Non-aqueous electrolyte and lithium secondary battery

Abstract

To provide a non-aqueous electrolyte and a lithium secondary battery to achieve excellent low-temperature discharge performance while also improving cycle performance.SOLUTION: The non-aqueous electrolyte includes vinylene carbonate and the compound of Formula I. On the basis of the total mass of the non-aqueous electrolyte, the mass percentage of the vinylene carbonate is A% with 0.01≤A≤3, and the mass percentage of the compound of Formula I is B%, with P=B / A and 0.5≤P≤50. The lithium secondary battery manufactured using the non-aqueous electrolyte provided in the present application exhibits excellent electrochemical performance, particularly excellent low-temperature discharge performance and cycle performance.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present application relates to the field of energy storage technology, and in particular to non-aqueous electrolytes and lithium secondary batteries. [Background technology]

[0002] With the continuous development of secondary batteries, the demand for their performance is increasing. While conventional technologies have improved the low-temperature discharge performance of secondary batteries, they often result in a decrease in cycle performance. Therefore, the challenge of improving the low-temperature discharge performance of secondary batteries while maintaining their cycle performance has attracted widespread attention. Summary of the Invention

[0003] The examples of the present application provide a nonaqueous electrolyte and a lithium secondary battery that achieve good low-temperature discharge performance while also improving cycle performance.

[0004] In a first aspect, an embodiment of the present application comprises vinylene carbonate and a compound of formula I:

[0005] [ka] In the formula, R represents an unsubstituted or Ra-substituted C2-C6 alkyl group, an unsubstituted or Ra-substituted C2-C6 alkenyl group, an unsubstituted or Ra-substituted C2-C6 alkynyl group, an unsubstituted or Ra-substituted C5-C 12 Nitrogen-containing heteroaromatic groups, unsubstituted or substituted with Ra, C6-C 12 and the substituents Ra of each group are each independently selected from fluorine or a C1 to C6 fluorinated alkyl group, and the mass percentage of the vinylene carbonate is A %, 0.01≦A≦3, the mass percentage of the compound of formula I is B %, P=B / A, 0.5≦P≦50, based on the total mass of the non-aqueous electrolyte.

[0006] Based on the non-aqueous electrolytes of the examples of this application, the inventors have discovered that when the non-aqueous electrolyte further contains a compound of formula I, and the mass percentage A of vinylene carbonate in the non-aqueous electrolyte and the ratio P of A to the mass percentage B of the compound of formula I satisfy the above ranges, they can cooperate to form a strong SEI / CEI layer that improves ion conduction. Vinylene carbonate can form a dense SEI / CEI film layer at the electrode interface during the battery formation process, thereby significantly improving the cycle performance of the secondary battery. However, the denseness of the film layer inhibits ion transmission to a certain extent, increasing the initial resistance of the secondary battery and reducing the discharge capacity, especially under low temperature conditions. The compound of formula I can form a lithium-containing inorganic compound rich in S and F elements at the electrode interface, introducing more crystal grain boundaries that can conduct ions, thereby modifying the SEI / CEI film formed by vinylene carbonate, maintaining the denseness of the passivation film and improving ion conduction. Therefore, it is possible to improve the low-temperature discharge performance of the lithium secondary battery and also improve the cycle performance.

[0007] In one embodiment, the mass percentage A% of vinylene carbonate in the non-aqueous electrolyte, the mass percentage B% of the compound of formula I, and the ratio P of the two satisfy at least one of the following conditions: (1) 0.1≦A≦2, (2) 0.5≦B≦5, (3) 1≦P≦5. Based on the above embodiment, by adjusting the mass percentage A% of vinylene carbonate, the mass percentage B% of the compound of formula I, and the ratio between the two to satisfy any one of the above conditions, it is possible to better blend vinylene carbonate and the compound of formula I in the non-aqueous electrolyte, thereby further improving the low-temperature discharge performance of the lithium secondary battery and simultaneously improving the cycle performance.

[0008] In one embodiment, the compound of formula I is

[0009] [ka] At least one of the following is selected.

[0010] Based on the above examples, by selecting the above type of compounds of formula I, it is possible to further improve the low-temperature discharge performance of lithium secondary batteries while simultaneously improving their cycle performance.

[0011] In one embodiment, the non-aqueous electrolyte further contains a cyclic carbonate selected from any two of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate, and the mass percentage of the cyclic carbonate is M%, based on the total mass of the non-aqueous electrolyte, and is 5≦M≦30. Based on the above embodiment, by further adding the above-mentioned amount of cyclic carbonate to the non-aqueous electrolyte of the present application and controlling the mass percentage of the cyclic carbonate within a specific range, it is possible to further improve the low-temperature discharge performance of the lithium secondary battery while also achieving improved cycle performance.

[0012] In one embodiment, the mass percentage of the cyclic carbonate in the non-aqueous electrolyte is M%, and the mass percentage B% of the compound of formula I and the mass percentage of the cyclic carbonate are M%, with 10≦M≦20 and / or 0.1≦B / M≦3. Based on the above embodiment, by controlling the M value of the mass percentage of the cyclic carbonate in the non-aqueous electrolyte and the ratio of the mass percentage B% of the compound of formula I to the mass percentage M% of the cyclic carbonate within the above ranges, it is possible to further improve the low-temperature discharge performance of the lithium secondary battery while also achieving improved cycle performance.

[0013] In one embodiment, the non-aqueous electrolyte further includes a chain ester including a fluorinated chain ester and a non-fluorinated chain ester, and the chain ester is: (1) the fluorinated chain ester is methyl difluoroethyl carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, methyl hexafluoroisopropyl carbonate, di(2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, hexafluoroisopropyl acetate, 2,2-difluoroethyl propionate, (1) the non-fluorinated chain ester is selected from at least one of dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate; and (2) the non-fluorinated chain ester is selected from at least one of dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. (3) The mass percentage of the chain ester, based on the total mass of the non-aqueous electrolyte, is N0%, and is 10≦N0≦70. Based on the above examples, by further adding a certain amount of chain ester to the non-aqueous electrolyte of the present application and controlling the total mass percentage of the chain ester within a specific range, it is possible to further improve the low-temperature discharge performance of the lithium secondary battery while also achieving improved cycle performance.

[0014] In one embodiment, the mass percentage N1% of the fluorinated chain ester, the mass percentage N2% of the non-fluorinated chain ester, and the mass percentage N0% of the chain ester, based on the total mass of the non-aqueous electrolyte, satisfy at least one of the following conditions: (1) 5≦N1≦50, (2) 5≦N2≦50, (3) 20≦N0≦60. Based on the above embodiment, by controlling the mass percentages of the fluorinated chain ester and the non-fluorinated chain ester in the chain ester, and the sum of the mass percentages of both, within the above ranges, it is possible to further improve the low-temperature discharge performance of the lithium secondary battery while also achieving improved cycle performance.

[0015] In one embodiment, the non-aqueous electrolyte further comprises a polycyano compound selected from at least one of succinonitrile, glutaronitrile, methylglutaronitrile, adiponitrile, pimelonitrile, suberonitrile, fumaronitrile, and 1,2-bis(cyanoethoxy)ethane, and the mass percentage of the polycyano compound, based on the total mass of the non-aqueous electrolyte, is X%, where 0.1≦X≦10. Based on the above embodiment, by further adding a certain amount of polycyano compound to the non-aqueous electrolyte of the present application and controlling the mass percentage X% of the polycyano compound within the above range, a transition metal complex layer can be formed on the surface of the positive electrode active material during the process of vinylene carbonate forming CEI, which reduces the complete oxidative decomposition of the passivation film formed by vinylene carbonate on the surface of the positive electrode material, suppresses gas generation due to oxidation, and improves high-temperature storage performance while simultaneously achieving improvements in low-temperature discharge performance and cycle performance.

[0016] In one embodiment, for the mass percentage X% of the polycyano compound, 0.5≦X≦5. Based on the above embodiment, by controlling the mass percentage X% of the polycyano compound in the non-aqueous electrolyte solution to fall within the above range, it is possible to further improve the high-temperature storage property, and simultaneously achieve improvements in both the low-temperature discharge performance and the cycle performance.

[0017] In some embodiments, the non-aqueous electrolyte further comprises a compound of Formula II and / or a compound of Formula III.

[0018] [ka]

[0019] [ka] wherein R1 to R5 are each independently selected from a hydrogen atom, a fluorine atom, a vinyl group, an ethynyl group, or an acid anhydride group, and based on the total mass of the non-aqueous electrolyte, the mass percentage of the compound of formula II is Y1%, the mass percentage of the compound of formula III is Y2%, Y%=Y1%+Y2%, 0.1≦Y≦0.5, and any two adjacent groups of R1 to R5 are present independently of each other or are linked by a covalent bond to form a ring together with the parent ring. Based on the above examples, by further adding a certain amount of the compound of formula II and the compound of formula III to the non-aqueous electrolyte of the present application, and controlling the total mass percentage Y1% of the compound of formula II and the mass percentage Y2% of the compound of formula III within the above range, it is possible to enrich them at the interface, and due to the presence of nitrogen-containing heterocycles, their frontier orbital energy levels are narrow, and they have low oxidation potentials and high reduction potentials, so that a molecular skeleton rich in nitrogen-containing heterocycles can be formed during the initial chemical formation process, which reduces the excessive reaction and consumption of vinylene carbonate and the molecule of formula I, thereby further improving high-temperature storage properties and simultaneously improving low-temperature discharge performance and cycle performance.

[0020] In some embodiments, 0.05≦Y1≦0.5, such as 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, or a value in a range consisting of any two of these values.

[0021] In some embodiments, 0.05≦Y2≦0.5, such as 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, or a range consisting of any two of these values.

[0022] In one embodiment, the compound of formula II is

[0023] [ka] is selected from at least one of The compound of formula III above is

[0024] [ka] At least one of the following is selected.

[0025] Based on the above examples, by selecting the above types of compounds of formula II and / or formula III, it is possible to further improve high-temperature storage performance while simultaneously improving low-temperature discharge performance and cycle performance.

[0026] In a second aspect, an embodiment of the present application provides a lithium secondary battery comprising: a positive electrode including a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector; a negative electrode including a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector; a separator; and the nonaqueous electrolyte solution. DETAILED DESCRIPTION OF THE INVENTION

[0027] In order to clarify the purpose, technical solution and advantages of the present application, the present application will be described in more detail below with reference to examples. It should be understood that the specific examples described herein are only for the purpose of interpreting the present application, and are not intended to limit the present application.

[0028] An embodiment of the present application provides a lithium secondary battery including a non-aqueous electrolyte, a positive electrode, a negative electrode, and a separator.

[0029] non-aqueous electrolyte The non-aqueous electrolyte used in the electrochemical device of the present invention includes an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the non-aqueous electrolyte includes a compound of Formula I: The non-aqueous electrolyte used in the lithium secondary battery of the present invention includes an electrolyte and a solvent for dissolving the electrolyte. In one embodiment, the non-aqueous electrolyte includes vinylene carbonate and a compound of Formula I.

[0030] [ka] In the formula, R is an unsubstituted or Ra-substituted C2-C6 alkyl group, an unsubstituted or Ra-substituted C2-C6 alkenyl group, an unsubstituted or Ra-substituted C2-C6 alkynyl group, an unsubstituted or Ra-substituted C5-C 12 Nitrogen-containing heteroaromatic groups, unsubstituted or substituted with Ra, C6-C 12 The substituents Ra of each group are each independently selected from fluorine or a C1 to C6 fluorinated alkyl group.

[0031] In one embodiment, the mass percentage of vinylene carbonate is A%, based on the total mass of the nonaqueous electrolyte, and is 0.01≦A≦3, preferably 0.1≦A≦2. For example, A is 0.01, 0.1, 1, 1.5, 2, 2.5, 3, or a value within a range consisting of any two of these values. The mass percentage of the compound of Formula I is B%, and is 0.5≦B≦5. For example, B is 0.5, 0.8, 1.0, 2.2, 3.8, 4.5, 5, or a value within a range consisting of any two of these values. The ratio P of the mass percentage B% of the compound of Formula I to the mass percentage A% of vinylene carbonate is B / A, and is 0.5≦P≦50, preferably 1≦P≦5. For example, P is 0.5, 2.0, 6.9, 10.1, 22.5, 39.3, 50, or a value within a range consisting of any two of these values. By adding vinylene carbonate and the compound of formula I to a non-aqueous electrolyte solution and controlling the mass percentage A% of vinylene carbonate, the mass percentage B% of the compound of formula I, and the ratio P between them to satisfy the above ranges, it is possible to improve low-temperature discharge performance and simultaneously improve cycle performance.

[0032] In one embodiment, the compound of formula I is

[0033] [ka] At least one of the following is selected. By adding the above-mentioned type of compound of formula I to the non-aqueous electrolyte, it is possible to further improve the low-temperature discharge performance of the lithium secondary battery while also improving the cycle performance.

[0034] In one embodiment, the non-aqueous electrolyte further contains a cyclic carbonate selected from at least two of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate, and the mass percentage of the cyclic carbonate is M%, based on the total mass of the non-aqueous electrolyte, and 5≦M≦30. In one embodiment, 10≦M≦20. For example, M is 5, 6.5, 7.6, 15.0, 19.5, 23.8, 30, or a value within a range consisting of any two of these values. By adding a certain amount of cyclic carbonate to the non-aqueous electrolyte and controlling the mass percentage of the cyclic carbonate to the above specific range, it is possible to further improve the low-temperature discharge performance of the lithium secondary battery while also achieving improved cycle performance.

[0035] In one embodiment, in the nonaqueous electrolyte, the ratio of the mass percentage B% of the compound of formula I to the mass percentage M% of the cyclic carbonate is 0.1≦B / M≦3. In one embodiment, 0.1≦B / M≦2. In one embodiment, 1≦B / M≦3. In one embodiment, 0.3≦B / M≦1. In one embodiment, 2≦B / M≦3. In one embodiment, 1.5≦B / M≦3. By controlling the ratio of the mass percentage B% of the compound of formula I to the mass percentage M% of the cyclic carbonate within the above range, it is possible to further improve the low-temperature discharge performance of the lithium secondary battery while also achieving improved cycle performance.

[0036] In one embodiment, the non-aqueous electrolyte further comprises a chain ester, including a fluorinated chain ester and a non-fluorinated chain ester.

[0037] In certain embodiments, the fluorinated chain ester is selected from at least one of methyl difluoroethyl carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, methyl hexafluoroisopropyl carbonate, di(2,2,2-trifluoroethyl)carbonate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, hexafluoroisopropyl acetate, 2,2-difluoroethyl propionate, 2,2,2-trifluoroethyl propionate, and hexafluoroisopropyl propionate.

[0038] In one embodiment, the non-fluorinated chain ester is selected from at least one of dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0039] In one embodiment, the mass percentage of the chain ester is N0%, based on the total mass of the non-aqueous electrolyte, and is 10≦N0≦70. For example, N0 is 10, 20, 30, 40, 50, 60, 70, or a value within a range formed by any two of these values. By further adding a certain amount of chain ester to the non-aqueous electrolyte and controlling the total mass percentage of the chain ester within a specific range, it is possible to further improve the low-temperature discharge performance of the lithium secondary battery while also achieving improved cycle performance.

[0040] In one embodiment, the mass percentage of the fluorinated chain ester, based on the total mass of the nonaqueous electrolyte, is N1%, and 5≦N1≦50. For example, N1 is 5, 10, 15, 20, 30, 40, 50, or a value within a range consisting of any two of these values.

[0041] In one embodiment, the mass percentage of the non-fluorinated chain ester is N2%, based on the total mass of the non-aqueous electrolyte, and is 5≦N2≦50. For example, N2 is 5, 10, 15, 20, 30, 40, 50, or a value within a range consisting of any two of these values. By controlling the mass percentages of the fluorinated chain ester and the non-fluorinated chain ester in the chain ester within the above range, it is possible to further improve the low-temperature discharge performance of the lithium secondary battery while simultaneously improving the cycle performance.

[0042] In one embodiment, the non-aqueous electrolyte further comprises a polycyano compound selected from at least one of succinonitrile, glutaronitrile, methylglutaronitrile, adiponitrile, pimelonitrile, suberonitrile, fumaronitrile, and 1,2-bis(cyanoethoxy)ethane, and the mass percentage of the polycyano compound is X% based on the total mass of the non-aqueous electrolyte, where 0.1≦X≦10. For example, X is 0.1, 0.5, 1.5, 2, 5, 7, 10, or a value within a range consisting of any two of these values. By adding a polycyano compound to the non-aqueous electrolyte and controlling the mass percentage X% of the polycyano compound within the above range, high-temperature storage stability can be improved, while low-temperature discharge performance and cycle performance can both be improved.

[0043] In some embodiments, the non-aqueous electrolyte includes a compound of Formula II and / or a compound of Formula III:

[0044] [ka]

[0045] [ka] In the formula, R1 to R5 are each independently selected from the group consisting of hydrogen, fluorine, vinyl, ethynyl, and acid anhydride. Based on the total mass of the non-aqueous electrolyte, the mass percentage of the compound of Formula II is Y1%, and the mass percentage of the compound of Formula III is Y2%, where Y% = Y1% + Y2%, and 0.1≦Y≦0.5. For example, it may be 0.1, 0.2, 0.3, 0.4, 0.5, or a value within a range consisting of any two of these values. Here, any two adjacent groups of R1 to R5 exist independently or are covalently linked to form a ring with the parent ring. By adding a certain amount of the compounds of Formula II and Formula III to the non-aqueous electrolyte and controlling the sum of the mass percentages Y1% of the compound of Formula II and Y2% of the compound of Formula III within the above range, high-temperature storage stability can be further improved, while achieving both improved low-temperature discharge performance and improved cycle performance.

[0046] In one embodiment, the compound of formula II is

[0047] [ka] At least one of the following is selected.

[0048] In one embodiment, the compound of formula III is

[0049] [ka] At least one of the following is selected.

[0050] By selecting the compounds of formula II and formula III of the above types, it is possible to further improve the high-temperature storage performance while simultaneously improving the low-temperature discharge performance and cycle performance.

[0051] The non-aqueous electrolyte may further contain a lithium salt and a non-aqueous solvent. The present application is not particularly limited by the type of lithium salt. As long as the object of the present application can be achieved, the lithium salt may include, for example, at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bistrifluoromethanesulfonylimide, lithium bis(fluorosulfonyl)imide, lithium bisoxalate borate, and lithium difluorooxalate borate. Based on the mass of the non-aqueous electrolyte, the mass percentage of the lithium salt may be 8% to 15%, for example, 8%, 9%, 10%, 11%, 12.5%, 13%, 15%, or a range consisting of any two of these values. The non-aqueous solvent may include, for example, at least one of an ether compound and other organic solvents.

[0052] The ether compound may include, for example, at least one of ethylene glycol dimethyl ether, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran.

[0053] The other organic solvent may include, for example, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, and trioctyl phosphate.

[0054] positive electrode The positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, and may be a single layer or multiple layers. Each layer in a multi-layer positive electrode active material may include the same or different positive electrode active materials. The positive electrode active material is any material that can reversibly insert and extract alkali metal ions. The positive electrode active material includes a lithium transition metal oxide containing nickel and other transition metals, in which the amount of nickel relative to the total number of moles of the transition metals may be 60 mol% or more, for example, 75 mol% or more, 80 mol% or more, 85 mol% or more, or 90 mol% or more.

[0055] In some embodiments, the positive electrode active material includes at least one active material selected from the group consisting of Li-Ni-Co-Al (NCA), Li-Ni-Co-Mn (NCM), lithium cobalt oxide (LiCoO), lithium manganese oxide (LiMnO), lithium nickel oxide (LiNiO), and lithium iron phosphate (LiFePO).

[0056] In one embodiment, the positive electrode active material layer includes a positive electrode conductive material. The type of positive electrode conductive material is not limited, and any known conductive material can be used. Examples of positive electrode conductive materials include, but are not limited to, carbon black such as acetylene black and SuPeR-P, amorphous carbon materials such as acicular coke, carbon nanotubes, and graphene. The above positive electrode conductive materials may be used alone or in any combination.

[0057] In one embodiment, the positive electrode material layer includes a positive electrode binder. The type of positive electrode binder is not particularly limited, and in the case of a coating method, any material that can be dissolved or dispersed in the liquid medium used in electrode production may be used. Examples of positive electrode binders include resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, or cellulose nitrate; rubber-like polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, or ethylene-propylene rubber; styrene-butadiene-styrene block copolymers or their hydrogenated products; ethylene-propylene-diene terpolymers (EPDM), styrene-ethylene-butadiene-ethylene copolymers; and styrene-butadiene-ethylene copolymers. Examples of the positive electrode binder include, but are not limited to, one or more of thermoplastic elastomeric polymers such as ethylene-isoprene-styrene block copolymers or their hydrides, soft resinous polymers such as syndiotactic 1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers, fluorine-based polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers, and polymer compositions having alkali metal ion conductivity. The above positive electrode binders may be used alone or in any combination.

[0058] The type of solvent used to form the positive electrode slurry is not limited, as long as it can dissolve or disperse the positive electrode active material, conductive material, positive electrode binder, and optional thickener. Examples of solvents used to form the positive electrode slurry include aqueous and organic solvents. Examples of aqueous media include, but are not limited to, a mixture of alcohol and water or water. Examples of organic media include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran; amides such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.

[0059] Thickeners are typically used to adjust the viscosity of the slurry. When using an aqueous medium, a slurry can be prepared using a thickener and a styrene-butadiene rubber emulsion. The type of thickener is not particularly limited, and examples include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphated starch, casein, and salts thereof. The above thickeners may be used alone or in any combination.

[0060] The type of positive electrode current collector is not particularly limited, and any known material suitable for use as a positive electrode current collector may be used. Examples of positive electrode current collectors include, but are not limited to, aluminum, stainless steel, nickel plating, metallic materials such as titanium or tantalum, carbon cloth, carbon paper, and the like. In some embodiments, the positive electrode current collector is a metallic material. In some embodiments, the positive electrode current collector is aluminum.

[0061] In order to reduce the electron contact resistance between the positive electrode current collector and the positive electrode active material layer, the surface of the positive electrode current collector may include a conductive aid or a conductive coating. Examples of the conductive aid include, but are not limited to, noble metals such as carbon, gold, platinum, or silver. Examples of the conductive coating include a mixture layer of an inorganic oxide, a conductive agent, and a binder.

[0062] Negative electrode The negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, and the negative electrode active material layer contains a negative electrode active material. In one embodiment, the chargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material, preventing lithium metal from being inadvertently deposited on the negative electrode during charging. ?

[0063] The negative electrode active material may include at least one of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), silicon, silicon-carbon composite, SiO x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate Li4Ti5O with a spinel structure 12 , Li-Al alloy, and metallic lithium. Further, the negative electrode active material may further include an amorphous carbon material, and the amorphous carbon may be soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, or calcined coke.

[0064] It seems there is a formatting issue in the original text around line 11 where "SiO" is incomplete. I've translated it as is, but it might need to be corrected in the original for a more accurate technical understanding.The negative electrode material layer of the present application further includes a negative electrode binder. The negative electrode binder can enhance the bonding between negative electrode active material particles and the bonding between the negative electrode active material and the current collector. There are no particular limitations on the type of negative electrode binder, as long as it is a material that is stable with respect to the electrolyte or the solvent used in electrode production. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include fluororesin, polyacrylonitrile (PAN), polyimide resin, acrylic resin, polyolefin resin, etc. When an aqueous solvent is used to prepare the negative electrode mixture slurry, the negative electrode binder may include carboxymethyl cellulose (CMC) or a salt thereof, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, etc.

[0065] The negative electrode layer of the present application further includes a conductive agent. The type of the negative electrode conductive agent is not particularly limited as long as the object of the present application can be achieved. For example, the negative electrode conductive agent may be at least one of acetylene black, ketjen black, carbon nanotubes, carbon fibers, carbon dots, graphene, etc., and the carbon nanotubes may include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0066] The present application does not limit the type of negative electrode current collector as long as it achieves the objectives of the present application. For example, the negative electrode current collector may include copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or a polymer substrate coated with a conductive metal. Here, the conductive metal includes, but is not limited to, copper, nickel, or titanium, and the polymer substrate material includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene terephthalate, polynaphthalenedicarboxylate, and polyparaphenylene terephthalamide. In the present application, the thickness of the negative electrode current collector and the negative electrode active material layer is not limited as long as it achieves the objectives of the present application. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the negative electrode active material layer on one side is 30 μm to 160 μm. In the present application, the negative electrode active material layer may be provided on one surface in the thickness direction of the negative electrode current collector, or on two surfaces in the thickness direction of the negative electrode current collector. The "surface" here may be the entire area of ​​the negative electrode current collector or a partial area of ​​the negative electrode current collector, and is not particularly limited in the present application as long as the object of the present application can be achieved.

[0067] In the present application, there is no particular limitation on the compaction density of the negative electrode pieces, as long as the object of the present application can be achieved. For example, the compaction density of the negative electrode pieces is 1.0 g / cm 3 ~1.85g / cm 3 In the present application, there is no particular limitation on the cold pressing pressure of the negative electrode pieces, as long as the object of the present application can be achieved. For example, the cold pressing pressure of the negative electrode pieces is 3 tons to 30 tons.

[0068] The negative electrode piece may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer. The present application does not limit the composition of the conductive layer, and it may be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. The present application does not limit the conductive agent and binder in the conductive layer, and it may be at least one of the above conductive agents and binders. The present application does not limit the mass ratio of the conductive agent and binder in the conductive layer, and those skilled in the art can select it according to actual needs as long as the objectives of the present application are achieved. The present application does not limit the thickness of the conductive layer, as long as the objectives of the present application are achieved. For example, the thickness of the conductive layer is 1 μm to 10 μm.

[0069] Separator In this application, a separator is typically provided between the positive and negative electrodes to separate the positive and negative electrode pieces, prevent short circuits within the secondary battery, allow the free passage of electrolyte ions, and not affect the electrochemical charge and discharge process.

[0070] The present application does not place any particular restrictions on the separator, and as long as the object of the present application can be achieved, for example, the separator material may include at least one of polyolefins (PO) mainly consisting of polyethylene (PE) and polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), polyurethane, and aramid, and the separator type may include at least one of a woven membrane, a nonwoven membrane, a microporous membrane, a composite membrane, a rolled membrane, and a spun membrane.

[0071] In the present application, the separator may include a substrate and a surface treatment layer. The substrate may be a porous nonwoven fabric or composite membrane, and the substrate material may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Alternatively, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. A surface treatment layer may be provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic material. For example, the inorganic layer may include inorganic particles and a binder. The inorganic particles are not particularly limited in the present application and may include, for example, at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The present application is not particularly limited to the binder, and may be, for example, at least one of the binders described above. The polymer layer includes a polymer, and the polymer material may include at least one of polyamide, polyacrylonitrile, acrylic ester polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0072] In the present application, the pore size of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above ranges, it is possible to ensure insulation properties and mechanical strength, as well as the magnification characteristics and energy density of the secondary battery.

[0073] The electrochemical device of the present application further includes a packaging bag, which is used to house the positive electrode pieces, separator, negative electrode pieces, and electrolyte, as well as other components known in the art for electrochemical devices, but the present application is not limited to these other components. The present application is not particularly limited to the packaging bag, and any packaging bag known in the art may be used as long as it can achieve the objectives of the present application.

[0074] Example Hereinafter, the embodiments of the secondary battery of the present application will be described in more detail with examples and comparative examples using a lithium ion battery as an example. Those skilled in the art will understand that the manufacturing methods described in this application are merely examples, and that any appropriate manufacturing method is within the scope of this application. Various tests and evaluations are performed according to the following methods. Unless otherwise specified, "parts" and "%" are based on mass.

[0075] Example 1-1 <Lithium-ion battery manufacturing> (1) Positive electrode production: Lithium cobalt oxide (positive electrode active material), conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95:2:3, N-methylpyrrolidone (NMP) is added, and the mixture is uniformly stirred using a vacuum mixer to obtain a positive electrode slurry with a solids content of 70 wt%. The positive electrode slurry is uniformly applied to one surface of an aluminum foil positive electrode current collector with a thickness of 9 μm and dried to obtain a positive electrode piece with a positive electrode mixture layer applied to one side. The above process is repeated on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode piece with a positive electrode mixture layer applied to both sides. After cold rolling, cutting, slitting, and drying, the resulting positive electrode piece is obtained with a specification of 74 mm x 867 mm.

[0076] (2) Preparation of non-aqueous electrolyte: In a glove box under a dry argon atmosphere, diethyl carbonate is used as a base solvent, and then vinylene carbonate, the compound of formula I, and lithium hexafluorophosphate (LIPF6) are dissolved in the base solvent to obtain an electrolyte, where the mass percentage of LIPF6 is 12.5% ​​based on the total mass of the electrolyte, the mass percentages of vinylene carbonate and the compound of formula I are as shown in Table 1, and the remainder is diethyl carbonate.

[0077] (3) Negative Electrode Fabrication: Artificial graphite was used as the negative electrode active material. The negative electrode active material, styrene butadiene rubber (SBR), polyacrylic acid (PAA), carbon nanotubes (CNT), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95.8:2.4:0.5:0.5:0.8. Deionized water was then added as a solvent and the mixture was stirred uniformly to prepare a negative electrode slurry with a solids content of 45 wt%. The negative electrode slurry was then uniformly coated onto one surface of a 6 μm-thick copper foil negative electrode current collector and dried to obtain a negative electrode chip with a negative electrode mixture layer coated on one side. The above process was repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode chip with a negative electrode mixture layer coated on both sides. The resulting mixture was then cold-pressed, cut, and separated, followed by drying, to obtain a negative electrode chip with dimensions of 76.6 mm x 875 mm.

[0078] (4) Preparation of separator: A porous polyethylene thin film with a thickness of 15 μm is used as the separator.

[0079] (5) Lithium-ion battery manufacturing: The positive electrode pieces, separator, and negative electrode pieces are stacked in order, with the separator positioned between the positive and negative electrode pieces to provide isolation, and then wound to obtain a bare battery core. The bare battery core is then placed in a packaging bag, filled with electrolyte, and sealed. After undergoing processes such as chemical formation, degassing, trimming, and capacity testing, a lithium-ion battery is obtained.

[0080] <Test Method> (1) Low-temperature discharge performance test The lithium-ion battery was placed in a high / low temperature box, adjusted to 25°C, and allowed to stand for 30 minutes to reach a constant temperature. Once at a constant temperature, the lithium-ion battery was discharged at a constant current of 0.5C to 3.0V, then charged at a constant current of 0.5C to 4.5V, and then charged at a constant voltage of 0.05C to 4.5V. Similarly, the battery was discharged at a constant current of 0.5C to 3.0V at 25°C, and the discharge capacity at this time was recorded as the initial discharge capacity. The battery was then charged at a constant current of 0.5C to 4.5V at 25°C, and then charged at a constant voltage of 0.05C to 4.5V. The lithium-ion battery was then left at 0°C for 30 minutes to allow its temperature to match the ambient temperature. The battery was then discharged at a constant current of 0.5C to 3.0V at 0°C, and the discharge capacity at this time was recorded as the low-temperature discharge capacity. Low temperature discharge capacity retention rate = (low temperature discharge capacity / initial discharge capacity) x 100%.

[0081] (2) Circulation performance test: The lithium-ion battery was placed in a thermostatic test box at 45°C and allowed to stand for 30 minutes to reach a constant temperature. It was then charged at a constant current of 0.5C to 4.5V, followed by constant voltage charging until the current reached 0.025C. The battery was then allowed to stand for 5 minutes, and discharged at a constant current of 0.5C to 3.0V, recording this as the initial discharge capacity, Co. This procedure was repeated 100 times, and the discharge capacity, C1, after 100 cycles was recorded to calculate the cycle capacity retention of the lithium-ion battery. Cycle capacity retention = C1 / Co × 100%.

[0082] (3) High-temperature storage performance test The lithium-ion battery was placed in a constant-temperature environment at 25°C and allowed to stand for 30 minutes to reach a constant temperature. It was then charged at a constant current of 0.5C to 4.5V, and then further charged at a constant voltage of 4.5V to a current of 0.025C. The thickness of the lithium-ion battery was recorded and used as the initial thickness. The lithium-ion battery was then transferred to a constant-temperature box at 60°C and stored for 30 days. During this period, the thickness of the lithium-ion battery was measured and recorded every six days. The thickness measured after 30 days was recorded as the storage thickness. The thickness expansion rate of the lithium-ion battery was calculated and used as an index to evaluate the high-temperature storage performance of the lithium-ion battery. High temperature storage thickness expansion rate = (storage thickness - initial thickness) / initial thickness x 100%.

[0083] The lithium ion batteries of the following Examples and Comparative Examples differ from Example 1-1 only in that the mass percentage A of vinylene carbonate, the type of compound of formula I, and the mass percentage B of the compound of formula I were adjusted according to Table 1, and the performance test results of the lithium ion batteries of each Example and Comparative Example are shown in Table 1 below.

[0084] [Table 1] In the above table, the mass percentage of each substance is based on the mass of the electrolyte, A is the mass percentage A% of vinylene carbonate, B is the mass percentage B% of the compound of formula I, and " / " indicates that the substance is not included.

[0085] As can be seen from Table 1, the nonaqueous electrolyte of the lithium ion battery prepared in the examples herein contains vinylene carbonate and the compound of Formula I, where the mass percentage of vinylene carbonate is A%, the mass percentage of the compound of Formula I is B%, and P = B / A. By controlling the mass percentages within the ranges of 0.01 ≦ A ≦ 3 and 0.5 ≦ P ≦ 50, it is possible to improve both the low-temperature discharge capacity retention of the lithium secondary battery and the cycle capacity retention. Here, when at least one of 0.1 ≦ A ≦ 2, 0.5 ≦ B ≦ 5, or 1 ≦ P ≦ 5 is satisfied, it is possible to further improve the low-temperature discharge capacity retention of the lithium secondary battery and to improve the cycle capacity retention.

[0086] The lithium ion batteries of the following Examples differ from Examples 1 to 3 only in that specific types and contents of cyclic carbonate and chain ester were added to the base solvent during the preparation of the electrolyte, and the mass percentages of both in the electrolyte are as shown in Table 2. The performance test results of the lithium ion batteries of each Example are shown in Table 2 below.

[0087] [Table 2] In the table above, the mass percentage of each substance is based on the mass of the electrolyte, and " / " indicates that the substance is not included. The compounds corresponding to each symbol are as follows: EC: ethylene carbonate, PC: propylene carbonate, FEC: fluoroethylene carbonate.

[0088] As can be seen from Table 2, when the nonaqueous electrolyte solution of the lithium ion battery prepared in the examples further contains a cyclic carbonate, and the mass percentage M% of the cyclic carbonate satisfies 5≦M≦30, the low-temperature discharge capacity retention of the lithium secondary battery can be further improved while also improving the cycle capacity retention. In particular, when at least one of 10≦M≦20 or 0.1≦B / M≦3 is satisfied, the effects of improving the low-temperature discharge capacity retention and cycle capacity retention of the lithium secondary battery are more significant. When the nonaqueous electrolyte solution of the lithium ion battery prepared in the examples further contains a chain ester, and the mass percentage N0% of the chain ester satisfies 10≦N0≦70, the low-temperature discharge capacity retention of the lithium secondary battery can be further improved while also improving the cycle capacity retention. In particular, when the mass percentage N1% of the fluorinated chain ester and the mass percentage N2% of the non-fluorinated chain ester satisfy at least one of 5≦N1≦50, 5≦N2≦50, or 20≦N0≦60, the effects of improving the low-temperature discharge capacity retention and cycle capacity retention of the lithium secondary battery become more significant.

[0089] The lithium ion batteries of Examples 3-1 to 3-19 below were prepared based on the parameters of Examples 1-3, and the lithium ion battery of Example 3-20 was prepared based on the parameters of Examples 2-28. The specific preparation involved adding specific types and amounts of polycyano compounds, compounds of formula II, and compounds of formula III to the base solvent during the preparation of the electrolyte, with the mass percentages of each substance in the electrolyte being as shown in Table 3. The performance test results of the lithium ion batteries of each Example are shown in Table 3 below.

[0090] [Table 3] In the above table, the mass percentage of each substance is based on the mass of the electrolyte, and " / " indicates that the substance is not included.

[0091] As can be seen from Table 3, when the nonaqueous electrolyte solution of the lithium ion battery prepared in the examples further contains a polycyano compound, and when the mass percentage X% of the polycyano compound satisfies 0.5≦X≦5, it can improve the high-temperature storage expansion rate of the lithium secondary battery while simultaneously improving the low-temperature discharge capacity retention and cycle capacity retention. When the nonaqueous electrolyte solution of the lithium ion battery prepared in the examples further contains an internal salt material, and when the mass percentage Y% of the internal salt material satisfies 0.1≦Y≦0.5, it can improve the high-temperature storage expansion rate of the lithium secondary battery while simultaneously improving the low-temperature discharge capacity retention and cycle capacity retention.

[0092] The above description is merely a preferred embodiment of the present application, and does not limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the scope of the principles of the present application shall all be included in the protection scope of the present application.

Claims

1. vinylene carbonate and a compound of formula I, 【Chemistry 1】 In the formula, R is unsubstituted or C substituted with Ra. ２ ~C ６ an alkyl group of the formula: ２ ~C ６ an alkenyl group of the formula: ２ ~C ６ an alkynyl group of the formula: ５ ~C １２ a nitrogen-containing heteroaromatic group of the formula: ６ ~C １２ The substituents Ra of each group are each independently selected from fluorine or C １ ~C ６ and the fluorinated alkyl group is selected from the group consisting of Based on the total mass of the non-aqueous electrolyte, the mass percentage of the vinylene carbonate is A%, where 0.01≦A≦3, and the mass percentage of the compound of Formula I is B%, A non-aqueous electrolyte solution characterized in that P=B / A and 0.5≦P≦50.

2. The nonaqueous electrolyte solution is (1) 0.1≦A≦2; (2) 0.5≦B≦5; (3) A nonaqueous electrolyte solution according to claim 1, which satisfies at least one of the following conditions: 1≦P≦5.

3. The compound of formula I is 【Chemistry 2】 2. The non-aqueous electrolyte according to claim 1, wherein the non-aqueous electrolyte is selected from at least one of the following:

4. the non-aqueous electrolyte solution further contains cyclic carbonates selected from any two of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate; The non-aqueous electrolyte according to any one of claims 1 to 3, wherein the mass percentage of the cyclic carbonate is M%, and 5≦M≦30, based on the total mass of the non-aqueous electrolyte.

5. 5. The nonaqueous electrolyte according to claim 4, wherein 10≦M≦20 and / or 0.1≦B / M≦3.

6. the nonaqueous electrolyte solution further contains a chain ester, The chain ester includes a fluorinated chain ester and a non-fluorinated chain ester, The chain ester is (1) the fluorinated chain ester is selected from at least one of methyl difluoroethyl carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, methyl hexafluoroisopropyl carbonate, di(2,2,2-trifluoroethyl)carbonate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, hexafluoroisopropyl acetate, 2,2-difluoroethyl propionate, 2,2,2-trifluoroethyl propionate, and hexafluoroisopropyl propionate; (2) the non-fluorinated chain ester is selected from at least one of dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate; (3) The mass percentage of the chain ester based on the total mass of the nonaqueous electrolyte solution is N ０ %, and 10≦N ０ 4. The nonaqueous electrolyte solution according to claim 1, wherein the nonaqueous electrolyte satisfies at least one of the following conditions:

7. Based on the total mass of the nonaqueous electrolyte, the nonaqueous electrolyte (1) The mass percentage of the fluorinated chain ester is N １ %, and 5≦N １ ≦50; (2) The mass percentage of the non-fluorinated chain ester is N ２ %, and 5≦N ２ ≦50; (3) 20≦N ０ 7. The nonaqueous electrolyte according to claim 6, wherein the nonaqueous electrolyte satisfies at least one of the following conditions:

8. the nonaqueous electrolyte solution further contains a polycyano compound, the polycyano compound is selected from at least one of succinonitrile, glutaronitrile, methylglutaronitrile, adiponitrile, pimelonitrile, suberonitrile, fumaronitrile, and 1,2-bis(cyanoethoxy)ethane; The non-aqueous electrolyte according to any one of claims 1 to 3, wherein the mass percentage of the polycyano compound is X%, and 0.1≦X≦10, based on the total mass of the non-aqueous electrolyte.

9. 9. The nonaqueous electrolyte according to claim 8, wherein 0.5≦X≦5.

10. The non-aqueous electrolyte solution further contains a compound of the following formula II and a compound of the following formula III: 【Transformation 3】 【Chemistry 4】 In the formula, R １ ~R ５ are each independently selected from a hydrogen atom, a fluorine atom, a vinyl group, an ethynyl group, or an acid anhydride group; Based on the total mass of the non-aqueous electrolyte, the mass percentage of the compound of formula II is １ %, and the mass percentage of the compound of formula III is Y ２ %, and Y%=Y １ %+Y ２ %, 0.1≦Y≦0.5, R １ ~R ５ The non-aqueous electrolyte according to any one of claims 1 to 3, wherein any two adjacent groups are present independently of each other or are linked by a covalent bond to form a ring together with the parent ring.

11. The compound of formula II is 【Transformation 5】 and / or The compound of formula III is 【Transformation 6】 The non-aqueous electrolyte according to claim 10, wherein the non-aqueous electrolyte is selected from at least one of the following:

12. a positive electrode including a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector; a negative electrode including a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector; A separator; A lithium secondary battery comprising the nonaqueous electrolyte solution according to any one of claims 1 to 11.

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