Manufacturing method of non-aqueous electrolyte secondary battery

Abstract

To provide a manufacturing method of a non-aqueous electrolyte secondary battery, capable of improving the resistance increase rate and the gas generation amount after charge and discharge cycles.SOLUTION: A manufacturing method of a non-aqueous electrolyte solution secondary battery, comprises: a preparation step of preparing a battery precursor which includes an electrode lamination body, in which a separator is arranged between a positive SS electrode and a negative electrode, and a non-aqueous electrolyte in a battery case; a preliminary charging step of charging the battery precursor to obtain a preliminarily charged battery precursor; an exhaust step of exhausting a gas contained in the battery case of the preliminarily charged battery precursor to the outside of the battery case to obtain an exhausted battery precursor; and a charging and discharging step of obtaining a non-aqueous electrolyte secondary battery by charging, discharging, or charging and discharging the exhausted battery precursor.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a non-aqueous electrolyte secondary battery.

Background Art

[0002] Power storage devices such as lithium-ion secondary batteries, which are small, lightweight, and have high output, have been further improved in performance in recent years. Along with the improvement in performance, they are being increasingly used not only in small electrical products but also in large product fields such as automobiles. Lithium-ion secondary batteries are required to meet specific requirements for various characteristics such as output characteristics, charge-discharge characteristics, and gas generation. For example, the capacity retention rate and output characteristics after a charge-discharge cycle test are also very important evaluation items.

[0003]

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of one aspect of the present disclosure is to provide a method for manufacturing a non-aqueous electrolyte secondary battery capable of improving the resistance increase rate and gas generation amount after charge-discharge cycles.

Means for Solving the Problems

[0006] ​As a result of intensive studies to solve the above problems, the inventors of the present disclosure have found that by discharging the gas contained in the battery case to the outside of the battery case after or simultaneously with pre-charging the battery precursor, the resistance increase rate and the gas generation amount after the charge-discharge cycle of the non-aqueous electrolyte secondary battery can be improved, and thus the present disclosure has been completed. That is, as one aspect of the present disclosure, the following can be mentioned.

[0007] <1> A method for manufacturing a non-aqueous electrolyte secondary battery, comprising a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, and a battery case, wherein the negative electrode contains at least one selected from the group consisting of single silicon particles, silicon oxide particles, and silicon carbide particles as a negative electrode active material, a preparation step of preparing a battery precursor in which an electrode laminate in which the separator is disposed between the positive electrode and the negative electrode and the non-aqueous electrolyte are enclosed in the battery case, a pre-charging step of charging the battery precursor to obtain a pre-charged battery precursor, an exhaust step of discharging the gas contained in the battery case of the pre-charged battery precursor to the outside of the battery case to obtain an exhausted battery precursor, and a charge-discharge step of charging, discharging, or charging and discharging the exhausted battery precursor to obtain a non-aqueous electrolyte secondary battery. A method for manufacturing a non-aqueous electrolyte secondary battery, including the above steps.

[0008] <2> The method for manufacturing a non-aqueous electrolyte secondary battery according to <1>, wherein the non-aqueous electrolyte in the battery precursor contains a cyclic sulfonic acid ester compound represented by the following formula (I).

[0009] [Chemical formula]

[0010] (In formula (I), R 11 represents a group represented by formula (i-1), a group represented by formula (i-2), or a divalent hydrocarbon group having 1 to 6 carbon atoms. In formula (i-1), R 12represents an oxymethylene group (-OCH2-), an oxyethylene group (-OCH2CH2-), an oxa group (-O-), or a divalent hydrocarbon group having 1 to 6 carbon atoms. In formula (i-2), R 13 represents a hydrocarbon group having 1 to 8 carbon atoms, or a hydrogen atom (-H).)

[0011] <3> The method for manufacturing a non-aqueous electrolyte secondary battery according to <1> or <2>, wherein the non-aqueous electrolyte in the battery precursor contains at least one selected from the group consisting of a difluorophosphate represented by the following formula (II-1) and a monofluorophosphate represented by the following formula (II-2).

[0012]

Chemical formula

[0013] (In formulas (II-1) and (II-2), (M 21 ) + each independently represents an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion.)

[0014] <4> The method for manufacturing a non-aqueous electrolyte secondary battery according to any one of <1> to <3>, wherein the non-aqueous electrolyte in the battery precursor contains a cyclic carbonate compound represented by the following formula (III).

[0015]

Chemical formula

[0016] (In formula (III), X is a fluoro group (-F), a chloro group (-Cl), or a bromo group (-Br), and R 31is independently a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), or a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an oxa group (-O-), and h represents an integer of 0 to 3.)

[0017] <5> The non-aqueous electrolyte in the battery precursor contains at least one selected from the group consisting of a cyclic sulfonic acid ester compound represented by the following formula (I), a difluorophosphate represented by the following formula (II-1), and a monofluorophosphate represented by the following formula (II-2), and a cyclic carbonate compound represented by the following formula (III). The method for manufacturing a non-aqueous electrolyte secondary battery according to <1>.

[0018]

Chemical formula

[0019] (In formula (I), R 11 represents a group represented by formula (i-1), a group represented by formula (i-2), or a divalent hydrocarbon group having 1 to 6 carbon atoms. In formula (i-1), R 12 represents an oxymethylene group (-OCH2-), an oxyethylene group (-OCH2CH2-), an oxa group (-O-), or a divalent hydrocarbon group having 1 to 6 carbon atoms. In formula (i-2), R 13 represents a hydrocarbon group having 1 to 8 carbon atoms or a hydrogen atom (-H).)

[0020]

Chemical formula

[0021] (In formulas (II-1) and (II-2), (M 21 ) + each independently represents an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion.)

[0022]

Chem.

[0023] (In formula (III), X represents a fluoro group (-F), a chloro group (-Cl), or a bromo group (-Br), and R 31 each independently represents a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an oxa group (-O-), and h represents an integer from 0 to 3.)

Advantages of the Invention

[0024] According to one aspect of the present disclosure, there is provided a method for manufacturing a non-aqueous electrolyte secondary battery, which can improve the resistance increase rate and the gas generation amount after charge and discharge cycles of the non-aqueous electrolyte secondary battery.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0026] In describing the present disclosure, specific examples will be given for explanation, but it is not limited to the following contents as long as it does not deviate from the gist of the present disclosure, and it can be implemented with appropriate modifications.

[0027] In the present disclosure, the numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. In the numerical ranges described step by step in the present disclosure, the upper limit value described in one numerical range may be replaced with the upper limit value of the numerical range described in other step-by-step descriptions, and the lower limit value described in one numerical range may be replaced with the lower limit value of the numerical range described in other step-by-step descriptions. Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, the amount of each component in the composition means the total amount of the plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified. In the present disclosure, a combination of preferred embodiments is a more preferred embodiment. In the present disclosure, the term "step" includes not only an independent step but also the step when it cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

[0028] 〔Method for manufacturing a non-aqueous electrolyte secondary battery〕 A method for manufacturing a non-aqueous electrolyte secondary battery (hereinafter, may be abbreviated as "the present battery" in some cases), which is an aspect of the present disclosure (hereinafter, may be abbreviated as "the present manufacturing method" in some cases), includes a "positive electrode", a "negative electrode", a "separator", a "non-aqueous electrolyte", and a "battery case", and the negative electrode includes "at least one selected from the group consisting of single silicon particles, silicon oxide particles, and silicon carbide particles as the negative electrode active material". And the present manufacturing method includes the following preparation step, the following preliminary charging step, the following exhaust step, and the following charge and discharge step. · Preparation step: A preparation step (hereinafter, may be abbreviated as "the preparation step" in some cases) of preparing a battery precursor (hereinafter, may be abbreviated as "the battery precursor" in some cases) in which an electrode laminate in which a separator is disposed between a positive electrode and a negative electrode and a non-aqueous electrolyte are enclosed in a case. · Preliminary charging step: A preliminary charging step (hereinafter, may be abbreviated as "the preliminary charging step" in some cases) of charging the battery precursor to obtain a preliminarily charged battery precursor (hereinafter, may be abbreviated as "the preliminarily charged battery precursor" in some cases). · Exhaust process: An exhaust process (hereinafter, may be abbreviated as "exhaust process") of discharging the gas contained in the battery case of the pre-charged battery precursor to the outside of the battery case to obtain an exhausted battery precursor (hereinafter, may be abbreviated as "exhausted battery precursor"). · Charge and discharge process: A charge and discharge process (hereinafter, may be abbreviated as "charge and discharge process") of charging, discharging, or charging and discharging the exhausted battery precursor to obtain a non-aqueous electrolyte secondary battery.

[0029] As a result of intensive studies on non-aqueous electrolyte secondary batteries with excellent battery characteristics after charge and discharge cycles, the inventors of the present disclosure have found that by discharging the gas contained in the battery case after or simultaneously with pre-charging the battery precursor to the outside of the battery case, it is possible to improve the resistance increase rate and gas generation amount after the charge and discharge cycle of the non-aqueous electrolyte secondary battery. Hereinafter, the "preparation process", "pre-charging process", "exhaust process", "charge and discharge process", etc. will be described in detail.

[0030] <Preparation process> The preparation process is a process of preparing a battery precursor in which an electrode laminate with a separator disposed between a positive electrode and a negative electrode and a non-aqueous electrolyte are enclosed in a battery case. Hereinafter, the "positive electrode", "negative electrode", "separator", "non-aqueous electrolyte", "battery case", "battery precursor", etc. will be described in detail.

[0031] (Positive electrode) The positive electrode is usually prepared by dispersing a positive electrode active material, a binder, a conductive assistant, and a thickener in a solvent as a slurry, applying this slurry to a current collector, drying, and compressing to form a positive electrode composite layer (also referred to as a "positive electrode active material layer") on the current collector.

[0032] Examples of the material of the positive electrode current collector include metals or alloys. Specifically, examples of the material of the positive electrode current collector include aluminum, nickel, stainless steel (SUS), copper, and the like. Among these, aluminum is preferable from the viewpoint of the balance between high conductivity and cost. Here, "aluminum" means pure aluminum or an aluminum alloy. As the positive electrode current collector, an aluminum foil is preferable. The material of the aluminum foil is not particularly limited, and examples include A1085 material and A3003 material.

[0033] The positive electrode composite layer contains a positive electrode active material and a binder.

[0034] The positive electrode active material is not particularly limited as long as it can occlude and release lithium ions, and can be appropriately adjusted according to the use of the lithium secondary battery precursor and the like.

[0035] Examples of the positive electrode active material include a first oxide, a second oxide, and the like. The first oxide has lithium (Li) and nickel (Ni) as constituent metal elements. The second oxide contains Li, Ni, and at least one metal element other than Li and Ni as constituent metal elements. Examples of the metal element other than Li and Ni include transition metal elements and typical metal elements. The second oxide preferably contains the metal element other than Li and Ni in a proportion similar to or less than that of Ni in terms of atomic number conversion. The metal element other than Li and Ni can be, for example, at least one selected from the group consisting of Co, Mn, Al, Cr, Fe, V, Mg, Ca, Na, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. These positive electrode active materials may be used alone or in combination of a plurality.

[0036] The positive electrode active material preferably contains a lithium-containing composite oxide represented by the following formula (P1) (hereinafter sometimes referred to as "NCM"). The lithium-containing composite oxide (NCM) has the advantages of high energy density per unit volume and excellent thermal stability. LiNi a Co b Mn cO2… Formula (P1) In formula (P1), a, b, and c are each independently greater than 0 and less than 1, and the sum of a, b, and c is 0.99 or more and 1.00 or less. Specific examples of NCM include LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2 and the like.

[0037] The positive electrode active material may contain a lithium-containing composite oxide represented by the following formula (P2) (hereinafter, may be referred to as "NCA"). Li t Ni 1-x-y Co x Al y O2… Formula (P2) In formula (P2), t is 0.95 or more and 1.15 or less, x is 0 or more and 0.3 or less, y is 0.1 or more and 0.2 or less, and the sum of x and y is less than 0.5. Specific examples of NCA include LiNi 0.8 Co 0.15 Al 0.05 O2 and the like.

[0038] When the positive electrode includes a positive electrode current collector and a positive electrode composite material layer containing a positive electrode active material and a binder, the content of the positive electrode active material in the positive electrode composite material layer is preferably 10% by mass or more and 99.9% by mass or less, more preferably 30% by mass or more and 99.9% by mass or less, still more preferably 50% by mass or more and 99% by mass or less, and particularly preferably 70% by mass or more and 99% by mass or less, based on the total amount of the positive electrode composite material layer.

[0039] Examples of binders include polyvinyl acetate, polymethyl methacrylate, nitrocellulose, fluororesins, and rubber particles. Examples of fluororesins include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and vinylidene fluoride-hexafluoropropylene copolymer. Examples of rubber particles include styrene-butadiene rubber particles and acrylonitrile rubber particles. Among these, fluororesins are preferred from the viewpoint of improving the oxidation resistance of the positive electrode composite material layer. One type of binder can be used alone, or two or more types can be combined and used as needed. From the viewpoint of achieving both the physical properties of the positive electrode composite material layer (e.g., electrolyte permeability, peel strength, etc.) and battery performance, the content of the binder in the positive electrode composite material layer is preferably 0.1% by mass or more and 4% by mass or less based on the total amount of the positive electrode composite material layer. When the content of the binder is 0.1% by mass or more, the adhesion of the positive electrode composite material layer to the positive electrode current collector and the binding property between the positive electrode active materials are further improved. When the content of the binder is 4% by mass or less, the amount of the positive electrode active material in the positive electrode composite material layer can be increased more, so the discharge capacity is further improved.

[0040] The positive electrode composite material layer preferably contains a conductive aid. As the material of the conductive aid, known conductive aids can be used. As the known conductive aids, carbon materials having conductivity are preferred. Examples of carbon materials having conductivity include graphite, carbon black, conductive carbon fibers, and fullerenes. These can be used alone or in combination of two or more types. Examples of conductive carbon fibers include carbon nanotubes, carbon nanofibers, and carbon fibers. Examples of graphite include artificial graphite and natural graphite. Examples of natural graphite include flaky graphite, massive graphite, and earthy graphite. The material of the conductive assistant may be a commercially available product. Examples of commercially available carbon blacks include Tokablack #4300, #4400, #4500, #5500, etc. (manufactured by Tokai Carbon Co., Ltd., furnace black), Printex L, etc. (manufactured by Degussa AG, furnace black), Raven7000, 5750, 5250, 5000ULTRAIII, 5000ULTRA, etc., Conductex SC ULTRA, Conductex 975ULTRA, etc., PUER BLACK100, 115, 205, etc. (manufactured by Columbian Chemicals Company, furnace black), #2350, #2400B, #2600B, #30050B, #3030B, #3230B, #3350B, #3400B, #5400B, etc. (manufactured by Mitsubishi Chemical Corporation, furnace black), MONARCH1400, 1300, 900, VulcanXC-72R, BlackPearls2000, LITX-50, LITX-200, etc. (manufactured by Cabot Corporation, furnace black), Ensaco250G, Ensaco260G, Ensaco350G, Super-P (manufactured by TIMCAL), Ketjenblack EC-300J, EC-600JD (manufactured by Akzo), Denka Black, Denka Black HS-100, FX-35 (manufactured by Denka Co., Ltd., acetylene black), and the like.

[0041] The positive electrode composite material layer may contain other components. Examples of other components include thickeners, surfactants, dispersants, wetting agents, defoaming agents, and the like.

[0042] (Negative electrode) In this manufacturing method, the negative electrode contains at least one selected from the group consisting of single silicon particles, silicon oxide particles, and silicon carbide particles as the negative electrode active material. However, the negative electrode used in the preparation process also contains at least one selected from the group consisting of single silicon particles, silicon oxide particles, and silicon carbide particles as the negative electrode active material. Note that the negative electrode is usually prepared by dispersing a negative electrode active material, a binder, a conductive assistant, and a thickener in a solvent to form a slurry, applying this slurry to a current collector, drying, and compressing it to form a negative electrode composite material layer (also referred to as a "negative electrode active material layer") on the current collector.

[0043] The single substance or compound serving as the negative electrode active material can be classified into (1) single carbon substances and carbon compounds capable of doping / dedoping lithium ions, (2) metals and alloys capable of alloying with lithium, and (3) oxides, nitrides, carbides, etc. capable of doping / dedoping lithium ions. When the negative electrode active material is a single silicon substance or the like, a single substance or compound in the form of particles (powders) is usually used. In addition, the negative electrode active material used is not limited to one type, and two or more types may be mixed and used.

[0044] In this manufacturing method, the negative electrode active material contains at least one selected from the group consisting of single silicon particles, silicon oxide particles, and silicon carbide particles. However, it is preferable that the negative electrode active material contains single carbon particles and at least one selected from the group consisting of single silicon particles, silicon oxide particles, and silicon carbide particles. Examples of the single carbon particles include graphite (natural graphite, artificial graphite) particles, carbon black particles, activated carbon particles, amorphous carbon particles, etc. Examples of artificial graphite include graphitized MCMB, graphitized MCF, etc. Examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500 °C or lower, mesophase pitch carbon fiber (MCF), etc.

[0045] When the single substance or compound serving as the negative electrode active material is in the form of through-particles (powders), specific shapes include fibrous, spherical, potato-shaped, and flake-shaped.

[0046] When the negative electrode active material contains single carbon particles, the median diameter D50 of the single carbon is usually 1 μm to 30 μm, preferably 10 μm or more, more preferably 15 μm or more, preferably 25 μm or less, and more preferably 20 μm or less.

[0047] When the negative electrode active material contains single carbon particles, the BET specific surface area of the single carbon is usually 1.0 m 2 / g to 5.0 m 2 / g, preferably 2.0 m 2 / g or more, more preferably 3.0 m2 above / g, preferably 4.5 m 2 / g or less, more preferably 4.0 m 2 / g or less.

[0048] Silicon oxide can be represented by SiO x , where x is a variable, that is, the content of oxygen atoms in silicon oxide is not particularly limited, but usually 0 ≦ x < 2, preferably 0.2 or more, more preferably 0.4 or more, still more preferably 0.6 or more, and preferably 1.8 or less, more preferably 1.6 or less, still more preferably 1.4 or less.

[0049] The median diameter D50 of the single silicon particles, silicon oxide particles, or silicon carbide particles is usually 0.5 μm to 20 μm, preferably 1.0 μm or more, more preferably 3.0 μm or more, and preferably 15 μm or less, more preferably 10 μm or less.

[0050] The BET specific surface area of the single silicon particles, silicon oxide particles, or silicon carbide particles is usually 1.0 m 2 / g to 5.0 m 2 / g, preferably 1.5 m 2 / g or more, more preferably 2.0 m 2 / g or more, preferably 4.5 m 2 / g or less, more preferably 4.0 m 2 / g or less.

[0051] When the negative electrode active material contains at least one selected from the group consisting of single carbon particles and single silicon particles, silicon oxide particles, and silicon carbide particles, the total charged mass of the single silicon particles, silicon oxide particles, and silicon carbide particles in the negative electrode active material is usually 1% by mass to 20% by mass when the total charged mass of the entire negative electrode active material is 100% by mass. Preferably 3% by mass or more, more preferably 5% by mass or more, and preferably 18% by mass or less, more preferably 15% by mass or less.

[0052] When the negative electrode active material contains single carbon particles and at least one selected from the group consisting of single silicon particles, silicon oxide particles, and silicon carbide particles, the total charged mass of the single carbon particles in the negative electrode active material is usually 70% to 99% by mass when the total charged mass of the entire negative electrode active material is 100% by mass. Preferably it is 80% by mass or more, preferably 95% by mass or less, more preferably 90% by mass or less. When the total charged mass of the single silicon particles or the like is within the above range, it becomes easier to ensure the balance between the energy density and the capacity retention rate of the lithium ion secondary battery.

[0053] The total content of the negative electrode active material in the negative electrode binder layer is usually 70% to 99.5% by mass when the entire negative electrode binder layer is 100% by mass. Preferably it is 75% by mass or more, preferably 99% by mass or less.

[0054] Examples of the binder for the negative electrode include styrene-butadiene rubber (SBR). The total content of the copolymer of the binder in the negative electrode binder layer is usually 0.1% to 5% by mass when the entire negative electrode binder layer is 100% by mass. Preferably it is 0.5% by mass or more, more preferably 1.0% by mass or more, preferably 3% by mass or less, more preferably 2% by mass or less.

[0055] The negative electrode binder layer preferably further contains a conductive assistant. Examples of the conductive assistant for the negative electrode include carbon black (for example, acetylene black), carbon nanotubes, amorphous whiskers, graphite, etc.

[0056] The total content of the conductive assistant in the negative electrode binder layer is usually 0.01% to 3% by mass when the entire negative electrode binder layer is 100% by mass. Preferably it is 0.05% by mass or more, more preferably 0.1% by mass or more, preferably 2% by mass or less, more preferably 1% by mass or less.

[0057] The negative electrode composite material layer preferably further contains a thickening agent. By including a thickening agent, it becomes easier to adjust the viscosity of the slurry, improving productivity. Examples of thickening agents for the negative electrode include cellulose derivatives such as carboxymethyl cellulose (CMC), carboxyethyl cellulose, and hydroxyethyl cellulose, polyoxyethylene and its modified forms, polyvinyl alcohol and its modified forms, and polysaccharides.

[0058] When the total content of the thickening agent in the negative electrode composite material layer is based on 100% by mass of the entire negative electrode composite material layer, it is usually 0.1% to 5% by mass. Preferably it is 0.5% by mass or more, more preferably 1.0% by mass or more, preferably 3% by mass or less, and more preferably 2% by mass or less.

[0059] The slurry may contain a solvent. Examples of the solvent include water, acetonitrile, N-methylpyrrolidone, acetylpyridine, cyclopentanone, dimethylformamide, dimethyl sulfoxide, methylformamide, methyl ethyl ketone, furfural, ethylenediamine, etc. Note that the solvent may be a mixed solvent obtained by mixing the aforementioned solvents.

[0060] Examples of the material of the current collector of the negative electrode include copper, nickel, stainless steel, nickel-plated steel, etc.

[0061] (Separator) Examples of the separator include a porous resin flat plate. Examples of the material of the porous resin flat plate include resin and non-woven fabric containing this resin. Examples of the resin include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polyester, cellulose, polyamide, etc. Among them, the separator is preferably a porous resin sheet having a single-layer or multi-layer structure. The material of the porous resin sheet is mainly composed of one or more polyolefin resins. The thickness of the separator is preferably 5 μm or more and 30 μm or less. The separator is preferably disposed between the positive electrode and the negative electrode.

[0062] (Non-aqueous electrolyte) In the preparation process, the non-aqueous electrolyte used preferably contains a cyclic sulfonic acid ester compound represented by the following formula (I).

[0063] [Chemical formula]

[0064] (In formula (I), R 11 represents a group represented by formula (i-1), a group represented by formula (i-2), or a divalent hydrocarbon group having 1 to 6 carbon atoms. In formula (i-1), R 12 represents an oxymethylene group (-OCH2-), an oxyethylene group (-OCH2CH2-), an oxa group (-O-), or a divalent hydrocarbon group having 1 to 6 carbon atoms. In formula (i-2), R 13 represents a hydrocarbon group having 1 to 8 carbon atoms, or a hydrogen atom (-H).)

[0065] R 11 represents "a group represented by formula (i-1)", "a group represented by formula (i-2)", or "a divalent hydrocarbon group having 1 to 6 carbon atoms". The "divalent hydrocarbon group" means a hydrocarbon group having two bonding positions, and is not limited to an aliphatic hydrocarbon group having a linear structure, and may be a group having at least one structure selected from the group consisting of a branched structure, a cyclic structure, and a carbon-carbon unsaturated bond structure (carbon-carbon double bond structure and carbon-carbon triple bond structure), or may be an aromatic hydrocarbon group. That is, an alkylene group, an alkenylene group, an alkynylene group, an arylene group, etc. are all included in the "divalent hydrocarbon group".

[0066] R 11 When R is a hydrocarbon group, the number of carbon atoms is preferably 5 or less, more preferably 4 or less, and still more preferably 3 or less.

[0067] The wavy lines in formula (i-1) and formula (i-2) mean that the tip thereof is respectively bonded to two oxygen atoms (-O-) of formula (I) to form a cyclic sulfate structure. Also, R 12represents an "oxymethylene group (-OCH2-)", "oxyethylene group (-OCH2CH2-)", "oxa group (-O-)", or "divalent hydrocarbon group having 1 to 6 carbon atoms", and the "divalent hydrocarbon group" is R 11 is synonymous with the case of R 12 When R is an oxymethylene group (-OCH2-), an oxyethylene group (-OCH2CH2-), or an oxa group (-O-), it means that the oxa group is bonded to the sulfur atom (-S(=O)2O-) of the formula (i-1) to form a cyclic sulfate structure.

[0068] R 12 As R, an oxymethylene group (-OCH2-) and an oxyethylene group (-OCH2CH2-) are particularly preferred.

[0069] R 13 represents a "hydrocarbon group having 1 to 8 carbon atoms" or a "hydrogen atom (-H)", and specifically, as the hydrocarbon group having 1 to 8 carbon atoms, there are a methyl group (-CH3), an ethyl group (-CH2CH3), a vinyl group (-CH=CH2), an n-propyl group (-CH2CH2CH3), an i-propyl group (-CH(CH3)2), an n-butyl group (-CH2CH2CH2CH3), an s-butyl group (-CH2CH(CH3)2), a t-butyl group (-C(CH3)2), a hexyl group (-CH2CH2CH2CH2CH2CH3), a cyclohexyl group (-C6H 11 ), and a phenyl group (-C6H5). As R 13 , an n-butyl group (-CH2CH2CH2CH3) and a hydrogen atom (-H) are particularly preferred.

[0070] Examples of the cyclic sulfate compound represented by the formula (I) include a cyclic sulfate compound represented by the following formula (I-1-1), a cyclic sulfate compound represented by the following formula (I-2-1), a cyclic sulfate compound represented by the following formula (I-2-2), and the like. The non-aqueous electrolyte may contain two or more cyclic sulfate compounds represented by the formula (I).

[0071]

Chemical formula

[0072] The total content of the cyclic sulfate compound represented by the formula (I) in the non-aqueous electrolyte is usually 0.01% by mass or more and 5.0% by mass or less, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more as the lower limit value, and preferably 4.0% by mass or less, more preferably 3.0% by mass or less, still more preferably 2.0% by mass or less, particularly preferably 1.5% by mass or less, based on the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass). When the total content of the cyclic sulfate compound represented by the formula (I) is within the above range, it becomes easy to control the capacity retention rate and the resistance increase rate after charge and discharge cycles to good values.

[0073] The non-aqueous electrolyte used in the preparation step preferably contains at least one selected from the group consisting of the difluorophosphate represented by the following formula (II-1) and the monofluorophosphate represented by the formula (II-2).

[0074]

Chemical formula

[0075] (In the formulas (II-1) and (II-2), (M 21 ) + each independently represents an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion.)

[0076] (M 21 ) + each independently represents an "alkali metal ion", an "alkaline earth metal ion", an "ammonium ion", an "imidazolium ion", a "pyridinium ion", a "pyrrolidinium ion", a "piperidinium ion", or a "phosphonium ion", and is particularly preferably a lithium ion.

[0077] Examples of the difluorophosphate represented by the formula (II-1) and the monofluorophosphate represented by the formula (II-2) include lithium difluorophosphate (LiPO2F2) represented by the following formula (II-1-1), lithium monofluorophosphate (Li2PO3F) represented by the following formula (II-2-1), and the like. The non-aqueous electrolyte may contain two or more difluorophosphates represented by the formula (II-1) and monofluorophosphates represented by the formula (II-2).

[0078]

Chem.

[0079] The total content of the difluorophosphate represented by the formula (II-1) and the monofluorophosphate represented by the formula (II-2) in the non-aqueous electrolyte is usually 0.01% by mass or more and 5.0% by mass or less, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more as the lower limit value, and preferably 4.0% by mass or less, more preferably 3.0% by mass or less, still more preferably 2.0% by mass or less, and particularly preferably 1.5% by mass or less with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass). When the total content of these compounds is within the above range, it is easy to control the capacity retention rate and the resistance increase rate after charge and discharge cycles to good values.

[0080] The non-aqueous electrolyte used in the preparation step preferably contains a cyclic carbonate compound represented by the following formula (III).

[0081]

Chem.

[0082] (In the formula (III), X is a fluoro group (-F), a chloro group (-Cl), or a bromo group (-Br), and R 31Each independently represents a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), or a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an oxa group (-O-), and h represents an integer of 0 to 3.)

[0083] X represents a "fluoro group (-F)", a "chloro group (-Cl)", or a "bromo group (-Br)", and the fluoro group (-F) is particularly preferred.)

[0084] R 31 Each independently represents a "fluoro group (-F)", a "chloro group (-Cl)", a "bromo group (-Br)", or a "hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an oxa group (-O-)", but the "hydrocarbon group" is not limited to an aliphatic hydrocarbon group having a linear structure, and may be a hydrocarbon group having at least one structure selected from the group consisting of a branched structure, a cyclic structure, and a carbon-carbon unsaturated bond structure (carbon-carbon double bond structure and carbon-carbon triple bond structure). Also, since the number of these structures is not limited, (acyclic) aliphatic hydrocarbon groups, monocyclic aliphatic hydrocarbon groups, polycyclic aliphatic hydrocarbon groups, monocyclic aromatic hydrocarbon groups, and polycyclic aromatic hydrocarbon groups are all included in the "hydrocarbon group". Also, of course, alkyl groups, alkenyl groups, alkynyl groups, aryl groups, etc. are all included in the "hydrocarbon group". Also, "which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-)" means that a hydrogen atom of the hydrocarbon group may be substituted with a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and a carbon atom of the hydrocarbon group may be substituted with an oxa group (-O-).

[0085] R 31When it is a hydrocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less.

[0086] R 31 Examples of [it] include a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), a methyl group (-CH3), an ethyl group (-CH2CH3), a vinyl group (-CH=CH2), an n-propyl group (-CH2CH2CH3), an i-propyl group (-CH(CH3)2), an n-butyl group (-CH2CH2CH2CH3), an s-butyl group (-CH2CH(CH3)2), a t-butyl group (-C(CH3)2), a hexyl group (-CH2CH2CH2CH2CH2CH3), a cyclohexyl group (-C6H 11 )), a phenyl group (-C6H5), etc.

[0087] h represents an integer from 0 to 3, and it is particularly preferably 0.

[0088] Examples of the cyclic carbonate compound represented by formula (III) include compounds represented by the following formula containing fluoroethylene carbonate (FEC). Note that the non-aqueous electrolyte may contain two or more cyclic carbonate compounds represented by formula (III).

[0089]

Chemical formula

[0090] The total content of the cyclic carbonate compound represented by the formula (III) in the non-aqueous electrolyte is usually 0.01% by mass or more and 5.0% by mass or less, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more as the lower limit value, and preferably 4.0% by mass or less, more preferably 3.5% by mass or less, still more preferably 3.0% by mass or less, particularly preferably 2.5% by mass or less with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass). When the total content of the cyclic carbonate compound represented by the formula (III) is within the above range, it becomes easier to control the capacity retention rate and the resistance increase rate after charge and discharge cycles to good values.

[0091] The cyclic carbonate compound represented by the formula (III) can also be used as a non-aqueous solvent described later. When used as a non-aqueous solvent, the total content of the cyclic carbonate compound represented by the formula (III) in the non-aqueous electrolyte is usually 5% by mass or more and 50% by mass or less, preferably 7% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more as the lower limit value, and preferably 40% by mass or less, more preferably 30% by mass or less, still more preferably 20% by mass or less, particularly preferably 15% by mass or less with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass).

[0092] The non-aqueous electrolyte generally contains a non-aqueous solvent. Various known non-aqueous solvents can be appropriately selected. The non-aqueous solvent may be only one kind or two or more kinds.

[0093] Examples of the non-aqueous solvent include cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, fluorine-containing chain carbonates, aliphatic carboxylic acid esters, fluorine-containing aliphatic carboxylic acid esters, γ-lactones, fluorine-containing γ-lactones, cyclic ethers, fluorine-containing cyclic ethers, chain ethers, fluorine-containing chain ethers, nitriles, amides, lactams, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, dimethyl sulfoxide phosphate, and the like. Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like. Examples of fluorine-containing cyclic carbonates include fluoroethylene carbonate (FEC), and the like. Examples of chain carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), dipropyl carbonate (DPC), and the like. Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, methyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylbutyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, ethyl isobutyrate, ethyl trimethylbutyrate, and the like. Examples of γ-lactones include γ-butyrolactone, γ-valerolactone, and the like. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, and the like. Examples of chain ethers include 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, 1,2-dibutoxyethane, and the like. Examples of nitriles include acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, and the like. Examples of amides include N,N-dimethylformamide, and the like. Examples of lactams include N-methylpyrrolidinone, N-methyloxazolidinone, N,N'-dimethylimidazolidinone, and the like.

[0094] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain carbonates. In this case, the total proportion of cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain carbonates is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and still more preferably 80% by mass or more and 100% by mass or less with respect to the total amount of the non-aqueous solvent.

[0095] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates and chain carbonates. In this case, the total proportion of cyclic carbonates and chain carbonates in the non-aqueous solvent is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and still more preferably 80% by mass or more and 100% by mass or less with respect to the total amount of the non-aqueous solvent.

[0096] The upper limit of the content of the non-aqueous solvent is preferably 99% by mass, preferably 97% by mass, and still more preferably 90% by mass with respect to the total amount of the non-aqueous electrolyte. The lower limit of the content of the non-aqueous solvent is preferably 60% by mass or more, more preferably 70% by mass or more with respect to the total amount of the non-aqueous electrolyte.

[0097] From the viewpoint of further improving the dissociation property of the electrolyte and the mobility of ions, the intrinsic viscosity of the non-aqueous solvent is preferably 10.0 mPa·s or less at 25°C.

[0098] Generally, the non-aqueous electrolyte contains an electrolyte.

[0099] The electrolyte preferably contains at least one of a lithium salt containing fluorine (hereinafter sometimes referred to as "fluorine-containing lithium salt") and a lithium salt not containing fluorine.

[0100] Examples of the fluorine-containing lithium salts include inorganic acid anion salts, organic acid anion salts, and the like. Examples of the inorganic acid anion salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluorotantalate (LiTaF6), and the like. Examples of the organic acid anion salts include lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N), lithium bis(pentafluoroethanesulfonyl)imide (Li(C2F5SO2)2N), and the like. Among them, lithium hexafluorophosphate (LiPF6) is more preferable as the fluorine-containing lithium salt.

[0101] Examples of the lithium salts without fluorine include lithium perchlorate (LiClO4), lithium aluminum tetrachloride (LiAlCl4), lithium decachlorodecaborate (Li2B 10 Cl 10 ), and the like.

[0102] When the electrolyte contains a fluorine-containing lithium salt, the content ratio of the fluorine-containing lithium salt is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and still more preferably 80% by mass or more and 100% by mass or less based on the total amount of the electrolyte. When the fluorine-containing lithium salt contains lithium hexafluorophosphate (LiPF6), the content ratio of lithium hexafluorophosphate (LiPF6) is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and still more preferably 80% by mass or more and 100% by mass or less based on the total amount of the electrolyte.

[0103] When the non-aqueous electrolyte contains an electrolyte, the concentration of the electrolyte in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 3 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less.

[0104] When the non-aqueous electrolyte contains lithium hexafluorophosphate (LiPF6), the concentration of lithium hexafluorophosphate (LiPF6) in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 3 mol / L or less, more preferably 0.5 mol / L or more and 2 mol / L or less.

[0105] (Battery case) The shape of the battery case and the like are not particularly limited and are appropriately selected according to the use of the lithium secondary battery precursor of the present disclosure and the like. Examples of the battery case include a case containing a laminate film, a battery case composed of a battery can and a battery can lid, and the like.

[0106] (Battery precursor) The battery precursor includes an electrode laminate in which a separator is disposed between a positive electrode and a negative electrode, and a non-aqueous electrolyte, which are enclosed in a case. FIG. 1 is a schematic cross-sectional view showing a laminated (pouch-type) lithium-ion secondary battery precursor, which is an example of the lithium-ion secondary battery precursor.

[0107] As shown in FIG. 1, the lithium-ion secondary battery precursor 1 is a laminated (pouch-type) battery precursor. Specifically, in the lithium-ion secondary battery precursor 1, the battery element 10 is enclosed inside the exterior body 30. The exterior body 30 is formed of a laminate film. Each of a positive electrode lead 21 and a negative electrode lead 22 is attached to the battery element 10. Each of the positive electrode lead 21 and the negative electrode lead 22 is led out in opposite directions from inside the exterior body 30 toward the outside.

[0108] As shown in FIG. 1, the battery element 10 is formed by laminating a positive electrode 11, a separator 13, and a negative electrode 12. The positive electrode 11 is formed by forming a positive electrode mixture layer 11B on both main surfaces of a positive electrode current collector 11A. The negative electrode 12 is formed by forming a negative electrode mixture layer 12B on both main surfaces of a negative electrode current collector 12A. The positive electrode mixture layer 11B formed on one main surface of the positive electrode current collector 11A of the positive electrode 11 and the negative electrode mixture layer 12B formed on one main surface of the negative electrode current collector 12A of the negative electrode 12 adjacent to the positive electrode 11 face each other with the separator 13 interposed therebetween.

[0109] A non-aqueous electrolyte is injected into the interior of the exterior body 30 of the lithium-ion secondary battery precursor 1. The non-aqueous electrolyte penetrates into the positive electrode composite layer 11B, the separator 13, and the negative electrode composite layer 12B. In the lithium-ion secondary battery precursor 1, one single battery layer 14 is formed by the adjacent positive electrode composite layer 11B, separator 13, and negative electrode composite layer 12B. Note that the positive electrode and the negative electrode may each have an active material layer formed on one surface of each current collector.

[0110] Note that the lithium-ion secondary battery precursor 1 is a laminated lithium-ion secondary battery precursor, but the lithium-ion secondary battery precursor is not limited thereto. For example, it may be a wound lithium-ion secondary battery precursor. The wound lithium-ion secondary battery precursor is formed by laminating a positive electrode, a separator, a negative electrode, and a separator in this order and winding them in a layered manner. The wound lithium-ion secondary battery precursor includes a cylindrical lithium-ion secondary battery precursor and a rectangular lithium-ion secondary battery precursor.

[0111] As shown in FIG. 1, in the lithium-ion secondary battery precursor 1, the directions in which the positive electrode lead 21 and the negative electrode lead 22 each protrude from the interior of the exterior body 30 toward the exterior are opposite to the exterior body 30, but the present disclosure is not limited thereto. For example, the manner in which the positive electrode lead 21 and the negative electrode lead 22 each protrude from the interior of the exterior body 30 toward the exterior may be the same direction with respect to the exterior body 30.

[0112] FIG. 2 is a schematic cross-sectional view showing a coin-type lithium secondary battery precursor which is another example of the lithium-ion secondary battery precursor of the present disclosure.

[0113] In the coin-type lithium-ion secondary battery precursor 2 shown in FIG. 2, a disk-shaped negative electrode 42, a separator 45 filled with a non-aqueous electrolyte, a disk-shaped positive electrode 41, and, if necessary, spacer plates 47 and 48 such as stainless steel or aluminum are laminated in this order and housed between a positive electrode can 43 (hereinafter also referred to as "battery can") and a sealing plate 44 (hereinafter also referred to as "battery can lid"). The positive electrode can 43 and the sealing plate 44 are caulked and sealed via a gasket 46.

[0114] <Pre-charging process> The pre-charging process is a process of charging the battery precursor to obtain a pre-charged battery precursor. The charging method is not particularly limited and can be appropriately selected according to the purpose. Specifically, constant current charging (CC charging), constant voltage charging (CV charging), constant power charging (CP charging), constant current constant voltage charging (CCCV charging), etc. can be mentioned, and constant current charging (CC charging) is preferred.

[0115] The temperature conditions in the pre-charging process are usually 0°C or higher, preferably 10°C or higher, more preferably 20°C or higher, and usually 60°C or lower, preferably 50°C or lower, more preferably 40°C or lower.

[0116] The battery voltage in the pre-charging process is usually 1.5V or higher, preferably 2.0V or higher, more preferably 2.5V or higher, and usually 4.5V or lower, preferably 4.2V or lower, more preferably 4.0V or lower.

[0117] The pre-charging process may be performed simultaneously with the exhaust process described later. For example, when charging the battery precursor, the gas generated in the battery case is directly discharged outside the battery case. More specifically, in the case of a laminated (pouch-type) battery precursor, charging is performed with the laminate film, which is the battery case, unsealed, and the pre-charging process and the exhaust process are performed simultaneously. Also, in the case of a wound-type lithium-ion secondary battery precursor or a coin-type lithium-ion secondary battery precursor, charging is performed with the opening left open without the lid of the battery can, and the pre-charging process and the exhaust process are performed simultaneously.

[0118] <Exhaust process> The exhaust process is a process of discharging the gas contained in the battery case of the pre-charged battery precursor to the outside of the battery case to obtain an exhausted battery precursor. The method of discharging the gas contained in the battery case is not particularly limited and can be appropriately selected according to the purpose. For example, in the case of a laminated (pouch-type) battery precursor, the laminate film that is the battery case can be opened, the gas can be discharged, and then sealed again. In addition, the pre-charging process can be performed with the opening of the battery can of the wound-type lithium-ion secondary battery precursor or the coin-type lithium-ion secondary battery precursor left open without covering the lid. Further, the gas can be discharged directly to the outside of the battery case using the internal pressure of the battery case, or the inside of the battery case can be depressurized.

[0119] The temperature conditions in the exhaust process are usually 0°C or higher, preferably 10°C or higher, more preferably 20°C or higher, and usually 60°C or lower, preferably 50°C or lower, more preferably 40°C or lower.

[0120] The pressure inside the battery case after the exhaust process is usually 1 kPa or higher, preferably 10 kPa or higher, more preferably 30 kPa or higher, and usually 200 kPa or lower, preferably 150 kPa or lower, more preferably 120 kPa or lower.

[0121] <Charge and discharge process> The charge and discharge process is a process of charging, discharging, or charging and discharging the exhausted battery precursor to obtain a non-aqueous electrolyte secondary battery. The charging method and the discharging method are not particularly limited and can be appropriately selected according to the purpose. Specifically, constant current charge and discharge (CC charge and discharge), constant voltage charge and discharge (CV charge and discharge), constant power charge and discharge (CP charge and discharge), constant current constant voltage charge and discharge (CCCV charge and discharge), etc. can be mentioned, and constant current charge and discharge (CC charge and discharge) is preferred.

[0122] The temperature conditions in the charge and discharge process are usually 0°C or higher, preferably 10°C or higher, more preferably 20°C or higher, and usually 100°C or lower, preferably 70°C or lower, more preferably 60°C or lower.

[0123] The upper limit charging voltage in the charge-discharge process is usually 2.0 V or higher, preferably 3.0 V or higher, more preferably 3.4 V or higher, and usually 5.5 V or lower, preferably 5.0 V or lower, more preferably 4.6 V or lower.

[0124] The charge-discharge process may include holding at a constant charge state of 1.0 V to 5.0 V for a certain period of time. The holding time is usually 0.01 hour or longer, preferably 1 hour or longer, more preferably 3 hours or longer, and usually 300 hours or shorter, preferably 200 hours or shorter, more preferably 150 hours or shorter.

[0125] The lower limit discharge potential in the charge-discharge process is usually 1.0 V or higher, preferably 1.5 V or higher, more preferably 2.5 V or higher, and usually 4.0 V or lower, preferably 3.5 V or lower, more preferably 3.3 V or lower.

Example

[0126] Examples of the present disclosure are shown below, but the present disclosure is not limited to the following examples. Hereinafter, “%” means “% by mass” unless otherwise specified.

[0127] 〔Example 1〕 <Preparation of non-aqueous electrolyte> Ethylene carbonate (hereinafter may be abbreviated as "EC"), dimethyl carbonate (hereinafter may be abbreviated as "DMC"), and ethyl methyl carbonate (hereinafter may be abbreviated as "EMC") were mixed at EC:DMC:EMC = 30:35:35 (volume ratio). Thereby, a mixed solvent was obtained as a non-aqueous solvent. To the obtained mixed solvent, LiPF6 as an electrolyte was dissolved so that the concentration in the finally obtained non-aqueous electrolyte became 1 mol / L, and then a cyclic sulfate compound (4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane)) represented by the following formula (I-1-1) was added at 1.0% by mass to obtain an electrolyte (hereinafter may be abbreviated as "basic electrolyte"). To the obtained basic electrolyte, a difluorophosphate (lithium difluorophosphate (LiPO2F2)) represented by the following formula (II-1-1) was added so that the content with respect to the total amount of the finally obtained non-aqueous electrolyte (the numerical value when the total amount of the non-aqueous electrolyte is 100% by mass) became the content (% by mass) described in Table 1 to obtain a non-aqueous electrolyte. In Table 1, in order to indicate that formula (I-1-1) is one of the phosphate compounds represented by formula (I), (I) was described in the column above the column described as (I-1-1). Similarly, (II) and (III) were described in the columns above the columns described as (II-1-1) and (III-1-1), respectively.

[0128]

Chemical formula

[0129] <Fabrication of the positive electrode> As the positive electrode active material, Li(Ni 0.8 Co 0.1 Mn 0.1O2), a mixture was obtained by adding carbon black as a conductive aid and polyvinylidene fluoride (PVdF) as a binder. The obtained mixture was dispersed in an N-methylpyrrolidone solvent to obtain a slurry for a positive electrode composite material. An aluminum foil with a thickness of 20 μm was prepared as a positive electrode current collector. The obtained slurry for the positive electrode composite material was applied onto the aluminum foil, and after drying, it was rolled with a press machine to obtain a sheet-like positive electrode raw plate. This positive electrode raw plate includes a region where an active material composite layer of the positive electrode (hereinafter referred to as the "positive electrode composite layer") is formed and a region where the positive electrode composite layer is not formed (hereinafter referred to as the "uncoated part for tab adhesion"). The uncoated part for tab adhesion is an uncoated part that becomes a margin. The obtained positive electrode raw plate was slit to obtain a positive electrode. The positive electrode has a positive electrode composite layer and an uncoated part for tab adhesion. The size of the positive electrode composite layer was 29 mm in width and 40 mm in length. The size of the uncoated part for tab adhesion was 5 mm in width and 11 mm in length.

[0130] <Fabrication of negative electrode> Negative electrode active material (graphite:SiO = 95:5; mass ratio), carbon black as a conductive aid, sodium carboxymethyl cellulose dispersed in pure water as a thickening agent, and styrene-butadiene rubber (SBR) dispersed in pure water as a binder were mixed to obtain a slurry for a negative electrode composite material. A copper foil with a thickness of 10 μm was prepared as a negative electrode current collector. The obtained slurry for the negative electrode composite material was applied onto the copper foil (negative electrode current collector), and after drying, it was rolled with a press machine to obtain a negative electrode raw plate. This negative electrode raw plate includes a region where an active material composite layer of the negative electrode (hereinafter referred to as the "negative electrode composite layer") is formed and a region where the negative electrode composite layer is not formed (hereinafter referred to as the "uncoated part for tab adhesion"). The uncoated part for tab adhesion is an uncoated part that becomes a margin. The obtained negative electrode raw plate was slit to obtain a negative electrode. The negative electrode has a negative electrode composite layer and an uncoated part for tab adhesion. The size of the negative electrode composite layer was 30 mm in width and 41 mm in length. The size of the uncoated part for tab adhesion was 5 mm in width and 11 mm in length.

[0131] <Preparation of separator> A porous polyethylene film was prepared as a separator.

[0132] <Fabrication of a laminated battery> A positive electrode, a negative electrode, and a separator were stacked to obtain an electrode laminate in such a direction that the coated surface of the negative electrode was in contact with the separator and the coated surface of the positive electrode was in contact with the separator. Next, an aluminum positive electrode tab (positive electrode lead) was joined to the uncoated portion for tab adhesion of the positive electrode of the obtained electrode laminate using an ultrasonic bonder. A nickel negative electrode tab (negative electrode lead) was joined to the uncoated portion for tab adhesion of the negative electrode of the obtained electrode laminate using an ultrasonic bonder. The electrode laminate to which the positive electrode tab and the negative electrode tab were joined was sandwiched between a pair of laminate films (cases) having both sides of aluminum coated with resin layers, and then three sides were heat-sealed to obtain a laminate body (assembly). At this time, the positive electrode tab and the negative electrode tab were made to protrude from one side in contact with the unsealed opening among the three sealed sides in the laminate body. Next, the non-aqueous electrolyte obtained as described above was injected from the opening of the laminate body, and the opening of the laminate was sealed under reduced pressure. Thereby, an aluminum laminate battery (precursor of a lithium-ion secondary battery) was obtained.

[0133] <Preparation for fabricating a lithium-ion secondary battery> The above-mentioned precursor of a lithium-ion secondary battery was subjected to CC charging up to 3.2 V at 25 °C to obtain a preliminarily charged precursor of a lithium-ion secondary battery. A laminate portion not including the electrode laminate (positive electrode, negative electrode, separator) of the preliminarily charged precursor of a lithium-ion secondary battery was cut out in a dry room environment with a dew point of -30 °C or lower (hereinafter, may be referred to as "laminate cutting"), and the gas in the preliminarily charged precursor of a lithium-ion secondary battery was removed (exhausted) by sealing again under reduced pressure. Thereby, an evacuated precursor of a lithium-ion secondary battery was obtained. The volume of the battery after removing the gas by the Archimedes method using ion-exchanged water as a solvent was measured at a temperature environment of 25 °C and used as the initial battery volume. Thereafter, charging at 3.2 V to 4.2 V, holding for 5 hours to 50 hours, charging up to 4.2 V, and discharging up to 2.5 V were performed in this order under a temperature range of 25 °C to 70 °C to obtain a lithium-ion secondary battery.

[0134] <Evaluation of resistance value after high-temperature cycle> A lithium-ion secondary battery was charged at 0.5C up to 4.2V in a 45°C constant temperature bath by CC-CV method, and then discharged at a constant current of 0.5C down to 2.5V. One cycle was defined as this process, and 100 cycles were performed (hereinafter sometimes abbreviated as "high-temperature cycle"). Next, the lithium-ion secondary battery after high-temperature cycle was discharged to 3.7V in a 25°C constant temperature bath, then cooled to -20°C in the constant temperature bath, and the voltage drop amount (= voltage before discharge start - voltage at the 10th second after discharge start) and each current value (i.e., each current value corresponding to discharge rates of 0.1C to 0.6C) for "CC10s discharge" at each of the discharge rates of 0.1C to 0.6C were measured. Based on these, the DC resistance [Ω] as the resistance value after high-temperature cycle (-20°C) was measured. Here, CC10s discharge means discharging for 10 seconds at a constant current (Constant Current). Therefore, the DC resistance (Ω) was measured based on each current value (i.e., each current value corresponding to each of the discharge rates of 0.1C to 0.6C) and each voltage drop amount corresponding to each current value (= voltage before discharge start - voltage at the 10th second after discharge start) in the above-mentioned "CC10s discharge" at each of the discharge rates of 0.1C to 0.6C. For Comparative Example 1 described later, the resistance value after high-temperature cycle (-20°C) was also measured by the same operation. When the resistance value after high-temperature cycle (-20°C) of the lithium-ion secondary battery in Comparative Example 1 was set to 100, the relative value of the resistance value after high-temperature cycle (-20°C) of Example 1 was calculated and designated as "resistance value after high-temperature cycle (-20°C, relative value)". The results are shown in Table 1.

[0135] <Evaluation of Gas Amount after High-Temperature Cycle> After the lithium-ion secondary battery after the resistance value evaluation after the above high-temperature cycle was allowed to cool at 25°C for 3 hours or more, the volume of the battery body after the high-temperature cycle was measured by the Archimedes method using ion-exchanged water as a solvent. As shown in the following formula (X1), the difference in the volume of the battery body after the high-temperature cycle between the initial battery volume of Comparative Example 1 and the battery volume after the high-temperature cycle of Example 1 was defined as the "gas amount after high-temperature cycle [%]" (see Table 1). For Comparative Example 1 described later, the volume of the battery body after the high-temperature cycle was also measured by the same operation, and when the difference between the initial battery volume and the battery volume after the high-temperature cycle of the lithium-ion secondary battery of Comparative Example 1 was set to 100, the relative value of the difference between the initial battery volume and the battery volume after the high-temperature cycle of the lithium-ion secondary battery of Example 1 was calculated and defined as the "gas amount after high-temperature cycle (relative value)". The results are shown in Table 1.

[0136] Gas amount after high-temperature cycle [relative value; %] = (Volume of battery body after high-temperature cycle of Example 1 [mL] - Initial battery volume of Example 1 [mL]) ÷ (Volume of battery body after high-temperature cycle of Comparative Example 1 [mL] - Initial battery volume of Comparative Example 1 [mL]) × 100…(X1)

[0137] 〔Comparative Example 1〕 A non-aqueous electrolyte solution was prepared by the same operation as described in Example 1, except that gas removal by laminating and resealing the lithium-ion secondary battery precursor was not performed, and a lithium-ion secondary battery was prepared. Furthermore, by the same operation as described in Example 1, the resistance value (-20°C) after the high-temperature cycle and the gas amount after the high-temperature cycle were measured, and used as the reference values of the "resistance after high-temperature cycle (-20°C, relative value)" and the "gas amount after high-temperature cycle" of Example 1, Example 2, and Comparative Example 2, respectively. The results are shown in Table 1.

[0138] 〔Comparative Example 2〕 A cyclic carbonate compound (fluoroethylene carbonate) represented by the formula (III-1-1) was added to the electrolytic solution, and a non-aqueous electrolytic solution was prepared by the same operations as described in Example 1 except that gas removal by laminate cutting and resealing was not performed on the lithium-ion secondary battery precursor, and a lithium-ion secondary battery was fabricated. Further, by the same operations as described in Example 1, the resistance value (-20°C) after high-temperature cycling and the gas amount after high-temperature cycling were measured, and the "resistance after high-temperature cycling (-20°C, relative value)" and "gas amount after high-temperature cycling" with respect to Comparative Example 1 were determined, respectively. The results are shown in Table 1.

[0139] [Example 2] A non-aqueous electrolytic solution was prepared by the same operations as described in Example 1 except that a cyclic carbonate compound (fluoroethylene carbonate) represented by the formula (III-1-1) was added to the electrolytic solution, and a lithium-ion secondary battery was fabricated. Further, by the same operations as described in Example 1, the resistance value (-20°C) after high-temperature cycling and the gas amount after high-temperature cycling were measured, and the "resistance after high-temperature cycling (-20°C, relative value)" and "gas amount after high-temperature cycling" with respect to Comparative Example 1 were determined, respectively. The results are shown in Table 1.

[0140] [Table 1]

[0141] In Table 1, "-" means that the corresponding additive is not contained. As is clear from the results shown in Table 1, after preliminary charging, as an exhaust process, the lithium-ion secondary battery in which the gas in the lithium-ion secondary battery precursor was removed has a reduced resistance increase rate and gas generation amount after high-temperature cycling compared to Comparative Examples 1 and 2 in which the exhaust process was not performed. [Explanation of Symbols]

[0142] 1, 2 Lithium-ion secondary battery precursors 10 Battery elements 11 Positive electrode 11A Positive electrode current collector 11B Positive electrode composite material layer 12 Negative electrode 12A Negative electrode current collector 12B Negative electrode composite material layer 13 Separator 14 Single battery layer 21 Positive electrode lead 22 Negative electrode lead 30 Exterior body 41 Disk-shaped positive electrode 42 Disk-shaped negative electrode 43 Positive electrode can 44 Sealing plate 45 Separator 46 Gasket 47, 48 Spacer plates

Claims

1. A method for manufacturing a non-aqueous electrolyte secondary battery, comprising a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, and a battery case, wherein the negative electrode contains at least one selected from the group consisting of silicon single particles, silicon oxide particles, and silicon carbide particles as a negative electrode active material, and a preparation step of preparing a battery precursor in which an electrode laminate in which the separator is disposed between the positive electrode and the negative electrode and the non-aqueous electrolyte are enclosed in the battery case; a preliminary charging step of charging the battery precursor to obtain a preliminarily charged battery precursor; a degassing step of discharging the gas contained in the battery case of the preliminarily charged battery precursor to the outside of the battery case to obtain a degassed battery precursor; and a charge / discharge step of performing charging, discharging, or charge / discharge on the degassed battery precursor to obtain a non-aqueous electrolyte secondary battery. A method for manufacturing a non-aqueous electrolyte secondary battery, including the above steps.

2. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte in the battery precursor contains a cyclic sulfonic acid ester compound represented by the following formula (I). 【Chemical 1】 (In formula (I), R １１ represents a group represented by formula (i-1), a group represented by formula (i-2), or a divalent hydrocarbon group having 1 to 6 carbon atoms. In formula (i-1), R １２ represents an oxymethylene group (—OCH ２ —), an oxyethylene group (—OCH ２ CH ２ —), an oxa group (—O—), or a divalent hydrocarbon group having 1 to 6 carbon atoms. In formula (i-2), R １３ represents a hydrocarbon group having 1 to 8 carbon atoms, or a hydrogen atom (—H). )

3. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1 or claim 2, wherein the non-aqueous electrolyte in the battery precursor contains at least one selected from the group consisting of a difluorophosphate represented by the following formula (II-1) and a monofluorophosphate represented by the following formula (II-2). 【Chemical 2】 (In formulas (II-1) and (II-2), (M ２１ )) ＋ each independently represents an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion.)

4. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1 or claim 2, wherein the non-aqueous electrolyte in the battery precursor contains a cyclic carbonate compound represented by the following formula (III). 【Chemical Formula 3】 (In formula (III), X represents a fluoro group (-F), a chloro group (-Cl), or a bromo group (-Br), and R ３１ each independently represents a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an oxa group (-O-), and h represents an integer of 0 to 3.)

5. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte in the battery precursor contains at least one selected from the group consisting of a cyclic sulfonic acid ester compound represented by the following formula (I), a difluorophosphate represented by the following formula (II-1), a monofluorophosphate represented by the following formula (II-2), and a cyclic carbonate compound represented by the following formula (III). 【Chemical Formula 4】 (In formula (I), R １１ represents a group represented by formula (i-1), a group represented by formula (i-2), or a divalent hydrocarbon group having 1 to 6 carbon atoms. In formula (i-1), R １２ represents an oxymethylene group (—OCH ２ —), an oxyethylene group (—OCH ２ CH ２ —), an oxa group (—O—), or a divalent hydrocarbon group having 1 to 6 carbon atoms. In formula (i-2), R １３ represents a hydrocarbon group having 1 to 8 carbon atoms, or a hydrogen atom (—H). ) 【Chemical Formula 5】 (In formulas (II-1) and (II-2), (M ２１ )) ＋ each independently represents an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion.) 【Chemical Formula 6】 (In formula (III), X represents a fluoro group (-F), a chloro group (-Cl), or a bromo group (-Br), and R ３１ each independently represents a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an oxa group (-O-), and h represents an integer of 0 to 3.)

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