Nonaqueous electrolyte secondary battery

Abstract

Provided is a nonaqueous electrolyte secondary battery which has a high capacity retention rate after high-temperature storage, a suppressed amount of stored gas after high-temperature storage, low resistance after high-temperature storage, little elution of metal from a positive electrode, and low calorific value at high temperatures. A non-aqueous electrolyte secondary battery provided with a positive electrode having a positive electrode active material capable of intercalating and deintercalating metal ions, a negative electrode having a negative electrode active material capable of intercalating and deintercalating metal ions, and a non-aqueous electrolyte, the positive electrode active material containing a lithium transition metal compound, the positive electrode active material containing at least Ni, Mn, and Co, the molar ratio of Mn / (Ni + Mn + Co) is greater than 0 and 0.32 or less, the molar ratio of Ni / (Ni + Mn + Co) is 0.45 or more, the plate density of the positive electrode is 3.0 g / cm3 or more, and the non-aqueous electrolyte solution contains a monofluorophosphate and / or a difluorophosphate.

Description

[0001] This application is a divisional application of the following application.

[0002] Application date for the parent case: August 7, 2018

[0003] Parent application number: 201880051775.8 (PCT / JP2018 / 029618)

[0004] Application title: Non-aqueous electrolyte secondary battery Technical Field

[0005] This invention relates to a non-aqueous electrolyte secondary battery. Background Technology

[0006] Lithium-ion non-aqueous electrolyte secondary batteries, which use lithium-containing transition metal oxides as the positive electrode and non-aqueous solvents as the electrolyte, are widely used in applications ranging from small power supplies for mobile phones and laptops to large power supplies for automobiles, railways, and load balancing due to their high energy density. However, in recent years, the demand for high-performance non-aqueous electrolyte secondary batteries has been increasing, creating a strong need for improvements in various characteristics.

[0007] For example, Patent Document 1 describes a non-aqueous electrolyte secondary battery that uses an electrolyte containing monofluorophosphate, difluorophosphate, etc., and can be a high-capacity, long-life, and high-power non-aqueous electrolyte secondary battery, even when used as a large battery.

[0008] Patent document 2 describes that, since power characteristics and cycle characteristics are extremely important when using non-aqueous electrolyte secondary batteries as power sources for hybrid vehicles and electric vehicles, by reducing the crystal defects of primary particles of lithium transition metal compounds and reducing the internal impedance of the crystal, positive electrode active materials for non-aqueous electrolyte secondary batteries with good cycle characteristics and long lifespan can be stably provided.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: International Publication No. 2007 / 055087

[0012] Patent Document 2: Japanese Patent Application Publication No. 2007-242288 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] However, compared to the recent requirements for improving the characteristics of non-aqueous electrolyte secondary batteries, the existing technologies described above cannot yet achieve a high level of performance that combines all the characteristics of non-aqueous electrolyte secondary batteries. For example, in the non-aqueous electrolyte secondary battery of Patent Document 1, it is necessary to further increase battery capacity and improve safety; in the non-aqueous electrolyte secondary battery of Patent Document 2, due to the decrease in capacity retention after high-temperature storage and the increase in the amount of stored gas and metal dissolution after high-temperature storage, it is necessary to improve high-temperature life and improve safety. In particular, for large batteries used in automobiles, the battery itself is kept at high temperatures due to heat from the electric motor, solar heat, and other environmental factors, depending on the operating environment. Therefore, a non-aqueous electrolyte secondary battery with excellent high-temperature characteristics (e.g., high capacity retention after high-temperature storage, low amount of stored gas after high-temperature storage) and high safety (e.g., low impedance after high-temperature storage, low metal dissolution from the positive electrode, and low heat generation at high temperatures) is desired.

[0015] The objective of this invention is to provide a non-aqueous electrolyte secondary battery that exhibits high capacity retention after high-temperature storage, low amount of stored gas after high-temperature storage, low impedance after high-temperature storage, minimal metal dissolution from the positive electrode, and low heat generation at high temperatures.

[0016] Methods for solving problems

[0017] The inventors, through in-depth research to solve the above-mentioned problems, discovered that by manufacturing a non-aqueous electrolyte secondary battery using a specific positive electrode and a non-aqueous electrolyte containing a specific compound, a non-aqueous electrolyte secondary battery with high capacity retention after high-temperature storage, low amount of stored gas after high-temperature storage, low impedance after high-temperature storage, low metal dissolution from the positive electrode, and low heat generation at high temperatures can be obtained, thus obtaining the present invention.

[0018] That is, the main idea of ​​this invention is as follows.

[0019] [1] A non-aqueous electrolyte secondary battery, comprising: a positive electrode having a positive electrode active material capable of intercalating and deintercalating metal ions, a negative electrode having a negative electrode active material capable of intercalating and deintercalating metal ions, and a non-aqueous electrolyte, wherein,

[0020] The positive electrode active material contains a lithium transition metal compound, and contains at least Ni, Mn, and Co. The Mn / (Ni + Mn + Co) molar ratio is greater than 0 and less than 0.32, the Ni / (Ni + Mn + Co) molar ratio is greater than 0.45, and the electrode plate density is 3.0 g / cm³. 3 The non-aqueous electrolyte described above contains monofluorophosphate and / or difluorophosphate.

[0021] [2] According to the non-aqueous electrolyte secondary battery of [1], the positive electrode active material contains a lithium transition metal compound as shown in the following formula (I).

[0022] Li 1＋x MO2 …(I)

[0023] (In the above formula (I), x is greater than -0.05 and less than 0.06, and M is composed of at least Ni, Mn and Co.)

[0024] [3] In the non-aqueous electrolyte secondary battery according to [2], x is 0.028 or less.

[0025] [4] In any one of the non-aqueous electrolyte secondary batteries according to [1] to [3], the molar ratio of Mn / (Ni+Mn+Co) is 0.28 or less.

[0026] [5] In any one of the non-aqueous electrolyte secondary batteries according to [1] to [4], the Ni / (Ni+Mn+Co) molar ratio is 0.55 or higher.

[0027] [6] In any one of [1] to [5], the non-aqueous electrolyte secondary battery has a positive electrode plate density of 3.2 g / cm³. 3 above.

[0028] [7] In any one of [1] to [6], the non-aqueous electrolyte secondary battery further comprises sulfate as the positive electrode active material.

[0029] [8] In the non-aqueous electrolyte secondary battery according to [7], the amount of sulfate contained in the positive electrode active material is 15 μmol / g or more.

[0030] [9] In any one of the non-aqueous electrolyte secondary batteries according to [1] to [8], the average valence of Ni in the uncharged state of the lithium transition metal compound is 2.1 or higher.

[0031]

[10] In any one of [1] to [9], the pH of the aqueous solution of the lithium transition metal compound is 11 or higher at a liquid temperature of 25°C.

[0032]

[11] In any one of [1] to

[10] , the non-aqueous electrolyte secondary battery, the positive electrode active material contains more than 10 μmol / g of carbonate.

[0033]

[12] In the non-aqueous electrolyte secondary battery according to any one of [1] to

[11] , the tap density of the lithium transition metal compound is 1.8 g / cm³. 3 above.

[0034] [Invention Effects]

[0035] According to the present invention, a non-aqueous electrolyte secondary battery with high capacity retention after high-temperature storage, low amount of stored gas after high-temperature storage, low impedance after high-temperature storage, low metal dissolution from the positive electrode, and low heat generation at high temperature can be obtained. Detailed Implementation

[0036] The embodiments for carrying out the present invention will be described in detail below. However, the descriptions described below are merely examples (representative examples) of embodiments of the present invention, and the present invention is not limited thereto without departing from the spirit of the claims.

[0037] Embodiments of the present invention relate to a non-aqueous electrolyte secondary battery, comprising: a positive electrode having a positive electrode active material capable of intercalating and deintercalating metal ions, a negative electrode having a negative electrode active material capable of intercalating and deintercalating metal ions, and a non-aqueous electrolyte. The components are described below.

[0038] [1. Non-aqueous electrolyte]

[0039] The non-aqueous electrolyte used in the secondary battery of the present invention, like a conventional non-aqueous electrolyte, contains an electrolyte and a non-aqueous solvent for dissolving it, and is characterized by containing monofluorophosphate and / or difluorophosphate.

[0040] [1-1. Monofluorophosphate, difluorophosphate]

[0041] There are no particular restrictions on whether monofluorophosphates and difluorophosphates are salts having at least one monofluorophosphate or difluorophosphate structure within their molecules. By using an electrolyte containing one or more of monofluorophosphates and difluorophosphates, the durability characteristics of non-aqueous electrolyte secondary batteries can be improved. Furthermore, by applying this electrolyte to non-aqueous secondary batteries with a specific positive electrode described later, non-aqueous electrolyte secondary batteries with high capacity retention after high-temperature storage, low storage gas content after high-temperature storage, low impedance after high-temperature storage, low metal dissolution from the positive electrode, and low heat generation at high temperatures can be obtained.

[0042] There are no particular limitations on the counter cations in monofluorophosphates and difluorophosphates; examples include lithium, sodium, potassium, magnesium, calcium, and NR. 121 R 122 R 123 R 124 (where R) 121 ~R 124 Ammonium, etc., which are independently represented by an organic group having 1 to 12 carbon atoms (either a hydrogen atom or a carbon atom). 121 ~R 124There are no particular limitations on the organic groups represented by having 1 to 12 carbon atoms. Examples include alkyl groups that can be substituted with fluorine atoms, cycloalkyl groups that can be substituted with halogen atoms or alkyl groups, aryl groups that can be substituted with halogen atoms or alkyl groups, and nitrogen-containing heterocyclic groups that can have substituents. Among these, R... 121 ~R 124 The preferred cations are hydrogen atoms, alkyl groups, cycloalkyl groups, or nitrogen-containing heterocyclic groups. Lithium, sodium, and potassium are preferred as counter cations, with lithium being the most preferred.

[0043] Examples of monofluorophosphates and difluorophosphates include lithium monofluorophosphate, sodium monofluorophosphate, potassium monofluorophosphate, lithium difluorophosphate, sodium difluorophosphate, and potassium difluorophosphate, with lithium monofluorophosphate and lithium difluorophosphate being preferred, and lithium difluorophosphate being more preferred.

[0044] The total content of monofluorophosphate and difluorophosphate, based on the concentration in the non-aqueous electrolyte, is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, particularly preferably 0.3% by mass or more, and most preferably 0.5% by mass or more. Furthermore, it is preferably 8% by mass or less, more preferably 4% by mass or less, particularly preferably 2% by mass or less, and most preferably 1.5% by mass or less. If the total content of monofluorophosphate and difluorophosphate is within this range, when a non-aqueous electrolyte secondary battery is manufactured, the capacity after high-temperature storage is large, battery expansion and metal dissolution are suppressed, thus resulting in excellent high-temperature life and safety, and avoiding increased manufacturing costs for non-aqueous electrolyte secondary batteries.

[0045] Monofluorophosphate and difluorophosphate can be used alone or in combination or ratio of two or more.

[0046] In addition, in this invention, monofluorophosphate and difluorophosphate are also included in the electrolyte and the battery.

[0047] [1-2. Electrolytes]

[0048] There are no restrictions on the electrolytes used in non-aqueous electrolytes. Any known substance can be used if it is suitable as an electrolyte for non-aqueous electrolyte secondary batteries. When using non-aqueous electrolytes in lithium secondary batteries, lithium salts are typically used as the electrolyte.

[0049] Specific examples of electrolytes include the following substances:

[0050] Inorganic lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiSbF6, LiSO3F, and LiN(FSO2)2;

[0051] Fluorine-containing organic lithium salts include LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic hexafluoropropane-1,3-disulfonylimide lithium, cyclic tetrafluoroethane-1,2-disulfonylimide lithium, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, and LiBF2(C2F5SO2)2.

[0052] Lithium salts containing dicarboxylic acid ligands, such as lithium di(oxalate)borate, lithium difluorooxalateborate, lithium tri(oxalate)phosphate, lithium difluorodi(oxalate)phosphate, and lithium tetrafluoro(oxalate)phosphate.

[0053] Among these electrolytes, from the perspective of solubility and dissociation in non-aqueous solvents, conductivity, and obtained battery characteristics, LiPF6, LiBF4, LiSO3F, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium di(oxalate)borate, lithium difluorooxalateborate, lithium tri(oxalate)phosphate, lithium difluorodi(oxalate)phosphate, and lithium tetrafluoro(oxalate)phosphate are preferred, with LiPF6 and LiBF4 being particularly preferred.

[0054] In addition, in this invention, LiBF4, LiSO3F, lithium difluorooxalate borate, lithium difluorodi(oxalate) phosphate, and lithium tetrafluoro(oxalate) phosphate also include those generated in the electrolyte and in the battery.

[0055] Furthermore, the electrolyte can be used alone or in combination with two or more in any combination and ratio. It is preferable to use two specific inorganic lithium salts together, or to use an inorganic lithium salt and a fluorinated organic lithium salt together, as this can suppress gas generation during trickle charging and inhibit degradation after high-temperature storage. In particular, it is preferable to use LiPF6 and LiBF4 together, and to use inorganic lithium salts such as LiPF6 and LiBF4 with fluorinated organic lithium salts such as LiCF3SO3, LiN(CF3SO2)2, and LiN(C2F5SO2)2.

[0056] Furthermore, when using LiPF6 and LiBF4, it is preferable that LiBF4 is contained in a ratio of 0.01% by mass or more and 50% by mass or less relative to the total electrolyte. More preferably, this ratio is 0.05% by mass or more, and particularly preferably 0.1% by mass or more. On the other hand, the upper limit is more preferably 20% by mass or less, further preferably 10% by mass or less, particularly preferably 5% by mass or less, and most preferably 3% by mass or less. By setting the ratio within the above range, the desired effect is easily obtained. Furthermore, due to the low degree of dissociation of LiBF4, the increase in electrolyte impedance can be suppressed.

[0057] On the other hand, inorganic lithium salts such as LiPF6 and LiBF4 are combined with inorganic lithium salts such as LiSO3F and LiN(FSO2)2; LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic hexafluoropropane-1,3-disulfonylimide lithium, cyclic tetrafluoroethane-1,2-disulfonylimide lithium, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, L When fluorinated organic lithium salts such as iPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, and LiBF2(C2F5SO2)2, and lithium salts containing dicarboxylic acid ligands such as lithium di(oxalate)borate, lithium tri(oxalate)phosphate, lithium difluorooxalateborate, lithium tri(oxalate)phosphate, lithium difluorodi(oxalate)phosphate, and lithium tetrafluoro(oxalate)phosphate are used in combination, the proportion of inorganic lithium salts in the total electrolyte is typically 70% by mass or more, preferably 80% by mass or more, and more preferably 85% by mass or more. Furthermore, it is typically 99% by mass or less, preferably 95% by mass or less.

[0058] The concentration of the electrolyte in the non-aqueous electrolyte can be arbitrary without impairing the effects of the present invention, and is typically 0.5 mol / L or more, preferably 0.6 mol / L or more, and more preferably 0.8 mol / L or more. Furthermore, it is typically 3 mol / L or less, preferably 2 mol / L or less, more preferably 1.8 mol / L or less, and even more preferably 1.6 mol / L or less. By maintaining the electrolyte concentration within the above range, the conductivity of the non-aqueous electrolyte becomes sufficiently high, and the decrease in conductivity caused by viscosity increase, i.e., the decrease in the performance of the non-aqueous electrolyte secondary battery, can be suppressed.

[0059] [1-3. Non-aqueous solvents]

[0060] As a non-aqueous solvent contained in a non-aqueous electrolyte, it is appropriate to select from solvents that are traditionally known as solvents for non-aqueous electrolytes.

[0061] Examples of commonly used non-aqueous solvents include cyclic carbonates, chain carbonates, chain and cyclic carboxylic esters, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents.

[0062] Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, and butyl carbonate. Cyclic carbonates typically have 3 to 6 carbon atoms. Among them, ethylene carbonate and propylene carbonate are preferred due to their high dielectric constant, easy dissolution in electrolytes, and good cycle characteristics when used in non-aqueous electrolyte secondary batteries.

[0063] Examples of chain carbonates include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, and di-n-propyl carbonate. The number of carbon atoms in the alkyl group constituting the chain carbonate is preferably 1 to 5, and particularly preferably 1 to 4. Dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferred from the perspective of improving battery performance.

[0064] In addition, examples of chain carbonates in which some of the hydrogen atoms of the alkyl group are replaced by fluorine can also be cited. Examples of fluorine-substituted chain carbonates include di(fluoromethyl) carbonate, di(difluoromethyl) carbonate, di(trifluoromethyl) carbonate, di(2-fluoroethyl) carbonate, di(2,2-difluoroethyl) carbonate, di(2,2,2-trifluoroethyl) carbonate, 2-fluoroethylmethyl carbonate, 2,2-difluoroethylmethyl carbonate, and 2,2,2-trifluoroethylmethyl carbonate.

[0065] Examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl neovalerate, ethyl neovalerate, and chain carboxylic acid esters in which some of the hydrogen atoms of these compounds are substituted with fluorine. Examples of fluorinated chain carboxylic acid esters include methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, and 2,2,2-trifluoroethyl trifluoroacetate.

[0066] From the perspective of improving battery characteristics, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, methyl valerate, methyl isobutyrate, ethyl isobutyrate, and methyl neovalerate are preferred.

[0067] Examples of cyclic carboxylic acid esters include γ-butyrolactone, γ-valerolactone, and cyclic carboxylic acid esters in which some of the hydrogen atoms of these compounds are replaced by fluorine.

[0068] Among them, γ-butyrolactone is preferred.

[0069] Examples of chain ethers include dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane, 1,2-ethoxymethoxyethane, and chain ethers in which some of the hydrogen atoms of these compounds are replaced by fluorine.

[0070] Examples of fluorine-substituted chain ethers include di(trifluoroethoxy)ethane, ethoxytrifluoroethoxyethane, methoxytrifluoroethoxyethane, 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-trifluoromethylpentane, 1,1,1,2,2,3,4,5,5,5-decafluoro-3-ethoxy-4-trifluoromethylpentane, 1,1,1,2,2,3,4,5,5,5-decafluoro-3-propoxy-4-trifluoromethylpentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and 2,2-difluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0071] More preferably, 1,2-dimethoxyethane and 1,2-diethoxyethane.

[0072] Examples of phosphorus-containing organic solvents include trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylene phosphate, ethylene phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, trimethylphosphine oxide, triethylphosphine oxide, triphenylphosphine oxide, and phosphorus-containing organic solvents in which some of the hydrogen atoms of these compounds are replaced by fluorine. Examples of phosphorus-containing organic solvents with fluorine substitution include tris(2,2,2-trifluoroethyl phosphate) and tris(2,2,3,3,3-pentafluoropropyl phosphate).

[0073] Examples of sulfur-containing organic solvents include sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methylpropyl sulfone, dimethyl sulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate, dibutyl sulfate, and sulfur-containing organic solvents in which some of the hydrogen atoms of these compounds are replaced by fluorine.

[0074] Examples of aromatic fluorinated solvents include fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and trifluorotoluene.

[0075] Among the aforementioned non-aqueous solvents, ethylene carbonate and / or propylene carbonate, which are cyclic carbonates, are preferred. In order to balance the high conductivity and low viscosity of the electrolyte, it is preferable to further use them in combination with chain carbonates.

[0076] The non-aqueous solvent can be used alone or in combination with two or more in any ratio. When using two or more, for example, cyclic carbonates and chain carbonates, the suitable content of the chain carbonate in the non-aqueous solvent is usually 20% by volume or more, preferably 40% by volume or more; furthermore, it is usually 95% by volume or less, preferably 90% by volume or less. On the other hand, the suitable content of the cyclic carbonate in the non-aqueous solvent is usually 5% by volume or more, preferably 10% by volume or more; furthermore, it is usually 80% by volume or less, preferably 60% by volume or less. By keeping the proportion of chain carbonate within the above range, the increase in viscosity of the non-aqueous electrolyte can be suppressed, and the decrease in conductivity of the non-aqueous electrolyte caused by the decrease in the degree of dissociation of the lithium salt as the electrolyte can be suppressed. In addition, in this specification, the volume of the non-aqueous solvent is the value measured at 25°C, but for substances such as ethylene carbonate that are solid at 25°C, the value measured at the melting point is used.

[0077] [1-4. Other additives]

[0078] Various additives may be included without significantly impairing the effects of the present invention. Conventionally known substances may be used as additives. Furthermore, additives may be used alone or in combination with two or more in any ratio.

[0079] Examples of conventionally known additives that can be added to non-aqueous electrolytes include cyclic carbonates with carbon-carbon unsaturated bonds, fluorinated cyclic carbonates, compounds with isocyanate groups (isocyanate groups), sulfur-containing organic compounds, phosphorus-containing organic compounds, organic compounds with cyano groups, silicon-containing compounds, aromatic compounds, non-fluorinated carboxylic acid esters, cyclic compounds with multiple ether bonds, compounds with isocyanuric acid skeletons, borates, oxalates, fluorosulfonates, etc.

[0080] The following text describes each additive individually, but these additives may include substances that have already been described above.

[0081] [1-4-1. Cyclic carbonates with carbon-carbon unsaturated bonds]

[0082] As a cyclic carbonate with carbon-carbon unsaturated bonds (hereinafter also referred to as "unsaturated cyclic carbonate"), there are no particular restrictions on whether it is a cyclic carbonate with carbon-carbon double bonds or carbon-carbon triple bonds, and any unsaturated carbonate can be used. In addition, cyclic carbonates with aromatic rings are also included in unsaturated cyclic carbonates.

[0083] Examples of unsaturated cyclic carbonates include vinylene carbonates, ethylene carbonates substituted with substituents having aromatic rings or carbon-carbon double or triple bonds, phenyl carbonates, ethylene carbonates, allyl carbonates, and catechol carbonates.

[0084] Among them, particularly preferred unsaturated cyclic carbonates include vinylene carbonate, methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, vinylene carbonate, 4,5-divinylene carbonate, allyl vinylene carbonate, 4,5-diallyl vinylene carbonate, vinyl ethylene carbonate, 4,5-divinyl ethylene carbonate, 4-methyl-5-vinyl ethylene carbonate, allyl ethylene carbonate, 4,5-diallyl ethylene carbonate, 4-methyl-5-allyl ethylene carbonate, 4-allyl-5-vinyl ethylene carbonate, ethynyl ethylene carbonate, 4,5-diethynyl ethylene carbonate, 4-methyl-5-ethynyl ethylene carbonate, and 4-vinyl-5-ethynyl ethylene carbonate. Furthermore, vinylene carbonate, vinyl ethylene carbonate, and ethynyl ethylene carbonate are preferred, more preferably, and even more preferably, vinylene carbonate, as they can further form a stable interfacial protective film.

[0085] The molecular weight of the unsaturated cyclic carbonate is not particularly limited and can be any value without significantly impairing the effects of the invention. The molecular weight is preferably 80 or more, more preferably 85 or more; furthermore, it is preferably 250 or less, more preferably 150 or less. Within this range, it is easy to ensure the solubility of the unsaturated cyclic carbonate in non-aqueous electrolytes, and it is easy to fully realize the effects of the invention.

[0086] There are no particular restrictions on the manufacturing method of unsaturated cyclic carbonates; any known method can be selected.

[0087] Unsaturated cyclic carbonates can be used alone or in combination with two or more in any ratio. Furthermore, the mixing amount of unsaturated cyclic carbonates is not particularly limited and can be arbitrary without significantly impairing the effects of the invention. The mixing amount of unsaturated cyclic carbonates in 100% by mass of the non-aqueous electrolyte can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more; furthermore, it can be 10% by mass or less, preferably 5% by mass or less, more preferably 4% by mass or less, even more preferably 3% by mass or less, and particularly preferably 2% by mass or less. Within this range, the non-aqueous electrolyte secondary battery readily exhibits a sufficiently improved cycle characteristic effect, and also shows good high-temperature storage characteristics, low gas generation, and good discharge capacity retention.

[0088] [1-4-2. Fluorinated cyclic carbonates]

[0089] Examples of fluorinated cyclic carbonates include fluorinated derivatives and their derivatives of cyclic carbonates having 2 to 6 carbon atoms, such as fluorinated ethylene carbonates (hereinafter also referred to as "fluorinated ethylene carbonates") and their derivatives. Examples of fluorinated derivatives of ethylene carbonates include fluorinated ethylene carbonates substituted with alkyl groups having 1 to 4 carbon atoms. Fluorinated ethylene carbonates and their derivatives with 1 to 8 fluorine atoms are preferred.

[0090] By adding fluorinated cyclic carbonates, high-temperature storage characteristics and cycle characteristics can be improved in batteries using this electrolyte.

[0091] Examples of fluoroethylene carbonates and their derivatives with 1 to 8 fluorine atoms include monofluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4,5-difluoro-4-methylethylene carbonate, 4-fluoro-5-methylethylene carbonate, 4,4-difluoro-5-methylethylene carbonate, 4-(fluoromethyl)-ethylene carbonate, 4-(difluoromethyl)-ethylene carbonate, 4-(trifluoromethyl)-ethylene carbonate, 4-(fluoromethyl)-4-fluoroethylene carbonate, 4-(fluoromethyl)-5-fluoroethylene carbonate, 4-fluoro-4,5-dimethylethylene carbonate, 4,5-difluoro-4,5-dimethylethylene carbonate, and 4,4-difluoro-5,5-dimethylethylene carbonate.

[0092] Among them, ethylene monofluorocarbonate, 4,4-difluoroethylene carbonate, and 4,5-difluoroethylene carbonate are preferred from the perspective of imparting high ionic conductivity to the electrolyte and facilitating the formation of a stable interfacial protective film.

[0093] Fluorinated cyclic carbonates can be used alone or in combination with two or more in any combination and ratio. The amount of fluorinated cyclic carbonate (total amount in the case of two or more) in 100% by mass of the electrolyte is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, further preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, particularly preferably 1% by mass or more, and most preferably 1.2% by mass or more; furthermore, it is preferably 10% by mass or less, more preferably 7% by mass or less, further preferably 5% by mass or less, particularly preferably 3% by mass or less, and most preferably 2% by mass or less. Furthermore, when using fluorinated cyclic carbonates as a non-aqueous solvent, the mixing amount in 100% by volume of the non-aqueous solvent is preferably 1% by volume or more, more preferably 5% by volume or more, and further preferably 10% by volume or more; furthermore, it is preferably 50% by volume or less, more preferably 35% by volume or less, and even more preferably 25% by volume or less.

[0094] By using the above-mentioned concentrations, the improved high-temperature storage and circulation characteristics can be fully obtained, while the generation of unnecessary gases can be suppressed.

[0095] [1-4-3. Compounds containing isocyanate groups]

[0096] Non-aqueous electrolytes may contain compounds with isocyanate groups. In the following text, they may also be referred to as "isocyanate compounds".

[0097] There are no particular limitations on the isocyanate compound if it is an organic compound having at least one isocyanate group in the molecule. The number of isocyanate groups in a molecule is preferably 1 to 4, more preferably 1 to 3, and even more preferably 1 to 2.

[0098] The isocyanate compound is preferably a compound having an isocyanate group bonded to a compound having the following structures: a straight-chain or branched alkylene group, a cycloalkylene group, a structure with cycloalkylene linked to alkylene, an aromatic hydrocarbon group, a structure with an aromatic hydrocarbon group linked to alkylene, an ether structure (-O-), a structure with an ether structure (-O-) linked to alkylene, a carbonyl group (-C(=O)-), a structure with a carbonyl group linked to alkylene, a sulfonyl group (-S(=O)-), a structure with a sulfonyl group linked to alkylene, or structures formed by halogenation thereof, etc. More preferably, it is a compound having an isocyanate group bonded to a structure having an isocyanate group bonded to a structure having cycloalkylene linked to alkylene. The molecular weight of the isocyanate compound is not particularly limited. The molecular weight is preferably 80 or more, more preferably 115 or more, and even more preferably 170 or more; furthermore, it is 300 or less, more preferably 230 or less. Within this range, the solubility of the isocyanate compound in non-aqueous electrolytes is easily ensured, and the effects of the present invention are readily achieved. There are no particular limitations on the method for manufacturing the isocyanate compound; any known method can be used. Furthermore, commercially available products can also be used.

[0099] Examples of isocyanate compounds include:

[0100] Compounds having one isocyanate group include alkyl isocyanates such as methyl isocyanate, ethyl isocyanate, propyl isocyanate, isopropyl isocyanate, butyl isocyanate, and tert-butyl isocyanate; cyclohexyl isocyanate and other cycloalkyl isocyanates; allyl isocyanate and propargyl isocyanate and other unsaturated isocyanates; phenyl isocyanate, trifluoromethyl phenyl isocyanate, and p-toluenesulfonyl isocyanate and other aromatic isocyanates.

[0101] Compounds having two isocyanate groups include monomethylene diisocyanate, dimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, decamethylene diisocyanate, 1,4-diisocyanate-2-butene, toluene diisocyanate, xylene diisocyanate, 1,3-di(isocyanate-methyl)cyclohexane, 1,4-diisocyanate-cyclohexane, dicyclohexylmethane-4,4'-diisocyanate, bicyclo[2.2.1]heptane-2,5-dimethylbis(methyl isocyanate), bicyclo[2.2.1]heptane-2,6-dimethylbis(methyl isocyanate), isophorone diisocyanate, carbonyl diisocyanate, 1,4-diisocyanate-butane-1,4-dione, trimethylhexamethylene diisocyanate, etc.

[0102] Compounds having three isocyanate groups include 1,6,11-triisocyanate undecane, 4-isocyanate methyl-1,8-octamethylene diisocyanate, 1,3,5-triisocyanate methylbenzene, 1,3,5-tris(6-isocyanate hex-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and trimethylolpropionic compounds derived from compounds having at least two isocyanate groups within the molecule (e.g., biuret, isocyanurates, adducts, and difunctional modified polyisocyanates).

[0103] Among these compounds, from the perspective of improving storage properties, preferred compounds include tert-butyl isocyanate, cyclohexyl isocyanate, p-toluenesulfonyl isocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, decamethylene diisocyanate, 1,3-di(isocyanate methyl)cyclohexane, dicyclohexylmethane-4,4'-diisocyanate, bicyclo[2.2.1]heptane-2,5-dimethylbis(methyl isocyanate), bicyclo[2.2.1]heptane-2,6-dimethylbis(methyl isocyanate), isophorone diisocyanate, trimethyl hexamethylene diisocyanate, etc., and more preferably cyclohexyl isocyanate, p-toluenesulfonyl isocyanate, hexamethylene diisocyanate, 1,3-di( The preferred diisocyanates are cyclohexane (isocyanate-methyl), dicyclohexylmethane-4,4'-diisocyanate, bicyclo[2.2.1]heptane-2,5-dimethylbis(methylisocyanate), bicyclo[2.2.1]heptane-2,6-dimethylbis(methylisocyanate), isophorone diisocyanate, trimethylhexamethylene diisocyanate, and more preferably cyclohexyl isocyanate, p-toluenesulfonyl isocyanate, hexamethylene diisocyanate, 1,3-di(isocyanate-methyl)cyclohexane, dicyclohexylmethane-4,4'-diisocyanate, bicyclo[2.2.1]heptane-2,5-dimethylbis(methylisocyanate), and bicyclo[2.2.1]heptane-2,6-dimethylbis(methylisocyanate).

[0104] Isocyanate compounds can be used alone or in combination with two or more in any ratio.

[0105] The amount of isocyanate compound (total amount in cases of two or more) in 100% by mass of the electrolyte can be 0.001% by mass or more, preferably 0.1% by mass or more, and more preferably 0.3% by mass or more; furthermore, it can be 10% by mass or less, preferably 5% by mass or less, and more preferably 3% by mass or less. If it is within this range, it is easy to control power characteristics, load characteristics, low temperature characteristics, cycle characteristics, high temperature storage characteristics, etc.

[0106] [1-4-4. Sulfur-containing organic compounds]

[0107] There are no particular limitations on the sulfur-containing organic compounds that have at least one sulfur atom within their molecule, but organic compounds with an S=O group within their molecule are preferred. Examples include chain sulfonates, cyclic sulfonates, chain sulfates, cyclic sulfates, chain sulfites, and cyclic sulfites. Compounds equivalent to fluorosulfonates are included in the fluorosulfonates described later as electrolytes, but not in the sulfur-containing organic compounds described later.

[0108] Preferably, the compounds are chain sulfonates, cyclic sulfonates, chain sulfates, cyclic sulfates, chain sulfites, and cyclic sulfites, and more preferably compounds having an S(=O)2 group.

[0109] Further preferred are chain sulfonates and cyclic sulfonates, more preferably cyclic sulfonates. Specific compounds of chain sulfonates, cyclic sulfonates, chain sulfates, cyclic sulfates, chain sulfites, and cyclic sulfites are illustrated below.

[0110] <Chain sulfonates>

[0111] Fluorosulfonates such as methyl fluorosulfonate and ethyl fluorosulfonate.

[0112] Methanesulfonates include methyl methanesulfonate, ethyl methanesulfonate, busulfan, methyl 2-(methanesulfonyloxy)propionate, ethyl 2-(methanesulfonyloxy)propionate, and ethyl methanesulfonyloxyethyl acetate.

[0113] Vinyl sulfonate esters include methyl vinyl sulfonate, ethyl vinyl sulfonate, allyl vinyl sulfonate, propargyl vinyl sulfonate, methyl allyl sulfonate, ethyl allyl sulfonate, allyl sulfonate, propargyl allyl sulfonate, and 1,2-bis(vinylsulfonyloxy)ethane, etc.

[0114] Alkyl disulfonates include methyl methanedisulfonate methoxycarbonyl methyl ester, methyl methanedisulfonate ethoxycarbonyl methyl ester, methyl 1,2-ethanedisulfonate methoxycarbonyl methyl ester, methyl 1,2-ethanedisulfonate ethoxycarbonyl methyl ester, methyl 1,3-propanedisulfonate methoxycarbonyl methyl ester, methyl 1,3-propanedisulfonate ethoxycarbonyl methyl ester, and ethyl 1,3-propanedisulfonate-1-methoxycarbonyl ester.

[0115] <Cyclic sulfonates>

[0116] Sulfonate lactones, including 1,3-propanesulfonate lactone, 1-fluoro-1,3-propanesulfonate lactone, 2-fluoro-1,3-propanesulfonate lactone, 3-fluoro-1,3-propanesulfonate lactone, 1-methyl-1,3-propanesulfonate lactone, 2-methyl-1,3-propanesulfonate lactone, 3-methyl-1,3-propanesulfonate lactone, 1-propenyl-1,3-sulfonate lactone, 2-propenyl-1,3-sulfonate lactone, 2-methyl-1-propenyl-1,3-sulfonate lactone, 1,4-butanesulfonate lactone, and 1,5-pentanesulfonate lactone.

[0117] Disulfonate compounds such as methylene disulfonate and ethylene disulfonate.

[0118] Nitrogen-containing compounds such as 1,2,3-oxathiazoline-2,2-dioxide.

[0119] Phosphorus-containing compounds such as 1,2,3-oxathiaphosphinane-2,2-dioxide.

[0120] <Chain sulfates>

[0121] Dialkyl sulfate compounds such as dimethyl sulfate, ethyl methyl sulfate, and diethyl sulfate.

[0122] <Cyclic Sulfates>

[0123] 1,2-Ethylene sulfate, 1,2-propylene sulfate, 1,3-propylene sulfate, 1,2-butenyl sulfate, 1,3-butenyl sulfate, 1,4-butenyl sulfate, 1,2-pentenyl sulfate, 1,3-pentenyl sulfate, 1,4-pentenyl sulfate, and 1,5-pentenyl sulfate, among other sulfated alkenyl ester compounds.

[0124] <Chain sulfites>

[0125] Dialkyl sulfite compounds such as dimethyl sulfite, ethyl methyl sulfite, and diethyl sulfite.

[0126] <Cyclic Sulfites>

[0127] 1,2-Vinyl sulfite, 1,2-propylene sulfite, 1,3-propylene sulfite, 1,2-butene sulfite, 1,3-butene sulfite, 1,4-butene sulfite, 1,2-pentene sulfite, 1,3-pentene sulfite, 1,4-pentene sulfite, and 1,5-pentene sulfite, etc., are all sulfite-based olefinic ester compounds.

[0128] Among these compounds, from the viewpoint of improving initial efficiency, methyl 2-(methanesulfonyloxy)propionate, ethyl 2-(methanesulfonyloxy)propionate, 2-(methanesulfonyloxy)propionate-2-propargyl ester, 1-methoxycarbonyl ethyl propanedisulfonic acid, 1-ethoxycarbonyl ethyl propanedisulfonic acid, 1-methoxycarbonyl ethyl butanedisulfonic acid, 1-ethoxycarbonyl ethyl butanedisulfonic acid, 1,3-propanesulfonyl lactone, 1-propenyl-1,3-sulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,2-sulfonyl lactone are preferred. Vinyl ester, 1,2-vinyl sulfite, methyl methanesulfonate and ethyl methanesulfonate, more preferably 1-methoxycarbonyl ethyl propanedisulfonate, 1-ethoxycarbonyl ethyl propanedisulfonate, 1-methoxycarbonyl ethyl butanedisulfonate, 1,3-propanesulfonate lactone, 1-propenyl-1,3-sulfonate lactone, 1,2-vinyl sulfate, 1,2-vinyl sulfite, and even more preferably 1,3-propanesulfonate lactone and 1-propenyl-1,3-sulfonate lactone.

[0129] Sulfur-containing organic compounds may be used alone or in combination with two or more in any ratio.

[0130] The content of sulfur-containing organic compounds (total in cases of two or more) in 100% by mass of the electrolyte can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, particularly preferably 0.3% by mass or more, and especially preferably 0.6% by mass or more; furthermore, it can be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, particularly preferably 1.5% by mass or less, and most preferably 1.0% by mass or less. Within this range, it is easy to control the battery's power characteristics, load characteristics, low-temperature characteristics, cycle characteristics, and high-temperature storage characteristics.

[0131] [1-4-5. Phosphorus-containing organic compounds]

[0132] There are no particular restrictions on the use of phosphorus-containing organic compounds, provided that the molecule contains at least one phosphorus atom. Using non-aqueous electrolytes containing phosphorus-containing organic compounds can improve battery durability.

[0133] Phosphorus-containing organic compounds are preferably phosphate esters, phosphonates, hypophosphites, and phosphites, more preferably phosphate esters and phosphonates, and even more preferably phosphonates. These esters may have substituents.

[0134] Examples of phosphorus-containing organic compounds include:

[0135] Diethyl vinyl phosphate, diethyl allyl phosphate, diethyl propargyl phosphate, trivinyl phosphate, triallyl phosphate, triargyl propargyl phosphate, diallyl phosphate, diargyl propargyl phosphate, diethyl 2-acryloyloxyethyl phosphate, tris(2-acryloyloxyethyl) phosphate, trimethylphosphonoformate, diethyl methylphosphonoformate, dipropyl methylphosphonoformate, dibutyl methylphosphonoformate, triethylphosphonoformate, dimethyl ethylphosphonoformate, dipropyl ethylphosphonoformate, dibutyl ethylphosphonoformate, tripropylphosphonoformate, dimethyl propylphosphonoformate, diethyl propylphosphonoformate, dibutyl propylphosphonoformate, tributylphosphonoformate, dibutylphosphonoformate Methyl ester, diethyl butylphosphonoformate, dipropyl butylphosphonoformate, bis(2,2,2-trifluoroethyl) methylphosphonoformate, bis(2,2,2-trifluoroethyl) ethylphosphonoformate, bis(2,2,2-trifluoroethyl) propylphosphonoformate, bis(2,2,2-trifluoroethyl) butylphosphonoformate, trimethylphosphonoacetate, diethyl methylphosphonoacetate, dipropyl methylphosphonoacetate, dibutyl methylphosphonoacetate, tripropylphosphonoacetate, dimethyl propylphosphonoacetate, diethyl propylphosphonoacetate, dibutyl ethylphosphonoacetate, tripropylphosphonoacetate, dimethyl propylphosphonoacetate, diethyl propylphosphonoacetate, dibutyl propylphosphonoacetate, tributylphosphonoacetate Acetates, dimethyl butylphosphonoacetate, diethyl butylphosphonoacetate, dipropyl butylphosphonoacetate, bis(2,2,2-trifluoroethyl) methylphosphonoacetate, bis(2,2,2-trifluoroethyl) ethylphosphonoacetate, bis(2,2,2-trifluoroethyl) propylphosphonoacetate, bis(2,2,2-trifluoroethyl) butylphosphonoacetate, dimethyl allylphosphonoacetate, diethyl allylphosphonoacetate, dimethyl 2-propargylphosphonoacetate, diethyl 2-propargylphosphonoacetate, trimethyl-3-phosphonopropionate, methyl-3-(diethylphosphono)propionate, methyl-3-(dipropylphosphono)propionate, methyl-3-(dibutylphosphono)propionate, triethyl-3-phosphono... propyl-3-(dimethylphosphoryl)propionate, ethyl-3-(dipropylphosphoryl)propionate, ethyl-3-(dibutylphosphoryl)propionate, tripropyl-3-phosphoryl propionate, propyl-3-(dimethylphosphoryl)propionate, propyl-3-(diethylphosphoryl)propionate, propyl-3-(dibutylphosphoryl)propionate, tributyl-3-phosphoryl propionate, butyl-3-(dimethylphosphoryl)propionate, butyl-3-(diethylphosphoryl)propionate, butyl-3-(diethylphosphoryl)propionate, methyl-3-(bis(2,2,2-trifluoroethyl)phosphoryl)propionate, ethyl-3-(bis(2,2,2-trifluoroethyl)phosphoryl)propionate, propyl ...2-Trifluoroethyl)phosphoryl)propionate, butyl-3-(bis(2,2,2-trifluoroethyl)phosphoryl)propionate, trimethyl-4-phosphorylbutyrate, methyl-4-(diethylphosphoryl)butyrate, methyl-4-(dipropylphosphoryl)butyrate, methyl-4-(dibutylphosphoryl)butyrate, triethyl-4-phosphoryl butyrate, ethyl-4-(dimethylphosphoryl)butyrate, ethyl-4-(dipropylphosphoryl)butyrate Acetates, ethyl-4-(dibutylphosphoyl)butyrate, tripropyl-4-phosphoyl butyrate, propyl-4-(dimethylphosphoyl)butyrate, propyl-4-(diethylphosphoyl)butyrate, propyl-4-(dibutylphosphoyl)butyrate, tributyl-4-phosphoyl butyrate, butyl-4-(dimethylphosphoyl)butyrate, butyl-4-(diethylphosphoyl)butyrate, butyl-4-(dipropylphosphoyl)butyrate, etc.

[0136] Phosphorus-containing organic compounds may be used alone or in combination with two or more in any ratio.

[0137] The content of phosphorus-containing organic compounds (total in cases of two or more) in 100% by mass of the electrolyte can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, further preferably 0.4% by mass or more, and particularly preferably 0.6% by mass or more; furthermore, it can be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, further preferably 2% by mass or less, particularly preferably 1.2% by mass or less, and most preferably 0.9% by mass or less. Within this range, power characteristics, load characteristics, low-temperature characteristics, cycle characteristics, and high-temperature storage characteristics are easily controlled.

[0138] [1-4-6. Organic compounds containing cyanide groups]

[0139] Examples of organic compounds containing a cyano group include pentonitrile, octonitrile, decanonitrile, dodecanoic acid, butenoic acid, butadionitrile, glutaronitrile, adiponitrile, heptanonitrile, octonitrile, as well as 3,9-bis(2-cyanoethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane, 1,2,3-tricyanopropane, 1,3,5-tricyanopentane, 1,4,7-tricyanohepane, 1,2,4-tricyanobutane, 1,2,5-tricyanopentane, 1,2,6-tricyanohexane, 1,3,6-tricyanohexane, and 1,2,7-tricyanohepane.

[0140] The electrolyte may contain cyano-containing organic compounds at concentrations of 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and particularly preferably 0.3% by mass or more; furthermore, 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, and particularly preferably 2% by mass or less. Within this range, power characteristics, load characteristics, low-temperature characteristics, cycle characteristics, and high-temperature storage characteristics are easily controlled.

[0141] Organic compounds containing cyanide groups can be used alone or in combination with two or more in any ratio.

[0142] [1-4-7. Silicon-containing compounds]

[0143] There are no particular restrictions on the silicon-containing compound if it has at least one silicon atom within its molecule. Using electrolytes containing silicon-containing compounds can improve the durability of non-aqueous electrolyte secondary batteries.

[0144] As a silicon-containing compound, the compound shown in formula (2-6) is preferred.

[0145]

Chemistry 1

[0146]

[0147] In equation (2-6), R 61 R 62 and R 63 Independently composed of hydrogen atoms, halogen atoms, or hydrocarbon groups having 1 to 10 carbon atoms.

[0148] X 61 An organic group containing at least one atom selected from the group consisting of oxygen, nitrogen and silicon atoms.

[0149] R 61 R 62 and R 63 Preferably, the atom is hydrogen, fluorine, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, or phenyl, and more preferably methyl.

[0150] X 61An organic group is an organic group containing at least one atom selected from the group consisting of oxygen, nitrogen, and silicon atoms, preferably an organic group containing at least an oxygen atom or a silicon atom. Here, an organic group refers to a group consisting of one or more atoms selected from the group consisting of carbon, hydrogen, nitrogen, oxygen, silicon, sulfur, phosphorus, and halogen atoms. Examples of organic groups include alkyl, alkenyl, alkynyl, aryl, alkoxy, CN, isocyanate, fluoro, alkylsulfonate, and trialkylsilyl groups. In addition, some monovalent organic groups may be replaced by fluorine atoms. Furthermore, the number of carbon atoms in the organic group may be 1 or more, preferably 3 or more, more preferably 5 or more; furthermore, it may be 15 or less, preferably 12 or less, more preferably 8 or less.

[0151] Among these, alkyl sulfonic acid groups, trialkyl silyl groups, borate groups, phosphate groups, and phosphorous acid groups are preferred.

[0152] Examples of silicon-containing compounds include the following.

[0153] Boric acid compounds such as tri(trimethylsilyl) borate, tri(trimethoxysilyl) borate, tri(triethylsilyl) borate, tri(triethoxysilyl) borate, tri(dimethylvinylsilyl) borate, and tri(diethylvinylsilyl) borate;

[0154] Phosphoric acid compounds such as trimethylsilyl phosphate, triethylsilyl phosphate, tripropylsilyl phosphate, triphenylsilyl phosphate, trimethoxysilyl phosphate, triethoxysilyl phosphate, triphenoxysilyl phosphate, dimethylvinylsilyl phosphate, and diethylvinylsilyl phosphate;

[0155] Phosphorous compounds such as trimethylsilyl phosphite, triethylsilyl phosphite, tripropylsilyl phosphite, triphenylsilyl phosphite, trimethoxysilyl phosphite, triethoxysilyl phosphite, triphenoxysilyl phosphite, dimethylvinylsilyl phosphite, and diethylvinylsilyl phosphite;

[0156] Sulfonic acid compounds such as trimethylsilyl methanesulfonate and trimethylsilyl tetrafluoromethanesulfonate;

[0157] Disilane compounds such as hexamethyldisilane, hexaethyldisilane, 1,1,2,2-tetramethyldisilane, 1,1,2,2-tetraethyldisilane, 1,2-diphenyltetramethyldisilane, and 1,1,2,2-tetraphenyldisilane.

[0158] Among these compounds, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, trimethylsilyl methanesulfonate, trimethylsilyl tetrafluoromethanesulfonate, hexamethyldisilane, hexaethyldisilane, 1,2-diphenyltetramethyldisilane, and 1,1,2,2-tetraphenyldisilane are preferred, and tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, and hexamethyldisilane are more preferred.

[0159] In addition, these silicon-containing compounds can be used alone or in combination with two or more in any ratio.

[0160] The electrolyte may contain 0.001% by mass or more of silicon-containing compounds (in the case of two or more, the total amount) in 100% by mass, preferably 0.1% by mass or more, more preferably 0.3% by mass or more; furthermore, it may contain 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less. If it is within this range, it is easy to control power characteristics, load characteristics, low temperature characteristics, cycle characteristics, high temperature storage characteristics, etc.

[0161] [1-4-8. Aromatic Compounds]

[0162] As an aromatic compound, there are no particular restrictions if it is an organic compound having at least one aromatic ring within its molecule.

[0163] Examples of aromatic compounds include the following.

[0164] Fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, trifluorotoluene, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphenyl carbonate, methyl phenyl carbonate, 2-phenylethyl acetate, 3-phenylpropyl acetate, methyl phenylacetate, ethyl phenylacetate, 2-phenylethyl phenylacetate, 3-phenylpropyl phenylacetate, methyl 3-phenylpropionate, ethyl 3-phenylpropionate, 2-phenylethyl 3-phenylpropionate, 3-phenylpropionate, methyl phenyl sulfonate, 2-tert-butylbenzene 4-tert-butylphenylmethanesulfonate, cyclohexylphenylmethanesulfonate, trimethylphenylsilane, tris(2-tert-butylphenyl) phosphate, tris(4-tert-butylphenyl) phosphate, tris(2-cyclohexylphenyl) phosphate, tris(4-cyclohexylphenyl) phosphate, diethylphenylphosphonate, diethylbenzylphosphonate, diethyl-(4-fluorobenzyl)phosphonate, 2-fluorophenylacetate, 4-fluorophenylacetate, 2,4-difluoroanisole, 2-fluorotoluene, 3-fluorotoluene, 4-fluorotoluene.

[0165] Preferred ingredients include fluorobenzene, trifluorotoluene, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphenyl carbonate, methyl phenyl carbonate, 2-phenylethyl phenylacetic acid, 4-tert-butylphenylmethanesulfonate, cyclohexylphenylmethanesulfonate, tris(2-tert-butylphenyl) phosphate, tris(4-tert-butylphenyl) phosphate, tris(4-cyclohexylphenyl) phosphate, 2,4-difluoroanisole, and 2-fluorotoluene.

[0166] In addition to the compounds listed above, other examples include:

[0167] 1-Pheny-1,3,3-trimethylindane, 2,3-dihydro-1,3-dimethyl-1-(2-methyl-2-phenylpropyl)-3-phenyl-1H-indane, 1-Pheny-1,3,3-trimethylindane, 2,3-dihydro-1,3-dimethyl-1-(2-methyl-2-phenylpropyl)-3-phenyl-1H-indane, 2,2-diphenylbutane, 3,3-diphenylpentane, 3,3-diphenylhexane, 4,4-diphenylheptane, 5,5-diphenyloctane, 6,6-diphenylnonane, 1,1-diphenyl-1,1-ditert-butylmethane, 1,1-diphenylcyclohexane, 1,1-diphenylcyclopentane, 1,1-diphenyl-4-methylcyclohexane.

[0168] 1,3-Bis(1-methyl-1-phenylethyl)-benzene, 1,4-Bis(1-methyl-1-phenylethyl)-benzene, 1-Pheny-1,3,3-trimethylindene, 2,2-diphenylbutane, 3,3-diphenylpentane, 1,1-diphenyl-1,1-di-tert-butyl-methane, 1,1-diphenylcyclohexane, 1,1-diphenylcyclopentane, 1,1-diphenyl-4-methylcyclohexane, 1,3-Bis(1-methyl-1-phenylethyl)-benzene, 1,4-Bis(1-methyl-1-phenylethyl)-benzene, 1-Pheny-1,3,3-trimethylindene -Trimethylindene, 2,2-diphenylbutane, 1,1-diphenylcyclohexane, 1,1-diphenyl-4-methylcyclohexane, 1,3-bis(1-methyl-1-phenylethyl)-benzene, 1,4-bis(1-methyl-1-phenylethyl)-benzene, 1-phenyl-1,3,3-trimethylindene, 1,1-diphenylcyclohexane, 1,1-diphenyl-4-methylcyclohexane, 1,3-bis(1-methyl-1-phenylethyl)-benzene, 1,4-bis(1-methyl-1-phenylethyl)-benzene, 1-phenyl-1,3,3-trimethylindene, etc.

[0169] Aromatic compounds can be used alone or in combination of two or more. In the total amount of non-aqueous electrolyte (100% by mass), the amount of aromatic compounds (total amount in the case of two or more) can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.05% by mass or more, further preferably 0.1% by mass or more, and even more preferably 0.4% by mass or more; furthermore, it can be 10% by mass or less, preferably 8% by mass or less, more preferably 5% by mass or less, further preferably 3% by mass or less, and particularly preferably 2.5% by mass or less. By placing it within the above range, the effects of the present invention can be easily achieved, and the increase in battery impedance can be prevented.

[0170] [1-4-9. Fluorine-free carboxylic esters]

[0171] Fluorine-free carboxylic esters can also be used as solvents as described above. There are no particular restrictions on fluorine-free carboxylic esters if they are carboxylic esters that do not have fluorine atoms in their molecules.

[0172] Examples of non-fluorinated chain carboxylic esters are as follows.

[0173] Methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, n-butyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, n-butyl butyrate, methyl valerate, ethyl valerate, n-propyl valerate, n-butyl valerate, methyl neovalerate, ethyl neovalerate, n-propyl neovalerate, n-butyl neovalerate.

[0174] In order to improve the ionic conductivity caused by the low viscosity of the electrolyte, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, and n-butyl propionate are preferred, methyl propionate, ethyl propionate, n-propyl propionate, and n-butyl propionate are even more preferred, and ethyl propionate and n-propyl propionate are particularly preferred.

[0175] Fluorine-free carboxylic esters can be used alone or in combination with two or more in any ratio.

[0176] The amount of fluorine-free carboxylic acid ester (total amount in cases of two or more) in 100% by mass of the electrolyte can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, further preferably 0.3% by mass or more, and particularly preferably 0.6% by mass or more; furthermore, it can be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, further preferably 2% by mass or less, and particularly preferably 1% by mass or less. Furthermore, when the fluorine-free carboxylic acid ester is used as a non-aqueous solvent, the mixing amount in 100% by volume of the non-aqueous solvent is preferably 1% by volume or more, more preferably 5% by volume or more, further preferably 10% by volume or more, and even more preferably 20% by volume or more; furthermore, it can contain 50% by volume or less, more preferably 45% by volume or less, and further preferably 40% by volume or less. Within such a range, the increase in negative electrode impedance can be suppressed, and power characteristics, load characteristics, low-temperature characteristics, cycle characteristics, and high-temperature storage characteristics can be easily controlled.

[0177] [1-4-10. Cyclic compounds with multiple ether bonds]

[0178] As a cyclic compound with multiple ether bonds, there are no particular restrictions if the cyclic compound has multiple ether bonds within the molecule. Cyclic compounds with multiple ether bonds contribute to improved high-temperature storage characteristics of batteries and can improve durability in non-aqueous electrolyte secondary batteries.

[0179] Examples of cyclic compounds with multiple ether bonds include tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, and methyltetrahydropyran.

[0180] A cyclic compound having multiple ether bonds can be used alone or in combination with two or more compounds in any ratio. The amount of the cyclic compound having multiple ether bonds (total amount in the case of two or more) in 100% by mass of the electrolyte can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, particularly preferably 0.3% by mass or more; furthermore, it can be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less. When the above ranges are met, power characteristics, load characteristics, low-temperature characteristics, cycle characteristics, high-temperature storage characteristics, etc., are easily controlled.

[0181] [1-4-11. As an additive for electrolytes]

[0182] Among additives, those that function as electrolytes include, for example, the following substances (borates, oxalates, and fluorosulfonates). Lithium salts are particularly preferred among these salts.

[0183] The total content of borates, oxalates, and fluorosulfonates in the non-aqueous electrolyte is preferably 0.01% by mass or more, particularly preferably 0.1% by mass or more. Furthermore, it is preferably 20% by mass or less, particularly preferably 10% by mass or less.

[0184] [1-4-11-1. Borate]

[0185] There are no particular limitations on whether a borate is a salt having at least one boron atom in its molecule. Substances belonging to oxalates are included in the oxalates described below, but not borates. The battery of the present invention improves its durability.

[0186] Examples of counter cations in borates include lithium, sodium, potassium, magnesium, calcium, rubidium, cesium, and barium, with lithium being the preferred choice.

[0187] Lithium salts are preferred as borates, and fluorinated lithium salts are suitable. Examples include LiBF4, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, and LiBF2(C2F5SO2)2. Among these, LiBF4 is preferred for its ability to improve initial charge-discharge efficiency and high-temperature cycling characteristics.

[0188] Borates can be used alone or in combination with two or more in any ratio.

[0189] The amount of borate (total amount in cases of two or more) can be 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and particularly preferably 0.4% by mass or more; furthermore, it is more preferably 10.0% by mass or less, preferably 5.0% by mass or less, more preferably 3.0% by mass or less, even more preferably 2.0% by mass or less, and particularly preferably 1.0% by mass or less. Within this range, side reactions at the negative electrode of the battery can be suppressed, making it less likely for the impedance to rise.

[0190] [1-4-11-2. Oxalate]

[0191] There are no particular limitations on whether the oxalate is a compound having at least one oxalic acid structure within the molecule. The battery of the present invention can improve durability characteristics.

[0192] As an oxalate, the metal salt expressed by formula (9) is preferred. This salt may be a salt with oxalic acid ligand as an anion.

[0193]

Chemistry 2

[0194]

[0195] In equation (9), M 1 M is an element selected from Groups 1 and 2 of the periodic table and the group consisting of aluminum (Al). 2 R represents elements selected from transition metals and elements in groups 13, 14, and 15 of the periodic table. 91 It is a group selected from the group consisting of halogens, alkyl groups with 1 to 11 carbon atoms and haloalkyl groups with 1 to 11 carbon atoms, where a and b are positive integers, c is 0 or a positive integer, and d is an integer from 1 to 3.

[0196] M 1 From the perspective of battery characteristics when using an electrolyte containing oxalate in a lithium secondary battery, lithium, sodium, potassium, magnesium, and calcium are preferred, with lithium being particularly preferred.

[0197] M 2 Boron and phosphorus are particularly preferred for their electrochemical stability when used in lithium secondary batteries.

[0198] As R 91 Examples of suitable compounds include fluorine, chlorine, methyl, trifluoromethyl, ethyl, pentafluoroethyl, propyl, isopropyl, butyl, sec-butyl, and tert-butyl, with fluorine and trifluoromethyl being preferred.

[0199] The following can be cited as examples of metal salts represented by equation (9).

[0200] Lithium oxalate borate salts such as lithium difluorooxalate borate and lithium di(oxalate) borate;

[0201] Lithium oxalate phosphate salts such as lithium tetrafluorooxalate phosphate, lithium difluorodi(oxalate) phosphate, and lithium tri(oxalate) phosphate;

[0202] Lithium di(oxalate)borate and lithium difluoro(oxalate)phosphate are preferred, with lithium di(oxalate)borate being more preferred.

[0203] Oxalates can be used alone or in combination with two or more in any ratio.

[0204] The amount of oxalate (total amount in cases of two or more) can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and particularly preferably 0.3% by mass or more; furthermore, it can be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, and particularly preferably 1% by mass or less. Within this range, it is easy to control the power characteristics, load characteristics, low-temperature characteristics, cycle characteristics, and high-temperature storage characteristics of the secondary battery.

[0205] [1-4-11-3. Fluorosulfonate]

[0206] As a fluorosulfonate, there are no particular limitations if it is a salt having at least one fluorosulfonic acid structure within the molecule. In the battery of the present invention, it can improve durability characteristics.

[0207] There are no particular limitations on the counter cations in fluorosulfonates; examples include lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, barium, and NR. 131 R 132 R 133 R 134 (where R) 131 ~R 134 Ammonium, etc., represented by organic groups (each consisting of 1 to 12 carbon atoms, individually hydrogen atoms). Lithium, sodium, and potassium are preferred as countercations, with lithium being the most preferred.

[0208] Examples of fluorosulfonates include lithium fluorosulfonate, sodium fluorosulfonate, potassium fluorosulfonate, rubidium fluorosulfonate, and cesium fluorosulfonate, with lithium fluorosulfonate being preferred. Imide salts with a fluorosulfonic acid structure, such as lithium bis(fluorosulfonyl)imide, can also be used as fluorosulfonates.

[0209] Fluorosulfonates can be used alone or in combination with two or more in any ratio.

[0210] The content of fluorosulfonate (total in cases of two or more) can be 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and particularly preferably 0.4% by mass or more; furthermore, it can be 10% by mass or less, preferably 8% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, and particularly preferably 1% by mass or less. Within this range, side reactions in the battery are fewer, and impedance is less likely to increase.

[0211] [2. Non-aqueous electrolyte secondary battery]

[0212] As one embodiment of the present invention, the non-aqueous electrolyte secondary battery is a non-aqueous electrolyte secondary battery having a positive electrode having a positive electrode active material capable of intercalating and deintercalating metal ions and a negative electrode active material capable of intercalating and deintercalating metal ions, and comprising a non-aqueous electrolyte.

[0213] [2-1. Non-aqueous electrolyte]

[0214] The above-described non-aqueous electrolyte is used as the non-aqueous electrolyte. Alternatively, other non-aqueous electrolytes may be mixed with the above-described non-aqueous electrolyte without departing from the spirit of the invention.

[0215] [2-2. Negative electrode]

[0216] The following describes the negative electrode active material used in the negative electrode. There are no particular restrictions on the negative electrode active material if it is a substance that can electrochemically insert and extract metal ions such as lithium ions. Specific examples include carbonaceous materials, alloy materials, and lithium-containing metal composite oxide materials. One of these can be used alone, or two or more can be used in any combination.

[0217] <Negative Electrode Active Material>

[0218] Examples of anode active materials include carbonaceous materials, alloy materials, and lithium-containing metal composite oxide materials.

[0219] As carbonaceous materials, examples include (1) natural graphite, (2) artificial graphite, (3) amorphous carbon, (4) carbon-coated graphite, (5) graphite-coated graphite, and (6) resin-coated graphite.

[0220] (1) Examples of natural graphite include vein graphite, flake graphite, earthy graphite, and / or graphite particles made by applying spheroidizing or densification treatments to these graphites. Among these, spherical or ellipsoidal graphite made by applying spheroidizing treatment is particularly preferred from the perspective of particle filling properties and charge / discharge rate characteristics.

[0221] (2) Examples of artificial graphite include substances manufactured by graphitizing organic compounds such as coal tar pitch, coal-based heavy oil, atmospheric residue, petroleum-based heavy oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene sulfide, polyphenylene ether, furfuryl alcohol resin, phenolic resin, and imide resin at temperatures typically above 2500°C and below 3200°C, and then pulverizing and / or classifying them as needed. Silicon-containing compounds and boron-containing compounds may also be used as graphitization catalysts. Furthermore, examples include artificial graphite obtained by graphitizing mesophase carbon microspheres separated during the heat treatment of pitch. Further examples include artificial graphite composed of granulated particles made from primary particles. For example, graphite particles can be formed by aggregating or combining multiple flat particles with non-parallel orientation surfaces. The flat particles are obtained by mixing graphitizable carbonaceous material powders such as mesophase carbon microspheres and coke with graphitizable binders such as tar and pitch and graphitization catalysts, and then pulverizing them as needed.

[0222] (3) As amorphous carbon, examples include: amorphous carbon particles made by using easily graphitized carbon precursors such as tar and pitch as raw materials and performing heat treatment once or more in a temperature range (400 to 2200°C) where graphitization does not occur; and amorphous carbon particles made by using difficult-to-graphitize carbon precursors such as resin as raw materials and performing heat treatment.

[0223] (4) As carbon-coated graphite, examples include: mixing natural graphite and / or artificial graphite with carbon precursors such as tar, pitch, resin, etc., and performing heat treatment once or more in the range of 400 to 2300°C to obtain natural graphite and / or artificial graphite, using it as the core graphite, and coating the core graphite with amorphous carbon to form a carbon-graphite composite. The composite can be formed by coating the entire or part of the surface, or by using carbon from the carbon precursor source as a binder to combine multiple primary particles. In addition, carbon-graphite composites can also be obtained by reacting natural graphite and / or artificial graphite with hydrocarbon gases such as benzene, toluene, methane, propane, and aromatic volatile components at high temperature to deposit (CVD) carbon on the graphite surface.

[0224] (5) As graphite-coated graphite, examples include: mixing natural graphite and / or artificial graphite with carbon precursors such as tar, asphalt, resin and other easily graphitized organic compounds, and performing heat treatment once or more in the range of 2400 to 3200°C to obtain natural graphite and / or artificial graphite, which are used as core graphite, and graphite-coated graphite coating the entire or part of the surface of the core graphite with graphitized material.

[0225] (6) As resin-coated graphite, examples include: mixing natural graphite and / or artificial graphite with resin, drying at a temperature of less than 400°C to obtain natural graphite and / or artificial graphite, using it as core graphite, and resin-coated graphite with resin or the like coating the core graphite.

[0226] In addition, the carbonaceous materials mentioned in (1) to (6) above can be used alone or in combination with two or more in any ratio.

[0227] As an alloy material that can be used as a negative electrode active material, if it allows for the insertion and extraction of lithium, it can be any one of elemental lithium, elemental metals and alloys that form lithium alloys, or compounds such as their oxides, carbides, nitrides, silicides, sulfides, or phosphides, without particular limitation. As for the elemental metals and alloys that form lithium alloys, materials containing metals and half-metals of Groups 13 and 14 (i.e., excluding carbon) are preferred, and elemental metals of aluminum, silicon, and tin and alloys or compounds containing these atoms are more preferred. These materials can be used alone or in any combination and ratio of two or more.

[0228] <Properties of Carbonaceous Materials>

[0229] When using carbonaceous materials as negative electrode active materials, it is desirable for the materials to have the following physical properties.

[0230] (X-ray parameters)

[0231] The d-value (layer distance) of the lattice plane (002 plane) of the carbonaceous material, obtained by X-ray diffraction according to the method of the Japan Society for the Promotion of Science, is typically 0.335 nm or more; furthermore, it is typically 0.360 nm or less, preferably 0.350 nm or less, and even more preferably 0.345 nm or less. In addition, the cell size (Lc) of the carbonaceous material, obtained by X-ray diffraction according to the method of the Japan Society for the Promotion of Science, is preferably 1.0 nm or more, and more preferably 1.5 nm or more.

[0232] (Volume-based average particle size)

[0233] The volume-based average particle size of the carbonaceous material is the average particle size (median particle size) of the volume basis obtained by laser diffraction and scattering method, which is typically 1 μm or more, preferably 3 μm or more, further preferably 5 μm or more, and particularly preferably 7 μm or more. Furthermore, it is typically 100 μm or less, preferably 50 μm or less, more preferably 40 μm or less, further preferably 30 μm or less, and particularly preferably 25 μm or less.

[0234] When the volumetric average particle size is below the above range, there is an irreversible increase in capacity, leading to initial battery capacity loss. Furthermore, when it is above the above range, uneven coating is easily formed during electrode fabrication, resulting in unsatisfactory battery manufacturing processes.

[0235] (BET specific surface area)

[0236] The BET specific surface area of ​​carbonaceous materials is the value of the specific surface area measured using the BET method, typically 0.1 m². 2 ·g -1 The preferred value is 0.7m. 2 ·g -1 The above, preferably 1.0m 2 ·g -1 The above, especially preferred, is 1.5m. 2 ·g -1 That's all. In addition, it's usually 100m. 2 ·g -1 The following is preferred: 25m 2 ·g -1 The following is more preferably 15m 2 ·g -1 The following is particularly preferred: 10m 2 ·g -1 the following.

[0237] If the BET specific surface area is below this range, when used as a negative electrode material, the lithium capacity during charging is prone to deterioration, lithium is more likely to deposit on the electrode surface, and stability may decrease. On the other hand, if it is above this range, when used as a negative electrode material, its reactivity with non-aqueous electrolytes increases, gas generation is more likely to increase, and it is difficult to obtain a preferred battery.

[0238] <Composition and Manufacturing Method of Negative Electrode>

[0239] The electrode can be manufactured using any known method without significantly impairing the effects of the present invention. For example, it can be formed by adding a binder, solvent, thickener as needed, conductive material, filler, etc. to the negative electrode active material to make a slurry, coating it on a current collector, drying it, and then pressing it.

[0240] In addition, when using alloy materials, a thin film layer (negative electrode active material layer) containing the above-mentioned negative electrode active material can also be formed by methods such as vapor deposition, sputtering, and plating.

[0241] (Electrode density)

[0242] There are no particular restrictions on the electrode structure when the negative electrode active material is polarized, but the density of the negative electrode active material present on the current collector is preferably 1 g·cm³. -3 The above, more preferably 1.2 g·cm -3 The above, especially preferred, is 1.3 g·cm³. -3 The above. Furthermore, 2.2 g·cm³ is preferred. -3 The following is more preferably 2.1 g·cm⁻¹ -3 The following is a further preferred value: 2.0 g·cm³ -3 The following is particularly preferred: 1.9 g·cm³ -3 the following.

[0243] When the density of the negative electrode active material present on the current collector is higher than the above range, the negative electrode active material particles are damaged, leading to an increase in initial irreversible capacity and deterioration of high current density charge-discharge characteristics due to reduced permeability of the non-aqueous electrolyte near the current collector / negative electrode active material interface. Furthermore, when the density is lower than the above range, the conductivity between the negative electrode active materials decreases, the battery impedance increases, and the capacity per unit volume decreases.

[0244] [2-3. Positive electrode]

[0245] <Positive Electrode Active Material>

[0246] In one embodiment of the present invention, the positive electrode active material used in the positive electrode comprises a lithium transition metal compound, which contains at least Ni, Mn, and Co, wherein the molar ratio of Mn / (Ni + Mn + Co) is greater than 0 and less than 0.32, and the molar ratio of Ni / (Ni + Mn + Co) is greater than 0.45. The lithium transition metal compound is described below.

[0247] <Lithium transition metal compounds>

[0248] Lithium transition metal compounds refer to compounds having a structure that allows for the insertion and extraction of Li ions. Examples of lithium transition metal compounds used in this invention include substances represented by formula (I). Furthermore, substances with a layered structure that allows for two-dimensional diffusion of lithium ions are preferred. Here, the layered structure is described in further detail. Representative crystal systems for substances with layered structures include α-NaFeO2 type substances such as LiCoO2 and LiNiO2, which are hexagonal and can be classified into space group based on their symmetry:

[0249]

Number 1

[0250]

[0251] (Hereinafter referred to as "layered R(-3)m structure").

[0252] The term "layered LiMeO2" does not imply that it is limited to a layered R(-3)m structure. In addition, LiMnO2, which can be referred to as layered Mn, is a layered compound with the orthorhombic space group Pm2m. Furthermore, Li2MnO3, which can be referred to as the 213 phase, and also represented as Li[Li] 1 / 3 Mn 2 / 3 Although O2 has a monoclinic space group C2 / m structure, it is also composed of stacked Li layers and [Li 1 / 3Mn 2 / 3 A layered compound consisting of a layer of oxygen and a layer of oxygen.

[0253] The lithium transition metal compound preferably comprises the lithium transition metal compound shown in the following formula (I), and more preferably the lithium transition metal compound shown in the following formula (I).

[0254] Li 1＋x MO2 …(I)

[0255] In formula (I), x is typically -0.20 or higher and 0.50 or lower. The lower limit of x is preferably -0.05 or higher, more preferably -0.03 or higher, particularly preferably -0.02 or higher, and most preferably -0.01 or higher. Furthermore, the upper limit of x can be 0.1 or lower, preferably 0.06 or lower, more preferably 0.028 or lower, further preferably 0.020 or lower, particularly preferably 0.010 or lower, and most preferably 0.005 or lower. When x is within the above range, it is easy to fully exert the gas generation suppression effect brought about by its combination with monofluorophosphate and / or difluorophosphate contained in the electrolyte, thereby obtaining sufficient charge and discharge capacity, and is therefore preferred.

[0256] Furthermore, in formula (I), M is composed of at least Ni, Mn and Co, and the molar ratio of Mn / (Ni+Mn+Co) is greater than 0 and less than 0.32.

[0257] The lower limit of the Mn / (Ni+Mn+Co) molar ratio is preferably 0.05 or more, more preferably 0.08 or more, further preferably 0.10 or more, particularly preferably 0.12 or more, and most preferably 0.14 or more. Furthermore, the upper limit of the Mn / (Ni+Mn+Co) molar ratio is preferably 0.28 or less, more preferably 0.26 or less, further preferably 0.25 or less, particularly preferably 0.24 or less, and most preferably 0.23 or less.

[0258] If the molar ratio of Mn / (Ni+Mn+Co) is within the range mentioned above, then the ratio of Mn, which is independent of charging and discharging, is sufficiently small, and the battery becomes high-capacity, which is therefore preferred.

[0259] Furthermore, the lower limit of the Ni / (Ni+Mn+Co) molar ratio is 0.45 or more, preferably 0.50 or more, and more preferably 0.55 or more. In addition, the upper limit of the Ni / (Ni+Mn+Co) molar ratio is typically 0.95 or less, but may also be 0.85 or less, preferably 0.80 or less, more preferably 0.75 or less, further preferably 0.70 or less, particularly preferably 0.68 or less, and most preferably 0.64 or less.

[0260] If the molar ratio of Ni / (Ni+Mn+Co) is within the range mentioned above, then the ratio of Ni related to charge and discharge is sufficiently large, and the battery becomes high-capacity, which is therefore preferred.

[0261] Furthermore, the lower limit of the Co / (Ni+Mn+Co) molar ratio is not particularly limited, but is preferably 0.05 or more, more preferably 0.08 or more, even more preferably 0.10 or more, and particularly preferably 0.15 or more. In addition, the upper limit of the Co / (Ni+Mn+Co) molar ratio is not particularly limited, but is preferably 0.33 or less, more preferably 0.30 or less, even more preferably 0.28 or less, particularly preferably 0.26 or less, and most preferably 0.24 or less.

[0262] If the Co / (Ni+Mn+Co) molar ratio is within the range mentioned above, the charge and discharge capacity will increase, and therefore it is preferred.

[0263] Furthermore, in the above formula (I), the atomic ratio of oxygen is represented as 2 for convenience; however, some degree of non-stoichiometry may exist. Additionally, x in formula (I) represents the feed composition during the manufacturing stage of the lithium transition metal compound. Typically, commercially available batteries undergo aging after assembly. Therefore, during charging and discharging, there is a loss of Li content in the positive electrode.

[0264] Furthermore, lithium transition metal compounds can also be doped with different elements. These different elements can be selected from any one or more of the following: B, Na, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Ru, Rh, Pd, Ag, In, Sb, Te, Ba, Ta, Mo, W, Re, Os, Ir, Pt, Au, Pb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Bi, N, F, S, Cl, Br, I, As, Ge, P, Pb, Sb, Si, and Sn. Preferably, at least one element is selected from the group consisting of Fe, Cu, W, Mo, Nb, V, Ta, Mg, Al, Ti, Zr, Zn, Ca, Be, B, Bi, Li, Na, and K.

[0265] These different elements can be incorporated into the crystal structure of lithium transition metal compounds, or they can remain unincorporated into the crystal structure of lithium transition metal compounds, but rather exist as elements or compounds unevenly distributed on the particle surface or grain boundaries.

[0266] (Properties of positive electrode active materials containing lithium transition metal compounds or lithium transition metal compounds)

[0267] (1) Sulfates

[0268] The positive electrode active material may also contain sulfates. There is no particular limitation on the amount of sulfate that can be contained in the positive electrode active material, but a content of 15 μmol / g or higher is preferred as it readily exhibits the gas generation suppression effect of monofluorophosphate and / or difluorophosphate.

[0269] Furthermore, a value of 20 μmol / g or higher is more preferred, 25 μmol / g or higher is even more preferred, 32 μmol / g or higher is particularly preferred, and 35 μmol / g or higher is most preferred. Additionally, as an upper limit, considering the increased gas production due to side reactions, a value of 100 μmol / g or lower is preferred, 80 μmol / g or lower is more preferred, 60 μmol / g or lower is even more preferred, 50 μmol / g or lower is particularly preferred, and 30 μmol / g or lower is most preferred.

[0270] In addition, the sulfates contained in the positive electrode active material can be determined, for example, by water extraction ion chromatography.

[0271] (2) Average valence state of Ni

[0272] The lithium transition metal compound contained in the positive electrode active material has no particular limitation on the average Ni valence state in the uncharged state, but a valence of 2.1 or higher can increase the Ni ratio, resulting in a high-capacity battery, and is therefore preferred. Furthermore, a valence of 2.3 or higher is more preferred, even more preferred is 2.5 or higher, particularly preferred is 2.55 or higher, and most preferred is 2.6 or higher. Moreover, as an upper limit, considering the reduced structural stability of the active material, a valence of 3 or lower is preferred, more preferably 2.9 or lower, particularly preferred is 2.8 or lower, and most preferably 2.7 or lower.

[0273] The valence state of Ni in this invention will be described in detail here.

[0274] First, when the composition of the lithium transition metal compound is changed to the following composition (I'), M' is composed of Li, Ni and Mn, or Li, Ni, Mn and Co.

[0275] LiM'O2 …(I')

[0276] Furthermore, in the above formula (I'), the atomic ratio of oxygen is denoted as 2 for convenience; however, some degree of non-stoichiometry may also exist. When non-stoichiometry exists, the atomic ratio of oxygen is typically in the range of 2 ± 0.2, preferably in the range of 2 ± 0.15, more preferably in the range of 2 ± 0.12, even more preferably in the range of 2 ± 0.10, and particularly preferably in the range of 2 ± 0.05.

[0277] Furthermore, lithium transition metal compounds are particularly preferred to have the atomic configuration at the M' site in formula (I') as shown in formula (II) below.

[0278] M'=Li z / （2＋z） {(Ni （1＋y） / 2 Mn （1-y） / 2 ) 1-x Co x} 2 / （2＋z） …(II)

[0279] Here, the chemical significance of the Li composition (z and x) in lithium nickel manganese cobalt composite oxides, which are suitable compositions for lithium transition metal compounds, will be explained in more detail below.

[0280] The layered structure described above is not limited to the R(-3)m structure, but substances that can be classified as R(-3)m structures are preferred in terms of electrochemical performance.

[0281] To determine the compositional formulas x, y, and z of the aforementioned lithium transition metal compounds, the ratios of Li / Ni / Mn / Co in the compounds can be calculated by analyzing each transition metal and Li using inductively coupled plasma atomic emission spectrometry (ICP-AES), further analyzing the surface impurities Li using water extraction ion chromatography, and then determining the ratios of Li / Ni / Mn / Co in the aforementioned lithium transition metal compounds.

[0282] From a structural perspective, it can be assumed that the Li involved in z can also be substituted into the transition metal sites. Here, due to the Li involved in z, the average valence state of Ni becomes larger than valence 2 (generating valence 3 Ni) due to the principle of electroneutrality. Since z increases the average valence state of Ni, it becomes an indicator of the Ni valence state (the proportion of Ni(III)).

[0283] Furthermore, based on the above composition formula, if we calculate the Ni valence state (m) accompanying the changes in z and z', assuming that Co has a valence state of 3 and Mn has a valence state of 4, then we have:

[0284]

Number 2

[0285] .

[0286] The calculation results indicate that the Ni valence state is not solely determined by z, but is also a function of x and y. If z = 0 and y = 0, then it is independent of the x value, and the Ni valence state remains at 2. When z becomes negative, it means that the amount of Li in the active material is insufficient to meet the stoichiometric value, and the presence of substances with excessively large negative values ​​may prevent the expression of the effects of this invention. On the other hand, it also means that even with the same z value, the more abundant the composition (larger y value) and / or the more abundant the composition (larger x value), the higher the Ni valence state. When used in batteries, this results in improved rate and power characteristics, but on the other hand, the capacity is more likely to decrease. Therefore, it can be said that it is more preferable to define the upper and lower limits of the z value as functions of x and y.

[0287] Furthermore, when the x value is 0≦x≦0.1, within the range of low Co content, it not only reduces costs but also improves charge / discharge capacity, cycle characteristics, and safety when used as a lithium secondary battery designed to be charged at a high charging potential.

[0288] (3) pH

[0289] The pH of the aqueous solution of the lithium transition metal compound is not particularly limited, but a pH of 11 or higher at a liquid temperature of 25°C is preferred as it readily exhibits the gas generation suppression effect resulting from its combination with the monofluorophosphate and / or difluorophosphate contained in the electrolyte. Furthermore, a pH of 11.2 or higher is more preferred at a liquid temperature of 25°C, even more preferred is 11.4 or higher, particularly preferred is 11.6 or higher, and most preferably is 11.8 or higher. Moreover, as an upper limit, to reduce gas generation caused by side reactions, a pH of 13 or lower is preferred at a liquid temperature of 25°C, more preferably 12.7 or lower, particularly preferably 12.4 or lower, and most preferably 12 or lower.

[0290] In addition, as a method for determining the pH of the above-mentioned lithium transition metal compounds, 50g of deionized water was weighed in a beaker, and 5g of the sample was added while stirring. The pH value and the sample temperature were measured 10 minutes after the sample was added, while the liquid temperature and pH value were monitored.

[0291] (4) Carbonates

[0292] The positive electrode active material may also contain carbonates. There are no particular limitations on the content of carbonates that can be included as the positive electrode active material, but a content of 10 μmol / g or more is preferred as it readily and sufficiently exerts the gas generation suppression effect resulting from the combination with monofluorophosphates and / or difluorophosphates contained in the electrolyte. Furthermore, a content of 20 μmol / g or more is more preferred, further preferred is 40 μmol / g or more, particularly preferred is 60 μmol / g or more, and most preferably is 80 μmol / g or more. Moreover, as an upper limit, to reduce gas generation caused by side reactions, a content of 100 μmol / g or less is preferred, more preferably 98 μmol / g or less, particularly preferably 96 μmol / g or less, and most preferably 94 μmol / g or less.

[0293] In addition, the amount of carbonate contained in the above-mentioned lithium transition metal compounds can be determined, for example, by water extraction ion chromatography.

[0294] (5) Tap density

[0295] The lithium transition metal compounds that constitute the positive electrode active material are usually in powder form, and their tap density is not particularly limited, but is typically 1.8 g / cm³. 3 The above-mentioned large charge / discharge capacity when used as a battery is preferred. Furthermore, 2 g / cm³ is more preferable.3 The above is further optimized to be 2.1 g / cm³. 3 The above, especially preferred, is 2.2 g / cm³. 3 The optimal value is 2.3 g / cm³. 3 That's all. Furthermore, as an upper limit, to ensure sufficient power characteristics, 4.0 g / cm³ is preferred. 3 The preferred value is 3.8 g / cm³. 3 The following is particularly preferred: 3.6 g / cm³ 3 The optimal value is 3.4 g / cm³. 3 the following.

[0296] By using lithium transition metal compounds with high tap density, high-density cathodes can be formed. If the tap density of the lithium transition metal compound is within the above range, the amount of dispersion medium necessary for cathode formation becomes appropriate, and the amounts of conductive material and binder are also appropriate. Therefore, it is not limited by the filling rate of the lithium transition metal compound on the cathode, and the impact on battery capacity is also reduced.

[0297] The tap density of lithium transition metal compounds can be determined as follows: The sample is passed through a sieve with 300 μm apertures and falls into a 20 cm... 3 After filling the container with a tapping cell, the sample is vibrated 200 times with a stroke length of 10 mm using a powder density meter (e.g., a Tap Denser manufactured by Seishin Enterprise Co., LTD). The density is then calculated from the volume and weight of the sample.

[0298] Alternatively, the sample can be easily dropped into a 10mL graduated cylinder to fill the volume, then vibrated 200 times. The density can then be calculated from the volume and mass of the sample at that point.

[0299] (6) Surface coating

[0300] It can also be used to attach a substance with a different composition from the main body of the lithium transition metal compound (hereinafter appropriately referred to as "surface-attached substance") to the surface of the aforementioned lithium transition metal compound. Examples of surface-attached substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0301] These surface-adhesive substances can be attached to the surface of lithium transition metal compounds by methods such as: dissolving or suspending them in a solvent, adding them to the lithium transition metal compound for soaking, and then drying; dissolving or suspending a surface-adhesive substance precursor in a solvent, adding it to the lithium transition metal compound for soaking, and then reacting it by heating or the like; adding it to a lithium transition metal compound precursor and simultaneously calcining it, etc. Alternatively, in the case of carbon attachment, a method can be used to mechanically attach the carbon material subsequently in the form of, for example, activated carbon.

[0302] The mass of the surface-attached material adhering to the surface of the lithium transition metal compound is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more, relative to the mass of the lithium transition metal compound. Furthermore, it is preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less.

[0303] By attaching substances to the surface, the oxidation reaction of non-aqueous electrolytes on the surface of lithium transition metal compounds can be suppressed, thereby improving battery life. Furthermore, if the amount of material attached is within the aforementioned range, its effect can be fully realized without hindering lithium-ion adsorption and desorption, or easily increasing impedance.

[0304] (7) Shape

[0305] Lithium transition metal compounds can be shaped in various ways, including conventionally used blocky, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar forms. Furthermore, primary particles can aggregate to form secondary particles, which can also be spherical or ellipsoidal in shape.

[0306] (8) Median particle size d50

[0307] The median particle size d50 of lithium transition metal compounds (the secondary particle size when primary particles agglomerate to form secondary particles) can be determined using a laser diffraction / dispersed particle size distribution measuring device.

[0308] The median particle size d50 is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1 μm or more, and particularly preferably 3 μm or more; furthermore, it is preferably 30 μm or less, more preferably 20 μm or less, even more preferably 16 μm or less, and particularly preferably 15 μm or less. If the median particle size d50 is within the above range, it is easy to obtain a product with high packing density. Furthermore, lithium diffusion within the particles does not consume time, and the battery characteristics are less likely to degrade. In addition, when the positive electrode of the battery is manufactured, even when the active material, conductive material, binder, etc. are slurried with solvent and coated into a thin film, it is less likely to produce streaks or other defects.

[0309] Furthermore, by mixing two or more lithium transition metal compounds with different median particle sizes (d50) in any ratio, the fillability during cathode fabrication can be further improved.

[0310] The median particle size d50 of lithium transition metal compounds can be determined using a 0.1% (w / w) sodium hexametaphosphate aqueous solution as the dispersion medium. The dispersion of the lithium transition metal compound is ultrasonically dispersed for 5 minutes using a particle size analyzer (e.g., Horiba Seisakusho LA-920). The refractive index is set to 1.24 for measurement.

[0311] (9) Average primary particle size

[0312] When primary particles agglomerate to form secondary particles, the average primary particle size of the lithium transition metal compound is preferably 0.01 μm or more, more preferably 0.05 μm or more, even more preferably 0.08 μm or more, and particularly preferably 0.1 μm or more; furthermore, it is preferably 3 μm or less, more preferably 2 μm or less, even more preferably 1 μm or less, and particularly preferably 0.6 μm or less. Within the above range, spherical secondary particles are easily formed, the powder filling capacity is moderate, and the specific surface area is sufficiently ensured, thus suppressing the reduction of battery performance such as power characteristics.

[0313] In addition, the average primary particle size of lithium transition metal compounds can be determined by observation using a scanning electron microscope (SEM). Specifically, the average value of the maximum intercepts of the left and right boundary lines of any 50 primary particles relative to a straight line in the horizontal direction is obtained by taking a photograph at 10,000x magnification.

[0314] (10) BET specific surface area

[0315] The BET specific surface area of ​​lithium transition metal compounds is the value of the specific surface area determined by the BET method, preferably 0.2 m². 2 ·g -1 The above, more preferably 0.3m 2 ·g -1 The above is further preferred to be 0.4m 2 ·g -1 The above; in addition, 4.0m is preferred. 2 ·g -1 The following is more preferably 2.5m 2 ·g -1 Hereinafter, 1.5m is further preferred. 2 ·g -1 The following applies: If the BET specific surface area is within the above range, it is easier to prevent the degradation of battery performance. Furthermore, it ensures sufficient tap density and improves the coating properties during positive electrode formation.

[0316] The BET specific surface area of ​​lithium transition metal compounds was measured using a surface area meter (e.g., a fully automated surface area measuring device developed by Okura). Specifically, after pre-drying the sample at 150°C for 30 minutes under nitrogen flow, the BET specific surface area was measured using a nitrogen-helium mixed gas with the relative pressure of nitrogen relative to atmospheric pressure accurately adjusted to 0.3, via the nitrogen adsorption BET 1-point method based on gas flow. The specific surface area obtained in this measurement is defined as the BET specific surface area of ​​the lithium transition metal compounds of this invention.

[0317] (Preparation method of positive electrode active material containing lithium transition metal compounds)

[0318] There are no particular limitations on the method for preparing the positive electrode active material containing lithium transition metal compounds without departing from the spirit of this invention, and various methods can be given, including the conventional method for manufacturing inorganic compounds.

[0319] In particular, various methods can be considered for producing spherical or ellipsoidal positive electrode active materials. As one example, one method is to dissolve or pulverize transition metal raw materials such as transition metal nitrates and sulfates, along with other raw materials of other elements as needed, in a solvent such as water. While stirring, the pH is adjusted to produce a spherical precursor. After drying it as needed, a Li source such as LiOH, Li2CO3, or LiNO3 is added and calcined at high temperature to obtain the positive electrode active material.

[0320] In addition, as an example of other methods, one can cite the method of dissolving or pulverizing transition metal raw materials such as transition metal nitrates, sulfates, hydroxides, and oxides, along with other raw materials of other elements as needed, in a solvent such as water, drying and shaping them into spherical or ellipsoidal precursors using a spray dryer, adding Li sources such as LiOH, Li2CO3, and LiNO3 to them, and calcining them at high temperature to obtain positive electrode active materials.

[0321] As another example of a different method, one could cite a method in which transition metal raw materials such as transition metal nitrates, sulfates, hydroxides, and oxides are dissolved or pulverized and dispersed in solvents such as water along with Li sources such as LiOH, Li2CO3, and LiNO3, and other raw materials of other elements as needed. The precursors are then dried and shaped into spherical or ellipsoidal shapes using a spray dryer or similar equipment, and finally calcined at high temperatures to obtain the positive electrode active material.

[0322] In addition, in the selection of transition metal raw materials, by adjusting the amount of sulfate and carbonate used, adjusting the firing temperature, and whether or not to clean, the sulfate and carbonate content of the positive electrode active material described above can be made to the desired values.

[0323] The lithium transition metal compounds used in the positive electrode active material can be used alone or in combination with two or more of the above-mentioned compounds. Furthermore, they can be mixed with sulfides, phosphate compounds, and other lithium transition metal complex oxides. Examples of sulfides include compounds with two-dimensional layered structures such as TiS2 and MoS2, and compounds with the general formula Me. x Compounds represented by Mo6S8 (where Me represents various transition metals including Pb, Ag, and Cu) are examples. As phosphate compounds, examples include substances with an olivine structure, generally represented by LiMePO4 (where Me is at least one transition metal), specifically LiFePO4, LiCoPO4, LiNiPO4, and LiMnPO4. As lithium transition metal composite oxides, examples include substances with a three-dimensionally diffusing spinel structure and layered structures that allow two-dimensional diffusion of lithium ions. Substances with a spinel structure are generally represented by LiMe2O4 (where Me is at least one transition metal), specifically LiMn2O4, LiCoMnO4, and LiNi... 0.5 Mn 1.5 O4, LiCoVO4, etc. Substances with a layered structure include, specifically, LiCoO2, LiNiO2, and LiNi. 1-x Co x O2, LiNi 1-x- y Co x Mn y O2, LiNi 0.5 Mn 0.5 O2, Li 1.2 Cr 0.4 Mn 0.4 O2, Li 1.2 Cr 0.4 Ti 0.4 O2, LiMnO2, etc.

[0324] <Composition and Manufacturing Method of Positive Electrode for Lithium Secondary Batteries>

[0325] The positive electrode for lithium secondary batteries is a substance formed by forming a layer of positive electrode active material containing the above-mentioned lithium transition metal compound and a binder on a current collector.

[0326] The positive electrode active material layer is usually made by dry mixing positive electrode active material containing lithium transition metal compounds, binder, and conductive materials and thickeners as needed, forming a sheet-like material, pressing it onto the positive electrode current collector, or dissolving or dispersing these materials in a liquid medium to form a slurry, coating it onto the positive electrode current collector, and then drying it.

[0327] As materials for the positive electrode current collector, commonly used materials include metals such as aluminum, stainless steel, nickel-plated materials, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper. Furthermore, in terms of shape, for metal materials, examples include metal foil, metal cylinder, metal coil, metal plate, metal film, stretched metal mesh, perforated metal mesh, and foamed metal; for carbon materials, examples include carbon plates, carbon films, and carbon cylinders.

[0328] In addition, the film can also be appropriately shaped into a mesh.

[0329] There are no particular restrictions on the binder used in the manufacture of the layer serving as the positive electrode active material. In the case of a coating method, any material that is stable relative to the liquid medium used in electrode manufacturing is acceptable. Specific examples include resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber, isoprene rubber, butadiene rubber, and ethylene-propylene rubber; and styrene-butadiene-styrene block copolymers. Thermoplastic elastomers such as their hydrogenation products, EPDM (ethylene-propylene-diene terpolymer), styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer and their hydrogenation products, soft resin-like polymers such as isotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, propylene-α-olefin copolymer, fluorinated polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, tetrafluoroethylene-ethylene copolymer, and polymer compositions with ionic conductivity of alkali metal ions (especially lithium ions), etc.

[0330] In addition, these substances can be used alone or in combination with two or more in any ratio.

[0331] The proportion of binder in the positive electrode active material layer is typically above 0.1% by mass and below 80% by mass. If the proportion of binder is too low, the lithium transition metal compounds may not be fully retained, resulting in insufficient mechanical strength of the positive electrode and potential deterioration of battery performance such as cycle characteristics. On the other hand, if the proportion is too high, it may lead to a decrease in battery capacity and conductivity.

[0332] The positive electrode active material layer usually contains conductive materials to improve conductivity.

[0333] There are no particular restrictions on the types of materials that can be used. For specific examples, one can include metallic materials such as copper and nickel; graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; and carbon materials such as needle coke and amorphous carbon.

[0334] In addition, these substances can be used alone or in combination with two or more in any ratio.

[0335] The proportion of conductive material in the positive electrode active material layer is typically between 0.01% and 50% by mass. If the proportion of conductive material is too low, the conductivity will be insufficient; conversely, if it is too high, the battery capacity will be reduced.

[0336] The liquid medium used to form the slurry is not particularly limited in type; it can dissolve or disperse the positive electrode active material containing lithium transition metal compounds, binder, and conductive materials and thickeners used as needed. Either aqueous or organic solvents can be used. Examples of aqueous solvents include water and alcohols, while examples of organic solvents include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran (THF), toluene, acetone, dimethyl ether, dimethylacetamide, hexamethylphosphoramide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, and hexane. Especially when using aqueous solvents, dispersants and thickeners can be added together, and latex such as SBR can be used for slurry formation.

[0337] In addition, these solvents can be used alone, or in any combination and ratio of two or more.

[0338] The proportion of lithium transition metal compounds, which serve as the cathode material, in the positive electrode active material layer is typically between 10% and 99.9% by mass. If the proportion of lithium transition metal compounds in the positive electrode active material layer is too high, the cathode strength tends to be insufficient; if it is too low, the capacity becomes inadequate.

[0339] In addition, the thickness of the positive electrode active material layer is usually between 10 and 200 μm.

[0340] Here, the positive electrode of the present invention has a plate density of 3.0 g / cm³. 3 The above. Furthermore, a concentration of 3.2 g / cm³ is preferred. 3 The above, more preferably 3.3 g / cm³ 3 The above is further optimized to be 3.4 g / cm³. 3 The above, especially preferred, is 3.6 g / cm³. 3 That's all. Furthermore, as an upper limit, to minimize the risk of a decrease in input / output power characteristics, 4.2 g / cm³ is preferred. 3 The preferred value is 4.1 g / cm³. 3 The following is specifically 4.0 g / cm 3 The optimal value is 3.9 g / cm³.3 the following.

[0341] To increase the plate density of the positive electrode to the aforementioned range, it can be achieved by compacting the coated and dried positive electrode active material layer using a roller press. To obtain the desired plate density, the pressure of the roller press can be adjusted appropriately.

[0342] [2-4. Diaphragm]

[0343] To prevent short circuits, a diaphragm is usually placed between the positive and negative electrodes. In this case, the non-aqueous electrolyte is typically used after immersing the diaphragm.

[0344] There are no particular restrictions on the material or shape of the diaphragm, and any known material may be used without significantly impairing the effect of the present invention. Among these, it is preferable to use porous sheet or non-woven fabric articles formed of materials that are stable relative to non-aqueous electrolytes and that employ resins, glass fibers, inorganic materials, etc., and have excellent liquid retention properties.

[0345] As membrane materials made of resin or glass fiber, for example, polyethylene, polypropylene and other polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, glass filter media, etc., can be used. Among these, glass filter media and polyolefins are preferred, and polyolefins are more preferred. These materials can be used alone or in combination with two or more in any ratio.

[0346] The thickness of the diaphragm is arbitrary, typically 1 μm or more, preferably 5 μm or more, and more preferably 10 μm or more. Furthermore, it is typically 50 μm or less, preferably 40 μm or less, and more preferably 30 μm or less.

[0347] When the separator is too thin compared to the aforementioned range, its insulation and mechanical strength decrease. Furthermore, when it is too thick compared to the aforementioned range, not only do battery performance characteristics such as rate characteristics decrease, but the overall energy density of the non-aqueous electrolyte secondary battery also decreases.

[0348] Furthermore, when porous materials such as porous sheets or nonwoven fabrics are used as the diaphragm, the porosity of the diaphragm is arbitrary, typically 20% or more, preferably 35% or more, and more preferably 45% or more. Additionally, it is typically 90% or less, preferably 85% or less, and more preferably 75% or less.

[0349] When the porosity is too small compared to the above range, there is a tendency for increased membrane impedance and deteriorated rate characteristics. Furthermore, when the porosity is too large compared to the above range, there is a tendency for decreased mechanical strength and reduced insulation of the membrane.

[0350] Furthermore, the average pore size of the membrane is arbitrary, typically 0.5 μm or less, preferably 0.2 μm or less. It is also typically 0.05 μm or more. When the average pore size is higher than the above range, short circuits are more likely to occur. Furthermore, when it is lower than the above range, membrane impedance increases and rate characteristics decrease.

[0351] On the other hand, as inorganic materials, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate can be used. Materials in granular or fibrous form can also be used.

[0352] As the form of the separator, separators in the shape of films such as non-woven fabrics, woven fabrics, and microporous films can be used. Among the film shapes, materials with a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm are suitable. In addition to the above-mentioned independent film shapes, separators formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive and / or negative electrodes can also be used. For example, a porous layer can be formed on both sides of the positive electrode using a fluororesin as an adhesive, with 90% of the alumina particles having a particle size of less than 1 μm forming a porous layer.

[0353] The characteristics of the separator in a non-aqueous electrolyte secondary battery can be understood through the Gurley value. The Gurley value indicates the difficulty of air passage in the thickness direction of the film, expressed as the number of seconds required for 100 ml of air to pass through the film. Therefore, a small value indicates easy passage, while a large value indicates difficult passage. That is, a small value indicates good connectivity in the thickness direction of the film, while a large value indicates poor connectivity. Connectivity refers to the degree of interconnection of pores in the thickness direction of the film. If the separator of the present invention has a low Gurley value, it can be used for various applications. For example, when used as a separator for a non-aqueous lithium secondary battery, a low Gurley value means easy movement of lithium ions and excellent battery performance, and is therefore preferred. The Gurley value of the separator is arbitrary, preferably 10 to 1000 seconds / 100 ml, more preferably 15 to 800 seconds / 100 ml, and even more preferably 20 to 500 seconds / 100 ml. If the Gurley value is below 1000 seconds / 100 ml, the resistance is substantially low, making it a preferred separator.

[0354] [2-5. Battery Design]

[0355] <Electrode Set>

[0356] The electrode assembly can be either a stacked structure formed by the positive electrode plate and the negative electrode plate separated by the diaphragm, or a structure in which the positive electrode plate and the negative electrode plate are wound into a spiral shape separated by the diaphragm.

[0357] The proportion of the electrode assembly volume in the battery internal volume (hereinafter referred to as the electrode assembly percentage) is typically 40% or more, preferably 50% or more. Furthermore, it is typically 90% or less, preferably 80% or less.

[0358] If the electrode assembly occupancy rate is lower than the above range, the battery capacity will decrease. In addition, if it is higher than the above range, the following situations will occur: there is less space, the components will expand due to the battery getting hot, the vapor pressure of the liquid components of the electrolyte will increase, the internal pressure will rise, and the battery's repeated charge and discharge performance, high temperature storage and other characteristics will decrease. Furthermore, the vent valve that releases the internal pressure will be activated.

[0359] <Protective Components>

[0360] As protective components, the following can be used: PTC (Positive Temperature Coefficient) which increases impedance when abnormally heated or when excessive current flows through it; thermal fuses; thermistors; and valves (current cut-off valves) that cut off the current flowing in the circuit due to a sharp rise in internal pressure or temperature of the battery when abnormally heated. Preferably, these protective components are designed to prevent activation under normal high-current use, and more preferably, they are designed to prevent abnormal heating or thermal runaway even without protective components.

[0361] <Exterior body>

[0362] The non-aqueous electrolyte secondary battery of the present invention is typically constructed by housing the aforementioned non-aqueous electrolyte, negative electrode, positive electrode, separator, etc., within an outer casing. This outer casing is not particularly limited, and any known material may be used without significantly impairing the effects of the present invention. Specifically, the material of the outer casing is arbitrary, and is generally suitable for materials such as nickel-plated steel sheet, stainless steel, aluminum or its alloys, magnesium alloys, nickel, titanium, or laminated films of resin and aluminum foil.

[0363] Among the aforementioned metal casings, examples include materials that form sealed structures by fusing metals together using laser welding, resistance welding, or ultrasonic welding, or materials that use the aforementioned metals to form a fastening structure through resin gaskets.

[0364] Examples of outer casings using the aforementioned laminated film include materials that form a sealed structure by thermally fusing resin layers together. To improve sealing, the resin layers may also be spaced with a resin different from the resin used for the laminated film.

[0365] In particular, when the resin layer is thermally fused to form a closed structure through the current collector terminal, since it is a combination of metal and resin, the resin used as the spacer is a resin with polar groups or a modified resin with polar groups introduced into it.

[0366] Furthermore, the shape of the outer casing is arbitrary, and can be any of the following: cylindrical, square, stacked, coin-shaped, large, etc.

[0367] <Battery Voltage>

[0368] The non-aqueous electrolyte secondary battery of the present invention is typically used with a battery voltage of 4.0V or higher. Preferably, the battery voltage is 4.1V or higher, more preferably 4.15V or higher, and most preferably 4.2V or higher. This is because increasing the battery voltage improves the battery's energy density.

[0369] On the other hand, increasing the battery voltage leads to an increase in the positive electrode potential and an increase in side reactions on the positive electrode surface. The battery of the present invention solves this problem; however, if the voltage is too high, the amount of side reactions on the positive electrode surface becomes excessive, and the battery characteristics deteriorate. Therefore, the upper limit of the battery voltage is preferably 5V or less, more preferably 4.8V or less, and most preferably 4.6V or less.

[0370] <Reasons for the effectiveness of this invention>

[0371] The reason for the effectiveness of this invention is not yet clear, but the following inferences can be made.

[0372] To increase the capacity of automotive batteries, researchers are experimenting with using high-capacity lithium transition metal compounds as positive electrode active materials. Such high-capacity lithium transition metal compounds can be achieved, for example, by reducing the amount of Mn and increasing the amount of Ni.

[0373] However, problems have been found in positive electrodes like these, such as low capacity retention after high-temperature storage, increased storage gas volume and metal dissolution after high-temperature storage, high impedance after high-temperature storage, and large heat generation at high temperatures when used as a secondary battery with a non-aqueous electrolyte.

[0374] After conducting research, the inventors presumed the following mechanism to exist.

[0375] That is, by decreasing the Mn content and increasing the Ni content, the Li content within the lithium transition metal compound crystal during charging will decrease to increase capacity. In this case, oxygen atoms within the lithium transition metal compound crystal become unstable and activated. Therefore, it can be assumed that while the oxidation capacity of the positive electrode increases, the surface crystal structure collapses, transforming into a rock salt structure. It is presumed that the lithium transition metal compound with increased oxidation capacity decomposes the non-aqueous electrolyte in the battery, causing gas generation, metal dissolution, and increased heat generation at high temperatures. Furthermore, it is presumed that the collapse of the crystal structure on the surface of the lithium transition metal compound leads to decreased capacity and increased impedance after high-temperature storage.

[0376] In contrast, the inventors discovered that by increasing the plate density of the positive electrode to a certain extent and including a specific phosphorus compound in the non-aqueous electrolyte, the instability of oxygen atoms in the crystal of lithium transition metal compounds can be suppressed, thereby inhibiting the decrease in capacity retention after high-temperature storage, reducing the amount of gas generated and metal dissolution caused by the decomposition of the non-aqueous solvent in the non-aqueous electrolyte, reducing the impedance after high-temperature storage, and reducing the heat generation at high temperatures.

[0377] The reason for this is not yet clear, but it is presumed that when the specific phosphorus compound of the present invention decomposes into LiF, the LiF appears on the surface of the lithium transition metal compound and can react with the surface of the lithium transition metal compound with increased oxidation capacity, suppressing the instability of oxygen atoms in the crystal, suppressing the decrease in capacity retention after high-temperature storage, gas generation and metal dissolution caused by electrolyte decomposition, reducing impedance after high-temperature storage, and reducing heat generation at high temperatures.

[0378]

Example

[0379] Next, specific embodiments will be described in more detail, but the present invention is not limited to these examples.

[0380] The abbreviations of the compounds used in this embodiment are shown below.

[0381] Compound 1: Lithium difluorophosphate

[0382] [Evaluation of Non-Aqueous Electrolyte Secondary Batteries]

[0383] • Initial charge and discharge

[0384] In a constant temperature bath at 25°C, sheet-shaped non-aqueous electrolyte secondary batteries were charged at 0.05C (the rated capacity of the 1-hour rate discharge is defined as the current value for discharging for 1 hour, and the same applies below) for 4 hours, and then discharged at a constant current of 0.2C until 2.5V. Next, two charge-discharge cycles were performed. As one cycle, the batteries were charged at a constant current-constant voltage of 0.2C until the specified voltage was reached, and then discharged at a constant current of 0.2C until 2.5V was reached.

[0385] Furthermore, after constant current-constant voltage charging at 0.2C to 4.0V, the battery is stabilized by storing it at 45°C for 42 hours. Then, it is constant current discharged at 25°C to 2.5V, followed by constant current-constant voltage charging at 0.2C to the specified voltage. Then, it is constant current discharged at 0.2C to 2.5V, and the discharge capacity at this point is taken as the capacity before storage (A). Next, it is constant current-constant voltage charged at 0.2C to the specified voltage. The specified voltage is typically 4.2V, but can also be 4.3V or 4.4V.

[0386] Storage test

[0387] The batteries, after initial charge-discharge, were stored at 85°C for 24 hours. After sufficient cooling, the batteries were immersed in an ethanol bath to measure their volume. The amount of gas generated was determined based on the volume change before and after the storage test and was taken as the storage gas amount. The proportion of the reduction in storage gas caused by the additives was taken as the "storage gas suppression rate" (for example, the storage gas suppression rate (%) of Example 1 = {(storage gas amount of Comparative Example 1 - storage gas amount of Example 1) / storage gas amount of Comparative Example 1} × 100). The discharge capacity of the battery when it was discharged at a constant current of 0.2C to 2.5V in a constant temperature bath at 25°C was taken as the storage capacity (B). The ratio of the storage capacity (B) to the storage capacity (A) was taken as the "storage capacity residual rate".

[0388] In addition, it can be said that the higher the residual capacity after storage, the better, and the smaller the value of the stored gas, the less the battery expansion, which is preferred.

[0389] Impedance after storage test

[0390] After storage testing, the device was charged at 0.2C using a constant current-constant voltage method until it reached 4.2V, and then a 10mV AC voltage (0.1Hz) was applied for measurement. This result was taken as the "impedance after storage," and the percentage reduction in impedance due to the additive was taken as the "impedance suppression rate."

[0391] • Metal leaching after storage test

[0392] The amount of metal leaching is determined by quantifying the amount of metal deposited on the negative electrode. The amount of metal deposited on the negative electrode is calculated by analyzing the total amount of Ni, Mn, and Co leached by ICP (Inductively Coupled Plasma) emission spectroscopy after the negative electrode acid is decomposed. Here, the reduction in metal leaching caused by additives is defined as the "metal leaching inhibition amount".

[0393] Methods for determining calorific value

[0394] After initial charge and discharge, the battery was charged at a constant current-constant voltage of 0.2C to 4.5V. The positive electrode was then removed from the battery and placed in a test battery along with the electrolyte. Measurements were performed using a Calvius calorimeter. The measurement was conducted by heating to 300°C at a rate of 1K / min. The ratio of the total heat generated from 100°C to 300°C to the charging capacity up to 4.5V was defined as the "heat generation per unit capacity." Furthermore, the percentage reduction in heat generation caused by additives was defined as the "heat suppression rate."

[0395] Method for determining tap density

[0396] The tap density of lithium transition metal compounds is determined by dropping the sample into a 10 mL graduated cylinder to fill the volume, then vibrating it 200 times. The density is then calculated from the volume at that point and the mass of the sample.

[0397] Methods for the determination of sulfates and carbonates

[0398] Sulfates and carbonates contained in the positive electrode active material can be determined by water extraction ion chromatography.

[0399] pH measurement methods

[0400] pH: Weigh 50g of deionized water into a beaker, add 5g of the sample while stirring, and stir at 25℃ for 30 minutes. Then, while maintaining the liquid temperature at 25℃, measure the pH value.

[0401] Methods for determining the valence state of Ni

[0402] The ratio of each transition metal to Li was analyzed by water extraction ion chromatography and inductively coupled plasma atomic emission spectrometry (ICP-AES), and the ratio was calculated accordingly.

[0403] [Example]

[0404] [Fabrication of Non-Aqueous Electrolyte Secondary Batteries]

[0405] <Preparation of non-aqueous electrolytes>

[0406] Based on a non-aqueous electrolyte solution in which 1 mol / L (based on the concentration in a non-aqueous electrolyte) of fully dried LiPF6 is dissolved in a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3:7) under a dry argon atmosphere, and further dissolved in 2% by mass of fully dried ethylene carbonate, two non-aqueous electrolyte solutions are further prepared: one in which 1% by mass (based on the concentration in a non-aqueous electrolyte) of compound 1 is dissolved, and the other in which compound 1 is not dissolved.

[0407] Using this non-aqueous electrolyte, a non-aqueous electrolyte secondary battery was fabricated using the following method, and the following evaluation was performed.

[0408] <The Making of Positive Electrode>

[0409] The lithium-nickel-manganese-cobalt composite oxide used as the positive electrode active material includes the following three types: NMC622 (Li 1.00 Ni 0.61 Mn 0.19 Co 0.20O2: Mn / (Ni+Mn+Co) molar ratio = 0.19, Ni / (Ni+Mn+Co) molar ratio = 0.61, sulfate concentration = 38 μmol / g, carbonate concentration = 91 μmol / g, average Ni valence state = 2.63, aqueous solution pH = 11.88, tap density = 2.39 g / cm³ 3 ), NMC532 (Li 1.05 Ni 0.52 Mn 0.29 Co 0.20 O2: Mn / (Ni+Mn+Co) molar ratio = 0.29, Ni / (Ni+Mn+Co) molar ratio = 0.52, sulfate concentration = 30 μmol / g, carbonate concentration = 16 μmol / g, average valence state of Ni = 2.51, aqueous solution pH = 11.75, tap density: 2.39 g / cm³ 3 ), or NMC111 (Li 1.05 Ni 0.34 Mn 0.33 Co 0.33 O2: Mn / (Ni+Mn+Co) molar ratio = 0.33, Ni / (Ni+Mn+Co) molar ratio = 0.34, sulfate concentration = 14 μmol / g, carbonate concentration = 12 μmol / g, average Ni valence state = 2.15, aqueous solution pH = 11.12, tap density: 1.55 g / cm³ 3 Various positive electrode active materials (94 parts by mass), acetylene black (3 parts by mass) as a conductive material, polyvinylidene fluoride (PVdF) (3 parts by mass) as a binder, and polyvinylpyrrolidone (0.07 parts by mass) as a dispersant are mixed and slurried in N-methyl-2-pyrrolidone. This mixture is then uniformly coated onto an aluminum foil with a thickness of 15 μm. After drying, it is rolled to form a positive electrode (hereinafter referred to as positive electrode 1). The electrode plate density of the positive electrode can be achieved by setting the rolling pressure to 0–13 kN / cm, resulting in 2.4, 2.8, 3.0, 3.2, or 3.3 g / cm³. 3 Five types of positive electrode densities.

[0410] <Making the Negative Electrode>

[0411] To 49 parts by weight of graphite powder, 50 parts by weight of an aqueous dispersion of sodium carboxymethyl cellulose (1% by weight) as a thickener and 1 part by weight of an aqueous dispersion of styrene-butadiene rubber (49% by weight) as a binder were added, and the mixture was stirred using a disperser to form a slurry. The resulting slurry was uniformly coated onto a 10 μm thick copper foil, dried, and then rolled to form a negative electrode.

[0412] <Manufacturing of Non-Aqueous Electrolyte Secondary Batteries>

[0413] The above-mentioned positive electrode, negative electrode, and polyolefin separator are stacked in the order of negative electrode, separator, and positive electrode. The battery element thus obtained is wrapped with an aluminum laminate film, injected with the aforementioned non-aqueous electrolyte, and then vacuum-sealed to produce a sheet-like non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 15 are produced with the following combinations: three positive electrode active materials, five positive electrode plate densities, and two non-aqueous electrolytes distinguished by the presence or absence of compound 1, as shown in Table 1.

[0414] Table 1

[0415]

[0416] Table 2 shows the residual capacity and storage gas suppression rate after storage. As shown in Table 2, when Compound 1 is added to the non-aqueous electrolyte of a non-aqueous electrolyte secondary battery containing a positive electrode active material with a specific composition and a specific electrode density, the residual capacity after storage is improved and the amount of storage gas is suppressed. That is, a non-aqueous electrolyte secondary battery with excellent high-temperature life is obtained. In Comparative Examples 6 and 8, the residual capacity is extremely low, with two significant figures representing "0.0%".

[0417] Table 2

[0418]

[0419] Table 3 shows the impedance and impedance suppression rate after storage. As shown in Table 3, adding Compound 1 to the non-aqueous electrolyte of a non-aqueous electrolyte secondary battery with a positive electrode containing a specific composition of positive electrode active material and a specific plate density can reduce the impedance after storage. Since the battery's internal impedance is related to the heat generated during charging, a non-aqueous electrolyte secondary battery with low heat generation during charging, even after high-temperature storage, can be obtained, exhibiting excellent safety.

[0420] Table 3

[0421]

[0422] Table 4 shows the heat generation and heat suppression rate per unit capacity. As shown in Table 4, adding Compound 1 to the non-aqueous electrolyte of a non-aqueous electrolyte secondary battery with a positive electrode containing a specific composition of positive electrode active material and a specific electrode density can reduce the heat generation per unit capacity. This results in a high-capacity non-aqueous electrolyte secondary battery with low heat generation and excellent safety.

[0423] Table 4

[0424]

[0425] Table 5 shows the metal dissolution inhibition amount. As shown in Table 5, adding Compound 1 to the non-aqueous electrolyte of a non-aqueous electrolyte secondary battery with a positive electrode containing a specific composition of positive electrode active material and a specific electrode density improves the metal dissolution inhibition effect. That is, a high-capacity non-aqueous electrolyte secondary battery with low metal dissolution from the positive electrode and excellent safety can be obtained.

[0426] Table 5

[0427]

[0428] [Example 5]

[0429] [Fabrication of Non-Aqueous Electrolyte Secondary Batteries]

[0430] <Preparation of non-aqueous electrolytes>

[0431] In a dry argon atmosphere, 1 mol / L (based on the concentration in the non-aqueous electrolyte) of thoroughly dried LiPF6 was dissolved in a mixture of ethylene carbonate and methyl ethyl carbonate (volume ratio 3:7). Further, 2% by mass of thoroughly dried ethylene carbonate and 1% by mass (based on the concentration in the non-aqueous electrolyte) of compound 1 were dissolved to prepare a non-aqueous electrolyte.

[0432] Using this non-aqueous electrolyte, a non-aqueous electrolyte secondary battery was fabricated using the following method, and the following evaluation was performed.

[0433] <The Making of Positive Electrode>

[0434] The lithium nickel manganese cobalt composite oxide (Li) will be used as the positive electrode active material. 1.00 Ni 0.61 Mn 0.19 Co 0.20 O2: Mn / (Ni+Mn+Co) molar ratio = 0.19, Ni / (Ni+Mn+Co) molar ratio = 0.61, sulfate concentration = 38 μmol / g, carbonate concentration = 91 μmol / g, average Ni valence state = 2.63, aqueous solution pH = 11.88, tap density = 2.39 g / cm³ 3 90 parts by weight of acetylene black (as a conductive material), 7 parts by weight of polyvinylidene fluoride (PVdF) (as a binder), and 0.07 parts by weight of polyvinylpyrrolidone (as a dispersant) were mixed and slurried in N-methyl-2-pyrrolidone. This mixture was then uniformly coated onto an aluminum foil with a thickness of 15 μm. After drying, it was rolled to form a positive electrode (hereinafter referred to as positive electrode 6). The electrode plate density of positive electrode 6 is 3.3 g / cm³. 3 .

[0435] <Making the Negative Electrode>

[0436] Similar to Examples 1-4 and Comparative Examples 1-15, the negative electrodes of Examples 5, 6 and Comparative Example 16 were prepared.

[0437] <Manufacturing of Non-Aqueous Electrolyte Secondary Batteries>

[0438] Similar to Examples 1-4 and Comparative Examples 1-15, sheet-shaped non-aqueous electrolyte secondary batteries of Examples 5, 6 and Comparative Example 16 were prepared.

[0439] [Comparative Example 16]

[0440] Except that the non-aqueous electrolyte does not contain compound 1, a non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 5.

[0441] Table 6 shows the residual capacity after storage, the amount of stored gas, and the amount of metal leaching after the storage test for Example 6 and Comparative Example 16.

[0442] [Example 6]

[0443] In addition to using lithium nickel manganese cobalt composite oxide (Li) as the positive electrode active material 1.05 Ni 0.52 Mn 0.29 Co 0.20 O2: Mn / (Ni+Mn+Co) molar ratio = 0.29, Ni / (Ni+Mn+Co) molar ratio = 0.52, sulfate concentration = 30 μmol / g, carbonate concentration = 16 μmol / g, average valence state of Ni = 2.51, aqueous solution pH = 11.75, tap density: 2.39 g / cm³ 3 Except for Example 5, a positive electrode (hereinafter referred to as positive electrode 7) was fabricated, and a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 5, except that the positive electrode was used. Furthermore, the plate density of positive electrode 7 was 3.3 g / cm³. 3 .

[0444] [Comparative Example 17]

[0445] Except for using the positive electrode 7 used in Example 6 above, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Comparative Example 16.

[0446] Table 7 shows the residual capacity after storage, storage gas suppression rate, and metal leaching after storage tests for Example 6 and Comparative Example 17.

[0447] Table 6

[0448]

[0449] Table 7

[0450]

[0451] As shown in Table 6, when Compound 1 is added to the non-aqueous electrolyte of a non-aqueous electrolyte secondary battery with a positive electrode active material containing a specific composition and a specific amount of sulfate, and a specific plate density, the residual capacity after storage is improved, the amount of stored gas is suppressed, and the amount of metal dissolution is reduced. That is, a non-aqueous electrolyte secondary battery with excellent high-temperature life and low heat generation at high temperatures can be obtained.

[0452] As shown in Table 7, when Compound 1 is added to the non-aqueous electrolyte of a non-aqueous electrolyte secondary battery with a sulfate-containing positive electrode, the residual capacity after storage is improved, the amount of stored gas is suppressed, and the amount of metal dissolution is reduced. That is, a non-aqueous electrolyte secondary battery with excellent high-temperature life and low heat generation at high temperatures can be obtained.

Claims

1. A non-aqueous electrolyte secondary battery, comprising: a positive electrode having a positive electrode active material capable of intercalating and deintercalating metal ions, a negative electrode having a negative electrode active material capable of intercalating and deintercalating metal ions, a non-aqueous electrolyte, and a separator. The positive electrode active material comprises a lithium transition metal compound, and contains at least Ni, Mn, and Co. The Mn / (Ni + Mn + Co) molar ratio is greater than 0 and less than 0.28, the Ni / (Ni + Mn + Co) molar ratio is greater than 0.45, and the electrode plate density is 3.0 g / cm³. 3 The non-aqueous electrolyte contains monofluorophosphate and / or difluorophosphate, and the total content of monofluorophosphate and difluorophosphate in the non-aqueous electrolyte is 0.01% by mass or more.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material comprises a lithium transition metal compound represented by formula (I) below. That 1＋x MO2 …(I) In the above formula (I), x is greater than -0.05 and less than 0.06, and M is composed of at least Ni, Mn and Co.

3. The non-aqueous electrolyte secondary battery according to claim 2, wherein x is 0.028 or less.

4. In the non-aqueous electrolyte secondary battery according to claim 1, the molar ratio of Mn / (Ni+Mn+Co) is 0.24 or less.

5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the Ni / (Ni+Mn+Co) molar ratio is 0.55 or higher.

6. The non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode plate density of the positive electrode is 3.2 g / cm³. 3 above.

7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the plate density of the positive electrode is 3.3 g / cm³. 3 above.

8. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material further comprises sulfate.

9. In the non-aqueous electrolyte secondary battery according to claim 8, the amount of sulfate contained in the positive electrode active material is 15 μmol / g or more.

10. The non-aqueous electrolyte secondary battery according to claim 1, wherein the average valence state of Ni in the lithium transition metal compound in the uncharged state is 2.1 or higher.

11. The non-aqueous electrolyte secondary battery according to claim 1, wherein the pH of the aqueous solution of the lithium transition metal compound is above 11 at a base temperature of 25°C.

12. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material comprises more than 10 μmol / g of carbonate.

13. The non-aqueous electrolyte secondary battery according to claim 1, wherein the tap density of the lithium transition metal compound is 1.8 g / cm³. 3 above.

14. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode has a positive electrode active material layer, the thickness of which is 10-200 μm.

15. The non-aqueous electrolyte secondary battery according to claim 1, wherein the thickness of the separator is more than 1 μm and less than 50 μm.

16. The non-aqueous electrolyte secondary battery according to claim 1, wherein the material of the separator comprises at least one selected from polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, and glass filter media.

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