Non-aqueous electrolyte secondary battery

Abstract

Provided is a non-aqueous electrolyte secondary batter comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode mixture layer supported by the positive electrode current collector. The positive electrode mixture layer contains a positive electrode active material and a fluorine-containing sulfonic acid compound. The ratio of the mass of the fluorine-containing sulfonic acid compound to the total mass of the positive electrode active material and the fluorine-containing sulfonic acid compound in the positive electrode mixture layer is 1.5% by mass or less.

Description

Non-aqueous electrolyte secondary battery CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2024-011916, filed on January 30, 2024 in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a non-aqueous electrolyte secondary battery.

[0003] Patent Document 1 discloses a compound of formula (1): R-SO ３ － and a Mn cation, wherein in formula (1), R is an alkyl group having 1 to 5 carbon atoms which may be substituted with a fluorine atom, an alkenyl group having 2 to 5 carbon atoms which may be substituted with a fluorine atom, an alkynyl group having 2 to 5 carbon atoms which may be substituted with a fluorine atom, or an aryl group which may be substituted with a fluorine atom.

[0004] Patent No. 7113995

[0005] However, non-aqueous electrolyte secondary batteries have a problem in that they generate heat quickly when an abnormality such as an internal short circuit occurs. One of the objects of the present disclosure is to suppress heat generation in non-aqueous electrolyte secondary batteries when an abnormality occurs.

[0006] The present disclosure relates to a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode includes a positive electrode current collector and a positive electrode mixture layer supported on the positive electrode current collector, the positive electrode mixture layer includes a positive electrode active material and a fluorine-containing sulfonic acid compound, and the ratio of the mass of the fluorine-containing sulfonic acid compound to the total mass of the positive electrode active material and the fluorine-containing sulfonic acid compound in the positive electrode mixture layer is 1.5 mass% or less.

[0007] The non-aqueous electrolyte secondary battery according to the present disclosure reduces the rate of heat generation in the event of an abnormality. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0008] 1 is a schematic vertical cross-sectional view of an example of a nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure.

[0009] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or greater and numerical value B or less." In the following description, when lower and upper limits for specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not greater than the upper limit. In the following description, when examples of components or methods are listed, only one of the listed examples may be used, or multiple of the listed examples may be used in combination, unless otherwise specified.

[0010] The present disclosure encompasses any combination of two or more claims arbitrarily selected from the appended claims, i.e., any combination of two or more claims arbitrarily selected from the appended claims may be combined unless a technical contradiction arises.

[0011] Non-aqueous electrolyte secondary batteries include lithium ion secondary batteries that use a liquid non-aqueous electrolyte, solid-state batteries that contain a gel electrolyte, all-solid-state batteries that use a solid electrolyte, and secondary batteries (metal secondary batteries) that use a consumable metal negative electrode (e.g., a negative electrode containing lithium metal).

[0012] A non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and a separator is usually disposed between the positive electrode and the negative electrode.

[0013] (Positive Electrode) The positive electrode according to the present disclosure includes a positive electrode current collector and a positive electrode mixture. The positive electrode mixture includes a positive electrode active material and a fluorine-containing sulfonic acid compound (hereinafter also referred to as "compound FS"). The positive electrode mixture may further include a binder, a conductive material, etc. The positive electrode mixture is supported on the positive electrode current collector to form a positive electrode mixture layer. The positive electrode mixture layer may be formed in the form of a film on the surface of the positive electrode current collector.

[0014] When an abnormality such as an internal short circuit occurs and the battery temperature rises, the compound FS quickly carbonizes, suppressing a further increase in the heat generation rate. Therefore, the safety of the non-aqueous electrolyte secondary battery is significantly improved when an abnormality occurs. The carbonized residue of the compound FS is a carbide with low flammability and is thought to act as a flame retardant. The carbide is thought to adhere to the surface of the positive electrode active material and suppress the release of oxygen due to decomposition of the positive electrode.

[0015] In the process of preparing the positive electrode mixture layer, the compound FS and particles of the positive electrode active material can be mixed in the positive electrode mixture layer. In this case, it is considered that the compound FS can cover at least a part of the surface of the positive electrode active material uniformly to some extent. Therefore, even a small amount of the compound FS can suppress the increase in the heat generation rate.

[0016] The ratio of the mass of the compound FS to the total mass of the positive electrode active material and the compound FS in the positive electrode mixture layer (i.e., the positive electrode mixture) (hereinafter also referred to as the "compound FS content") is sufficient if it is 1.5 mass% or less. The compound FS content may be 1.0 mass% or less, 0.5 mass% or less, 0.2 mass% or less, or 0.1 mass% or less. From the viewpoint of obtaining a high effect of the compound FS, the compound FS content may be 0.01 mass% or more, 0.03 mass% or more, or 0.05 mass% or more. The compound FS content may be, for example, 0.01 mass% or more and 1.5 mass% or less, 0.05 mass% or more and 1.5 mass% or less, or 0.01 mass% or more and 1.0 mass% or less.

[0017] The trace amount of compound FS described above also has the effect of improving the initial charge-discharge efficiency of the secondary battery. Compound FS is presumed to have the effect of uniformly facilitating the migration of lithium ions from the positive electrode during charging. When the positive electrode mixture layer contains compound FS, a uniform reaction is likely to proceed at the negative electrode as well. As a result, it is believed that the initial charge-discharge efficiency is improved.

[0018] In non-aqueous electrolyte secondary batteries, a coating called a solid electrolyte interface (SEI) is formed on the surface of the active material during initial charge and discharge cycles. Compound FS is thought to be involved in the formation of a high-quality SEI coating.

[0019] When the compound FS content is more strictly controlled, the compound FS may also exhibit the effect of reducing the internal resistance of the nonaqueous electrolyte secondary battery. It is believed that the formation of a high-quality SEI coating film reduces the internal resistance by suppressing fluctuations and disproportionation of the conductive network in the positive electrode mixture layer. For example, when the compound FS content is less than 0.2 mass%, the effect of reducing the internal resistance is likely to be significant.

[0020] (Specific Example of Compound FS) Compound FS is, for example, a compound represented by formula (1): R—SO ３ － The sulfonate anion may be represented by the following formula:

[0021] In formula (1), R is not particularly limited, but may be, for example, an alkyl group, an alkenyl group, or an alkynyl group. Among these, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an alkynyl group having 2 to 5 carbon atoms is preferred because they can suppress an increase in internal resistance and are easily converted into a carbide quickly. However, in the alkyl group having 1 to 5 carbon atoms, the alkenyl group having 2 to 5 carbon atoms, and the alkynyl group having 2 to 5 carbon atoms, at least one hydrogen atom is substituted with a fluorine atom. That is, an alkyl group having 1 to 5 carbon atoms is a fluoroalkyl group, an alkenyl group having 2 to 5 carbon atoms is a fluoroalkenyl group, and an alkynyl group having 2 to 5 carbon atoms is a fluoroalkynyl group. These fluoroalkyl groups, fluoroalkenyl groups, and fluoroalkynyl groups may each independently be linear or branched.

[0022] Examples of alkyl groups that serve as the base for fluoroalkyl groups having 1 to 5 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, n-pentyl, and t-pentyl groups. Among these, methyl, ethyl, n-propyl, and n-butyl groups are preferred. Considering the balance between the internal resistance of the secondary battery and the suppression of an increase in the heat generation rate due to the formation of carbides, groups having 2 to 4 carbon atoms are preferred, and butyl groups (especially n-butyl groups) are particularly preferred. In the alkyl group, the proportion of hydrogen atoms substituted with fluorine atoms is preferably 100% (perfluoroalkyl groups are preferred), but the proportion of hydrogen atoms substituted with fluorine atoms may be 30 atomic % or more, 50 atomic % or more, or 80 atomic % or more.

[0023] Examples of alkenyl groups that serve as the base for fluoroalkenyl groups having 2 to 5 carbon atoms include vinyl, allyl, propenyl, isopropenyl, 1-butenyl, 2-butenyl, 3-butenyl, isobutenyl, and 1-propenyl groups. Of these, vinyl, allyl, propenyl, and butenyl groups are preferred. The proportion of hydrogen atoms substituted with fluorine atoms in the alkenyl group is preferably 100%, but may be 30 atomic % or more, 50 atomic % or more, or 80 atomic % or more.

[0024] Examples of alkynyl groups that can serve as the base for fluoroalkynyl groups having 2 to 5 carbon atoms include 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl, and 3-butynyl. The proportion of hydrogen atoms substituted with fluorine atoms in the alkynyl group is preferably 100%, but may be 30 atomic % or more, 50 atomic % or more, or 80 atomic % or more.

[0025] A preferred example of a sulfonate anion is nonafluorobutanesulfonate ion (nonafluorobutanesulfonate anion (C ４ F ９ -SO ３ －However, sulfonate anions with similar molecular weights and structures are considered to have a good balance between suppressing the increase in the internal resistance of the secondary battery and the rate of heat generation due to the formation of char.

[0026] The compound FS may be a salt of a sulfonate anion and a cation. The type of cation is not particularly limited, but alkali metal ions and alkaline earth metal ions are preferred due to their excellent stability in non-aqueous electrolytes. That is, the compound FS may be at least one selected from the group consisting of fluorine-containing alkali metal sulfonates and fluorine-containing alkaline earth metal sulfonates (hereinafter also referred to as "compound FS alkaline earth metal salt"). The compound FS alkaline earth metal salt may account for 50% by mass or more of the compound FS, or may account for 80% by mass or more, or 100% of the compound FS may be the compound FS alkaline earth metal salt.

[0027] Among the cations constituting the compound FS alkaline (earth) metal salt, alkali metal ions are preferred because they have excellent stability in non-aqueous electrolytes. Preferred examples of compound FS include fluorine-containing potassium sulfonate, fluorine-containing lithium sulfonate, and fluorine-containing sodium sulfonate. For example, fluorine-containing potassium sulfonate (e.g., R-SO ３ K (e.g. C ４ F ９ -SO ３ K)) has an excellent balance between the internal resistance of the secondary battery and the suppression of an increase in the rate of heat generation due to the formation of carbides.

[0028] When a fluorine-containing potassium sulfonate is used as at least a part of the compound FS, the content of potassium ions in the positive electrode mixture layer is preferably 0.0005% by mass or more and 0.2% by mass or less, and may be 0.0005% by mass or more and 0.01% by mass or less.

[0029] (Positive Electrode Active Material) A preferred example of the positive electrode active material includes a lithium-containing composite oxide containing at least Ni. From the viewpoint of increasing capacity, the proportion of Ni in the metal elements other than Li in the lithium-containing composite oxide is preferably 80 atomic % or more. Among these, the lithium-containing composite oxide is preferably a lithium nickel oxide (composite oxide N) containing Li and Ni, in which the proportion of Ni in the metal elements other than Li is 80 atomic % or more and which has a layered rock salt crystal structure. The proportion of Ni in the metal elements other than Li may be 88 atomic % or more, 90 atomic % or more, or 95 atomic % or more. In the composite oxide N, the proportion of Ni in the metal elements other than Li is less than 100 atomic %, may be 99 atomic % or less, or may be 98 atomic % or less.

[0030] The positive electrode active material may contain other materials, but the proportion of the composite oxide N in the positive electrode active material is, for example, 70% by mass or more, 90% by mass or more, 95% by mass or more, or even 100%.

[0031] The composite oxide N may further contain Co and Mn, which contribute to stabilizing the crystal structure of the composite oxide N.

[0032] From the viewpoint of reducing costs and increasing capacity, the proportion of Co in the metal elements other than Li contained in the composite oxide N is preferably 0 atomic % or more and 20 atomic % or less, and more preferably more than 0 atomic % and 5 atomic % or less.

[0033] From the viewpoint of cost reduction, the ratio of Mn to the metal elements other than Li contained in the composite oxide N may be 1 atomic % or more and 10 atomic % or less, 2 atomic % or more and 5 atomic % or less, or 3 atomic % or more and 5 atomic % or less.

[0034] The composite oxide N may further contain Al. Al contributes to stabilizing the crystal structure of the composite oxide N. The composite oxide N containing Co, Mn, and Al is highly alkaline, so the role of the organic additive is particularly important.

[0035] The proportion of Al in the metal elements other than Li contained in the composite oxide N may be 0.1 atomic % or more and 5 atomic % or less, 0.2 atomic % or more and 3 atomic % or less, or 0.5 atomic % or more and 1 atomic % or less.

[0036] The composite oxide N is, for example, a compound represented by the formula: Li ｙ Ni ｘ M （１－ｘ） O ２－δ (0.8≦x≦1, 0<y≦1.2, and −0.05≦δ≦0.05). Here, the element M may include at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca, Zr, W, and B. x, which indicates the atomic ratio of Ni, may be 0.98 or less, or 0.95 or less. x increases or decreases due to charging and discharging of the secondary battery.

[0037] The element M is represented by the formula: Co １－ｘ－ａ－ｂ Mn ａ Al ｂ (0<a<0.05 and 0<b<0.05).

[0038] The thickness of the positive electrode mixture layer is not particularly limited, but may be, for example, 50 μm to 150 μm, or 75 μm to 125 μm. A single positive electrode active material layer may be formed by a plurality of layers having different morphologies. For example, two or more layers containing positive electrode active materials with different average particle sizes may be stacked, or two or more layers containing positive electrode active materials of different types or compositions may be stacked.

[0039] The average particle size (D50) of the composite oxide N particles is, for example, 1 μm or more and 50 μm or less, and may be 5 μm or more and 25 μm or less. The average particle size (D50) refers to the median diameter at which the cumulative volume is 50% in a volume-based particle size distribution. The volume-based particle size distribution can be measured using a commercially available laser diffraction / scattering particle size distribution measuring device.

[0040] (Binder) Preferred binders include, for example, fluorine-containing polymers and hydrogenated nitrile butadiene rubber. Preferred examples of fluorine-containing polymers include vinylidene fluoride polymers. Examples of vinylidene fluoride polymers include polymers of monomers containing vinylidene fluoride. The fluorine-containing polymer may be a combination of a vinylidene fluoride polymer and another fluorine-containing polymer. The vinylidene fluoride polymer may be a copolymer of vinylidene fluoride and another monomer. Examples of vinylidene fluoride polymers include polyvinylidene fluoride (PVDF) and vinylidene fluoride-hexafluoropropylene copolymer. The vinylidene fluoride polymer contains monomer units derived from vinylidene fluoride in a proportion of, for example, 50 mol% or more, and preferably 80 mol% or more.

[0041] In the positive electrode mixture layer, the amount of binder per 100 parts by mass of the positive electrode active material may be 0.1 parts by mass or more, or 0.5 parts by mass or more, and may be 2.0 parts by mass or less, or 1.2 parts by mass or less.

[0042] (Conductive Material) The conductive material that may be contained as an optional component in the positive electrode mixture layer is not particularly limited, and known conductive materials may be used. Among them, conductive carbonaceous materials are preferred. Examples of conductive carbonaceous materials include conductive carbon particles such as carbon black and graphite, carbon nanotubes (CNTs), and carbon fibers other than CNTs.

[0043] (Positive Electrode Current Collector) The positive electrode current collector is made of a sheet-like conductive material. Examples of the positive electrode current collector include non-porous conductive substrates (such as metal foil) and porous conductive substrates (such as mesh, net, and punched sheet). The positive electrode mixture layer is supported in the form of a film on one or both surfaces of the positive electrode current collector. The material of the positive electrode current collector is not particularly limited, but stainless steel, aluminum, aluminum alloy, titanium, and the like can be used. Alternatively, the positive electrode current collector may be a laminated sheet in which a metal or alloy such as stainless steel, aluminum, aluminum alloy, or titanium is laminated on the surface of a resin film. The resin material of the resin film is not particularly limited, but examples thereof include polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polyethylene, polypropylene, polyamide, and polyimide.

[0044] (Method for Manufacturing Positive Electrode) An example of a method for manufacturing a positive electrode used in a nonaqueous electrolyte secondary battery according to the present disclosure (hereinafter also referred to as "manufacturing method (M)") will be described. The manufacturing method (M) includes a first step of preparing a positive electrode slurry and a second step of forming a positive electrode mixture layer on the surface of a positive electrode current collector using the positive electrode slurry. The second step includes a step of preparing a positive electrode current collector, forming a coating film of the positive electrode slurry on the surface of the positive electrode current collector, and a step of heating and drying the coating film.

[0045] The positive electrode slurry prepared in the first step of manufacturing method (M) includes a liquid medium and a positive electrode mixture dispersed in the liquid medium. The positive electrode mixture is the same as that described above. For example, the positive electrode slurry can be prepared by mixing a positive electrode active material, a binder, compound FS, a conductive material, and a liquid medium. Compound FS is preferably soluble in the liquid medium. The positive electrode slurry can be prepared by mixing the positive electrode mixture with the liquid medium. A solution in which compound FS is previously dissolved in a liquid medium may be mixed with other components. The mixing method is not particularly limited, and known mixing methods may be used.

[0046] The liquid medium may be an organic solvent or water. As the organic solvent, N-methyl-2-pyrrolidone (NMP) is preferred, but alcohols such as ethanol, ethers such as tetrahydrofuran, amides such as dimethylformamide, ketones such as cyclohexanone, etc. may also be used.

[0047] In the second step, the step of forming a coating film of the positive electrode slurry on the surface of the positive electrode current collector can be performed using a coating device such as a bar coater, a gravure coater, a blade coater, a roll coater, a comma coater, a die coater, a lip coater, etc. Multiple positive electrode slurries with different compositions may be prepared, and two or more layers of these slurries may be coated one on top of the other.

[0048] In the second step, the coating film is preferably dried at 200° C. or less, and the coating film may be dried at a temperature of, for example, 150° C. to 190° C. The coating film drying step causes the liquid medium to volatilize, forming an unrolled coating film.

[0049] Usually, the unrolled coating film is then rolled to form a positive electrode mixture layer. The conditions for the rolling are not particularly limited. The density of the positive electrode active material in the positive electrode mixture layer is, for example, 3.3 g / cm ３ Above, 4.0g / cm ３ or less, and 3.5 g / cm ３ 4.0g / cm or more ３ The following is also acceptable.

[0050] The positive electrode mixture layer may be formed on only one surface of the positive electrode current collector, or on both surfaces of the positive electrode current collector, depending on the structure of the battery.

[0051] (Analysis) Next, the identification of compound FS contained in the positive electrode mixture layer and the measurement of the compound FS content will be described. The identification of compound FS and the measurement of the compound FS content can be performed by collecting a positive electrode from a battery in a discharged state, peeling the positive electrode mixture layer (positive electrode mixture) from the positive electrode current collector, and analyzing the compound FS separated from the positive electrode mixture. Compound FS can be separated, for example, by weighing out a sample equivalent to 1.0 g of the positive electrode mixture, mixing it with 30 mL of NMP, shaking it for 30 seconds to dissolve the compound FS, and filtering it, thereby obtaining an NMP solution containing compound FS.

[0052] Examples of analytical methods include IR spectroscopy (infrared spectroscopy), UV spectroscopy (ultraviolet-visible spectroscopy), NMR analysis (nuclear magnetic resonance spectroscopy), LC-MS (liquid chromatography mass spectroscopy), GC-MS (gas chromatography mass spectroscopy), and ICP-AES (inductively coupled plasma atomic emission spectroscopy). Furthermore, a cross section of the positive electrode mixture layer of the positive electrode sampled from the battery in a discharged state may be analyzed using SEM-EDX (scanning electron microscope-energy dispersive X-ray analysis), TOF-SIMS (time-of-flight secondary ion mass spectroscopy), or the like. The cross section of the positive electrode mixture layer may be processed using a cross-section polisher (CP), a focused ion beam (FIB), or the like.

[0053] When the positive electrode mixture layer contains alkali metal ions or alkaline earth metal ions, the ions can also be identified and quantified by any of the above methods.

[0054] In the nonaqueous electrolyte secondary battery according to the present disclosure, the components other than the positive electrode are not particularly limited, and components used in known nonaqueous electrolyte secondary batteries may be applied. Examples of the components of the nonaqueous electrolyte secondary battery are described below.

[0055] (Negative Electrode) The negative electrode may have at least a negative electrode current collector. The negative electrode may or may not have a negative electrode mixture layer. The negative electrode may be a negative electrode in which lithium metal (or a lithium alloy) precipitates during charging and dissolves in a non-aqueous electrolyte during discharge. That is, the non-aqueous electrolyte secondary battery according to the present disclosure may be a lithium metal secondary battery. In the case of a lithium ion secondary battery, the negative electrode typically includes a negative electrode mixture containing a negative electrode active material. The negative electrode mixture is supported on a negative electrode current collector to form a negative electrode mixture layer. The negative electrode mixture layer is formed on the surface of the negative electrode current collector.

[0056] Lithium metal secondary batteries, in which lithium metal precipitates on the negative electrode during charging and dissolves in a non-aqueous electrolyte during discharge, are expected to have higher capacities than lithium-ion batteries, but they suffer from a significant problem: rapid heat generation when an abnormality occurs. This is because the lithium metal at the negative electrode is highly reactive with oxygen released from the positive electrode. On the other hand, when compound FS is uniformly contained in the positive electrode mixture layer (in other words, when particles of the positive electrode active material and compound FS are mixed in the positive electrode mixture layer), heat generation when an abnormality occurs is significantly suppressed and the heat generation rate is significantly reduced, even in lithium metal secondary batteries.

[0057] A trace amount of compound FS is presumed to have the effect of uniformly transferring lithium ions from the positive electrode during charging, and in lithium metal secondary batteries, it is possible to uniformly deposit lithium metal on the negative electrode, thereby improving the initial charge / discharge efficiency of the secondary battery.

[0058] In a lithium metal secondary battery, for example, 70% or more of the rated capacity is achieved by the deposition and dissolution of lithium metal. The movement of electrons at the negative electrode during charging and discharging is mainly due to the deposition and dissolution of lithium metal at the negative electrode. Specifically, 70 to 100% (e.g., 80 to 100% or 90 to 100%) of the movement of electrons (or current from another perspective) at the negative electrode during charging and discharging is due to the deposition and dissolution of lithium metal. The negative electrode of a lithium metal secondary battery differs from a negative electrode in which the movement of electrons at the negative electrode during charging and discharging is mainly due to the absorption and release of lithium ions by the negative electrode active material (e.g., graphite).

[0059] In a battery in which lithium metal is deposited on the negative electrode during charging, the open circuit potential (OCP) of the negative electrode at full charge is, for example, 70 mV or less relative to lithium metal (lithium dissolution and deposition potential). A fully charged state refers to a state in which the battery is charged to a state of charge (SOC) of, for example, 0.98×C or more, where C is the rated capacity of the battery. The open circuit potential (OCP) of the negative electrode at full charge can be measured by disassembling a fully charged battery under an argon atmosphere, removing the negative electrode, and assembling a cell using lithium metal as a counter electrode. The nonaqueous electrolyte of the cell may have the same composition as the nonaqueous electrolyte in the disassembled battery.

[0060] The negative electrode mixture contains a negative electrode active material as an essential component. The negative electrode mixture may contain optional components such as a binder, a thickener, and a conductive material. These optional components may include the components exemplified as the components of the positive electrode.

[0061] The negative electrode mixture layer may be formed by applying a negative electrode slurry, in which the components of the negative electrode mixture are dispersed in a liquid medium (dispersion medium), to the surface of the negative electrode current collector and drying the applied film. The dried coating may be rolled as necessary. The liquid medium may be any of the liquid media exemplified for the positive electrode slurry.

[0062] (Negative Electrode Active Material) The negative electrode active material is selected depending on the type of non-aqueous electrolyte secondary battery. An example of the negative electrode active material is a material capable of absorbing and releasing lithium ions. Examples of such materials include carbonaceous materials and Si-containing materials. The negative electrode active material may contain or be a Si-containing material. Metallic lithium, a lithium alloy, or the like may be used as the negative electrode active material. The negative electrode may contain one type of negative electrode active material or a combination of two or more types.

[0063] Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and hardly graphitizable carbon (hard carbon). One type of carbonaceous material may be used alone, or two or more types may be used in combination. Graphite is preferred because it has excellent charge / discharge stability and a small irreversible capacity. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles.

[0064] Examples of Si-containing materials include simple Si, silicon alloys, silicon compounds (such as silicon oxides), and composite materials in which a silicon phase is dispersed in a lithium ion conductive phase (matrix). Examples of silicon oxides include SiO ｘ The lithium ion conductive phase may include SiO particles. For example, x is 0.5≦x<2, and may be 0.8≦x≦1.6. ２ At least one selected from the group consisting of a silicate phase, a silicate phase, and a carbon phase may be used.

[0065] (Negative electrode current collector) A metal foil may be used for the negative electrode current collector. The negative electrode current collector may be porous. The material of the negative electrode current collector is not particularly limited, and stainless steel, nickel, nickel alloy, copper, copper alloy, etc. may be used. Alternatively, a laminated sheet in which a metal or alloy such as stainless steel, nickel, nickel alloy, copper, or copper alloy is laminated on the surface of a resin film may be used as the negative electrode current collector. The resin material of the resin film is not particularly limited, and examples thereof include polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polyethylene, polypropylene, polyamide, and polyimide.

[0066] (Non-aqueous electrolyte) The non-aqueous electrolyte includes a solvent (non-aqueous solvent) and a solute dissolved in the solvent. Examples of the solute include a lithium salt. Various additives may be added to the non-aqueous electrolyte.

[0067] The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution), a gel electrolyte, or a solid electrolyte. The liquid electrolyte is, for example, an electrolytic solution containing a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The concentration of the lithium salt in the electrolytic solution is, for example, 0.5 mol / L or more and 2 mol / L or less. The electrolytic solution may contain known additives.

[0068] The gel electrolyte contains a lithium salt and a matrix polymer, or a lithium salt, a non-aqueous solvent, and a matrix polymer. The matrix polymer is, for example, a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, polyether resin, and polyethylene oxide.

[0069] As the solid electrolyte, for example, a material known in all-solid-state lithium ion secondary batteries (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) can be used.

[0070] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent, which generates lithium ions and anions.

[0071] The anion is BF ４ － , ClO ４ － , P.F. ６ － , C.F. ３ SO ３ － , C.F. ３ CO ２ － , anions of imides, anions of oxalate complexes, etc. Examples of the anions of imides include N(SO ２ F) ２ － , N(SO ２ CF ３ ) ２ － , N(C ｍ F ２ｍ＋１ SO ２ ) ｘ (C ｎ F ２ｎ＋１SO ２ ) y － (m and n are each independently an integer of 0 or 1 or more, and x and y are each independently 0, 1, or 2, satisfying the relationship x+y=2). The anion of the oxalate complex may contain boron and / or phosphorus. Examples of the anion of the oxalate complex include bisoxalate borate anion and difluorooxalate borate anion (BF ２ (C ２ O ４ ) － ), P.F. ４ (C ２ O ４ ) － , P.F. ２ (C ２ O ４ ) ２ － The non-aqueous electrolyte may contain one of these anions alone or two or more of them.

[0072] From the viewpoint of suppressing the deposition of lithium metal in a dendritic form, the nonaqueous electrolyte preferably contains at least an anion of an oxalate complex, and more preferably contains an oxalate complex anion having fluorine. The interaction between the oxalate complex anion having fluorine and lithium facilitates the uniform deposition of lithium metal in the form of fine particles. This makes it easier to suppress local deposition of lithium metal. The oxalate complex anion having fluorine may be combined with another anion. The other anion may be PF ６ － and / or an anion of an imide.

[0073] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and halogen-substituted derivatives thereof. The non-aqueous electrolyte may contain one or more of these non-aqueous solvents. Examples of halogen-substituted derivatives include fluorides.

[0074] Examples of esters include carbonate esters and carboxylic acid esters. Examples of cyclic carbonate esters include ethylene carbonate, propylene carbonate, and fluoroethylene carbonate (FEC). Examples of chain carbonate esters include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate. Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Examples of chain carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0075] Examples of the ether include cyclic ethers and chain ethers. Examples of the cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of the chain ethers include 1,2-dimethoxyethane (DME), diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diethylene glycol dimethyl ether.

[0076] The concentration of the lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 3.5 mol / L or less. The concentration of the anion in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less. Furthermore, the concentration of the anion of the oxalate complex in the non-aqueous electrolyte may be 0.05 mol / L or more and 1 mol / L or less.

[0077] The non-aqueous electrolyte may contain an additive. The additive may form a coating on the negative electrode. The formation of a coating derived from the additive on the negative electrode makes it easier to suppress the formation of dendrites. Examples of such additives include vinylene carbonate, FEC, and vinyl ethyl carbonate (VEC).

[0078] (Separator) The separator is disposed between the positive electrode and the negative electrode. The separator preferably has high ion permeability and adequate mechanical strength and insulating properties. The separator may be made of a microporous thin film, woven fabric, nonwoven fabric, or the like. Examples of separator materials include polyolefins (polypropylene, polyethylene, etc.) and other resins.

[0079] (Exterior Body) The exterior body (battery case) houses the electrode group and the non-aqueous electrolyte. The exterior body is not particularly limited, and a known exterior body may be used. The electrode group is composed of a positive electrode, a negative electrode, and a separator. The configuration of the electrode group is not particularly limited, and may be a wound type or a laminated type. A wound type electrode group is formed by winding a positive electrode and a negative electrode with a separator interposed therebetween. A laminated type electrode group is formed by stacking a positive electrode and a negative electrode with a separator interposed therebetween. The shape of the non-aqueous electrolyte secondary battery is not particularly limited, and may be cylindrical, prismatic, coin-shaped, button-shaped, laminate-shaped, etc.

[0080] 1 is a longitudinal cross-sectional view of a cylindrical secondary battery 10 (hereinafter also simply referred to as "battery 10") according to the present disclosure. However, the present disclosure is not limited to the following configuration.

[0081] In FIG. 1 , a battery 10 includes an electrode group 18, a nonaqueous electrolyte (not shown), and a cylindrical battery case (metal can) 22 with a bottom that accommodates these components. A sealing body 11 is crimped to the opening of the battery case 22 via a gasket 21, thereby sealing the interior of the battery 10. The sealing body 11 includes an internal pressure-activated safety valve that cuts off current and, if necessary, ruptures when the battery's internal pressure increases excessively. Specifically, the sealing body includes a valve body 12 having a thin portion, a metal plate 13, and an annular insulating member 14 interposed between the valve body 12 and the metal plate 13. The valve body 12 and the metal plate 13 are electrically connected to each other at their respective centers. A positive electrode lead 15a extending from a positive electrode 15 is connected to the metal plate 13. Thus, the valve body 12 functions as both an external terminal for the positive electrode 15 and a safety valve. When the internal pressure of the battery increases, the connection between the valve body 12 and the metal plate 13 is severed, interrupting the current. Furthermore, when the thin-walled portion breaks, gas is released to the outside, ensuring safety. The negative electrode lead 16a extending from the negative electrode 16 is connected to the inner bottom surface of the battery case 22. An annular groove 22a is formed near the open end of the battery case 22. A first insulating plate 23 is disposed between one end face of the electrode group 18 and the annular groove 22a. A second insulating plate 24 is disposed between the other end face of the electrode group 18 and the bottom of the battery case 22. The electrode group 18 is formed by winding the positive electrode 15 and the negative electrode 16 together with the separator 17 interposed therebetween into a cylindrical shape. The outermost periphery of the electrode group 18 is formed at the end of the winding of the negative electrode 16. In other words, in the electrode group 18, the outermost periphery of the negative electrode 16 is disposed outside the outermost periphery of the positive electrode 15.

[0082] (Additional Notes) The above description discloses the following technologies. (Technology 1) A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode includes a positive electrode current collector and a positive electrode mixture layer supported on the positive electrode current collector, and the positive electrode mixture layer includes a positive electrode active material and a fluorine-containing sulfonic acid compound, and the ratio of the mass of the fluorine-containing sulfonic acid compound to the total mass of the positive electrode active material and the fluorine-containing sulfonic acid compound in the positive electrode mixture layer is 1.5 mass% or less. (Technology 2) The non-aqueous electrolyte secondary battery according to Technology 1, wherein the ratio of the mass of the fluorine-containing sulfonic acid compound to the total mass of the positive electrode active material and the fluorine-containing sulfonic acid compound in the positive electrode mixture layer is 0.05 mass% or more. (Technology 3) The fluorine-containing sulfonic acid compound is a compound represented by the formula (1): R—SO ３ － The nonaqueous electrolyte secondary battery according to Technology 1 or 2, wherein the nonaqueous electrolyte secondary battery contains a sulfonate anion represented by the formula (1): wherein R is an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an alkynyl group having 2 to 5 carbon atoms, and wherein at least one hydrogen atom of each of the alkyl group, the alkenyl group, and the alkynyl group is substituted with a fluorine atom. (Technology 4) The nonaqueous electrolyte secondary battery according to Technology 3, wherein the sulfonate anion is nonafluorobutanesulfonate (nonafluorobutanesulfonic acid anion). (Technology 5) The nonaqueous electrolyte secondary battery according to any one of Technology 1 to 4, wherein the fluorine-containing sulfonic acid compound is at least one selected from the group consisting of fluorine-containing alkali metal sulfonate and fluorine-containing alkaline earth metal sulfonate. (Technology 6) The nonaqueous electrolyte secondary battery according to any one of Technology 1 to 5, wherein the fluorine-containing sulfonic acid compound contains a fluorine-containing potassium sulfonate. (Technology 7) The nonaqueous electrolyte secondary battery according to Technology 5 or Technology 6, wherein the content of potassium ions in the positive electrode mixture layer is 0.0005 mass% or more and 0.2 mass% or less. (Technology 8) The nonaqueous electrolyte secondary battery according to any one of Technology 1 to Technology 7, wherein lithium metal precipitates in the negative electrode during charging and the lithium metal dissolves in the nonaqueous electrolyte during discharging.

[0083] The present disclosure will be specifically described below based on examples, but the present disclosure is not limited to the following examples.

[0084] (Preparation of Positive Electrode Slurry A1) Positive electrode active material (LiNi ０．９ Co ０．０４ Mn ０．０７ Al ０．０３ O ２ ) 99.95 parts by mass as compound FS, potassium nonafluorobutanesulfonate (C ４ F ９ -SO ３ Positive electrode slurry A1 was prepared by mixing 0.05 parts by mass of fluorine-containing polymer (F) (Fiber-Resin-Coated Polymer), 0.6 parts by mass of polyvinylidene fluoride (PVDF) as a binder, 0.8 parts by mass of acetylene black (conductive material) as a conductive material, and an appropriate amount of NMP (liquid medium). The positive electrode active material, compound FS, PVDF, and conductive material are components of the positive electrode mixture. The compound FS content was 0.05% by mass.

[0085] (Preparation of Positive Electrode Slurry A2) The positive electrode mixture was prepared by mixing 99.9 parts by mass of the positive electrode active material, 10 parts by mass of the compound FS(C ４ F ９ -SO ３ Positive electrode slurry A2 was prepared in the same manner and under the same conditions as positive electrode slurry A1, except that the additives used were changed to 0.1 parts by mass of fluorine-containing polymer (F), 0.6 parts by mass of polyvinylidene fluoride (PVDF), and 0.8 parts by mass of acetylene black. The content of compound FS was 0.1% by mass.

[0086] (Preparation of Positive Electrode Slurry A3) The positive electrode mixture was prepared by mixing 99.8 parts by mass of the positive electrode active material, 10 parts by mass of the compound FS(C ４ F ９ -SO ３ Positive electrode slurry A3 was prepared in the same manner and under the same conditions as positive electrode slurry A1, except that the additives used were changed to 0.2 parts by mass of fluorine-containing polymer (F), 0.6 parts by mass of polyvinylidene fluoride (PVDF), and 0.8 parts by mass of acetylene black. The content of compound FS was 0.2% by mass.

[0087] (Preparation of Positive Electrode Slurry A4) The positive electrode mixture was prepared by mixing 99 parts by mass of the positive electrode active material, 10 parts by mass of the compound FS(C ４ F ９ -SO ３Positive electrode slurry A4 was prepared in the same manner and under the same conditions as positive electrode slurry A1, except that the additives used were changed to 1 part by mass of fluorine-containing polymer K), 0.6 parts by mass of polyvinylidene fluoride (PVDF), and 0.8 parts by mass of acetylene black. The content of compound FS was 1% by mass.

[0088] (Preparation of Positive Electrode Slurry A5) The positive electrode mixture was prepared by mixing 98.5 parts by mass of the positive electrode active material, 10 parts by mass of the compound FS(C ４ F ９ -SO ３ Positive electrode slurry A5 was prepared in the same manner and under the same conditions as positive electrode slurry A1, except that the additives used were changed to 1.5 parts by mass of cellulose acetate (C1), 0.6 parts by mass of polyvinylidene fluoride (PVDF), and 0.8 parts by mass of acetylene black. The content of compound FS was 1.5% by mass.

[0089] (Preparation of Positive Electrode Slurry B1) Positive electrode slurry B1 was prepared in the same manner and under the same conditions as positive electrode slurry A1, except that the positive electrode mixture was changed to 100 parts by mass of positive electrode active material, 0.6 parts by mass of polyvinylidene fluoride (PVDF), and 0.8 parts by mass of acetylene black. Compound FS was not used (compound FS content: 0%).

[0090] (Preparation of Positive Electrode Slurry B2) The positive electrode mixture was prepared by mixing 98 parts by mass of the positive electrode active material, 10 parts by mass of the compound FS(C ４ F ９ -SO ３ Positive electrode slurry B2 was prepared in the same manner and under the same conditions as positive electrode slurry A1, except that the additives used were changed to 2 parts by mass of cellulose acetate (C10), 0.6 parts by mass of polyvinylidene fluoride (PVDF), and 0.8 parts by mass of acetylene black. The content of compound FS was 2% by mass.

[0091] Examples 1 to 5 and Comparative Examples 1 and 2 (1) Preparation of Positive Electrodes The above-described positive electrode slurry was applied to the surface of an aluminum foil (positive electrode current collector) to form a coating film. After drying, the coating film was rolled and cut to a predetermined size. In this manner, positive electrodes including aluminum foil and positive electrode mixture layers formed on both sides thereof were prepared. The positive electrodes prepared using positive electrode slurries A1 to A5 were designated positive electrodes A1 to A5, respectively, and the positive electrodes prepared using positive electrode slurries B1 and B2 were designated positive electrodes B1 and B2, respectively.

[0092] (2) Preparation of Negative Electrode An electrolytic copper foil (thickness: 10 μm) was cut into a predetermined electrode size to prepare a negative electrode.

[0093] (3) Preparation of Non-Aqueous Electrolyte Dimethoxyethane (DME) and fluorinated ether (1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether) were mixed in a volume ratio of 1:1, and LiN(SO ２ F) ２ (LiFSI) was dissolved at a concentration of 1 mol / L, and LiBF ２ (C ２ O ４ ) was dissolved in a concentration of 0.1 mol / L to prepare an electrolyte solution.

[0094] (4) Fabrication of Secondary Batteries Leads were attached to the positive and negative electrodes. Next, a separator was placed between the positive and negative electrodes, and the positive and negative electrodes and the separator were spirally wound to fabricate an electrode group. The electrode group and the above-mentioned electrolyte were housed in a case made of a laminate sheet containing aluminum foil. In this way, example batteries A1 to A5 having positive electrodes A1 to A5 and comparative batteries B1 and B2 having positive electrodes B1 and B2 were fabricated.

[0095] Comparative Example 3: Compound FS(C) was added to the electrolyte at a concentration of 0.024% by mass. ４ F ９ -SO ３ A battery B3 of Comparative Example 3 was fabricated in the same manner as the battery of Comparative Example 1 (i.e., using the positive electrode B1), except that compound FS(C) was dissolved in the battery B3. ４ F ９ -SO ３ The absolute amount of K) was the same as that of Battery A2.

[0096] [Evaluation] The initial charge / discharge efficiency, internal resistance, and safety during heat generation of each battery were measured. The results are shown in Table 1.

[0097] <Charge / Discharge Efficiency> Each battery was charged at a constant current equivalent to 0.1 It in a 25°C environment until the battery voltage reached 4.2 V, and then continuously charged at a constant voltage of 4.2 V until the current value reached 0.01 It, and the charge capacity Cc was determined. After charging, the battery was rested for 20 minutes, and then discharged at a constant current equivalent to 0.1 It until the battery voltage reached 3.0 V, and the discharge capacity Cd was determined. The charge / discharge efficiency (100Cd / Cc (%)) was calculated from Cc and Cd.

[0098] <Internal Resistance> In a temperature environment of 25°C, the battery was charged at a constant current of 0.3 It until the voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current reached 0.05 It. Next, the battery was discharged at a constant current of 0.3 It for 100 minutes to bring the state of charge (SOC) to 50%.

[0099] The battery with an SOC of 50% was discharged for 10 seconds at currents of 0 A, 0.1 A, 0.5 A, and 1.0 A, and the voltage was measured. The relationship between the discharge current and the voltage after 10 seconds was approximated to a straight line using the least squares method, and the internal resistance (ACIR) was calculated from the absolute value of the slope. The values ​​in Table 1 are relative values, with the evaluation result of Battery B1 being 100, and the smaller the value, the better the performance.

[0100] <Safety during heat generation> An ARC (Accelerating Rate Calorimetry) test was conducted. The battery was charged to 4.3 V at a constant current of 40 mA, and then inserted into a cylindrical sample container made of stainless steel (SUS304). Using an ARC tester manufactured by NETZSTH, the battery was heated to 300°C in the Heat-wait-search measurement mode. The temperature rise due to the self-heating of the battery from 110°C was measured, and the time until the temperature rise rate reached 10°C / min or more was measured. The longer this time, the slower the heat generation rate and the higher the safety.

[0101]

[0102] From Table 1, it can be seen that when compound FS is added to the positive electrode mixture, if the content of compound FS is 1.5 mass% or less, safety in the event of an abnormality can be significantly improved while maintaining a low internal resistance. It can also be seen that adding compound FS to the electrolyte solution does not provide an effective way of improving safety.

[0103] It can also be seen that when the content of compound FS is small (for example, 0.1 mass % or less), the internal resistance tends to decrease. Furthermore, when the content of compound FS is 1.5 mass % or less, it can also be seen that the charge / discharge efficiency is improved.

[0104] The nonaqueous electrolyte secondary battery according to the present disclosure is useful as a main power source for mobile communication devices, portable electronic devices, electric vehicles, and the like. Although the present invention has been described with reference to presently preferred embodiments, such disclosure should not be construed as limiting. Various modifications and alterations will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. Accordingly, the appended claims should be construed to cover all modifications and alterations without departing from the true spirit and scope of the present invention.

[0105] 10: Secondary battery, 11: Sealing body, 12: Valve body, 13: Metal plate, 14: Insulating member, 15: Positive electrode, 15a: Positive electrode lead, 16: Negative electrode, 16a: Negative electrode lead, 17: Separator, 18: Electrode group, 21: Gasket, 22: Battery can, 22a: Groove, 23: First insulating plate, 24: Second insulating plate, 16: Negative electrode

Claims

1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode includes a positive electrode current collector and a positive electrode mixture layer supported on the positive electrode current collector, the positive electrode mixture layer includes a positive electrode active material and a fluorine-containing sulfonic acid compound, and the ratio of the mass of the fluorine-containing sulfonic acid compound to the total mass of the positive electrode active material and the fluorine-containing sulfonic acid compound in the positive electrode mixture layer is 1.5 mass% or less.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the ratio of the mass of the fluorine-containing sulfonic acid compound to the total mass of the positive electrode active material and the fluorine-containing sulfonic acid compound in the positive electrode mixture layer is 0.05 mass % or more.

3. The fluorine-containing sulfonic acid compound is represented by the formula (1): R—SO ３ － wherein in formula (1), R is an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an alkynyl group having 2 to 5 carbon atoms, and at least one hydrogen atom in each of the alkyl group, the alkenyl group, and the alkynyl group is substituted with a fluorine atom.

4. The nonaqueous electrolyte secondary battery according to claim 3, wherein the sulfonate anion is a nonafluorobutanesulfonate ion (nonafluorobutanesulfonic acid anion).

5. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the fluorine-containing sulfonic acid compound is at least one selected from the group consisting of fluorine-containing alkali metal sulfonates and fluorine-containing alkaline earth metal sulfonates.

6. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the fluorine-containing sulfonic acid compound includes a fluorine-containing potassium sulfonate.

7. The nonaqueous electrolyte secondary battery according to claim 6, wherein the content of potassium ions in the positive electrode mixture layer is 0.0005% by mass or more and 0.2% by mass or less.

8. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein lithium metal precipitates on the negative electrode during charging, and the lithium metal dissolves in the non-aqueous electrolyte during discharging.

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