Lithium ion battery and manufacturing method for lithium ion battery

Abstract

To provide a lithium ion battery and a manufacturing method for the lithium ion battery, in which an aging time required for detecting a conductive foreign substance mixed into the lithium ion battery can be shortened and the corrosion of a member such as a current collector and a lithium ion battery active material can be suppressed.SOLUTION: A lithium ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte solution. The electrolyte solution contains LiFSI. The positive electrode, the negative electrode, and the separator are battery members. A chlorine element is contained by 0.0001 ppm or more and 2,200 ppm or less relative to the entire battery members.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a lithium-ion battery and a method for manufacturing a lithium-ion battery. [Background technology]

[0002] If conductive foreign matter such as metal gets into a lithium-ion battery, a short circuit may occur between the positive and negative electrodes during use, causing a drop in voltage and heat generation. Therefore, during the manufacturing process of lithium-ion batteries, batteries that have been contaminated with conductive foreign matter are detected and removed from the product as defective products.

[0003] Patent Document 1 describes a technique for detecting conductive foreign matter that has become mixed into a lithium-ion battery. Patent Document 1 discloses a method for inspecting a lithium secondary battery for the presence or absence of conductive foreign matter in the battery, which has a positive electrode using a lithium transition metal composite oxide as the positive electrode active material and a negative electrode using a carbon material as the negative electrode active material, arranged with a polyolefin separator between them, the method comprising the steps of charging the lithium secondary battery at least once, determining the voltage drop after leaving the lithium secondary battery for a predetermined period of time at an environmental temperature of 45°C or higher, and determining that the conductive foreign matter is present in the lithium secondary battery if the determined voltage drop is greater than a preset voltage drop standard. Patent Document 1 describes that if a conductive foreign object is present between the positive and negative electrodes and the separator, and the lithium secondary battery is left for a predetermined time at an environmental temperature of 45° C. or higher, the conductive foreign object will grow a conductive crystal, and the conductive foreign object will penetrate the separator in a short time, causing an internal short circuit, resulting in a voltage drop that exceeds a normal voltage drop. Patent Document 1 also describes that the inspection method of Patent Document 1 focuses on this principle, determines the voltage drop after the battery is left for a predetermined time, and determines that a conductive foreign object is present in the lithium secondary battery if the determined voltage drop is greater than a preset voltage drop standard. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-158643 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a lithium ion battery and a method for manufacturing a lithium ion battery that can shorten the aging time required to detect conductive foreign matter that has become mixed into the lithium ion battery and can suppress corrosion of components such as current collectors and lithium ion battery active materials. [Means for solving the problem]

[0006] That is, according to the present invention, there are provided a lithium ion battery and a method for manufacturing a lithium ion battery as described below. [1] A lithium ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, the electrolyte comprises LiFSI; a lithium ion battery having the positive electrode, the negative electrode and the separator as battery components, the battery components having a chlorine element content of 0.0001 ppm or more and 2200 ppm or less. [2] The lithium ion battery according to [1] above, wherein the content of the LiFSI in the electrolyte is 0.001 mol / L or more and 5 mol / L or less. [3] The lithium ion battery according to the above [1] or [2], wherein the electrolyte further contains a lithium salt other than LiFSI. [4] The lithium ion battery according to [3] above, wherein the content of the lithium salt different from LiFSI is 0.001 mol / L or more and 5 mol / L or less. [5] The lithium ion battery according to any one of the above [1] to [4], wherein the electrolytic solution further contains a solvent. [6] The lithium ion battery according to [5] above, wherein the solvent contains a carbonate. [7] The lithium ion battery according to any one of the above [1] to [6], wherein the content of chlorine element in the positive electrode is 0.0001 ppm or more and 2200 ppm or less. [8] The lithium ion battery according to any one of the above [1] to [7], wherein the positive electrode contains a lithium-containing composite oxide. [9] The lithium ion battery according to any one of the above [1] to [8], wherein the content of chlorine element in the negative electrode is 0.0001 ppm or more and 2200 ppm or less.

[10] The lithium ion battery according to any one of the above [1] to [9], wherein the negative electrode contains a carbonaceous material.

[11] The lithium ion battery according to any one of the above [1] to

[10] , wherein the negative electrode contains a styrene-butadiene rubber.

[12] The lithium ion battery according to any one of the above [1] to

[11] , wherein the negative electrode contains carboxymethyl cellulose.

[13] The lithium ion battery according to any one of the above [1] to

[12] , wherein the content of chlorine element in the separator is 0.0001 ppm or more and 2200 ppm or less.

[14] The lithium ion battery according to any one of the above [1] to

[13] , wherein the separator includes the substrate and a ceramic layer provided on at least one surface of the substrate.

[15] The lithium ion battery according to any one of the above [1] to

[14] , wherein the separator includes a substrate and an adhesive layer.

[16] A method for producing a lithium ion battery according to any one of the above [1] to

[15] , A method for manufacturing a lithium ion battery, comprising an aging step of aging a lithium ion battery.

[17] a foreign object detection step of detecting the presence or absence of a conductive foreign object in the lithium ion battery by measuring an amount of voltage drop of the lithium ion battery during the aging step and comparing the amount of voltage drop with a reference value; a sorting step of sorting out lithium ion batteries in which the conductive foreign matter is not detected as non-defective products; The method for producing a lithium ion battery according to

[16] above, further comprising:

[18] The method for producing a lithium ion battery according to the above

[16] or

[17] , wherein the environmental temperature in the aging step is 0°C or higher and 100°C or lower.

[19] The method for producing a lithium ion battery according to any one of the above

[16] to

[18] , wherein the aging time in the aging step is from 1 hour to 720 hours.

[20] The method for producing a lithium ion battery according to any one of the above

[16] to

[19] , further comprising discharging the lithium ion battery after the aging step, and setting the voltage of the lithium ion battery in the foreign matter detection step to 2.5 V or more and 4.5 V or less. Effect of the Invention

[0007] According to the present invention, a lithium ion battery and a method for manufacturing a lithium ion battery are provided that can shorten the aging time required to detect conductive foreign matter that has become mixed into a lithium ion battery and can suppress corrosion of components such as current collectors and lithium ion battery active materials. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the present invention will be described based on an embodiment.

[0009] [Lithium-ion battery] The lithium ion battery according to this embodiment will be described below.

[0010] The lithium ion battery according to this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte, the electrolyte including LiFSI, the positive electrode, the negative electrode, and the separator being battery components, and the chlorine content of the entire battery components is 0.0001 ppm or more and 2200 ppm or less. The content of elemental chlorine in the entire battery components can be obtained by dividing the total mass (b) of elemental chlorine contained in each battery component by the total mass (a) of each battery component. In other words, the content of elemental chlorine in the entire battery components is the value of (b) / (a).

[0011] From the viewpoint of further shortening the aging time, the content of chlorine element in the entire battery components is preferably 0.0002 ppm or more, more preferably 0.00025 ppm or more, even more preferably 0.0005 ppm or more, even more preferably 0.00075 ppm or more, even more preferably 0.001 ppm or more, even more preferably 0.0025 ppm or more, even more preferably 0.005 ppm or more, even more preferably 0.0075 ppm or more, even more preferably 0.01 ppm or more, even more preferably 0.025 ppm or more, even more preferably 0.05 ppm or more, even more preferably 0.075 ppm or more, even more preferably 0.1 ppm or more, and from the viewpoint of further suppressing corrosion of battery components, it is preferably 2000 ppm or less, more preferably 1000 ppm or less, even more preferably 750 ppm or less, even more preferably 500 ppm or less, even more preferably 250 ppm or less, even more preferably 200 ppm or less, even more preferably 100 ppm or less, even more preferably 50 ppm or less, even more preferably 25 ppm or less, even more preferably 10 ppm or less, even more preferably 5 ppm or less, and even more preferably 2 ppm or less. The method for quantifying the amount of chlorine in the battery material of the lithium ion battery according to the present embodiment is not particularly limited, and can be performed by a known method such as ion chromatography. Ion chromatography is preferred because it has a low detection limit and high reliability. As a method for preparing a solution for ion chromatography from the battery material, for example, a method of dissolving a chlorine-containing gas generated by burning the battery material in a solvent to prepare a solution can be mentioned.

[0012] The present inventors have found through their investigations that when the battery components contain chlorine element, the chlorine element in the battery components dissolves into the electrolyte, causing the electrolyte to contain chlorine element. The present inventors further investigated the battery characteristics when the electrolyte contains chlorine element. As a result, it was found that the aging time until foreign matter is detected in the battery can be shortened when chlorine element and lithium bis(fluorosulfonyl)imide (LiFSI) coexist in the electrolyte. The mechanism by which the aging time is shortened is not clear, but it is speculated that when chlorine element and LiFSI coexist in the electrolyte, the chlorine element first destroys the passive film on the surface of the conductive foreign matter, thereby initiating the dissolution of the conductive foreign matter, and once the dissolution begins, the LiFSI promotes the dissolution, which in turn promotes the growth of crystals of the conductive foreign matter, thereby shortening the time until the conductive foreign matter appears.

[0013] Furthermore, as a result of investigations, the present inventors have found that when the content of elemental chlorine in the battery components is equal to or less than a certain level, corrosion of the battery components can be suppressed.

[0014] Hereinafter, each component of the lithium ion battery according to this embodiment will be described.

[0015] <Electrolyte> First, the electrolyte will be described.

[0016] From the viewpoint of further shortening the aging time, the content of LiFSI in the electrolyte of the lithium ion battery according to this embodiment is preferably 0.0001 mol / L or more, more preferably 0.00025 mol / L or more, even more preferably 0.0005 mol / L or more, even more preferably 0.00075 mol / L or more, more preferably 0.001 mol / L or more, even more preferably 0.0025 mol / L or more, even more preferably 0.005 mol / L or more, even more preferably 0.0075 mol / L or more, even more preferably 0.01 mol / L or more, and even more preferably and from the viewpoint of further suppressing corrosion of battery components, it is, for example, 5 mol / L or less, preferably 2.5 mol / L or less, more preferably 1 mol / L or less, even more preferably 0.75 mol / L or less, even more preferably 0.5 mol / L or less, even more preferably 0.25 mol / L or less, even more preferably 0.1 mol / L or less, even more preferably 0.075 mol / L or less, and even more preferably 0.05 mol / L or less.

[0017] From the viewpoint of improving ion conductivity, the electrolyte solution of the lithium ion battery according to this embodiment preferably further contains a lithium salt different from LiFSI.

[0018] Examples of lithium salts different from LiFSI according to the present embodiment include LiClO4, LiBF6, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, and LiB 10 Cl 10 , LiAlCl4, LiCl, LiBr, LiB(C2H5)4, CF3SO3Li, CH3SO3Li, LiCF3SO3, LiC4F9SO3, Li(CF3SO2)2N and lower fatty acid lithium carboxylates, preferably comprising one or more selected from the group consisting of LiPF6 and LiCl, and more preferably comprising LiPF6.

[0019] The content of the lithium salt different from LiFSI in the electrolyte of the lithium ion battery according to this embodiment is, from the viewpoint of improving ion conductivity, preferably 0.01 mol / L or more, more preferably 0.025 mol / L or more, even more preferably 0.05 mol / L or more, even more preferably 0.075 mol / L or more, even more preferably 0.1 mol / L or more, even more preferably 0.25 mol / L or more, even more preferably 0.5 mol / L or more, even more preferably 0.75 mol / L or more, and even more preferably 1.0 mol / L or more, and from the viewpoint of further suppressing corrosion of the battery components, for example, 5 mol / L or less, preferably 2.5 mol / L or less, more preferably 2.0 mol / L or less, even more preferably 1.5 mol / L or less, and even more preferably 1.25 mol / L or less. When the electrolyte of the lithium ion battery according to this embodiment contains a plurality of lithium salts other than LiFSI, the total amount of all the lithium salts other than LiFSI is the content of the lithium salt other than LiFSI.

[0020] The electrolyte of the lithium ion battery according to this embodiment further contains a solvent.

[0021] The solvent contained in the electrolyte of the lithium ion battery according to this embodiment is not particularly limited as long as it is used as a liquid that dissolves the electrolyte, and examples of the solvent include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), and vinylene carbonate (VC); lactones such as γ-butyrolactone and γ-valerolactone; ethers such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran; and dimethyl sulfide. the organic acid esters include methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, and the like; phosphate triesters and diglymes; triglymes; sulfolanes such as sulfolane and methylsulfolane; oxazolidinones such as 3-methyl-2-oxazolidinone; and sultones such as 1,3-propane sultone, 1,4-butane sultone, naphtha sultone, and the like, and preferably includes carbonates.

[0022] The viscosity of the electrolyte of the lithium ion battery according to this embodiment is, for example, 1.5 mPa·s or more, and from the viewpoint of detecting conductive foreign matter in the battery in a shorter period of time, is preferably 4.5 mPa·s or less, more preferably 4.0 mPa·s or less, and even more preferably 3.5 mPa·s or less. When the viscosity of the electrolyte is equal to or less than the upper limit, the diffusion of ions of conductive foreign matter in the electrolyte is improved, and the seeds of conductive foreign matter can grow more quickly, so that conductive foreign matter in the lithium ion battery can be detected in a shorter period of time. The viscosity of the electrolyte can be adjusted by adjusting the type and amount of each component of the electrolyte for a battery.

[0023] <Electrode> Next, the electrodes, that is, the negative electrode and the positive electrode, will be described.

[0024] From the viewpoint of further shortening the aging time, the content of chlorine element in the positive electrode of the lithium ion battery according to this embodiment is preferably 0.0001 ppm or more, more preferably 0.0002 ppm or more, even more preferably 0.00025 ppm or more, even more preferably 0.0005 ppm or more, even more preferably 0.00075 ppm or more, even more preferably 0.001 ppm or more, even more preferably 0.0025 ppm or more, even more preferably 0.005 ppm or more, even more preferably 0.0075 ppm or more, even more preferably 0.01 ppm or more, even more preferably 0.025 ppm or more, even more preferably 0.05 ppm or more, even more preferably 0.075 ppm or more, even more preferably 0.1 ppm or more, It is preferably 0.25 ppm or more, more preferably 0.5 ppm or more, even more preferably 0.75 ppm or more, and even more preferably 1 ppm or more, and from the viewpoint of further suppressing corrosion of battery components, it is preferably 2200 ppm or less, more preferably 2000 ppm or less, even more preferably 1500 ppm or less, even more preferably 1000 ppm or less, even more preferably 750 ppm or less, even more preferably 500 ppm or less, even more preferably 250 ppm or less, even more preferably 200 ppm or less, even more preferably 100 ppm or less, even more preferably 50 ppm or less, even more preferably 25 ppm or less, even more preferably 10 ppm or less, even more preferably 5 ppm or less, and even more preferably 2 ppm or less. The amount of chlorine in the positive electrode can be calculated by dividing the mass of chlorine in the positive electrode (d) by the mass of the positive electrode (c). In other words, the amount of chlorine in the positive electrode is the value of (d) / (c). The means for incorporating elemental chlorine in the positive electrode is not particularly limited. Chlorine may be provided by chlorine contained as an impurity in the positive electrode material described below, or chlorine may be incorporated by adding a sodium salt such as sodium chloride when producing the positive electrode.

[0025] From the viewpoint of further shortening the aging time, the content of chlorine element in the negative electrode of the lithium ion battery according to this embodiment is preferably 0.0001 ppm or more, more preferably 0.0002 ppm or more, even more preferably 0.00025 ppm or more, even more preferably 0.0005 ppm or more, even more preferably 0.00075 ppm or more, even more preferably 0.001 ppm or more, even more preferably 0.0025 ppm or more, even more preferably 0.005 ppm or more, even more preferably 0.0075 ppm or more, even more preferably 0.01 ppm or more, even more preferably 0.025 ppm or more, even more preferably 0.05 ppm or more, even more preferably 0.075 ppm or more, even more preferably 0.1 ppm or more, It is preferably 0.25 ppm or more, more preferably 0.5 ppm or more, even more preferably 0.75 ppm or more, and even more preferably 1 ppm or more, and from the viewpoint of further suppressing corrosion of battery components, it is preferably 2200 ppm or less, more preferably 2000 ppm or less, even more preferably 1500 ppm or less, even more preferably 1000 ppm or less, even more preferably 750 ppm or less, even more preferably 500 ppm or less, even more preferably 250 ppm or less, even more preferably 200 ppm or less, even more preferably 100 ppm or less, even more preferably 50 ppm or less, even more preferably 25 ppm or less, even more preferably 10 ppm or less, even more preferably 5 ppm or less, and even more preferably 2 ppm or less. The amount of chlorine in the negative electrode can be calculated by dividing the mass of chlorine in the negative electrode (f) by the mass of the negative electrode (e). In other words, the amount of chlorine in the negative electrode is the value of (f) / (e). The means for incorporating elemental chlorine into the negative electrode is not particularly limited. Chlorine may be provided by chlorine contained as an impurity in the negative electrode material described below, or chlorine may be incorporated by adding a sodium salt such as sodium chloride during the production of the negative electrode.

[0026] The positive electrode and the negative electrode of the lithium ion battery according to this embodiment can be manufactured, for example, as follows.

[0027] First, an electrode slurry is prepared. The electrode slurry can be prepared according to a generally known method, and is not particularly limited. For example, the active material, binder, thickener, and conductive assistant are mixed with a mixer, and dispersed or dissolved in an arbitrary solvent. The mixing ratio of each material in the electrode slurry is appropriately determined according to the intended use of the battery. As the mixer, a known one such as a ball mill or a planetary mixer can be used, and is not particularly limited. The mixing method is also not particularly limited, and can be performed according to a known method.

[0028] The active material is not particularly limited and is appropriately selected depending on the intended use of the battery, etc. When a positive electrode is produced, a positive electrode active material is used, and when a negative electrode is produced, a negative electrode active material is used.

[0029] The positive electrode active material is not particularly limited as long as it is a positive electrode active material that can be used for the positive electrode of a lithium ion battery. From the viewpoint of using a material that can reversibly release and absorb lithium ions and has high electronic conductivity so as to facilitate electron transport, examples of the positive electrode active material include lithium-containing composite oxides such as lithium-nickel composite oxide, lithium-cobalt composite oxide, lithium-manganese composite oxide, lithium-manganese-nickel composite oxide, and lithium-nickel-cobalt-aluminum composite oxide; transition metal sulfides such as TiS2, FeS, and MoS2; MnO, VO5, and VO 13 The oxide contains one or more selected from the group consisting of transition metal oxides such as TiO2 and olivine-type lithium phosphate, and preferably contains a lithium-containing composite oxide.

[0030] The negative electrode active material is not particularly limited as long as it is a negative electrode active material that can be used in the negative electrode of a lithium ion battery, and includes, for example, one or more selected from the group consisting of carbonaceous materials such as natural graphite, artificial graphite, resin carbon, carbon fiber, activated carbon, hard carbon, and soft carbon; lithium-based metals such as lithium metal and lithium alloy; metals such as silicon and tin; and conductive polymers such as polyacene, polyacetylene, and polypyrrole, and preferably includes a carbonaceous material.

[0031] The electrode slurry may further include a binder that functions to bind the active materials together and between the active materials and the current collector.

[0032] The binder is not particularly limited as long as it is a binder that can be used in lithium ion batteries, and may include, for example, one or more types selected from the group consisting of polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose, polytetrafluoroethylene, polyvinylidene fluoride (PVdF), styrene-butadiene rubber, and polyimide, and preferably includes one or more types selected from the group consisting of polyvinylidene fluoride and styrene-butadiene rubber in terms of excellent binding property.

[0033] The positive electrode of the lithium ion battery according to this embodiment preferably contains polyvinylidene fluoride.

[0034] The negative electrode of the lithium ion battery according to this embodiment preferably contains one or more materials selected from the group consisting of polyvinylidene fluoride and styrene-butadiene rubber, and more preferably contains styrene-butadiene rubber.

[0035] The form of the binder is not particularly limited, but from the viewpoints of environmental friendliness and excellent binding properties, the binder is preferably dispersed or dissolved in a latex state in an aqueous solvent, that is, a so-called aqueous binder. From the viewpoint of further improving the battery performance, it is preferable to use the aqueous binder in the negative electrode.

[0036] The electrode slurry may further contain a thickener in order to ensure a fluidity suitable for application.

[0037] The thickener preferably contains elemental chlorine, which allows the electrode to contain elemental chlorine.

[0038] The thickener is not particularly limited as long as it is a thickener that can be used in lithium ion batteries, and includes, for example, one or more selected from the group consisting of cellulose-based polymers such as carboxymethyl cellulose (CMC), methyl cellulose, and hydroxypropyl cellulose, and their ammonium salts and alkali metal salts, water-soluble polymers such as polycarboxylic acids, polyethylene oxide, polyvinylpyrrolidone, polyacrylates, and polyvinyl alcohol, and preferably includes CMC.

[0039] Carboxymethyl cellulose may have a process of using elemental chlorine in its manufacturing process, and the carboxymethyl cellulose thus manufactured contains elemental chlorine. From the viewpoint of including elemental chlorine in the electrode (positive electrode or negative electrode), the thickener preferably includes CMC containing elemental chlorine.

[0040] The positive electrode of the lithium ion battery according to this embodiment preferably contains carboxymethyl cellulose (CMC).

[0041] The negative electrode of the lithium ion battery according to this embodiment preferably contains carboxymethyl cellulose (CMC).

[0042] The electrode slurry may further contain a conductive assistant. The conductive assistant is not particularly limited as long as it is a conductive assistant that can be used in lithium ion batteries, and includes, for example, one or more carbon materials selected from the group consisting of acetylene black, ketjen black, carbon black, and vapor-grown carbon fiber.

[0043] The solvent for dispersing or dissolving each material of the electrode slurry is not particularly limited, and known solvents can be appropriately used. For example, one or more solvents selected from the group consisting of N-methyl-2-pyrrolidone (NMP), dimethylsulfoxide (DMSO), dimethylformamide (DMF) and water can be used.

[0044] The resulting electrode slurry is then applied onto a current collector and dried.

[0045] The electrode slurry can be applied onto the current collector by a generally known method, such as a reverse roll method, a direct roll method, a doctor blade method, a knife method, an extrusion method, a curtain method, a gravure method, a bar method, a dip method, and a squeeze method.

[0046] The electrode slurry may be applied to only one side or both sides of the current collector. When applying to both sides of the current collector, the slurry may be applied to each side sequentially or simultaneously. The slurry may be applied to the surface of the current collector continuously or intermittently. The thickness, length and width of the coating layer may be appropriately determined depending on the size of the battery.

[0047] The applied electrode slurry can be dried by a commonly known method. Hot air, vacuum, infrared rays, far infrared rays, electron beams, and low-temperature air are preferably used alone or in combination. The drying temperature is, for example, in the range of 30°C to 350°C.

[0048] The current collector is not particularly limited as long as it is usable for lithium ion batteries, but aluminum is preferable for the positive electrode and copper is preferable for the negative electrode from the viewpoints of cost, availability, electrochemical stability, etc. The shape of the current collector is also not particularly limited, but for example, a foil-shaped current collector having a thickness in the range of 0.001 to 0.5 mm can be used.

[0049] The electrode of the lithium ion battery according to this embodiment may be pressed as necessary. As a pressing method, a generally known method can be used. For example, a die pressing method or a calendar pressing method can be used. The pressing pressure is not particularly limited, but is, for example, 0.2 to 3 t / cm. 2 The range is.

[0050] The composition of the electrodes of the lithium ion battery according to this embodiment is not particularly limited as it is appropriately determined depending on the intended use of the battery, and can be set in accordance with generally known information.

[0051] The thickness and density of the electrodes of the lithium ion battery according to this embodiment are not particularly limited as they are appropriately determined depending on the intended use of the battery, and can be set in accordance with generally known information.

[0052] <separator> Next, the separator will be described.

[0053] From the viewpoint of further shortening the aging time, the content of chlorine element in the separator of the lithium ion battery according to this embodiment is preferably 0.0001 ppm or more, more preferably 0.0002 ppm or more, even more preferably 0.00025 ppm or more, even more preferably 0.0005 ppm or more, even more preferably 0.00075 ppm or more, even more preferably 0.001 ppm or more, even more preferably 0.0025 ppm or more, even more preferably 0.005 ppm or more, even more preferably 0.0075 ppm or more, even more preferably 0.01 ppm or more, even more preferably 0.025 ppm or more, even more preferably 0.05 ppm or more, even more preferably 0.075 ppm or more, even more preferably 0.1 ppm or more, It is preferably 0.25 ppm or more, more preferably 0.5 ppm or more, even more preferably 0.75 ppm or more, and even more preferably 1 ppm or more, and from the viewpoint of further suppressing corrosion of battery components, it is preferably 2200 ppm or less, more preferably 2000 ppm or less, even more preferably 1500 ppm or less, even more preferably 1000 ppm or less, even more preferably 750 ppm or less, even more preferably 500 ppm or less, even more preferably 250 ppm or less, even more preferably 200 ppm or less, even more preferably 100 ppm or less, even more preferably 50 ppm or less, even more preferably 25 ppm or less, even more preferably 10 ppm or less, even more preferably 5 ppm or less, and even more preferably 2 ppm or less. The content of chlorine in the separator can be obtained by dividing the mass of chlorine in the separator (h) by the mass of the separator (g). In other words, the content of chlorine in the separator is the value of (h) / (g). The means for incorporating elemental chlorine into the separator is not particularly limited. Chlorine may be provided by chlorine contained as an impurity in the separator material described below, or chlorine may be incorporated by adding a sodium salt such as sodium chloride during the production of the separator.

[0054] The separator preferably includes a substrate and a ceramic layer provided on at least one surface of the substrate. This can further improve heat resistance. This can also reduce the thermal shrinkage of the separator, further suppressing short circuits between the electrodes. The substrate can be made of polyethylene, polypropylene, or a polyolefin film laminated with these. The substrate is, for example, a porous substrate.

[0055] The ceramic layer can be formed, for example, by applying a ceramic layer-forming material onto a substrate and drying the applied material. As the ceramic layer-forming material, for example, a material in which an inorganic filler, a binder, etc. are dispersed or dissolved in an arbitrary solvent can be used.

[0056] The inorganic filler is not particularly limited as long as it is a known material used in the separator of a lithium ion battery. For example, oxides, nitrides, sulfides, carbides, etc. having high insulation properties are preferred, and the filler contains one or more types selected from the group consisting of oxide-based ceramics such as titanium oxide, aluminum oxide, alumina, silica, magnesia, zirconia, zinc oxide, iron oxide, ceria, yttria, etc., and preferably contains one or more types selected from the group consisting of titanium oxide and alumina.

[0057] The inorganic filler preferably contains a chlorine element. The inorganic filler may contain a chlorine element as an impurity, and it is preferable to use such an inorganic filler, for example.

[0058] The binder is not particularly limited as long as it is a binder that can be used in lithium ion batteries, and includes, for example, one or more selected from the group consisting of polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose, polytetrafluoroethylene, polyvinylidene fluoride (PVdF), styrene-butadiene rubber, and polyimide, preferably includes one or more selected from the group consisting of PVdF and styrene-butadiene rubber, and more preferably includes PVdF.

[0059] The form in which the binder is used is not particularly limited, but from the viewpoints of environmental friendliness and excellent binding properties, the binder is preferably used by dispersing or dissolving the binder in a latex state in an aqueous solvent, that is, a so-called aqueous binder.

[0060] The ceramic layer-forming material may further contain a thickener in order to ensure fluidity suitable for application.

[0061] The thickener preferably contains elemental chlorine, which allows the separator to contain elemental chlorine.

[0062] The thickener is not particularly limited as long as it is a thickener that can be used in lithium ion batteries, and includes, for example, one or more selected from the group consisting of cellulose-based polymers such as carboxymethyl cellulose (CMC), methyl cellulose, and hydroxypropyl cellulose, and their ammonium salts and alkali metal salts, water-soluble polymers such as polycarboxylic acids, polyethylene oxide, polyvinylpyrrolidone, polyacrylates, and polyvinyl alcohol, and preferably includes CMC.

[0063] Carboxymethyl cellulose may have a process of using elemental chlorine in its production process, and the carboxymethyl cellulose produced in this manner contains elemental chlorine. From the viewpoint of including elemental chlorine in the separator, it is preferable that the thickener includes CMC containing elemental chlorine.

[0064] The separator of the lithium ion battery according to this embodiment preferably contains carboxymethyl cellulose (CMC).

[0065] The solvent used for the ceramic layer forming material is not particularly limited, and known solvents can be used as appropriate. For example, one or more solvents selected from the group consisting of N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and water can be used.

[0066] The thickness of the ceramic layer is preferably 1 μm or more and 20 μm or less, and more preferably 1 μm or more and 12 μm or less, from the viewpoint of improving the balance of performance among mechanical strength, handleability, and lithium ion conductivity.

[0067] The separator of the lithium ion battery according to this embodiment may include a substrate and an adhesive layer.

[0068] The adhesive layer can be formed, for example, by applying an adhesive. The components of the adhesive are not particularly limited, and any known adhesive can be used, such as an adhesive containing PVdF.

[0069] The adhesive preferably contains a chlorine element. The adhesive may contain a chlorine element as an impurity, and it is preferable to use such an adhesive, for example.

[0070] The lithium ion battery according to this embodiment can be obtained by stacking the positive electrode and the negative electrode with a separator interposed therebetween in a dry air or inert gas atmosphere, or by winding the stacked electrodes, and then housing the stacked electrodes in a battery can or sealing the battery can with a flexible film made of a laminate of synthetic resin and metal foil.

[0071] In the lithium ion battery according to this embodiment, the positive electrode and the negative electrode are disposed opposite each other with a separator interposed therebetween that is immersed in an electrolyte solution, for example.

[0072] The shape of the lithium ion battery can be various, such as a square type, a paper type, a laminated type, a cylindrical type, a coin type, etc. The exterior material and other constituent members are not particularly limited and may be selected according to the shape of the battery.

[0073] [Lithium-ion battery manufacturing method] The method for manufacturing the lithium ion battery according to this embodiment will be described below.

[0074] The method for producing a lithium ion battery according to this embodiment is a method for producing the above-mentioned lithium ion battery, and includes an aging step (A2) of aging the lithium ion battery containing the above-mentioned electrolyte for lithium ion batteries.

[0075] The manufacturing method for a lithium ion battery according to this embodiment preferably further includes a foreign matter detection step of measuring the amount of voltage drop of the lithium ion battery during the aging step and detecting the presence or absence of conductive foreign matter in the lithium ion battery by comparing the amount of voltage drop with a reference value, and a sorting step of selecting, as a non-defective product, the lithium ion battery in which no conductive foreign matter is detected.

[0076] The method for producing a lithium ion battery according to this embodiment preferably includes an initial charging step (A1) of the battery prior to the aging step (A2).

[0077] It is preferable that the aging step (A2) is performed without any charging or discharging after the initial charging step (A1) of the battery, so that conductive foreign matter can be detected in a shorter period of time.

[0078] The environmental temperature T1 [°C] in the initial charging step (A1) is, for example, 0°C or higher, preferably 10°C or higher, more preferably 20°C or higher, and, for example, 100°C or lower, preferably 80°C or lower, more preferably 60°C or lower, even more preferably 40°C or lower, and even more preferably 30°C or lower.

[0079] The environmental temperature in the aging step (A2) is preferably 0°C or higher, more preferably 10°C or higher, even more preferably 20°C or higher, even more preferably 30°C or higher, even more preferably 35°C or higher, and even more preferably 40°C or higher, from the viewpoint of growing crystals of conductive foreign matter more quickly and detecting conductive foreign matter in the battery in a shorter period of time, and is preferably 100°C or lower, more preferably 90°C or lower, even more preferably 80°C or lower, even more preferably 70°C or lower, and even more preferably 65°C or lower, from the viewpoint of further suppressing deterioration of the battery cell characteristics (particularly charge / discharge capacity) in the aging step (A2).

[0080] From the viewpoint of detecting conductive foreign matter with higher sensitivity, the time for the aging step (A2) is preferably 1 hour or more, more preferably 6 hours or more, even more preferably 12 hours or more, even more preferably 24 hours or more, even more preferably 48 hours or more, and even more preferably 72 hours or more. According to the method for producing a lithium ion battery according to this embodiment, conductive foreign matter in a lithium ion battery can be detected with high sensitivity in a short period of time, so the time for the aging step (A2) is preferably 720 hours or less, more preferably 600 hours or less, even more preferably 480 hours or less, even more preferably 360 hours or less, even more preferably 300 hours or less, and even more preferably 240 hours or less.

[0081] The voltage of the lithium-ion battery at the start of the aging step (A2) is preferably 2.5 V or more, more preferably 3.0 V or more, even more preferably 3.5 V or more, and even more preferably 4.0 V or more, from the viewpoint of detecting conductive foreign matter with higher sensitivity and in a shorter period of time, and is preferably 4.50 V or less, more preferably 4.30 V or less, even more preferably 4.25 V or less, and even more preferably 4.20 V or less, from the viewpoint of further suppressing deterioration of the battery cell characteristics (particularly charge / discharge capacity) in the aging step (A2).

[0082] The viscosity of the electrolyte in the lithium ion battery in the aging step (A2) is, for example, 1.5 mPa·s or more, and from the viewpoint of detecting conductive foreign matter in the battery in a shorter period of time, is preferably 4.5 mPa·s or less, more preferably 4.0 mPa·s or less, and even more preferably 3.5 mPa·s or less. When the viscosity of the electrolyte is equal to or less than the upper limit, the diffusion of ions of conductive foreign matter in the electrolyte becomes good, and the seeds of conductive foreign matter can grow more quickly, so that conductive foreign matter in the lithium ion battery can be detected in a shorter period of time. Here, the viscosity of the electrolyte in the lithium ion battery in the aging step (A2) can be adjusted by adjusting the environmental temperature in the aging step (A2) and by adjusting the type and amount of each component of the electrolyte for lithium ion batteries according to this embodiment.

[0083] In the foreign object detection step (A3), the voltage drop of the lithium ion battery is measured and the presence or absence of conductive foreign objects in the lithium ion battery is detected by comparing the voltage drop with a reference value. A lithium ion battery in which no conductive foreign objects are detected is determined to be a non-defective product.

[0084] The reference value for comparing the voltage drop amounts may be determined in advance, or a specific production lot may be inspected in its entirety, the voltage drop amounts expressed as a normal distribution, the standard deviation σ calculated, and the average value ±nσ used as the reference value (n is preferably 2 to 5, but is not limited to this), with anything outside this range deemed defective.

[0085] The foreign object detection in the foreign object detection process includes detecting the possible presence of a foreign object.

[0086] The foreign matter detection step (A3) may be performed simultaneously with the aging step (A2) or after the aging step (A2). For example, the voltage drop amount may be constantly monitored during the aging step (A2), or the voltage value may be measured after the aging step (A2) to determine the voltage drop amount.

[0087] The foreign matter detection step (A3) is performed, for example, by self-discharge. The lithium ion battery is left at a specified temperature for a specified period of time to allow it to self-discharge. The specified temperature is, for example, 15°C or higher and, for example, 40°C or lower. The specified period is, for example, 1 day or more, preferably 2 days or more, and more preferably 3 days or more, from the viewpoint of detecting conductive foreign matter with higher accuracy. The specified period is, for example, 20 days or less, preferably 14 days or less, and more preferably 7 days or less. According to the manufacturing method for a lithium ion battery according to this embodiment, conductive foreign matter in a lithium ion battery can be detected with high sensitivity, so that even if the leaving period in the foreign matter detection step (A3) is set to the above upper limit value or less, lithium ion batteries containing conductive foreign matter can be accurately detected and removed, and a lithium ion battery in which short-circuiting between positive and negative electrodes is unlikely to occur can be efficiently obtained. In most lithium-ion batteries, self-discharge normally occurs due to factors other than conductive foreign matter. Therefore, batteries that are experiencing abnormal self-discharge, which is greater than the normal self-discharge, are judged to be contaminated batteries.

[0088] The voltage drop amount can be calculated as the difference between the voltage before self-discharge and the voltage after self-discharge. For example, if the voltage drop amount is less than a reference value, it is determined that there is no conductive foreign object in the battery. On the other hand, if the voltage drop amount is equal to or greater than the reference value, it is determined that there is a conductive foreign object in the battery.

[0089] The reference value can be experimentally determined in advance using a battery of the same specifications as the battery to be manufactured. For example, it can be determined as follows. First, prepare a lithium ion battery before the first charge that is known in advance to be free of conductive foreign matter. Next, as described above, proceed to the foreign matter detection step (A3). Next, after measuring the voltage before self-discharge, a resistor having a predetermined electrical resistance is connected to the positive and negative terminals. The predetermined electrical resistance can be determined based on the size or electrical conductivity of the conductive foreign object to be detected. When the conductive foreign object to be detected is small and has low electrical conductivity, it is preferable to use a resistor with a large electrical resistance. Next, self-discharge is performed to obtain the value of the voltage after self-discharge. The difference between the voltage before self-discharge and the voltage after self-discharge can be used as a reference value according to the above-mentioned standard battery.

[0090] In the method for producing a lithium ion battery according to this embodiment, the lithium ion battery is discharged after the aging step (A2), and the voltage of the lithium ion battery in the foreign matter detection step (A3) is preferably set to 2.5 V to 4.5 V, more preferably 3.0 V to 4.3 V, and even more preferably 3.5 V to 4.2 V. When the voltage of the lithium ion battery is within the above range, the amount of voltage drop due to self-discharge is large, so that the presence or absence of conductive foreign matter in the lithium ion battery can be detected with high accuracy.

[0091] The present invention is not limited to the above-described embodiment, and modifications and improvements within the scope of the present invention that can achieve the object of the present invention are included in the present invention. EXAMPLES

[0092] The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0093] [Examples 1 to 10 and Comparative Examples 1 to 4] <1. Preparation of electrolyte> Lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 30:70 to give a concentration of 1.0 mol / L, and lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was further dissolved in the mixed solvent to give concentrations as shown in Table 1 to prepare an electrolyte solution.

[0094] <2. Manufacturing of laminated lithium-ion batteries> Cathode active material (LiNi 0.5 Co 0.2 Mn 0.3O2), a conductive additive (acetylene black), and a binder (PVdF) were mixed in a mass ratio of 95:2.5:2.5, and this was dispersed in a solvent (N-methyl-2-pyrrolidone) to form a positive electrode mixture slurry, which was then coated on one side of a 15 μm-thick aluminum foil (positive electrode current collector) and dried. The positive electrode mixture slurry was then similarly coated on the back side to produce a double-sided coated positive electrode plate. A negative electrode active material (natural graphite), a binder (styrene-butadiene rubber), and a thickener (carboxymethyl cellulose) were mixed in a mass ratio of 96:2:2, and the negative electrode mixture slurry dispersed in water was applied to one side of a 10 μm-thick copper foil (negative electrode current collector) and dried to prepare a negative electrode plate. The positive electrode plate obtained above was cut into a flag shape so that the coated area was 26 mm × 26 mm in size, leaving an uncoated aluminum foil area 8 mm wide and 20 mm long for current collection. The negative electrode plate obtained above was cut into a flag shape so that the coated area was 30 mm × 30 mm in size, leaving an uncoated copper foil area 10 mm wide and 20 mm long for current collection. Next, a separator was prepared. Aluminum oxide particles with an average particle size of 0.5 μm, a binder (PVdF), and sodium chloride were mixed and dispersed in a solvent (N-methyl-2-pyrrolidone) to prepare a slurry. At this time, the content of chlorine element in the separator was set to the amount shown in Table 1. The content of chlorine element in the positive electrode and the negative electrode was 0 mol / L. That is, in this embodiment, the content of chlorine element in the separator is the content of chlorine element in the entire battery component. The prepared slurry was then applied to both sides of a polyethylene substrate so that the thickness after drying was 3 μm, and then dried to obtain a separator, which was then cut into a 34 mm×34 mm square. In order to evaluate the detection time for conductive foreign matter, spherical stainless steel particles (SUS304) with a diameter of 100 μm were embedded in the center of one side of the coated portion of the positive electrode plate prepared above. The positive electrode plate and the two negative electrode plates coated on one side were stacked with the coated surfaces facing each other through a separator. The aluminum foil and copper foil parts cut out for current collection were placed on one side of the rectangular electrode plate, and the aluminum foil and the copper foil were arranged on opposite sides of one side of the rectangle so that they would not come into contact with each other. The laminate thus produced was wrapped in a folded laminate film, and the aluminum foil and the copper foil cut out for current collection were protruding from the laminate, and the edge including the protruding part of the foil for current collection and the opposite side were heat-welded to produce a laminated battery with only one side open. A predetermined amount of the electrolyte solution prepared in <1. Preparation of electrolyte solution> above was poured into the opening of the laminate cell, and the cell was sealed under reduced pressure to complete a laminate battery.

[0095] <3. Aging test> The obtained laminated battery was charged to a battery voltage of 3.2 V at a charging current of 0.2 C in an environment at a temperature of 25° C., and then preconditioned by leaving it for 12 hours in an environment at a temperature of 25° C. Thereafter, constant current charging was performed at a temperature of 25° C. and a charging current of 0.2 C to a battery voltage of 4.2 V, and after the battery voltage reached 4.2 V, constant voltage charging was performed until the current value decreased to 0.05 C. The battery charged under the above conditions was stored for 480 hours in an environment at 45°C while the battery voltage was monitored. The time it took for the battery voltage to drop by 100mV from the voltage at the start of aging was defined as the detection time for conductive foreign matter. If the voltage did not drop by 100mV from the start of aging even after 480 hours of storage, it was determined that no conductive foreign matter was detectable. The results are shown in Table 1.

[0096] <4. Check for corrosion> After performing the above-mentioned <3. Aging test>, the battery was disassembled and the corrosion of the battery components was evaluated. Specifically, the surfaces of the positive and negative electrodes were visually inspected and evaluated according to the following criteria. The results are shown in Table 1. Yes: Corrosion was observed in either or both of the positive and negative electrodes. No: There was no corrosion on either the positive or negative electrodes.

[0097] [Comparative Example 5] In addition, in order to compare the transition of the battery voltage during aging of a normal battery, a laminated battery was fabricated using a positive electrode in which spherical stainless steel particles (SUS304) with a diameter of 100 μm were not embedded, and this was designated Comparative Example 5. The detection time for conductive foreign matter and corrosion of the battery components were evaluated under the same conditions as in Examples 1 to 10 and Comparative Examples 1 to 4. The results are shown in Table 1.

[0098] [Table 1]

[0099] As shown in Table 1, in the examples, the aging time required to detect conductive foreign matter that had entered the lithium ion battery could be shortened, and corrosion of the battery components could be suppressed. On the other hand, the aging time could not be shortened and conductive foreign matter could not be detected within the specified time in Comparative Examples 1 and 3 to 5. Moreover, in the manufacturing method according to Comparative Example 2, the battery components were corroded. From these findings, it can be seen that according to this embodiment, the aging time required to detect conductive foreign matter that has become mixed into a lithium ion battery can be shortened, and corrosion of the battery components can be suppressed.

[0100] Below, we will describe what can be learned from comparisons between the examples. A comparison of Examples 1 to 9 shows that, while an increase in the chlorine content tends to shorten the detection time for conductive foreign objects, when the chlorine content is 1 ppm or more, the effect of shortening the detection time tends to decrease. A comparison between Examples 7 and 10 shows that an increase in the LiFSI content tends to shorten the detection time for conductive foreign objects.

Claims

1. A lithium ion battery including a positive electrode, a negative electrode, a separator, and an electrolyte, the electrolyte solution contains LiFSI; a lithium ion battery having the positive electrode, the negative electrode, and the separator as battery components, and a chlorine element content of the entire battery components is 0.0001 ppm or more and 2200 ppm or less.

2. 2. The lithium ion battery according to claim 1, wherein the content of LiFSI in the electrolyte solution is 0.001 mol / L or more and 5 mol / L or less.

3. 3. The lithium ion battery according to claim 1, wherein the electrolyte further comprises a lithium salt different from LiFSI.

4. 4. The lithium ion battery according to claim 3, wherein the content of the lithium salt different from LiFSI is 0.001 mol / L or more and 5 mol / L or less.

5. The lithium ion battery according to claim 1 or 2, wherein the electrolyte solution further comprises a solvent.

6. 6. The lithium ion battery of claim 5, wherein the solvent comprises a carbonate.

7. 3. The lithium ion battery according to claim 1, wherein the content of chlorine element in the positive electrode is 0.0001 ppm or more and 2200 ppm or less.

8. The lithium ion battery according to claim 1 or 2, wherein the positive electrode comprises a lithium-containing composite oxide.

9. 3. The lithium ion battery according to claim 1, wherein the content of chlorine element in the negative electrode is 0.0001 ppm or more and 2200 ppm or less.

10. 3. The lithium ion battery of claim 1, wherein the negative electrode comprises a carbonaceous material.

11. 3. The lithium ion battery according to claim 1, wherein the negative electrode comprises a styrene-butadiene rubber.

12. 3. The lithium ion battery of claim 1, wherein the negative electrode comprises carboxymethyl cellulose.

13. 3. The lithium ion battery according to claim 1, wherein the content of chlorine element in the separator is 0.0001 ppm or more and 2200 ppm or less.

14. 3. The lithium ion battery according to claim 1, wherein the separator comprises a substrate and a ceramic layer provided on at least one surface of the substrate.

15. 3. The lithium ion battery of claim 1, wherein the separator comprises a substrate and an adhesive layer.

16. A method for manufacturing the lithium ion battery according to claim 1 or 2, a method for manufacturing a lithium ion battery, the method including an aging step of aging the lithium ion battery.

17. a foreign matter detection step of detecting the presence or absence of conductive foreign matter in the lithium ion battery by measuring the amount of voltage drop of the lithium ion battery during the aging step and comparing the amount of voltage drop with a reference value; a sorting step of sorting out the lithium ion batteries in which the conductive foreign matter is not detected as non-defective products; 17. The method of claim 16, further comprising:

18. The method for producing a lithium ion battery according to claim 16, wherein the environmental temperature in the aging step is 0°C or higher and 100°C or lower.

19. The method for producing a lithium ion battery according to claim 16, wherein the aging time in the aging step is from 1 hour to 720 hours.

20. 17. The method for manufacturing a lithium ion battery according to claim 16, wherein the lithium ion battery is discharged after the aging step, and the voltage of the lithium ion battery in the foreign object detection step is set to 2.5 V or more and 4.5 V or less.