Nonaqueous electrolyte and nonaqueous secondary battery

Abstract

The present invention provides a nonaqueous electrolyte solution for a nonaqueous lithium ion secondary battery that is provided with a negative electrode containing graphite, while comprising a nonaqueous electrolyte solution in an amount of X mass% relative to the mass of the negative electrode excluding the negative electrode collector, wherein X is 50 to 2,000. This nonaqueous electrolyte solution contains a lithium salt and a nonaqueous solvent; acetonitrile is contained as the nonaqueous solvent in an amount of A volume% relative to the volume of the nonaqueous solvent, wherein A is 5 to 70; the nonaqueous electrolyte solution contains vinylene carbonate (VC) as an additive; and the content of VC is (7 × A / X) mass% to 10 mass% relative to the nonaqueous electrolyte solution.

Description

[Technical field]

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

[0002] The applications of non-aqueous secondary batteries such as lithium-ion batteries are changing with the global trend of electrification of automobiles. Non-aqueous secondary batteries are characterized by their light weight, high energy, and long life, and are widely used as power sources for various portable electronic devices. In recent years, they have also attracted attention in the field of power storage, such as industrial power tools and residential power storage systems. In particular, in order to develop batteries with excellent output performance for on-board batteries, research has been conducted on electrolytes using acetonitrile, which has low viscosity. On the other hand, additives that form a coating on the negative electrode have been studied to prevent the reductive decomposition of easily reduced solvents at the negative electrode.

[0003] For example, Patent Document 1 describes the addition of an additive such as vinylene carbonate to an electrolyte solvent to prevent the electrolyte solvent from decomposing at the negative electrode.

[0004] Patent Document 2 discloses an invention related to a non-aqueous electrolyte applied to non-aqueous secondary batteries such as lithium ion batteries. Patent Document 1 discloses a non-aqueous electrolyte solution combining acetonitrile (AcN) and an additive having a LUMO (lowest unoccupied molecular orbital) and a HOMO (highest occupied molecular orbital) in a specific potential band.

[0005] Patent Document 3 describes an invention related to a multi-stage electrolyte injection process during lithium-ion battery manufacturing. In Patent Document 3, it is considered that cell swelling due to gas during electrolyte film formation can be eliminated by adding a negative electrode film forming additive in an amount of more than 50% of the total amount to the initial electrolyte injection, and injecting the electrolyte again after the initial charge / discharge.

[0006] Patent Document 4 describes an invention related to a multi-stage liquid injection process during lithium-ion battery manufacturing. In Patent Document 4, it is considered that a lithium-ion secondary battery with improved cycle characteristics can be provided by injecting liquid again after the initial charge / discharge and forming a good coating on the newly formed surface caused by the expansion of the negative electrode active material. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2005-166553 A [Patent Document 2] International Publication No. 2012 / 057311 [Patent Document 3] JP 2006-294282 A [Patent Document 4] JP 2010-129192 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, in electrolytes whose main component is a solvent such as acetonitrile that increases the resistance of the battery through reduction, more detailed consideration of additives is required to prevent the reductive decomposition.

[0009] Vinylene carbonate, a typical additive for forming a negative electrode film, is effective in preventing the decomposition of acetonitrile on the negative electrode, but unless a sufficient amount of vinylene carbonate is added to form a film relative to the amount of negative electrode active material, a good quality negative electrode film cannot be formed during the first charge of the battery. In addition, the ratio of the amount of negative electrode active material to the electrolyte varies depending on the design of the battery shape or battery capacity, and it is important to design the electrolyte so that an appropriate amount of additive is added accordingly.

[0010] Such problems are not seen in electrolytes mainly composed of carbonate, which is relatively less affected by reductive decomposition at the negative electrode, but are thought to occur only when the electrolyte mainly contains a solvent that is easily reduced. However, the above patent documents do not state that the amount of additives varies depending on the battery design. Therefore, the first problem that the present invention aims to solve is to provide an electrolyte that can stably operate a battery even if a solvent that is easily reductively decomposed, such as acetonitrile, is used as the main component.

[0011] Secondly, during the manufacture of lithium-ion secondary batteries, the discharge capacity of the battery is not constant, and in some cases the initial capacity may gradually increase from a state where it is smaller than the capacity expected by the design. This type of capacity change is considered to be a phenomenon that is clearly different from the capacity decrease seen during normal battery deterioration, and is expected to occur when the electrolyte is difficult to diffuse within the electrodes. If the capacity increases while remaining unstable, multiple charge / discharge cycles are required until the capacity stabilizes, which increases the manufacturing time, and therefore reduces the efficiency of the manufacturing process.

[0012] Therefore, the second problem to be solved by the present invention is to promote the diffusion of lithium inside the electrode by using acetonitrile with low viscosity, while forming a strong negative electrode coating during the first charge, thereby preventing the reduction of acetonitrile and quickly stabilizing the capacity of the battery.

[0013] Thirdly, acetonitrile-based electrolytes require the formation of a film on the negative electrode surface to suppress reduction electrolysis, and film-forming agents such as vinylene carbonate (VC) and ethylene sulfite (ES) are used. As an effect of ES in electrolytes, there have been many patents on the film-forming ability, but no discussion has been held on the compounds generated by excessive reduction of ES. In this context, the inventors discovered that when acetonitrile is contained in an electrolyte, a large number of compounds containing sulfur atoms with a valence of -2 or more and 0 or less are deposited on the negative electrode film due to the excessive reduction reaction of ES, and that these compounds have no ionic conductivity, which reduces the battery performance.

[0014] In addition, in recent battery manufacturing processes, a method has been developed in which the initial charge and discharge is performed under reduced pressure in order to remove gas from within the cell and impregnate the battery with electrolyte. However, when this method is applied to a high-concentration acetonitrile electrolyte, it has been confirmed that the composition of the electrolyte changes significantly due to the evaporation of acetonitrile, and defects occur due to a lack of electrolyte.

[0015] In order to solve these conventional problems, a multi-stage injection method has been considered as a method for increasing the concentration of the film-forming agent in the electrolyte before the first charge and simultaneously decreasing the acetonitrile concentration. However, there have been no reported examples of applying such a multi-stage injection process to an acetonitrile-based electrolyte.

[0016] Therefore, a third problem to be solved by the present invention is to provide a nonaqueous battery having desired battery performance by increasing the concentration of the negative electrode film-forming agent in the initial electrolyte by multi-stage injection and decreasing the acetonitrile concentration, thereby suppressing the volatilization of the electrolyte under reduced pressure conditions and also suppressing the reduction reaction of excess ethylene sulfite during the initial charge, in the manufacture of a nonaqueous battery containing an acetonitrile electrolyte. [Means for solving the problem]

[0017] The present inventors have conducted extensive research to solve the above problems and have found that the problems can be solved by the following technical means. That is, the present invention is as follows. (1) A non-aqueous electrolyte for a non-aqueous lithium ion secondary battery having a negative electrode containing graphite and containing X% by mass of the non-aqueous electrolyte relative to the mass of the negative electrode excluding the negative electrode current collector, X is between 50 and 2000, The non-aqueous electrolyte solution contains a lithium salt and a non-aqueous solvent, The non-aqueous solvent contains A% by volume of acetonitrile relative to the volume of the non-aqueous solvent, A is between 5 and 70, and The non-aqueous electrolyte solution contains vinylene carbonate (VC) as an additive, and the content of VC is (7×A / X) mass% or more and 10 mass% or less with respect to the non-aqueous electrolyte solution. Non-aqueous electrolyte. (2) The nonaqueous electrolyte solution according to item 1, wherein X is 200 or less. (3) The nonaqueous electrolyte solution according to item 1 or 2, wherein A is 16 or more and 35 or less. (4) The nonaqueous electrolyte solution according to any one of items 1 to 3, wherein the VC content is from (15×A / X) mass % to 9 mass % with respect to the nonaqueous electrolyte solution. (5) The nonaqueous electrolyte solution according to any one of items 1 to 4, wherein X is 98 or less. (6) The nonaqueous electrolyte solution according to any one of items 1 to 5, which contains ethylene sulfite. (7) The nonaqueous electrolyte solution according to any one of items 1 to 6, which contains at least one of a sulfate ion and a sulfite ion. (8) The nonaqueous electrolyte solution according to any one of items 1 to 7, wherein the VC content is 7% by mass or less based on the mass of the nonaqueous electrolyte solution. (9) The nonaqueous electrolyte solution according to any one of items 1 to 8, wherein X is 65 or more. (10) A nonaqueous lithium ion secondary battery comprising: a positive electrode having a positive electrode active material layer on one or both sides of a positive electrode current collector; a negative electrode having a negative electrode active material layer containing the graphite on one or both sides of the negative electrode current collector; a separator; and the nonaqueous electrolyte solution according to any one of items 1 to 9. (11) A nonaqueous secondary battery comprising a negative electrode, a positive electrode, a separator, and a nonaqueous electrolyte, The nonaqueous secondary battery has been charged at least once, the negative electrode contains at least one inorganic lithium compound and at least one organic lithium compound that can be extracted by immersion in an extraction solvent; The nonaqueous electrolyte solution of the nonaqueous secondary battery contains a lithium salt, acetonitrile as a nonaqueous solvent, and a cyclic carbonate. (12) An inorganic lithium compound (a) comprising a component extractable from the negative electrode by using water as the extraction solvent, the inorganic lithium compound (a) being at least one of the following: (a) LiF and at least the following organolithium compounds (b) to (d); (b)LiOCOOCH 2 CH 2 O-COOLi (c)CH 3 CH 2 O-COOLi (d)CH 3 O-COOLi and Item 12. The nonaqueous secondary battery according to item 11, wherein the molar ratios of the (a) to (d) with respect to the total content of the (a) to (d) are, respectively, 20 to 70 mol% for the (a), 20 to 70 mol% for the (b), 1 to 20 mol% for the (c), and 1 to 20 mol% for the (d). (13) The nonaqueous secondary battery according to item 11 or 12, wherein the cyclic carbonate contains ethylene carbonate and vinylene carbonate, and the molar ratio of vinylene carbonate to ethylene carbonate is 0.01 to 30 mol %. (14) The nonaqueous lithium ion secondary battery according to item 10 or the nonaqueous secondary battery according to any one of items 11 to 13, wherein a positive electrode active material of the positive electrode contains lithium iron phosphate. (15) The nonaqueous secondary battery according to any one of items 11 to 13, which uses the nonaqueous electrolyte solution according to any one of items 1 to 9. (16) A process for producing a secondary battery, comprising at least two electrolyte injection steps for injecting a nonaqueous electrolyte into a battery exterior, and at least one charging step after a first electrolyte injection step and before a final electrolyte injection step, wherein in an electrolyte injection step after the first, an electrolyte having a higher volumetric ratio of acetonitrile to the total electrolyte than the electrolyte used in the first electrolyte injection step is injected into the battery exterior. (17) The process for producing a secondary battery according to item 16, wherein in the electrolyte injection step after the first injection, an electrolyte containing 20 vol% to 100 vol% acetonitrile is injected into the battery exterior. (18) A nonaqueous secondary battery comprising a nonaqueous electrolyte solution containing 5 volume % or more and 60 volume % or less of acetonitrile and ethylene sulfite, a positive electrode having a positive electrode active material layer on one or both sides of a positive electrode current collector, a negative electrode having a negative electrode active material layer on one or both sides of a negative electrode current collector, and a separator, wherein a negative electrode coating after an initial charge and discharge contains a compound containing a sulfur atom having a valence of -2 or more and 0 or less, and the compound contains at least one of sulfur and copper sulfide, and the nonaqueous secondary battery has at least one charging step after an initial electrolyte solution injection step and before a final electrolyte solution injection step, and the nonaqueous secondary battery is obtained by a method in which, in an electrolyte solution injection step after the initial one, an electrolyte solution having a higher volume ratio of acetonitrile to the entire electrolyte solution than the electrolyte solution used in the initial electrolyte solution injection step is injected into the battery exterior. (19) The nonaqueous secondary battery according to item 18, wherein the concentration of ethylene sulfite in the nonaqueous electrolyte solution is 0.01% by volume or more and 4% by volume or less. (20) The nonaqueous secondary battery according to item 18 or 19, wherein the nonaqueous electrolyte further contains vinylene carbonate. Effect of the Invention

[0018] According to the first embodiment of the present invention, it is possible to provide a lithium ion secondary battery having high charge / discharge efficiency and stable charge / discharge cycle characteristics even when an electrolyte solution containing acetonitrile is used.

[0019] According to the second embodiment of the present invention, a secondary battery can be provided that has a coating suitable for preventing acetonitrile from reductive decomposition, while containing low-viscosity acetonitrile, thereby quickly stabilizing the initial battery capacity, thereby contributing to the efficiency of the manufacturing process.

[0020] According to the third embodiment of the present invention, a two-step liquid injection method is developed as a method for reducing the deposition on the negative electrode, and the reduction reaction at the defective portion of the negative electrode film peculiar to the cell using a high-concentration acetonitrile electrolyte can be suppressed. Further, by controlling or reducing the compound containing sulfur atoms whose valence on the negative electrode film becomes -2 or more and 0 or less due to the reduction reaction of ethylene sulfite (ES), a non-aqueous secondary battery having high stability can also be provided.

Brief Description of Drawings

[0021]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0022] Hereinafter, embodiments for carrying out the present invention (hereinafter simply referred to as "embodiments") will be described in detail. In this specification, the numerical range described using "~" includes the numerical values described before and after it.

[0023] The non-aqueous secondary battery according to the first, second, and third embodiments of the present invention is a secondary battery including a non-aqueous electrolyte together with a positive electrode and a negative electrode, and may be, for example, a lithium ion battery. More specifically, it may be a lithium ion battery schematically showing a plan view in FIG. 1 and a cross-sectional view in 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) sandwiching the laminate of them (separator 170, positive electrode 150 and negative electrode 160), a negative electrode lead body 140 (connected to the negative electrode 160), and a battery exterior 110 housing them. The laminate in which the positive electrode 150, the separator 170, and the negative electrode 160 are laminated is impregnated with the non-aqueous electrolyte according to the first, second, and third embodiments.

[0024] <I. First Embodiment> The first embodiment of the present invention will be described in detail below. In the first embodiment, a non-aqueous electrolyte for a non-aqueous lithium-ion secondary battery and a non-aqueous lithium-ion secondary battery including the same are provided. The non-aqueous lithium-ion secondary battery according to the first embodiment may have the configuration of the lithium-ion battery 100 shown in FIGS. 1 and 2, although it is not limited thereto.

[0025] <I-1. Non-aqueous electrolyte> The "non-aqueous electrolyte" in the first embodiment refers to a non-aqueous electrolyte in which water is 1% by mass or less with respect to the total amount of the non-aqueous electrolyte and which contains a non-aqueous solvent and a lithium salt. The non-aqueous electrolyte according to the first embodiment preferably contains as little water as possible, but may contain a very small amount of water as long as it does not inhibit the solution of the problems of the present invention. The content of such water is 300 ppm by mass or less, preferably 200 ppm by mass or less, per total amount of the non-aqueous electrolyte. For the non-aqueous electrolyte, as long as it has a configuration for achieving the solution of the problems of the present invention, for other components, constituent materials in known non-aqueous electrolytes used in lithium-ion batteries can be appropriately selected and applied.

[0026] <I-1-1. Non-aqueous solvent> The "non-aqueous solvent" in the first embodiment refers to an element obtained by removing a lithium salt and various additives from the non-aqueous electrolyte. When the non-aqueous electrolyte contains an additive for electrode protection in the first embodiment, the "non-aqueous solvent" refers to an element obtained by removing a lithium salt and additives other than the additive for electrode protection from the non-aqueous electrolyte. Examples of the non-aqueous solvent include alcohols such as methanol and ethanol; aprotic solvents and the like. Among them, as the non-aqueous solvent, an aprotic solvent is preferable. As long as it does not inhibit the solution of the problems of the present invention, the non-aqueous solvent may contain a solvent other than the aprotic solvent.

[0027] The non-aqueous solvent related to the non-aqueous electrolyte of the first embodiment contains acetonitrile as an aprotic solvent. The non-aqueous solvent contains acetonitrile, which improves the ionic conductivity of the non-aqueous electrolyte, thereby increasing the diffusibility of lithium ions in the battery. Therefore, when the non-aqueous electrolyte contains acetonitrile, even in a positive electrode in which the positive electrode active material layer is thickened to increase the amount of positive electrode active material filled, lithium ions can be well diffused to the area near the current collector where lithium ions are difficult to reach during high load discharge. As a result, it is possible to extract sufficient capacity even during high load discharge, and a non-aqueous secondary battery with excellent load characteristics can be obtained.

[0028] Furthermore, the non-aqueous solvent contains acetonitrile, which can improve the rapid charging characteristics of the non-aqueous secondary battery. In constant current (CC)-constant voltage (CV) charging of a non-aqueous secondary battery, the 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 non-aqueous solvent of the non-aqueous 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, so that the time from the start of charging to fully charging the non-aqueous secondary battery can be significantly shortened.

[0029] In addition, acetonitrile is easily electrochemically reduced and decomposed, so when acetonitrile is used, it is preferable to use another solvent (e.g., an aprotic solvent other than acetonitrile) together with acetonitrile as a non-aqueous solvent and / or to add an additive for protecting an electrode for forming a protective film on the electrode.

[0030] The content of acetonitrile in the non-aqueous solvent is preferably 5 to 70% by volume based on the total amount of the non-aqueous solvent. The lower limit of the content of acetonitrile is more preferably 8% by volume or more based on the total amount of the non-aqueous solvent, and more preferably 16% by volume or more. The upper limit of the content of acetonitrile is more preferably 60% by volume or less based on the total amount of the non-aqueous solvent, and more preferably 35% by volume or less. When the content of acetonitrile is 5% by volume or more based on the total amount of the non-aqueous solvent, the ionic conductivity of the non-aqueous electrolyte increases, and the non-aqueous secondary battery tends to exhibit high output characteristics, and furthermore, the dissolution of the lithium salt can be promoted. In addition, when the content of acetonitrile 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.

[0031] 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.

[0032] Acetonitrile, which is one component of the nonaqueous solvent, is easily reduced and decomposed electrochemically. Therefore, by adding vinylene carbonate to the nonaqueous solvent in addition to acetonitrile, the nonaqueous electrolyte solution according to the first embodiment stabilizes the charge and discharge amount of the battery when used in a nonaqueous secondary battery.

[0033] When the nonaqueous solvent according to the first embodiment contains acetonitrile, vinylene carbonate (VC) as a cyclic carbonate, and ethylene sulfite as an organic compound having a sulfur atom, when the nonaqueous electrolyte is used in a nonaqueous secondary battery, the battery can be operated at a high current density.

[0034] The high resistance of the negative electrode protective film derived from vinylene carbonate tends to lead to a decrease in performance during rapid charging and in low-temperature environments, and to battery swelling due to gas generation during decomposition. Ethylene sulfite has a lower lowest unoccupied molecular orbital (LUMO) level than other oxygen-containing sulfur compounds, and can be reductively decomposed at a lower potential than vinylene carbonate to form a negative electrode protective film, making it possible to solve the problems caused by the negative electrode protective film derived from vinylene carbonate by reducing the amount of vinylene carbonate added. In addition, the negative electrode protective film derived from ethylene sulfite has low resistance over a wide temperature range, and furthermore, it promotes the formation of a negative electrode SEI (Solid Electrolyte Interface) that is highly durable against acetonitrile and its decomposition products, making it possible to provide a nonaqueous electrolyte and a nonaqueous secondary battery that can operate stably at a high current density.

[0035] In the first embodiment, the total content of vinylene carbonate and ethylene sulfite in the nonaqueous electrolyte is preferably 0.1% by volume or more and less than 15% by volume with respect to the total amount of the nonaqueous solvent, from the viewpoint of suppressing an increase in internal resistance. The content of ethylene sulfite is preferably 0.1% by volume or more and less than 6% by volume, more preferably 1% by volume or more and less than 5% by volume, with respect to the total amount of the nonaqueous solvent.

[0036] 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 (VC), 4,5-dimethylvinylene carbonate, and vinylethylene carbonate;

[0037] Fluoroethylene carbonates include, for example, 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, 4,4,5,5-tetrafluoro-1,3-dioxolane-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxolane-2-one;

[0038] Lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone;

[0039] Examples of organic compounds having sulfur atoms 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;

[0040] 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;

[0041] Cyclic ethers include, for example, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane;

[0042] Examples of mononitriles other than acetonitrile include propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile;

[0043] Alkoxy group-substituted nitriles include, for example, methoxyacetonitrile and 3-methoxypropionitrile;

[0044] 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-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dimethylglutaronitrile;

[0045] Cyclic nitriles include, for example, benzonitrile;

[0046] 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 isopropyl 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;

[0047] Chain ethers include, for example, dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme;

[0048] Examples of fluorinated ethers include Rf 20 -OR 21 (In the formula, Rf 20 represents an alkyl group containing a fluorine atom, and R 21 represents a monovalent organic group which may contain a fluorine atom;

[0049] Ketones, for example, acetone, methyl ethyl ketone, and methyl isobutyl ketone;

[0050] Examples of the aprotic solvent compound in which some or all of the H atoms have been replaced with halogen atoms include compounds in which the halogen atoms are fluorine; The following can be mentioned.

[0051] Here, examples of fluorinated chain carbonates include methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethyl methyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, and methyl 2,2,3,3-tetrafluoropropyl carbonate. The above-mentioned fluorinated chain carbonates are represented by the following general formula: R 1 -OC(O)OR 2 {where, R 1 and R 2 is CH 3 , C.H. 2 CH 3 , C.H. 2 CH 2 CH 3 , CH(CH 3 ) 2 , and C.H. 2 Rf 3 Rf is at least one selected from the group consisting of 3 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 1 and / or R 2 contains at least one fluorine atom. It can be expressed as:

[0052] 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 10 -C(O)OR 11 {where, R 10 is CH 3 , C.H. 2 CH 3 , C.H. 2 CH 2 CH 3 , CH(CH 3 ) 2 , C.F. 3 CF 2 H, CFH 2 , C.F. 2 Rf 12 , CFHRf 12 , and C.H. 2 Rf 13 and R is at least one selected from the group consisting of 11 is CH 3 , C.H. 2 CH 3 , C.H. 2 CH 2 CH 3 , CH(CH 3 ) 2 , and C.H. 2 Rf 13 Rf is at least one selected from the group consisting of 12 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 13 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 10 and / or R 11 contains at least one fluorine atom, and R 10 CF 2 If H, then R 11 CH 3 isn't it.} It can be expressed as:

[0053] In the first embodiment, the aprotic solvent other than acetonitrile may be used alone or in combination of two or more.

[0054] In the first embodiment, it is preferable from the viewpoint of improving the stability of the non-aqueous electrolyte that the non-aqueous solvent uses, together with acetonitrile, one or more of cyclic carbonates and chain carbonates. From this viewpoint, it is more preferable that the non-aqueous solvent in the first embodiment uses a cyclic carbonate together with acetonitrile, and it is still more preferable to use both a cyclic carbonate and a chain carbonate together with acetonitrile.

[0055] When using a cyclic carbonate other than vinylene carbonate (VC) together with acetonitrile, it is particularly preferable that such a cyclic carbonate contains ethylene carbonate and / or fluoroethylene carbonate.

[0056] <I-1-2. Electrolyte salt> The non-aqueous electrolyte of the first embodiment is for a lithium-ion secondary battery, and it suffices to contain a lithium salt as the electrolyte salt, and there is no particular limitation on other electrolyte salts. For example, in the first embodiment, as the lithium salt, LiPF 6 and a lithium-containing imide salt may be included.

[0057] The lithium-containing imide salt is a lithium salt represented by LiN(SO 2 C m F 2m+1 ) 2 [wherein, m is an integer of 0 to 8], and specifically, LiN(SO 2 F) 2 , and LiN(SO 2 CF 3 ) 2 It is preferable to contain at least one of them. Only one of these imide salts may be contained or both may be contained. Or, an imide salt other than these imide salts may be contained.

[0058] When acetonitrile is contained in the non-aqueous solvent, since the saturation concentration of the lithium-containing imide salt with respect to acetonitrile is higher than the saturation concentration of LiPF 6 , LiPF 6It is preferable to contain the lithium-containing imide salt at a molar concentration that satisfies the condition of ≦lithium-containing imide salt, since this can suppress association and precipitation of the lithium salt and acetonitrile at low temperatures. In addition, it is preferable that the content of the lithium-containing imide salt is 0.5 mol to 3 mol per 1 L of the non-aqueous solvent from the viewpoint of the amount of ions supplied. LiN(SO 2 F) 2 , and LiN(SO 2 CF 3 ) 2 According to the acetonitrile-containing nonaqueous electrolyte solution containing at least one of the above, it is possible to effectively suppress the decrease in ion conductivity in a low temperature range such as −10° C. or −30° C., and obtain excellent low-temperature characteristics. In this way, by limiting the content, it is also possible to more effectively suppress the increase in resistance during high-temperature heating.

[0059] In addition, LiPF 6 The lithium salt may further include a fluorine-containing inorganic lithium salt other than LiBF. 4 , LiAsF 6 , Li 2 SiF 6 , LiSbF 6 , Li 2 B 12 F b H 12-bIn the first embodiment, the inorganic lithium salt may contain a fluorine-containing inorganic lithium salt such as LiF (wherein b is an integer of 0 to 3). In the first embodiment, the term "inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in the anion and is soluble in acetonitrile. In the first embodiment, the term "fluorine-containing inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in the anion, contains a fluorine atom in the anion, and is soluble in acetonitrile. The fluorine-containing inorganic lithium salt is excellent in that it forms a passive film on the surface of the metal foil that is the positive electrode current collector, and inhibits the corrosion of the positive electrode current collector. These fluorine-containing inorganic lithium salts are used alone or in combination of two or more. As the fluorine-containing inorganic lithium salt, a compound that is a double salt of LiF and a Lewis acid is desirable, and among them, it is more preferable to use a fluorine-containing inorganic lithium salt having a phosphorus atom, since it is easy to release free fluorine atoms. Representative fluorine-containing inorganic lithium salts are soluble to form PF 6 LiPF that releases anions 6 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 is easy to capture excess free acid components that may cause battery deterioration. From this viewpoint, LiBF 4 is particularly preferred.

[0060] The content of the fluorine-containing inorganic lithium salt in the non-aqueous electrolyte of the first 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 the 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 ion conductivity increases and high output characteristics tend to be exhibited. In addition, 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 the 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 ion conductivity increases, high output characteristics can be exhibited, and the decrease in ion conductivity associated with an increase in viscosity at low temperatures tends to be suppressed, and 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 the non-aqueous electrolyte.

[0061] The nonaqueous electrolyte solution of the first embodiment may further contain an organic lithium salt. In the first embodiment, the "organic lithium salt" refers to a lithium salt that contains a carbon atom in the anion and is soluble in acetonitrile.

[0062] As the organic lithium salt, an organic lithium salt having an oxalic acid group can be mentioned. A specific example of the organic lithium salt having an oxalic acid group is LiB(C 2 O 4 ) 2 , LiBF 2 (C 2 O 4 ), LiPF 4 (C 2 O 4 ), and LiPF 2 (C 2 O 4 ) 2 Among them, LiB(C 2 O 4 ) 2 and LiBF 2 (C 2 O4 It is preferable to use at least one lithium salt selected from the lithium salts represented by the formula (I) and (II). It is more preferable 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 non-aqueous electrolyte solution or may be contained in a negative electrode (negative electrode active material layer).

[0063] The amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte 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, in order to better ensure the effect of its use. However, if the amount of the organic lithium salt having an oxalic acid group in the non-aqueous electrolyte is too large, there is a risk of precipitation. Therefore, the amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte 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.

[0064] It is known that organic lithium salts having oxalic acid groups are poorly soluble in organic solvents with low polarity, particularly in chain carbonates. Organic lithium salts having oxalic acid groups may contain a small amount of lithium oxalate, and may react with a small amount of water contained in other raw materials when mixed to form a non-aqueous electrolyte solution, resulting in the generation of new white precipitation of lithium oxalate. Therefore, the content of lithium oxalate in the non-aqueous electrolyte solution of the first embodiment is not particularly limited, but is preferably 0 to 500 ppm.

[0065] 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 the first embodiment. Specific examples of other lithium salts include, for example, LiClO 4 , LiAlO 4 , LiAlCl 4 , LiB 10 Cl 10Inorganic lithium salts that do not contain fluorine atoms in the anion, such as chloroborane Li; LiCF 3 SO 3 , LiCF 3 CO 2 , Li 2 C 2 F 4 (SO 3 ) 2 , LiC(CF 3 SO 2 ) 3 , LiC n F (2n+1) SO 3 {where n≧2}, lower aliphatic carboxylic acid Li, tetraphenylborate Li, LiB(C 3 O 4 H 2 ) 2 Organic lithium salts such as LiPF 5 (CF 3 ) and other LiPFs n (C p F 2p+1 ) 6-n [In the formula, n is an integer of 1 to 5, and p is an integer of 1 to 8]; LiBF 3 (CF 3 ) and other LiBFs 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 combined with a polyvalent anion; The following formula (sa): LiC(SO 2 R A )(SO 2 R B )(SO 2 R C ) (sa) {where, R A , R B , and R C may be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms. The following formula (sb): LiN(SO 2 OR D )(SO 2 ORE ) (sb) {In the formula, R D , and R E may be the same as or different from each other, and each represents a perfluoroalkyl group having 1 to 8 carbon atoms.}, and the following formula (sc) LiN(SO 2 R F )(SO 2 OR G ) (sc) {In the formula, R F , and R G may be the same as or different from each other, and each represents a perfluoroalkyl group having 1 to 8 carbon atoms.} Examples thereof include organolithium salts represented by each of the above, and one or more of these can be used together with a fluorine-containing inorganic lithium salt.

[0066] <I-1-3. Additive> The non-aqueous electrolyte according to the first embodiment may contain an additive in addition to the non-aqueous solvent and the electrolyte salt described above.

[0067] <Vinylene carbonate> The non-aqueous electrolyte in the first embodiment contains vinylene carbonate (VC). Vinylene carbonate (VC) causes a reduction reaction on the surface of the negative electrode active material to form a coating, so an amount of vinylene carbonate (VC) that corresponds to the mass of the negative electrode is required. When a non-aqueous electrolyte containing A volume % of acetonitrile is contained in X mass % relative to the mass of the negative electrode excluding the negative electrode current collector, the content of vinylene carbonate (VC) in the non-aqueous electrolyte is 7×A / X mass % or more. In this range, the coating film is formed well in the first charge after the non-aqueous electrolyte is contained, and the capacity efficiency at room temperature tends to improve. The VC content is preferably 10×A / X mass % or more, more preferably 15×A / X mass % or more. In this range, the capacity efficiency is improved even over a long period of time and in a high-temperature environment, and the charge capacity and discharge capacity are stable even in a non-aqueous electrolyte containing acetonitrile. On the other hand, since the addition of an excessive amount of vinylene carbonate (VC) may cause a decrease in the viscosity of the non-aqueous electrolyte, a decrease in low-temperature properties, and excessive gas generation, the amount of vinylene carbonate (VC) added is preferably 10 mass % or less, more preferably 9 mass % or less, further preferably 8 mass % or less, and particularly preferably 7 mass % or less, based on the mass of the non-aqueous electrolyte. From the viewpoints of suppressing the reduction reaction on the surface of the negative electrode active material, the formation of the negative electrode SEI, the decrease in the viscosity and low-temperature properties of the non-aqueous electrolyte, and the suppression of excessive gas generation, it is preferable that X is 50 or more and 2000 or less, and / or A is 5 or more and 70 or less.

[0068] In addition, by reducing the content of the nonaqueous electrolyte in the nonaqueous lithium ion secondary battery, the battery capacity per volume and weight of the battery can be optimized. From this viewpoint, in the nonaqueous lithium ion secondary battery containing the nonaqueous electrolyte of the first embodiment in X mass % relative to the negative electrode mass excluding the negative electrode current collector, X is more preferably 200 or less, and even more preferably 98 or less. However, if the content of the nonaqueous electrolyte relative to the negative electrode mass excluding the negative electrode current collector is less than a certain value, impregnation into the electrode or separator may be insufficient. From this viewpoint, X in the nonaqueous lithium ion secondary battery containing the nonaqueous electrolyte of the first embodiment is more preferably 55 or more, even more preferably 60 or more, and particularly preferably 65 or more. When the content of acetonitrile relative to the volume of the nonaqueous solvent is expressed as A volume %, it is expected that the output performance will be improved by containing acetonitrile in the nonaqueous electrolyte. From this viewpoint, A is more preferably 8 or more, and even more preferably 16 or more. In addition, when the content of acetonitrile is equal to or less than a certain value, impregnation into electrodes and separators is improved, and thermal stability also tends to be improved. From this viewpoint, A is more preferably 60 or less, and further preferably 35 or less.

[0069] <Sulfuric acid / sulfite ion> The non-aqueous electrolyte in the first embodiment preferably contains one or both of sulfate ions and sulfite ions. It is believed that sulfate ions bind to metal impurities, thereby preventing the metal impurities from accumulating on the negative electrode and damaging the SEI. The lower limit of the amount of sulfate ions added is not particularly set, but is preferably equal to or greater than the concentration of metal impurities in the electrolyte material. Taking into account metal elution from the electrode, the amount is preferably 1 ppm or more, more preferably 10 ppm or more, relative to the mass of the non-aqueous electrolyte. In addition, the addition of an excessive amount may cause a large amount of sulfate and sulfite to precipitate, which may damage the SEI, and since sulfate ions are reducible, they may react with vinylene carbonate (VC) on the negative electrode and become an inhibitor of film formation. Therefore, the content of sulfate ions is preferably 7×A / X mass% or less or lower than 7×A / X mass% relative to the mass of the non-aqueous electrolyte, and is preferably 10 mass% or less relative to the mass of vinylene carbonate (VC), more preferably 8 mass% or less, and particularly preferably 5 mass% or less. In addition, the non-aqueous electrolyte in the first embodiment may contain sulfite ions, which are also expected to bind with metal elution components and prevent damage to the SEI. The amount of sulfite ions added is preferably 10 mass% or less relative to the mass of vinylene carbonate (VC) in the non-aqueous electrolyte, more preferably 8 mass% or less, and particularly preferably 5 mass% or less.

[0070] From the same viewpoint as above, the total content of sulfate ions and sulfite ions in the nonaqueous electrolyte solution is preferably 1 ppm or more and 7×A / X or less by mass with respect to the mass of the nonaqueous electrolyte solution, and is preferably 10% or less by mass of the VC content in the nonaqueous electrolyte solution.

[0071] The method of adding each ion to the nonaqueous electrolyte is not particularly limited, but it is sufficient that the ions are contained in the nonaqueous electrolyte by decomposition of an organic compound in the nonaqueous electrolyte, addition of a sulfate or sulfite, etc. When adding by an inorganic salt, addition by, for example, lithium sulfate or lithium sulfite is preferable because it does not give metal impurities to the composition of the nonaqueous electrolyte for lithium ion secondary batteries.

[0072] <Other electrode protection additives> Other electrode protection additives are not particularly limited as long as they do not impede the solution of the problems by the present invention, and may substantially overlap with the substances that act as a solvent for dissolving lithium salts (i.e., the above-mentioned non-aqueous solvents) (excluding acetonitrile, vinylene carbonate, and ethylene sulfite as the organic compound having a sulfur atom described above). The electrode protection additive is preferably a substance that contributes to improving the performance of the non-aqueous electrolyte and the non-aqueous secondary battery in the first embodiment, but also includes substances that are not directly involved in the electrochemical reaction.

[0073] Specific examples of other electrode protection additives include, for example, 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, 4,4,5,5-tetrafluoro-1,3-dioxolane-2-one, 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. lactones, cyclic ethers, cyclic ethers, cyclic sulfur compounds, cyclic sulfur compounds, cyclic sulfur compounds, cyclic anhydrides ...

[0074] The content of the electrode protection additive in the nonaqueous electrolyte solution in the first embodiment is not particularly limited, but the content of the electrode protection additive relative to the total amount of the nonaqueous solvent is preferably 0.1 to 30 volume %, more preferably 0.3 to 15 volume %, and even more preferably 0.5 to 4 volume %.

[0075] In the first embodiment, the greater the content of the electrode protection additive, the more the deterioration of the non-aqueous electrolyte solution is suppressed. However, the smaller the content of the electrode protection additive, the more the high-output characteristics of the non-aqueous secondary battery in a low-temperature environment are improved. Therefore, by adjusting the content of the electrode protection additive within the above-mentioned range, it is possible to maximize the excellent performance based on the high ionic conductivity of the non-aqueous electrolyte solution without impairing the basic function of the non-aqueous secondary battery. By preparing the non-aqueous electrolyte solution with such a composition, it is possible to further improve all of the cycle performance of the non-aqueous secondary battery, the high-output performance in a low-temperature environment, and other battery characteristics.

[0076] <Other optional additives> In the first embodiment, for the purpose of improving the charge-discharge cycle characteristics, high-temperature storage properties, and safety (e.g., prevention of overcharging) of the nonaqueous secondary battery, a nonaqueous electrolyte solution is added containing, for example, a sulfonic acid ester, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, a phosphoric acid ester [ethyl diethyl phosphonoacetate (EDPA): (C 2 H 5 O) 2 (P=O)-CH 2 (C=O)OC 2 H 5 , tris(trifluoroethyl) phosphate (TFEP): (CF 3 CH 2 O) 3 P=O, triphenyl phosphate (TPP): (C 6 H 5 O) 3 P=O:(CH 2 =CHCH 2 O) 3 It is also possible to appropriately contain optional additives selected from compounds having no steric hindrance around the unshared electron pair (e.g., triaryl phosphate, triaryl phosphate, etc.), nitrogen-containing cyclic compounds having no steric hindrance around the unshared electron pair (e.g., pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole, etc.), and derivatives of these compounds. Phosphate esters are particularly effective because they suppress side reactions during storage.

[0077] In the first embodiment, the content of other optional additives is calculated as a mass percentage with respect to the total mass of all components constituting the non-aqueous electrolyte. There is no particular limitation on the content of other optional additives, but it is preferably in the range of 0.01% by mass or more and 10% by mass or less, more preferably 0.02% by mass or more and 5% by mass or less, and still more preferably 0.05% by mass or more and 3% by mass or less with respect to the total amount of the non-aqueous electrolyte. By adjusting the content of other optional additives within the above range, it tends to be possible to add better battery characteristics without impairing the basic functions as a non-aqueous secondary battery.

[0078] <I-2. Cathode and Cathode Current Collector> The cathode 150 shown in FIGS. 1 and 2 is composed of a cathode active material layer made from a cathode mixture and a cathode current collector. The cathode 150 is not particularly limited as long as it functions as the cathode of a non-aqueous secondary battery, and a known one may be used. The cathode in the first embodiment preferably contains a lithium-containing compound containing Fe, and more preferably also contains nickel (Ni) at a relatively high ratio.

[0079] The cathode active material layer is disposed on one or both sides of the cathode current collector, contains a cathode active material, and preferably further contains a conductive assistant and a binder as necessary.

[0080] The cathode active material layer preferably contains, as a cathode active material, a material capable of occluding and releasing lithium ions. When such a material is used, it is preferable because it tends to be possible to obtain a high voltage and a high energy density.

[0081] As the cathode active material contained in the cathode active material layer, the following general formula (1): Li w MPO 4 ·····(1) {In the formula, M represents one or more transition metal elements, the value of w is determined by the charge and discharge state of the battery, represents a number from 0 to 1.2, and preferably represents a number from 0.05 to 1.10.} A metal phosphate compound containing lithium and a transition metal element represented by , and / or the following general formula (2) containing at least one transition metal element selected from the group consisting of, for example, Ni, Mn, and Co: Li p Ni q Co r Mn s M t O u ·····(2) {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.} At least one Li-containing metal oxide selected from the Li-containing metal oxides represented by is preferred.

[0082] Specific examples of the positive electrode active material include, for example, Li w FePO 4 and other Li compounds, or lithium cobalt oxides represented by LiCoO 2 ; lithium manganese oxides represented by LiMnO 2 LiMn 2 O 4 and Li 2 Mn 2 O 4 ; lithium nickel oxides represented by LiNiO 2 ; LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 LiNi 0.5 Co 0.2 Mn 0.3 O 2 LiNi 0.8 Co 0.2 O 2 represented by Liz MO 2 (wherein M contains at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and 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 examples thereof include lithium-containing composite metal oxides represented by the formula.

[0083] In particular, when the Ni content ratio q of the Li-containing metal oxide represented by the general formula (2) 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 the energy density are achieved. Examples of such a positive electrode active material include, for example, LiNi 0.6 Co 0.2 Mn 0.2 O 2 、LiNi 0.75 Co 0.15 Mn 0.15 O 2 、LiNi 0.8 Co 0.1 Mn 0.1 O 2 、LiNi 0.85 Co 0.075 Mn 0.075 O 2 、LiNi 0.8 Co 0.15 Al 0.05 O 2 、LiNi 0.81 Co 0.1 Al 0.09 O 2 、LiNi 0.85 Co 0.1 Al 0.05 O 2 、and examples thereof include lithium-containing composite metal oxides represented by the formula.

[0084] On the other hand, the higher the Ni content ratio in the positive electrode active material layer, the more degradation tends to progress at low voltage. The positive electrode active material of the Li-containing metal oxide represented by the general formula (2) essentially has active sites that oxidize and deteriorate the non-aqueous electrolyte, but these active sites may unintentionally consume the compound added to protect the negative electrode on the positive electrode side. Among them, acid anhydrides tend to be easily affected. In particular, when acetonitrile is contained as the non-aqueous solvent, the effect of adding an acid anhydride is enormous, so that the consumption of the acid anhydride on the positive electrode side is a fatal problem.

[0085] In addition, the decomposition products of these additives that are taken in and deposited on the positive electrode side not only increase the internal resistance of the non-aqueous secondary battery, but also accelerate the deterioration of the lithium salt. Furthermore, the protection of the negative electrode surface, which was the original purpose, becomes insufficient. In order to deactivate the active sites that essentially cause the oxidative deterioration of the non-aqueous electrolyte, it is important to control the Jahn-Teller distortion or to coexist with a component that plays a role as a neutralizer. Therefore, it is preferable that the positive electrode active material contains at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba.

[0086] 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 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 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 ZrO 2 , TiO 2 , Al 2 O 3 , NbO 3 , and LiNbO 2 It is particularly preferable that the carbon nanotube is coated with at least one oxide selected from the group consisting of the following, since this does not inhibit the permeation of lithium ions.

[0087] The positive electrode active material may be a lithium-containing compound other than the Li-containing metal oxide represented by formula (1) and (2), 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, 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 D 2 (Xa) In the formula, D represents a chalcogen element, and M I represents one or more transition metal elements, and the value of v is determined depending on the charge / discharge state of the battery and represents a number from 0.05 to 1.10.}, and The following formula (Xb): Li t M II u SiO 4 (Xb) {In formula, M II represents one or more transition metal elements, 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 the compounds include those represented by the following formula:

[0088] The lithium-containing compound represented by the above formula (Xa) has a layered structure, and the compounds represented by the above formula (1) and the above formula (Xb) have an olivine structure. These lithium-containing compounds may be those in which a part of the transition metal element is replaced by Al, Mg, or other transition metal element, those in which these metal elements are included in the crystal grain boundaries, those in which a part of the oxygen atoms is replaced by fluorine atoms, etc., and those in which at least a part of the surface of the positive electrode active material is coated with another positive electrode active material, etc., for the purpose of stabilizing the structure.

[0089] As the positive electrode active material in the first embodiment, only the lithium-containing compound as described above may be used, or the lithium-containing compound may be used in combination with other positive electrode active materials.

[0090] 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 MnO 2 , FeO 2 , FeS 2 , V 2 O 5 , V 6 O 13 , TiO 2 , TiS 2 , MoS 2 , and NbSe 2 Examples of the conductive polymer include oxides, sulfides, and selenides of metals other than lithium, such as those represented by the following formula: Examples of the conductive polymer include conductive polymers represented by polyaniline, polythiophene, polyacetylene, and polypyrrole.

[0091] The above-mentioned other positive electrode active materials can be used alone 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 can reversibly and stably absorb and release lithium ions and achieve high energy density.

[0092] 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 two is preferably 80 mass % or more, and more preferably 85 mass % or more, of the lithium-containing compound relative to the total positive electrode active material.

[0093] Examples of the conductive assistant include carbon black typified by graphite, acetylene black, and ketjen black, and carbon fibers. The content ratio of the conductive assistant is preferably 10 parts by mass or less, more preferably 1 to 5 parts by mass, relative to 100 parts by mass of the positive electrode active material.

[0094] Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene-butadiene rubber, and fluororubber. The content ratio of the binder is preferably 10 parts by mass or less, more preferably 0.5 to 8 parts by mass, relative to 100 parts by mass of the positive electrode active material.

[0095] The positive electrode active material layer is formed by applying and drying (removing the solvent), and if necessary, pressing a positive electrode mixture-containing slurry in which a positive electrode mixture obtained by mixing a positive electrode active material, a conductive assistant, and a binder as necessary is dispersed in a solvent, onto a positive electrode current collector. There is no particular limitation on such a solvent, and conventionally known ones can be used. For example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water, etc. can be mentioned.

[0096] The positive electrode current collector is composed of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode current collector may have a carbon coat on its surface or may be processed into a mesh shape. 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.

[0097] <I-3. Negative Electrode and Negative Electrode Current Collector> The negative electrode 160 shown in FIGS. 1 and 2 is composed of a negative electrode active material, a conductive assistant as necessary, a binder, and a negative electrode current collector. The negative electrode 160 can act as a negative electrode of a non-aqueous secondary battery.

[0098] The negative electrode active material layer is disposed on one or both sides of the negative electrode current collector, and preferably contains a negative electrode active material and, if necessary, a conductive assistant and a binder. As described above, the nonaqueous lithium ion secondary battery according to the first embodiment preferably has a structure capable of containing X% by mass of a nonaqueous electrolyte solution relative to the negative electrode mass excluding the negative electrode current collector.

[0099] Examples of the negative electrode active material 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 fibers, activated carbon, carbon colloids, 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, and organic polymer compounds. The negative electrode active material is used alone or in combination of two or more. As the negative electrode active material, graphite is preferable from the viewpoint of the use of the nonaqueous electrolyte according to the first embodiment.

[0100] The negative electrode active material layer uses lithium ions as the negative electrode active material at 0.4V vs. Li / Li in order to increase the battery voltage. + It is preferable that the hydrogen-containing gas contains a material capable of absorbing at a potential lower than the hydrogen potential.

[0101] Examples of the conductive assistant include carbon black, such as graphite, acetylene black, and ketjen black, and carbon fiber. The content of the conductive assistant is preferably 20 parts by mass or less, and more preferably 0.1 to 10 parts by mass, relative to 100 parts by mass of the negative electrode active material.

[0102] Examples of the binder include carboxymethyl cellulose, PVDF, PTFE, polyacrylic acid, and fluororubber. Also included are diene rubbers such as styrene-butadiene rubber. The content of the binder is preferably 10 parts by mass or less, more preferably 0.5 to 8 parts by mass, based on 100 parts by mass of the negative electrode active material.

[0103] 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 assistant and a binder, in a solvent to form a negative electrode mixture-containing slurry, applying the slurry to a negative electrode current collector, drying (solvent removal), and pressing if necessary. There is no particular restriction on such a solvent, and a conventionally known solvent may be used. Examples of the solvent include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0104] The negative electrode current collector is made of a metal foil such as copper foil, nickel foil, stainless steel foil, etc. The surface of the negative electrode current collector may be carbon-coated or processed into a mesh shape. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and further preferably 7 to 30 μm.

[0105] <I-4.セパレータ> 2, the nonaqueous secondary battery 100 in the first 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 that included in known nonaqueous secondary batteries, and is preferably an insulating thin film having 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 preferable.

[0106] As the synthetic resin microporous film, for example, a microporous film containing polyethylene or polypropylene as a main component, or a polyolefin-based microporous film such as a microporous film containing both of these polyolefins is preferably used. As the nonwoven fabric, for example, a porous film made of a heat-resistant resin such as glass, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, or aramid can be used.

[0107] Separator 170 may be a single layer or multiple layers of one type of microporous film, or a laminate of two or more types of microporous films. Separator 170 may be a single layer or multiple layers of a mixed resin material obtained by melting and kneading two or more types of resin materials.

[0108] For the purpose of providing functions, inorganic particles may be present on the surface or inside of the separator, or other organic layers may be further coated or laminated. Also, a crosslinked structure may be included. In order to improve the safety performance of the non-aqueous secondary battery, these methods may be combined as necessary.

[0109] By using such a separator 170, it is possible to realize the good input / output characteristics and low self-discharge characteristics required for the lithium ion battery for the above-mentioned high-power applications.

[0110] 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 is preferably 500 μm or less from the viewpoint of permeability. The thickness of the microporous membrane is preferably 5 μm or more and 30 μm or less, and more preferably 10 μm or more and 25 μm or less, from the viewpoint of use in high-output applications such as safety tests that have a relatively high heat generation amount and require self-discharge characteristics higher than conventional ones, and from the viewpoint of winding properties in a large battery winding machine. In addition, the thickness of the microporous membrane is more preferably 15 μm or more and 25 μm or less when emphasis is placed on both short circuit resistance and output performance, but is more preferably 10 μm or more and less than 15 μm when emphasis is placed on both high energy density and output performance.

[0111] The porosity of the microporous membrane that can be used as a separator is preferably 30% or more and 90% or less, more preferably 35% or more and 80% or less, and still more preferably 40% or more and 70% or less, from the viewpoint of following the rapid movement of lithium ions during high output. When giving priority to improving the output performance while ensuring safety, the porosity of the microporous membrane is particularly preferably 50% or more and 70% or less. When attaching importance to achieving both short-circuit resistance performance and output performance, it is particularly preferably 40% or more and less than 50%.

[0112] Regarding the air permeability of the microporous membrane that can be used as a separator, from the viewpoint of balance with the membrane thickness and porosity, it is preferably 1 second / 100 cm 3 or more and 400 seconds / 100 cm 3 or less, more preferably 100 seconds / 100 cm 3 or more and 350 second / 100 cm 3 or less. When attaching importance to achieving both short-circuit resistance performance and output performance, the air permeability of the microporous membrane is particularly preferably 150 seconds / 100 cm 3 or more and 350 seconds / 100 cm 3 or less. When giving priority to improving the output performance while ensuring safety, it is particularly preferably 100 second / 100 cm 3 more than or more and less than 150 seconds / 100 cm 3 is particularly preferable. On the other hand, when combining a non-aqueous electrolyte with low ionic conductivity and a separator within the above range, regarding the movement speed of lithium ions, it is not the structure of the separator but the high ionic conductivity of the non-aqueous electrolyte that becomes the rate-determining factor, and there is a tendency that the expected input / output characteristics cannot be obtained. Therefore, the ionic conductivity of the non-aqueous non-aqueous electrolyte is preferably 10 mS / cm or more, more preferably 15 mS / cm more than and still more preferably 20 mS / cm more than . However, the membrane thickness, air permeability, and porosity of the separator, and the ionic conductivity of the non-aqueous electrolyte are not limited to the above examples.

[0113] <I-5. Battery exterior> The configuration of the battery exterior 110 of the non-aqueous secondary battery 100 shown in FIGS. 1 and 2 is not particularly limited. For example, either a battery can or a laminated film exterior can be used as the battery exterior. As the battery can, for example, a metal can such as a rectangular, square tube, cylindrical, elliptical, flat, coin, or button type made of steel, stainless steel, aluminum, or a clad material can be used. As the laminated film exterior, for example, a laminated film having a three-layer structure of a heat-melt resin / metal film / resin can be used.

[0114] The laminated film exterior can be used as an exterior by stacking two sheets with the heat-melt resin side facing inward, or by bending it so that the heat-melt resin side faces inward and sealing the ends by heat-sealing. When using the laminated film exterior, a positive electrode lead body 130 (or a positive electrode terminal and a lead tab connected to the positive electrode terminal) can be connected to the positive electrode current collector, and a negative electrode lead body 140 (or a negative electrode terminal and a lead tab connected to the negative electrode terminal) can be connected to the negative electrode current collector. In this case, the laminated film exterior can 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) drawn out to the outside of the exterior.

[0115] <I-6. Method for manufacturing battery> The non-aqueous secondary battery 100 in the first embodiment may be manufactured by a known method using the above-described non-aqueous electrolyte, 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 exterior 110, and a separator 170 as required.

[0116] First, a laminate composed of the positive electrode 150, the negative electrode 160, and, if necessary, the separator 170 is formed. For example: A mode in which a long positive electrode 150 and a negative electrode 160 are wound in a laminated state with the long separator interposed between the positive electrode 150 and the negative electrode 160 to form a laminate having a wound structure; A mode in which the positive electrode 150 and the negative electrode 160 are cut into a plurality of sheets having a certain area and shape, and the positive electrode sheets and the negative electrode sheets are alternately stacked with a separator sheet interposed therebetween to form a laminate having a laminated structure; A mode in which a long separator is zigzag-folded and positive electrode sheets and negative electrode sheets are alternately inserted between the zigzag-folded separators to form a laminate having a laminate structure; The above are possible, but not limited to these.

[0117] Next, the above-mentioned laminate may be housed in a battery exterior 110 (battery case) and the nonaqueous electrolyte according to the first embodiment may be sealed inside the battery case to produce the nonaqueous secondary battery according to the first embodiment.

[0118] 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 necessary, and then the laminated structure may be housed in battery exterior 110 to prepare nonaqueous secondary battery 100.

[0119] In addition, if the arrangement of the electrodes is designed so that there is a portion where the outer peripheral edge of the negative electrode active material layer overlaps with the outer peripheral edge 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, the position of the electrodes may be shifted during battery assembly, which may deteriorate the charge-discharge cycle characteristics of the non-aqueous secondary battery. Therefore, it is preferable that the electrode positions of the electrode body used in the non-aqueous secondary battery are fixed in advance by tapes such as polyimide tape, polyphenylene sulfide tape, and polypropylene (PP) tape, adhesives, etc.

[0120] In the first embodiment, when a non-aqueous electrolyte using acetonitrile is used, the lithium ions released from the positive electrode during the initial charge of the non-aqueous secondary battery may diffuse throughout the negative electrode due to its high ionic conductivity. In non-aqueous secondary batteries, the area of ​​the negative electrode active material layer is generally made larger than that of the positive electrode active material layer. However, if lithium ions diffuse and are absorbed to a portion of the negative electrode active material layer that does not face the positive electrode active material layer, the lithium ions will not be released during the initial discharge and will remain in the negative electrode. Therefore, the contribution of the lithium ions that are not released becomes the irreversible capacity. For these reasons, the initial charge / discharge efficiency may be low in non-aqueous secondary batteries using a non-aqueous electrolyte containing acetonitrile.

[0121] 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 they are the same, current concentration is likely to occur at the edge portions of the negative electrode active material layer during charging, making it easier for lithium dendrites to form.

[0122] For the above reasons, 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.

[0123] 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 ratio of 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 reduce as much as possible the amount of lithium ions absorbed in the portion of the negative electrode active material layer that does not face the positive electrode active material layer among the lithium ions released from the positive electrode during the initial charge (i.e., the amount of lithium ions that are not released from the negative electrode during the initial discharge and become 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 generation of lithium dendrites.

[0124] The non-aqueous secondary battery 100 in the first embodiment can function as a battery by the first charge, but is stabilized by the decomposition of a part of the non-aqueous electrolyte during the first charge. There is no particular limitation on the method of the first charge, but the first charge 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 first charge is performed via constant voltage charging in the middle. By setting the voltage range in which the lithium salt participates in the electrochemical reaction for a long time, a stable and strong SEI is formed on the surface of the electrode (negative electrode 160), and there is an effect of suppressing the increase in the internal resistance. In addition, the reaction products are not firmly fixed only to the negative electrode 160, but in some form, they also have a good effect on members other than the negative electrode 160, such as the positive electrode 150 and the separator 170. Therefore, it is very effective to perform the first charge in consideration of the electrochemical reaction of the lithium salt dissolved in the non-aqueous electrolyte. Also, the capacity that the negative electrode can occlude is preferably larger than the charge capacity that can be taken out from the positive electrode during charging, and lithium precipitation on the negative electrode can be prevented. The charge capacity in the range of the environmental temperature of 23 to 30 °C is preferably 70% or more and 99% or less with respect to the capacity of the negative electrode active material. When the above capacity relationship is satisfied, there is no risk of lithium electrodeposition on the negative electrode, and by not leaving unnecessary negative electrode capacity, the energy density per weight and the energy density per volume are improved.

[0125] The non-aqueous secondary battery 100 in the first embodiment can also be used as a battery pack in which a plurality of non-aqueous secondary batteries 100 are connected in series or in parallel. From the viewpoint of managing the charge and discharge state of the battery pack, the operating voltage range per unit is preferably 2 to 5 V.

[0126] As described above, the first embodiment of the present invention has been described, but the present invention is not limited to the above embodiment. The present invention can be variously modified without departing from the gist thereof.

[0127] <II. Second Embodiment> Hereinafter, a second embodiment of the present invention will be described in detail. In the second embodiment, a non-aqueous secondary battery is provided. The non-aqueous secondary battery according to the second embodiment may have the configuration of the lithium-ion battery 100 shown in FIGS. 1 and 2, although it is not limited thereto.

[0128] <II-1. Non-aqueous secondary battery> The non-aqueous secondary battery according to the second embodiment includes a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte, and the non-aqueous secondary battery has been charged one or more times. The negative electrode contains at least one kind of inorganic lithium compound and at least one kind of organic lithium compound that can be extracted by immersing in an extraction solvent. The positive electrode preferably contains one or more positive electrode active materials capable of occluding and releasing lithium ions, and the negative electrode preferably contains a negative electrode active material containing graphite. Further, the non-aqueous electrolyte includes acetonitrile as a non-aqueous solvent and a cyclic carbonate.

[0129] The negative electrode preferably contains components extractable from the negative electrode by using water as an extraction solvent, as follows (a) to (d): (a) LiF (b) LiOCOOCH 2 CH 2 OCOOLi (c) CH 3 CH 2 OCOOLi (d) CH 3 OCOOLi More preferably, at least one of them is included as a component of the negative electrode film. Here, the negative electrode film contains products composed of decomposition products of a non-aqueous solvent and an additive accompanying a reduction reaction that proceeds at the negative electrode when the non-aqueous secondary battery is charged one or more times. The components of the negative electrode film in the second embodiment can be extracted by an extraction solvent, for example, by immersing in heavy water for 72 hours or more, but the extraction method is not limited thereto. Also, the quantification of the extracted components is preferably performed by, for example, ion chromatography for the component of (a) and NMR for the components of (b) to (d) from the viewpoint of detection sensitivity, but is not particularly limited thereto.

[0130] In the second embodiment, the component (a) can be classified as an inorganic lithium compound, and the components (b) to (d) can be classified as organic lithium compounds. From the viewpoints of preventing reductive decomposition of acetonitrile, quickly stabilizing the initial battery capacity, and improving the efficiency of the manufacturing process, the negative electrode according to the second embodiment preferably contains the component (a) and at least one or all of the components (b) to (d).

[0131] The above components are mainly generated on the surface of the negative electrode active material by the reduction reaction of the cyclic carbonate, and become SEI (Solid Electrolyte Interface). The SEI forms a film that conducts Li ions but does not conduct electrons, preventing other solvents from further reducing. On the other hand, the nonaqueous secondary battery of the second embodiment contains acetonitrile as a nonaqueous solvent of the nonaqueous electrolyte. Acetonitrile has low viscosity and high dielectric constant, and is easily coordinated to Li ions and moves near the electrode active material during charging and discharging. This characteristic is likely to improve the input / output characteristics and quickly stabilize the electrode capacity. On the other hand, acetonitrile may cause decomposition due to reduction on the surface of the negative electrode active material. The negative electrode coating component in the second embodiment containing acetonitrile contains the above-mentioned components (a) to (d), and the molar ratios of each component relative to the total amount (i.e., total content) of (a) to (d) are preferably 20 to 70 mol% for (a), 20 to 70 mol% for (b), 1 to 20 mol% for (c), and 1 to 20 mol% for (d), respectively, and more preferably 20 to 65 mol% for (a), 25 to 65 mol% for (b), 5 to 20 mol% for (c), and 5 to 20 mol% for (d). As described above, the components (a) to (d) contain relatively large amounts of (a) and (b), and relatively small amounts of (c) and (d) in the composition ratio in which the coating is formed, tend to quickly stabilize the discharge capacity.

[0132] At this time, the negative electrode is PF 6 It may contain an anion, and N(SO 2 F) 2 Anions and / or N(SO 2 CF3 ) 2 The electrolyte may contain an anion. 6 Anion, N(SO 2 CF 3 ) 2 or N(SO 2 F) 2 The positive electrode may contain at least one anion selected from the group consisting of anions, which are preferable from the viewpoint of suppressing an increase in internal resistance because the anion promotes the formation of a protective coating and also forms a non-conductive film on the surface of the surface foil, which is the positive electrode current collector.

[0133] Specifically, the nonaqueous secondary battery of the second embodiment may be the nonaqueous secondary battery shown in Figures 1 and 2. Here, Figure 1 is a plan view that shows a schematic diagram of the nonaqueous secondary battery, and Figure 2 is a cross-sectional view taken along line AA in Figure 1.

[0134] The nonaqueous secondary battery 100 shown in Fig. 1 and Fig. 2 is composed of a pouch-type cell. The nonaqueous secondary battery 100 accommodates a laminated electrode body formed by laminating a positive electrode 150 and a negative electrode 160 with a separator 170 interposed therebetween, and a nonaqueous electrolyte (not shown) in a space 120 of a battery exterior 110 formed of two aluminum laminate films. The battery exterior 110 is sealed at its outer periphery by heat-sealing the upper and lower aluminum laminate films. The laminate formed by laminating the positive electrode 150, the separator 170, and the negative electrode 160 in this order is impregnated with a nonaqueous electrolyte.

[0135] The aluminum laminate film constituting the battery exterior 110 is preferably made of aluminum foil coated on both sides with a polyolefin resin.

[0136] The positive electrode 150 is connected to the positive electrode lead body 130 inside the non-aqueous secondary battery 100. Although not shown, the negative electrode 160 is also connected to the negative electrode lead body 140 inside the non-aqueous secondary battery 100. Then, one end sides of the positive electrode lead body 130 and the negative electrode lead body 140 are drawn out to the outside of the battery enclosure 110 so that they can be connected to external devices or the like, and their ionomer portions are heat-sealed together with one side of the battery enclosure 110.

[0137] In the non-aqueous secondary battery 100 illustrated in FIGS. 1 and 2, the positive electrode 150 and the negative electrode 160 each have a single-layer electrode body, but the number of stacked layers of the positive electrode 150 and the negative electrode 160 can be appropriately increased according to the capacity design. In the case of a stacked electrode body having a plurality of positive electrodes 150 and negative electrodes 160, tabs of the same pole may be joined by welding or the like and then joined to a single lead body by welding or the like and taken out to the outside of the battery. As the tabs of the same pole, a mode composed of an exposed portion of the current collector, a mode in which a metal piece is welded to the exposed portion of the current collector, etc. are possible.

[0138] The positive electrode 150 is composed of a positive electrode active material layer made from a positive electrode mixture and a positive electrode current collector. The negative electrode 160 is composed of a negative electrode active material layer made from a negative electrode mixture and a negative electrode current collector. The positive electrode 150 and the negative electrode 160 are arranged such that the positive electrode active material layer and the negative electrode active material layer face each other with the separator 170 interposed therebetween.

[0139] These members are not particularly limited, and materials provided in conventional lithium ion batteries can be used. Hereinafter, each member of the non-aqueous secondary battery will be described in more detail.

[0140] <II-2. Non-aqueous electrolyte> Regarding the non-aqueous electrolyte according to the second embodiment, it can have the configuration of the non-aqueous electrolyte according to the first embodiment shown above. Further, regarding the non-aqueous electrolyte, materials used in the non-aqueous electrolyte of conventional lithium ion batteries can be applied as long as the effects of the present invention are not impaired.

[0141] The "non-aqueous electrolyte" in the second embodiment refers to an electrolyte that contains a non-aqueous solvent and a lithium salt, and has water in an amount of 1 mass% or less relative to the total amount of the non-aqueous electrolyte. The proportion of water is preferably 300 ppm or less, more preferably 200 ppm or less. The non-aqueous electrolyte may contain an additive.

[0142] (Non-aqueous solvent) Here, the non-aqueous solvent will be described. In the second embodiment, the "non-aqueous solvent" refers to the elements of the electrolyte excluding the lithium salt. In the second embodiment, when the electrolyte contains an additive, the "non-aqueous solvent" refers to the elements of the electrolyte excluding the lithium salt and the additive.

[0143] The non-aqueous solvent of the second embodiment contains acetonitrile as an essential component. The content of acetonitrile is preferably 1% by mass or more and 60% by mass or less, more preferably 3% by mass or more and 50% by mass or less, and even more preferably 5% by mass or more and 40% by mass or less, based on the total amount of the non-aqueous electrolyte. By containing a certain amount of acetonitrile, the non-aqueous secondary battery of the second embodiment tends to have excellent input / output performance. However, the non-aqueous solvent may contain another non-aqueous solvent other than acetonitrile. Examples of non-aqueous solvents other than acetonitrile include alcohols such as methanol and ethanol; aprotic solvents, and the like. Among them, aprotic polar solvents are preferable.

[0144] Specific examples of the aprotic solvent among the non-aqueous solvents 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, and cyclic carbonates such as vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinylethylene carbonate; 4-fluoro-1,3-dioxolatane; fluoroethylene carbonates represented by 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, 4,4,5,5-tetrafluoro-1,3-dioxolane-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxolane-2-one; γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ- lactones, such as valerolactone, δ-caprolactone, and ε-caprolactone; sulfur compounds, such as ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methylsulfolane, 1,3-propane sultone, 1,4-butane sultone, 1-propene 1,3-sultone, dimethylsulfoxide, tetramethylene sulfoxide, and ethylene glycol sulfite; tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1, Cyclic ethers typified by 3-dioxane; linear carbonates typified by ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl propyl carbonate, and methyl trifluoroethyl carbonate; linear fluorinated carbonates typified by trifluorodimethyl carbonate, trifluorodiethyl carbonate, and trifluoroethyl methyl carbonate;Mononitriles such as propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile; alkoxy-substituted nitriles such as methoxyacetonitrile and 3-methoxypropionitrile; malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanoheptane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanoheptane, 1,9-dicyanoheptane, 2,10-dicyanoheptane, 2,11-dicyanoheptane, 2,20-dicyanoheptane, 2,3-dicyanoheptane, 2,4-dicyanoheptane, 2,5-dicyanoheptane, 2,6-dicyanoheptane, 2,7-dicyanoheptane, 2,8-dicyanoheptane, 2,9-dicyanoheptane, 2,20-dicyanoheptane, 2,3-dicyanoheptane, 2,4-dicyanoheptane, 2,5-dicyanoheptane, 2,6-dicyanoheptane, 2,7-dicyanoheptane, 2,8-dicyanoheptane, 2,8-dicyanoheptane, 2,9-dicyanoheptane, 2,10 ... Dinitriles such as anooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dimethylglutaronitrile; cyclic nitriles such as benzonitrile; linear esters such as methyl propionate; linear ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme; Rf; 4 -OR 5 (In the formula, Rf 4 is an alkyl group containing a fluorine atom, R 5 is an organic group which may contain a fluorine atom); ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, as well as halides thereof such as fluorides. These may be used alone or in combination of two or more.

[0145] Among these other non-aqueous solvents, it is preferable to use one or more of cyclic carbonates and chain carbonates. In the non-aqueous secondary battery of the second embodiment, it is more preferable to include a cyclic carbonate in the non-aqueous electrolyte, and it is particularly preferable to include ethylene carbonate and vinylene carbonate as the cyclic carbonate. Only one of the other cyclic carbonates and chain carbonates exemplified above may be selected and used, or two or more (for example, two or more of the cyclic carbonates exemplified above, two or more of the chain carbonates exemplified above, or two or more of the cyclic carbonates exemplified above and one or more of the chain carbonates exemplified above) may be used. Among these, propylene carbonate or fluoroethylene carbonate is more preferable as the cyclic carbonate, and ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate is more preferable as the chain carbonate.

[0146] The vinylene carbonate is highly reactive and is consumed according to the amount of the negative electrode during the first charge, promoting the formation of the SEI. In order to form a good SEI in the second embodiment, it is considered that the SEI formation proceeds faster than the reduction reaction of acetonitrile on the surface of the negative electrode active material by adding ethylene carbonate and vinylene carbonate sufficiently before the first charge of the battery so that a certain amount of them remains even after the film formation. Such a rapid SEI formation reaction is considered to be achieved by the competitive reaction of ethylene carbonate and vinylene carbonate, and it is preferable that both are contained in a predetermined ratio. After the SEI formation reaction proceeds by the first charge, the molar ratio of the remaining vinylene carbonate to the ethylene carbonate contained in the nonaqueous electrolyte of the second embodiment is preferably 0.01 to 30 mol%, more preferably 0.1 to 30 mol%, even more preferably 0.3 to 25 mol%, and particularly preferably 1 to 20 mol%.

[0147] As described above, in order to leave a certain amount of vinylene carbonate relative to ethylene carbonate, the nonaqueous secondary battery in the second embodiment may contain an appropriate nonaqueous electrolyte before the first charge. The content of vinylene carbonate is preferably 0.1% by mass or more and 10% by mass or less with respect to the total amount of the nonaqueous electrolyte in order to maintain good reactivity. On the other hand, if the remaining vinylene carbonate disappears after the first charge, it is necessary to adjust the amount of addition as needed so that the first charge and discharge are stable according to the content of the nonaqueous electrolyte in the battery, the content of acetonitrile, and the amount of the negative electrode of the battery. From this viewpoint, in order to manufacture the nonaqueous secondary battery in the second embodiment, the nonaqueous electrolyte to be sealed in the battery may have the configuration of the first embodiment. Furthermore, since ethylene carbonate not only contributes to the formation of the SEI reaction but also serves as a suitable solvent for dissolving lithium salts, the content of ethylene carbonate is preferably 5 mass% or more and 35 mass% or less, and more preferably 10 mass% or more and 30 mass% or less, based on the total amount of the nonaqueous electrolyte solution.

[0148] (Lithium salts) The lithium salt is not particularly limited as long as the effects of the present invention are not impaired. For example, in the second embodiment, the lithium salt may include a fluorine-containing inorganic lithium salt and / or an imide salt.

[0149] Imide salts are LiN(SO 2 C m F 2m+1 ) 2 [wherein m is an integer of 0 to 8], and specifically, LiN(SO 2 F) 2 , and / or LiN(SO 2 CF 3 ) 2It is preferable that the imide salt contains the imide salt. Since the imide salt has a high decomposition temperature, the increase in resistance during high-temperature storage is suppressed. In addition, since the viscosity of the nonaqueous electrolyte can be kept low, excellent output performance can be exhibited, particularly in the low-temperature region. The content of the imide salt is preferably in the range of 0.1 to 40 mass %, more preferably in the range of 0.2 to 30 mass %, and further preferably in the range of 0.5 to 20 mass %, based on the total amount of the nonaqueous electrolyte of the second embodiment. By being in this range, the ionic conductivity of the nonaqueous electrolyte can be prevented from decreasing, and the performance at low temperatures can be improved.

[0150] Representative fluorine-containing inorganic lithium salts dissolve to produce PF 6 LiPF that releases anions 6 However, the non-aqueous electrolyte is LiPF 6 Other fluorine-containing inorganic lithium salts may be included, such as LiBF 4 , LiAsF 6 , Li 2 SiF 6 , LiSbF 6 , Li 2 B 12 F b H 12-b (wherein b is an integer of 0 to 3). In the second embodiment, the term "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. The fluorine-containing inorganic lithium salt is excellent in that it forms a passive film on the surface of the metal foil that is the positive electrode current collector, and inhibits the corrosion of the positive electrode current collector. These fluorine-containing inorganic lithium salts are used alone or in combination of two or more.

[0151] The content of the fluorine-containing inorganic lithium salt in the non-aqueous electrolyte of the second embodiment is not particularly limited, but is preferably 0.1 mol or more, more preferably 0.2 mol or more, and even more preferably 0.25 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, ion conductivity increases and high output characteristics tend to be exhibited.

[0152] The nonaqueous electrolyte solution of the second embodiment may further contain an organic lithium salt. In the second embodiment, the "organic lithium salt" refers to a lithium salt containing a carbon atom in the anion.

[0153] As the organic lithium salt, an organic lithium salt having an oxalic acid group can be mentioned. A specific example of the organic lithium salt having an oxalic acid group is LiB(C 2 O 4 ) 2 , LiBF 2 (C 2 O 4 ), LiPF 4 (C 2 O 4 ), and LiPF 2 (C 2 O 4 ) 2 Among them, LiB(C 2 O 4 ) 2 and LiBF 2 (C 2 O 4 It is more preferable to use at least one lithium salt selected from the lithium salts represented by the following formula (I):

[0154] The amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte 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, in order to better ensure the effect of its use. However, if the amount of the organic lithium salt having an oxalic acid group in the non-aqueous electrolyte is too large, there is a risk of precipitation. Therefore, the amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte 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.

[0155] It is known that organic lithium salts having oxalic acid groups are poorly soluble in organic solvents with low polarity, particularly in chain carbonates. Organic lithium salts having oxalic acid groups may contain a small amount of lithium oxalate, and may react with a small amount of water contained in other raw materials when mixed as a non-aqueous electrolyte solution, and may generate new white precipitation of lithium oxalate. Therefore, the content of lithium oxalate in the non-aqueous electrolyte solution of the second embodiment is not particularly limited, but is preferably 0 to 500 ppm.

[0156] In addition to the above, other lithium salts generally used in non-aqueous secondary batteries may be added supplementarily as the lithium salt in the second embodiment. Specific examples of other lithium salts include, for example, LiClO 4 , LiAlO 4 , LiAlCl 4 , LiB 10 Cl 10 Inorganic lithium salts that do not contain fluorine atoms in the anion, such as chloroborane Li; LiCF 3 SO 3 , LiCF 3 CO 2 , Li 2 C 2 F 4 (SO 3 ) 2 , LiC(CF 3 SO 2 ) 3 , LiC n F 2n+1 SO 3 (wherein n is ≧2), organic lithium salts such as lower aliphatic carboxylic acid Li and tetraphenylborate LiPF 5 (CF 3 ) and other LiPFs n (C p F 2p+1 ) 6-n [In the formula, n is an integer of 1 to 5, and p is an integer of 1 to 8]; LiBF 3 (CF 3 ) and other LiBFs q (C s F 2s+1 )4-q [wherein q is an integer of 1 to 3, and s is an integer of 1 to 8]; lithium salts bound to polyvalent anions; the following formulae (7a), (7b), and (7c); LiC(SO 2 R 6 )(SO 2 R 7 )(SO 2 R 8 ) (7a) LiN(SO 2 OR 9 )(SO 2 OR 10 ) (7b) LiN(SO 2 R 11 )(SO 2 OR 12 ) (7c) {where, R 6 , R 7 , R 8 , R 9 , R 10 , R 11 , and R 12 may be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms.} and the like, and one or more of these can be used together with at least one selected from the group consisting of fluorine-containing inorganic lithium salts, imide salts, and organic lithium salts.

[0157] (Additives) In the second embodiment, the non-aqueous electrolyte solution may contain, for example, an anhydrous acid, a sulfonic acid ester, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, a phosphoric acid ester [ethyl diethyl phosphonoacetate (EDPA): (C 2 H 5 O) 2 (P=O)-CH 2 (C=O)OC 2 H 5 , tris(trifluoroethyl) phosphate (TFEP): (CF 3 CH 2 O) 3P=O, triphenyl phosphate (TPP): (C 6 H 5 O) 3 P=O:(CH 2 =CHCH 2 O) 3 It is also possible to appropriately contain optional additives selected from the group consisting of phosphate esters, triaryl phosphate, etc., and derivatives of these compounds. In particular, the phosphate esters are effective in suppressing side reactions during storage.

[0158] (Other optional additives) In the second embodiment, for the purpose of improving the high-temperature storage property and safety of the non-aqueous secondary battery, for example, sulfonic acid ester, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, phosphoric acid ester [ethyl diethyl phosphonoacetate (EDPA): (C 2 H 5 O) 2 (P=O)-CH 2 (C=O)OC 2 H 5 , tris(trifluoroethyl) phosphate (TFEP): (CF 3 CH 2 O) 3 P=O, triphenyl phosphate (TPP): (C 6 H 5 O) 3 P=O:(CH 2 =CHCH 2 O) 3 It is also possible to appropriately contain optional additives selected from compounds having no steric hindrance around the unshared electron pair (e.g., triaryl phosphate, triaryl phosphate, etc.), nitrogen-containing cyclic compounds having no steric hindrance around the unshared electron pair (e.g., pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole, etc.), and derivatives of these compounds. In particular, the phosphate ester is effective in suppressing side reactions during high-temperature storage.

[0159] The content of other optional additives is calculated as a mass percentage with respect to the total mass of all components constituting the non-aqueous electrolyte. There is no particular limitation on the content of other optional additives, but it is preferably in the range of 0.01% by mass or more and 10% by mass or less, more preferably 0.02% by mass or more and 5% by mass or less, and still more preferably 0.05 to 3% by mass with respect to the total amount of the non-aqueous electrolyte. By adjusting the content of other optional additives within the above range, it tends to be possible to add better battery characteristics without impairing the basic functions as a non-aqueous secondary battery.

[0160] <II-3. Cathode> The cathode 150 is composed of a cathode active material layer made from a cathode mixture and a cathode current collector. The cathode 150 is not particularly limited as long as it acts as a cathode of a non-aqueous secondary battery within the scope of the present invention.

[0161] The cathode active material layer contains a cathode active material and may further contain a conductive assistant and a binder in some cases.

[0162] The cathode active material layer preferably contains a material capable of occluding and releasing lithium ions as the cathode active material. The cathode active material layer preferably contains a conductive assistant and a binder as necessary together with the cathode active material. When using such a material, it is preferable because it tends to be possible to obtain a high voltage and a high energy density. Examples of the cathode active material include the following formulas (8a) and (8b): Li x MO 2 (8a) Li y M 2 O 4 (8b) {In the formula, M represents one or more metal elements including at least one transition metal element, x represents a number from 0 to 1.1, and y represents a number from 0 to 2.} Lithium-containing compounds represented by each of them, and other lithium-containing compounds.

[0163] Examples of the lithium-containing compounds represented by the formulas (8a) and (8b) include LiCoO 2 Lithium cobalt oxide, represented by LiMnO 2 , LiMn 2 O 4 , and Li 2 Mn 2 O 4 Lithium manganese oxides, such as LiNiO 2 Lithium nickel oxide, represented by Li z MO 2 (wherein M contains at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and 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).

[0164] The lithium-containing compound other than the lithium-containing compounds represented by the formulas (8a) and (8b) 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 (e.g., Li t M u SiO 4 where M is the same as in formula (8a), t is a number from 0 to 1, and u is a number from 0 to 2. In terms of obtaining a higher voltage, the lithium-containing compound is preferably a composite oxide containing lithium and at least one transition metal element selected from the group consisting of cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), chromium (Cr), vanadium (V), and titanium (Ti), or a metal phosphate compound.

[0165] More specifically, the lithium-containing compound is preferably a composite oxide containing lithium and a transition metal element, a metal chalcogenide containing lithium and a transition metal element, or a metal phosphate compound containing lithium, and examples of the lithium-containing compound include those represented by the following formulas (9a) and (9b), respectively: Li v M I D 2 (9a) Li w M II PO 4 (9b) In the formula, D represents oxygen or a chalcogen element, and M I and M II each represents one or more transition metal elements, the values ​​of v and w are determined depending on the charge / discharge state of the battery, v represents a number from 0.05 to 1.10, and w represents a number from 0.05 to 1.10.

[0166] The lithium-containing compound represented by the above formula (9a) has a layered structure, and the compound represented by the above formula (9b) has an olivine structure. These lithium-containing compounds may be those in which a part of the transition metal element is replaced by Al, Mg, or other transition metal element, those in which these metal elements are included in the crystal grain boundaries, those in which a part of the oxygen atoms is replaced by fluorine atoms, etc., and those in which at least a part of the surface of the positive electrode active material is coated with another positive electrode active material, etc., for the purpose of stabilizing the structure.

[0167] As the positive electrode active material in the second embodiment, only the lithium-containing compound as described above may be used, or the lithium-containing compound may be used in combination with other positive electrode active materials.

[0168] 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 MnO 2 , FeO 2 , FeS 2 , V 2 O 5 , V6 O 13 , TiO 2 , TiS 2 , MoS 2 , and NbSe 2 Examples of the conductive polymer include oxides, sulfides, and selenides of metals other than lithium, such as those represented by the following formula: Examples of the conductive polymer include conductive polymers represented by polyaniline, polythiophene, polyacetylene, and polypyrrole.

[0169] The above-mentioned other positive electrode active materials can be used alone 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 can reversibly and stably absorb and release lithium ions and achieve high energy density.

[0170] 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 two is preferably 80 mass % or more, and more preferably 85 mass % or more, of the lithium-containing compound relative to the total positive electrode active material.

[0171] 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, relative to 100 parts by mass of the positive electrode active material.

[0172] Examples of the binder 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, and more preferably 0.5 to 4 parts by mass, relative to 100 parts by mass of the positive electrode active material.

[0173] The positive electrode active material layer is formed by applying and drying (removing the solvent), and if necessary, pressing a positive electrode mixture-containing slurry in which a positive electrode mixture obtained by mixing a positive electrode active material, a conductive assistant and a binder as necessary is dispersed in a solvent, onto a positive electrode current collector. Such a solvent is not particularly limited, and known solvents can be used. For example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water, etc. can be mentioned.

[0174] The positive electrode current collector is composed of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode current collector may have a carbon coating on its surface or may be processed into a mesh shape. 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.

[0175] <II-4. Negative electrode> The negative electrode 160 is composed of a negative electrode active material layer made from a negative electrode mixture and a negative electrode current collector. The negative electrode 160 is not particularly limited as long as it functions as a negative electrode of a non-aqueous secondary battery within the scope of the present invention.

[0176] From the viewpoint of increasing the battery voltage, the negative electrode active material layer preferably contains a material capable of occluding lithium ions at a potential lower than 0.4V vs. Li / Li + The negative electrode active material layer preferably contains an additive, a conductive assistant and a binder as necessary, together with the negative electrode active material. Here, as described above, the negative electrode active material layer contains decomposition products of cyclic carbonates such as inorganic lithium compounds and organic lithium compounds.

[0177] Examples of the negative electrode active material include carbon materials typified by amorphous carbon (hard carbon), artificial graphite, natural graphite, graphite, pyrolytic carbon, coke, glassy carbon, baked bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, carbon colloids, and carbon black, as well as metallic lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, silicon alloys, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, and organic polymer compounds.

[0178] In the second embodiment, the negative electrode active material may contain SiOx (0.5≦x≦1.5) or an element capable of forming an alloy with lithium, and examples of such elements include silicon. Silicon may be in any form of crystal, low crystal, or amorphous. It is also preferable to improve the conductivity between particles by coating the surface of the active material with a conductive material. In particular, silicon has an operating potential of about 0.5 V (vs Li / Li+), which is slightly higher than the operating potential of graphite, which is about 0.05 V (vs Li / Li+), so the risk of lithium electrodeposition is reduced. Since acetonitrile used in the non-aqueous solvent according to the second embodiment reacts with lithium metal to generate gas, a negative electrode active material that is difficult to electrodeposit lithium is preferable in combination with a nitrile electrolyte. On the other hand, a negative electrode active material with a too high operating potential reduces the energy density of the battery, so from the viewpoint of improving the energy density, the negative electrode active material is preferably 0.4 V vs. Li / Li + It is preferable to operate at a potential less noble than that of the .alpha.-oxide.

[0179] The silicon content is preferably in the range of 0.1 to 100 mass %, more preferably in the range of 1 to 80 mass %, and even more preferably in the range of 3 to 60 mass %, based on the total amount of the negative electrode mixture of the second embodiment. By adjusting the silicon content within the above range, it is possible to ensure a balance between high capacity and charge / discharge cycle performance of the nonaqueous secondary battery.

[0180] The negative electrode active materials may be used alone or in combination of two or more.

[0181] 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, relative to 100 parts by mass of the negative electrode active material.

[0182] Examples of the binder include carboxymethyl cellulose, PVDF, PTFE, polyacrylic acid, styrene-butadiene rubber, polyimide, polyamide-imide, and fluororubber. The content of the binder is preferably 10 parts by mass or less, more preferably 0.5 to 6 parts by mass, based on 100 parts by mass of the negative electrode active material.

[0183] 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 assistant and a binder, in a solvent to form a negative electrode mixture-containing slurry, applying the slurry to a negative electrode current collector, drying (solvent removal), and pressing if necessary. There is no particular restriction on such a solvent, and any known solvent can be used. Examples of such a solvent include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0184] The negative electrode current collector is made of a metal foil such as copper foil, nickel foil, stainless steel foil, etc. The surface of the negative electrode current collector may be carbon-coated or processed into a mesh shape. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and further preferably 7 to 30 μm.

[0185] <II-5.セパレータ> In the second embodiment, the nonaqueous secondary battery 100 is preferably provided with 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 that provided in known nonaqueous secondary batteries, and is preferably an insulating thin film having 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 preferable.

[0186] As the synthetic resin microporous film, for example, a microporous film containing polyethylene or polypropylene as a main component, or a polyolefin-based microporous film such as a microporous film containing both of these polyolefins is preferably used. As the nonwoven fabric, for example, a porous film made of a heat-resistant resin such as glass, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, or aramid can be used.

[0187] Separator 170 may be configured as a single layer or multiple layers of one type of microporous film, or may be configured as a stack 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.

[0188] By using such a separator 170, it is possible to realize good input / output characteristics and low self-discharge characteristics particularly required for the above-mentioned high-output lithium-ion secondary batteries. The film thickness of the microporous membrane is not particularly limited, but is preferably 1 μm or more from the viewpoint of film strength, and preferably 500 μm or less from the viewpoint of permeability. From the viewpoint of being used in high-output applications where the calorific value is relatively high, such as safety tests, and self-discharge characteristics higher than those of the conventional ones are required, and from the viewpoint of winding property in a large battery winding machine, the film thickness is preferably 5 μm or more and 30 μm or less, and more preferably 10 μm or more and 25 μm or less. In addition, when emphasizing the compatibility between short-circuit resistance performance and output performance, the film thickness is more preferably 15 μm or more and 25 μm or less, but when emphasizing the compatibility between high energy density and output performance, the film thickness is more preferably 10 μm or more and less than 15 μm. The porosity of the membrane is preferably 30% or more and 90% or less, more preferably 35% or more and 80% or less, and still more preferably 40% or more and 70% or less from the viewpoint of following the rapid movement of lithium ions during high output. In addition, when giving priority to improving output performance while ensuring safety, the porosity of the membrane is particularly preferably 50% or more and 70% or less, and when emphasizing the compatibility between short-circuit resistance performance and output performance, the porosity is particularly preferably 40% or more and less than 50%. The air permeability of the membrane is preferably 1 second / 100 cm 3 or more and 400 seconds / 100 cm 3 or less, and more preferably 100 seconds / 100 cm 3 or more and 350 second / 100 cm 3 or less. In addition, when emphasizing the compatibility between short-circuit resistance performance and output performance, the air permeability of the membrane is particularly preferably 150 seconds / 100 cm 3 or more and 350 seconds / 100 cm 3 or less, and when giving priority to improving output performance while ensuring safety, the air permeability is particularly preferably 100 second / 100 cm 3 more than or more and 150 seconds / 100 cm 3 or less.

[0189] <II-6. Battery exterior> The configuration of the battery exterior 110 of the non-aqueous secondary battery 100 in the second embodiment is not particularly limited. For example, either a battery can or a laminate film exterior can be used as the battery exterior. As the battery can, for example, a metal can made of steel or aluminum can be used. As the laminate film exterior, for example, a laminate film having a three-layer structure of a heat-melt resin / metal film / resin can be used.

[0190] The laminate film exterior can be used as an exterior by stacking two sheets with the heat-melt resin side facing inward, or by bending it so that the heat-melt resin side faces inward and sealing the ends by heat-sealing. When using the laminate film exterior, a positive electrode lead body 130 (or a positive electrode terminal and a lead tab connected to the positive electrode terminal) can be connected to the positive electrode current collector, and a negative electrode lead body 140 (or a negative electrode terminal and a lead tab connected to the negative electrode terminal) can be connected to the negative electrode current collector. In this case, the laminate film exterior can 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) drawn outside the exterior.

[0191] <II-7. Method for manufacturing non-aqueous electrolyte> The non-aqueous electrolyte of the second embodiment can be manufactured by mixing an acetonitrile and a non-aqueous solvent containing a cyclic carbonate with a lithium salt by any means. Further, in addition to vinylene carbonate, additional additives can be mixed by any means to manufacture the non-aqueous electrolyte.

[0192] <II-8. Method for manufacturing battery> The non-aqueous secondary battery 100 in the second embodiment is manufactured by a known method using the above-described non-aqueous electrolyte, 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 exterior 110, and, if necessary, a separator 170.

[0193] First, a laminate is formed consisting of the positive electrode 150, the negative electrode 160, and, if necessary, the separator 170. For example, possible modes include a mode in which the long positive electrode 150 and the 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 laminate with a wound structure; a mode in which the positive electrode sheets and the negative electrode sheets obtained by cutting the positive electrode 150 and the negative electrode 160 into a plurality of sheets having a certain area and shape are alternately stacked with a separator sheet between to form a laminate with a laminate structure; a mode in which a long separator is folded zigzag and a positive electrode body sheet and a negative electrode body sheet are alternately inserted between the zigzag folded separators to form a laminate with a laminate structure; and the like.

[0194] Next, the laminate described above is housed in a battery exterior 110 (battery case) and the nonaqueous electrolyte according to the second embodiment is sealed inside the battery case, thereby producing a nonaqueous secondary battery according to the second embodiment. The nonaqueous electrolyte may have the configuration of the first embodiment.

[0195] Alternatively, a gel-state electrolyte membrane may be prepared in advance by impregnating a substrate made of a polymer material with an electrolytic 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 necessary, and then the laminated structure may be housed in battery exterior 110 to prepare nonaqueous secondary battery 100.

[0196] The shape of the nonaqueous secondary battery 100 in the second embodiment is not particularly limited, and may be, for example, a cylindrical shape, an elliptical shape, a square tube shape, a button shape, a coin shape, a flat shape, a laminate shape, or the like. In the second embodiment, however, the battery is particularly preferably applied to a laminate shape.

[0197] In addition, when the arrangement of the electrodes is designed so that there is a portion where the outer peripheral edge of the negative electrode active material layer overlaps with the outer peripheral edge 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, the position of the electrodes may be shifted during battery assembly, which may deteriorate the charge-discharge cycle characteristics of the non-aqueous secondary battery. Therefore, it is preferable that the electrode positions of the electrode body used in the non-aqueous secondary battery are fixed in advance by tapes such as polyimide tape, polyphenylene sulfide tape, and PP tape, adhesives, etc.

[0198] The nonaqueous secondary battery 100 in the second embodiment can function as a battery by initial charging, but is stabilized by decomposing a part of the electrolyte during the initial charging. There is no particular restriction on the method of initial charging, but 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. A preferable result is also obtained when the initial charging is performed via a constant voltage charging in the middle. By setting the voltage range in which the lithium salt is involved in the electrochemical reaction to be long, the SEI is formed on the electrode surface, and there is an effect of suppressing an increase in the internal resistance including the positive electrode 150. In addition, the reaction product is not firmly fixed only to the negative electrode 160, but in some way has a good effect on the members other than the negative electrode 160, such as the positive electrode 150 and the separator 170. For this reason, it is very effective to perform the initial charging in consideration of the electrochemical reaction of the lithium salt dissolved in the nonaqueous electrolyte.

[0199] The nonaqueous secondary battery 100 in the second embodiment can also be used as a cell 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 cell pack, the operating voltage range per nonaqueous secondary battery is preferably 2 to 5 V, more preferably 2 to 4.5 V, and particularly preferably 2 V to 4 V.

[0200] As described above, the second embodiment of the present invention has been explained. However, the present invention is not limited to the above-described embodiments. The present invention can be variously modified without departing from the gist thereof.

[0201] <III. Third Embodiment> Hereinafter, the third embodiment of the present invention will be described in detail. In the third embodiment, a non-aqueous secondary battery, a method for manufacturing the same, and a secondary battery manufacturing process are provided. The non-aqueous secondary battery according to the third embodiment may have the configuration of the lithium ion battery 100 shown in FIGS. 1 and 2, although not limited thereto.

[0202] <III-1. Non-aqueous Electrolyte> The "non-aqueous electrolyte" in the third embodiment refers to a non-aqueous electrolyte containing water in an amount of 1% by mass or less based on the total amount of the non-aqueous electrolyte and containing a non-aqueous solvent and LiPF 6 6. The non-aqueous electrolyte according to the third embodiment preferably contains as little water as possible, but may contain a very small amount of water as long as it does not inhibit the solution of the problems of the present invention. The content of such water is 300 ppm by mass or less, preferably 200 ppm by mass or less, per unit amount of the non-aqueous electrolyte. Regarding the non-aqueous electrolyte, as long as it has a configuration for achieving the solution of the problems of the present invention, for other components, the constituent materials in known non-aqueous electrolytes used in lithium ion batteries can be appropriately selected and applied.

[0203] <III-1-1. Non-aqueous Solvent> In the third embodiment, the term "non-aqueous solvent" refers to elements in the non-aqueous electrolyte excluding lithium salt and various additives. In the third embodiment, when the non-aqueous electrolyte contains an additive for protecting an electrode, the term "non-aqueous solvent" refers to elements in the non-aqueous electrolyte excluding lithium salt and additives other than the additive for protecting an electrode. Examples of non-aqueous solvents include alcohols such as methanol and ethanol; aprotic solvents, etc. Among them, aprotic solvents are preferred as non-aqueous solvents. The non-aqueous solvent may contain a solvent other than the aprotic solvent as long as it does not hinder the problem solving of the present invention.

[0204] The non-aqueous solvent related to the non-aqueous electrolyte of the third embodiment contains acetonitrile as an aprotic solvent. The non-aqueous solvent contains acetonitrile, which improves the ionic conductivity of the non-aqueous electrolyte, thereby increasing the diffusibility of lithium ions in the battery. Therefore, when the non-aqueous electrolyte contains acetonitrile, even in a positive electrode in which the positive electrode active material layer is thickened to increase the amount of positive electrode active material filled, lithium ions can be well diffused to the area near the current collector where lithium ions are difficult to reach during high load discharge. As a result, it is possible to extract sufficient capacity even during high load discharge, and a non-aqueous secondary battery with excellent load characteristics can be obtained.

[0205] Furthermore, by including acetonitrile in the nonaqueous solvent, the rapid charging characteristics of the nonaqueous secondary battery can be improved. In constant current (CC)-constant voltage (CV) charging of a nonaqueous secondary battery, the 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 of the 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, so that the time from the start of charging to fully charging the nonaqueous secondary battery can be significantly shortened.

[0206] In addition, acetonitrile is easily electrochemically reduced and decomposed, so when acetonitrile is used, it is preferable to use another solvent (e.g., an aprotic solvent other than acetonitrile) together with acetonitrile as a non-aqueous solvent and / or to add an additive for protecting an electrode for forming a protective film on the electrode.

[0207] The content of acetonitrile in the non-aqueous solvent is preferably 5 to 60% by volume based on the total amount of the non-aqueous solvent. The lower limit of the content of acetonitrile is preferably 5% by volume or more based on the total amount of the non-aqueous solvent, and more preferably 10% by volume or more. The upper limit of the content of acetonitrile is more preferably 60% by volume or less based on the total amount of the non-aqueous solvent, and even more preferably 50% by volume or less. In addition, when the content of acetonitrile in the non-aqueous solvent is within the above range, there is a tendency that the high-temperature cycle characteristics and other battery characteristics of the non-aqueous secondary battery can be further improved while maintaining the excellent performance of acetonitrile.

[0208] 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.

[0209] Since acetonitrile, which is one component of a nonaqueous solvent, is easily reduced and decomposed electrochemically, by adding vinylene carbonate to the nonaqueous electrolyte solution according to the third embodiment, the charge and discharge amount of the battery is stabilized when the nonaqueous electrolyte solution is used in a nonaqueous secondary battery.

[0210] A nonaqueous electrolyte solution according to the third embodiment, in which the nonaqueous solvent contains acetonitrile, vinylene carbonate as a cyclic carbonate, and ethylene sulfite as an organic compound having a sulfur atom, can operate the battery at a high current density when used in a nonaqueous secondary battery.

[0211] The high resistance of the negative electrode protective film derived from vinylene carbonate tends to lead to a decrease in performance during rapid charging and in low-temperature environments, and to battery swelling due to gas generation during decomposition. Ethylene sulfite has a lower lowest unoccupied molecular orbital (LUMO) level than other oxygen-containing sulfur compounds, and can be reduced and decomposed at a higher potential than vinylene carbonate to form a negative electrode protective film, making it possible to solve the problems caused by the negative electrode protective film derived from vinylene carbonate by reducing the amount of vinylene carbonate added. In addition, the negative electrode protective film derived from ethylene sulfite has low resistance over a wide temperature range, and furthermore, it promotes the formation of a negative electrode SEI (Solid Electrolyte Interface) that is highly durable against acetonitrile and its decomposition products, making it possible to provide a nonaqueous electrolyte and a nonaqueous secondary battery that can operate stably at a high current density.

[0212] In the third embodiment, the total content of vinylene carbonate and ethylene sulfite in the nonaqueous electrolyte solution is preferably 0.1 vol % or more and less than 15 vol % with respect to the total amount of the nonaqueous solvent, from the viewpoint of suppressing an increase in internal resistance.

[0213] 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;

[0214] Fluoroethylene carbonates include, for example, 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, 4,4,5,5-tetrafluoro-1,3-dioxolane-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxolane-2-one;

[0215] Lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone;

[0216] Examples of organic compounds having sulfur atoms 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;

[0217] 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;

[0218] Cyclic ethers include, for example, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane;

[0219] Examples of mononitriles other than acetonitrile include propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile;

[0220] Alkoxy group-substituted nitriles include, for example, methoxyacetonitrile and 3-methoxypropionitrile;

[0221] 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-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dimethylglutaronitrile;

[0222] Cyclic nitriles include, for example, benzonitrile;

[0223] 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 isopropyl 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;

[0224] Chain ethers include, for example, dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme;

[0225] Examples of fluorinated ethers include Rf 20 -OR 21 (In the formula, Rf 20 represents an alkyl group containing a fluorine atom, and R 21 represents a monovalent organic group which may contain a fluorine atom;

[0226] Ketones, for example, acetone, methyl ethyl ketone, and methyl isobutyl ketone;

[0227] Examples of the aprotic solvent compound in which some or all of the H atoms have been replaced with halogen atoms include compounds in which the halogen atoms are fluorine; The following can be mentioned.

[0228] Here, 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 above-mentioned fluorinated chain carbonates are represented by the following general formula: R 1 -OC(O)OR 2 {where, R 1 and R 2 is CH 3 , C.H. 2 CH 3 , C.H. 2 CH 2 CH 3 , CH(CH 3 ) 2 , and C.H. 2 Rf 3 Rf is at least one selected from the group consisting of 3 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 1 and / or R 2 contains at least one fluorine atom. It can be expressed as:

[0229] 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 10 -C(O)OR 11 {where, R 10 is CH 3 , C.H. 2 CH 3 , C.H. 2 CH 2 CH 3 , CH(CH 3 ) 2 , C.F. 3 CF 2 H, CFH 2 , C.F. 2 Rf 12 , CFHRf 12 , and C.H. 2 Rf 13 and R is at least one selected from the group consisting of 11 is CH 3 , C.H. 2 CH 3 , C.H. 2 CH 2 CH 3 , CH(CH 3 ) 2 , and C.H. 2 Rf 13 Rf is at least one selected from the group consisting of 12 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 13 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 10 and / or R 11 contains at least one fluorine atom, and R 10 CF 2 If H, then R 11 CH 3 isn't it.} It can be expressed as:

[0230] In the third embodiment, the aprotic solvent other than acetonitrile may be used alone or in combination of two or more.

[0231] In the third embodiment, it is preferable from the viewpoint of improving the stability of the non-aqueous electrolyte that the non-aqueous solvent uses, together with acetonitrile, one or more of cyclic carbonate and chain carbonate. From this viewpoint, it is more preferable that the non-aqueous solvent in the third embodiment uses cyclic carbonate together with acetonitrile, and it is still more preferable to use both cyclic carbonate and chain carbonate together with acetonitrile.

[0232] When using a cyclic carbonate other than vinylene carbonate together with acetonitrile, it is particularly preferable that such cyclic carbonate contains ethylene carbonate and / or fluoroethylene carbonate.

[0233] <III-1-2. Electrolyte Salt> The non-aqueous electrolyte of the third embodiment only needs to contain LiPF 6 and is not particularly limited with respect to other electrolyte salts. For example, in the third embodiment, as the lithium salt, it contains LiPF 6 and a lithium-containing imide salt.

[0234] The lithium-containing imide salt is a lithium salt represented by LiN(SO 2 C m F 2m+1 ) 2 [wherein, m is an integer of 0 to 8], and specifically, LiN(SO 2 F) 2 , and LiN(SO 2 CF 3 ) 2 Preferably contains at least one of them. It may contain only one of these imide salts or both. Or, it may contain an imide salt other than these imide salts.

[0235] When acetonitrile is contained in the non-aqueous solvent, since the saturation concentration of the lithium-containing imide salt with respect to acetonitrile is higher than the saturation concentration of LiPF 6 , LiPF 6It is preferable to contain the lithium-containing imide salt at a molar concentration that satisfies the condition of ≦lithium-containing imide salt, since this can suppress association and precipitation of the lithium salt and acetonitrile at low temperatures. In addition, it is preferable that the content of the lithium-containing imide salt is 0.5 mol to 3 mol per 1 L of the non-aqueous solvent from the viewpoint of the amount of ions supplied. LiN(SO 2 F) 2 , and LiN(SO 2 CF 3 ) 2 According to the acetonitrile-containing nonaqueous electrolyte solution containing at least one of the above, it is possible to effectively suppress the decrease in ion conductivity in a low temperature range such as −10° C. or −30° C., and obtain excellent low-temperature characteristics. In this way, by limiting the content, it is also possible to more effectively suppress the increase in resistance during high-temperature heating.

[0236] In addition, LiPF 6 The lithium salt may further include a fluorine-containing inorganic lithium salt other than LiBF. 4 , LiAsF 6 , Li 2 SiF 6 , LiSbF 6 , Li 2 B 12 F b H 12-bIn the third embodiment, the term "inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in the anion and is soluble in acetonitrile. In the third embodiment, the term "fluorine-containing inorganic lithium salt" refers to a lithium salt that does not contain a carbon atom in the anion, contains a fluorine atom in the anion, and is soluble in acetonitrile. The fluorine-containing inorganic lithium salt is excellent in that it forms a passive film on the surface of the metal foil that is the positive electrode current collector, and inhibits corrosion of the positive electrode current collector. These fluorine-containing inorganic lithium salts are used alone or in combination of two or more. As the fluorine-containing inorganic lithium salt, a compound that is a double salt of LiF and a Lewis acid is desirable, and among them, it is more preferable to use a fluorine-containing inorganic lithium salt having a phosphorus atom, since it is easy to release free fluorine atoms. Representative fluorine-containing inorganic lithium salts are those that dissolve to form PF 6 LiPF that releases anions 6 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 is easy to capture excess free acid components that may cause battery deterioration. From this viewpoint, LiBF 4 is particularly preferred.

[0237] The content of the fluorine-containing inorganic lithium salt in the non-aqueous electrolyte of the third 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 the 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 ion conductivity increases and high output characteristics tend to be exhibited. In addition, 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 the 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 ion conductivity increases, high output characteristics can be exhibited, and the decrease in ion conductivity associated with an increase in viscosity at low temperatures tends to be suppressed, and 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 the non-aqueous electrolyte.

[0238] The nonaqueous electrolyte solution of the third embodiment may further contain an organic lithium salt. In the third embodiment, the "organic lithium salt" refers to a lithium salt that contains a carbon atom in the anion and is soluble in acetonitrile.

[0239] As the organic lithium salt, an organic lithium salt having an oxalic acid group can be mentioned. A specific example of the organic lithium salt having an oxalic acid group is LiB(C 2 O 4 ) 2 , LiBF 2 (C 2 O 4 ), LiPF 4 (C 2 O 4 ), and LiPF 2 (C 2 O 4 ) 2 Among them, LiB(C 2 O 4 ) 2 and LiBF 2 (C 2 O4 It is preferable to use at least one lithium salt selected from the lithium salts represented by the formula (I) and (II). It is more preferable 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 non-aqueous electrolyte solution or may be contained in a negative electrode (negative electrode active material layer).

[0240] The amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte 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, in order to better ensure the effect of its use. However, if the amount of the organic lithium salt having an oxalic acid group in the non-aqueous electrolyte is too large, there is a risk of precipitation. Therefore, the amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte 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.

[0241] It is known that organic lithium salts having oxalic acid groups are poorly soluble in organic solvents with low polarity, particularly in chain carbonates. Organic lithium salts having oxalic acid groups may contain a small amount of lithium oxalate, and may react with a small amount of water contained in other raw materials when mixed as a non-aqueous electrolyte solution, and may generate new white precipitation of lithium oxalate. Therefore, the content of lithium oxalate in the non-aqueous electrolyte solution of the third embodiment is not particularly limited, but is preferably 0 to 500 ppm.

[0242] 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 the third embodiment. Specific examples of other lithium salts include, for example, LiClO 4 , LiAlO 4 , LiAlCl 4 , LiB 10 Cl 10Inorganic lithium salts that do not contain fluorine atoms in the anion, such as chloroborane Li; LiCF 3 SO 3 , LiCF 3 CO 2 , Li 2 C 2 F 4 (SO 3 ) 2 , LiC(CF 3 SO 2 ) 3 , LiC n F (2n+1) SO 3 {where n≧2}, lower aliphatic carboxylic acid Li, tetraphenylborate Li, LiB(C 3 O 4 H 2 ) 2 Organic lithium salts such as LiPF 5 (CF 3 ) and other LiPFs n (C p F 2p+1 ) 6-n [In the formula, n is an integer of 1 to 5, and p is an integer of 1 to 8]; LiBF 3 (CF 3 ) and other LiBFs 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 combined with a polyvalent anion; The following formula (sa): LiC(SO 2 R A )(SO 2 R B )(SO 2 R C ) (sa) {where, R A , R B , and R C may be the same or different and represent a perfluoroalkyl group having 1 to 8 carbon atoms. The following formula (sb): LiN(SO 2 OR D )(SO 2 ORE ) (sb) {Wherein, R D , and R E may be the same as or different from each other and each represents a perfluoroalkyl group having 1 to 8 carbon atoms.}, and the following formula (sc) LiN(SO 2 R F )(SO 2 OR G ) (sc) {Wherein, R F , and R G may be the same as or different from each other and each represents a perfluoroalkyl group having 1 to 8 carbon atoms.} Examples thereof include organolithium salts represented by each of them, and one or more of these can be used together with a fluorine-containing inorganic lithium salt.

[0243] <III-1-3. Additive> The non-aqueous electrolyte according to the third embodiment may contain an additive in addition to the non-aqueous solvent and the electrolyte salt described above.

[0244] <Vinylene carbonate> The non-aqueous electrolyte in the third embodiment preferably contains vinylene carbonate (VC). Since vinylene carbonate causes a reduction reaction on the surface of the negative electrode active material to form a film, an addition amount corresponding to the mass of the negative electrode active material is required. From the viewpoint of film formation, the concentration of vinylene carbonate in the non-aqueous electrolyte is preferably 0.1% by volume or more based on the total amount of the non-aqueous solvent. Also, adding an excessive amount of vinylene carbonate may reduce the viscosity of the electrolyte, deteriorate the low-temperature characteristics, and cause excessive gas generation. Therefore, the addition amount of vinylene carbonate is preferably 10% by volume or less, preferably 8% by volume or less, and more preferably 6% by volume or less based on the total amount of the non-aqueous solvent. When multi-stage liquid injection is performed in the manufacturing process of the non-aqueous secondary battery, it is preferable that the VC concentration falls within the above range in the final composition of the non-aqueous electrolyte contained in the battery.

[0245] <Ethylene sulfite> The non-aqueous electrolyte in the third embodiment contains ethylene sulfite (ES). Ethylene sulfite decomposes at a higher potential than vinylene carbonate and causes a reduction reaction on the surface of the negative electrode active material to form a coating, so an amount of ethylene sulfite that corresponds to the mass of the negative electrode active material is required. From the viewpoint of coating formation, the ES concentration in the non-aqueous electrolyte is preferably 0.01% by volume or more with respect to the total amount of the non-aqueous solvent. On the other hand, the addition of an excessive amount of ethylene sulfite may cause excessive gas generation or impurity by-production accompanied by excessive reduction reaction, so the ES concentration in the non-aqueous electrolyte is preferably 4% by volume or less with respect to the total amount of the non-aqueous solvent. When multi-stage injection is performed in the manufacturing process of a non-aqueous secondary battery, it is preferable that the ES concentration in the final composition of the non-aqueous electrolyte contained in the battery falls within the above range.

[0246] <Inorganic sulfur compounds> The nonaqueous secondary battery in the third embodiment has at least two electrolyte injection steps for injecting a nonaqueous electrolyte into the battery exterior, and at least one charging step after the first electrolyte injection step and before the final electrolyte injection step. In the electrolyte injection steps after the first, an electrolyte having a higher volume ratio of acetonitrile to the entire electrolyte than the electrolyte used in the first electrolyte injection step is injected into the battery exterior, and contains an inorganic sulfur compound containing a sulfur atom with a valence of -2 or more and a valence of 0 or less, such as sulfur or copper sulfide, on the negative electrode coating after the first charge and discharge. The sulfur referred to here may be, for example, a solid, crystal, semisolid, gel, liquid, vapor, or a combination thereof consisting essentially of sulfur (S) atoms, except for unavoidable impurities. It is a compound observed in the region of 160 to 165 eV in binding energy in X-ray photoelectron spectroscopy (XPS) measurement. Non-aqueous secondary batteries using non-aqueous electrolytes can function as batteries after the initial charge. However, if the acetonitrile concentration is high during the initial charge, defects will occur in the negative electrode coating, and it is assumed that these defects will cause excessive reductive decomposition reactions of ES and that these compounds will be formed by reacting with copper ions eluted from the current collector after the reduction reaction.

[0247] These compounds have low ionic conductivity and are deposited in large amounts on the negative electrode, causing a decrease in output performance and a decrease in cycle life performance. Therefore, the amount of the compound containing a sulfur atom with a valence of -2 or more and 0 or less in the negative electrode coating is preferably 3.80% or less, more preferably 3.00% or less, compared to the amount of the compound containing a lithium (Li) atom. On the other hand, from the viewpoint of battery stability or control of the reduction reaction at the negative electrode, the amount of the compound containing a sulfur atom with a valence of -2 or more and 0 or less in the negative electrode coating is preferably 0.1% or more, compared to the amount of the compound containing a Li atom. The amount of substance referred to here may be, for example, a value based on molecular weight.

[0248] <Other electrode protection additives> Other additives for protecting an electrode are not particularly limited as long as they do not impede the solution of the problems by the present invention, and may substantially overlap with the substance that plays the role of a solvent for dissolving a lithium salt (i.e., the above-mentioned non-aqueous solvent) (excluding acetonitrile and vinylene carbonate). The additives for protecting an electrode are preferably substances that contribute to improving the performance of the non-aqueous electrolyte and the non-aqueous secondary battery in the third embodiment, but also include substances that are not directly involved in the electrochemical reaction.

[0249] Specific examples of other electrode protection additives include, for example, 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, 4,4,5,5-tetrafluoro-1,3-dioxolane-2-one, 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. lactones, cyclic ethers, cyclic ethers, cyclic sulfur compounds, cyclic sulfur compounds, cyclic sulfur compounds, cyclic anhydrides ...

[0250] The content of the electrode protection additive in the nonaqueous electrolyte solution in the third embodiment is not particularly limited, but the content of the electrode protection additive relative to the total amount of the nonaqueous solvent is preferably 0.1 to 30 volume %, more preferably 0.3 to 15 volume %, and even more preferably 0.5 to 4 volume %.

[0251] In the third embodiment, the greater the content of the electrode protection additive, the more the deterioration of the non-aqueous electrolyte solution is suppressed. However, the smaller the content of the electrode protection additive, the more the high-output characteristics of the non-aqueous secondary battery in a low-temperature environment are improved. Therefore, by adjusting the content of the electrode protection additive within the above-mentioned range, it is possible to maximize the excellent performance based on the high ionic conductivity of the non-aqueous electrolyte solution without impairing the basic function of the non-aqueous secondary battery. By preparing the non-aqueous electrolyte solution with such a composition, it is possible to further improve all of the cycle performance of the non-aqueous secondary battery, the high-output performance in a low-temperature environment, and other battery characteristics.

[0252] <Other optional additives> In a third embodiment, for the purpose of improving the charge / discharge cycle characteristics, high-temperature storage property, and safety (e.g., prevention of overcharging) of a nonaqueous secondary battery, a nonaqueous electrolyte solution may contain, for example, a sulfonic acid ester, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, a phosphoric acid ester [ethyl diethyl phosphonoacetate (EDPA): (C 2 H 5 O) 2 (P=O)-CH 2 (C=O)OC 2 H 5 , tris(trifluoroethyl) phosphate (TFEP): (CF 3 CH 2 O) 3 P=O, triphenyl phosphate (TPP): (C 6 H 5 O) 3 P=O:(CH 2 =CHCH 2 O) 3 It is also possible to appropriately contain optional additives selected from compounds having no steric hindrance around the unshared electron pair (e.g., triaryl phosphate, triaryl phosphate, etc.), nitrogen-containing cyclic compounds having no steric hindrance around the unshared electron pair (e.g., pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole, etc.), and derivatives of these compounds. Phosphate esters are particularly effective because they suppress side reactions during storage.

[0253] The content of other optional additives in the third embodiment is calculated as a mass percentage with respect to the total mass of all components constituting the non-aqueous electrolyte. Regarding the content of other optional additives, there is no particular limitation, but it is preferably in the range of 0.01% by mass or more and 10% by mass or less, more preferably 0.02% by mass or more and 5% by mass or less, and even more preferably 0.05% by mass or more and 3% by mass or less with respect to the total amount of the non-aqueous electrolyte. By adjusting the content of other optional additives within the above range, it tends to be possible to add better battery characteristics without impairing the basic functions as a non-aqueous secondary battery.

[0254] <III-2. Positive Electrode and Positive Current Collector> The positive electrode 150 shown in FIGS. 1 and 2 is composed of a positive electrode active material layer made from a positive electrode mixture and a positive current collector. The positive electrode 150 is not particularly limited as long as it functions as the positive electrode of a non-aqueous secondary battery, and may be a known one. The positive electrode in the third embodiment contains a lithium-containing compound containing Fe, and preferably also contains nickel (Ni) in a relatively high ratio.

[0255] The positive electrode active material layer preferably contains a positive electrode active material, and further preferably contains a conductive assistant and a binder as necessary.

[0256] The positive electrode active material layer preferably contains, as the positive electrode active material, a material capable of occluding and releasing lithium ions. When such a material is used, it is preferable because it tends to be possible to obtain a high voltage and a high energy density.

[0257] As the positive electrode active material, the following general formula (1): Li w MPO 4 ·····(1) {In the formula, M represents at least one transition metal element, and the value of w is determined by the charge and discharge state of the battery and represents a number from 0 to 1.2.} At least one lithium-containing compound having an olivine structure represented by, or the following general formula (2) containing at least one transition metal element selected from the group consisting of, for example, Ni, Mn, and Co: Li p Ni q Co r Mn s M t O u ·····(2) {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.} At least one Li-containing metal oxide selected from lithium (Li)-containing metal oxides represented by is preferable. The lithium-containing compound represented by the general formula (1) is preferably a metal phosphate compound containing lithium and a transition metal element. In the formula (1), the value of w is determined by the charge and discharge state of the battery and preferably represents a number in the range of 0.05 to 1.10.

[0258] Specific examples of the positive electrode active material include, for example, Li w FePO 4 and other Li compounds, or lithium cobalt oxides represented by LiCoO 2 ; lithium manganese oxides represented by LiMnO 2 LiMn 2 O 4 and Li 2 Mn 2 O 4 ; lithium nickel oxides represented by LiNiO 2 ; lithium nickel 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 LiNi 0.5Co 0.2 Mn 0.3 O 2 、LiNi 0.8 Co 0.2 O 2 represented by Li z MO 2 (wherein M contains at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and 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) include lithium-containing composite metal oxides represented thereby.

[0259] In particular, when the Ni content ratio q of the Li-containing metal oxide represented by the general formula (2) is 0.5 < q < 1.2, it is preferable because both the reduction of the usage amount of Co, which is a rare metal, and the increase in the energy density are achieved. Examples of such a positive electrode active material include, for example, LiNi 0.6 Co 0.2 Mn 0.2 O 2 、LiNi 0.75 Co 0.15 Mn 0.15 O 2 、LiNi 0.8 Co 0.1 Mn 0.1 O 2 、LiNi 0.85 Co 0.075 Mn 0.075 O 2 、LiNi 0.8 Co 0.15 Al 0.05 O 2 、LiNi 0.81 Co 0.1 Al 0.09 O 2 、LiNi 0.85 Co 0.1 Al 0.05 O 2 、etc., include lithium-containing composite metal oxides represented thereby.

[0260] On the other hand, the higher the Ni content ratio in the positive electrode active material layer, the more degradation tends to progress at low voltage. The positive electrode active material of the Li-containing metal oxide represented by the general formula (2) essentially has active sites that oxidize and deteriorate the non-aqueous electrolyte, but these active sites may unintentionally consume the compound added to protect the negative electrode on the positive electrode side. Among them, acid anhydrides tend to be easily affected. In particular, when acetonitrile is contained as the non-aqueous solvent, the effect of adding an acid anhydride is enormous, so that the consumption of the acid anhydride on the positive electrode side is a fatal problem.

[0261] In addition, the decomposition products of these additives that are taken in and deposited on the positive electrode side not only increase the internal resistance of the non-aqueous secondary battery, but also accelerate the deterioration of the lithium salt. Furthermore, the protection of the negative electrode surface, which was the original purpose, becomes insufficient. In order to deactivate the active sites that essentially cause the oxidative deterioration of the non-aqueous electrolyte, it is important to control the Jahn-Teller distortion or to coexist with a component that plays a role as a neutralizer. Therefore, it is preferable that the positive electrode active material contains at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba.

[0262] 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 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 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 ZrO 2 , TiO 2 , Al 2 O 3 , NbO 3 , and LiNbO 2 It is particularly preferable that the carbon nanotube is coated with at least one oxide selected from the group consisting of the following, since this does not inhibit the permeation of lithium ions.

[0263] The positive electrode active material may be a lithium-containing compound other than the Li-containing metal oxide represented by the above general formulas (1) and (2), 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, 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 D 2 (Xa) In the formula, 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 represents a number from 0.05 to 1.10.}, and The following formula (Xb): Li t M II u SiO 4 (Xb) {In formula, M II 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 the compounds include those represented by the following formula:

[0264] The lithium-containing compound represented by the above formula (Xa) has a layered structure, and the compounds represented by the above formula (1) and the above formula (Xb) have an olivine structure. These lithium-containing compounds may be those in which a part of the transition metal element is replaced by Al, Mg, or other transition metal element, those in which these metal elements are included in the crystal grain boundaries, those in which a part of the oxygen atoms is replaced by fluorine atoms, etc., and those in which at least a part of the surface of the positive electrode active material is coated with another positive electrode active material, etc., for the purpose of stabilizing the structure.

[0265] As the positive electrode active material in the third embodiment, only the lithium-containing compound as described above may be used, or the lithium-containing compound may be used in combination with other positive electrode active materials.

[0266] 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 MnO 2 , FeO 2 , FeS 2 , V 2 O 5 , V 6 O 13 , TiO 2 , TiS 2 , MoS 2 , and NbSe 2 Examples of the conductive polymer include oxides, sulfides, and selenides of metals other than lithium, such as those represented by the following formula: Examples of the conductive polymer include conductive polymers represented by polyaniline, polythiophene, polyacetylene, and polypyrrole.

[0267] The above-mentioned other positive electrode active materials can be used alone 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 can reversibly and stably absorb and release lithium ions and achieve high energy density.

[0268] 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 two is preferably 80 mass % or more, and more preferably 85 mass % or more, of the lithium-containing compound relative to the total positive electrode active material.

[0269] Examples of the conductive assistant include carbon blacks typified by graphite, acetylene black, and ketjen black, and carbon fibers. The content ratio of the conductive assistant is preferably 10 parts by mass or less, more preferably 1 to 5 parts by mass, per 100 parts by mass of the positive electrode active material.

[0270] Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene-butadiene rubber, and fluororubber. The content ratio of the binder is preferably 10 parts by mass or less, more preferably 0.5 to 8 parts by mass, per 100 parts by mass of the positive electrode active material.

[0271] The positive electrode active material layer is formed by applying and drying (removing the solvent), and if necessary, pressing, a positive electrode mixture-containing slurry in which a positive electrode mixture obtained by mixing a positive electrode active material, a conductive assistant and a binder as required is dispersed in a solvent, onto a positive electrode current collector. There is no particular limitation on such a solvent, and conventionally known ones can be used. For example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water, etc. may be mentioned.

[0272] The positive electrode current collector is composed of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode current collector may be carbon-coated on the surface or may be processed into a mesh shape. 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.

[0273] <III-3. Negative Electrode and Negative Electrode Current Collector> The negative electrode 160 shown in FIGS. 1 and 2 is composed of a negative electrode active material layer made from a negative electrode mixture and a negative electrode current collector. The negative electrode 160 can act as the negative electrode of a non-aqueous secondary battery.

[0274] The negative electrode active material layer preferably contains a negative electrode active material and, if necessary, a conductive assistant and a binder.

[0275] Examples of the negative electrode active material 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 fibers, activated carbon, carbon colloids, 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 material may be used alone or in combination of two or more.

[0276] The negative electrode active material layer uses lithium ions as the negative electrode active material at 0.4V vs. Li / Li in order to increase the battery voltage. + It is preferable that the hydrogen-containing gas contains a material capable of absorbing at a potential lower than the hydrogen potential.

[0277] 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, relative to 100 parts by mass of the negative electrode active material.

[0278] Examples of the binder include carboxymethyl cellulose, PVDF, PTFE, polyacrylic acid, and fluororubber. Also included are diene rubbers such as styrene-butadiene rubber. The content of the binder is preferably 10 parts by mass or less, more preferably 0.5 to 8 parts by mass, based on 100 parts by mass of the negative electrode active material.

[0279] 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 assistant and a binder, in a solvent to form a negative electrode mixture-containing slurry, applying the slurry to a negative electrode current collector, drying (solvent removal), and pressing if necessary. There is no particular restriction on such a solvent, and a conventionally known solvent may be used. Examples of the solvent include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0280] The negative electrode current collector is made of a metal foil such as copper foil, nickel foil, stainless steel foil, etc. The surface of the negative electrode current collector may be carbon-coated or processed into a mesh shape. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and further preferably 7 to 30 μm.

[0281] <III-4.セパレータ> 2, the nonaqueous secondary battery 100 in the third embodiment is preferably provided with 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 that provided in known nonaqueous secondary batteries, and is preferably an insulating thin film having 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 preferable.

[0282] As the synthetic resin microporous film, for example, a microporous film containing polyethylene or polypropylene as a main component, or a polyolefin-based microporous film such as a microporous film containing both of these polyolefins is preferably used. As the nonwoven fabric, for example, a porous film made of a heat-resistant resin such as glass, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, or aramid can be used.

[0283] Separator 170 may be a single layer or multiple layers of one type of microporous film, or a laminate of two or more types of microporous films. Separator 170 may be a single layer or multiple layers of a mixed resin material obtained by melting and kneading two or more types of resin materials.

[0284] For the purpose of providing functions, inorganic particles may be present on the surface or inside of the separator, or other organic layers may be further coated or laminated. Also, a crosslinked structure may be included. In order to improve the safety performance of the non-aqueous secondary battery, these methods may be combined as necessary.

[0285] By using such a separator 170, it is possible to realize the good input / output characteristics and low self-discharge characteristics required for the lithium ion battery for the above-mentioned high-power applications.

[0286] 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 is preferably 500 μm or less from the viewpoint of permeability. The thickness of the microporous membrane is preferably 5 μm or more and 30 μm or less, and more preferably 10 μm or more and 25 μm or less, from the viewpoint of use in high-output applications such as safety tests that have a relatively high heat generation and require self-discharge characteristics higher than conventional ones, and from the viewpoint of winding properties in a large battery winding machine. In addition, the thickness of the microporous membrane is more preferably 15 μm or more and 25 μm or less when emphasis is placed on achieving both short circuit resistance and output performance, and more preferably 10 μm or more and less than 15 μm when emphasis is placed on achieving both high energy density and output performance.

[0287] The porosity of the microporous membrane that can be used as a separator is preferably 30% or more and 90% or less, more preferably 35% or more and 80% or less, and still more preferably 40% or more and 70% or less, from the viewpoint of following the rapid movement of lithium ions during high output. When giving priority to improving the output performance while ensuring safety, the porosity of the microporous membrane is particularly preferably 50% or more and 70% or less. When emphasizing the compatibility between the short-circuit resistance performance and the output performance, it is particularly preferably 40% or more and less than 50%.

[0288] Regarding the air permeability of the microporous membrane that can be used as a separator, from the viewpoint of the balance with the membrane thickness and porosity, it is preferably 1 second / 100 cm 3 or more and 400 seconds / 100 cm 3 or less, more preferably 100 seconds / 100 cm 3 or more and 350 second / 100 cm 3 or less. When emphasizing the compatibility between the short-circuit resistance performance and the output performance, the air permeability of the microporous membrane is particularly preferably 150 seconds / 100 cm 3 or more and 350 seconds / 100 cm 3 or less. When giving priority to improving the output performance while ensuring safety, it is particularly preferably 100 second / 100 cm 3 more than or more and less than 150 seconds / 100 cm 3 is particularly preferred. On the other hand, when combining a non-aqueous electrolyte with low ionic conductivity and a separator having air permeability and porosity within the above range, regarding the movement speed of lithium ions, it is not the structure of the separator but the high ionic conductivity of the non-aqueous electrolyte that becomes the rate-determining factor, and there is a tendency that the expected input / output characteristics cannot be obtained. Therefore, the ionic conductivity of the non-aqueous electrolyte is preferably 10 mS / cm or more, more preferably 15 mS / cm more than and still more preferably 20 mS / cm more than . However, the membrane thickness, air permeability, and porosity of the separator, as well as the ionic conductivity of the non-aqueous electrolyte, are not limited to the above examples.

[0289] <III-5. Battery exterior> The configuration of the battery exterior 110 of the non-aqueous secondary battery 100 shown in FIGS. 1 and 2 is not particularly limited. For example, either a battery can or a laminated film exterior can be used as the battery exterior. As the battery can, for example, a metal can such as a rectangular, square tube, cylindrical, elliptical, flat, coin-shaped, or button-shaped can made of steel, stainless steel, aluminum, or a clad material can be used. As the laminated film exterior, for example, a laminated film having a three-layer structure of a heat-melt resin / metal film / resin can be used.

[0290] The laminated film exterior can be used as an exterior by stacking two sheets with the heat-melt resin side facing inward, or by folding it so that the heat-melt resin side faces inward and sealing the ends by heat-sealing. When using the laminated film exterior, a positive electrode lead body 130 (or a positive electrode terminal and a lead tab connected to the positive electrode terminal) can be connected to the positive electrode current collector, and a negative electrode lead body 140 (or a negative electrode terminal and a lead tab connected to the negative electrode terminal) can be connected to the negative electrode current collector. In this case, the laminated film exterior can 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) drawn out to the outside of the exterior.

[0291] <III-6. Method for manufacturing battery> The non-aqueous secondary battery 100 in the third embodiment can be manufactured using the above-described non-aqueous electrolyte, 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 exterior 110, and a separator 170 as required. The method for manufacturing the non-aqueous secondary battery according to the third embodiment includes at least two electrolyte injection steps (hereinafter sometimes referred to as "two-stage injection") of injecting a non-aqueous electrolyte into the battery exterior. After the first electrolyte injection step and before the final electrolyte injection step, there is at least one charging step, and in the electrolyte injection step after the first injection, an electrolyte having a higher volume ratio of acetonitrile to the total electrolyte than the electrolyte used in the first electrolyte injection step can be injected.

[0292] First, a laminate consisting of a positive electrode 150, a negative electrode 160, and optionally a separator 170 is formed. For example: A mode 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 laminate having a wound structure; A mode in which the positive electrode 150 and the negative electrode 160 are cut into a plurality of sheets having a certain area and shape, and the positive electrode sheets and the negative electrode sheets are alternately stacked with a separator sheet interposed therebetween to form a laminate having a laminated structure; A mode in which a long separator is zigzag-folded and positive electrode sheets and negative electrode sheets are alternately inserted between the zigzag-folded separators to form a laminate having a laminate structure; etc. are possible.

[0293] Next, the above-mentioned laminate is housed in a battery exterior 110 (battery case), the nonaqueous electrolyte solution according to the third embodiment is poured into the battery case, and the laminate is immersed in the nonaqueous electrolyte solution and sealed, thereby producing a nonaqueous secondary battery in the third embodiment.

[0294] 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 necessary, and then the laminated structure may be housed in battery exterior 110 to produce nonaqueous secondary battery 100.

[0295] In addition, if the arrangement of the electrodes is designed so that there is a portion where the outer peripheral edge of the negative electrode active material layer overlaps with the outer peripheral edge 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, the position of the electrodes may be shifted during battery assembly, which may deteriorate the charge-discharge cycle characteristics of the non-aqueous secondary battery. Therefore, it is preferable that the electrode positions of the electrode body used in the non-aqueous secondary battery are fixed in advance by tapes such as polyimide tape, polyphenylene sulfide tape, and polypropylene (PP) tape, adhesives, etc.

[0296] In the third embodiment, when a non-aqueous electrolyte using acetonitrile is used, the lithium ions released from the positive electrode during the initial charge of the non-aqueous secondary battery may diffuse throughout the negative electrode due to its high ionic conductivity. In non-aqueous secondary batteries, the area of ​​the negative electrode active material layer is generally made larger than that of the positive electrode active material layer. However, if lithium ions diffuse and are absorbed to a portion of the negative electrode active material layer that does not face the positive electrode active material layer, the lithium ions will not be released during the initial discharge and will remain in the negative electrode. Therefore, the contribution of the lithium ions that are not released becomes the irreversible capacity. For these reasons, the initial charge / discharge efficiency may be low in non-aqueous secondary batteries using a non-aqueous electrolyte containing acetonitrile.

[0297] 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 they are the same, current concentration is likely to occur at the edge portions of the negative electrode active material layer during charging, making lithium dendrites more likely to form.

[0298] For the above reasons, 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.

[0299] 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 ratio of 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 reduce as much as possible the amount of lithium ions absorbed in the portion of the negative electrode active material layer that does not face the positive electrode active material layer among the lithium ions released from the positive electrode during the initial charge (i.e., the amount of lithium ions that are not released from the negative electrode during the initial discharge and become 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 generation of lithium dendrites.

[0300] The nonaqueous secondary battery 100 in the third embodiment can function as a battery by initial charging, but is stabilized by decomposing a part of the nonaqueous electrolyte during the initial charging. There is no particular limitation on the method of initial charging, but 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 is performed via a constant voltage charge in the middle. By setting the voltage range in which the lithium salt is involved in the electrochemical reaction to be long, a stable and strong SEI is formed on the surface of the electrode (negative electrode 160), which has the effect of suppressing an increase in internal resistance, and the reaction product is not firmly fixed only to the negative electrode 160, but in some way has a good effect on members other than the negative electrode 160, such as the positive electrode 150 and the separator 170. For this reason, it is very effective to perform the initial charging in consideration of the electrochemical reaction of the lithium salt dissolved in the nonaqueous electrolyte. The initial discharge is not particularly limited, but is preferably performed at 0.002C to 1.0C.

[0301] In the non-aqueous secondary battery 100 of the third embodiment, the initial charge and aging treatment may be performed under reduced pressure conditions for the purpose of impregnating the separator and electrodes with the electrolyte and removing gas present in the cell. The temperature under reduced pressure conditions is preferably 15°C or higher from the viewpoint of electrolyte impregnation, more preferably 20°C or higher, and even more preferably 25°C or higher. Regarding the degree of reduced pressure, from the viewpoint of electrolyte impregnation and gas removal, the degree of reduced pressure is preferably 900hPa or lower, more preferably 800hPa. In addition, in the production under such reduced pressure conditions, the volatilization of the electrolyte can generally be a problem, but by applying the two-stage injection in the third embodiment of the present invention, the amount of volatilization of the electrolyte is reduced, and the production problem can be solved.

[0302] The nonaqueous secondary battery 100 in the third 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.

[0303] In the manufacturing process of the nonaqueous secondary battery 100 in the third embodiment, an electrolyte injection step of injecting a nonaqueous electrolyte into the battery exterior may be performed two or more times. When the electrolyte injection step is performed multiple times, at least one charging step is performed after the first electrolyte injection step and before the final electrolyte injection step, and the composition of the electrolyte injected in each electrolyte injection step may be different.

[0304] From the viewpoint of forming a negative electrode film, the electrolyte used in the first electrolyte injection step (hereinafter sometimes referred to as "first injection electrolyte") preferably contains VC and ES at higher concentrations than the electrolyte used in the electrolyte injection steps after the first one. From the same viewpoint, the first injection electrolyte preferably contains VC at 0.1 vol. % or more, more preferably 2 vol. % or more, and even more preferably 4 vol. % or more. Moreover, the first injection electrolyte preferably contains ES at 0.1 vol. % or more, and more preferably 2 vol. % or more.

[0305] From the viewpoint of reducing the volatilization of the electrolyte, the electrolyte used in the electrolyte injection step after the first preferably contains a higher concentration of acetonitrile (AcN) than the first electrolyte injection step, and more preferably has a higher volumetric ratio of AcN to the entire electrolyte than the first electrolyte injection step. From the same viewpoint, the first electrolyte injection preferably contains 50% or less by volume of AcN, more preferably 35% or less by volume, and even more preferably 20% or less by volume. In addition, from the viewpoint of improving the ionic conductivity of the electrolyte, the electrolyte used in the electrolyte injection step after the first preferably contains 20% or more by volume of AcN, more preferably 35% or more by volume, and even more preferably 50% or more by volume. In addition, the electrolyte used in the electrolyte injection step after the first may contain, for example, 100% or less by volume of AcN.

[0306] Although the third embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. The present invention can be modified in various ways without departing from the gist of the present invention. EXAMPLES

[0307] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0308] <Examples, Comparative Examples, and Reference Examples According to the First Embodiment>

[0309] (1) Preparation of non-aqueous electrolyte In an inert atmosphere, various non-aqueous solvents and various additives were mixed to a predetermined concentration, and various lithium salts were added to a predetermined volume molar concentration (M) to prepare non-aqueous electrolyte solutions (1-S1) to (1-S20). The abbreviations of the non-aqueous solvents, lithium salts, and additives in Table 1-1 have the following meanings. (Lithium salts) LiFSI: Lithium bis(fluorosulfonyl)imide LiPF 6 : Lithium hexafluorophosphate (Non-aqueous solvent) AcN: Acetonitrile EMC: Ethyl methyl carbonate EC: Ethylene carbonate ES: Ethylene sulfite

[0310] [Table 1-1]

[0311] (2) Preparation of non-aqueous secondary battery (2-1) Preparation of positive electrode (A) LiFePO as positive electrode active material 4 (B) acetylene black powder as a conductive assistant, and (C) polyvinylidene fluoride (PVDF) and / or carbon nanotubes (CNT) as a binder were mixed in a specific mass ratio shown in Table 1-2 to obtain a positive electrode mixture.

[0312] The obtained positive electrode mixture was mixed with N-methyl-2-pyrrolidone as a solvent to prepare a positive electrode mixture-containing slurry. The positive electrode mixture-containing slurry was applied to one or both sides of an aluminum foil having a thickness of 15 μm to serve as a positive electrode current collector while adjusting the basis weight, and the solvent was dried and removed in a hot air drying oven. Then, the density of the positive electrode active material layer was adjusted to 1.9 g / cm by roll pressing. 3 By rolling the positive electrode mixture until the density of the positive electrode active material layer reached 2.2 g / cm, positive electrodes (1-C1 to C3) were obtained, each consisting of a positive electrode active material layer and a positive electrode current collector corresponding to the positive electrode mixture compositions of 1-C1 to C3 in Table 2. The positive electrode mixture-containing slurry was applied to one or both sides of an aluminum foil serving as a positive electrode current collector foil while adjusting the basis weight, and the solvent was dried and removed in a hot air drying furnace. Then, the positive electrode active material layer was roll-pressed until the density of the positive electrode active material layer reached 2.2 g / cm. 3 By rolling the electrodes so that the positive electrode mixture compositions of 1-C4 and 1-C5 in Table 1-2 were obtained, the positive electrodes (1-C4, 1-C5) were obtained which consisted of a positive electrode active material layer and a positive electrode current collector corresponding to the positive electrode mixture compositions of 1-C4 and 1-C5 in Table 1-2. In addition, leads were welded to the positive electrodes 1-C3 to C5. After that, the positive electrodes were vacuum dried at 120°C for 12 hours or more to obtain positive electrodes. The basis weight of each positive electrode excluding the positive electrode current collector is shown in Table 1-2.

[0313] (2-2) Preparation of negative electrode (a) Graphite as a negative electrode active material, (b) a conductive additive, and (c) a binder were mixed in the mass ratio shown in Table 1-2 to obtain a negative electrode mixture.

[0314] The obtained negative electrode mixture was mixed with water as a solvent to prepare a negative electrode mixture-containing slurry. The slurry was applied to one or both sides of a copper foil having a thickness of 10 μm to be used as a negative electrode current collector, and the solvent was dried and removed in a hot air drying oven. Then, the density of the negative electrode active material layer was adjusted to 1.4 g / cm by roll pressing. 3 The negative electrode (1-A1 to A3) was obtained by rolling the negative electrode active material layer and the negative electrode current collector. The negative electrode mixture-containing slurry was applied to one or both sides of a 10 μm-thick copper foil serving as the negative electrode current collector, and the solvent was dried and removed in a hot air drying furnace. Then, the negative electrode active material layer was rolled to a density of 1.6 g / cm. 3 The negative electrodes (1-A4, 1-A5) were obtained by rolling the negative electrode active material layer and the negative electrode current collector corresponding to the negative electrode mixtures 1-A4 and 1-A5 in Table 1-2. In addition, leads were welded to the negative electrodes 1-A3 to A5. After that, the negative electrodes were vacuum dried at 80°C for 12 hours or more to obtain negative electrodes. The basis weight of the negative electrode active material layer is shown in Table 1-2.

[0315] In the table below, the binder type PVDF is polyvinyl vinylidene fluoride, CMC is carboxymethyl cellulose, and SBR is styrene butadiene rubber.

[0316] [Table 1-2]

[0317] (2-3) Assembly of non-aqueous secondary battery (coin type) In a nitrogen glove box with a dew point temperature of -60 to -20 ° C, a polypropylene gasket was set in a CR2032 type battery case (SUS304 / Al clad), and the positive electrode (1-C1, 1-C2) obtained as described above was punched into a disk shape with a diameter of 15.958 mm and set in the center with the positive electrode active material layer facing up. On top of that, a glass fiber filter paper (Advantec, GA-100) was punched into a disk shape with a diameter of 16.156 mm and set, and the amount of non-aqueous electrolyte was 150 μL, and the weight of the non-aqueous electrolyte was calculated from the specific gravity of the non-aqueous electrolyte. The negative electrode (1-A1, 1-A2) obtained as described above was punched into a disk shape with a diameter of 16.156 mm and set with the negative electrode active material layer facing down to form a laminate consisting of an electrode and a separator. After setting the spacer and spring, the battery cap was fitted and crimped with a crimping machine. The laminate was kept at 25°C for 12 hours to allow the non-aqueous electrolyte to fully penetrate the laminate, and a coin-type non-aqueous secondary battery (hereinafter, also simply referred to as "coin battery") was obtained. Here, the battery combining electrodes 1-C1 and 1-A1 was called Coin 1, and the battery combining electrodes 1-C2 and 1-A2 was called Coin 2, and the design capacities of Coin 1 and Coin 2 were 3.0 mAh and 6.0 mAh, respectively.

[0318] (2-4) Assembly of non-aqueous secondary battery (laminate type) The cut positive electrode with lead (1-C3) and the negative electrode with lead (1-A3) were stacked together with a polyethylene microporous membrane separator (thickness 20 μm) in a dry room with a dew point temperature of −80° C. to −20° C. to form a laminate, and the laminate was housed in an aluminum laminate sheet exterior. Next, the exterior was sealed with the nonaqueous electrolyte solution contained in the exterior to produce a laminate type nonaqueous secondary battery with the appearance shown in FIG. 1 and the cross-sectional structure shown in FIG. 2. The battery was kept at 25° C. for 48 hours to allow the nonaqueous electrolyte solution to fully penetrate the laminate, thereby obtaining a laminate sheet type (pouch type) nonaqueous secondary battery (hereinafter, also simply referred to as a “laminated battery”). Here, the area of ​​the electrodes, the number of layers, the area of ​​the laminate sheet, and the amount of non-aqueous electrolyte were changed according to the design capacity of the battery. For the 30mAh single-layer cell (hereinafter referred to as Lami 1), the positive electrode was 30mm square, the negative electrode was 32mm square, the laminate sheet was 55mm x 70mm, and the electrolyte was 0.522g. For the 1Ah wound cell (hereinafter referred to as Lami 2), the positive electrode was 56mm wide x 378mm long and 56mm wide x 304mm long, and the negative electrode was 58mm wide x 401mm long and 58mm wide x 342mm long, and the electrodes were alternately laminated and wound with a separator sandwiched between them, and the laminate sheet was 60mm x 75mm, and the electrolyte was 7.0g. In addition, the 5Ah laminated cell (hereinafter referred to as Lami 3) has six double-sided coated positive electrodes of 94 mm width x 174 mm length, seven double-sided coated negative electrodes of 100 mm width x 180 mm length, laminated alternately with separators in between, the laminate sheet is 150 mm x 220 mm, and the electrolyte is 18.5 to 21.0 g. Also, Figures 1 and 2 are overviews of the Lami battery, and Lami 1 to 3 do not necessarily have the same appearance.

[0319] In a dry room with a dew point temperature of -80°C to -20°C, the positive electrode with lead (1-C4) and the negative electrode with lead (1-A4) after cutting were stacked in six sheets with a polyethylene microporous membrane separator (thickness 12 μm) interposed therebetween to form a laminate, and this laminate was housed in an aluminum laminate sheet exterior. Then, the exterior was sealed with a predetermined amount of nonaqueous electrolyte contained in the exterior, to produce a laminate type nonaqueous secondary battery with the appearance shown in FIG. 1 and the cross-sectional structure shown in FIG. 2. The battery was kept at 25°C for 12 hours to allow the nonaqueous electrolyte to fully penetrate the laminate, thereby obtaining a laminate sheet type (pouch type) nonaqueous secondary battery (hereinafter referred to as Lami A). Here, the amount of nonaqueous electrolyte was 0.22g, 0.44g, or 0.50g. In addition, the cut positive electrode (1-C5) and the negative electrode (1-A5) with the lead were stacked in eight sheets with a polyethylene microporous membrane separator (thickness 12 μm) in a dry room with a dew point temperature of −80° C. to −20° C., and the stack was housed in an aluminum laminate sheet exterior. Then, the exterior was sealed with a predetermined amount of nonaqueous electrolyte contained in the exterior, and a laminate type nonaqueous secondary battery with the appearance shown in FIG. 1 and the cross-sectional structure shown in FIG. 2 was produced. The battery was kept at 25° C. for 12 hours, and the nonaqueous electrolyte was thoroughly absorbed into the laminate to obtain a laminate sheet type nonaqueous secondary battery (hereinafter referred to as Lami B). Here, the amount of nonaqueous electrolyte was 0.84 g or 0.90 g.

[0320] (3) Evaluation of non-aqueous secondary batteries The coin batteries and lami batteries obtained as described above were first charged and their initial charge / discharge capacity was measured according to the procedure in (3-1) below. Next, the coin batteries and lami batteries were evaluated according to the procedure in (3-2). The coin batteries were charged and discharged 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., and the lami batteries were charged and discharged using TOSCAT-300 (product name) manufactured by Toyo Systems Co., Ltd. and LU-123 (product name) or BTS-408C (product name) manufactured by ESPEC.

[0321] In the first embodiment, 1C means a current value at which a fully charged battery is expected to be discharged at a constant current for one hour. In addition, when a non-aqueous secondary battery is simply referred to, it includes both the coin battery and the laminated battery.

[0322] (3-1a) Initial charge / discharge treatment of non-aqueous secondary batteries (coin batteries and Lami batteries 1-3) The ambient temperature of the fabricated non-aqueous secondary batteries was set to 25°C, and the coin batteries were charged at a constant current of 0.1C, and the Lami batteries 1 to 3 were charged at a constant current of 0.025C until the battery voltage reached 3.5V. The constant voltage charging was then continued for 2 hours while attenuating the current while keeping the battery voltage at 3.5V, or until the charge capacity reached 90% of the design capacity. After charging, the coin batteries were rested for 10 minutes, and the Lami batteries were rested for 20 minutes, and then the batteries were discharged at a constant current of 0.1C until the battery voltage reached 2.0V.

[0323] (3-2a) Final charge / discharge treatment (coin battery and lami battery 1-3) After the treatment of (3-1a), the ambient temperature of the non-aqueous secondary battery was set to 25°C, and the battery was charged to 3.5V at a constant current of 0.2C. The battery was then charged at a constant voltage of 2 hours while the current was attenuated while maintaining the voltage at 3.5V, or until the current value attenuated to 0.05C. After charging, the coin battery was rested for 10 minutes, and the lami batteries 1 to 3 were rested for 20 minutes. The battery was then discharged to 2.0V at a constant current of 0.2C. The ratio of the discharge capacity to the charge capacity in this operation was calculated as the capacity efficiency (%) of the charge and discharge. The irreversible rate (%) of the charge and discharge capacity was also calculated by subtracting the capacity efficiency of the charge and discharge from 100.

[0324] (3-1b) Initial charge / discharge treatment of non-aqueous secondary batteries (Lami batteries A and B) The ambient temperature of the fabricated non-aqueous secondary battery was set to 25°C, and Lami batteries A and B were charged at a constant current of 0.025 C until the battery voltage reached 3.6 V. Constant voltage charging was then continued while maintaining the battery voltage at 3.6 V until the current decayed to 0.02 C. After charging, a rest period of 20 minutes was taken, and then the battery was discharged to 2.0 V at a constant current of 0.1 C.

[0325] (3-2b) Final charge / discharge process (Lami battery A, B) After the treatment of (3-1b), the ambient temperature of the non-aqueous secondary battery was set to 25°C, and the battery was charged to 3.6V at a constant current of 0.2C. The battery was then charged at a constant voltage of 2 hours while the current was attenuated while maintaining the voltage at 3.6V, or until the current value attenuated to 0.05C. A rest period of 20 minutes was taken after charging. Then, the battery was discharged to 2.0V at a constant current of 0.2C. The ratio of the discharge capacity to the charge capacity in this operation was calculated as the capacity efficiency (%) of the charge / discharge. The irreversible rate (%) of the charge / discharge capacity was also calculated by subtracting the capacity efficiency from 100.

[0326] (3-3a) Charge-discharge cycle test of non-aqueous secondary batteries (coin batteries and laminated batteries 1 to 3) The ambient temperature of the fabricated non-aqueous secondary batteries (coin batteries 1 and 2, lami batteries 1 to 3) was set to 50°C, and charging was performed at a constant current of 1C until the battery voltage reached 3.5V. Thereafter, constant voltage charging was continued until the current attenuated to 0.05C while maintaining the battery voltage at 3.5V. After charging, a 10-minute rest period was taken, and then the battery was discharged to 2.0V at a constant current of 1C. The above charge and discharge operations were repeated 50 times. In addition, the ratio of the discharge capacity to the charge capacity in each charge and discharge operation was calculated, and the cycle average capacity efficiency was calculated by calculating the average of the 50 times, and the cycle average irreversibility rate (%) was calculated by subtracting the cycle average capacity efficiency from 100.

[0327] (3-3b) Charge-discharge cycle test of non-aqueous secondary batteries (Lami batteries A and B) The ambient temperature of the fabricated non-aqueous secondary batteries (Lami batteries A and B) was set to 50°C, and charging was performed at a constant current of 1C until the battery voltage reached 3.6V. Thereafter, constant voltage charging was continued while maintaining the battery voltage at 3.6V until the current attenuated to 0.05C. After charging, a 10-minute rest period was taken, and then the battery was discharged to 2.0V at a constant current of 1C. The above charge and discharge operations were repeated 50 times. In addition, the ratio of the discharge capacity to the charge capacity in each charge and discharge operation was calculated, and the cycle average capacity efficiency was calculated by calculating the average of the 50 times, and the cycle average irreversibility rate (%) was calculated by subtracting the cycle average capacity efficiency from 100.

[0328] (3-4) Output test of non-aqueous secondary battery (LAMI battery A) The prepared Lami battery A with 0.5g of electrolyte was charged at a constant current of 0.3C at an ambient temperature of 25°C until the battery voltage reached 3.6V. The battery was then charged at a constant voltage of 0.05C while maintaining the battery voltage at 3.6V. After a 10-minute rest period, the battery was discharged at a constant current of 0.3C to 2.0V. The same charge and discharge operation was repeated with a discharge current of 2C. The ratio of the discharge capacity at 0.3C discharge to the discharge capacity at 2C discharge was calculated to calculate the output performance (2C capacity / 0.3C capacity).

[0329] (3-5) Non-aqueous secondary battery [Examples 1-1 to 1-42 and Comparative Examples 1-1 to 1-5] For each non-aqueous electrolyte prepared as shown in Table 1-1, the amounts of vinylene carbonate (VC) and sulfate ion (SO) shown in Table 1-3 or Table 1-4 were added. 4 2- ), sulfite ion (SO 3 2-) was added, and a nonaqueous secondary battery was assembled as described above, and the initial charge / discharge process and the final charge / discharge were performed, and the charge / discharge efficiency and the irreversibility rate of the charge / discharge capacity in the final charge / discharge were calculated. Here, the solution content ratio X (mass%) is the ratio of the mass of the nonaqueous electrolyte to the mass of the negative electrode excluding the negative electrode current collector, and A (volume%) is the content of acetonitrile relative to the volume of the nonaqueous solvent. The interpretation of each test result is described below.

[0330] [Table 1-3]

[0331] [Table 1-4]

[0332] The capacity efficiency in the above-mentioned final charge and discharge is preferably more than 97.5% and less than 2.5% as the irreversible capacity rate. In Examples 1-1 to 1-42, the irreversible capacity rate is less than 2.5%, and the additive has a stabilizing effect on performance. On the other hand, in Comparative Examples 1-1 to 1-5, irreversible reactions were unavoidable during charging, and the capacity efficiency was significantly low, the irreversible capacity exceeded 2.5%, or significant charging failure occurred, making it impossible to discharge. From this, it can be seen that the battery tends to operate stably by adding vinylene carbonate and sulfate ions or sulfite ions to the non-aqueous electrolyte so as to fall within a predetermined range.

[0333] The cycle average irreversible rate is preferably 0.19% or less, and more preferably 0.17% or less. In the batteries in which X is 200% or less as in Examples 1-37 to 1-42, the irreversible rate tended to be below 0.19% within a predetermined range in which the acetonitrile content was 35% by volume or less and the amount of vinylene carbonate added was 15×A / X or more. In these batteries, it is considered that the effect of forming the negative electrode film was improved, and the batteries operated stably for a long time even in a high-temperature environment.

[0334] [Examples 1-43 to 1-54 and Reference Example 1-1] For each non-aqueous electrolyte prepared as shown in Table 1-5, the amounts of vinylene carbonate (VC) and sulfate ions (SO) shown in Table 1-5 were added. 4 2- ) was added, and a non-aqueous secondary battery was assembled as described above, and the initial charge / discharge treatment and the final charge / discharge were performed. Then, the output test of the Lami battery A was performed according to the procedure described in (3-4) above. In addition, a cycle test was performed according to the procedure described in (3-3). Here, the content ratio X (mass%) is the ratio of the mass of the non-aqueous electrolyte contained in the battery to the mass of the negative electrode excluding the negative electrode current collector, and in this output test, the amount of electrolyte is the same for each electrolyte, so X=98. Also, A (volume%) is the content of acetonitrile relative to the volume of the non-aqueous solvent. Below, the results of the output test and the cycle test will be explained together, and their interpretation will be described.

[0335] [Table 1-5]

[0336] Examples 1-43 to 1-54 contained a predetermined amount of vinylene carbonate, and the capacity efficiency in the cycle test was 0.19% or less. More preferably, it was 0.17% or less, and there was a tendency for batteries containing ethylene sulfite or sulfate ions to show better capacity efficiency. On the other hand, the ratio of 2C capacity / 0.3C capacity, which indicates output performance, is preferably 83% or more, and more preferably 84% or more. The 2C capacity / 0.3C capacity tended to be higher as the content of acetonitrile increased, and it was possible to achieve both cycle performance and output performance. In addition, it was found that when an electrolyte solution not containing acetonitrile was used as Reference Example 1-1, long-term stability of capacity efficiency and output performance were not compatible.

[0337] (4-1) Preparation of nickel-containing electrodes and non-aqueous secondary batteries The positive electrode active material is a composite oxide of lithium, nickel, manganese and cobalt (LiNi 0.8 Mn 0.1 Co 0.1 O 2) was mixed with carbon black powder as a conductive assistant and polyvinylidene fluoride (PVDF) as a binder in a mass ratio of 94:3:3 to obtain a positive electrode mixture. N-methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture and further mixed to prepare a positive electrode mixture-containing slurry. This positive electrode mixture-containing slurry was applied to one side of an aluminum foil with a thickness of 20 μm to serve as a positive electrode current collector in an amount of 8.4 mg / cm. 2 or 16.6 mg / cm 2 The positive electrode active material layer was then coated while adjusting the density so that the density became 2.91 g / cm. 3 The positive electrodes (1-C6, 1-C7) were obtained by rolling the positive electrode active material layer and the positive electrode current collector so that the coating weight of 1-C6 was 8.4 mg / cm 2 , 1-C7 has a basis weight of 16.6mg / cm 2 Let us assume that.

[0338] Following the procedure for producing the coin batteries described above, a battery (coin 4) combining the positive electrode 1-C6 and the negative electrode 1-A1, and a battery (coin 5) combining the positive electrode 1-C7 and the negative electrode 1-A2 were produced.

[0339] (4-2) Initial charge / discharge treatment of nickel-containing electrodes non-aqueous secondary batteries The ambient temperature of the small non-aqueous secondary battery was set to 25°C, and it was charged at a constant current equivalent to 0.025C until it reached 3.1V, after which it was charged for 1.5 hours at a constant voltage of 3.1V. After a 3-hour pause, the battery was charged at a constant current equivalent to 0.05C until it reached 4.2V, after which it was charged for 1.5 hours at a constant voltage of 4.2V. The battery was then discharged to 3.0V at a constant current equivalent to 0.15C.

[0340] (4-3) Final charge / discharge process After the treatment of (4-1), the ambient temperature of the nonaqueous secondary battery was set to 25°C, and the battery was charged to 4.2V at a constant current of 0.2C. The battery was then charged at a constant voltage of 4.2V for 2 hours or until the current value attenuated to 0.05C. After charging, the battery was rested for 10 minutes. The battery was then discharged to 3.0V at a constant current of 0.2C. The ratio of the discharge capacity to the charge capacity in this operation was calculated as the charge / discharge capacity efficiency (%). The irreversible rate (%) of the charge / discharge capacity was also calculated by subtracting the charge / discharge efficiency from 100.

[0341] (4-4) Non-aqueous secondary battery [Examples 1-55 to 57] Vinylene carbonate and sulfate ions were added to each electrolyte solution prepared in Table 1-1 in the amounts shown in Table 1-6, and nonaqueous secondary batteries were assembled as described above, and initial charge / discharge treatment and final charge / discharge were performed, and the charge / discharge efficiency and the irreversibility rate of the charge / discharge capacity in the final charge / discharge were calculated. Here, the solution content ratio X (mass%) is the ratio of the mass of the nonaqueous electrolyte solution to the mass of the negative electrode excluding the negative electrode current collector, and A (volume%) is the content of acetonitrile relative to the volume of the nonaqueous solvent.

[0342] [Table 1-6]

[0343] When nickel is contained in the positive electrode, the capacity efficiency is preferably 97.0% or more, and more preferably 97.3% or more. The irreversible capacity rate of the capacity is preferably 3% or less, and more preferably 2.7% or less. In Examples 1-55 to 1-57, the irreversible capacity rate was 2.7% or less, and stable operation of the battery was confirmed.

[0344] <Examples and Comparative Examples According to the Second Embodiment>

[0345] (Examples 2-1 to 2-3 and Comparative Examples 2-1 and 2-2) Examples 2-1 to 2-3 and Comparative Examples 2-1 and 2-2 will be described below.

[0346] [Preparation of Positive Electrode] LiFePO as the positive electrode active material 4 The positive electrode mixture was obtained by mixing acetylene black powder as a conductive assistant, carbon nanotubes, and polyvinylidene fluoride (PVDF) as a binder in a mass ratio of 94:2:1:3. N-methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture and further mixed to prepare a positive electrode mixture-containing slurry. The positive electrode mixture-containing slurry was applied to one side of an aluminum foil having a thickness of 15 μm to serve as a positive electrode current collector in an amount of about 9.9 mg / cm. 2 When the positive electrode mixture-containing slurry was applied to the aluminum foil, an uncoated region was formed so that a part of the aluminum foil was exposed. Then, the density of the positive electrode active material layer was adjusted to 2.2 g / cm by roll pressing. 3 By rolling the positive electrode layer so as to obtain a positive electrode composed of the positive electrode active material layer and the positive electrode current collector.

[0347] Next, this positive electrode was cut so that the area of ​​the positive electrode mixture layer was 30 mm × 50 mm and included the exposed part of the aluminum foil. An aluminum lead piece for extracting current was welded to the exposed part of the aluminum foil, and the resulting product was dried in vacuum at 120°C for 12 hours to obtain a positive electrode with a lead.

[0348] [Preparation of negative electrode] A negative electrode mixture was obtained by mixing graphite, a binder, carboxymethyl cellulose, and a latex of styrene butadiene rubber, both of which were binders, in a mass ratio of 100:1.1:1.5. An appropriate amount of water was added to the obtained negative electrode mixture, which was then thoroughly mixed to prepare a negative electrode mixture-containing slurry. This slurry was applied to one side of a copper foil with a thickness of 10 μm, with a basis weight of about 5.1 mg / cm. 2 When the negative electrode mixture-containing slurry was applied to the copper foil, an uncoated area was formed so that part of the copper foil was exposed. Then, the density of the negative electrode active material layer was adjusted to 1.60 g / cm by roll pressing. 3 By rolling the negative electrode so as to obtain a negative electrode composed of the negative electrode active material layer and the negative electrode current collector.

[0349] Next, this negative electrode was cut so that the area of ​​the negative electrode mixture layer was 32 mm × 52 mm and included the exposed part of the copper foil. A nickel lead body for extracting current was welded to the exposed part of the copper foil, and the resultant was dried in vacuum at 80 ° C for 12 hours to obtain a negative electrode with a lead.

[0350] [Battery Construction] [Assembly of single-layer laminate battery] A laminated electrode body was prepared by stacking a lead-attached positive electrode and a lead-attached negative electrode with a polyethylene microporous membrane separator (12 μm thick) between them so that the composite-coated surfaces of the electrodes faced each other. This laminated electrode body was housed in an aluminum laminate sheet exterior body of 90 mm × 80 mm, and vacuum-dried at 80 ° C for 5 hours to remove moisture. Next, 0.4 g of each electrolyte solution shown in Table 2-1 was injected into the exterior body, and the exterior body was sealed to prepare a single-layer laminate type (pouch type) nonaqueous secondary battery (hereinafter also simply referred to as a "single-layer laminate battery" or "single-layer laminate").

[0351] The nonaqueous electrolyte was obtained by mixing each material in an argon glove box with a dew point temperature of −110° C. to −70° C. In Table 2-1, the abbreviations for each material of the nonaqueous electrolyte injected into the secondary battery before the first charge are as follows. LiFSI: Lithium bis(fluorosulfonyl)imide AcN: Acetonitrile EC: Ethylene carbonate VC: Vinylene carbonate ES: Ethylene sulfite EMC: Ethyl methyl carbonate

[0352] [Table 2-1]

[0353] [Evaluation of single-layer laminated batteries] The evaluation batteries obtained as described above were first charged according to the procedure in (1-1) below. Then, the batteries were evaluated according to the procedure in (1-2) below and the procedure for analyzing the components of the negative electrode protective film. Charging and discharging were performed using a charging and discharging device ACD-01 (product name) manufactured by Asuka Electronics Co., Ltd. and a thermostatic bath PLM-63S (product name) manufactured by Futaba Scientific Co., Ltd. In the second embodiment, 1C means a current value at which a fully charged battery is expected to be discharged to completion in one hour when discharged at a constant current.

[0354] (1-1) Initial charge / discharge treatment of single-layer laminate battery The battery was set at an ambient temperature of 25°C and charged at a constant current of 2.1mA (equivalent to 0.1C) until it reached 3.6V, then charged at a constant voltage of 3.6V until the charge capacity reached 1.8mAh. It was then discharged to 2V at a constant current of 2.1mA (equivalent to 0.1C).

[0355] (1-2) Room temperature cycle of single-layer laminate battery The battery was initially charged and discharged according to the method described in (1-1) above. The battery was charged at a constant current of 23 mA, which corresponds to 1 C, at 25° C. and reached 3.6 V. The battery was then discharged at a constant voltage of 3.6 V until the charging current attenuated to 0.05 C. The battery was then discharged at a constant current of 21 mA to 2 V. One cycle was defined as one charge and discharge, and 100 charge and discharge cycles were performed. The rate of change in capacity when the discharge capacity had stopped increasing and the capacity had become constant was calculated based on the initial discharge capacity of the test.

[0356] (Examples 2-4 and 2-5) Examples 2-4 and 2-5 are described below.

[0357] [Preparation of Positive Electrode] LiFePO as the positive electrode active material 4The positive electrode mixture was obtained by mixing acetylene black powder as a conductive assistant and polyvinylidene fluoride (PVDF) as a binder in a mass ratio of 87:8:5. N-methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture and further mixed to prepare a positive electrode mixture-containing slurry. The positive electrode mixture-containing slurry was applied to one side of an aluminum foil having a thickness of 15 μm to serve as a positive electrode current collector in an amount of about 20.7 mg / cm. 2 When the positive electrode mixture-containing slurry was applied to the aluminum foil, an uncoated region was formed so that a part of the aluminum foil was exposed. Then, the density of the positive electrode active material layer was adjusted to 1.9 g / cm by roll pressing. 3 By rolling the positive electrode layer so as to obtain a positive electrode composed of the positive electrode active material layer and the positive electrode current collector.

[0358] Next, this positive electrode was cut so that the area of ​​the positive electrode mixture layer was 29 mm × 56 mm and included the exposed part of the aluminum foil. An aluminum lead piece for extracting current was welded to the exposed part of the aluminum foil, and the resultant was vacuum dried at 120 ° C for 12 hours to obtain a positive electrode with a lead.

[0359] [Preparation of negative electrode] A negative electrode mixture was obtained by mixing graphite, a binder, carboxymethyl cellulose, and a latex of styrene butadiene rubber, which was also a binder, in a mass ratio of 100:1.1:1.5. An appropriate amount of water was added to the obtained negative electrode mixture and then thoroughly mixed to prepare a negative electrode mixture-containing slurry. This slurry was applied to one side of a copper foil having a thickness of 10 μm in a weight ratio of about 8.8 mg / c m 2 When the negative electrode mixture-containing slurry was applied to the copper foil, an uncoated area was formed so that part of the copper foil was exposed. Then, the density of the negative electrode active material layer was adjusted to 1.60 g / cm by roll pressing. 3 By rolling the negative electrode so as to obtain a negative electrode composed of the negative electrode active material layer and the negative electrode current collector.

[0360] Next, this negative electrode was cut so that the area of ​​the negative electrode mixture layer was 31 mm × 58 mm and included the exposed part of the copper foil. A nickel lead body for extracting current was welded to the exposed part of the copper foil, and the resultant was dried in vacuum at 80 ° C for 12 hours to obtain a negative electrode with a lead.

[0361] [Assembly of stacked laminate batteries] A laminated electrode body was prepared by stacking a lead-attached positive electrode and a lead-attached negative electrode through a polyethylene microporous membrane separator (20 μm thick) so that the composite-coated surfaces of the electrodes faced each other. The laminated electrode body was housed in an aluminum laminate sheet exterior body of 90 mm×80 mm, and vacuum-dried at 80° C. for 5 hours to remove moisture. Next, 5.6 g of each of the electrolyte solutions 2-S2 and 2-S3 shown in Table 2-1 above was poured into the exterior body, and the exterior body was sealed to prepare a laminated (pouch-type) nonaqueous secondary battery (hereinafter also simply referred to as a "laminated battery" or "laminated").

[0362] [Evaluation of laminated batteries] The evaluation batteries obtained as described above were first charged according to the procedure in (1-1) below. Then, the batteries were evaluated according to the procedure in (1-2) below and the procedure for analyzing the components of the negative electrode protective film. Charging and discharging were performed using a charging and discharging device ACD-01 (product name) manufactured by Asuka Electronics Co., Ltd. and a thermostatic bath PLM-63S (product name) manufactured by Futaba Scientific Co., Ltd. Here, 1C means the current value at which a fully charged battery is expected to be discharged to completion in 1 hour when discharged at a constant current, as explained above in [Evaluation of Single-Layer Laminate Battery].

[0363] (1-1) Initial charge / discharge treatment of laminated battery The battery was charged at an ambient temperature of 25°C at a constant current of 23 mA, equivalent to 0.025 C, until it reached 3.5 V, and then charged at a constant voltage of 3.5 V until the charge capacity reached 800 mAh. It was then discharged to 2 V at a constant current of 91 mA, equivalent to 0.1 C.

[0364] (1-2) Room temperature cycle of laminated battery The battery was set at an ambient temperature of 25°C, and charged at a constant current of 182mA, equivalent to 1C, until it reached 3.5V. It was then charged at a constant voltage of 3.5V until the current decayed to 0.05C. It was then discharged to 2V at a constant current of 182mA, equivalent to 1C. This operation was repeated 10 times, and the discharge capacity was found to have stabilized by that point. The rate of change in capacity when the increase in discharge capacity had stopped and the capacity had become constant was calculated based on the initial discharge capacity of the test.

[0365] [Analysis of the components of the negative electrode protective coating] The negative electrode protective coating of the example according to the second embodiment is poorly soluble in non-aqueous electrolytes, and therefore has low solubility in organic solvents. Therefore, heavy water was used to extract the negative electrode protective coating. In addition, as a method for analyzing the components of the negative electrode protective coating, IC measurement was used for the compound represented by the above general formula (a), and NMR measurement was used for the compounds represented by the above general formulas (b) to (d). The molar ratio of each compound to the total content of (a) to (d) was calculated assuming that the molar mass of each compound was 25.94 g / mol for (a), 161.95 g / mol for (b), 96.01 g / mol for (c), and 81.98 g / mol for (d).

[0366] (Extraction of negative electrode coating components) Under an argon atmosphere, one negative electrode was taken out from the single-layer laminate battery or multi-layer laminate battery after the test, and a negative electrode piece (including the current collector) measuring 3 mm square was cut out and placed in a glass screw tube, into which 1.5 mL of heavy water was injected using a syringe and sealed with a lid. After leaving the tube to stand for 72 hours to extract the electrode coating, the tube was filtered through a cotton plug using a Pasteur pipette filled with glass wool to obtain an extract.

[0367] (IC measurement) The extract was diluted 1000-fold with distilled water, and 30 μL of the diluted solution was injected into the column to perform IC measurement. The measurement device was a Tosoh IC-2010, and the column was a Tosoh TSKgel-SuperIC-AZ, with the column temperature set at 40°C and the flow rate set at 0.8 mL / min.

[0368] (NMR measurement) The obtained extract was placed in an NMR tube with a diameter of 3 mm and sealed. Separately, tetrafluorobenzene (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved as a standard substance in deuterated chloroform (manufactured by Sigma-Aldrich) containing tetramethylsilane as a chemical shift standard, and the solution was placed in an NMR tube with a diameter of 5 mm. The above NMR tube with a diameter of 3 mm was inserted into this NMR tube, and the double tube method was used. 1 H NMR measurements were performed. In addition, a heavy water solution of dimethyl sulfoxide (concentration 0.398 mg / mL) was prepared as a quantitative standard substance, and 1 H NMR measurements were performed. The measurement device used was a JNM-ECS-400 FT NMR device manufactured by JEOL RESONANCE Co., Ltd. Deuterated chloroform was used as the lock solvent, the number of integrations was 256, and tetramethylsilane (0 ppm) was used as the chemical shift standard. Quantitative calculations were performed by taking the integral value of the peak attributed to the protons of tetrafluorobenzene as 2000 and calculating the integral value corresponding to one proton per unit concentration from the integral value of the signal of the standard substance, dimethyl sulfoxide, and using this value to calculate from the integral value of each peak.

[0369] [Analysis of non-aqueous electrolyte components] Under an argon atmosphere, an incision was made in the laminate exterior of the single-layer laminate battery or multi-layer laminate battery after the test, and the non-aqueous electrolyte was collected from the inside with a syringe, placed in an NMR tube with a diameter of 3 mm, and diluted with dimethoxyethane. Separately, tetrafluorobenzene (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved as a standard substance in deuterated chloroform (manufactured by Sigma-Aldrich) containing tetramethylsilane as a chemical shift standard, and placed in an NMR tube with a diameter of 5 mm. The NMR tube with a diameter of 3 mm was inserted into this NMR tube, and the double tube method was used to measure the non-aqueous electrolyte. 1 H NMR measurements were performed. In addition, a heavy water solution of dimethyl sulfoxide (concentration 0.398 mg / mL) was prepared as a quantitative standard substance, and 1 H NMR measurements were performed. The weight ratio of each component was calculated from the integral value of the signal of each component normalized with a standard substance.

[0370] The evaluation results for each example according to the second embodiment will be discussed below. Table 2-2 shows the initial discharge capacity of the cycle test relative to the design capacity for the single-layer laminate. Here, in calculating the design capacity, it is assumed that the capacity of 170 mAh can theoretically be extracted per gram of lithium iron phosphate, which is the positive electrode active material, and the ratio of active material in the positive electrode (94%) and the coating area (15 cm2) are taken into consideration. 2 ) The design capacity of this single-layer laminated battery was calculated to be 23.7mAh. In addition, the rate of change in capacity when the increase in discharge capacity stops and the capacity becomes constant is calculated based on the initial discharge capacity of the test.

[0371] [Table 2-2]

[0372] In the secondary battery containing acetonitrile in the non-aqueous electrolyte and having a constant composition ratio of the coating component after the test, a capacity of 77% or more of the design capacity was obtained in the first discharge, and the rate of change in capacity until the discharge capacity stabilized to a constant value was small at 2.1% or less. On the other hand, in Comparative Example 2-1, which does not contain acetonitrile and has a coating component ratio of (c) and (d) exceeding 20 mol%, only a capacity of less than 73% of the design capacity was obtained, and the rate of change in capacity until the discharge capacity stabilized to a constant value was 5.6%, and the capacity was unstable. In Comparative Example 2-2, in which the remaining vinylene carbonate in the battery was gone when the SEI was formed, the first charge and discharge could not be performed. In this way, by having a certain amount of vinylene carbonate remaining in the battery even after the coating was formed, there was a tendency for the battery capacity to be quickly stabilized while forming a good coating against the electrolyte containing acetonitrile.

[0373] Table 2-3 below shows the ratio of the initial discharge capacity of the cycle test to the design capacity for the laminate. Here, in calculating the design capacity, it is assumed that the capacity of 170 mAh can be theoretically extracted per gram of lithium iron phosphate, which is the positive electrode active material, and the ratio of the active material in the positive electrode (87%) and the coating area (16.24 cm2) are taken into consideration. 2) and the number of electrode layers (24), the design capacity of this laminated battery was calculated to be 1193mAh. In addition, the rate of change in capacity when the discharge capacity increase ended and the capacity became constant was calculated based on the initial discharge capacity of the test.

[0374] [Table 2-3]

[0375] In Examples 2-4 and 2-5, the specified coating was formed, and a capacity of 75% or more of the designed capacity was obtained. Furthermore, the rate of change until the capacity stabilized was sufficiently small at 1.1% or less in both cases, and relatively rapid capacity stabilization was observed.

[0376] <Example III according to the third embodiment and Comparative Example III> (1) Preparation of non-aqueous electrolyte In an inert atmosphere, various non-aqueous solvents and various additives were mixed to a predetermined concentration, and various lithium salts were added to a predetermined concentration to prepare non-aqueous electrolyte solutions (3-S1) to (3-S14). The abbreviations of the non-aqueous solvents, lithium salts, and additives in Table 3-1 have the following meanings. (Lithium salts) LiFSI: Lithium bis(fluorosulfonyl)imide LiPF 6 : Lithium hexafluorophosphate (Non-aqueous solvent or additive) AcN: Acetonitrile EMC: Ethyl methyl carbonate EC: Ethylene carbonate ES: Ethylene sulfite VC: Vinylene carbonate

[0377] [Table 3-1]

[0378] (2) Preparation of non-aqueous secondary battery (2-1) Preparation of positive electrode (A) LiNi as the positive electrode active material 0 . 5 Co 0 . 2 Mn 0 . 3 O 2 (NCM523) or LiFePO 4 (LFP), (B) carbon black powder as a conductive assistant, and (C) polyvinylidene fluoride (PVDF) as a binder were mixed in a specific mass ratio shown in Table 3-2 to obtain a positive electrode mixture.

[0379] The obtained positive electrode mixture was mixed with N-methyl-2-pyrrolidone as a solvent to prepare a positive electrode mixture-containing slurry. The positive electrode mixture-containing slurry was applied to one or both sides of an aluminum foil having a thickness of 15 μm as a positive electrode current collector while adjusting the basis weight, and the solvent was dried and removed in a hot air drying oven. Then, the density of the positive electrode active material layer was adjusted to 1.9 g / cm by roll pressing. 3 The positive electrodes (3-C1, 3-C2) were obtained by rolling the positive electrode active material layer and the positive electrode current collector so that the positive electrode active material layer and the positive electrode current collector were formed. The positive electrodes were then obtained by vacuum drying at 80° C. for 12 hours or more. The basis weight excluding the positive electrode current collector is shown in Table 3-2.

[0380] (2-2) Preparation of negative electrode (a) Graphite as a negative electrode active material, (b) a conductive additive (carbon black), and (c) a binder were mixed in the mass ratio shown in Table 2 to obtain a negative electrode mixture.

[0381] The obtained negative electrode mixture was mixed with water as a solvent to prepare a negative electrode mixture-containing slurry. The slurry was applied to one or both sides of a copper foil having a thickness of 10 μm to be used as a negative electrode current collector, and the solvent was dried and removed in a hot air drying oven. Then, the density of the negative electrode active material layer was adjusted to 1.4 g / cm by roll pressing. 3 The negative electrode (3-A1) was obtained by rolling the negative electrode active material layer and the negative electrode current collector. The negative electrode was then obtained by vacuum drying at 80° C. for 12 hours or more. The weight of the negative electrode active material layer is shown in Table 3-2.

[0382] [Table 3-2]

[0383] (2-3) Preparation of separator <Preparation of polypropylene resin composition> Ultra-high molecular weight polypropylene resin (PP, MFR = 0.25) and ethylene / 1-butene copolymer (C2 / C4: density = 0.893 g / cm 3 The pellets of PP:C2 / C4 (melting point = 80°C, MFR = 6.7) were dry-blended in a mass ratio of PP:C2 / C4 = 50:50 (mass%), and then melt-kneaded using ZSK40 (manufactured by Coperion, L / D = 46). In order to minimize the decomposition and denaturation of the resin, the resin inlet hopper to the raw material tank was completely sealed, and nitrogen was continuously flowed from the bottom of the hopper to control the oxygen concentration near the raw material inlet to 50 ppm or less. In addition, all vents were completely sealed to eliminate air leakage into the cylinder. This oxygen concentration reduction effect significantly suppressed the decomposition and denaturation of the polymer even under high temperature conditions, and further enabled the fine dispersion of the ethylene / 1-butene copolymer. After melt-kneading, the strand was pulled from the die (8 holes) and the molten kneaded product was cooled in a water-cooled bath, and then cut using a pelletizer to obtain pellets.

[0384] <Preparation of microporous membrane (single layer)> The pellets were dry-blended with ultra-high molecular weight polypropylene resin (PP, MFR = 0.25) in a mass ratio of PP:pellets = 90:10 (mass%), then melted in a 2.5-inch extruder and fed to an annular die using a gear pump. This resulted in a resin charge ratio of PP:C2 / C4 = 95:5 (mass%).

[0385] The die temperature was set to 230°C, and the molten polymer was cooled by blown air and then wound up on a roll. The extruded precursor (raw film) had a thickness of 15 μm, and the raw film was then annealed at 130°C for 15 minutes. The annealed film was then cold stretched to 21% at room temperature, then hot stretched to 156% at 120°C, and relaxed to 126% at 125°C to form a separator (F1) having a structure with a single layer of microporous membrane. After the above stretching and perforation, the physical properties of the microporous membrane were measured.

[0386] (2-4) Assembly of small non-aqueous secondary batteries The positive electrode (3-C1) obtained as described above was punched out into a disk shape having a diameter of 15.958 mm, and the negative electrode (3-A1) obtained as described above was punched out into a disk shape having a diameter of 16.156 mm. These were then used to form the separator (F1) obtained as described above (pore size ratio 8.1, film thickness 25 μm, air resistance 217 sec / 100 cm 3 A laminate was obtained by overlapping the laminate on both sides of a 3-C1 / F1 / 3-A1 laminate (porosity: 55%). The laminate was inserted into a disk-shaped battery case made of SUS. Next, a predetermined amount of non-aqueous electrolyte was poured into the battery case, and the laminate was immersed in the non-aqueous electrolyte. The battery case was then sealed, and the non-aqueous electrolyte was allowed to fully penetrate the laminate to obtain a small non-aqueous secondary battery (3-C1 / F1 / 3-A1).

[0387] Using the same procedure, 3-C2 was used for the positive electrode, 3-A1 for the negative electrode, and separator F1 (pore size ratio 8.1, film thickness 25 μm, air resistance 217 sec / 100 cm 3 A small nonaqueous secondary battery (3-C2 / F1 / 3-A1) was obtained using a 3-C2 / F1 / 3-A1 composite material with a porosity of 55%.

[0388] (3) Evaluation of small non-aqueous secondary batteries The small non-aqueous secondary batteries obtained as described above were first subjected to an initial charge process and an initial charge / discharge capacity measurement according to the procedure in (3-1) below. Next, each small non-aqueous secondary battery was evaluated according to the procedure in (3-2). Charging and discharging were performed using a charge / discharge device ACD-M01A (product name) manufactured by Asuka Electronics Co., Ltd. and a programmable thermostatic chamber IN804 (product name) manufactured by Yamato Scientific Co., Ltd.

[0389] In the third embodiment, 1C means a current value at which a fully charged battery is expected to be discharged completely in one hour when discharged at a constant current.

[0390] Specifically, for the small nonaqueous secondary battery (3-C1 / F1 / 3-A1), 1C means the current value expected to be discharged from a fully charged state of 4.2 V to 2.5 V at a constant current, with the discharge expected to be completed in one hour. For the small nonaqueous secondary battery (3-C2 / F1 / 3-A1), 1C means the current value expected to be discharged from a fully charged state of 3.6 V to 2.0 V at a constant current, with the discharge expected to be completed in one hour.

[0391] The small non-aqueous secondary batteries (3-C1 / F1 / 3-A1, 3-C2 / F1 / 3-A1) assembled according to the procedure in (2-4) above are 3mAh class cells, and the battery voltages in a fully charged state are set to 4.2V and 3.6V, and the current value equivalent to 1C is set to 3mA. Hereinafter, unless otherwise specified, the notation of current value and voltage will be omitted for convenience.

[0392] (3-1) Initial charge / discharge treatment of small non-aqueous secondary batteries The ambient temperature of the small non-aqueous secondary battery (3-C1 / F1 / 3-A1 or 3-C2 / F1 / 3-A1) was set to 25°C, and the battery was charged at a constant current equivalent to 0.1C until it reached a fully charged state, after which it was charged at a constant voltage for 1.5 hours. The initial efficiency was calculated by dividing the discharge capacity when charging and discharging at 0.1C by the charge capacity. For batteries with an initial efficiency of less than 80%, the specified battery capacity was not met, and it was difficult to obtain correct evaluation results, so subsequent evaluation tests could not be carried out.

[0393] (3-2) Two-stage electrolyte injection process for small non-aqueous secondary batteries For the cells that had been subjected to the initial charge / discharge treatment by the method (3-1) above, the battery case was opened in an argon (Ar) box, electrolyte was added using a pipette, and the cells were then fully charged at a constant current equivalent to 1 C, and discharged twice at a constant current equivalent to 1 C. The compositions and volumes of the initial electrolyte injection and the two-stage electrolyte injection for each cell are shown in Table 3-3.

[0394] [Table 3-3]

[0395] (3-3) Output test of small non-aqueous secondary batteries (3-C1 / F1 / 3-A1) The small nonaqueous secondary battery (3-C1 / F1 / 3-A1) that had been subjected to the initial charge / discharge treatment and two-stage electrolyte injection by the methods described in (3-1) and (3-2) above was charged at a constant current of 1 C at an ambient temperature of 25° C. until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value attenuated to 0.025 C. It was then discharged at 0.1 C to 2.8 V.

[0396] Next, the battery was charged at a constant current of 1 C until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value attenuated to 0.025 C. It was then discharged at 0.5 C to 2.8 V. Next, the battery was charged at a constant current of 1 C until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value attenuated to 0.025 C. It was then discharged at 1.0 C to 2.8 V. Next, the battery was charged at a constant current of 1 C until it reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value attenuated to 0.025 C. It was then discharged at 5.0 C to 2.8 V. Next, the battery was charged at a constant current of 1C until it reached 4.2V, and then charged at a constant voltage of 4.2V until the current value attenuated to 0.025C. It was then discharged at 10C to 2.8V. Next, the battery was charged at a constant current of 1 C until it reached 3.5 V, and then charged at a constant voltage of 3.5 V until the current value attenuated to 0.025 C. It was then discharged at 20 C to 2.0 V. Next, the battery was charged at a constant current of 1C until it reached 4.2V, and then charged at a constant voltage of 4.2V until the current value attenuated to 0.025C. It was then discharged at 0.1C to 2.8V. The discharge capacity at each discharge rate was recorded.

[0397] (3-4) Cycle test of small non-aqueous secondary battery (3-C2 / F1 / 3-A1) The small nonaqueous secondary battery (3-C2 / F1 / 3-A1) that had been subjected to the initial charge / discharge treatment and two-stage electrolyte injection by the methods described in (3-1) and (3-2) above was charged at a constant current of 1 C at an ambient temperature of 25° C. until it reached 3.5 V, and then charged at a constant voltage of 3.5 V until the current value attenuated to 0.025 C. It was then discharged at 0.1 C to 2.7 V.

[0398] The ambient temperature was set to 25°C for the small non-aqueous secondary battery (3-C2 / F1 / 3-A1) that had been subjected to two-stage injection according to the method described in (3-2) above. First, the battery was charged at a constant current of 3mA equivalent to 1C until it reached 4.2V, and then charged at a constant voltage of 4.2V until the current attenuated to 0.025C. The battery was then discharged to 2.7V at a constant current of 3mA. This process of charging and discharging once each constitutes one cycle, and 100 cycles of charging and discharging were performed. The discharge capacity at the 100th cycle, when the discharge capacity at the first cycle was taken as 100%, was taken as the capacity retention rate of the 25°C cycle test. Similarly, the capacity retention rate at the 50th cycle was also obtained.

[0399] (4) XPS analysis of negative electrode coating The negative electrode film of the small non-aqueous secondary battery prepared and tested as described above was analyzed after two-step injection and two-cycle charging and discharging as described above (3-2). The battery was disassembled in an air-free environment, the negative electrode was removed, and the electrolyte was removed by immersing it in EMC for 5 minutes, and then vacuum dried at room temperature to obtain a sample. The obtained sample was held in a sample holder in an inert atmosphere and subjected to XPS measurement. The relative element concentration ratio (Sred / Li) of the compound containing a sulfur atom with a valence of -2 or more and 0 or less, and the Li compound, which are generated by the reduction of ES contained in the negative electrode film, was measured. The XPS measurement was performed using Versa Probe II manufactured by ULVAC-PHI, Inc., and the measurement conditions are shown below.

[0400] [Measurement conditions] Excitation source: mono.AlKα 20kV×5mA 100W Analysis size: 100μmφ×1.4mm 100μmφ X-ray beam vibrates with a width of 1.4mm Photoelectron extraction angle: 45° Capture Area Survey scan: 0~1,100eV Narrow scan:C 1s, O 1s, Li 1s, S 2p, F 1s, N 1s, Cu 2p3 / 2 Pass Energy Survey scan: 117.4eV Narrow scan: 46.95eV

[0401] The method for deriving the relative element concentrations of sulfur atoms and Li compounds with a valence of -2 to 0 is shown below. [Derivation of relative element concentrations] The following formula was used to calculate the value.

number

[0402] Furthermore, the S concentration was quantified by curve fitting the S 2p spectrum, which is a reduced sulfur component, Sred. Sred:162~164eV The components are sufficiently discrete that valleys between peaks can be observed, and the purpose of this curve fitting process is to quantitatively separate the components. Therefore, no constraints were placed on the components during curve fitting.

[0403] [Examples 3-1 to 3-2, Comparative Example 3-1] Here, we will explain the composition of the negative electrode coating of the small nonaqueous secondary battery (3-C1 / F1 / 3-A1) and the interpretation of the output test results. The small nonaqueous secondary battery (3-C1 / F1 / 3-A1) was fabricated according to the method described in (2) above. Next, the preparation of each small nonaqueous secondary battery (3-C1 / F1 / 3-A1) and the negative electrode coating and output performance were evaluated according to the procedures described in (3) and (4) above. The test results are shown in Table 3-4.

[0404] [Table 3-4]

[0405] As shown in Table 3-4, Examples 3-1 and 3-2 are characterized in that the ratio (Sred / Li) of compounds containing sulfur atoms with a valence of -2 to 0 in the negative electrode coating after two-stage injection is 0.1% to 3.80%, and it was confirmed that the smaller the Sred / Li value, the higher the discharge capacity at a high rate. On the other hand, it was confirmed that the Sred / Li value in the cell (Comparative Example 3-1) in which two-stage injection was not performed was more than 3.80%, and the discharge capacity was also low.

[0406] With the two-stage injection, charging and discharging is performed with an electrolyte having a lower acetonitrile concentration than the electrolyte composition after the two-stage injection in the first injection, and then, by adding a higher concentration of acetonitrile, it is possible to suppress excessive reductive decomposition of the electrolyte on the negative electrode surface while maintaining high ionic conductivity. As a result, it is believed that good output performance was obtained.

[0407] [Examples 3-3 to 3-6, Comparative Examples 3-2 to 3-4] Here, we will explain the interpretation of the test results of the small nonaqueous secondary battery (3-C2 / F1 / 3-A1). The small nonaqueous secondary battery (3-C2 / F1 / 3-A1) was fabricated according to the method described in (2) above. Next, the preparation of each small nonaqueous secondary battery (3-C2 / F1 / 3-A1) and the negative electrode coating and cycle performance were evaluated according to the procedures described in (3) and (4) above. The test results are shown in Table 3-5.

[0408] [Table 3-5]

[0409] As shown in Table 3-5, in the cells to which two-stage injection was applied, the Sred / Li value was 3.80% or less, and in the cells to which only the first injection was applied (Comparative Examples 3-2 to 3-4), the Sred / Li value did not tend to decrease even when the amount of VC was increased. On the other hand, in the cells to which two-stage injection was applied, the Sred / Li value tended to decrease with an increase in VC.

[0410] Cells that only underwent an initial electrolyte injection showed a low initial charge / discharge efficiency of less than 40% and a decrease in capacity retention during the cycles, whereas the application of the two-stage electrolyte injection confirmed that a battery with high stability during charging and discharging could be obtained, even if the final electrolyte composition was the same.

[0411] In addition, in the two-stage injection method, when the amount of VC was the same, it was confirmed that the cycle performance tended to be higher as the acetonitrile concentration of the initial injection electrolyte was lower.

[0412] By reducing the acetonitrile concentration of the initial electrolyte injection, it is possible to suppress excessive reductive decomposition of the electrolyte on the negative electrode surface during the initial charge, and it is believed that deterioration is suppressed by making the negative electrode coating uniform.

[0413] According to the non-aqueous lithium ion secondary battery containing acetonitrile to which the two-stage injection according to the third embodiment of the present invention is applied, in addition to suppressing excessive reductive decomposition of the electrolyte on the negative electrode surface, good output performance and cycle performance can be obtained by strengthening the negative electrode SEI with a small amount of negative electrode additive. Therefore, if a non-aqueous secondary battery using an acetonitrile electrolyte has the composition of the negative electrode coating as described above in the state in which the initial charge is performed, it can be assumed that the manufacturing process of the non-aqueous electrolyte according to the third embodiment is included. [Industrial Applicability]

[0414] The nonaqueous electrolyte solution and nonaqueous secondary battery according to the present invention are expected to be used, for example, as automotive storage batteries for hybrid automobiles, plug-in hybrid automobiles, electric automobiles, and the like, as well as industrial storage batteries for power tools, drones, electric motorcycles, and the like, and further as residential electricity storage systems. [Explanation of symbols]

[0415] 100 Nonaqueous secondary battery 110 Battery housing 120 Space in battery housing 130 Positive electrode lead body 140 Negative electrode lead body 150 positive electrode 160 negative electrode 170 Separator

Claims

1. A non-aqueous electrolyte for a non-aqueous lithium ion secondary battery having a negative electrode containing graphite, the non-aqueous electrolyte being X% by mass relative to a negative electrode mass excluding a negative electrode current collector, X is equal to or greater than 50 and equal to or less than 200; The non-aqueous electrolyte solution contains a lithium salt and a non-aqueous solvent, The non-aqueous solvent contains A% by volume of acetonitrile relative to the volume of the non-aqueous solvent, A is 5 or more and 70 or less, and The non-aqueous electrolyte solution contains vinylene carbonate (VC) as an additive, and the content of VC is (7×A / X) mass% or more and 10 mass% or less with respect to the non-aqueous electrolyte solution. Non-aqueous electrolyte.

2. The nonaqueous electrolyte solution according to claim 1 , wherein A is 16 or more and 35 or less.

3. The non-aqueous electrolyte solution according to claim 1 or 2, wherein the content of VC is from (15×A / X) mass% to 9 mass% with respect to the non-aqueous electrolyte solution.

4. The nonaqueous electrolyte solution according to claim 3 , wherein X is 98 or less.

5. The non-aqueous electrolyte solution according to claim 1 or 2, comprising ethylene sulfite.

6. 3. The nonaqueous electrolyte solution according to claim 1, further comprising at least one of a sulfate ion and a sulfite ion.

7. The non-aqueous electrolyte solution according to claim 1 or 2, wherein the content of the VC is 7 mass% or less relative to the non-aqueous electrolyte solution.

8. The nonaqueous electrolyte solution according to claim 1 or 2, wherein X is 65 or more.

9. 2. A non-aqueous lithium ion secondary battery comprising: a positive electrode having a positive electrode active material layer on one or both sides of a positive electrode current collector; a negative electrode having a negative electrode active material layer containing the graphite on one or both sides of the negative electrode current collector; a separator; and the non-aqueous electrolyte solution according to claim 1.

10. A non-aqueous secondary battery comprising a negative electrode, a positive electrode, a separator, and the non-aqueous electrolyte solution according to claim 1, The nonaqueous secondary battery has been charged at least once; The negative electrode of the nonaqueous secondary battery contains at least one type of inorganic lithium compound and at least one type of organic lithium compound that can be extracted by immersion in an extraction solvent.

11. The negative electrode comprises a component that can be extracted from the negative electrode by using water as the extraction solvent, and the component comprises at least the following inorganic lithium compound (a): (a) LiF and at least the following organolithium compounds (b) to (d): (b)LiOCOOCH ２ CH ２ OCOOLi (c)CH ３ CH ２ OCOOLi (d)CH ３ OCOOLi and The nonaqueous secondary battery according to claim 10, wherein the molar ratios of the components (a) to (d) relative to the total content of the components (a) to (d) are, respectively, 20 to 70 mol% for the component (a), 20 to 70 mol% for the component (b), 1 to 20 mol% for the component (c), and 1 to 20 mol% for the component (d).

12. 12. The nonaqueous secondary battery according to claim 10, wherein the nonaqueous electrolyte solution contains ethylene carbonate and the vinylene carbonate (VC), and the molar ratio of the vinylene carbonate (VC) to the ethylene carbonate is 0.01 to 30 mol%.

13. The nonaqueous secondary battery according to claim 10 or 11, wherein the positive electrode active material of the positive electrode contains lithium iron phosphate.

14. 13. A process for producing a secondary battery comprising at least two electrolyte injection steps of injecting a nonaqueous electrolyte into a battery exterior, at least one charging step being performed after a first electrolyte injection step and before a final electrolyte injection step, in which an electrolyte having a higher volumetric ratio of acetonitrile to the entire electrolyte than the electrolyte used in the first electrolyte injection step is injected into the battery exterior in an electrolyte injection step subsequent to the first, and finally comprising the nonaqueous electrolyte according to claim 1.

15. 15. The process for producing a secondary battery according to claim 14, wherein in the electrolyte injection step after the first injection, the electrolyte containing 20% ​​by volume or more and 100% by volume or less of the acetonitrile is injected into the battery exterior.

16. A method for obtaining a nonaqueous secondary battery comprising the nonaqueous electrolyte solution according to claim 1, a positive electrode having a positive electrode active material layer on one or both sides of a positive electrode collector, a negative electrode having a negative electrode active material layer on one or both sides of a negative electrode collector, and a separator, wherein the nonaqueous electrolyte solution contains 5 volume % or more and 60 volume % or less of the acetonitrile and ethylene sulfite, and contains in a negative electrode coating after an initial charge and discharge a compound containing a sulfur atom having a valence of -2 or more and 0 or less, the compound containing at least one of sulfur and copper sulfide, and having at least one charging step after an initial electrolyte injection step and before a final electrolyte injection step, and in an electrolyte injection step after the initial one, an electrolyte having a higher volume ratio of the acetonitrile to the entire electrolyte than the electrolyte used in the initial electrolyte injection step is injected into the battery exterior.

17. The method according to claim 16, wherein the concentration of ethylene sulfite in the non-aqueous electrolyte solution is 0.01% by volume or more and 4% by volume or less.

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