Non-aqueous electrolyte and non-aqueous secondary battery

Abstract

To provide a nonaqueous electrolyte solution which is superior in solubility, and which is arranged so that a high capacity keeping rate can be achieved by suppressing a positive electrode resistance, and a nonaqueous battery arranged by use thereof.SOLUTION: Provided is a nonaqueous electrolyte solution comprising a nonaqueous solvent and LiPF6-containing lithium salt. In the nonaqueous electrolyte solution, the nonaqueous solvent contains acetonitrile, vinylene carbonate and ethylene sulfite, and a volume ratio of the vinylene carbonate in the nonaqueous solvent is smaller than that of the ethylene sulfite. Further, it contains, as at least one organic silicon compound, a silane compound or disiloxane compound. The organic silicon compound includes a silicon-oxygen (Si-O) bond and a silicon-carbon (Si-C) bond, and it satisfies the requirement given by the following expression (1): 1<(Number of C atoms that connect to Si) / (Number of O atoms that connect to Si)<6 (1). The content of the organic silicon compound is 1 mass% or more and 15 mass% or less to a total quantity of the nonaqueous solvent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte solution and a non-aqueous secondary battery using the same. [Background technology]

[0002] The use of lithium-ion batteries, which were previously used as single cells for mobile applications, has undergone major changes amid the global trend toward electrification of automobiles. In automotive batteries, the need for both reduced cobalt usage and improved energy density has led to research into technologies for stably using chemically unstable nickel (Ni)-based positive electrode active materials, and several reports have been published. In particular, there have been reports on the effects of free acid in the electrolyte or the positive electrode coating on battery performance.

[0003] For example, Patent Document 1 below shows that the use of a specific siloxane compound (such as disiloxane) in an electrolyte removes free acid generated initially, improving the initial capacity of the battery, and also shows that increasing the amount of added siloxane further promotes the removal of free acid. Non-Patent Document 1 also shows that the addition of a specific silane compound to an electrolyte reacts with hydrogen fluoride (HF), which is also a free acid, to produce silane fluoride, improving the charge-discharge cycle performance of the battery at high temperatures, and shows that this reaction with hydrogen fluoride progresses at high temperatures. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-5328 [Non-patent literature]

[0005] [Non-Patent Document 1] Electrochimica Acta 236 (2017) 61-71 Summary of the Invention [Problem to be solved by the invention]

[0006] However, additives such as those described in Non-Patent Document 1 react with trace amounts of water in the electrode or electrolyte to produce polysiloxane, which forms a positive electrode film and increases resistance. Side reactions can be prevented by completely removing water from the battery, but it is generally difficult to completely remove water.

[0007] Furthermore, some of the disiloxanes and the like shown in Patent Document 1 are presumed to have structures that make it difficult to generate polysiloxanes, while some of the disiloxanes also have structures that make them difficult to dissolve in highly polar acetonitrile electrolytes.

[0008] Therefore, an object of the present invention is to provide a nonaqueous electrolyte solution that, when it contains acetonitrile, has excellent solubility of other ingredients and can achieve a high capacity retention rate by suppressing positive electrode resistance, and a nonaqueous battery that uses the nonaqueous electrolyte solution. [Means for solving the problem]

[0009] The present invention has been made in view of the above circumstances, and it has been discovered that the use of a silane compound or disiloxane compound having a specific structure in a non-aqueous electrolyte solution makes it possible to suppress electrode deterioration while also suppressing side reactions caused by the additives, thereby improving the capacity retention rate, which has led to the completion of the present invention.

[0010] That is, the present invention is as follows. [1] A non-aqueous electrolyte solution containing a non-aqueous solvent and a lithium salt, the lithium salt comprises LiPF6, the non-aqueous solvent contains acetonitrile, vinylene carbonate, and ethylene sulfite, and the volume ratio of vinylene carbonate in the non-aqueous solvent is lower than the volume ratio of ethylene sulfite; Furthermore, the non-aqueous electrolyte solution contains at least one organosilicon compound, the organosilicon compound is a silane compound or a disiloxane compound, The organosilicon compound contains a silicon-oxygen (Si—O) bond and a silicon-carbon (Si—C) bond and is represented by the following formula 1: 1<(number of C atoms bonded to Si) / (number of O atoms bonded to Si)<6 (Equation 1) Fulfilling The non-aqueous electrolyte solution has a content of the organosilicon compound of 1% by mass or more and 15% by mass or less based on the total amount of the non-aqueous solvent. [2] Item 2. The nonaqueous electrolyte solution according to item 1, wherein the organosilicon compound contains at least one aryl group. [3] The silane compound is represented by the following general formula (2): Si(R 1 R 2 R 3 )-OR 4 Formula (2) {where, R 1 ~R 3 each independently represents an alkyl group having 1 to 4 carbon atoms which may be substituted with a halogen atom, or an aryl group which may be substituted with an alkyl group or a halogen atom, and R 1 ~R 3 At least one of R is an aryl group; 4 represents an alkyl group having 1 to 4 carbon atoms, or an aryl group which may be substituted with an alkyl group or a halogen atom} or an alkoxysilane compound represented by the formula: The disiloxane compound is represented by the following general formula (3): Si(R 5 R 6 )(OR 9 )-OSi(R 7 R 8 )(OR 10 ) Formula (3) {where, R 5 ~R 8 each independently represents an alkyl group having 1 to 4 carbon atoms which may be substituted with a halogen atom, or an aryl group which may be substituted with an alkyl group or a halogen atom, and R5 ~R 8 At least one of R is an aryl group; 9 and R 10 represents an alkyl group having 1 to 4 carbon atoms, or an aryl group which may be substituted with an alkyl group or a halogen atom} 3. The nonaqueous electrolyte solution according to item 1 or 2, wherein the alkoxydisiloxane compound is represented by the following formula: [4] 4. The nonaqueous electrolyte solution according to any one of items 1 to 3, wherein the organosilicon compound is at least one selected from the group consisting of methoxytriphenylsilane, ethoxytriphenylsilane, dimethoxytetraphenyldisiloxane, diethoxytetraphenyldisiloxane, and methoxyethoxytetraphenyldisiloxane. [5] 5. The non-aqueous electrolyte solution according to any one of items 1 to 4, wherein the content of the acetonitrile is 5 to 97% by volume based on the total amount of the non-aqueous solvent. [6] 6. The nonaqueous electrolyte solution according to any one of items 1 to 5, wherein the lithium salt further comprises lithium bis(fluorosulfonyl)imide. [7] A nonaqueous secondary battery comprising: a positive electrode having a positive electrode active material layer on one or both sides of a current collector; a negative electrode having a negative electrode active material layer on one or both sides of a current collector; a separator; and the nonaqueous electrolyte solution according to any one of items 1 to 6, The positive electrode active material layer is formed by adding a compound represented by the following general formula (4): Li p Ni q Co r Mn s M t O u Formula (4) {In the formula, M is at least one metal selected from the group consisting of aluminum (Al), tin (Sn), indium (In), iron (Fe), vanadium (V), copper (Cu), magnesium (Mg), titanium (Ti), zinc (Zn), molybdenum (Mo), zirconium (Zr), strontium (Sr), and barium (Ba), and 0 < p < 1.3, 0 < q < 1.2, 0 < r < 1.2, 0 ≦ s < 0.5, 0 ≦ t < 0.3, 0.7 ≦ q + r + s + t ≦ 1.2, 1.8 < u < 2.2, and p is a value determined by the charge and discharge state of the battery} A non-aqueous secondary battery containing at least one selected from the group consisting of lithium-containing metal oxides represented by . [8] The non-aqueous secondary battery according to item 7, wherein the nickel (Ni) content ratio q of the lithium-containing metal oxide represented by the general formula (4) is 0.5 < q < 1.2. [Advantages of the Invention]

[0011] According to the present invention, by including a silane compound and a disiloxane compound having a specific structure containing silicon-oxygen (Si-O) bonds and silicon-carbon (Si-C) bonds in a non-aqueous electrolyte, deterioration of the electrode can be suppressed, and a non-aqueous electrolyte that maintains a high battery capacity can be provided because an increase in resistance due to side reactions does not occur. [Brief Description of the Drawings]

[0012] [Figure 1] It is a plan view schematically showing an example of the non-aqueous secondary battery of the present embodiment. [Figure 2] It is a cross-sectional view taken along line A-A of FIG. 1. [Modes for Carrying Out the Invention]

[0013] Hereinafter, modes for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. In the present specification, a numerical range described using "~" includes the numerical values described before and after it.

[0014] <Non-aqueous secondary battery> The nonaqueous secondary battery of this embodiment is a secondary battery including a positive electrode, a negative electrode, and the nonaqueous electrolyte solution. For example, it may be a lithium-ion battery. More specifically, it may be the lithium-ion battery shown in the schematic plan view of FIG. 1 and the schematic cross-sectional view of FIG. 2. The lithium-ion battery 100 shown in FIGS. 1 and 2 includes a separator 170, a positive electrode 150 and a negative electrode 160 sandwiching the separator 170 from both sides, a positive electrode lead body 130 (connected to the positive electrode 150) and a negative electrode lead body 140 (connected to the negative electrode 160) sandwiching a laminate of the separator 170, the positive electrode 150, and the negative electrode 160, and a battery exterior 110 that houses them. The laminate of the positive electrode 150, the separator 170, and the negative electrode 160 is impregnated with the nonaqueous electrolyte solution according to this embodiment.

[0015] <1.Non-aqueous electrolyte> The non-aqueous electrolyte solution according to this embodiment contains a non-aqueous solvent and a lithium salt, the lithium salt comprises LiPF6, the non-aqueous solvent contains acetonitrile, vinylene carbonate, and ethylene sulfite, and the volume ratio of vinylene carbonate in the non-aqueous solvent is lower than the volume ratio of ethylene sulfite; Furthermore, the non-aqueous electrolyte solution contains at least one organosilicon compound, the organosilicon compound is a silane compound or a disiloxane compound, The organosilicon compound contains a silicon-oxygen (Si—O) bond and a silicon-carbon (Si—C) bond and is represented by the following formula 1: 1<(number of C atoms bonded to Si) / (number of O atoms bonded to Si)<6 (Equation 1) Fulfilling The content of the organosilicon compound is 1% by mass or more and 15% by mass or less based on the total amount of the non-aqueous solvent.

[0016] The nonaqueous electrolyte solution according to this embodiment preferably contains as little water as possible, but may contain a very small amount of water as long as it does not impede the solution of the problems of the present invention. The water content is 1% by mass or less, 300 ppm by mass or less, and preferably 200 ppm by mass or less, based on the total amount of the nonaqueous electrolyte solution. As long as the nonaqueous electrolyte solution has a configuration that achieves the problem of the present invention, the other components can be appropriately selected and applied from the constituent materials of known nonaqueous electrolyte solutions used in lithium-ion batteries.

[0017] <1-1. Non-aqueous solvents> In this embodiment, the term "non-aqueous solvent" refers to the elements remaining in the non-aqueous electrolyte solution excluding the lithium salt, the organosilicon compound, and various additives. When the non-aqueous electrolyte solution contains an electrode protection additive, the term "non-aqueous solvent" refers to the elements remaining in the non-aqueous electrolyte solution excluding the lithium salt and additives other than the electrode protection additive. Examples of non-aqueous solvents include alcohols such as methanol and ethanol; and aprotic solvents. Among these, aprotic solvents are preferred as non-aqueous solvents. The non-aqueous solvent may contain a solvent other than an aprotic solvent, as long as it does not impede the solution of the problems of the present invention.

[0018] The nonaqueous solvent for the nonaqueous electrolyte solution of the present invention contains acetonitrile as an aprotic solvent. The inclusion of acetonitrile in the nonaqueous solvent improves the ionic conductivity of the nonaqueous electrolyte solution, thereby increasing the diffusibility of lithium ions within the battery. Therefore, when the nonaqueous electrolyte solution contains acetonitrile, lithium ions can be effectively diffused even to regions near the current collector that are difficult for lithium ions to reach during high-load discharge, particularly in positive electrodes with thicker positive electrode active material layers and increased positive electrode active material loading. This allows for sufficient capacity to be extracted even during high-load discharge, resulting in a nonaqueous secondary battery with excellent load characteristics.

[0019] Furthermore, the inclusion of acetonitrile in the nonaqueous solvent can improve the rapid charging characteristics of nonaqueous secondary batteries. In constant current (CC)-constant voltage (CV) charging of nonaqueous secondary batteries, the charge capacity per unit time during the CC charging period is greater than the charge capacity per unit time during the CV charging period. When acetonitrile is used as the nonaqueous solvent in a nonaqueous electrolyte, the range in which CC charging is possible can be expanded (CC charging time can be extended), and the charging current can also be increased, significantly shortening the time from the start of charging to fully charging a nonaqueous secondary battery.

[0020] Acetonitrile is easily electrochemically reductively decomposed, and therefore, when acetonitrile is used, it is preferable to use another solvent (e.g., an aprotic solvent other than acetonitrile) in combination with acetonitrile as a non-aqueous solvent, and / or to add an electrode protection additive for forming a protective film on the electrode.

[0021] The content of acetonitrile in the non-aqueous solvent is preferably 5 to 97% by volume, based on the total amount of the non-aqueous solvent. The lower limit of the acetonitrile content is more preferably 10% by volume or more, and even more preferably 20% by volume or more, based on the total amount of the non-aqueous solvent. The upper limit of the acetonitrile content is more preferably 85% by volume or less, and even more preferably 66% by volume or less, based on the total amount of the non-aqueous solvent. When the acetonitrile content is 5% by volume or more, based on the total amount of the non-aqueous solvent, the ionic conductivity of the non-aqueous electrolyte solution increases, tending to enable the non-aqueous secondary battery to exhibit high-power characteristics and further promoting the dissolution of the lithium salt. Furthermore, when the acetonitrile content in the non-aqueous solvent is within the above range, the high-temperature cycle characteristics and other battery characteristics of the non-aqueous secondary battery tend to be further improved while maintaining the excellent performance of acetonitrile.

[0022] Examples of aprotic solvents other than acetonitrile include cyclic carbonates, fluoroethylene carbonate, lactones, organic compounds having sulfur atoms, chain fluorinated carbonates, cyclic ethers, mononitriles other than acetonitrile, alkoxy group-substituted nitriles, dinitriles, cyclic nitriles, short-chain fatty acid esters, chain ethers, fluorinated ethers, ketones, and compounds in which some or all of the H atoms of the aprotic solvents have been substituted with halogen atoms.

[0023] Acetonitrile, which is one component of non-aqueous solvents, is easily electrochemically reductively decomposed. Therefore, the non-aqueous electrolyte solution according to this embodiment is characterized in that the non-aqueous solvent contains, in addition to acetonitrile, vinylene carbonate and ethylene sulfite, and the volume ratio of vinylene carbonate is lower than the volume ratio of ethylene sulfite.

[0024] When the non-aqueous solvent according to this embodiment contains acetonitrile, vinylene carbonate as a cyclic carbonate, and ethylene sulfite as an organic compound having a sulfur atom, when the non-aqueous electrolyte solution is used in a non-aqueous secondary battery, deterioration of a positive electrode active material having a high nickel (Ni) ratio is suppressed, and the battery operates at a high current density.

[0025] Vinylene carbonate-derived anode protective coatings have high resistance, which tends to lead to performance degradation during rapid charging and low-temperature environments, as well as battery swelling due to gas generation during decomposition. Ethylene sulfite has a lower lowest unoccupied molecular orbital (LUMO) level than other oxygen- and sulfur-containing compounds, and can reductively decompose to form anode protective coatings at lower potentials than vinylene carbonate. This allows for the reduction of vinylene carbonate addition, thereby addressing the issues associated with vinylene carbonate-derived anode protective coatings. Furthermore, ethylene sulfite-derived anode protective coatings have low resistance over a wide temperature range and promote the formation of anode SEI (solid electrolyte interface) that is highly resistant to acetonitrile and its decomposition products, thereby providing nonaqueous electrolytes and nonaqueous secondary batteries that can operate stably at high current densities.

[0026] In this embodiment, the total content of vinylene carbonate and ethylene sulfite in the nonaqueous electrolyte solution is preferably 0.1% by volume or more and less than 10% by volume with respect to the total amount of the nonaqueous solvent, from the viewpoint of suppressing an increase in internal resistance.

[0027] Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, trans-2,3-pentylene carbonate, cis-2,3-pentylene carbonate, vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinylethylene carbonate;

[0028] Fluoroethylene carbonates include, for example, 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, cis-4,5-difluoro-1,3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, 4,4,5,5-tetrafluoro-1,3-dioxolan-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one;

[0029] Lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone;

[0030] Examples of organic compounds having a sulfur atom include ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methyl sulfolane, 1,3-propane sultone, 1,4-butane sultone, 1-propene 1,3-sultone, dimethyl sulfoxide, tetramethylene sulfoxide, and ethylene glycol sulfite;

[0031] Examples of chain carbonates include ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl propyl carbonate, and diisobutyl carbonate;

[0032] Cyclic ethers include, for example, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane;

[0033] Examples of mononitriles other than acetonitrile include propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile;

[0034] Alkoxy-substituted nitriles include, for example, methoxyacetonitrile and 3-methoxypropionitrile;

[0035] Dinitriles include, for example, malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanoctane, 2,7-dicyanoctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dimethylglutaronitrile;

[0036] Cyclic nitriles include, for example, benzonitrile;

[0037] Examples of short-chain fatty acid esters include methyl acetate, methyl propionate, methyl isobutyrate, methyl butyrate, methyl isovalerate, methyl valerate, methyl pivalate, methyl hydroangelate, methyl caproate, ethyl acetate, ethyl propionate, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl pivalate, ethyl hydroangelate, ethyl caproate, propyl acetate, propyl propionate, propyl isobutyrate, propyl butyrate, propyl isovalerate, propyl valerate, propyl pivalate, propyl hydroangelate, propyl caproate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate, isopropyl valerate, and iso pivalate. propyl, isopropyl hydroangelate, isopropyl caproate, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl pivalate, butyl hydroangelate, butyl caproate, isobutyl acetate, isobutyl propionate, isobutyl isobutyrate, isobutyl butyrate, isobutyl isovalerate, isobutyl valerate, isobutyl pivalate, isobutyl hydroangelate, isobutyl caproate, tert-butyl acetate, tert-butyl propionate, tert-butyl isobutyrate, tert-butyl butyrate, tert-butyl isovalerate, tert-butyl valerate, tert-butyl pivalate, tert-butyl hydroangelate, and tert-butyl caproate;

[0038] Chain ethers include, for example, dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme;

[0039] Examples of fluorinated ethers include Rf 11 -OR 12 (In the formula, Rf 11 represents an alkyl group containing a fluorine atom, and R 12 represents a monovalent organic group which may contain a fluorine atom;

[0040] Ketones, for example, acetone, methyl ethyl ketone, and methyl isobutyl ketone;

[0041] Examples of the compound in which some or all of the H atoms of the aprotic solvent have been substituted with halogen atoms include compounds in which the halogen atoms are fluorine; Examples include:

[0042] Examples of fluorinated chain carbonates include methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethylmethyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, and methyl 2,2,3,3-tetrafluoropropyl carbonate. The fluorinated chain carbonates are represented by the following general formula: R 13 -OC(O)OR 14 {where, R 13 and R 14 are CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf 15 and Rf 15 is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom is substituted with at least one fluorine atom, and R 13 and / or R 14 contains at least one fluorine atom. It can be expressed as:

[0043] In addition, examples of fluorinated short-chain fatty acid esters include fluorinated short-chain fatty acid esters such as 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2,3,3-tetrafluoropropyl acetate. Fluorinated short-chain fatty acid esters are represented by the following general formula: R 16 -C(O)OR 17 {where, R 16is CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CF3CF2H, CFH2, CF2H, CF2Rf 18 , CFHRf 18 , and CH2Rf 19 and R is at least one selected from the group consisting of 17 are CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf 19 and Rf 18 is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom may be substituted with at least one fluorine atom, and Rf 19 is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom is substituted with at least one fluorine atom, and R 16 and / or R 17 contains at least one fluorine atom, and R 16 If is CF2H, R 17 is not CH3. It can be expressed as:

[0044] In the present embodiment, the aprotic solvent other than acetonitrile may be used alone or in combination of two or more.

[0045] In the present embodiment, the non-aqueous solvent is preferably one or more of cyclic carbonates and chain carbonates in combination with acetonitrile from the viewpoint of improving the stability of the non-aqueous electrolyte solution. From this viewpoint, the non-aqueous solvent in the present embodiment is more preferably one of cyclic carbonates in combination with acetonitrile, and further preferably one of cyclic carbonates and chain carbonates in combination with acetonitrile.

[0046] When a cyclic carbonate other than vinylene carbonate is used together with acetonitrile, it is particularly preferred that such cyclic carbonate includes ethylene carbonate and / or fluoroethylene carbonate.

[0047] <1-2. Lithium salts> The nonaqueous electrolyte solution of this embodiment is not particularly limited as long as it contains LiPF. For example, in this embodiment, it is preferable that the nonaqueous electrolyte solution contains LiPF as the lithium salt and a lithium-containing imide salt.

[0048] Lithium-containing imide salts are LiN(SO2C m F 2m+1 )2 (wherein m is an integer of 0 to 8), and specifically, it preferably contains at least one of lithium bis(fluorosulfonyl)imide, represented as LiN(SO2F)2, and LiN(SO2CF3)2. Either one or both of these imide salts may be contained. Alternatively, it may contain an imide salt other than these imide salts.

[0049] When acetonitrile is included in the non-aqueous solvent, the saturation concentration of the lithium-containing imide salt relative to acetonitrile is higher than that of LiPF. Therefore, it is preferable to include the lithium-containing imide salt at a molar concentration such that LiPF is less than or equal to the lithium-containing imide salt, since this suppresses association and precipitation of the lithium salt and acetonitrile at low temperatures. Furthermore, from the viewpoint of ion supply, it is preferable for the content of the lithium-containing imide salt to be 0.5 mol to 3 mol per liter of non-aqueous solvent. A non-aqueous electrolyte solution containing at least one of LiN(SO2F)2 and LiN(SO2CF3)2 can effectively suppress the decrease in ionic conductivity at low temperatures, such as -10°C or -30°C, thereby achieving excellent low-temperature characteristics. Thus, limiting the content can more effectively suppress the increase in resistance during high-temperature heating.

[0050] The lithium salt may further include fluorine-containing inorganic lithium salts other than LiPF, such as LiBF, LiAsF, LiSiF, LiSbF, and LiB. 12 F b H 12-b(wherein b is an integer of 0 to 3) may also be included. "Inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in the anion and is soluble in acetonitrile. "Fluorine-containing inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in the anion but contains a fluorine atom in the anion and is soluble in acetonitrile. Fluorine-containing inorganic lithium salts are excellent in that they form a passivation film on the surface of the metal foil serving as the positive electrode current collector, thereby inhibiting corrosion of the positive electrode current collector. These fluorine-containing inorganic lithium salts may be used alone or in combination of two or more. Compounds that are double salts of LiF and Lewis acids are desirable as fluorine-containing inorganic lithium salts. Among these, fluorine-containing inorganic lithium salts containing phosphorus atoms are more preferred because they facilitate the release of free fluorine atoms. A typical fluorine-containing inorganic lithium salt is LiPF6, which dissolves and releases PF6 anions. When a fluorine-containing inorganic lithium salt having a boron atom is used as the fluorine-containing inorganic lithium salt, it is preferable because it makes it easier to capture excess free acid components that may cause battery deterioration, and from this viewpoint, LiBF4 is particularly preferable.

[0051] The content of the fluorine-containing inorganic lithium salt in the non-aqueous electrolyte solution of this embodiment is not particularly limited, but is preferably 0.01 mol or more, more preferably 0.02 mol or more, and even more preferably 0.03 mol or more per 1 L of non-aqueous solvent. When the content of the fluorine-containing inorganic lithium salt is within the above-mentioned range of 0.01 mol or more, the ionic conductivity tends to increase and high-power characteristics tend to be exhibited. Furthermore, the content of the fluorine-containing inorganic lithium salt is preferably less than 1.5 mol, more preferably less than 0.5 mol, and even more preferably less than 0.1 mol per 1 L of non-aqueous solvent. When the content of the fluorine-containing inorganic lithium salt is within the above-mentioned range of less than 1.5 mol, the ionic conductivity tends to increase and high-power characteristics can be exhibited, and the decrease in ionic conductivity due to an increase in viscosity at low temperatures tends to be suppressed. This tends to further improve the high-temperature cycle characteristics and other battery characteristics of the non-aqueous secondary battery while maintaining the excellent performance of the non-aqueous electrolyte solution.

[0052] The nonaqueous electrolyte solution of this embodiment may further contain an organic lithium salt. The "organic lithium salt" refers to a lithium salt that contains a carbon atom in the anion and is soluble in acetonitrile.

[0053] Examples of organic lithium salts include organic lithium salts having an oxalic acid group. Specific examples of organic lithium salts having an oxalic acid group include organic lithium salts represented by LiB(C2O4)2, LiBF2(C2O4), LiPF4(C2O4), and LiPF2(C2O4)2. Among these, at least one lithium salt selected from the group consisting of LiB(C2O4)2 and LiBF2(C2O4) is preferred. It is more preferred to use one or more of these together with a fluorine-containing inorganic lithium salt. This organic lithium salt having an oxalic acid group may be added to a nonaqueous electrolyte solution or incorporated into the negative electrode (negative electrode active material layer).

[0054] In order to ensure the effects of its use, the amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte solution is preferably 0.005 mol or more, more preferably 0.02 mol or more, and even more preferably 0.05 mol or more per 1 L of the non-aqueous solvent of the non-aqueous electrolyte solution. However, if the amount of the organic lithium salt having an oxalic acid group in the non-aqueous electrolyte solution is too large, precipitation may occur. Therefore, the amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte solution is preferably less than 1.0 mol, more preferably less than 0.5 mol, and even more preferably less than 0.2 mol per 1 L of the non-aqueous solvent of the non-aqueous electrolyte solution.

[0055] It is known that organic lithium salts having an oxalic acid group are poorly soluble in low-polarity organic solvents, particularly chain carbonates. Organic lithium salts having an oxalic acid group may contain a trace amount of lithium oxalate. Furthermore, when mixed to form a non-aqueous electrolyte solution, they may react with trace amounts of water contained in other raw materials to generate new white precipitates of lithium oxalate. Therefore, the content of lithium oxalate in the non-aqueous electrolyte solution of this embodiment is not particularly limited, but is preferably 0 to 500 ppm.

[0056] In addition to the lithium salts listed above, lithium salts generally used for non-aqueous secondary batteries may be added supplementarily as the lithium salt in this embodiment. Specific examples of other lithium salts include LiClO4, LiAlO4, LiAlCl4, and LiB 10 Cl 10 Inorganic lithium salts that do not contain fluorine atoms in the anion, such as chloroborane Li; LiCF3SO3, LiCF3CO2, Li2C2F4(SO3)2, LiC(CF3SO2)3, LiC n F (2n+1) SO3 {wherein n≧2}, organic lithium salts such as lower aliphatic carboxylic acids, Li tetraphenylborate, and LiB(C3O4H2)2; LiPF such as LiPF5(CF3) n (C p F 2p+1 ) 6-n an organic lithium salt represented by the formula (wherein n is an integer of 1 to 5 and p is an integer of 1 to 8); LiBF such as LiBF(CF); q (C s F 2s+1 ) 4-q an organic lithium salt represented by the formula (wherein q is an integer of 1 to 3, and s is an integer of 1 to 8); a lithium salt bound to a polyvalent anion; The following formula (a): LiC(SO2R A )(SO2R B )(SO2R C ) (a) {where, R A , R B , and R Cmay be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms. The following formula (b): LiN(SO2OR D )(SO2OR E ) (b) {where, R D , and R E may be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms.}, and The following formula (c) LiN(SO2R F )(SO2OR G ) (c) {where, R F , and R G may be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms.} One or more of these can be used together with the fluorine-containing inorganic lithium salt.

[0057] <1-3.Organosilicon compounds> The non-aqueous electrolyte solution according to this embodiment contains, in addition to the non-aqueous solvent and electrolyte salt described above, an organosilicon compound having Si-O bonds and Si-C bonds. In this embodiment, the organosilicon compound is a silane compound or a disiloxane compound. The organosilicon compound has a structure in which the ratio of the number of carbon atoms directly bonded to silicon to the number of oxygen atoms directly bonded to silicon (hereinafter referred to as the C / O ratio) is greater than 1 and less than 6. Specifically, the organosilicon compound is represented by the following formula 1: 1<(number of C atoms bonded to Si) / (number of O atoms bonded to Si)<6 (Equation 1) This structure satisfies the above. This structure can suppress the generation of polysiloxanes due to side reactions, even if the electrolyte contains water. In the present disclosure, in the case of Si-O-Si, overlapping of the number of oxygen atoms (O) directly bonded to silicon is not permitted, so the number of oxygen atoms (O) directly bonded to silicon is assumed to be 1, not 2. When the C / O ratio is less than 6, the number of silicon-carbon (Si-C) bonds is controlled, and it is predicted that the polarity of the organosilicon compound will not decrease. As a result, from the viewpoint of high solubility of the organosilicon compound in the highly polar nonaqueous electrolyte used in this embodiment and sufficient addition, the C / O ratio is more preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less.

[0058] Furthermore, organosilicon compounds containing at least one aryl group with large steric hindrance are preferred in order to suppress side reactions.

[0059] More specifically, the silane compound is represented by the following general formula (2): Si(R 1 R 2 R 3 )-OR 4 Formula (2) {where, R 1 ~R 3 each independently represents an alkyl group having 1 to 4 carbon atoms which may be substituted with a halogen atom, or an aryl group which may be substituted with an alkyl group or a halogen atom, and R 1 ~R 3 At least one of R is an aryl group; 4 represents an alkyl group having 1 to 4 carbon atoms, or an aryl group which may be substituted with an alkyl group or a halogen atom} It is preferable that the alkoxysilane compound is an alkoxysilane compound represented by the following formula:

[0060] The disiloxane compound may be represented by the following general formula (3): Si(R 5 R 6 )(OR 9 )-OSi(R 7 R 8 )(OR10 ) Formula (3) {where, R 5 ~R 8 each independently represents an alkyl group having 1 to 4 carbon atoms which may be substituted with a halogen atom, or an aryl group which may be substituted with an alkyl group or a halogen atom, and R 5 ~R 8 At least one of R is an aryl group; 9 and R 10 represents an alkyl group having 1 to 4 carbon atoms, or an aryl group which may be substituted with an alkyl group or a halogen atom} Preferably, the alkoxydisiloxane compound is represented by the following formula:

[0061] Specific examples of the alkoxysilane compound represented by the general formula (2) include methoxytriphenylsilane, ethoxytriphenylsilane, methoxydimethylphenylsilane, methoxydiethylphenylsilane, ethoxydimethylphenylsilane, and ethoxydiethylphenylsilane.

[0062] Specific examples of the alkoxydisiloxane compound represented by general formula (3) include dimethoxytetraphenyldisiloxane, diethoxytetraphenyldisiloxane, methoxyethoxytetraphenyldisiloxane, dimethoxydimethyldiphenyldisiloxane, dimethoxydiethyldiphenyldisiloxane, diethoxydimethyldiphenyldisiloxane, and diethoxydiethyldiphenyldisiloxane.

[0063] The organosilicon compound preferably contains one or both of an alkoxysilane compound represented by general formula (2) and an alkoxydisiloxane compound represented by general formula (3). From the viewpoint that the sterically hindered phenyl group can suppress side reactions, it is more preferable that the organosilicon compound is at least one selected from the group consisting of methoxytriphenylsilane, ethoxytriphenylsilane, dimethoxytetraphenyldisiloxane, diethoxytetraphenyldisiloxane, and methoxyethoxytetraphenyldisiloxane.

[0064] The content of the organosilicon compound in this embodiment is not particularly limited, but is preferably in the range of 1% by mass or more and 15% by mass or less, based on the total amount of the non-aqueous solvent. The lower limit of the content of the organosilicon compound is more preferably 1.5% by mass or more, and even more preferably 2% by mass or more, based on the total amount of the non-aqueous solvent. The upper limit of the content of the organosilicon compound is more preferably 10% by mass or less, and even more preferably 7% by mass or less, based on the total amount of the non-aqueous solvent. By adjusting the content of the organosilicon compound containing Si-O bonds within the above range, it tends to be possible to add even better battery characteristics without impairing the basic functions of a non-aqueous secondary battery.

[0065] <Electrode protection additive> The electrode protection additive is not particularly limited as long as it does not impede the solution of the problems of the present invention, and may substantially overlap with the substance that serves as a solvent for dissolving lithium salts (i.e., the non-aqueous solvents described above) (however, acetonitrile, vinylene carbonate, ethylene sulfite, and organosilicon compounds are excluded). The electrode protection additive is preferably a substance that contributes to improving the performance of the non-aqueous electrolyte solution and non-aqueous secondary battery in this embodiment, but also includes substances that are not directly involved in the electrochemical reaction.

[0066] Specific examples of the electrode protection additive include 4-fluoro-1,3-dioxolane-2-one, 4,4-difluoro-1,3-dioxolane-2-one, cis-4,5-difluoro-1,3-dioxolane-2-one, trans-4,5-difluoro-1,3-dioxolane-2-one, 4,4,5-trifluoro-1,3-dioxolane-2-one, and 4,4,5,5-tetrafluoro-1,3-dioxolane. Fluoroethylene carbonates such as 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one; unsaturated bond-containing cyclic carbonates such as 4,5-dimethylvinylene carbonate and vinylethylene carbonate; γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone. Examples of suitable anhydrides include lactones, cyclic ethers such as 1,4-dioxane, cyclic sulfur compounds such as propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methyl sulfolane, 1,3-propane sultone, 1,4-butane sultone, 1-propene-1,3-sultone, and tetramethylene sulfoxide, chain acid anhydrides such as acetic anhydride, propionic anhydride, and benzoic anhydride, cyclic acid anhydrides such as malonic anhydride, succinic anhydride, glutaric anhydride, maleic anhydride, phthalic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 2,3-naphthalenedicarboxylic anhydride, and naphthalene-1,4,5,8-tetracarboxylic dianhydride, and mixed acid anhydrides formed by dehydration condensation of different acids, such as two different carboxylic acids or a carboxylic acid and a sulfonic acid. These may be used alone or in combination of two or more.

[0067] The content of the electrode protection additive in the non-aqueous electrolyte solution in this embodiment is not particularly limited, but the content of the electrode protection additive relative to the total amount of the non-aqueous solvent is preferably 0.1 to 30% by volume, more preferably 0.3 to 15% by volume, and even more preferably 0.5 to 4% by volume.

[0068] In this embodiment, the higher the content of the electrode protection additive, the more suppressed the deterioration of the nonaqueous electrolyte solution. However, the lower the content of the electrode protection additive, the more improved the high-power performance of the nonaqueous secondary battery in a low-temperature environment. Therefore, by adjusting the content of the electrode protection additive within the above-mentioned range, the excellent performance based on the high ionic conductivity of the nonaqueous electrolyte solution tends to be maximized without impairing the basic functions of the nonaqueous secondary battery. By preparing a nonaqueous electrolyte solution with such a composition, the cycle performance of the nonaqueous secondary battery, the high-power performance in a low-temperature environment, and all other battery characteristics tend to be further improved.

[0069] <Optional Additives> In this embodiment, for the purpose of improving the charge / discharge cycle characteristics, high-temperature storage properties, and safety (e.g., preventing overcharge) of the nonaqueous secondary battery, an optional additive selected from sulfonic acid esters, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, phosphate esters [ethyl diethylphosphonoacetate (EDPA): (C2H5O)2(P=O)-CH2(C=O)OC2H5, tris(trifluoroethyl)phosphate (TFEP): (CF3CHO)3P=O, triphenylphosphate (TPP): (C6H5O)3P=O: (CH2=CHCHO)3P=O, triallyl phosphate, etc.], nitrogen-containing cyclic compounds with no steric hindrance around the unshared electron pair [pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole, etc.], and derivatives of these compounds may be appropriately added to the nonaqueous electrolyte solution. In particular, phosphate esters are effective in suppressing side reactions during storage.

[0070] The content of other optional additives in this embodiment is calculated as a mass percentage relative to the total mass of all components constituting the non-aqueous electrolyte solution. There are no particular restrictions on the content of other optional additives, but it is preferably in the range of 0.01 mass% to 10 mass% of the total amount of the non-aqueous electrolyte solution, more preferably 0.02 mass% to 5 mass% and even more preferably 0.05 mass% to 3 mass%. By adjusting the content of other optional additives within the above range, it tends to be possible to add even better battery characteristics without impairing the basic functions of a non-aqueous secondary battery.

[0071] <2. Positive electrode and positive electrode current collector> 1 and 2 is composed of a positive electrode active material layer made from a positive electrode mixture and a positive electrode current collector. The positive electrode 150 is not particularly limited as long as it functions as a positive electrode for a nonaqueous secondary battery, and may be any known positive electrode. The positive electrode of the present invention contains a lithium-containing compound containing Fe, and preferably also contains nickel (Ni) in a relatively high proportion.

[0072] The positive electrode active material layer preferably contains a positive electrode active material and further contains a conductive additive and a binder as required.

[0073] The positive electrode active material layer preferably contains a material capable of absorbing and releasing lithium ions as the positive electrode active material, since use of such a material tends to enable a high voltage and a high energy density to be obtained.

[0074] The positive electrode active material may be, for example, a positive electrode active material containing at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and may be represented by the following general formula (4): Li p Ni q Co r Mn s M t O u Formula (4) {In the formula, M is at least one metal selected from the group consisting of aluminum (Al), tin (Sn), indium (In), iron (Fe), vanadium (V), copper (Cu), magnesium (Mg), titanium (Ti), zinc (Zn), molybdenum (Mo), zirconium (Zr), strontium (Sr), and barium (Ba), and 0 < p < 1.3, 0 < q < 1.2, 0 < r < 1.2, 0 ≦ s < 0.5, 0 ≦ t < 0.3, 0.7 ≦ q + r + s + t ≦ 1.2, 1.8 < u < 2.2, and p is a value determined by the charge-discharge state of the battery} At least one Li-containing metal oxide selected from the lithium (Li)-containing metal oxides represented by is preferable. From the viewpoint of energy density, it is more preferable that the nickel (Ni) content ratio q of the lithium-containing metal oxide represented by the general formula (4) is 0.5 < q < 1.2.

[0075] Specific examples of the positive electrode active material include, for example, lithium cobalt oxide typified by LiCoO2; lithium manganese oxides typified by LiMnO2, LiMn2O4, and Li2Mn2O4; lithium nickel oxide typified by LiNiO2; LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.2 O2; lithium-containing composite metal oxides represented by Li z MO2 (where M contains at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and / or represents two or more metal elements selected from the group consisting of Ni, Mn, Co, Al, and Mg, and z represents a number greater than 0.9 and less than 1.2), and the like.

[0076] In particular, when the Ni content ratio q of the Li-containing metal oxide represented by the general formula (4) is 0.5 < q < 1.2, it is preferable because both reduction of the usage amount of Co, which is a rare metal, and increase in energy density are achieved. Examples of such a positive electrode active material include, for example, LiNi 0.6 Co0.2 Mn 0.2 O2, LiNi 0.75 Co 0.15 Mn 0.15 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.85 Co 0.075 Mn 0.075 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.81 Co 0.1 Al 0.09 O2, LiNi 0.85 Co 0.1 Al 0.05 O2, etc.

[0077] On the other hand, the higher the Ni content in the positive electrode active material layer, the more degradation tends to occur at low voltages. The Li-containing metal oxide positive electrode active material represented by general formula (4) inherently contains active sites that cause oxidative degradation of non-aqueous electrolytes. These active sites can unintentionally consume compounds added to protect the negative electrode at the positive electrode. Acid anhydrides, in particular, tend to be susceptible to this effect. In particular, when acetonitrile is used as the non-aqueous solvent, the effect of adding an acid anhydride is enormous, so the consumption of the acid anhydride at the positive electrode is a fatal problem.

[0078] Furthermore, the decomposition products of these additives that are incorporated into and deposited on the positive electrode side not only increase the internal resistance of non-aqueous secondary batteries but also accelerate the degradation of the lithium salt. Furthermore, the original purpose of protecting the negative electrode surface is insufficient. To deactivate the active sites that essentially cause oxidative degradation of non-aqueous electrolytes, it is important to control Jahn-Teller distortion or to include a component that acts as a neutralizer. Therefore, it is preferable that the positive electrode active material contain at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba.

[0079] For the same reason, it is preferable that the surface of the positive electrode active material is coated with a compound containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. It is also more preferable that the surface of the positive electrode active material is coated with an oxide containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. Furthermore, it is particularly preferable that the surface of the positive electrode active material is coated with at least one oxide selected from the group consisting of ZrO2, TiO2, Al2O3, NbO3, and LiNbO2, because this does not inhibit the permeation of lithium ions.

[0080] The positive electrode active material may be a lithium-containing compound other than the Li-containing metal oxide represented by the general formula (4) above, and is not particularly limited as long as it contains lithium. Examples of such lithium-containing compounds include composite oxides containing lithium and a transition metal element, metal chalcogenides containing lithium, metal phosphate compounds containing lithium and a transition metal element, and metal silicate compounds containing lithium and a transition metal element. From the viewpoint of obtaining a higher voltage, the lithium-containing compound is preferably a metal phosphate compound containing lithium and at least one transition metal element selected from the group consisting of Co, Ni, Mn, Fe, Cu, Zn, Cr, V, and Ti. More specifically, the lithium-containing compound is represented by the following formula (Xa): Li v M I D2(Xa) {wherein D represents a chalcogen element, and M I represents at least one transition metal element, and the value of v is determined depending on the charge / discharge state of the battery and is a number between 0.05 and 1.10. The following formula (Xb): Li w M II PO4(Xb) {In formula, M II represents at least one transition metal element, and the value of w is determined depending on the charge / discharge state of the battery and represents a number of 0.05 to 1.10.}, and The following formula (Xc): Li t MIII u SiO4(Xc) {In formula, M III represents at least one transition metal element, the value of t is determined depending on the charge / discharge state of the battery and represents a number from 0.05 to 1.10, and u represents a number from 0 to 2.} Examples of compounds include compounds represented by the following formulae:

[0081] The lithium-containing compound represented by the formula (Xa) has a layered structure, and the compounds represented by the formulas (Xb) and (Xc) have an olivine structure. These lithium-containing compounds may be, for the purpose of stabilizing the structure, a part of the transition metal element is substituted with Al, Mg, or another transition metal element, a part of the transition metal element is contained in the grain boundary, a part of the oxygen atoms is substituted with fluorine atoms, or at least a part of the surface of the positive electrode active material may be coated with another positive electrode active material.

[0082] As the positive electrode active material in this embodiment, the lithium-containing compound as described above may be used alone, or the lithium-containing compound may be used in combination with other positive electrode active materials.

[0083] Examples of such other positive electrode active materials include metal oxides or metal chalcogenides having a tunnel structure and a layer structure, sulfur, conductive polymers, etc. Examples of metal oxides or metal chalcogenides having a tunnel structure and a layer structure include MnO2, FeO2, FeS2, VO5, and VO. 13 Examples of the conductive polymer include oxides, sulfides, and selenides of metals other than lithium, such as TiO2, TiS2, MoS2, and NbSe2. Examples of the conductive polymer include conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole.

[0084] The other positive electrode active materials described above may be used singly or in combination of two or more, and are not particularly limited. However, it is preferable that the positive electrode active material layer contains at least one transition metal element selected from Ni, Mn, and Co, because it is possible to reversibly and stably store and release lithium ions and achieve a high energy density.

[0085] When a lithium-containing compound and another positive electrode active material are used in combination as the positive electrode active material, the ratio of the lithium-containing compound to the total positive electrode active material is preferably 80 mass% or more, and more preferably 85 mass% or more.

[0086] Examples of the conductive additive include carbon black, such as graphite, acetylene black, and ketjen black, and carbon fiber. The content of the conductive additive is preferably 10 parts by mass or less, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the positive electrode active material.

[0087] Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene-butadiene rubber, and fluororubber. The content of the binder is preferably 6 parts by mass or less, more preferably 0.5 to 4 parts by mass, per 100 parts by mass of the positive electrode active material.

[0088] The positive electrode active material layer is formed by dispersing a positive electrode mixture, which is a mixture of a positive electrode active material and, if necessary, a conductive additive and a binder, in a solvent to form a positive electrode mixture-containing slurry, which is then applied to a positive electrode current collector, dried (solvent removal), and, if necessary, pressed. The solvent is not particularly limited, and any conventionally known solvent can be used. Examples of such a solvent include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0089] The positive electrode current collector is made of a metal foil such as aluminum foil, nickel foil, or stainless steel foil. The surface of the positive electrode current collector may be coated with carbon or may be processed into a mesh. The thickness of the positive electrode current collector is preferably 5 to 40 μm, more preferably 7 to 35 μm, and even more preferably 9 to 30 μm.

[0090] <3. Negative electrode and negative electrode current collector> 1 and 2 is composed of a negative electrode active material layer made of a negative electrode mixture and a negative electrode current collector. The negative electrode 160 can function as the negative electrode of a non-aqueous secondary battery.

[0091] The negative electrode active material layer preferably contains a negative electrode active material, and optionally a conductive additive and a binder.

[0092] Examples of negative electrode active materials include amorphous carbon (hard carbon), graphite (e.g., artificial graphite, natural graphite, etc.), pyrolytic carbon, coke, glassy carbon, baked bodies of organic polymer compounds, mesocarbon microbeads, carbon fiber, activated carbon, carbon colloid, and carbon black, as well as metal lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, silicon alloys, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, organic polymer compounds, etc. The negative electrode active materials may be used alone or in combination of two or more.

[0093] The negative electrode active material layer uses lithium ions as the negative electrode active material to increase the battery voltage. + It is preferable that the material contains a material capable of occluding at a potential lower than the potential of the metal.

[0094] Examples of the conductive additive include carbon black, such as graphite, acetylene black, and ketjen black, and carbon fiber. The content of the conductive additive is preferably 20 parts by mass or less, and more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the negative electrode active material.

[0095] Examples of binders include carboxymethyl cellulose, PVDF, PTFE, polyacrylic acid, and fluororubber. Also included are diene rubbers such as styrene-butadiene rubber. The binder content is preferably 10 parts by mass or less, more preferably 0.5 to 6 parts by mass, per 100 parts by mass of the negative electrode active material.

[0096] The negative electrode active material layer is formed by dispersing a negative electrode mixture, which is a mixture of a negative electrode active material and, if necessary, a conductive additive and a binder, in a solvent to form a negative electrode mixture-containing slurry, which is then applied to a negative electrode current collector, dried (solvent removal), and, if necessary, pressed. The solvent is not particularly limited, and any conventionally known solvent can be used. Examples of such a solvent include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0097] The negative electrode current collector is made of a metal foil such as copper foil, nickel foil, or stainless steel foil. The surface of the negative electrode current collector may be coated with carbon or may be processed into a mesh. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and even more preferably 7 to 30 μm.

[0098] <4. Separator> 2, the nonaqueous secondary battery 100 of this embodiment preferably includes a separator 170 between the positive electrode 150 and the negative electrode 160 from the viewpoint of preventing short circuits between the positive electrode 150 and the negative electrode 160 and providing safety such as shutdown. The separator 170 is not limited, but may be the same as those included in known nonaqueous secondary batteries, and is preferably an insulating thin film with high ion permeability and excellent mechanical strength. Examples of the separator 170 include woven fabric, nonwoven fabric, and synthetic resin microporous membrane, and among these, synthetic resin microporous membrane is preferred.

[0099] Suitable synthetic resin microporous films include, for example, microporous films containing polyethylene or polypropylene as a main component, or polyolefin-based microporous films containing both of these polyolefins. Suitable nonwoven fabrics include, for example, porous films made of heat-resistant resins such as glass, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, and aramid.

[0100] Separator 170 may be configured as a single layer or multiple layers of one type of microporous film, or may be configured as a layer of two or more types of microporous films. Separator 170 may be configured as a single layer or multiple layers of a mixed resin material obtained by melting and kneading two or more types of resin materials.

[0101] To provide functionality, inorganic particles may be present on the surface or inside of the separator, or other organic layers may be coated or laminated thereon. Furthermore, a crosslinked structure may be included. These methods may be combined as needed to enhance the safety performance of nonaqueous secondary batteries.

[0102] By using such a separator 170, it is possible to achieve the good input / output characteristics and low self-discharge characteristics required for the lithium ion battery for high-power applications described above.

[0103] The thickness of the microporous membrane usable as a separator is not particularly limited, but is preferably 1 μm or more from the viewpoint of membrane strength, and preferably 500 μm or less from the viewpoint of permeability. From the viewpoint of use in high-power applications requiring a relatively high heat output and better self-discharge characteristics than conventional ones, such as safety tests, and from the viewpoint of winding ease in large battery winding machines, the thickness of the microporous membrane is preferably 5 μm to 30 μm, and more preferably 10 μm to 25 μm. When prioritizing both short-circuit resistance and power performance, the thickness of the microporous membrane is more preferably 15 μm to 25 μm, but more preferably 10 μm to less than 15 μm when prioritizing both high energy density and power performance.

[0104] The porosity of a microporous membrane usable as a separator is preferably 30% to 90%, more preferably 35% to 80%, and even more preferably 40% to 70%, from the viewpoint of following the rapid movement of lithium ions during high power output. If priority is given to improving power performance while ensuring safety, the porosity of the microporous membrane is particularly preferably 50% to 70%, and if emphasis is placed on achieving both short-circuit resistance and power performance, the porosity is particularly preferably 40% to less than 50%.

[0105] The air permeability of a microporous membrane that can be used as a separator should be 1 second / 100 cm from the viewpoint of the balance between the membrane thickness and porosity. 3 More than 400 seconds / 100cm 3 Less than 100 seconds / 100cm is preferable. 3 More than 350 seconds / 100cm 3 When emphasis is placed on achieving both short circuit resistance and output performance, the air permeability of the microporous membrane is preferably 150 sec / 100 cm. 3 More than 350 seconds / 100cm 3 The following is particularly preferable. If you prioritize improving output performance while ensuring safety, 100 seconds / 100cm is recommended. 3 More than 150 seconds / 100cm 3 It is particularly preferable that the ionic conductivity is less than 10 mS / cm. On the other hand, when a nonaqueous electrolyte solution with low ionic conductivity is combined with a separator within the above range, the lithium ion migration rate is determined not by the separator structure but by the high ionic conductivity of the nonaqueous electrolyte solution, and the expected input / output characteristics tend not to be obtained. Therefore, the ionic conductivity of the nonaqueous electrolyte solution is preferably 10 mS / cm or more, more preferably 15 mS / cm, and even more preferably 20 mS / cm. However, the membrane thickness, air permeability, and porosity of the separator, and the ionic conductivity of the nonaqueous electrolyte solution are not limited to the above examples.

[0106] <5. Battery exterior> The configuration of the battery exterior 110 of the nonaqueous secondary battery 100 shown in Figures 1 and 2 is not particularly limited, and for example, either a battery can or a laminate film exterior can be used. As the battery can, for example, a metal can made of steel, stainless steel, aluminum, clad material, or the like, which may be prismatic, rectangular, cylindrical, cylindrical, oval, flat, coin-shaped, or button-shaped, can be used. As the laminate film exterior, for example, a laminate film having a three-layer structure of heat-melt resin / metal film / resin can be used.

[0107] The laminate film exterior can be used as an exterior by stacking two sheets with the heat-melt resin side facing inward, or by folding the laminate film exterior so that the heat-melt resin side faces inward and sealing the ends with heat sealing. When using a laminate film exterior, the positive electrode lead body 130 (or a lead tab connected to a positive electrode terminal and a positive electrode terminal) may be connected to the positive electrode current collector, and the negative electrode lead body 140 (or a lead tab connected to a negative electrode terminal and a negative electrode terminal) may be connected to the negative electrode current collector. In this case, the laminate film exterior may be sealed with the ends of the positive electrode lead body 130 and the negative electrode lead body 140 (or the lead tabs connected to the positive electrode terminal and the negative electrode terminal, respectively) extended to the outside of the exterior.

[0108] 6. Battery manufacturing method The nonaqueous secondary battery 100 in this embodiment is produced by a known method using the above-mentioned nonaqueous electrolyte solution, a positive electrode 150 having a positive electrode active material layer on one or both sides of a current collector, a negative electrode 160 having a negative electrode active material layer on one or both sides of a current collector, a battery casing 110, and, if necessary, a separator 170.

[0109] First, a laminate consisting of a positive electrode 150, a negative electrode 160, and optionally a separator 170 is formed. For example: An embodiment in which a long positive electrode 150 and a long negative electrode 160 are wound in a stacked state with the long separator interposed between the positive electrode 150 and the negative electrode 160 to form a wound laminate; A mode in which the positive electrode 150 and the negative electrode 160 are cut into a plurality of sheets each having a certain area and shape, and the resulting positive electrode sheets and negative electrode sheets are alternately stacked with separator sheets interposed therebetween to form a laminate having a laminated structure; A mode in which a long separator is folded zigzag and positive electrode sheets and negative electrode sheets are alternately inserted between the zigzag-folded separators to form a laminated body; etc. are possible.

[0110] Next, the above-mentioned laminate is housed in a battery exterior 110 (battery case), the nonaqueous electrolyte solution according to this embodiment is poured into the battery case, and the laminate is immersed in the nonaqueous electrolyte solution and sealed, thereby producing the nonaqueous secondary battery according to this embodiment.

[0111] Alternatively, a gel-state electrolyte membrane may be prepared in advance by impregnating a substrate made of a polymer material with a nonaqueous electrolyte solution, and a laminated structure may be formed using sheet-like positive electrode 150, negative electrode 160, and electrolyte membrane, as well as separator 170 as needed, and then housed in battery exterior 110 to prepare nonaqueous secondary battery 100.

[0112] If the electrodes are arranged so that there is a portion where the outer peripheral edge of the negative electrode active material layer overlaps with that of the positive electrode active material layer, or there is a portion where the width is too small in the non-facing portion of the negative electrode active material layer, misalignment of the electrodes may occur during battery assembly, which may result in a deterioration in the charge-discharge cycle characteristics of the non-aqueous secondary battery. Therefore, it is preferable to fix the positions of the electrodes of the electrode body used in the non-aqueous secondary battery in advance using tapes such as polyimide tape, polyphenylene sulfide tape, and polypropylene (PP) tape, adhesives, etc.

[0113] In this embodiment, when a nonaqueous electrolyte containing acetonitrile is used, its high ionic conductivity may cause lithium ions released from the positive electrode during the initial charge of the nonaqueous secondary battery to diffuse throughout the negative electrode. In nonaqueous secondary batteries, the area of ​​the negative electrode active material layer is generally larger than that of the positive electrode active material layer. However, if lithium ions diffuse and are absorbed in a portion of the negative electrode active material layer that does not face the positive electrode active material layer, these lithium ions will not be released during the initial discharge and will remain in the negative electrode. Therefore, the contribution of these unreleased lithium ions will be the irreversible capacity. For these reasons, nonaqueous secondary batteries using a nonaqueous electrolyte containing acetonitrile may have low initial charge / discharge efficiency.

[0114] On the other hand, if the area of ​​the positive electrode active material layer is larger than that of the negative electrode active material layer or if the two are the same, current tends to concentrate at the edge portions of the negative electrode active material layer during charging, making it easier for lithium dendrites to form.

[0115] For the reasons described above, the ratio of the area of ​​the entire negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other is not particularly limited, but is preferably greater than 1.0 and less than 1.1, more preferably greater than 1.002 and less than 1.09, even more preferably greater than 1.005 and less than 1.08, and particularly preferably greater than 1.01 and less than 1.08. In a nonaqueous secondary battery using a nonaqueous electrolyte solution containing acetonitrile, the initial charge-discharge efficiency can be improved by reducing the ratio of the area of ​​the entire negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other.

[0116] Reducing the ratio of the area of ​​the entire negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other means limiting the area of ​​the portion of the negative electrode active material layer that does not face the positive electrode active material layer. This makes it possible to minimize the amount of lithium ions released from the positive electrode during the initial charge that are absorbed in the portion of the negative electrode active material layer that does not face the positive electrode active material layer (i.e., the amount of lithium ions that are not released from the negative electrode during the initial discharge and result in irreversible capacity). Therefore, by designing the ratio of the area of ​​the entire negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other within the above range, it is possible to improve the load characteristics of the battery by using acetonitrile, increase the initial charge / discharge efficiency of the battery, and further suppress the formation of lithium dendrites.

[0117] The nonaqueous secondary battery 100 of this embodiment can function as a battery after initial charging, but is stabilized by partial decomposition of the nonaqueous electrolyte during initial charging. While there are no particular limitations on the initial charging method, the initial charging is preferably performed at 0.001 to 0.3 C, more preferably at 0.002 to 0.25 C, and even more preferably at 0.003 to 0.2 C. It is also preferable that the initial charging be performed via a constant voltage charge. The constant current required to discharge the design capacity in one hour is 1 C. By extending the voltage range in which the lithium salt participates in the electrochemical reaction, a stable and strong SEI is formed on the surface of the electrode (negative electrode 160), suppressing an increase in internal resistance. Furthermore, the reaction product is not firmly fixed only to the negative electrode 160, but also has a beneficial effect on components other than the negative electrode 160, such as the positive electrode 150 and separator 170. Therefore, it is highly effective to perform the initial charging while taking into account the electrochemical reaction of the lithium salt dissolved in the nonaqueous electrolyte.

[0118] The nonaqueous secondary battery 100 of this embodiment can also be used as a battery pack in which a plurality of nonaqueous secondary batteries 100 are connected in series or in parallel. From the viewpoint of managing the charge / discharge state of the battery pack, the operating voltage range per battery is preferably 2 to 5 V, more preferably 2.5 to 5 V, and particularly preferably 2.75 V to 5 V.

[0119] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit and scope of the present invention. [Example]

[0120] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. Furthermore, the examples were carried out at room temperature unless otherwise specified.

[0121] (1) Preparation of non-aqueous electrolyte Acetonitrile, ethyl methyl carbonate, ethylene carbonate, vinylene carbonate, and ethylene sulfite were mixed in an inert atmosphere in a volume ratio of 20:63.7:10:2.5:3.8. Lithium hexafluorophosphate (LiPF6) was then added to the mixed solvent at 0.3 M and lithium bis(fluorosulfonyl)imide at 1 M to prepare nonaqueous electrolyte solution (S01). Various organosilicon compounds were then added to the mixture at the concentrations shown in Table 1 to prepare nonaqueous electrolyte solutions (S02) to (S13). The C / O ratio in Table 1 refers to the ratio of the number of carbon atoms directly bonded to silicon in the additive to the number of oxygen atoms directly bonded to silicon. The abbreviations for each organosilicon compound are as follows: (organosilicon compounds) MTPS: methoxytriphenylsilane DMTPDS: 1,3-dimethoxy-1,1,3,3-tetraphenyldisiloxane DMDPS: dimethoxydiphenylsilane TMPS: Trimethoxyphenylsilane TEVS: Triethoxyvinylsilane HPDS: Hexaphenyldisiloxane

[0122] [Table 1]

[0123] In S13, in which HPDS with a C / O ratio of 6 was added to the entire amount of the nonaqueous solvent, residual residue was observed, whereas in S02 to S12, in which other organosilicon compounds were added, residual residue was not observed. For this reason, in the nonaqueous electrolyte solution of this embodiment, a C / O ratio of less than 6 is preferred, in which a certain degree of polarity can be expected, with a C / O ratio of 5 or less being more preferred, 4 or less being more preferred, and 3 or less being particularly preferred. It is also preferred that the lower limit of the C / O ratio be greater than 1.

[0124] (2) Fabrication of non-aqueous secondary batteries (2-1) Preparation of the positive electrode (A) A composite oxide of lithium, nickel, manganese, and cobalt (LiNi 0.8 Mn 0.1 Co 0.1 O2), (B) acetylene black powder as a conductive additive, and (C) polyvinylidene fluoride (PVDF) as a binder were mixed in a mass ratio of 94:3:3 to obtain a positive electrode mixture.

[0125] N-methyl-2-pyrrolidone was added as a solvent to the resulting positive electrode mixture to a solids content of 68% by mass, and the mixture was further mixed to prepare a positive electrode mixture-containing slurry. The positive electrode mixture-containing slurry was applied to one side of a 15 μm-thick, 280 mm-wide aluminum foil serving as a positive electrode current collector, adjusting the basis weight of the slurry, using a three-roll transfer coater to create a coating pattern with a coating width of 240-250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was then dried and removed in a hot air drying oven. The resulting electrode roll was trimmed on both sides and dried under reduced pressure at 130°C for 8 hours. The density of the positive electrode active material layer was then adjusted to 2.7 g / cm using a roll press. 3A positive electrode consisting of the positive electrode active material layer and the positive electrode current collector was obtained by rolling the positive electrode active material layer so that the weight per unit area excluding the positive electrode current collector was 8.4 mg / cm. 2 It was.

[0126] (2-2) Preparation of negative electrode (a) Graphite powder as the negative electrode active material, (b) carbon black powder (Super-P) as a conductive additive, and (c) polyvinylidene fluoride (PVDF) as a binder were mixed in a solid mass ratio of 90:3:7 to obtain a negative electrode mixture.

[0127] Water was added as a solvent to the resulting negative electrode mixture to a solids content of 45% by mass, and the mixture was further mixed to prepare a negative electrode mixture-containing slurry. The negative electrode mixture-containing slurry was applied to one side of a copper foil with a thickness of 8 μm and a width of 280 mm, which served as a negative electrode current collector, while adjusting the basis weight, using a three-roll transfer coater to obtain a coating pattern with a coating width of 240 to 250 mm, a coating length of 125 mm, and an uncoated length of 20 mm. The solvent was then dried and removed in a hot air drying oven. The resulting electrode roll was trimmed on both sides and dried under reduced pressure at 80°C for 12 hours. The density of the negative electrode active material layer was then adjusted to 1.3 g / cm using a roll press. 3 The negative electrode active material layer and the negative electrode current collector were rolled to a weight of 5.4 mg / cm excluding the negative electrode current collector. 2 It was.

[0128] (2-3) Assembly of non-aqueous secondary batteries A polypropylene gasket was placed in a CR2032-type battery case (SUS304 / Al clad). The positive electrode obtained as described above was punched into a 15.958 mm diameter disk and placed in the center with the positive electrode active material layer facing up. A glass fiber filter paper (GA-100, manufactured by Advantec Co., Ltd.) punched into a 16.156 mm diameter disk was placed on top of the positive electrode, and 150 μL of nonaqueous electrolyte was poured into it. The negative electrode obtained as described above was punched into a 16.156 mm diameter disk and placed with the negative electrode active material layer facing down. After the spacer and spring were placed, the battery cap was inserted and crimped with a crimping machine. The electrolyte that spilled from the case was wiped off with a rag. The battery was then stored at 25°C for 12 hours to allow the nonaqueous electrolyte to fully soak into the laminate, yielding a coin-type nonaqueous secondary battery.

[0129] (3) Evaluation of non-aqueous secondary batteries The coin-type nonaqueous secondary batteries obtained as described above were first subjected to an initial charge treatment and initial charge / discharge capacity measurement according to the procedure in (3-1) below. Next, each coin-type nonaqueous secondary battery was evaluated according to the procedure in (3-2). Charge / discharge was performed using a charge / discharge device ACD-M01A (product name) manufactured by Asuka Electronics Co., Ltd. and a programmable thermostatic bath IN804 (product name) manufactured by Yamato Scientific Co., Ltd.

[0130] Here, 1C means the current value at which a fully charged battery is expected to be discharged completely in one hour when discharged at a constant current.

[0131] (3-1) Initial charge / discharge treatment of non-aqueous secondary batteries The ambient temperature of the nonaqueous secondary battery was set to 25°C, and it was charged at a constant current of 0.075 mA (equivalent to 0.025 C) until it reached 3.1 V, and then at a constant current of 0.15 mA (equivalent to 0.05 C) until it reached 4.2 V. It was then charged at a constant voltage of 4.2 V until the current decayed to 0.025 C. The battery was then discharged to 3.0 V at a constant current of 0.45 mA (equivalent to 0.15 C).

[0132] Next, the battery was charged at a constant current of 0.6 mA, equivalent to 0.2 C, until it reached 4.2 V, after which it was charged at a constant voltage of 4.2 V until the current decayed to 0.025 C. The battery was then discharged at a current of 0.6 mA, equivalent to 0.2 C, to 3 V. The same charge / discharge cycle as above was then repeated.

[0133] (3-2) Cycle test The nonaqueous secondary battery, which had undergone the initial charge-discharge treatment described in (3-1) above, was charged at an ambient temperature of 50°C at a constant current of 6 mA (corresponding to 2 C) until it reached 4.2 V, and then at a constant voltage of 4.2 V until the current decayed to 0.025 C. The battery was then discharged to 3 V at a current of 6 mA (corresponding to 2 C). The same charge-discharge cycles were then repeated for 100 cycles. However, for the first, 51st, and 101st cycles, the battery was charged at a constant current of 3 mA (corresponding to 1 C) until it reached 4.2 V, and then at a constant voltage of 4.2 V until the current decayed to 0.025 C. The battery was then discharged to 3 V at a current of 0.9 mA (corresponding to 0.3 C).

[0134] The discharge capacity at the 100th cycle in the cycle test was calculated as the capacity retention rate, assuming that the discharge capacity at the second cycle in the cycle test was 100%.

[0135] (3-3) Non-aqueous secondary battery [Examples 1 to 6 and Comparative Examples 1 to 4] Non-aqueous secondary batteries were assembled as described above using each of the electrolyte solutions shown in Table 2, and an initial charge-discharge treatment and a cycle test were carried out. The interpretation of each test result will now be described.

[0136] The capacity retention rate is an index showing the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 2nd cycle. In the above cycle test, charge and discharge are repeated at a higher current density than in a general cycle test, and the higher the value, the less capacity deterioration occurs when the battery is repeatedly charged and discharged. The capacity retention rate is preferably 87% or more, more preferably 88% or more, and even more preferably 89% or more.

[0137] [Table 2]

[0138] In Examples 1 to 4, when MTPS with a C / O ratio of 3 was used as the organosilicon compound, it was confirmed that the capacity retention rate was 88.5% or higher, regardless of the amount added. Similarly, in Examples 5 and 6, it was confirmed that the addition of DMTPDS with a C / O ratio of 1.3 resulted in a capacity retention rate exceeding 88.5%. Since the capacity retention rate of Comparative Example 1, which used electrolyte solution S01 without any added organosilicon compound, was 87.5%, these organosilicon compounds have the effect of improving the capacity retention rate, and no side reaction that would lead to a decrease in the capacity retention rate was observed even when the amount added was up to 10% by mass relative to the total amount of the non-aqueous solvent. On the other hand, Comparative Examples 2 to 4 had lower capacity retention rates than Comparative Example 1, indicating the influence of side reactions. For example, in Comparative Example 2, 5% by mass of TMPS was added, which had a C / O ratio of 0.33 (shown as "0.3" in Table 1 due to rounding), but the capacity retention rate was significantly reduced. Similarly, in Comparative Examples 3 and 4, 2% or 5% by mass of TEVS was added, but the capacity retention rate decreased as the amount added increased, which is presumably due to the effects of side reactions.

[0139] From the above results, it was confirmed that in this embodiment, by adding an organosilicon compound having a specific structure such as MTPS or DMTPDS to a non-aqueous solvent, the battery can operate stably while suppressing the effects of side reactions.

[0140] (3-4) AC impedance measurement The coin-type nonaqueous secondary batteries that had been subjected to the initial charge-discharge treatment and cycle test according to the methods described in (3-1) and (3-2) above were charged at a constant current of 1 C at an ambient temperature of 25°C until they reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value decayed to 0.025 C. Then, AC impedance measurements were performed.

[0141] AC impedance measurements were performed using a Solartron Frequency Response Analyzer 1400 (product name) and a Solartron Potentio-Galvanostat 1470E (product name). An AC signal was applied while varying the frequency from 1000 kHz to 0.1 Hz, and the impedance was measured from the voltage-current response signal. The positive electrode interface resistance was estimated from the arc on the low-frequency side of the complex impedance plane plot (Cole-Cole plot) corresponding to the positive electrode interface resistance. For the battery specifications used in this study, the positive electrode interface resistance was calculated as the difference between the real components of the impedance at 100 Hz and 0.1 Hz. The amplitude of the applied AC voltage was ±5 mV. The ambient temperature for the battery during AC impedance measurements was 25°C.

[0142] The positive electrode resistance after the cycle test tends to increase due to the deterioration of the positive electrode active material by hydrogen fluoride or the deposition of resistive deposits resulting from side reactions of the additives. Therefore, it is preferable that the resistance be less than 20 Ω, and more preferably less than 19 Ω. Here, we compare the positive electrode interface resistance of batteries using electrolytes S04, S05, S07-S09, S11, and S12 containing additives with that of electrolyte S01 without additives to examine the impact of side reactions. Table 3 shows the measurement results.

[0143] [Table 3]

[0144] As shown in Tables 1 to 3, the positive electrode interface resistance of the electrolyte containing 5% by mass of MTPS was 16.5 Ω. Even when the amount of MTPS was increased to 10% by mass, the positive electrode interface resistance was 18.8 Ω, which is smaller than the positive electrode interface resistance of 21.9 Ω for Comparative Example 5, which did not contain an organosilicon compound. This suppresses positive electrode degradation while also preventing the effects of side reactions. Similarly, in Example 9, electrolyte S07 containing 5% by mass of DMTPDS was used, but no increase in resistance due to side reactions was observed. Thus, the ability to suppress side reactions was not confirmed in Comparative Examples 6 to 9, and resistance generally tended to be higher than in Comparative Example 5, which contained no additives.

[0145] From the above, it is believed that in this embodiment, the side reaction that accompanies an increase in the positive electrode interface resistance does not occur, and therefore the battery operates stably. [Industrial Applicability]

[0146] The nonaqueous secondary battery of the present invention is expected to be used as an automotive storage battery for hybrid vehicles, plug-in hybrid vehicles, electric vehicles, etc., as well as an industrial storage battery for power tools, drones, electric motorcycles, etc., and even as a residential power storage system. [Explanation of symbols]

[0147] 100 Nonaqueous secondary battery 110 Battery casing 120 Battery enclosure space 130 Positive electrode lead body 140 negative electrode lead body 150 positive electrode 160 negative electrode 170 Separator

Claims

1. A non-aqueous electrolyte solution containing a non-aqueous solvent and a lithium salt, The lithium salt is LiPF ６ Including, the non-aqueous solvent contains acetonitrile, vinylene carbonate, and ethylene sulfite, and the volume ratio of vinylene carbonate in the non-aqueous solvent is lower than the volume ratio of ethylene sulfite; Furthermore, the non-aqueous electrolyte solution contains at least one organosilicon compound, the organosilicon compound is at least one selected from the group consisting of methoxytriphenylsilane, ethoxytriphenylsilane, dimethoxytetraphenyldisiloxane, diethoxytetraphenyldisiloxane, and methoxyethoxytetraphenyldisiloxane; The nonaqueous electrolyte solution has a content of the organosilicon compound of 1% by mass or more and 15% by mass or less based on the total amount of the nonaqueous solvent.

2. 2. The nonaqueous electrolyte solution according to claim 1, wherein the content of the acetonitrile is 5 to 97% by volume based on the total amount of the nonaqueous solvent.

3. 3. The nonaqueous electrolyte solution according to claim 1, wherein the lithium salt further comprises lithium bis(fluorosulfonyl)imide.

4. A non-aqueous secondary battery comprising: a positive electrode having a positive electrode active material layer on one or both sides of a current collector; a negative electrode having a negative electrode active material layer on one or both sides of a current collector; a separator; and the non-aqueous electrolyte solution according to any one of claims 1 to 3, The positive electrode active material layer is formed by adding a compound represented by the following general formula (4): Li ｐ Ni ｑ Co ｒ Mn ｓ M ｔ O ｕ Formula (4) In the formula, M is at least one metal selected from the group consisting of aluminum (Al), tin (Sn), indium (In), iron (Fe), vanadium (V), copper (Cu), magnesium (Mg), titanium (Ti), zinc (Zn), molybdenum (Mo), zirconium (Zr), strontium (Sr), and barium (Ba), and is within the ranges of 0<p<1.3, 0<q<1.2, 0<r<1.2, 0≦s<0.5, 0≦t<0.3, 0.7≦q+r+s+t≦1.2, and 1.8<u<2.2, and p is a value determined by the charge / discharge state of the battery. A non-aqueous secondary battery containing at least one selected from the group consisting of lithium-containing metal oxides represented by the following formula:

5. 5. The nonaqueous secondary battery according to claim 4, wherein the nickel (Ni) content ratio q of the lithium-containing metal oxide represented by the general formula (4) is 0.5<q<1.2.

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