Nonaqueous electrolyte secondary battery

Abstract

This nonaqueous electrolyte secondary battery is provided with a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte. The positive electrode contains LiMn (1-y) FeyPO4 (wherein 0 < y < 1) as a positive electrode active material, and the non-aqueous electrolyte solution contains a compound represented by formula (1). In formula (1), Q represents an alkylene group, an alkenylene group or the like, and X represents a group represented by formula (2a) or formula (2b). R1 represents an alkyl group, an alkenyl group, an alkynyl group, an aryl group, a hydroxyl group, a lithium oxygen group or the like;

Description

Technical Field

[0001] This invention relates to a non-aqueous electrolyte secondary battery. Background Technology

[0002] With growing concern for solving environmental problems and achieving a sustainable circular society, research is extensively being conducted on non-aqueous electrolyte secondary batteries, represented by lithium-ion batteries. Lithium-ion batteries possess high voltage and energy density, making them suitable as power sources for laptops, mobile phones, electric vehicles, and more.

[0003] In lithium-ion batteries, various additives are typically added to the electrolyte to improve battery performance. One such additive, for example, is known to decompose during the initial charge-discharge cycle and form a coating called the solid electrolyte interface (SEI) on the negative electrode surface. The formation of the SEI is considered to play a crucial role in suppressing the degradation of the secondary battery during repeated charge-discharge cycles and improving various battery performance characteristics.

[0004] For example, Patent Document 1 discloses a method in which 1,3-propanesulfonate lactone and / or 1,4-butanesulfonate lactone are added as additives to the electrolyte in a lithium secondary battery with lithium cobalt oxide or lithium manganese oxide as the positive electrode active material, thereby improving cycle characteristics, etc.

[0005] Patent document 2 discloses the following method: in an energy storage device using lithium NCM composite metal oxide as the positive electrode active material, a cyclic sulfonate compound is added to the electrolyte as an additive to improve the storage stability at high temperature.

[0006] Patent document 3 discloses a method in which 1,3-dioxanes are added to the electrolyte as additives to improve the storage stability at high temperatures in an energy storage device that uses lithium NCM composite metal oxide or lithium olivine phosphate as the positive electrode active material.

[0007] Previous technical documents Patent documents Patent Document 1: Japanese Patent No. 3978881 Patent Document 2: International Publication No. 2012 / 147818 Patent Document 3: International Publication No. 2018 / 116879 Summary of the Invention

[0008] The technical problem to be solved by the invention Recently, lithium manganese iron phosphate (LFP), among the aforementioned lithium-containing olivine-type phosphates, has attracted attention for its superior stability as a positive electrode active material. However, for non-aqueous electrolyte secondary batteries containing LFP as the positive electrode active material, a suitable formulation for improving storage stability at high temperatures has not yet been established. One aspect of the present invention relates to a method for improving the high-temperature storage stability of non-aqueous electrolyte secondary batteries containing LFP as the positive electrode active material.

[0009] means for solving technical problems One aspect of the present invention relates to non-aqueous electrolyte secondary batteries.

[0010] Item 1. A non-aqueous electrolyte secondary battery comprises a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein... The positive electrode contains LiMn. （1-y） Fe y PO4 is used as the positive electrode active material, and y is a value that satisfies 0 < y < 1. The non-aqueous electrolyte contains a compound represented by the following formula (1), In formula (1), Q represents a group that forms a ring structure with the sulfur atom of the sulfonyl group and is selected from alkylene groups having 4 to 6 carbon atoms and alkenyl groups having 4 to 6 carbon atoms and having 1 or more substituents; X is a group represented by formula (2a) or formula (2b) below. In equations (2a) and (2b), R 1 It refers to an alkyl group having 1 to 4 carbon atoms that can have fluorine atoms as substituents, an alkenyl group having 2 to 4 carbon atoms that can have fluorine atoms as substituents, an alkynyl group having 2 to 4 carbon atoms that can have fluorine atoms as substituents, and an aryl, hydroxyl, or lithiumoxy group having 6 to 10 carbon atoms that can have fluorine atoms as substituents.

[0011] Item 2. According to the non-aqueous electrolyte secondary battery described in item 1, wherein... In formula (1), Q is an alkylene group with 4 carbon atoms that may have more than one substituent or an alkenyl group with 4 carbon atoms that may have more than one substituent.

[0012] Item 3. According to the non-aqueous electrolyte secondary battery described in item 1 or item 2, wherein, In equations (2a) and (2b), R 1It can be an alkyl group having 1 to 2 carbon atoms as a substituent, an alkenyl group having 2 to 4 carbon atoms as a substituent, an alkynyl group having 3 to 4 carbon atoms as a substituent, or a phenyl group having fluorine atoms as a substituent.

[0013] Item 4. According to any one of items 1 to 3, the non-aqueous electrolyte secondary battery, wherein, X is a group represented by formula (2a).

[0014] Item 5. According to any one of items 1 to 3, the non-aqueous electrolyte secondary battery, wherein, X is a group represented by formula (2b).

[0015] Item 6. According to any one of items 1 to 5, the non-aqueous electrolyte secondary battery, wherein, The compound represented by formula (1) is a compound represented by the following formula (1a). In equation (1a), the meaning of X is the same as that of X in equation (1).

[0016] Item 7. According to any one of items 1 to 5, the non-aqueous electrolyte secondary battery, wherein, The compound represented by formula (1) is a compound represented by the following formula (1b). In equation (1b), the meaning of X is the same as that of X in equation (1).

[0017] Invention Effects According to one aspect of the present invention, a non-aqueous electrolyte secondary battery containing lithium manganese iron phosphate as the positive electrode active material and exhibiting excellent storage stability at high temperatures can be provided. Attached Figure Description

[0018] Figure 1 This is a cross-sectional view showing an example of a non-aqueous electrolyte secondary battery. Detailed Implementation

[0019] Hereinafter, several examples relating to one aspect of the present invention will be described in detail.

[0020] The non-aqueous electrolyte secondary battery of this invention comprises a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. The positive electrode contains LiMn. （1-y） Fe yPO4 is used as the positive electrode active material. y is a value that satisfies 0 < y < 1. The non-aqueous electrolyte contains a compound represented by formula (1).

[0021] <Non-aqueous electrolyte secondary batteries> Figure 1 This is a cross-sectional view schematically illustrating an example of a non-aqueous electrolyte secondary battery. Figure 1 The non-aqueous electrolyte secondary battery 1 shown includes alternately stacked negative electrodes 4 and positive electrodes 9, a non-aqueous electrolyte 5 disposed between the negative electrodes 4 and positive electrodes 9, and a separator 6 disposed in the non-aqueous electrolyte 5. Multiple negative electrodes 4 and positive electrodes 9 are stacked such that the main surfaces of the negative electrodes 4 and the main surfaces of the positive electrodes 9 are separated by the separator 6. The non-aqueous electrolyte secondary battery 1 has multiple layers of negative electrodes 4 and multiple layers of positive electrodes 9, but... Figure 1 In the diagram, a portion of the repeating structure is omitted. The negative electrode 4 has a sheet-like negative electrode current collector 3 and negative electrode active material layers 2 disposed on both sides of the negative electrode current collector 3. The positive electrode 9 has a sheet-like positive electrode current collector 8 and positive electrode active material layers 7 disposed on both sides of the positive electrode current collector 8.

[0022] (positive electrode) The positive electrode active material layer contains LiMn （1-y） Fe y PO4 is used as the positive electrode active material. Here, y in the formula represents a value satisfying 0 < y < 1. From the perspective of achieving high energy density, y can be a value satisfying 0.1 < y < 0.9, 0.1 < y < 0.8, 0.1 < y < 0.7, 0.1 < y < 0.6, 0.1 < y < 0.5, 0.2 < y < 0.9, 0.2 < y < 0.8, 0.2 < y < 0.7, 0.2 < y < 0.6, 0.2 < y < 0.5, 0.3 < y < 0.9, 0.3 < y < 0.8, 0.3 < y < 0.7, 0.3 < y < 0.6, or 0.3 < y < 0.5.

[0023] The positive electrode active material may also be doped with one or more metals selected from Mg, Ca, Sr, Al, Ti, Cr, Zn, and W. A portion of the Mn and / or Fe contained in the positive electrode active material may be replaced by one or more metals selected from Mg, Ca, Sr, Al, Ti, Cr, Zn, and W.

[0024] In addition to containing LiMn as a positive electrode active material, the positive electrode active material layer can also contain other materials. （1-y） Fe y Besides PO4, it may also contain other components such as binders and conductive additives (described later). Based on the total mass of the positive electrode active material layer, the LiMn content in the positive electrode active material layer... （1-y） Fe yThe PO4 content can be, for example, 60% or more by mass, 80% or more by mass, or less than 99.9% by mass.

[0025] The positive electrode current collector can contain electronically conductive materials. Examples of electronically conductive materials include conductive substances such as carbon, titanium, chromium, molybdenum, ruthenium, rhodium, tantalum, tungsten, osmium, iridium, platinum, gold, and aluminum, as well as alloys containing two or more conductive substances (metals) (e.g., stainless steel). From the viewpoint of high electronic conductivity, excellent stability in the electrolyte, and good oxidation resistance, the electronically conductive materials constituting the positive electrode current collector can include carbon, aluminum, or stainless steel. From an economic point of view, the electronically conductive materials constituting the positive electrode current collector can include aluminum.

[0026] The positive electrode current collector can be a foil. In other words, the positive electrode current collector can be in foil form. When the positive electrode current collector is a foil, from the viewpoint of further achieving high capacity, the positive electrode current collector can have a base coating disposed on the surface of the foil. When the positive electrode current collector has a base coating, the adhesion between the positive electrode active material layer and the positive electrode current collector can be improved. The base coating can be formed, for example, by applying an adhesive containing a carbon-based conductive additive to the surface of the foil. The thickness of the base coating can be from 0.1 μm to 50 μm.

[0027] The positive current collector can have a three-dimensional shape. Examples of positive current collectors with three-dimensional shapes include foamed metal, mesh, woven fabric, nonwoven fabric, and expanded metal mesh. When the positive current collector has a three-dimensional shape, even if the material used to make the electrode (e.g., binder) has low adhesion to the positive current collector, it is possible to produce an electrode with high capacity density. Therefore, high-rate charge-discharge characteristics can be further improved.

[0028] (negative electrode) The negative electrode consists of a negative current collector and a negative active material layer. The negative current collector typically contains metals such as aluminum, copper, nickel, and stainless steel. From a processability and economic perspective, the negative current collector may contain copper. The negative current collector can be a foil; in other words, it can be in foil form. The surface of the negative current collector can be roughened.

[0029] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material is a material capable of inserting and deintercalating lithium. Examples of negative electrode active materials include carbon materials such as graphite and amorphous carbon, oxide materials such as indium oxide, silicon oxide, tin oxide, lithium titanate, zinc oxide, and lithium oxide, lithium metal, and metallic materials capable of forming alloys with lithium. Examples of metallic materials capable of forming alloys with lithium include copper, tin, silicon, cobalt, manganese, iron, antimony, and silver. The negative electrode active material may contain two or more metals selected from these metals. Based on the total mass of the negative electrode active material layer, the content of the negative electrode active material in the negative electrode active material layer may be, for example, 60% by mass or more, 80% by mass or more, or 99.9% by mass or less.

[0030] From the perspective of achieving high energy density, the negative electrode active material can include carbon materials such as graphite and Si-based active materials selected from Si, Si alloys, and Si oxides. From the perspective of balancing cycle performance and high energy density, the negative electrode active material can include both graphite and Si-based active materials. In this case, the mass ratio of the Si-based active material to the total mass of the carbon material and the Si-based active material can be 0.5% by mass or more, 1% by mass or more, or 2% by mass or more, or it can be 95% by mass or less, 50% by mass or less, or 40% by mass or less. The mass ratio of the Si-based active material to the total mass of the carbon material and the Si-based active material can be 0.5% by mass or more, 1% by mass or more, or 2% by mass or more, and can be 95% by mass or less. The mass ratio of the Si-based active material to the total mass of the carbon material and the Si-based active material can be 0.5% by mass or more, 1% by mass or more, or 2% by mass or more, and can be 40% by mass or less.

[0031] (Other ingredients) The positive and negative electrode active material layers may further contain binders. Examples of binders include polyvinylidene fluoride (PVDF), PVDF-hexafluoropropylene copolymer, PVDF-tetrafluoroethylene copolymer, styrene-butadiene copolymer (SBR), carboxymethyl cellulose (CMC), polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide-imide, polyacrylic acid, polyvinyl alcohol, polyacrylonitrile, polyacrylamide, polymethacrylic acid, and copolymers thereof. The positive and negative electrode active material layers may contain the same or different binders. When the positive electrode active material layer contains a binder, the binder contained in the positive electrode active material layer may include polyvinylidene fluoride (PVDF). When the negative electrode active material layer contains a binder, the binder contained in the negative electrode active material layer may include CMC and / or SBR. Based on the total mass of the positive electrode active material layer, the content of binder in the positive electrode active material layer may, for example, be more than 0.1% by mass, less than 20% by mass, or less than 10% by mass. Based on the mass of the negative electrode active material layer, the content of the binder in the negative electrode active material layer can be, for example, more than 0.1% by mass, less than 20% by mass, or less than 10% by mass.

[0032] Both the positive and negative electrode active material layers may further contain conductive additives. These conductive additives can be substances containing conductive materials such as carbon. Examples of carbon-containing substances include carbonaceous particles such as graphite, carbon black, acetylene black, and Ketjen black, as well as carbon fibers. Carbon-containing substances can also function as negative electrode active materials. Carbon-containing substances used in combination with other negative electrode active materials can also be considered conductive additives. Based on the mass of the positive electrode active material layer, the content of the conductive additive in the positive electrode active material layer can be, for example, 0.1% by mass or more, or 20% by mass or less, or 10% by mass or less. Based on the total mass of the negative electrode active material layer, the content of the conductive additive in the negative electrode active material layer can be, for example, 0.1% by mass or more, or 20% by mass or less, or 10% by mass or less.

[0033] (Diaphragm) The diaphragm 6 can be a porous membrane. A porous membrane can, for example, contain a resin selected from the group consisting of polyethylene, polypropylene, and fluoropolymers. The diaphragm 6 can be a single layer or have multiple layers.

[0034] The specific shapes, thicknesses, and other details of the components constituting non-aqueous electrolyte secondary batteries such as lithium-ion batteries can be appropriately determined by those skilled in the art.

[0035] <Non-aqueous electrolyte> The non-aqueous electrolyte contains a compound represented by formula (1). If the non-aqueous electrolyte contains a compound represented by formula (1), the high-temperature storage stability of the non-aqueous electrolyte secondary battery, which includes the combination of the non-aqueous electrolyte and a positive electrode active material containing lithium manganese iron phosphate, is improved. The reason for the improved high-temperature storage stability due to the non-aqueous electrolyte containing a compound represented by formula (1) is not yet clear, but it is believed to be due to the formation of a passivation coating called CEI on the surface of the positive electrode.

[0036] In formula (1), Q is a group that forms a ring structure together with the sulfur atom of the sulfonyl group (-S(=O)2-) in formula (1). Q represents a group selected from alkylene groups having 4 to 6 carbon atoms that may have one or more substituents and alkenyl groups having 4 to 6 carbon atoms that may have one or more substituents. In the compound represented by formula (1), the number of carbon atoms of the alkylene group and alkenyl group as Q is preferably 4. In this case, the battery resistance can be further reduced. The group represented by -X in formula (1) is bonded to a carbon atom at any position in the alkylene group and alkenyl group as Q. The alkylene group and alkenyl group as Q may further have substituents other than the group represented by -X.

[0037] In formula (1), X (a group represented by -X) represents a group represented by formula (2a) or formula (2b) below.

[0038] In equations (2a) and (2b), R 1 This indicates an alkyl group having 1 to 4 carbon atoms that can have a fluorine atom as a substituent, an alkenyl group having 2 to 4 carbon atoms that can have a fluorine atom as a substituent, an alkynyl group having 2 to 4 carbon atoms that can have a fluorine atom as a substituent, or an aryl, hydroxyl, or lithiumoxy group having 6 to 10 carbon atoms that can have a fluorine atom as a substituent. As R 1 The alkyl, alkenyl, alkynyl, and aryl groups can each have one or more fluorine atoms as substituents. If it is used as R... 1 If each group has fluorine atoms as substituents, the battery resistance can be further reduced. From the viewpoint of reducing charge transfer resistance, X is preferably a group represented by the formula (2a).

[0039] In equations (2a) and (2b), R is used as... 1 The alkyl group has 1 to 4 carbon atoms. As R 1The alkyl group can have 1 to 3 or 1 to 2 carbon atoms. The alkyl group can be straight-chain or branched. Examples of such alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, trifluoromethyl, and 1,1,1-trifluoroethyl. From the viewpoint of more easily reducing battery resistance, the alkyl group can be an unsubstituted methyl group or a methyl group having a fluorine atom as a substituent.

[0040] In equations (2a) and (2b), R is used as... 1 The alkenyl group has 2 to 4 carbon atoms. This alkenyl group can be linear or branched. Examples of this alkenyl group include vinyl, allyl, methyl allyl (2-methyl allyl), 1-butenyl, 2-butenyl, 3-butenyl, isobutenyl, and 1,1-difluoro-1-propenyl. This alkenyl group can be vinyl, allyl, or methyl allyl, which can have a fluorine atom as a substituent. When the alkenyl group is allyl or methyl allyl, which can have a fluorine atom as a substituent, a stronger CEI is more easily formed.

[0041] In equations (2a) and (2b), R is used as... 1 The number of carbon atoms in the alkynyl group is 2 to 4, or possibly 3 to 4. This alkynyl group can be linear or branched. Examples of this alkynyl group include 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl, and 3-butynyl. The alkynyl group can be 2-propynyl, which can have a fluorine atom as a substituent. When the alkynyl group is 2-propynyl, which can have a fluorine atom as a substituent, a more robust CEI is easily formed.

[0042] In equations (2a) and (2b), R is used as... 1 The aryl group has 6 to 10 carbon atoms. Examples of aryl groups with 6 to 10 carbon atoms include phenyl, toluenesulfonyl, xylyl, naphthyl, fluorophenyl, and pentafluorophenyl. The aryl group can be a phenyl group that has a fluorine atom as a substituent. The aryl group can be phenyl, 4-fluorophenyl, or pentafluorophenyl.

[0043] From the perspective of the storage stability of batteries at high temperatures, the compound of formula (1) can be a compound represented by formula (1a) or formula (1b) below.

[0044] In equation (1a), X is defined as described above.

[0045] In equation (1b), X is defined as described above.

[0046] As specific examples of compounds represented by the above formula (1), compounds represented by the following formulas (1-1), (1-2), (1-3), (1-4), (1-5), (1-6), (1-7), (1-8), or (1-9) can be given.

[0047] The non-aqueous electrolyte may contain one or more compounds as compounds represented by the formula (1).

[0048] Based on the total mass of the non-aqueous electrolyte, the content of the compound represented by formula (1) in the non-aqueous electrolyte is, for example, 0.005 to 10% by mass. If the content of the compound represented by formula (1) is 0.005% by mass or more, the stability of the SEI is improved, and better battery characteristics can be obtained. If the content of the compound represented by formula (1) is 10% by mass or less, the viscosity increase of the non-aqueous electrolyte can be suppressed. Based on the total mass of the non-aqueous electrolyte, the content of the compound represented by formula (1) can be 0.005 to 5% by mass.

[0049] (Non-aqueous solvent) From the viewpoint of suppressing the viscosity of non-aqueous electrolytes to a low level, the non-aqueous solvent used in non-aqueous electrolytes can be an aprotic solvent. The non-aqueous solvent can be at least one selected from the group consisting of cyclic carbonates, chain carbonates, aliphatic carboxylic esters, lactones, lactams, cyclic ethers, chain ethers, sulfones (excluding compounds represented by formula (1)), nitriles, and their halogen derivatives. The non-aqueous solvent can contain at least one of cyclic carbonates and chain carbonates, or a combination of cyclic carbonates and chain carbonates.

[0050] Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butenyl carbonate, and fluoroethylene carbonate. Examples of chain carbonates include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of aliphatic carboxylic acid esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, and trimethylacetate. Examples of lactones include γ-butyrolactone. Examples of lactams include ε-caprolactam and N-methylpyrrolidone. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, and 1,3-dioxolane. Examples of chain ethers include 1,2-diethoxyethane and ethoxymethoxyethane. Examples of sulfones include sulfolane. Examples of nitriles include acetonitrile. Examples of halogen derivatives include 4-fluoro-1,3-dioxolane-2-one, 4-chloro-1,3-dioxolane-2-one, and 4,5-difluoro-1,3-dioxolane-2-one. The non-aqueous electrolyte may contain one or more non-aqueous solvents selected from these.

[0051] (electrolytes) Non-aqueous electrolytes typically contain a lithium salt as the ion source for lithium ions. The lithium salt can be at least one selected from the group consisting of LiAlCl4, LiBF4, LiPF6, LiClO4, LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiFSI (lithium bis(fluorosulfonyl)imide), LiAsF6, and LiSbF6. Non-aqueous electrolytes can contain one or more electrolytes selected from these groups. The electrolyte can contain LiBF4, LiPF6, or combinations thereof. When the electrolyte contains LiBF4 and / or LiPF6, it exhibits high dissociation and improves the ionic conductivity of the electrolyte. Through its antioxidant properties, it can suppress the performance degradation of non-aqueous electrolyte secondary batteries caused by long-term use.

[0052] When the electrolyte is LiBF4, LiPF6, or a combination thereof, the non-aqueous solvent may contain cyclic carbonates and chain carbonates. For example, LiBF4 and / or LiPF6 may be combined with ethylene carbonate and diethyl carbonate.

[0053] Based on the total volume of the non-aqueous electrolyte, the electrolyte concentration can be above 0.1 mol / L or above 0.5 mol / L, or below 2.0 mol / L or below 1.5 mol / L. Based on the total volume of the non-aqueous electrolyte, if the electrolyte concentration is above 0.1 mol / L or above 0.5 mol / L, it is easy to obtain good conductivity of the electrolyte, while if it is below 2.0 mol / L or below 1.5 mol / L, the increase in electrolyte viscosity can be suppressed. Based on the total volume of the non-aqueous electrolyte, the electrolyte concentration can be above 0.1 mol / L and can be below 2.0 mol / L or below 1.5 mol / L, or above 0.5 mol / L and below 2.0 mol / L or below 1.5 mol / L.

[0054] (Other ingredients) The non-aqueous electrolyte may contain other components that differ from the compound represented by formula (1), the non-aqueous solvent, and the electrolyte, as needed. Examples of other components include negative electrode protectants, positive electrode protectants, flame retardants, overcharge inhibitors, cyclic carbonate compounds, nitrile compounds, isocyanate compounds, compounds having acetylene-1,2-diyl (-C≡C-), compounds having sulfonyl groups (>S(=O)2) (excluding compounds represented by formula (1)), phosphate compounds, acid anhydrides, cyclic phosphazene compounds, cyclic dioxazole compounds, cycloboroxane derivatives, silicon-containing compounds, and alkali metal salt compounds (e.g., lithium salt compounds).

[0055] Examples of the cyclic carbonate compounds include 4-fluoro-1,3-dioxolane-2-one (FEC), trans- or cis-4,5-difluoro-1,3-dioxolane-2-one (DFEC), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), and 4-ethynyl-1,3-dioxolane-2-one (EEC). The cyclic carbonate compound can be VC, FEC, VEC, or a combination thereof.

[0056] Examples of the nitrile compounds include acetonitrile, propionitrile, succinate, glutaronitrile, adiponitrile, heptacyanide, caprylate, and sebaconitrile. The nitrile compound can be succinate, adiponitrile, or a combination thereof.

[0057] Examples of the isocyanate compounds include methyl isocyanate, ethyl isocyanate, butyl isocyanate, phenyl isocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 1,4-phenylene diisocyanate, 2-Isocyanatoethyl acrylate, and 2-Isocyanatoethyl methacrylate.

[0058] Examples of compounds having acetylene-1,2-diyl (-C≡C-) include 2-propynyl methyl carbonate, 2-propynyl acetate, 2-propynyl formate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, 2-propynyl 2-(methanesulfonyloxy)propionic acid, di(2-propynyl)oxalate, methyl-2-oxalate propynyl ester, ethyl-2-oxalate propynyl ester, di(2-propynyl)glutarate, 2-butyn-1,4-dimethyl dimethylsulfonate, 2-butyn-1,4-dimethyl dicarboxylate, and 2,4-hexadiyne-1,6-dimethylsulfonate diester.

[0059] Examples of compounds having a sulfonyl group (>S(=O)2) include 1,3-propanesulfonyl lactone (PS), 1,3-butanesulfonyl lactone, 2,4-butanesulfonyl lactone, 1,4-butanesulfonyl lactone, 1,3-propenesulfonyl lactone, 2,2-dioxide-1,2-oxothiacyclopentan-4-yl acetate, 5,5-dimethyl-1,2-oxothiacyclopentan-4-one 2,2-dioxide, etc., sulfonyl lactones, vinyl sulfite, vinyl sulfate, and hexahydrobenzene. Cyclic sulfites such as [1,3,2]dioxane-2-oxide (also known as 1,2-cyclohexanediol cyclic sulfite), 5-vinyl-hexahydro-1,3,2-benzodioxane-2-oxide, butane-2,3-dimethanesulfonate diester, butane-1,4-dimethanesulfonate diester, methylene methane disulfonate, 1,3-propanedisulfonic anhydride sulfonate, divinyl sulfone, 1,2-bis(vinylsulfonyl)ethane, and bis(2-vinylsulfonylethyl) ether.

[0060] Examples of the phosphate ester compounds mentioned above include trimethyl phosphate, tributyl phosphate, trioctyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) 2,2-difluoroethyl phosphate, bis(2,2,2-trifluoroethyl) 2,2,3,3-tetrafluoropropyl phosphate, bis(2,2-difluoroethyl) 2,2,2-trifluoroethyl phosphate, bis(2,2,3,3-tetrafluoropropyl) 2,2,2-trifluoroethyl phosphate, (2,2,2-trifluoroethyl)(2,2,3,3-tetrafluoropropyl) methyl phosphate, tris(1,1,1,3,3,3-hexafluoropropane-2-yl) phosphate, methyl methylenebisphosphonate, and methylenebisphosphonate. Ethyl phosphonate, methyl ethyl bisphosphonate, ethyl ethyl bisphosphonate, methyl butyl bisphosphonate, ethyl butyl bisphosphonate, methyl 2-(dimethylphosphono)acetate, ethyl 2-(dimethylphosphono)acetate, methyl 2-(diethylphosphono)acetate, ethyl 2-(diethylphosphono)acetate, 2-propynyl 2-(dimethylphosphono)acetate, 2-propynyl 2-(diethylphosphono)acetate, methyl 2-(dimethoxyphosphono)acetate, ethyl 2-(diethoxyphosphono)acetate, ethyl 2-(diethoxyphosphono)acetate, 2-propynyl 2-(diethoxyphosphono)acetate, 2-propynyl 2-(diethoxyphosphono)acetate, methyl pyrophosphate and ethyl pyrophosphate.

[0061] Examples of such anhydrides include acetic anhydride, propionic anhydride, succinic anhydride, maleic anhydride, 3-allyl succinic anhydride, glutaric anhydride, itaconic anhydride, and 3-sulfonyl-propionic anhydride.

[0062] Examples of the cyclic phosphazene compounds include methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, and ethoxyheptafluorocyclotetraphosphazene.

[0063] Examples of the cyclic dioxazole compounds include 3-phenyl-1,4,2-dioxazol-5-one, 3-(2-fluorophenyl)-1,4,2-dioxazol-5-one, 3-(3-fluorophenyl)-1,4,2-dioxazol-5-one, 3-(4-fluorophenyl)-1,4,2-dioxazol-5-one, 3-(4-methoxyphenyl)-1,4,2-dioxazol-5-one, 3-(2-thienyl)-1,4,2-dioxazol-5-one, 3-(2,3,4,5,6-pentafluorophenyl)-1,4,2-dioxazol-5-one, 3-[4-(trifluoromethyl)phenyl]-1,4,2-dioxazol-5-one, and 3-(4-nitrophenyl)-1,4,2-dioxazol-5-one.

[0064] Examples of the aforementioned cycloboroxane derivatives include cycloboroxane, trimethylcycloboroxane, trimethoxycycloboroxane, triethylcycloboroxane, triethoxycycloboroxane, triisopropoxycycloboroxane, triisopropoxycycloboroxane, tri-n-propylcycloboroxane, tri-n-propoxycycloboroxane, tri-n-butylcycloboroxane, tri-n-butoxycycloboroxane, triphenylcycloboroxane, triphenoxycycloboroxane, tricyclohexylcycloboroxane, and tricyclohexyloxycycloboroxane.

[0065] Examples of silicon-containing compounds include hexamethylcyclotrisiloxane, hexaethylcyclotrisiloxane, hexaphenylcyclotrisiloxane, 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, trimethylfluorosiloxane, triethylfluorosiloxane, tripropylfluorosiloxane, phenyldimethylfluorosiloxane, triphenylfluorosiloxane, vinyldimethylfluorosiloxane, vinyldiethylfluorosiloxane, vinyldiphenylfluorosiloxane, divinyldifluorosilane, divinyldimethylsilane, trimethoxyfluorosiloxane, triethoxyfluorosiloxane, dimethyldifluorosiloxane, diethyldifluorosiloxane, trivinylfluorosiloxane, trivinylmethylsiloxane, ethylvinyldifluorosiloxane, methyltrifluorosiloxane, ethyltrifluorosiloxane, hexamethyldisiloxane, 1 3-Diethyltetramethyldisiloxane, hexaethyldisiloxane, octamethyltrisiloxane, methoxytrimethylsiloxane, ethoxytrimethylsiloxane, dimethoxydimethylsilane, trimethoxymethylsiloxane, tetramethoxysilane, tetravinylsilane, tetraallylsilane, tetrabutenylsilane, bis(trimethylsilyl)peroxide, trimethylsilyl acetate, triethylsilyl acetate, trimethylsilyl propionate, trimethylsilyl methacrylate, trimethylsilyl trifluoroacetate, trimethylsilyl methanesulfonate, trimethylsilyl ethanesulfonate, triethylsilyl methanesulfonate, trimethylsilyl fluoromethanesulfonate, bis(trimethylsilyl)sulfate, tri(trimethylsilyl)boron, tri(trimethylsilyl)phosphate, and tri(trimethylsilyl)phosphite.

[0066] Examples of the lithium salt compounds include lithium salts with a phosphate backbone such as lithium difluorophosphate, lithium bis(oxalate)borate (LiBOB), lithium tetrafluoro(oxalate)phosphate (LiTFOP), lithium difluorooxalateborate (LiDFOB), lithium difluorodioxalate phosphate (LiDFOP), lithium tetrafluoroborate, lithium difluorosulfonylimide, lithium tetrafluoro(oxalate)phosphate, and Li₂PO₃F; and lithium salts with an S (=O) group such as lithium trifluoro((methanesulfonyl)oxy)borate, lithium pentafluoro((methanesulfonyl)oxy)phosphate, lithium methyl sulfate, lithium ethyl sulfate, 2,2,2-trifluoroethyl sulfate, and lithium fluorosulfonate. The lithium salt compound may be one or more lithium salts selected from the group consisting of lithium difluorophosphate, lithium bis(oxalate)borate, lithium tetrafluoro(oxalate)phosphate, lithium difluorooxalateborate, lithium difluorodioxalate phosphate, lithium methyl sulfate, lithium ethyl sulfate, and lithium fluorosulfonate.

[0067] Other examples of the alkali metal salt compounds include sodium difluorophosphate, potassium difluorophosphate, sodium bis(oxalate)borate, potassium bis(oxalate)borate, sodium tetrafluorooxalate phosphate, potassium tetrafluorooxalate phosphate, sodium difluorobis(oxalate) phosphate, potassium difluorobis(oxalate) phosphate, sodium difluorooxalate borate, and potassium difluorooxalate borate.

[0068] Based on the total mass of the non-aqueous electrolyte, the content of other components can be 0.005–10% by mass or 0.01–10% by mass. If the content of other components is above 0.005% by mass, it is easier to obtain better battery characteristics. If the content of other components is below 10% by mass, the viscosity increase of the non-aqueous electrolyte can be further suppressed.

[0069] Example The following examples illustrate embodiments of the present invention in more detail.

[0070] 1. Synthesis of the compound represented by formula (1) Manufacturing Example 1 3-Sulfolene (236.3 g, 2.0 mol) and 500 mL of water were added to a 2 L four-necked flask equipped with a stirrer, condenser, and thermometer. The flask was heated to 40 °C to prepare a homogeneous solution. Sodium hydroxide (104.0 g, 2.6 mol) was added to this solution, and the solution was stirred for 10 hours while maintaining 40 °C. The flask was then cooled in an ice bath. Concentrated sulfuric acid (130.1 g, 1.3 mol) was added dropwise to the obtained reaction solution over 30 minutes to make the reaction solution acidic. The reaction solution was concentrated to precipitate a solid. After removing the precipitated solid by filtration, the filtrate was concentrated to obtain 250.59 g of 3-hydroxysulfolane (92% yield relative to 3-sulfolene).

[0071] Manufacturing Example 2: Synthesis of the compound represented by formula (1-1) To a 200 mL four-necked flask equipped with a stirrer, condenser, thermometer, and dropping funnel, 5.4 g (40 mmol) of 3-hydroxycyclobutane (obtained in Preparation Example 1), 5.4 g (44 mmol) of methanesulfonyl chloride, and 20 mL of acetonitrile were added. The flask was cooled in an ice bath, the reaction mixture was stirred, and triethylamine (4.0 g (40 mmol) was added dropwise. After the addition was complete, the temperature was maintained at 0–5 °C, and the reaction mixture was stirred for 1 hour. Water was then added, and the precipitated white solid was recovered by filtration. After washing the recovered solid with methanol, the solid was dried under reduced pressure to obtain a white solid compound (represented by formula (1-1)) (7.0 g, yield 82% relative to 3-hydroxycyclobutane).

[0072] 1 H-NMR (400MHz, CD3CN) δ (ppm): 2.53 (m, 2H), 3.11 (s, 3H), 3.16 (m, 2H), 3.36 (m, 2H), 5.39 (s, 1H) Manufacturing Example 3: Synthesis of the compound represented by formula (1-4) To a 200 mL four-necked flask equipped with a stirrer, condenser, thermometer, and dropping funnel, 5.4 g (40 mmol) of 3-hydroxycyclobutane (obtained in Preparation Example 1), 7.8 g (44 mmol) of benzenesulfonyl chloride, and 20 mL of acetonitrile were added. The flask was cooled in an ice bath, the reaction mixture was stirred, and triethylamine (4.0 g (40 mmol) was added dropwise. After the addition was complete, the temperature was maintained at 0–5 °C, and the reaction mixture was stirred for 1 hour. Water was then added, and the precipitated white solid was recovered by filtration. After washing the recovered solid with methanol, the white solid compound (represented by formulas (1–4)) was obtained by drying under reduced pressure (8.2 g, yield 68% relative to 3-hydroxycyclobutane).

[0073] 1 H-NMR (400MHz, CD3CN) δ (ppm): 2.39 (m, 2H), 3.18 (m, 4H), 5.25 (m, 1H), 7.66 (m, 2H), 7.79 (m, 1H), 7.94 (m, 2H) Manufacturing Example 4: Synthesis of the compound represented by formula (1-5) Sodium 2-methyl-2-propene-1-sulfonate (8.04 g, 50 mmol), N,N-dimethylformamide (0.37 g, 5 mmol), and 30 mL of dichloromethane were added to a 200 mL four-necked flask equipped with a stirrer, condenser, thermometer, and dropping funnel. The reaction mixture in the flask was stirred, and thionyl chloride (7.14 g, 60 mmol) was added dropwise at room temperature (25 °C). After the addition was completed, the reaction mixture was maintained at 20–25 °C and stirred for 24 hours. Then, the mixture was separated by water, and the oil layer was concentrated to obtain 2-methyl-2-propene-1-sulfonyl chloride (7.73 g, 100% yield relative to sodium 2-methyl-2-propene-1-sulfonate).

[0074] Next, 3-hydroxycyclobutanesulfone (5.45 g, 40 mmol), 2-methyl-2-propen-1-sulfonyl chloride (6.80 g, 44 mmol), and 20 mL of acetonitrile were added to a 200 mL four-necked flask equipped with a stirrer, condenser, thermometer, and dropping funnel. The flask was cooled in an ice bath, the reaction mixture was stirred, and triethylamine (4.05 g, 40 mmol) was added dropwise. After the addition was complete, the temperature was maintained at 0–5 °C, and the reaction mixture was stirred for 1 hour. Then, water was added, and the precipitated white solid was recovered by filtration. After washing the recovered solid with methanol, the white solid compound (represented by formulas (1–5)) was obtained by drying under reduced pressure (5.84 g, 50% yield relative to 3-hydroxycyclobutanesulfone).

[0075] 1 H-NMR (400MHz, CD3CN) δ (ppm): 1.93 (m, 3H), 2.53 (m, 2H), 3.18 (m, 2H), 3.36 (dd, 1H), 3.41 (dd, 1H), 3.97 (s, 2H), 5.15 (s, 1H), 5.22 (s, 1H), 5.42 (m, 1H) 2. Fabrication of non-aqueous electrolyte secondary batteries (Example 1) A mixed non-aqueous solvent was obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of EC:EMC = 30:70. LiPF6 was dissolved in the obtained mixed non-aqueous solvent as an electrolyte to achieve a concentration of 1.0 mol / L. A non-aqueous electrolyte was prepared by adding a compound represented by formula (1-1) as an additive to the obtained solution. The content of the compound represented by formula (1-1) was set to 1.0% by mass based on the total mass of the non-aqueous electrolyte.

[0076] Next, LiMn was prepared.0.6 Fe 0.4 Positive electrode sheet (manufactured by Hassan Co., Ltd.) using PO4 as the positive active material and negative electrode sheet (manufactured by Hassan Co., Ltd.) containing graphite as the negative active material. The positive electrode sheet has an aluminum foil (20 μm thick) serving as the positive current collector and positive active material layers formed on both sides thereon. The positive active material layers contain LiMn as the positive active material. 0.6 Fe 0.4 PO4, acetylene black (AB) as a conductive additive, single-walled CNTs (SWCNTs), and polyvinylidene fluoride (PVDF) as a binder. Their mass ratio is LiMn 0.6 Fe 0.4 PO4:AB:SWCNT:PVDF=94:3:0.1:2.9. The negative electrode has a copper foil (10μm thick) as the negative electrode current collector and negative electrode active material layers formed on both sides thereon. The negative electrode active material layers contain graphite (Gr) as the negative electrode active material and sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as binders. Their mass ratio is Gr:CMC:SBR=98:1:1. A battery element with 5 layers of negative electrode and 4 layers of positive electrode (a total of 9 layers) is fabricated by alternately stacking positive and negative electrode sheets separated by a polypropylene separator.

[0077] The battery element fabricated using the above method is inserted into a bag formed of a laminated film, with the ends of the positive and negative electrodes protruding from the bag. This laminated film has aluminum (40 μm thick) and resin layers covering both sides. Next, a non-aqueous electrolyte is injected into the bag, and the bag is vacuum-sealed, thus obtaining a sheet-like non-aqueous electrolyte secondary battery. To improve the adhesion between the electrodes, the sheet-like non-aqueous electrolyte secondary battery is clamped with a glass plate and pressurized, thus fabricating a non-aqueous electrolyte secondary battery.

[0078] (Example 2) The compound represented by formula (1-1) was changed to the compound represented by formula (1-4), and a non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1.

[0079] (Example 3) The compound represented by formula (1-1) was changed to the compound represented by formula (1-5), and a non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1.

[0080] (Comparative Example 1) The compound represented by formula (1-1) was replaced with 1,3-propanesulfonate lactone (PS, manufactured by Tokyo Chemical Industry Co., Ltd.), and a non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1.

[0081] 3. Evaluation of battery characteristics <Battery preparation before evaluation> (Aging process) Each non-aqueous electrolyte secondary battery was charged for 1 hour at 25°C with a current equivalent to 0.1C, and held at 25°C for 10 hours. Then, it was charged for 5 hours at a current equivalent to 0.1C and held at 45°C for 24 hours. Next, it was discharged to 3.0V at 25°C with a current equivalent to 0.1C, followed by degassing. The batteries were then stabilized by sequentially performing the following aging operations: repeating 3 cycles of charging to 4.2V with a current equivalent to 0.2C and discharging to 3V with a current equivalent to 0.2C; repeating 3 cycles of charging to 4.2V with a current equivalent to 0.5C and discharging to 3.0V with a current equivalent to 0.5C; and repeating 3 cycles of charging to 4.2V with a current equivalent to 1.0C and discharging to 3.0V with a current equivalent to 1.0C.

[0082] (High-temperature preservation process) For the non-aqueous electrolyte secondary batteries after the above aging process, they were charged to 4.2V at 1.0C at 25°C and then maintained at 60°C for 30 days. Then, the non-aqueous electrolyte secondary batteries were cooled to 25°C and discharged to 3.0V at a current equivalent to 1.0C.

[0083] <Measurement of charge transfer resistance> For batteries that have completed the aging and high-temperature storage processes, two charge-discharge cycles (4.2V to 3.0V) were performed at a current equivalent to 1.0C. After charging at a current equivalent to 1.0C, the batteries were discharged at a current equivalent to 1.0C to achieve a state of charge (SOC) of 50%. After the non-aqueous electrolyte secondary batteries with an SOC of 50% were left to stand at 25°C for 2 hours, they were tested using a Solartoron SI1260 (measurement conditions: 0.01Hz to 1×10⁻⁶). 6 The charge transfer resistance (Rct) of the positive and negative electrodes was measured at Hz and amplitude of 5mV. The results are shown in Table 1.

[0084] <Determination of Metal Dissolution> After the charge transfer resistance of the non-aqueous electrolyte secondary battery was measured, it was discharged to 3.0V at a current equivalent to 1.0C. The battery was then disassembled, and the negative electrode was removed. The negative electrode was cleaned with dimethyl carbonate (DMC) and then vacuum-dried for 10 minutes. The active material layer on the negative electrode was then scraped off and powdered. 60% nitric acid was added to the recovered powder, and the powder was dissolved by heating to prepare the assay solution. The mass of Fe and Mn in the assay solution was determined by analysis using an inductively coupled plasma atomic emission spectrometer (manufactured by Thermo Fisher Scientific Inc.). The amount of Fe or Mn dissolved per unit mass of the active material layer was calculated using the following formula. The results are shown in Table 1.

[0085] The leaching amount of Fe or Mn (ppm) = (mass of Fe or Mn contained in the test solution / mass of the scraped negative electrode active material layer) [Table 1]

[0086] Industrial availability As described above, according to one aspect of the present invention, a non-aqueous electrolyte secondary battery is provided, which contains lithium manganese iron phosphate as the positive electrode active material, and exhibits excellent high-temperature storage stability, such as suppressing the increase in charge transfer resistance even when stored at a high temperature of 60°C for 30 days. From the viewpoint of reducing waste by extending battery life, this non-aqueous electrolyte secondary battery can help solve environmental problems and has great industrial applicability.

[0087] Explanation of reference numerals in the attached figures 1-Non-aqueous electrolyte secondary battery, 2-Negative electrode active material layer, 3-Negative electrode current collector, 4-Negative electrode, 5-Negative electrolyte, 6-Separator, 7-Positive electrode active material layer, 8-Positive electrode current collector, 9-Positive electrode.

Claims

1. A non-aqueous electrolyte secondary battery, comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein, The positive electrode contains LiMn. （1-y） Fe y PO4 is used as the positive electrode active material, and y is a value that satisfies 0 < y < 1. The non-aqueous electrolyte contains a compound represented by the following formula (1), In formula (1), Q represents a group that forms a ring structure with the sulfur atom of the sulfonyl group and is selected from alkylene groups having 4 to 6 carbon atoms and alkenyl groups having 4 to 6 carbon atoms and having 1 or more substituents; X represents a group represented by formula (2a) or formula (2b) below. In equations (2a) and (2b), R 1 It refers to an alkyl group having 1 to 4 carbon atoms that can have fluorine atoms as substituents, an alkenyl group having 2 to 4 carbon atoms that can have fluorine atoms as substituents, an alkynyl group having 2 to 4 carbon atoms that can have fluorine atoms as substituents, and an aryl, hydroxyl, or lithiumoxy group having 6 to 10 carbon atoms that can have fluorine atoms as substituents.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein, In formula (1), Q is an alkylene group with 4 carbon atoms that may have more than one substituent or an alkenyl group with 4 carbon atoms that may have more than one substituent.

3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, In equations (2a) and (2b), R 1 It can be an alkyl group having 1 to 2 carbon atoms as a substituent, an alkenyl group having 2 to 4 carbon atoms as a substituent, an alkynyl group having 3 to 4 carbon atoms as a substituent, or a phenyl group having fluorine atoms as a substituent.

4. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, X is a group represented by formula (2a).

5. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, X is a group represented by formula (2b).

6. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The compound represented by formula (1) is a compound represented by the following formula (1a). In equation (1a), the meaning of X is the same as that of X in equation (1).

7. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The compound represented by formula (1) is a compound represented by the following formula (1b). In equation (1b), the meaning of X is the same as that of X in equation (1).

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