a value obtained by dividing the former by the latter, that is, (number of moles of hetero-element-containing organic solvent contained in the electrolytic solution of the present invention) / (metal contained in the electrolytic solution of the present invention). The number of moles of salt). In the secondary battery using the electrolytic solution of the present invention, the SEI film formed at the electrode / electrolyte interface is mainly composed of a metal salt-derived component having a low resistance S = O structure rather than a conventional organic solvent-derived component. The reaction resistance is relatively small due to the reason that the Li ion concentration in the film is high. The meaning of the range of the molar ratio of 3 to 5 is a range in which the reaction resistance of the secondary battery is relatively small and the ionic conductivity of the electrolytic solution is in a suitable range. In the electrolytic solution of the present invention, the molar ratio of the heteroelement-containing organic solvent and the metal salt is more preferably in the range of 3.2 to 4.8, and still more preferably in the range of 3.5 to 4.5. In addition, the conventional electrolyte solution has a molar ratio of the hetero-element-containing organic solvent and the electrolyte or metal salt of about 10 in general.

In the electrolytic solution of the present invention, it is presumed that the metal salt and the heteroelement-containing organic solvent are interacting with each other. Microscopically, the electrolytic solution of the present invention has a stable cluster composed of a metal salt and a heteroelement-containing organic solvent formed by coordination bonding between the metal salt and the heteroelement of the heteroelement-containing organic solvent. Presumed to contain.

It can be said that the electrolytic solution of the present invention has a higher proportion of metal salt than the conventional electrolytic solution. If it does so, it can be said that the electrolyte solution of this invention differs in the presence environment of a metal salt and an organic solvent compared with the conventional electrolyte solution. Therefore, in a power storage device such as a secondary battery using the electrolytic solution of the present invention, an improvement in the transport rate of metal ions in the electrolytic solution, an improvement in the reaction rate at the interface between the electrode and the electrolytic solution, a high rate charge / discharge of the secondary battery It can be expected to alleviate the uneven distribution of metal salt concentration in the electrolyte, improve the electrolyte retention at the electrode interface, suppress the so-called drainage state where the electrolyte is insufficient at the electrode interface, and increase the capacity of the electric double layer. . Furthermore, in the electrolytic solution of the present invention, the vapor pressure of the organic solvent contained in the electrolytic solution is lowered. As a result, volatilization of the organic solvent from the electrolytic solution of the present invention can be reduced.

The density d (g / cm ³ ) of the electrolytic solution of the present invention will be described. In addition, in this specification, a density means the density in 20 degreeC. The density d (g / cm ³ ) of the electrolytic solution of the present invention is preferably 1.0 ≦ d, and more preferably 1.1 ≦ d.

For reference, the densities (g / cm ³ ) of typical heteroelement-containing organic solvents are listed in Table 2.

Describing the viscosity η (mPa · s) of the electrolytic solution of the present invention, a range of 3 <η <50 is preferable, a range of 4 <η <40 is more preferable, and a range of 5 <η <30 is more preferable.

Also, the higher the ion conductivity σ (mS / cm) of the electrolytic solution, the easier the ions move in the electrolytic solution. For this reason, such an electrolyte can be an excellent battery electrolyte. The ion conductivity σ (mS / cm) of the electrolytic solution of the present invention is preferably 1 ≦ σ. Regarding the ionic conductivity σ (mS / cm) of the electrolytic solution of the present invention, when a suitable range including the upper limit is shown, a range of 2 ≦ σ <100 is preferable, and a range of 3 ≦ σ <50 is more preferable. A range of 4 ≦ σ <30 is more preferable.

Incidentally, the electrolytic solution of the present invention contains a metal salt cation in a high concentration. For this reason, in the electrolytic solution of the present invention, the distance between adjacent cations is extremely short. When a cation such as lithium ion moves between the positive electrode and the negative electrode during charge / discharge of the secondary battery, the cation closest to the destination electrode is first supplied to the electrode. And the other cation adjacent to the said cation moves to the place with the said supplied cation. In other words, in the electrolytic solution of the present invention, it is expected that a domino-like phenomenon occurs in which adjacent cations change one by one toward the electrode to be supplied one by one. For this reason, the movement distance of the cation at the time of charging / discharging is short, and it is thought that the movement speed | rate of a cation is high by that much. And it originates in this and it is thought that the reaction rate of the secondary battery which has the electrolyte solution of this invention is high.

The electrolyte solution of the present invention may contain, in addition to the specific organic solvent, an organic solvent composed of the other hetero organic solvent or a hydrocarbon having no hetero element. In the electrolytic solution of the present invention, the specific organic solvent is preferably contained in an amount of 80% by volume or more, more preferably 90% by volume or more, and 95% by volume with respect to the total solvent contained in the electrolytic solution of the present invention. More preferably, it is contained in% or more. The electrolyte solution of the present invention preferably contains a specific organic solvent at 80 mol% or more, more preferably 90 mol% or more, based on the total solvent contained in the electrolyte solution of the present invention. More preferably, it is contained at 95 mol% or more.

As one aspect of the electrolytic solution of the present invention, a specific organic solvent having a relative dielectric constant of 10 or less and / or a dipole moment of 5D or less, a chemical structure represented by the above general formula (1) with lithium as a cation, and an anion An electrolytic solution containing a metal salt to be used at a molar ratio of 3 to 5 can be mentioned.

In addition, the electrolytic solution of the present invention containing other hetero organic solvents in addition to the specific organic solvent has a higher viscosity or ionic conductivity than the electrolytic solution of the present invention not containing other hetero organic solvents. May decrease. Furthermore, the reaction resistance of the secondary battery using the electrolytic solution of the present invention containing another hetero organic solvent in addition to the specific organic solvent may increase.

In addition, the electrolyte solution of the present invention containing an organic solvent composed of the above hydrocarbon in addition to the specific organic solvent can be expected to have an effect of lowering the viscosity.

Specific examples of the organic solvent composed of the hydrocarbon 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 increased. Examples of the flame retardant solvent include halogen solvents such as carbon tetrachloride, tetrachloroethane, and hydrofluoroether, and phosphoric acid derivatives such as trimethyl phosphate and triethyl phosphate.

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

As the polymer, a polymer used for a battery such as a lithium ion secondary battery or a general chemically crosslinked polymer can be employed. In particular, a polymer that can absorb an electrolyte such as polyvinylidene fluoride and polyhexafluoropropylene and gel can be used, and a polymer such as polyethylene oxide in which an ion conductive group is introduced.

Specific polymers include polymethyl acrylate, polymethyl methacrylate, polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, polyglycidol, polytetrafluoroethylene, polyhexafluoropropylene, Polycarboxylic acid such as polysiloxane, polyvinyl acetate, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polyitaconic acid, polyfumaric acid, polycrotonic acid, polyangelic acid, carboxymethylcellulose, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene , Polycarbonate, unsaturated polyester copolymerized with maleic anhydride and glycols, Polyethylene oxide derivative having a group, a copolymer of vinylidene fluoride and hexafluoropropylene can be exemplified. Further, as the polymer, a copolymer obtained by copolymerizing two or more 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. Moreover, you may employ | adopt the material containing these polysaccharides as said polymer, The agar containing polysaccharides, such as agarose, can be illustrated as the said material.

The inorganic filler is preferably an inorganic ceramic such as oxide or nitride.

Inorganic ceramics have hydrophilic and hydrophobic functional groups on the surface. Therefore, when the functional group attracts the electrolytic solution, a conductive path can be formed in the inorganic ceramic. Furthermore, the inorganic ceramics dispersed in the electrolytic solution can form a network between the inorganic ceramics by the functional groups and serve to contain the electrolytic solution. With such a function of the inorganic ceramics, it is possible to more suitably suppress the leakage of the electrolytic solution in the battery. In order to suitably exhibit the above functions of the inorganic ceramics, the inorganic ceramics preferably have a particle shape, and particularly preferably have a particle size of nano level.

Examples of the inorganic ceramics include general alumina, silica, titania, zirconia, and lithium phosphate. Further, the inorganic ceramic itself may be lithium conductive, and specifically, Li ₃ N, LiI, LiI—Li ₃ N—LiOH, LiI—Li ₂ S—P ₂ O ₅ , LiI—Li ₂ S —P ₂ S ₅ , LiI—Li ₂ S—B 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 illustrated.

Glass ceramics may be employed 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 , a compound obtained by substituting a part of S of the compound with another element, and a P of the compound. An example in which the part is replaced with germanium can be exemplified.

In addition, a known additive may be added to the electrolytic solution of the present invention without departing from the spirit of the present invention.

Next, the layered rock salt structure lithium metal composite oxide provided in the lithium ion secondary battery of the present invention will be described.

The lithium metal composite oxide having a layered rock salt structure provided in the lithium ion secondary battery of the present invention is 1.10 ≦ (peak integrated intensity I (003) derived from (003) plane) in powder X-ray diffraction measurement. / ((104) plane integrated intensity I (104)) <2.0 or general formula Li _a (Ni _x Co _y M _z ) O _b (1.05 ≦ a ≦ 1.20, 0.15 ≦ x ≦ 0.55, 0.25 ≦ y ≦ 0.75, 0.01 ≦ z ≦ 0.29, x + y + z = 1, 1.7 ≦ b ≦ 2.3 , M is represented by Mn, Zr, Mg, Ti, Al, W, Si, Mo, Fe, B, Zn, Cu).

As the lithium metal composite oxide having a layered rock salt structure provided in the lithium ion secondary battery of the present invention, the integrated intensity I (003) of the peak derived from 1.10 ≦ ((003) plane in powder X-ray diffraction measurement. ) / ((104) plane-derived integrated intensity I (104)) <2.0, and the general formula Li _a (Ni _x Co _y M _z ) O _b (1.05 ≦ a ≦ 1.20, 0.15 ≦ x ≦ 0.55, 0.25 ≦ y ≦ 0.75, 0.01 ≦ z ≦ 0.29, x + y + z = 1, 1.7 ≦ b ≦ 2.3, M is What is represented by at least one of Mn, Zr, Mg, Ti, Al, W, Si, Mo, Fe, B, Zn, and Cu) is preferable.

Hereinafter, (integrated intensity I of peak derived from (003) plane I (003)) / (integrated intensity of peak derived from (104) plane I (104)) may be referred to as a parameter of the present invention. The technical significance of the parameters of the present invention will be described.

In the lithium metal composite oxide having a layered rock salt structure, the integrated intensity I (003) of the peak derived from the (003) plane in powder X-ray diffraction measurement is the (003) plane when the layered rock salt structure is expressed by the Miller index. The integrated intensity of the peak on the powder X-ray diffraction chart corresponding to the diffracted light from, that is, the peak area. This peak is observed in the vicinity of 2θ = 17 to 20 ° in the powder X-ray diffraction chart, and is considered to be unique to the layered rock salt structure.

Similarly, in the lithium metal composite oxide having a layered rock salt structure, the integrated intensity I (104) of the peak derived from the (104) plane in the powder X-ray diffraction measurement is the value when the layered rock salt structure is expressed by the Miller index ( 104) The integrated intensity of the peak on the powder X-ray diffraction chart corresponding to the diffracted light from the plane, that is, the peak area. This peak is observed around 2θ = 43 to 46 ° in the powder X-ray diffraction chart. However, it is considered that the peak is not unique only to the layered rock salt structure but also observed from the cubic rock salt structure.

Therefore, in the lithium metal composite oxide, if the value of the parameter of the present invention is low, it means that the ratio of the layered rock salt structure is low. On the other hand, in the lithium metal composite oxide, when the value of the parameter of the present invention is too high, a crystal habit in which only a specific axis or plane of the layered rock salt structure has grown significantly occurs, or lithium, transition metal, oxygen It can be said that the balance of the blending amount of is lacking.

In general, in a lithium metal composite oxide having a layered rock salt structure, the parameters of the present invention are an index for determining the degree of mixing of a transition metal such as nickel into the lithium site of the layered rock salt structure, and a lithium metal composite oxide. It is regarded as an index of the reactivity between the product and the electrolyte. In general, the lithium metal composite oxide having a layered rock salt structure is preferably in the range of 1.10 ≦ parameter of the present invention <4.0.

Here, it is said that the lithium metal composite oxide having a parameter of less than 1.10 according to the present invention has a remarkably high degree of mixing of transition metals such as nickel into lithium sites having a layered rock salt structure. Since the amount of lithium ions that can contribute to charging / discharging of such a lithium metal composite oxide is reduced, the charge / discharge characteristics of a lithium ion secondary battery using the lithium metal composite oxide as a positive electrode active material are reduced. .

In addition, in a lithium ion secondary battery using a lithium metal composite oxide having a parameter of 4.0 or more of the present invention as a positive electrode active material, an adverse reaction between the lithium metal composite oxide and the electrolyte can easily occur. .

In the present invention, the preferred range of parameters of the present invention is defined as 1.10 ≦ parameters of the present invention <2.0. If the lithium metal composite oxide has a layered rock salt structure in this range, the lithium metal composite oxide does not have a high degree of mixing of transition metals such as nickel into the lithium site of the layered rock salt structure. The reaction is not easily caused.

Formula _{Li a (Ni x Co y M} z) O b (1.05 ≦ a ≦ 1.20,0.15 ≦ x ≦ 0.55,0.25 ≦ y ≦ 0.75,0.01 ≦ z ≦ 0.29, x + y + z = 1, 1.7 ≦ b ≦ 2.3, M is at least one of Mn, Zr, Mg, Ti, Al, W, Si, Mo, Fe, B, Zn, Cu) In the above, a, x, y, z, and b may be within the above-described ranges.

Preferred a range is 1.05 ≦ a ≦ 1.15, preferred x range is 0.45 ≦ x ≦ 0.55, preferred y range is 0.25 ≦ y ≦ 0.35, and preferred z range is For example, 0.1 ≦ z ≦ 0.25.

M can also be expressed as Mn _z1 D _z2 (z1 + z2 = z, D is selected from Zr, Mg, Ti, Al, W, Si, Mo, Fe, B, Zn, Cu). Examples of preferable z1 ranges include 0.01 ≦ z1 ≦ 0.29 and 0.1 ≦ z1 ≦ 0.25. Examples of preferable z2 ranges include 0 ≦ z2 ≦ 0.1 and 0.01 ≦ z2 ≦ 0.05.

The lithium metal composite oxide having a layered rock salt structure may have a hollow structure in which the surface layer portion is dense and the inside is sparse, or a solid structure in which the surface layer portion and the inside are both dense.

The lithium metal complex oxide having a layered rock salt structure is usually composed of secondary particles in which a plurality of primary particles are bonded. The shape of the secondary particles is not particularly limited, but from the viewpoint of imparting excellent characteristics to the secondary battery, the secondary particles are preferably uniform and have an appropriate particle size. In a secondary battery having a lithium metal composite oxide having a remarkably large particle size, it becomes difficult to secure a sufficient reaction area between the lithium metal composite oxide and the electrolyte, resulting in problems such as a decrease in capacity and an increase in resistance. there is a possibility. On the other hand, the lithium metal composite oxide having a remarkably small particle size is difficult to handle. In addition, in a secondary battery having a lithium metal composite oxide with poor uniformity of size, that is, with a wide particle size distribution of secondary particles, it is applied to each secondary particle due to a significant difference in particle diameter. As a result, the secondary voltage may be selectively deteriorated and defects such as a decrease in capacity and an increase in resistance may occur.

In summary of the above findings, from the viewpoint of size, the average particle diameter of the secondary particles of the lithium metal composite oxide is preferably in the range of 0.5 to 7 μm, and more preferably in the range of 1 to 6 μm. From the viewpoint of uniformity, secondary particles having a value of 100 × (standard deviation of particle diameter of secondary particles) / (average particle diameter of secondary particles) of less than 24 are preferable. In the present specification, the average particle diameter means D50 when measured with a general laser diffraction particle size distribution analyzer. Further, “secondary particle size” and “secondary particle size standard deviation” are values calculated by measuring lithium metal composite oxide with a general laser diffraction particle size distribution analyzer. .

Primary particles mean particles exhibiting a specific crystal orientation. The primary particles are presumed to be single crystals. When the appearance of the lithium metal composite oxide is observed with a microscope, it can be seen that many primary particles are bonded to form secondary particles.

There is no particular limitation on the shape of the primary particles. The present inventor analyzed the relationship between the major axis length of the primary particles and the shear stress at the grain boundary by the phase field method. As a result, it was found that the shear stress at the grain boundary decreases as the major axis length of the primary particles decreases. However, it may be difficult to produce secondary particles composed only of primary particles having a remarkably small major axis length with good reproducibility. In addition, since the density of secondary particles composed of only primary particles having a remarkably small major axis length may deviate greatly from the true density of the material, it may be disadvantageous from the viewpoint of the capacity of the active material. On the other hand, it can be said that the secondary particles composed of primary particles having a remarkably large major axis length are likely to be cracked because the shear stress at the grain boundary is increased. Furthermore, the secondary battery comprising a lithium metal composite oxide composed of secondary particles composed of primary particles having a remarkably large major axis length tends to significantly deteriorate the battery characteristics due to the change in the charge / discharge rate. . Taking these findings together, the shape of the primary particles is preferably within the range of 0.1 to 2 μm, and more preferably within the range of 0.2 to 1 μm. The “major axis length” means the length of the longest portion of the primary particles when observing the primary particles. The “average length of major axis length” means an arithmetic average value of “major axis length” obtained from 10 or more primary particles.

Further, from the analysis results of the above phase field method, (major particle length of primary particles) / (minor particle length of primary particles) is 1.1 to 5.0, preferably 1.7 to 4.0, more preferably. Is within the range of 2.0 to 4.0, it was found that the shear stress at the grain boundary is minimized. From this knowledge, the primary particles preferably have an average value of (primary particle major axis length) / (primary particle minor axis length) in the range of 1.1 to 5.0, and 1.7 to 4 Within the range of 0.0, more preferably within the range of 2.0 to 4.0. The “major axis length of the primary particles” means the length of the longest portion of the primary particles when observing the primary particles, as described above. “The minor axis length of the primary particles” means the length of the longest portion in the orthogonal direction of the major axis in the primary particles during primary particle observation. And, “the average value of (major axis length of primary particles) / (minor axis length of primary particles)” means “(major axis length of primary particles) / (primary particle length) obtained from 10 or more primary particles. It means the arithmetic mean value of the minor axis length of the particle).

The primary particle observation is performed based on an image obtained by measuring a cross section of the lithium metal composite oxide with a scanning electron microscope (SEM), a transmission electron microscope (TEM), an electron beam backscatter diffraction (EBSD), or the like. Good. You may analyze the said image using image analysis software.

A method for producing a lithium metal composite oxide having a layered rock salt structure will be described. The lithium metal composite oxide having a layered rock salt structure is produced from various materials by, for example, a production method including the following steps a) to d).
a) Step of preparing a transition metal ion aqueous solution by dissolving a transition metal salt in water b) Step of preparing a basic aqueous solution c) Supplying the transition metal ion aqueous solution to the basic aqueous solution, Step of forming d) Step of growing transition metal hydroxide particles e) Step of mixing and baking transition metal hydroxide particles and lithium salt

a) A process is demonstrated. The composition of the transition metal ion aqueous solution in step a) is the basis for the transition metal composition in the lithium metal composite oxide. Therefore, when there are a plurality of transition metals in the lithium metal composite oxide, the molar ratio of the plurality of transition metals in the transition metal ion aqueous solution in step a) is set to a desired ratio.
What is necessary is just to employ | adopt the well-known thing used for manufacture of lithium metal complex oxide as a metal salt used at a process. Examples of the salt in the case where the lithium metal composite oxide contains nickel, cobalt, and manganese. Examples of the nickel salt include nickel sulfate, nickel carbonate, nickel nitrate, nickel acetate, and nickel chloride. Examples of the cobalt salt used include cobalt sulfate, cobalt carbonate, cobalt nitrate, cobalt acetate, and cobalt chloride. Examples of the manganese salt include manganese sulfate, manganese carbonate, manganese nitrate, manganese acetate, and manganese chloride.

A preferable transition metal ion concentration range of the aqueous transition metal ion solution is 0.01 to 4 mol / L, more preferably 0.05 to 3 mol / L, still more preferably 0.1 to 2 mol / L, and particularly preferably. Is 0.5 to 1.5 mol / L.

Step b) is a step of preparing a basic aqueous solution by dissolving a basic compound in water. The pH of the basic aqueous solution in step b) is preferably in the range of 9 to 14, more preferably in the range of 10 to 13.5, and even more preferably in the range of 11 to 13. In addition, pH prescribed | regulated by this specification says the value at the time of measuring at 25 degreeC. The basic compound that can be used is not particularly limited as long as it dissolves in water and exhibits basicity, and examples thereof include alkali metal hydroxides such as ammonia, sodium hydroxide, potassium hydroxide, and lithium hydroxide, sodium carbonate, and carbonate. Alkali metal carbonates such as potassium and lithium carbonate, alkali metal phosphates such as trisodium phosphate, tripotassium phosphate and trilithium phosphate, alkali metal acetates such as sodium acetate, potassium acetate and lithium acetate, oxalic acid Mention may be made of alkali metal oxalates such as sodium, potassium oxalate and lithium oxalate. A basic compound may be used independently and may use multiple together. Since the pH of the aqueous solution in step c) following step b) is preferably kept in a suitable range, the basic aqueous solution in step b) preferably contains a basic compound having a buffering capacity. Examples of the basic compound having a buffering ability include ammonia, alkali metal carbonates, alkali metal phosphates, alkali metal acetates, and alkali metal oxalates.

The step b) is preferably carried out in a reaction vessel equipped with a stirring device, and further carried out in a reaction vessel equipped with a device capable of introducing an inert gas such as nitrogen or argon and an oxidizing gas such as oxygen or dry air. Is preferred. Moreover, the reaction tank provided with the apparatus used as a constant temperature condition is more preferable. The specific example of b) process is given below. Water is charged into a reaction vessel equipped with a stirrer, a nitrogen gas introducing device and a heating device, and heated to 40 ° C. An inert gas is introduced into the reaction vessel to create an inert gas atmosphere. An aqueous sodium hydroxide solution and aqueous ammonia are added to the reaction vessel to prepare a basic aqueous solution.

Step c) is a step of supplying transition metal ion aqueous solution to the basic aqueous solution to form transition metal hydroxide particles. Step c) is preferably carried out in a reaction vessel under the same conditions as described in step b). The stirring speed and temperature conditions may be appropriately set within a range suitable for nucleation and particle formation of transition metal hydroxide particles. When the pH of the basic aqueous solution fluctuates with the supply of the transition metal ion aqueous solution or when a basic compound such as ammonia is lost from the reaction tank due to vaporization, an aqueous solution containing the basic compound employed in step b) is appropriately used. The pH and ammonia concentration suitable for the nucleation and particle formation may be maintained. From the viewpoint of process stability, the supply rate of the transition metal ion aqueous solution is preferably constant. A preferable supply rate is 1 to 30 mL / min. More preferably 1.5 to 15 mL / min. More preferably 2 to 8 mL / min. Can be mentioned.

D) The step is a step of growing the transition metal hydroxide particles. If d) process is described by a concrete operation | work, d) process is a process of hold | maintaining and / or stirring the liquid of c) process, reducing the liquid of c) process as needed. Step d) is preferably carried out continuously with step c). Furthermore, in step d), as in step c), an aqueous transition metal ion solution and an aqueous solution containing a basic compound may be appropriately supplied. It may be difficult to strictly distinguish between step d) and step c). In step d), the liquid is preferably held and / or stirred until the desired particle size is obtained. The resulting particles can be separated by filtration. The separated particles may be subjected to step d) again as necessary. The separated particles are preferably dehydrated under heating conditions. Examples of heating conditions include 100 to 600 ° C. and 1 to 30 hours.

Step e) is a step in which the transition metal hydroxide particles and lithium salt obtained in step d) are mixed and fired to obtain a lithium metal composite oxide. Examples of the lithium salt include lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, lithium oxalate, and lithium halide. What is necessary is just to determine the compounding quantity of lithium salt suitably so that it may become a lithium metal complex oxide of a desired lithium composition. As an example, the lithium salt is used so that the molar ratio of lithium to the total of nickel, cobalt, and manganese is within the range of 1.05: 1 to 1.2: 1 in the entire raw material used in step e). What is necessary is just to determine the compounding quantity of.

Examples of the mixing device include a mortar and pestle, a stirring mixer, a V-type mixer, a W-type mixer, a ribbon-type mixer, a drum mixer, and a ball mill.

The firing conditions may be set appropriately within a range of, for example, 500 to 1000 ° C. and 1 to 30 hours. The temperature may be changed during firing, and firing may be performed at a plurality of temperatures. As an example of suitable firing conditions, primary firing is performed under conditions of 500 to 800 ° C. and 3 to 20 hours, and then secondary firing is performed under conditions of 800 to 1000 ° C. and 3 to 20 hours. it can. The lithium metal composite oxide obtained after calcination preferably has a constant particle size distribution through a washing step, a pulverization step, a classification step such as sieving, if necessary.

The lithium ion secondary battery of the present invention comprises the electrolytic solution of the present invention and the above-described lithium metal composite oxide. Specifically, the lithium ion secondary battery of the present invention includes a positive electrode including a lithium metal composite oxide, a negative electrode, and the electrolytic solution of the present invention.

The positive electrode has a current collector and a positive electrode active material layer bound to the surface of the current collector. The positive electrode active material layer includes a positive electrode active material and, if necessary, a binder and / or a conductive aid.

The positive electrode current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used. For example, silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin , Indium, titanium, ruthenium, tantalum, chromium, molybdenum, and metal materials such as stainless steel.

When the potential of the positive electrode is 4 V or higher with respect to lithium, it is preferable to employ aluminum as the current collector.

Specifically, it is preferable to use a material made of aluminum or an aluminum alloy as the positive electrode current collector. Here, aluminum refers to pure aluminum, and aluminum having a purity of 99.0% or more is referred to as pure aluminum. An alloy obtained by adding various elements to pure aluminum is referred to as 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.

Specific examples of aluminum or aluminum alloy include, for example, A1000 series alloys (pure aluminum series) such as JIS A1085 and A1N30, A3000 series alloys (Al-Mn series) such as JIS A3003 and A3004, JIS A8079, A8021, etc. A8000-based alloy (Al-Fe-based).

The current collector may be covered with a known protective layer. What collected the surface of the electrical power collector by the well-known method may be used as an electrical power collector.

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

The lithium metal composite oxide described above is used as the positive electrode active material. As the positive electrode active material, the above-described lithium metal composite oxide may be used alone or in combination. It should be noted that other known positive electrode active materials and polarizable electrode materials such as activated carbon may be used in combination in the lithium ion secondary battery of the present invention without departing from the spirit of the present invention.

The negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector. The negative electrode active material layer includes a negative electrode active material and, if necessary, a binder and / or a conductive aid. The negative electrode current collector may be appropriately selected from those described for the positive electrode.

As the negative electrode active material, a material capable of inserting and extracting lithium ions can be used. Accordingly, there is no particular limitation as long as it is a simple substance, alloy, or compound that can occlude and release lithium ions. For example, as a negative electrode active material, Li, group 14 elements such as carbon, silicon, germanium and tin, group 13 elements such as aluminum and indium, group 12 elements such as zinc and cadmium, group 15 elements such as antimony and bismuth, magnesium , Alkaline earth metals such as calcium, and group 11 elements such as silver and gold may be employed alone. When silicon or the like is used for the negative electrode active material, a silicon atom reacts with a plurality of lithiums, so that it becomes a high-capacity active material. However, there is a problem that volume expansion and contraction due to insertion and extraction of lithium becomes significant. In order to reduce the fear, it is also preferable to employ an alloy or compound in which another element such as a transition metal is combined with a simple substance such as silicon as the negative electrode active material. Specific examples of the alloy or compound include tin-based materials such as Ag—Sn alloy, Cu—Sn alloy and Co—Sn alloy, carbon-based materials such as various graphites, SiO _x (disproportionated into silicon simple substance and silicon dioxide). Examples thereof include silicon-based materials such as 0.3 ≦ x ≦ 1.6), silicon alone, or composites obtained by combining silicon-based materials and carbon-based materials. Further, as the negative electrode active material, oxides such as Nb ₂ O ₅ , TiO ₂ , Li ₄ Ti ₅ O ₁₂ , WO ₂ , MoO ₂ , Fe ₂ O ₃ , or Li _3-x M _x N (M = A nitride represented by (Co, Ni, Cu) may be employed. One or more of these materials can be used as the negative electrode active material.

The binder plays a role of connecting the active material and the conductive auxiliary agent to the surface of the current collector.

Binders include fluorine-containing resins 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. What is necessary is just to employ | adopt well-known things, such as rubber | gum.

Also, a polymer having a hydrophilic group may be employed as the binder. 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 phosphate group. Among them, a polymer containing a carboxyl group in a molecule such as polyacrylic acid, carboxymethylcellulose, or polymethacrylic acid, or a polymer containing a sulfo group such as poly (p-styrenesulfonic acid) is preferable.

Polymers containing a large amount of carboxyl groups and / or sulfo groups, such as polyacrylic acid or a copolymer 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 by, for example, a method of polymerizing an acid monomer or a method of imparting a carboxyl group to the polymer. Acid monomers include acrylic acid, methacrylic acid, vinyl benzoic acid, crotonic acid, pentenoic acid, angelic acid, tiglic acid, etc., acid monomers having one carboxyl group in the molecule, itaconic acid, mesaconic acid, citraconic acid, fumaric acid Examples include maleic acid, 2-pentenedioic acid, methylene succinic acid, allyl malonic acid, isopropylidene succinic acid, 2,4-hexadiene diacid, acetylenedicarboxylic acid, and other acid monomers having two or more carboxyl groups in the molecule. Is done.

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

Further, for example, a polymer containing in its molecule an acid anhydride group formed by condensation of carboxyl groups of a copolymer of acrylic acid and itaconic acid as described in JP2013-065493A It is also preferable to use 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 etc. before the electrolyte decomposition reaction occurs during charging. It is considered. Furthermore, since the polymer has more carboxyl groups per monomer than polyacrylic acid or polymethacrylic acid, the acidity is increased, but since the predetermined amount of carboxyl groups is changed to acid anhydride groups, the acidity is increased. Is not too high. Therefore, a secondary battery having a negative electrode using the polymer as a binder has improved initial efficiency and improved input / output characteristics.

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

Conductive aid is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent. The conductive auxiliary agent may be any chemically inert electronic high conductor, such as carbon black, graphite, acetylene black, ketjen black (registered trademark), or vapor grown carbon fiber (Vapor Grown Carbon). Fiber: VGCF) and various metal particles are exemplified. These conductive assistants can be added to the active material layer alone or in combination of two or more. The blending ratio of the conductive assistant in the active material layer is preferably, as a mass ratio, active material: conductive assistant = 1: 0.01 to 1: 0.5. This is because if the amount of the conductive auxiliary is too small, an efficient conductive path cannot be formed, and if the amount of the conductive auxiliary is too large, the moldability of the active material layer is deteriorated and the energy density of the electrode is lowered.

In order to form an active material layer on the surface of the current collector, a current collecting 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 can be used. An active material may be applied to the surface of the body. Specifically, an active material layer-forming composition containing an active material and, if necessary, a binder and a conductive aid is prepared, and an appropriate solvent is added to the composition to make a paste, and then the collection is performed. After applying to the surface of the electric body, it is 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 product may be compressed.

In the lithium ion secondary battery of the present invention, a separator is used as necessary. The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit of current due to contact between the two electrodes. A known separator may be employed, such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polyamide), polyester, polyacrylonitrile, or other synthetic resin, cellulose, amylose, or other polysaccharides, fibroin. And porous materials, nonwoven fabrics, woven fabrics, and the like using one or more electrical insulating materials such as natural polymers such as keratin, lignin, and suberin, and ceramics. The separator may have a multilayer structure.

The specific example of the manufacturing method of the lithium ion secondary battery of this invention is demonstrated.
If necessary, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. The electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched. After connecting the current collector of the positive electrode and the current collector of the negative electrode to the positive electrode terminal and the negative electrode terminal leading to the outside using a current collecting lead or the like, the electrolyte solution of the present invention is added to the electrode body and lithium ions are added. A secondary battery may be used. Moreover, the lithium ion secondary battery of this invention should just be charged / discharged in the voltage range suitable for the kind of active material contained in an electrode.

The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape 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 generated by a lithium ion secondary battery for all or a part of its power source. For example, the vehicle may be 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. Examples of devices equipped with lithium ion secondary batteries include various home appliances driven by batteries such as personal computers and portable communication devices, office devices, and industrial devices in addition to vehicles. Furthermore, the lithium ion secondary battery of the present invention includes wind power generation, solar power generation, hydroelectric power generation and other power system power storage devices and power smoothing devices, power supplies for ships and / or auxiliary power supply sources, aircraft, Power supply for spacecraft and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as a power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charging station for electric vehicles.

Incidentally, it is generally known that a film is formed on the surfaces of the negative electrode and the positive electrode in the secondary battery. The film is also referred to as SEI (Solid Electrolyte Interface) and is composed of a reductive decomposition product of an electrolytic solution. For example, Japanese Patent Application Laid-Open No. 2007-19027 describes an SEI film.

The SEI film on the negative electrode surface and the positive electrode surface allows passage of charge carriers such as lithium ions. In addition, the SEI film on the negative electrode surface exists between the negative electrode surface and the electrolytic solution, and is considered to suppress further reductive decomposition of the electrolytic solution. In particular, the presence of a SEI film is considered essential for a low potential negative electrode using graphite or a Si-based negative electrode active material.

If the continuous decomposition of the electrolytic solution is suppressed due to the presence of the SEI film, it is considered that the discharge characteristics of the secondary battery after the charge / discharge cycle elapses can be improved. However, on the other hand, in the conventional secondary battery, the SEI film on the negative electrode surface and the positive electrode surface did not necessarily contribute to the improvement of the battery characteristics.

In the electrolytic solution of the present invention, the chemical structure of the general formula (1) of the metal salt contains SO ₂ . And it is estimated that a part of said metal salt decomposes | disassembles by charging / discharging of the lithium ion secondary battery of this invention, and an S and O containing film | membrane is formed in the surface of a positive electrode and / or a negative electrode. It is presumed that the S and O-containing coating has an S = O structure. Since the electrode is covered with the film, the deterioration of the electrode and the electrolytic solution is suppressed, and as a result, the durability of the lithium ion secondary battery of the present invention is considered to be improved.

In the electrolytic solution of the present invention, a cation and an anion are present in the vicinity compared to the conventional electrolytic solution, and the anion is more easily reduced and decomposed than the conventional electrolytic solution by being strongly affected by electrostatic influence from the cation. It is considered to be. . In a conventional secondary battery using a conventional electrolytic solution, an SEI film is constituted by a decomposition product generated by reductive decomposition of cyclic carbonate such as ethylene carbonate contained in the electrolytic solution. However, as described above, in the electrolytic solution of the present invention contained in the secondary battery of the present invention, the anion is easily reduced and decomposed, and the metal salt is contained at a higher concentration than the conventional electrolytic solution. High anion concentration. For this reason, it is considered that the SEI film, that is, the S and O-containing film in the lithium ion secondary battery of the present invention contains a large amount derived from anions. In the lithium ion secondary battery of the present invention, the SEI film can be formed without using a cyclic carbonate such as ethylene carbonate.

In addition, the S and O-containing coating in the lithium ion secondary battery of the present invention may change state with charge / discharge. For example, depending on the state of charge and discharge, the thickness of the S and O-containing coating and the ratio of elements in the coating may change reversibly. For this reason, the S and O-containing film in the lithium ion secondary battery of the present invention has a part derived from the above-described anion decomposition product and fixed in the film, and a part that reversibly increases and decreases with charge and discharge. Presumed to exist.

In addition, since it is thought that S and O containing membrane | film | coat originates in the decomposition product of electrolyte solution, it is thought that most or all of S and O containing membrane | film | coats produce | generate after the first charge / discharge of a secondary battery. That is, the lithium ion secondary battery of the present invention has an S and O containing film on the surface of the negative electrode and / or the surface of the positive electrode in use. It is considered that the constituent components of the S and O-containing coating may differ depending on the components contained in the electrolytic solution, the composition of the electrode, and the like. In the S and O-containing film, the content ratio of S and O is not particularly limited. Furthermore, components and amounts other than S and O contained in the S and O-containing coating are not particularly limited. Since it is considered that the S and O-containing film is mainly derived from the anion of the metal salt contained in the electrolytic solution of the present invention, it is preferable that the component derived from the anion of the metal salt is contained more than the other components.

The S and O-containing film may be formed only on the negative electrode surface, or may be formed only on the positive electrode surface. The S and O-containing coating is preferably formed on both the negative electrode surface and the positive electrode surface.

The lithium ion secondary battery of the present invention has an S and O containing film on the electrode, and the S and O containing film has an S═O structure and is thought to contain many cations. And it is thought that the cation contained in the S and O containing film is preferentially supplied to the electrode. Therefore, since the lithium ion secondary battery of the present invention has an abundant cation source in the vicinity of the electrode, it is considered that the cation transport rate is also improved in this respect. Therefore, in the lithium ion secondary battery of this invention, it is thought that the outstanding battery characteristic is exhibited by cooperation with the electrolyte solution of this invention, and the S and O containing film | membrane of an electrode.

As mentioned above, although embodiment of the lithium ion secondary battery of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art. Further, in the description of the lithium ion secondary battery of the present invention, a part or all of the negative electrode active material and / or a part of the positive electrode active material is replaced with activated carbon or the like used as a polarizable electrode material. A hybrid capacitor such as an ion capacitor may be used.

Hereinafter, the present invention will be specifically described with reference to examples and comparative examples. In addition, this invention is not limited by these Examples. In the following, unless otherwise specified, “part” means part by mass, and “%” means mass%.

Example 1-1
A metal salt (FSO ₂ ) ₂ NLi is dissolved in dimethyl carbonate, which is a specific organic solvent, to produce an electrolyte solution of Example 1-1 in which the concentration of (FSO ₂ ) ₂ NLi is 3.0 mol / L. did. In the electrolyte solution of Example 1-1, the molar ratio of the organic solvent to the metal salt is 3.

Example 1-2
A metal salt (FSO ₂ ) ₂ NLi is dissolved in dimethyl carbonate, which is a specific organic solvent, to produce an electrolytic solution of Example 1-2 in which the concentration of (FSO ₂ ) ₂ NLi is 2.7 mol / L. did. In the electrolytic solution of Example 1-2, the molar ratio of the organic solvent to the metal salt is 3.5.

(Example 1-3)
A metal salt (FSO ₂ ) ₂ NLi is dissolved in dimethyl carbonate, which is a specific organic solvent, to produce an electrolytic solution of Example 1-3 in which the concentration of (FSO ₂ ) ₂ NLi is 2.3 mol / L. did. In the electrolytic solution of Example 1-3, the molar ratio of the organic solvent to the metal salt is 4.

(Example 1-4)
A metal salt (FSO ₂ ) ₂ NLi is dissolved in dimethyl carbonate, which is a specific organic solvent, to produce an electrolyte solution of Example 1-4 in which the concentration of (FSO ₂ ) ₂ NLi is 2.0 mol / L. did. In the electrolytic solution of Example 1-4, the molar ratio of the organic solvent to the metal salt is 5.

Example 2-1
Certain organic solvents in which dimethyl carbonate and a specific organic solvent in which diethyl carbonate 9: a solvent mixture in a molar ratio of a metal salt by _{(FSO 2)} dissolving the _{2 NLi, (FSO 2) 2} NLi An electrolyte solution of Example 2-1 having a concentration of 2.9 mol / L was produced. In the electrolyte solution of Example 2-1, the molar ratio of the organic solvent to the metal salt is 3.

(Example 2-2)
Certain organic solvents in which dimethyl carbonate and a specific organic solvent in which diethyl carbonate 7: a solvent mixture in a molar ratio of a metal salt by _{(FSO 2)} dissolving the _{2 NLi, (FSO 2) 2} NLi An electrolyte solution of Example 2-2 having a concentration of 2.9 mol / L was produced. In the electrolytic solution of Example 2-2, the molar ratio of the organic solvent to the metal salt is 3.

(Example 3)
(FSO ₂ ) ₂ NLi, which is a metal salt, is dissolved in a mixed solvent in which dimethyl carbonate, which is a specific organic solvent, and propylene carbonate, which is another hetero organic solvent, are mixed at a molar ratio of 7: 1, and (FSO ₂ ) ₂ The electrolytic solution of Example 3 having a concentration of NLi of 3.0 mol / L was produced. In the electrolytic solution of Example 3, the molar ratio of the organic solvent to the metal salt is 3.

Example 4
A metal salt (FSO ₂ ) ₂ NLi is dissolved in a mixed solvent in which dimethyl carbonate, which is a specific organic solvent, and ethylene carbonate, which is another hetero organic solvent, are mixed at a molar ratio of 7: 1, and (FSO ₂ ) ₂ The electrolytic solution of Example 4 having a concentration of NLi of 3.0 mol / L was produced. In the electrolyte solution of Example 4, the molar ratio of the organic solvent to the metal salt is 3.1.

(Example 5)
(FSO ₂ ) ₂ NLi, which is a metal salt, was dissolved in ethyl methyl carbonate, which is a specific organic solvent, to produce an electrolyte solution of Example 5 in which the concentration of (FSO ₂ ) ₂ NLi was 2.2 mol / L. . In the electrolytic solution of Example 5, the molar ratio of the organic solvent to the metal salt is 3.5.

(Example 6)
(FSO ₂ ) ₂ NLi, which is a metal salt, was dissolved in diethyl carbonate, which is a specific organic solvent, to produce an electrolyte solution of Example 6 in which the concentration of (FSO ₂ ) ₂ NLi was 2.0 mol / L. In the electrolytic solution of Example 6, the molar ratio of the organic solvent to the metal salt is 3.5.

Example 7-1
(FSO ₂ ) ₂ NLi, which is a metal salt, was dissolved in acetonitrile, which is a specific organic solvent, to produce an electrolyte solution of Example 7-1 in which the concentration of (FSO ₂ ) ₂ NLi was 4.0 mol / L. . In the electrolytic solution of Example 7-1, the molar ratio of the organic solvent to the metal salt is 3.

(Example 7-2)
(FSO ₂ ) ₂ NLi, which is a metal salt, was dissolved in acetonitrile, which is a specific organic solvent, to produce an electrolyte solution of Example 7-2 in which the concentration of (FSO ₂ ) ₂ NLi was 3.0 mol / L. . In the electrolytic solution of Example 7-2, the molar ratio of the organic solvent to the metal salt is 4.7.

Example 8-1
(FSO ₂ ) ₂ NLi which is a metal salt is dissolved in 1,2-dimethoxyethane which is a specific organic solvent, and the concentration of (FSO ₂ ) ₂ NLi is 2.4 mol / L. An electrolyte was produced. In the electrolytic solution of Example 8-1, the molar ratio of the organic solvent to the metal salt is 3.3.

(Example 8-2)
In Example 8-2, the metal salt (FSO ₂ ) ₂ NLi is dissolved in 1,2-dimethoxyethane, which is a specific organic solvent, and the concentration of (FSO ₂ ) ₂ NLi is 2.0 mol / L. An electrolyte was produced. In the electrolytic solution of Example 8-2, the molar ratio of the organic solvent to the metal salt is 4.

Example 9
(CF ₃ SO ₂ ) ₂ NLi which is a metal salt is dissolved in acetonitrile which is a specific organic solvent, and the electrolytic solution of Example 9 in which the concentration of (CF ₃ SO ₂ ) ₂ NLi is 3.0 mol / L is obtained. Manufactured. In the electrolytic solution of Example 9, the molar ratio of the organic solvent to the metal salt is 3.5.

(Example 10)
Example in which (CF ₃ SO ₂ ) ₂ NLi as a metal salt is dissolved in 1,2-dimethoxyethane as a specific organic solvent, and the concentration of (CF ₃ SO ₂ ) ₂ NLi is 1.6 mol / L Ten electrolyte solutions were produced. In the electrolytic solution of Example 10, the molar ratio of the organic solvent to the metal salt is 4.7.

(Example 11-1)
Certain organic solvents in which dimethyl carbonate and a specific organic solvent in which ethylmethyl carbonate 9: a solvent mixture in a molar ratio of a metal salt by _{(FSO 2)} dissolving the ₂ NLi, _{(FSO 2)} 2 An electrolyte solution of Example 11-1 having an NLi concentration of 2.9 mol / L was produced. In the electrolytic solution of Example 11-1, the molar ratio of the organic solvent to the metal salt is 3.

(Example 11-2)
Certain organic solvents in which dimethyl carbonate and a specific organic solvent in which ethylmethyl carbonate 9: a solvent mixture in a molar ratio of a metal salt by _{(FSO 2)} dissolving the ₂ NLi, _{(FSO 2)} 2 An electrolyte solution of Example 11-2 having an NLi concentration of 2.6 mol / L was produced. In the electrolytic solution of Example 11-2, the molar ratio of the organic solvent to the metal salt is 3.6.

(Comparative Example 1)
An attempt was made to dissolve (FSO ₂ ) ₂ NLi, which is a metal salt, in toluene, and to produce an electrolytic solution in which the molar ratio of toluene to the metal salt corresponds to the electrolytic solution of the present invention, but (FSO ₂ ) ₂ NLi was It did not dissolve and became a suspension.

(Comparative Example 2)
Hexane is a metal salt by dissolving _{(FSO 2) 2} NLi, although the molar ratio of hexane and metal salt was attempted to manufacture an electrolyte corresponding to become an electrolytic solution of the present _{invention, (FSO 2) 2} NLi is It did not dissolve and became a suspension.

(Comparative Example 3-1)
A metal salt (FSO ₂ ) ₂ NLi is dissolved in dimethyl carbonate, which is a specific organic solvent, to produce an electrolytic solution of Comparative Example 3-1 in which the concentration of (FSO ₂ ) ₂ NLi is 4.5 mol / L. did. In the electrolytic solution of Comparative Example 3-1, the molar ratio of the organic solvent to the metal salt is 1.6.

(Comparative Example 3-2)
A metal salt (FSO ₂ ) ₂ NLi is dissolved in dimethyl carbonate, which is a specific organic solvent, to produce an electrolytic solution of Comparative Example 3-2 in which the concentration of (FSO ₂ ) ₂ NLi is 3.9 mol / L. did. In the electrolytic solution of Comparative Example 3-2, the molar ratio of the organic solvent to the metal salt is 2.

(Comparative Example 3-3)
A metal salt (FSO ₂ ) ₂ NLi is dissolved in dimethyl carbonate, which is a specific organic solvent, to produce an electrolytic solution of Comparative Example 3-3 in which the concentration of (FSO ₂ ) ₂ NLi is 1.0 mol / L. did. In the electrolytic solution of Comparative Example 3-3, the molar ratio of the organic solvent to the metal salt is 11.

(Comparative Example 4-1)
A metal salt (FSO ₂ ) ₂ NLi was dissolved in acetonitrile, which is a specific organic solvent, to produce an electrolytic solution of Comparative Example 4-1, in which the concentration of (FSO ₂ ) ₂ NLi was 5.0 mol / L. . In the electrolytic solution of Comparative Example 4-1, the molar ratio of the organic solvent to the metal salt is 2.1.

(Comparative Example 4-2)
(FSO ₂ ) ₂ NLi, which is a metal salt, was dissolved in acetonitrile, which is a specific organic solvent, to produce an electrolytic solution of Comparative Example 4-2 in which the concentration of (FSO ₂ ) ₂ NLi was 4.5 mol / L. . In the electrolytic solution of Comparative Example 4-2, the molar ratio of the organic solvent to the metal salt is 2.4.

(Comparative Example 4-3)
(FSO ₂ ) ₂ NLi, which is a metal salt, was dissolved in acetonitrile, which is a specific organic solvent, to produce an electrolytic solution of Comparative Example 4-3 in which the concentration of (FSO ₂ ) ₂ NLi was 2.0 mol / L. . In the electrolytic solution of Comparative Example 4-3, the molar ratio of the organic solvent to the metal salt is 7.9.

(Comparative Example 4-4)
A metal salt (FSO ₂ ) ₂ NLi was dissolved in acetonitrile, which is a specific organic solvent, to produce an electrolytic solution of Comparative Example 4-4 in which the concentration of (FSO ₂ ) ₂ NLi was 1.0 mol / L. . In the electrolytic solution of Comparative Example 4-4, the molar ratio of the organic solvent to the metal salt is 17.

(Comparative Example 5-1)
In the specific organic solvent 1,2-dimethoxyethane, the metal salt (FSO ₂ ) ₂ NLi was dissolved, and the concentration of (FSO ₂ ) ₂ NLi was 4.0 mol / L. An electrolyte was produced. In the electrolytic solution of Comparative Example 5-1, the molar ratio of the organic solvent to the metal salt is 1.5.

(Comparative Example 5-2)
(FSO ₂ ) ₂ NLi as a metal salt is dissolved in 1,2-dimethoxyethane as a specific organic solvent, and the concentration of (FSO ₂ ) ₂ NLi is 3.6 mol / L. An electrolyte was produced. In the electrolytic solution of Comparative Example 5-2, the molar ratio of the organic solvent to the metal salt is 1.9.

(Comparative Example 5-3)
In Comparative Example 5-3, the metal salt (FSO ₂ ) ₂ NLi is dissolved in 1,2-dimethoxyethane, which is a specific organic solvent, and the concentration of (FSO ₂ ) ₂ NLi is 1.0 mol / L. An electrolyte was produced. In the electrolytic solution of Comparative Example 5-3, the molar ratio of the organic solvent to the metal salt is 8.8.

(Comparative Example 5-4)
In Comparative Example 5-4, the metal salt (FSO ₂ ) ₂ NLi is dissolved in 1,2-dimethoxyethane, which is a specific organic solvent, and the concentration of (FSO ₂ ) ₂ NLi is 0.5 mol / L. An electrolyte was produced. In the electrolytic solution of Comparative Example 5-4, the molar ratio of the organic solvent to the metal salt is 18.

(Comparative Example 5-5)
In Comparative Example 5-5, the metal salt (FSO ₂ ) ₂ NLi is dissolved in 1,2-dimethoxyethane, which is a specific organic solvent, and the concentration of (FSO ₂ ) ₂ NLi is 0.1 mol / L. An electrolyte was produced. In the electrolytic solution of Comparative Example 5-5, the molar ratio of the organic solvent to the metal salt is 93.

(Comparative Example 6)
LiPF ₆ as an electrolyte was dissolved in dimethyl carbonate as a specific organic solvent to produce an electrolytic solution of Comparative Example 6 having a LiPF ₆ concentration of 3.2 mol / L. In the electrolytic solution of Comparative Example 6, the molar ratio of the organic solvent to the electrolyte is 3.

(Comparative Example 7)
LiBF ₄ as an electrolyte was dissolved in dimethyl carbonate as a specific organic solvent to produce an electrolytic solution of Comparative Example 7 having a LiBF ₄ concentration of _3.4 mol / L. In the electrolytic solution of Comparative Example 7, the molar ratio of the organic solvent to the electrolyte is 3.

(Comparative Example 8)
LiPF ₆ as an electrolyte is dissolved in a mixed solvent in which diethyl carbonate as a specific organic solvent and ethylene carbonate as another hetero organic solvent are mixed at a volume ratio of 7: 3, so that the concentration of LiPF ₆ is 1.0 mol / The electrolyte solution of Comparative Example 8 which is L was produced. In the electrolytic solution of Comparative Example 8, the molar ratio of the organic solvent to the electrolyte is approximately 10.

(Comparative Example 9-1)
(FSO ₂ ) ₂ NLi which is a metal salt is dissolved in a mixed solvent in which dimethyl carbonate which is a specific organic solvent and propylene carbonate which is another hetero organic solvent are mixed at a molar ratio of 95: 5, and (FSO ₂ ) ₂ An electrolytic solution of Comparative Example 9-1 having a concentration of NLi of 4.0 mol / L was produced. In the electrolytic solution of Comparative Example 9-1, the molar ratio of the organic solvent to the metal salt is 2.

(Comparative Example 9-2)
(FSO ₂ ) ₂ NLi, which is a metal salt, is dissolved in a mixed solvent in which dimethyl carbonate, which is a specific organic solvent, and propylene carbonate, which is another hetero organic solvent, are mixed at a molar ratio of 90:10, and (FSO ₂ ) ₂ An electrolytic solution of Comparative Example 9-2 having a concentration of NLi of 4.0 mol / L was produced. In the electrolytic solution of Comparative Example 9-2, the molar ratio of the organic solvent to the metal salt is 2.

(Comparative Example 9-3)
(FSO ₂ ) ₂ NLi, which is a metal salt, is dissolved in a mixed solvent obtained by mixing dimethyl carbonate, which is a specific organic solvent, and propylene carbonate, which is another hetero organic solvent, in a molar ratio of 80:20, and (FSO ₂ ) ₂ An electrolytic solution of Comparative Example 9-3 having a concentration of NLi of 4.0 mol / L was produced. In the electrolytic solution of Comparative Example 9-3, the molar ratio of the organic solvent to the metal salt is 2.

(Comparative Example 9-4)
(FSO ₂ ) ₂ NLi, which is a metal salt, is dissolved in a mixed solvent in which dimethyl carbonate, which is a specific organic solvent, and propylene carbonate, which is another hetero organic solvent, are mixed at a molar ratio of 50:50, and (FSO ₂ ) ₂ An electrolytic solution of Comparative Example 9-4 having a concentration of NLi of 4.0 mol / L was produced. In the electrolytic solution of Comparative Example 9-4, the molar ratio of the organic solvent to the metal salt is 2.

(Comparative Example 10)
Ethylene carbonate is dimethyl carbonate and ethyl methyl carbonate and other hetero organic solvent which is a specific organic solvent 4: 3: a solvent mixture in a volume ratio of 3, by dissolving LiPF ₆ as the electrolyte, the LiPF ₆ An electrolytic solution of Comparative Example 10 having a concentration of 1.0 mol / L was produced. In the electrolytic solution of Comparative Example 10, the molar ratio of the organic solvent to the metal salt is approximately 10.

Table 3-1 shows a list of the electrolyte solutions of the examples, and Table 3-2 shows a list of the electrolyte solutions of the comparative examples. From the results of Comparative Examples 1 and 2, it can be said that an organic solvent not containing a hetero element such as toluene or hexane cannot suitably dissolve the metal salt.

The meanings of the abbreviations in Table 3-1 and the following table are as follows.
LiFSA: (FSO ₂ ) ₂ NLi
LiTFSA: (CF ₃ SO ₂ ) ₂ NLi
DMC: Dimethyl carbonate EMC: Ethyl methyl carbonate DEC: Diethyl carbonate AN: Acetonitrile DME: 1,2-Dimethoxyethane PC: Propylene carbonate EC: Ethylene carbonate

(Evaluation Example 1: Ionic conductivity)
The ionic conductivity of the electrolyte solutions of Examples and Comparative Examples was measured under the following conditions. The results are shown in Tables 4-1 and 4-2. The blank in the table means no measurement.

Ionic conductivity measurement conditions In an Ar atmosphere, an electrolytic solution was sealed in a glass cell with a platinum constant and a known cell constant, and impedance at 30 ° C. and 1 kHz was measured. The ion conductivity was calculated from the impedance measurement result. As the measuring instrument, Solartron 147055BEC (Solartron) was used.

The electrolyte solutions of the examples all showed suitable ionic conductivity. Therefore, it can be understood that any of the electrolytic solutions of the present invention can function as an electrolytic solution for various power storage devices. Further, looking at the results of the electrolytic solutions of Example 1-1, Comparative Example 6, and Comparative Example 7, the metal salt used in the electrolytic solution of the present invention exhibits a suitable ionic conductivity as compared with other electrolytes. I understand that. In addition, the results of the electrolyte solutions of Example 1-1, Example 3, and Example 4 show that when a hetero element-containing organic solvent in which a part of the specific organic solvent is substituted with another hetero organic solvent is used. It can be seen that the ionic conductivity decreases.

Here, for the electrolytes of Examples 1-1 and 1-4 and Comparative Examples 3-1 to 3-3, where the metal salt is LiFSA and the specific organic solvent is DMC belonging to a chain carbonate, the specific organic solvent The relationship between the molar ratio of the metal salt and the ionic conductivity was graphed. The graph is shown in FIG.

From FIG. 1, in the electrolyte solution in which the metal salt is LiFSA and the specific organic solvent is DMC belonging to the chain carbonate, the maximum value of ionic conductivity is within the range of the molar ratio of the specific organic solvent to the metal salt in the range of 3 to 5. It is suggested that

(Evaluation Example 2: Density)
The density at 20 ° C. of the electrolyte solutions of Examples and Comparative Examples was measured. The results are shown in Table 5-1 and Table 5-2. The blank in the table means no measurement.

(Evaluation Example 3: Viscosity)
The viscosity of the electrolyte solution of an Example and a comparative example was measured on condition of the following. The results are shown in Table 6-1 and Table 6-2.

Viscosity measurement conditions Using a falling ball viscometer (Lovis 2000 M manufactured by Anton Paar GmbH (Anton Paar)), an electrolytic solution was sealed in a test cell under an Ar atmosphere, and the viscosity was measured at 30 ° C.

It can be seen that the viscosity of the electrolyte solution of the example is neither too low nor too high. It can be seen that the electrolyte solution outside the range of the molar ratio between the specific organic solvent and the metal salt defined by the electrolyte solution of the present invention may have a viscosity that is too low or too high. If the viscosity of the electrolytic solution is too low, there is a concern that a large amount of the electrolytic solution leaks when a power storage device including such an electrolytic solution is damaged. On the other hand, when the viscosity of the electrolytic solution is too high, there is a concern that the ionic conductivity of the electrolytic solution is lowered, and there is a concern that productivity is lowered because the permeability of the electrolytic solution to the electrode, the separator, or the like is inferior when the power storage device is manufactured.

In addition, the results of the electrolyte solutions of Example 1-1, Example 3, and Example 4 show that when a hetero element-containing organic solvent in which a part of the specific organic solvent is substituted with another hetero organic solvent is used. It can be seen that the viscosity increases.

(Evaluation Example 4: Low temperature storage test)
The electrolytic solutions of Example 1-1, Example 1-3, Example 1-4, Comparative Example 3-2, and Comparative Example 3-3 were placed in containers, filled with an inert gas, and sealed. These were stored in a freezer at −20 ° C. for 2 days. Each electrolyte was observed after storage. The results are shown in Table 7.

It turns out that it becomes easy to solidify at low temperature, so that the value of the molar ratio of a specific organic solvent and a metal salt becomes large, ie, it approaches the conventional value. Although the electrolytic solution of Example 1-4 was solidified by storing at −20 ° C. for 2 days, it was difficult to solidify as compared with the electrolytic solution of Comparative Example 3-3, which is a conventional concentration electrolytic solution. I can say that.

(Example A)
A half cell using the electrolyte solution of Example 1-1 was produced as follows.
An aluminum foil (JIS A1000 series) having a diameter of 13.82 mm, an area of 1.5 cm ² and a thickness of 20 μm was used as a working electrode, and the counter electrode was metal Li. As the separator, Whatman glass filter nonwoven fabric having a thickness of 400 μm: product number 1825-055 was used.
A working cell, a counter electrode, a separator, and the electrolyte solution of Example 1-1 were accommodated in a battery case (CR2032 type coin cell case manufactured by Hosen Co., Ltd.) to form a half cell. This was designated as the half cell of Example A.

(Comparative Example A)
A half cell of Comparative Example A was produced in the same manner as the half cell of Example A, except that the electrolytic solution of Comparative Example 3-3 was used.

(Evaluation example A: cyclic voltammetry evaluation with working electrode Al)
For the half cells of Example A and Comparative Example A, cyclic voltammetry evaluation was performed for 10 cycles under the conditions of 3.0 V to 4.5 V and 1 mV / s, and then 3.0 V to 5.0 V, 1 mV / s. The cyclic voltammetry evaluation of 10 cycles was performed on condition of s. Graphs showing the relationship between the potential and response current for the half cells of Example A and Comparative Example A are shown in FIGS.

4 and 5, it can be seen that in the half cell of Comparative Example A, the current flows from 3.0 V to 4.5 V after the second cycle, and the current increases as the potential increases. This current is presumed to be the oxidation current of Al due to the corrosion of the working electrode aluminum.

2 and 3, it can be seen that in the half cell of Example A, almost no current flows from 3.0 V to 4.5 V after 2 cycles. In particular, after the third cycle, there is almost no increase in current up to 4.5V. In the half cell of Example A, an increase in current is observed after 4.5 V, which is a high potential, which is much smaller than the current value after 4.5 V in the half cell of Comparative Example A. .

From the results of the cyclic voltammetry evaluation, it can be said that the corrosiveness and oxidative decomposability of the electrolytic solution of Example 1-1 to aluminum are low even under a high potential condition of at least about 4.5V. That is, the electrolytic solution of Example 1-1 can be said to be a preferable electrolytic solution for a power storage device using aluminum as a current collector or the like.

(Reference Example A)
A half cell using the electrolytic solution of Comparative Example 3-2 was produced as follows.
90 parts by mass of graphite having an average particle diameter of 10 μm as an active material and 10 parts by mass of polyvinylidene fluoride as a binder were mixed. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. A copper foil having a thickness of 20 μm was prepared as a current collector. 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 joined product was heat-dried at 120 ° C. for 6 hours with a vacuum dryer to obtain a copper foil on which an active material layer was formed. This was the working electrode.

The counter electrode was metal Li.

A working cell, a counter electrode, a 400 μm-thick Whatman glass fiber filter paper as a separator sandwiched between them, and the electrolyte of Comparative Example 3-2 are accommodated in a battery case (CR2032 type coin cell case manufactured by Hosen Co., Ltd.) and a half cell. Configured. This was designated as the half cell of Reference Example A.

(Reference Example B)
A half cell of Reference Example B was produced in the same manner as Reference Example A, except that the electrolyte of Comparative Example 9-1 was used as the electrolyte.

(Reference Example C)
A half cell of Reference Example C was produced in the same manner as Reference Example A, except that the electrolyte of Comparative Example 9-2 was used as the electrolyte.

(Reference Example D)
A half cell of Reference Example D was produced in the same manner as Reference Example A, except that the electrolyte of Comparative Example 9-3 was used as the electrolyte.

(Reference Example E)
A half cell of Reference Example E was produced in the same manner as Reference Example A, except that the electrolyte of Comparative Example 9-4 was used as the electrolyte.

(Reference evaluation example A: rate capacity test)
The rate capacities of the half cells of Reference Examples A to E were tested by the following method.
For each half-cell, discharging from 2.0 V to 0.01 V and charging from 0.01 V to 2.0 V are performed at 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, 5 C, 10 C, and 0. A charge / discharge cycle test was performed three times for each rate in the order of 1C rate. Table 8 shows the results of calculating the ratio of the second discharge capacity at the 5C rate and the 10C rate to the first discharge capacity at the first 0.1C rate. In this description, the counter electrode is regarded as a negative electrode and the working electrode is regarded as a positive electrode. 1C means a current value required to fully charge or discharge a battery in one hour at a constant current.

From Table 8, in the heteroelement-containing organic solvent of the electrolytic solution, as the ratio of the specific organic solvent decreases, in other words, as the ratio of the other heteroorganic solvent exhibiting a high dielectric constant and a high dipole moment increases, It can be seen that the capacity at the high rate decreases. This fact suggests that the reaction resistance at the electrode increases as the ratio of the specific organic solvent decreases or the ratio of the other hetero organic solvent increases in the heteroelement-containing organic solvent of the electrolyte. Yes.

(Reference Example I)
A lithium ion secondary battery of Reference Example I using the electrolyte solution of Example 1-1 was produced as follows.

90 parts by mass of a lithium-containing metal oxide having a layered rock salt structure represented by LiNi _5/10 Co _2/10 Mn _3/10 O _{2 as} a positive electrode active material, 8 parts by mass of acetylene black as a conductive auxiliary agent, and a binder 2 parts by mass of polyvinylidene fluoride as an agent was mixed. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. An aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector. The slurry was applied to the surface of the aluminum foil using a doctor blade so as to form a film. The aluminum foil coated with the slurry was dried at 80 ° C. for 20 minutes to remove N-methyl-2-pyrrolidone by volatilization. Thereafter, this aluminum foil was pressed to obtain a bonded product. The obtained joined product was heat-dried at 120 ° C. for 6 hours with a vacuum dryer to obtain an aluminum foil on which a positive electrode active material layer was formed. This was used as a positive electrode.

98 parts by mass of spherical graphite as a negative electrode active material, 1 part by mass of styrene butadiene rubber as a binder, and 1 part by mass of carboxymethyl cellulose were mixed. This mixture was dispersed in an appropriate amount of ion-exchanged water to prepare a slurry. A copper foil having a thickness of 20 μm was prepared as a negative electrode current collector. 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 water, and then the copper foil was pressed to obtain a bonded product. The obtained joined product was dried by heating at 100 ° C. for 6 hours with a vacuum dryer to obtain a copper foil on which a negative electrode active material layer was formed. This was used as a negative electrode.

A cellulose nonwoven fabric having a thickness of 20 μm was prepared as a separator.

A separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, the three sides were sealed, and then the electrolyte solution of Example 1-1 was poured into the bag-like laminated film. Thereafter, the remaining one side was sealed to obtain a lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. This battery was a lithium ion secondary battery of Reference Example I.

(Reference Example II)
A lithium ion secondary battery of Reference Example II was obtained in the same manner as Reference Example I, except that the electrolyte of Example 1-3 was used as the electrolyte.

(Reference Comparative Example I)
A lithium ion secondary battery of Reference Comparative Example I was obtained in the same manner as Reference Example I, except that the electrolyte of Comparative Example 3-2 was used as the electrolyte.

(Reference Comparative Example II)
A lithium ion secondary battery of Reference Comparative Example II was obtained in the same manner as Reference Example I, except that the electrolyte of Comparative Example 4-2 was used as the electrolyte.

(Reference Comparative Example III)
A lithium ion secondary battery of Reference Comparative Example III was obtained in the same manner as Reference Example I, except that the electrolytic solution of Comparative Example 8 was used as the electrolytic solution.

(Reference Evaluation Example I: Internal resistance of battery)
For the lithium ion secondary batteries of Reference Examples I to II and Reference Comparative Examples I to III, the internal resistance of the batteries was evaluated by the following method.
For each lithium ion secondary battery, CC charge / discharge, that is, constant current charge / discharge was repeated at room temperature in the range of 3.0 V to 4.1 V (vs. Li standard). And the alternating current impedance after the first charge / discharge and the alternating current impedance after 100 cycles progress were measured. Based on the obtained complex impedance plane plot, the reaction resistances of the electrolytic solution, the negative electrode, and the positive electrode were each analyzed. As shown in FIG. 6, two arcs were seen in the complex impedance plane plot. The arc on the left side in FIG. 6, that is, the side where the real part of the complex impedance is small is called a first arc. The arc on the right side in FIG. 6 is called the second arc. The reaction resistance of the negative electrode was analyzed based on the size of the first arc, and the reaction resistance of the positive electrode was analyzed based on the size of the second arc. The resistance of the electrolytic solution was analyzed based on the leftmost plot in FIG. 6 continuous with the first arc. The analysis results are shown in Tables 9 and 10. Table 9 shows the resistance (so-called solution resistance) of the electrolytic solution after the first charge / discharge, the reaction resistance of the negative electrode, and the reaction resistance of the positive electrode, and Table 10 shows each resistance after 100 cycles.

From the results of Reference Example I, Reference Example II, and Reference Comparative Example I in Table 9, it can be seen that the solution resistance decreases as the molar ratio of the specific organic solvent to the metal salt increases. When considered together with the results of ionic conductivity shown in Table 4 and FIG. 1, the electrolyte solution of the present invention within the range of the molar ratio of the specific organic solvent to the metal salt of 3 to 5 is suitable for both ionic conductivity and reaction resistance. It can be seen that the electrolyte solution satisfies the above. Further, the lithium ion secondary battery of Reference Comparative Example III had remarkably high positive electrode reaction resistance.

From Table 9 and Table 10, the lithium ion secondary battery comprising an electrolyte solution in which the specific organic solvent is DMC and the metal salt is LiFSA has a solution resistance, a negative electrode reaction resistance, and a positive electrode reaction resistance after charge / discharge cycles. It turns out that it is equivalent or falls compared with the initial stage. On the other hand, it can be seen that in the lithium ion secondary battery including the electrolyte in which the specific organic solvent is AN and the metal salt is LiFSA, the positive electrode reaction resistance after the charge / discharge cycle is increased compared to the initial stage.

(Reference Evaluation Example II: Capacity maintenance rate)
The capacity retention rates of the lithium ion secondary batteries of Reference Examples I to II and Reference Comparative Examples I to III were evaluated by the following method.
For each lithium ion secondary battery, CC charge / discharge was repeated at room temperature in the range of 3.0 V to 4.1 V (vs. Li standard). The discharge capacity at the first charge / discharge and the discharge capacity at 300 cycles were measured. And the capacity | capacitance maintenance factor (%) of each lithium ion secondary battery at the time of 300 cycles was computed by making the capacity | capacitance of each lithium ion secondary battery at the time of initial charge / discharge into 100%. The results are shown in Table 11.

The lithium ion secondary batteries of Reference Examples I to II showed a capacity maintenance rate equal to or higher than the lithium ion secondary batteries of Reference Comparative Examples I to III. It was confirmed that the lithium ion secondary battery comprising the electrolytic solution of the present invention exhibits excellent durability against charge / discharge cycles.

(Reference Evaluation Example III: Analysis of S and O-containing film of electrode)
The lithium ion secondary battery of Reference Example II passed through Reference Evaluation Example II and Reference Evaluation Example II was disassembled, and the positive electrode was taken out. The positive electrode was washed three times with dimethyl carbonate, dried, and then analyzed. It was. In addition, all the processes from the disassembly of the lithium ion secondary battery to the conveyance of the positive electrode as the analysis target to the analyzer were performed in an Ar gas atmosphere. The positive electrode to be analyzed was analyzed under the following conditions using X-ray photoelectron spectroscopy. FIG. 7 shows an analysis chart for the sulfur element, and FIG. 8 shows an analysis chart for the oxygen element. In each figure, the dotted line is the peak of the positive electrode of the lithium ion secondary battery of Reference Example II before Reference Evaluation Example II, and the solid line is the positive electrode of the lithium ion secondary battery of Reference Example II after Reference Evaluation Example II. It is a peak.

Device: ULVAC-PHI PHI5000 VersaProbeII
X-ray source: Monochromatic AlKα ray, voltage 15 kV, current 10 mA

7 and 8, it can be seen that an S- and O-containing coating is newly formed on the positive electrode of the lithium ion secondary battery of Reference Example II that has passed Reference Evaluation Example II. The peak near 170 eV observed in FIG. 7 is considered to be a peak derived from S═O bond. Therefore, it can be said that S = O bond exists in the S and O containing film of the positive electrode. The lithium ion secondary battery of Reference Example II includes a metal salt having S and S═O bond, and does not have any other one having S or S═O bond. And the S or S = O bond of the O-containing film can be said to be derived from the metal salt.

(Reference Evaluation Example IV: Confirmation of elution of Ni, Mn and Co)
For the lithium ion secondary batteries of Reference Example II and Reference Comparative Example II, the amounts of Ni, Mn, and Co deposited on the negative electrode were analyzed by the following method.
For each lithium ion secondary battery, constant current charging / discharging was repeated 200 times at a 1C rate in the range of 3.0V to 4.1V at 60 ° C. Thereafter, each lithium ion secondary battery was disassembled, and the negative electrode was taken out. The amount of Ni, Mn and Co deposited on the surface of the negative electrode was analyzed by high frequency inductively coupled plasma emission spectroscopy. Table 12 shows the measurement results. The amounts of Ni, Mn, and Co (%) in the table are the mass ratios of Ni, Mn, and Co in the negative electrode active material layer.

In the negative electrode of the lithium ion secondary battery of Reference Example II, the amounts of Ni, Mn, and Co were less than the detection limit of each element. On the other hand, Ni, Mn, and Co were all detected in the negative electrode of the lithium ion secondary battery of Reference Comparative Example II. Here, it is presumed that Ni, Mn, and Co detected from the negative electrode are eluted from the positive electrode into the electrolytic solution and deposited on the negative electrode. That is, in the lithium ion secondary battery of Reference Example II having the electrolytic solution of the present invention, it can be said that the transition metal of the positive electrode is extremely difficult to elute into the electrolytic solution of the present invention. In other words, it can be said that the electrolytic solution of the present invention suitably suppresses the elution of transition metal from the positive electrode.

(Reference Example III)
A lithium ion secondary battery of Reference Example III comprising the electrolyte solution of Example 1-2 was produced as follows.

90 parts by mass of LiNi _5/10 Co _2/10 Mn _3/10 O ₂ as a positive electrode active material, 8 parts by mass of acetylene black as a conductive additive, and 2 parts by mass of polyvinylidene fluoride as a binder were mixed. . This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. An aluminum foil corresponding to JIS A1000 series having a thickness of 20 μm was prepared as a positive electrode current collector. The slurry was applied to the surface of the aluminum foil using a doctor blade so as to form a film. The aluminum foil coated with the slurry was dried at 80 ° C. for 20 minutes to remove N-methyl-2-pyrrolidone. Thereafter, this aluminum foil was pressed to obtain a bonded product. The obtained joined product was heat-dried at 120 ° C. for 6 hours with a vacuum dryer to obtain an aluminum foil on which a positive electrode active material layer was formed. This was used as a positive electrode. The positive electrode active material layer was formed on the positive electrode current collector at 5.5 mg / cm ² per unit area of the coated surface, and the density of the positive electrode active material layer was 2.4 g / cm ³ .

As a negative electrode active material, 98 parts by mass of spherical graphite, 1 part by mass of styrene butadiene rubber as a binder and 1 part by mass of carboxymethyl cellulose were mixed. This mixture was dispersed in an appropriate amount of ion-exchanged water to prepare a slurry. A copper foil having a thickness of 20 μm was prepared as a negative electrode current collector. 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 water, and then the copper foil was pressed to obtain a bonded product. The obtained joined product was dried by heating at 100 ° C. for 6 hours with a vacuum dryer to obtain a copper foil on which a negative electrode active material layer was formed. This was used as a negative electrode. Note that the negative electrode active material layer was formed on the negative electrode current collector at 3.8 mg / cm ² per unit area of the coated surface, and the density of the negative electrode active material layer was 1.1 g / cm ³ .

A cellulose nonwoven fabric having a thickness of 20 μm was prepared as a separator.
A separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed. Then, the electrolytic solution of Example 1-2 was injected into the bag-like laminated film. Thereafter, the remaining one side was sealed to obtain a lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. This battery was designated as a lithium ion secondary battery of Reference Example III.

(Reference Example IV)
A lithium ion secondary battery of Reference Example IV was obtained in the same manner as Reference Example III, except that the electrolyte of Example 1-3 was used as the electrolyte.

(Reference Comparative Example IV)
A lithium ion secondary battery of Reference Comparative Example IV was obtained in the same manner as Reference Example III, except that the electrolyte of Comparative Example 3-2 was used as the electrolyte.

(Reference Comparative Example V)
A lithium ion secondary battery of Reference Comparative Example V was obtained in the same manner as Reference Example III, except that the electrolyte of Comparative Example 4-2 was used as the electrolyte.

(Reference Comparative Example VI)
A lithium ion secondary battery of Reference Comparative Example VI was obtained in the same manner as Reference Example III, except that the electrolytic solution of Comparative Example 8 was used as the electrolytic solution.

(Reference Evaluation Example V: Capacity maintenance ratio <2> and DC resistance)
The lithium ion secondary batteries of Reference Example III, Reference Example IV, and Reference Comparative Example IV to Reference Comparative Example VI were subjected to the following tests to evaluate the capacity retention rate and DC resistance.

For each lithium ion secondary battery, charge to 4.1 V at a constant current at a temperature of 25 ° C. and 1 C rate, pause for 1 minute, discharge to 3.0 V at a constant current at 1 C rate, and pause for 1 minute. The charge / discharge cycle was repeated 300 cycles. The capacity maintenance rate was calculated by the following formula.
Capacity maintenance rate (%) = 100 × (discharge capacity at 300 cycles) / (initial discharge capacity)

Also, for each lithium ion secondary battery after 300 cycles, the voltage was adjusted to 3.5 V at a constant current of 25 ° C. and a constant current of 0.5 C, and then discharged at a constant current of 10 seconds at a 3 C rate. From the voltage change amount and the current value, the direct current resistance during discharge was calculated according to Ohm's law.

Further, for each lithium ion secondary battery after 300 cycles, the voltage was adjusted to 3.5 V at a constant current of 25 ° C. and a constant current of 0.5 C, and then charged at a constant current of 10 seconds at a 3 C rate. The direct current resistance at the time of charging was calculated from the voltage change amount and the current value according to Ohm's law.

Table 13 shows the above test results.

From the results in Table 13, it can be seen that the lithium ion secondary battery comprising the electrolytic solution of the present invention suitably maintains the capacity even after the charge / discharge cycle and has a low DC resistance during charge / discharge. On the other hand, it can be seen that the lithium ion secondary batteries of Reference Comparative Example IV and Reference Comparative Example VI have a large DC resistance during charging and discharging, and the lithium ion secondary battery of Reference Comparative Example V is inferior in capacity retention.

(Reference Example V)
The lithium of Reference Example V was the same as Reference Example III, except that the electrolyte of Example 1-1 was used as the electrolyte and the density of the positive electrode active material layer was 2.3 g / cm ^3. An ion secondary battery was obtained.

(Reference Example VI)
A lithium ion secondary battery of Reference Example VI was obtained in the same manner as Reference Example V, except that the electrolyte of Example 2-1 was used as the electrolyte.

(Reference Example VII)
A lithium ion secondary battery of Reference Example VII was obtained in the same manner as Reference Example V, except that the electrolyte of Example 2-2 was used as the electrolyte.

(Reference Comparative Example VII)
A lithium ion secondary battery of Reference Comparative Example VII was obtained in the same manner as Reference Example V, except that the electrolytic solution of Comparative Example 8 was used as the electrolytic solution.

(Reference Evaluation Example VI: Capacity maintenance ratio <3> and DC resistance <2>)
The lithium ion secondary batteries of Reference Example V, Reference Example VI, Reference Example VII, and Reference Comparative Example VII were tested in the same manner as in Reference Evaluation Example V, and the capacity retention rate and DC resistance were evaluated. The results are shown in Table 14.

From the results shown in Table 14, it can be seen that the lithium ion secondary battery including the electrolytic solution of the present invention suitably maintains the capacity even after the charge / discharge cycle and has a low DC resistance during charge / discharge. On the other hand, it can be seen that the lithium ion secondary battery of Reference Comparative Example VII has a large DC resistance during charging and discharging.

(Production Example 1)
The lithium metal composite oxide of Production Example 1 was produced as follows.

a) Step Nickel sulfate, cobalt sulfate and manganese sulfate are dissolved in water, the molar ratio of Ni: Co: Mn is 5: 3: 2, and the total concentration of Ni, Co and Mn is 0.9 mol / L. A transition metal ion aqueous solution was prepared.

b) Process Water was put into a reaction vessel equipped with a stirrer and a nitrogen introduction tube, and heated to 50 ° C. with stirring. After replacing the reaction tank with nitrogen, an appropriate amount of 16% by mass sodium hydroxide aqueous solution and 28% by mass ammonia water was respectively added while maintaining the space in the reaction tank at an oxygen concentration of 0.1% or less under a nitrogen stream. A basic aqueous solution having a pH of 11.6 at a liquid temperature of 25 ° C. and an ammonia concentration of 9 g / L in the liquid phase was prepared.

c) Process b) The transition metal ion aqueous solution, 16 mass% sodium hydroxide aqueous solution, and 3 mass% aqueous ammonia are added to the basic aqueous solution in the reaction vessel under the same oxygen atmosphere as in the step b) under stirring conditions at a constant rate. By supplying each from a different inflow route, transition metal hydroxide particles were formed while maintaining the reaction solution at a pH of 11.6 and an ammonia concentration of 9 g / L, and the particles were crystallized from the reaction solution.

d) Step The reaction solution in the reaction vessel is concentrated, and the supply rate of the transition metal ion aqueous solution, 16% by mass sodium hydroxide aqueous solution and 3% by mass ammonia water is adjusted, and the reaction solution is adjusted to pH 11.4 and ammonia concentration The transition metal hydroxide particles were grown under stirring conditions while controlling the amount to 9 g / L.
After performing d) process so far twice, it filtered and washed with water, and the transition metal hydroxide particle was isolated. The transition metal hydroxide particles were heat-treated at 300 ° C. for 20 hours in an air atmosphere.

e) Step The transition metal hydroxide particles after the heat treatment and Li ₂ CO ₃ were mixed so that the molar ratio of (Ni + Co + Mn): Li was 1: 1.10 to obtain a mixture. The mixture was first fired at 600 ° C. for 16 hours, and then second fired at 840 ° C. for 5 hours to obtain a fired product. The fired product was crushed after cooling and classified by sieving to obtain a lithium metal composite oxide represented by Li _1.10 Ni _0.5 Co _0.3 Mn _0.2 O ₂ .

(Production Example 2)
In the same manner as in Production Example 1, except that the molar ratio of Ni: Co: Mn in the step a) was set to 50:35:15, and the second firing temperature in the step e) was set to 820 ° C., Li _1.10. A lithium metal composite oxide represented by Ni _0.5 Co _0.35 Mn _0.15 O ₂ was obtained. This was designated as the lithium metal composite oxide of Production Example 2.

(Production Example 3)
In the same manner as in Production Example 1, except that the molar ratio of Ni: Co: Mn in the step a) was set to 40:45:15, and the temperature of the second baking in the step e) was 830 ° C., Li _1.10. A lithium metal composite oxide represented by Ni _0.4 Co _0.45 Mn _0.15 O ₂ was obtained. This was designated as the lithium metal composite oxide of Production Example 3.

(Production Example 4)
a) step Ni: Co: the molar ratio of Mn to 20:65:15, except that the temperature of the second firing of step e) to 870 ° C. in a similar manner as in Preparation Example _{1, Li 1.10} A lithium metal composite oxide represented by Ni _0.2 Co _0.65 Mn _0.15 O ₂ was obtained. This was designated as the lithium metal composite oxide of Production Example 4.

(Production Example 5)
b) The same method as in Production Example 1 except that the oxygen concentration in the step was maintained at 0.5%, d) the heating temperature in the step was 120 ° C., and e) the step was as follows. Thus, a lithium metal composite oxide represented by Li _1.10 Ni _0.48 Co _0.29 Mn _0.19 Mg _0.04 O ₂ was obtained. This was designated as the lithium metal composite oxide of Production Example 5.
e) Step The transition metal hydroxide particles after the heat treatment and Li ₂ CO ₃ were mixed so that the molar ratio of (Ni + Co + Mn): Li was 1: 1.10 to obtain a mixture. The mixture was first fired at 700 ° C. for 5 hours, and then 0.5% by weight of magnesium oxide was added to the powder after the first firing and mixed to obtain a mixture. The mixture was second baked at 840 ° C. for 5 hours to obtain a baked product. The fired product is crushed after cooling and classified by sieving to obtain a lithium metal composite oxide represented by Li _1.10 Ni _0.48 Co _0.29 Mn _0.19 Mg _0.04 O _2. It was.

(Production Example 6)
e) A lithium metal composite oxide represented by Li _1.10 Ni _0.5 Co _0.3 Mn _0.2 O ₂ in the same manner as in Production Example 5 except that magnesium oxide was not added in the step. Got. This was designated as the lithium metal composite oxide of Production Example 6.

(Comparative Production Example 1)
In the same manner as in Production Example 1, except that the molar ratio of Ni: Co: Mn in step a) was set to 5: 2: 3, and the second firing temperature in step e) was set to 850 ° C., Li _1.10. A lithium metal composite oxide represented by Ni _0.5 Co _0.2 Mn _0.3 O ₂ was obtained. This was designated as the lithium metal composite oxide of Comparative Production Example 1.

(Production evaluation example 1)
With respect to the lithium metal composite oxides of Production Example 1, Production Example 5, Production Example 6, and Comparative Production Example 1, X-ray diffraction patterns were measured using a powder X-ray diffractometer with CuKα rays. The X-ray diffraction charts of the lithium metal composite oxides of Production Example 1 and Comparative Production Example 1 are shown in FIGS. The peak derived from the (003) plane was observed at 18 to 19 °, and the peak derived from the (104) plane was observed at 44 to 45 °. The value of (integral intensity of peak derived from (003) plane I (003)) / (integrated intensity of peak derived from (104) plane I (104)) is 1 in the lithium metal composite oxide of Production Example 1. .27, 1.31 for the lithium metal composite oxide of Production Example 5, 1.22 for the lithium metal composite oxide of Production Example 6, and 1.08 for the lithium metal composite oxide of Comparative Production Example 1 .
From this result, the order in which the degree of mixing of transition metal such as nickel into the lithium site in the layered rock salt structure of each lithium metal composite oxide is as follows is Production Example 5, Production Example 1, Production Example 6, and Comparative Production Example 1. It can be said that there is. The order in which the charge / discharge characteristics at a large current are excellent is also considered as the above order.

(Production evaluation example 2)
For the lithium metal composite oxides of Production Example 1, Production Example 5, Production Example 6, and Comparative Production Example 1, a laser diffraction particle size distribution measuring device (Microtrac MT3300EX, Nikkiso Co., Ltd.) was used and N-methylpyrrolidone as a circulating solvent Was used to calculate the average particle size (D50), 100 × (standard deviation of particle size) / (average particle size) (hereinafter, sometimes referred to as “CV% of particle size”). The results are shown in Table 15.

(Production evaluation example 3)
For the lithium metal composite oxide of Production Example 1 and Comparative Production Example 1, a cross section was formed by Ar ion milling using an ion slicer (EM-09100IS, manufactured by JEOL Ltd.), and the cross section was obtained by SEM and EBSD. Observed. From each SEM image obtained, it was confirmed that any lithium metal composite oxide was a secondary particle in which a plurality of primary particles were bonded. Further, the lithium metal composite oxides of Production Example 1 and Comparative Production Example 1 were both dense in the surface layer and inside, and could not be said to be hollow.
From the respective EBSD images, the average value of the major axis length of primary particles, the value of (major axis length of primary particles) / (minor axis length of primary particles) (referred to as “aspect ratio” in the following table). Was calculated. The results are shown in Table 16.

Example I
A lithium ion secondary battery of Example I using the electrolytic solution of Example 2-1 and the lithium metal composite oxide of Production Example 1 was produced as follows.

As a positive electrode active material, 90 parts by mass of the lithium metal composite oxide of Production Example 1, 8 parts by mass of acetylene black as a conductive auxiliary agent, and 2 parts by mass of polyvinylidene fluoride as a binder were mixed. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry. An aluminum foil corresponding to JIS A1000 series having a thickness of 20 μm was prepared as a positive electrode current collector. The slurry was applied to the surface of the aluminum foil using a doctor blade so as to form a film. The aluminum foil coated with the slurry was dried at 80 ° C. for 20 minutes to remove N-methyl-2-pyrrolidone. Thereafter, this aluminum foil was pressed to obtain a bonded product. The obtained joined product was heat-dried at 120 ° C. for 6 hours with a vacuum dryer to obtain an aluminum foil on which a positive electrode active material layer was formed. This was used as a positive electrode. The positive electrode active material layer was formed at 5.5 mg / cm ² on the coated surface of the positive electrode current collector, and the density of the positive electrode active material layer was 2.5 g / cm ³ .

As a negative electrode active material, 98 parts by mass of spherical graphite, 1 part by mass of styrene butadiene rubber as a binder and 1 part by mass of carboxymethyl cellulose were mixed. This mixture was dispersed in an appropriate amount of ion-exchanged water to prepare a slurry. A copper foil having a thickness of 20 μm was prepared as a negative electrode current collector. 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 water, and then the copper foil was pressed to obtain a bonded product. The obtained joined product was dried by heating at 100 ° C. for 6 hours with a vacuum dryer to obtain a copper foil on which a negative electrode active material layer was formed. This was used as a negative electrode. Incidentally, the negative electrode active material layer is formed by 3.8 mg / cm ² in the coated surface of the negative electrode current collector, also, the density of the negative electrode active material layer was 1.1 g / cm ^3.

As a separator, a polypropylene porous membrane having a thickness of 20 μm was prepared.

A separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then the electrolyte solution of Example 2-1 was injected into the bag-like laminated film. Thereafter, the remaining one side was sealed to obtain a lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. This battery was referred to as a lithium ion secondary battery of Example I.

Example II
A lithium ion secondary battery of Example II was obtained in the same manner as in Example I except that the lithium metal composite oxide of Production Example 2 was used as the positive electrode active material.

Example III
A lithium ion secondary battery of Example III was obtained in the same manner as in Example I except that the lithium metal composite oxide of Production Example 3 was used as the positive electrode active material.

Example IV
A lithium ion secondary battery of Example IV was obtained in the same manner as in Example I except that the lithium metal composite oxide of Production Example 4 was used as the positive electrode active material.

(Example V)
The lithium ion secondary of Example V was prepared in the same manner as in Example I, except that the lithium metal composite oxide of Production Example 5 was used as the positive electrode active material, and the electrolytic solution of Example 11-2 was used as the electrolytic solution. A battery was obtained.

Example VI
A lithium ion secondary battery of Example VI was obtained in the same manner as in Example V except that the lithium metal composite oxide of Production Example 6 was used as the positive electrode active material.

(Comparative Example I)
A lithium ion secondary battery of Comparative Example I was obtained in the same manner as in Example I except that the lithium metal composite oxide of Comparative Production Example 1 was used as the positive electrode active material.

(Comparative Example II)
A lithium ion secondary battery of Comparative Example II was obtained in the same manner as in Example I except that the electrolytic solution of Comparative Example 10 was used as the electrolytic solution.

(Comparative Example III)
The lithium ion secondary battery of Comparative Example III was the same as Example I except that the lithium metal composite oxide of Comparative Production Example 1 was used as the positive electrode active material and the electrolytic solution of Comparative Example 10 was used as the electrolytic solution. Got.

Table 17 shows a list of lithium ion secondary batteries of Examples I to IV and Comparative Examples I to III.

(Evaluation Example I: DC resistance and capacity maintenance rate)
For the lithium ion secondary batteries of Example I and Comparative Examples I to III, the following tests were conducted to evaluate DC resistance and capacity retention.

For each lithium ion secondary battery, the voltage is equivalent to 15% SOC at a temperature of 25 ° C. and a constant current of 0.5 C (Example I, Comparative Example II is 3.44 V, Comparative Example I, III is 3.49 V). After the adjustment, constant current discharge was performed at a 15 C rate for 2 seconds. The direct current resistance of each lithium ion secondary battery during discharge was calculated from the voltage change amount and current value before and after discharge according to Ohm's law. The results are shown in Table 18.

In addition, for each lithium ion secondary battery, the battery was charged to 4.1 V at a constant current at a temperature of 60 ° C. and 1 C rate, paused for 1 minute, discharged to 3.0 V at a constant current at a 1 C rate, and 1 minute. The charging / discharging cycle of resting was repeated 200 cycles. The capacity maintenance rate was calculated by the following formula. The results are shown in Table 18.
Capacity retention rate (%) = 100 × (200 cycle discharge capacity) / (initial discharge capacity)

From the results of Table 18, the lithium ion secondary battery of Example I comprising the electrolyte solution of Example 2-1 and the lithium metal composite oxide of Production Example 1 has low resistance and the capacity retention rate after cycling. Is high.

As described in Production Evaluation Example 1, the value of the parameter of the present invention was 1.27 in the lithium metal composite oxide of Production Example 1, and 1.08 in the lithium metal composite oxide of Comparative Production Example 1. . Since the lithium metal composite oxide of Production Example 1 has a larger value of the parameter of the present invention, the degree of mixing of transition metals such as nickel into the lithium site of the layered rock salt structure is low. It can be said that the direct current resistance of the lithium ion secondary battery including the metal composite oxide is suppressed to be low.

Further, due to the effects of the electrolytic solution of the present invention, such as formation of S and O-containing films on the electrode shown in Reference Evaluation Example III and suppression of elution of transition metals shown in Reference Evaluation Example IV, the It can be said that the capacity retention rate of the lithium ion secondary battery provided with the electrolytic solution of Example 2-1 as a liquid was excellent.

Examine the results for DC resistance in Table 18 in detail. From the results of the lithium ion secondary batteries of Comparative Example I and Comparative Example III, it can be seen that the DC resistance was changed from 8.2Ω to 3.4Ω by changing the electrolyte from Comparative Example 10 to Example 2-1. . Since the value of 3.4 / 8.2 is 0.41, it is expected that the DC resistance is reduced 0.41 times by changing the electrolyte from Comparative Example 10 to Example 2-1. However, from the results of the lithium ion secondary batteries of Example I and Comparative Example II, the direct current resistance changed from 4.4Ω to 1.6Ω by changing the electrolyte from Comparative Example 10 to Example 2-1. Here, the value of 1.6 / 4.4 was 0.36. In other words, in the lithium ion secondary battery of Example I, it can be said that the value of the direct current resistance decreased more than expected by changing the electrolyte from Comparative Example 10 to Example 2-1.

In addition, from the results of the lithium ion secondary batteries of Comparative Example II and Comparative Example III, the positive electrode active material changed from Comparative Production Example 1 to Production Example 1, and thus the DC resistance changed from 8.2Ω to 4.4Ω. I understand. Since the value of 4.4 / 8.2 is 0.54, it is expected that the direct current resistance is reduced by a factor of 0.54 when the positive electrode active material is changed from Comparative Production Example 1 to Production Example 1. However, from the results of the lithium ion secondary batteries of Example I and Comparative Example I, the positive electrode active material was changed from Comparative Production Example 1 to Production Example 1, whereby the DC resistance was changed from 3.4Ω to 1.6Ω. Here, the value of 1.6 / 3.4 was 0.47. That is, in the lithium ion secondary battery of Example I, it can be said that the value of the direct current resistance was decreased more than expected by changing the positive electrode active material from Comparative Production Example 1 to Production Example 1.

From the above considerations, it can be said that the lithium ion secondary battery of Example I had an unprecedented DC resistance reduction effect due to the combination of the electrolytic solution and the positive electrode active material. It was confirmed that the lithium ion secondary battery of the present invention has a synergistic effect due to the combination of a specific electrolyte and a specific lithium metal composite oxide.

(Evaluation Example II: Low-temperature DC resistance)
The lithium ion secondary batteries of Example V and Example VI were subjected to the following tests to evaluate low-temperature DC resistance.

Each lithium ion secondary battery was adjusted to a voltage equivalent to 15% SOC of 3.45 V at a constant current of -10 ° C. and 0.5 C rate, and then discharged at a constant current of 3 C for 2 seconds. The direct current resistance of each lithium ion secondary battery during discharge was calculated from the voltage change amount and current value before and after discharge according to Ohm's law. The results are shown in Table 19.

From the results of Table 19, the lithium ion secondary battery of Example V provided with the lithium metal composite oxide doped with Mg was the lithium ion secondary battery of Example VI provided with the lithium metal composite oxide not doped with Mg. It can be seen that the resistance is lower than that.

(Example VII)
A lithium ion secondary battery of Example VII was obtained in the same manner as in Example V except that the lithium metal composite oxide of Production Example 1 was used as the positive electrode active material.

Example VIII
A lithium ion secondary battery of Example VIII was obtained in the same manner as in Example V except that the lithium metal composite oxide of Production Example 2 was used as the positive electrode active material.

Example IX
A lithium ion secondary battery of Example IX was obtained in the same manner as in Example V except that the lithium metal composite oxide of Production Example 3 was used as the positive electrode active material.

(Comparative Example IV)
A lithium ion secondary battery of Comparative Example IV was obtained in the same manner as in Example V except that the lithium metal composite oxide of Comparative Production Example 1 was used as the positive electrode active material.

(Evaluation Example III)
The following tests were performed on the lithium ion secondary batteries of Examples VII to IX and Comparative Example IV, and the DC resistance and capacity retention rate were evaluated. Each lithium ion secondary battery was adjusted to 3.65 V at a constant current of 0.5 C rate at a temperature of -10 ° C. and then charged at a constant current of 10 seconds at a 3 C rate. From the voltage change amount and current value before and after charging, the DC resistance during charging was calculated according to Ohm's law. Similarly, each lithium ion secondary battery was adjusted to 3.65 V at a constant current of -10 ° C. and 0.5 C rate, and then discharged at a constant current of 3 C for 2 seconds. From the voltage change amount and current value before and after the discharge, the direct current resistance at the time of discharge was calculated according to Ohm's law.

Further, for each lithium ion secondary battery, the battery was charged to 4.1 V at a constant current at a temperature of 25 ° C. and 1 C rate, paused for 1 minute, discharged to 3.0 V at a constant current at a 1 C rate, and 1 minute. The charging / discharging cycle of resting was repeated 200 cycles. The capacity maintenance rate was calculated by the following formula. Table 20-1 shows a list of electrolytes and lithium metal composite oxides used in the lithium ion secondary batteries of Examples VII to IX and Comparative Example IV, and the above evaluation results are shown in Table 20-2.
Capacity retention rate (%) = 100 × (discharge capacity at 200 cycles) / (initial discharge capacity)

It can be said that the lithium ion secondary battery using the electrolytic solution of the present invention can suitably maintain the capacity. Moreover, it was confirmed that the lithium ion secondary battery of this invention which combined the electrolyte solution of this invention with the lithium metal complex oxide prescribed | regulated by this invention has low DC resistance at the time of charging / discharging.

Claims (12)

1. Heteroelement-containing organic solvent containing a specific organic solvent having a dielectric constant of 10 or less and / or a dipole moment of 5D or less, and a metal salt having lithium as a cation and a chemical structure represented by the following general formula (1) as an anion An electrolyte solution in a molar ratio of 3 to 5,
   And
   In powder X-ray diffraction measurement, 1.10 ≦ (integral intensity of peak derived from (003) plane I (003)) / (integrated intensity of peak derived from (104) plane I (104)) <2.0 Satisfied or general formula Li _a (Ni _x Co _y M _z ) O _b (1.05 ≦ a ≦ 1.20, 0.15 ≦ x ≦ 0.55, 0.25 ≦ y ≦ 0.75, 0.01 ≦ z ≦ 0.29, x + y + z = 1, 1.7 ≦ b ≦ 2.3, M is Mn, Zr, Mg, Ti, Al, W, Si, Mo, Fe, B, Zn, Cu A lithium ion secondary battery comprising a lithium metal composite oxide having a layered rock salt structure represented by at least one of them.
   (R ¹ X ¹ ) (R ² SO ₂ ) N General formula (1)
   (R ¹ is hydrogen, halogen, an alkyl group which may be substituted with a substituent, a cycloalkyl group which may be substituted with a substituent, an unsaturated alkyl group which may be substituted with a substituent, or a substituent. An unsaturated cycloalkyl group which may be substituted with, an aromatic group which may be substituted with a substituent, a heterocyclic group which may be substituted with a substituent, or an alkoxy group which may be substituted with a substituent , An unsaturated alkoxy group that may be substituted with a substituent, a thioalkoxy group that may be substituted with a substituent, an unsaturated thioalkoxy group that may be substituted with a substituent, CN, SCN, or OCN Is done.
   R ² represents hydrogen, halogen, an alkyl group which may be substituted with a substituent, a cycloalkyl group which may be substituted with a substituent, an unsaturated alkyl group which may be substituted with a substituent, or a substituent. An unsaturated cycloalkyl group which may be substituted, an aromatic group which may be substituted with a substituent, a heterocyclic group which may be substituted with a substituent, an alkoxy group which may be substituted with a substituent, Selected from an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, CN, SCN, OCN The
   R ¹ and R ² may be bonded to each other to form a ring.
   X ¹ is selected from SO ₂ , C = O, C = S, R ^a P = O, R ^b P = S, S = O, Si = O.
   R ^a and R ^b are each independently hydrogen, halogen, an alkyl group that may be substituted with a substituent, a cycloalkyl group that may be substituted with a substituent, or a group that may be substituted with a substituent. A saturated alkyl group, an unsaturated cycloalkyl group that may be substituted with a substituent, an aromatic group that may be substituted with a substituent, a heterocyclic group that may be substituted with a substituent, and a substituent An alkoxy group which may be substituted, an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, OH , SH, CN, SCN, and OCN.
   R ^a and R ^b may combine with R ¹ or R ² to form a ring. )
2. The lithium ion secondary battery according to claim 1, wherein the hetero element-containing organic solvent contains the specific organic solvent in an amount of 80% by volume or more or 80% by mole or more.
3. A specific organic solvent having a relative dielectric constant of 10 or less and / or a dipole moment of 5D or less, and a metal salt having lithium as a cation and a chemical structure represented by the general formula (1) according to claim 1 as an anion An electrolyte containing a molar ratio of 3 to 5,
   And
   In powder X-ray diffraction measurement, 1.10 ≦ (integral intensity of peak derived from (003) plane I (003)) / (integrated intensity of peak derived from (104) plane I (104)) <2.0 Satisfied or general formula Li _a (Ni _x Co _y M _z ) O _b (1.05 ≦ a ≦ 1.20, 0.15 ≦ x ≦ 0.55, 0.25 ≦ y ≦ 0.75, 0.01 ≦ z ≦ 0.29, x + y + z = 1, 1.7 ≦ b ≦ 2.3, M is Mn, Zr, Mg, Ti, Al, W, Si, Mo, Fe, B, Zn, Cu A lithium ion secondary battery comprising a lithium metal composite oxide having a layered rock salt structure represented by at least one of them.
4. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the specific organic solvent contains carbonate in a chemical structure.
5. The lithium ion secondary battery according to any one of claims 1 to 4, wherein the specific organic solvent is a chain carbonate represented by the following general formula (2).
   R ²⁰ OCOOR ²¹ general formula (2)
   (R ²⁰ and R ²¹ each independently represent C _n H _a F _b Cl _c Br _d I _e which is a chain alkyl, or C _m H _f F _g Cl _h Br _i I containing a cyclic alkyl in the chemical structure. selected from _j , n is an integer of 1 or more, m is an integer of 3 or more, a, b, c, d, e, f, g, h, i, j are each independently an integer of 0 or more 2n + 1 = a + b + c + d + e, 2m = f + g + h + i + j is satisfied.)
6. A hetero element-containing organic solvent containing a chain carbonate represented by the general formula (2) according to claim 5 and lithium as a cation, and a chemical structure represented by the general formula (1) according to claim 1 An electrolyte containing a metal salt as an anion at a molar ratio of 3 to 5,
   And
   In powder X-ray diffraction measurement, 1.10 ≦ (integral intensity of peak derived from (003) plane I (003)) / (integrated intensity of peak derived from (104) plane I (104)) <2.0 Satisfied or general formula Li _a (Ni _x Co _y M _z ) O _b (1.05 ≦ a ≦ 1.20, 0.15 ≦ x ≦ 0.55, 0.25 ≦ y ≦ 0.75, 0.01 ≦ z ≦ 0.29, x + y + z = 1, 1.7 ≦ b ≦ 2.3, M is Mn, Zr, Mg, Ti, Al, W, Si, Mo, Fe, B, Zn, Cu A lithium ion secondary battery comprising a lithium metal composite oxide having a layered rock salt structure represented by at least one of them.
7. The lithium ion secondary battery according to any one of claims 1 to 6, wherein the chemical structure of the anion of the metal salt is represented by the following general formula (1-1).
   (R ³ X ² ) (R ⁴ SO ₂ ) N Formula (1-1)
   (R ³ and R ⁴ are each independently C _n H _a F _b Cl _c Br _d I _e (CN) _f (SCN) _g (OCN) _h .
   n, a, b, c, d, e, f, g, and h are each independently an integer of 0 or more, and satisfy 2n + 1 = a + b + c + d + e + f + g + h.
   R ³ and R ⁴ may combine with each other to form a ring, in which case 2n = a + b + c + d + e + f + g + h is satisfied.
   X ^{2 _{is, SO 2, C = O,}} C = S, R c P = O, R d P = S, S = O, is selected from Si = O.
   R ^c and R ^d are each independently hydrogen, halogen, an alkyl group that may be substituted with a substituent, a cycloalkyl group that may be substituted with a substituent, or a group that may be substituted with a substituent. A saturated alkyl group, an unsaturated cycloalkyl group that may be substituted with a substituent, an aromatic group that may be substituted with a substituent, a heterocyclic group that may be substituted with a substituent, and a substituent An alkoxy group which may be substituted, an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, OH , SH, CN, SCN, and OCN.
   R ^c and R ^d may combine with R ³ or R ⁴ to form a ring. )
8. The lithium ion secondary battery according to any one of claims 1 to 7, wherein the chemical structure of the anion of the metal salt is represented by the following general formula (1-2).
   (R ⁵ SO ₂ ) (R ⁶ SO ₂ ) N Formula (1-2)
   (R ⁵ and R ⁶ are each independently C _n H _a F _b Cl _c Br _d I _e .
   n, a, b, c, d, and e are each independently an integer of 0 or more, and satisfy 2n + 1 = a + b + c + d + e.
   R ⁵ and R ⁶ may combine with each other to form a ring, in which case 2n = a + b + c + d + e is satisfied. )
9. The metal salt is (CF ₃ SO ₂ ) ₂ NLi, (FSO 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 The lithium ion secondary battery according to any one of claims 1 to 8, which is NLi) or (SO ₂ CF ₂ CF ₂ CF ₂ SO ₂ ) NLi.
10. The lithium ion secondary battery according to any one of claims 1 to 9, wherein the specific organic solvent or the chain carbonate is selected from dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.
11. The lithium ion secondary battery according to any one of claims 1 to 10, comprising a positive electrode current collector made of aluminum.
12. The lithium ion secondary battery according to any one of claims 1 to 11, wherein a film containing S and O is formed on a surface of the positive electrode and / or the negative electrode.

Images