Lithium secondary battery and electric device

Abstract

The invention provides a lithium secondary battery and a power utilization device. A non-aqueous electrolyte of the battery comprises a first additive, a second additive and a non-aqueous solvent, the first additive comprises a cyclic sulfate compound as shown in a formula I, the second additive comprises an isocyanate compound as shown in a formula II, and the non-aqueous solvent comprises ethylene carbonate accounting for 10%-50% of the total mass of the non-aqueous electrolyte. The non-aqueous electrolyte has good positive and negative electrode interface protection capability, reduces the occurrence of positive and negative electrode surface side reactions, reduces the impedance of a battery cell, and can improve the cycle performance and storage performance of the lithium secondary battery.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and more particularly to a lithium secondary battery and an electrical device. Background Technology

[0002] Lithium-ion batteries have become the most popular energy storage system due to their high operating potential, long lifespan, and environmental friendliness, and are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids, and other fields. With increasing demands for longer battery cycle life, the development of lithium-ion battery systems with long cycle stability is urgently needed.

[0003] Electrolytes can undergo side reactions with the positive and negative electrodes of a secondary battery, damaging the structure of the electrode sheets and degrading the cell impedance, thus affecting the cycle life of the secondary battery. Typically, film-forming additives are added to the electrolyte to protect the positive and negative electrodes. However, most existing film-forming additives are reduced to form a solid electrolyte interphase (SEI) film at the negative electrode during cell formation, with only a very small amount participating in the formation of a positive electrode electrolyte interphase (CEI) film at the positive electrode. This results in insufficient protection of the positive electrode interface and excessive protection of the negative electrode interface, ultimately affecting the battery's cycle performance and storage performance.

[0004] Therefore, it is necessary to provide an electrolyte that can improve the protection of the positive and negative electrode interfaces of lithium-ion batteries. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a lithium secondary battery with stable positive and negative electrode surfaces and low cell impedance, and significantly improved cycle performance and storage performance.

[0006] The first aspect of this application provides a lithium secondary battery, including a non-aqueous electrolyte, said non-aqueous electrolyte comprising a first additive, a second additive, and a non-aqueous solvent.

[0007] The first additive comprises a cyclic sulfate compound represented by Formula I.

[0008]

[0009] R1, R2, R3, and R4 are each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C1-C3 alkyl, substituted or unsubstituted C1-C3 alkoxy, or substituted or unsubstituted 5-6 member saturated cyclic sulfate groups.

[0010] The second additive includes an isocyanate-based compound as shown in Formula II.

[0011]

[0012] R5 is selected from phenylene groups substituted with 0, 1, 2, 3 or 4 substituents selected from halogen, methyl, ethyl, alkylene groups, substituted or unsubstituted 2 to 3 cyclic fused-ring aromatic hydrocarbon groups, C1-C8 alkylene groups including saturated or unsaturated groups, substituted or unsubstituted 5 to 6 membered alicyclic groups, and C1-C3 alkylene diphenylene groups.

[0013] The non-aqueous solvent includes ethylene carbonate, and the mass content of ethylene carbonate is greater than or equal to 10% and less than or equal to 50% based on the total mass of the non-aqueous electrolyte.

[0014] In the electrolyte provided in this application, the cyclic sulfate compound can react with residual alkali on the surface of the positive electrode active material and participate in the formation of the positive electrode CEI film. Furthermore, the cyclic sulfate compound can also participate in the formation of the SEI film, reducing side reactions between the non-aqueous electrolyte and the negative electrode. The isocyanate group in the isocyanate compound has strong electrophilicity and preferentially reacts with water or acid in the electrolyte, thereby reducing side reactions between the cyclic sulfate compound and the electrolyte and allowing it to participate more in the interfacial film formation reaction. Simultaneously, the isocyanate compound also participates in the initial formation and stabilization process of the SEI film, improving the stability of the negative electrode material. Ethyl carbonate readily undergoes dehydrogenation at the electrode surface, producing gas and water. These decomposition products can react with the cyclic sulfate compound and the isocyanate compound, consuming the first and second additives, thus affecting their film formation effects at the positive and negative electrodes. Reducing the ethylene carbonate content helps reduce the side reactions of the first and second additives, allowing them to participate more in interfacial film formation, thereby improving the interfacial protection of the positive and negative electrodes in lithium secondary batteries.

[0015] In some embodiments, one of R1 and R2 is selected from hydrogen, methyl, ethyl, fluorine, trifluoromethyl, cyano, or... The other is selected from hydrogen; or, both R1 and R2 are selected from methyl; one of R3 and R4 is selected from hydrogen, methyl, ethyl, n-propyl, fluorine, ethoxy, or The other is selected from hydrogen; R5 is selected from methylene, hexane, 5- to 6-membered alicyclic group, Among them, R 51 R 52 R 53 R 54 Each time it appears, it is independently selected from hydrogen, halogen, methyl, and ethyl.

[0016] In any embodiment, the ethylene carbonate content is 15%-40% based on the total mass of the non-aqueous electrolyte, which helps to further reduce the side reactions of cyclic sulfate compounds and isocyanate compounds in the electrolyte and participate more in interfacial film formation.

[0017] In any embodiment, the cyclic sulfate compound includes

[0018] At least one of them.

[0019] The cyclic sulfate compound interacts with residual alkali on the positive electrode surface, and one sulfate ring (or monocyclic ring) in the cyclic sulfate compound undergoes a ring-opening reaction. The monocyclic ring-opening product participates in CEI film formation and improves the film composition during the formation process. The sulfate groups in the cyclic sulfate compound undergo nucleophilic reactions with oxygen atoms on the surface of the positive electrode active material, modifying the surface of the positive electrode particles in situ and improving the stability of the CEI film. At the same time, the cyclic sulfate compound can also participate in the formation of SEI on the negative electrode, reducing the destructive effects of reduction side reactions between the non-aqueous electrolyte and the negative electrode surface, as well as solvent co-intercalation, on the structural stability of the negative electrode. The cyclic sulfate compound helps improve the stability of both the positive and negative electrodes and reduce cell impedance, thereby improving the cycle performance and storage performance of the lithium secondary battery.

[0020] In any embodiment, the isocyanate-based compound includes

[0021]

[0022] At least one of them.

[0023] The isocyanate groups in the isocyanate-based compound can react with trace amounts of water and acid in the electrolyte, reducing the damage to the positive electrode interface film caused by the reaction of the first additive and certain lithium salts (such as LiPF6) with water, as well as the unintended consumption of the first additive, thus promoting the formation of a good CEI film at the positive electrode. Furthermore, the isocyanate-based compound forms a thin and uniform SEI film at the negative electrode of the secondary battery, improving the film-forming composition and enhancing the stability of the negative electrode material while effectively reducing the consumption of active lithium, thereby improving the battery's storage performance.

[0024] In any embodiment, the non-aqueous electrolyte comprises one of the following:

[0025] (1) The first additive includes at least one of the cyclic sulfate compounds numbered C1-1, C1-2, C1-3, C1-4, C1-5, C1-6, C1-7, C1-8, C1-9, C1-10, C1-11, C1-12, C1-13, C1-14, C1-15, and C1-16; the second additive includes an isocyanate compound numbered C2-17;

[0026] (2) The first additive includes cyclic sulfate compounds numbered C1-16; the second additive includes at least one of isocyanate compounds numbered C2-1, C2-2, C2-3, C2-4, C2-5, C2-6, C2-7, C2-8, C2-9, C2-10, C2-11, C2-12, C2-13, C2-14, C2-15, C2-16, C2-17, and C2-18.

[0027] By using the first additive and the second additive in combination, the consumption of the first additive can be reduced. Without using too much additive, a stable and uniform interface film can be formed on both the positive and negative electrodes of the secondary battery, improving the protection of the positive and negative electrode interfaces and enhancing the cycle performance and storage performance of the lithium secondary battery.

[0028] In any embodiment, the non-aqueous electrolyte satisfies at least one of the following conditions:

[0029] (1) Based on the total mass of the non-aqueous electrolyte, the mass content of the first additive is 0.05%-20%;

[0030] (2) Based on the total mass of the non-aqueous electrolyte, the mass content of the second additive is 0.01%-20%;

[0031] (3) The mass ratio of the first additive to the second additive is 0.02-50.

[0032] In any embodiment, the non-aqueous electrolyte satisfies at least one of the following conditions:

[0033] (1) Based on the total mass of the non-aqueous electrolyte, the mass content of the first additive is 0.05%-8%;

[0034] (2) Based on the total mass of the non-aqueous electrolyte, the mass content of the second additive is 0.1%-8%;

[0035] (3) The mass ratio of the first additive to the second additive is 0.2-8;

[0036] (4) Based on the total mass of the non-aqueous electrolyte, the mass content of the ethylene carbonate is 15%-25%.

[0037] When the mass content of the first and second additives in the non-aqueous electrolyte is within a suitable range, it helps to form SEI and CEI films of appropriate thickness on both the positive and negative electrodes, reducing side reactions on both electrodes without excessively increasing the cell impedance.

[0038] When the mass ratio of the first additive to the second additive is within a suitable range, it can promote the synergistic effect of the two. The second additive helps to reduce the side reactions of the first additive, allowing it to participate more in the positive electrode film formation reaction. At the same time, the second additive can still form an excellent negative electrode SEI film, so that both the positive and negative electrodes have good interface protection. It can also take into account a moderate cell internal resistance and not deteriorate the positive and negative electrode interface.

[0039] Within a suitable range, the mass content of ethylene carbonate helps reduce the degree of dehydrogenation reaction on the positive electrode surface, slows down the dehydrogenation side reaction, enhances the oxidation resistance of the non-aqueous electrolyte, reduces the destructive effect of protons on the negative electrode, and thus extends battery life; it also helps reduce gas production in secondary batteries and improves the electrical and safety performance of secondary batteries.

[0040] In any embodiment, the water content of the non-aqueous electrolyte is 10ppm-100ppm based on the total mass of the non-aqueous electrolyte.

[0041] In any embodiment, the water content of the non-aqueous electrolyte is 10ppm-50ppm based on the total mass of the non-aqueous electrolyte.

[0042] The first and second additives can undergo hydrolysis, producing hydrolysis products with poor film-forming properties. Their dissolution in non-aqueous electrolytes can also affect the film-forming effect of the positive electrode. Maintaining a suitable water content in the non-aqueous electrolyte can reduce the hydrolysis of the first and second additives, thus improving the protection of the positive and negative electrode interfaces.

[0043] In any embodiment, the lithium secondary battery includes a positive electrode sheet, the positive electrode sheet having a water content of 50ppm-150ppm, optionally 50ppm-100ppm.

[0044] Controlling the water content of the positive electrode within a suitable range can reduce the side reactions of the first and second additives caused by water entering the non-aqueous electrolyte, which helps to improve the film formation effect of the positive and negative electrodes of the secondary battery.

[0045] In any embodiment, the positive electrode sheet comprises a positive active material, wherein the BET specific surface area of ​​the positive active material is less than or equal to 1.5 m². 2 / g, optional 0.5m 2 / g-1m 2 / g.

[0046] Controlling the BET specific surface area of ​​the cathode active material within a suitable range helps to increase the degree of reaction between the first additive and the residual alkali on the surface of the cathode active material, thus promoting the interfacial reaction of the first additive at the cathode. Simultaneously, having sufficient active sites on the surface of the cathode active material allows lithium ions to insert and extract, which is beneficial for improving the cycle performance of the secondary battery.

[0047] In any embodiment, the positive electrode sheet includes a positive electrode active material, which includes LiNi. x Co y Mn z M 1-x-y-z O2, where x+y+z≤1, 0.5≤x≤1, 0≤y≤0.5, 0≤z≤0.5; M includes at least one of Ti, Al, Zr, Mg, Zn, Ba, Mo, and B, which helps to improve the capacity and energy density of secondary batteries.

[0048] In any embodiment, the lithium secondary battery includes a negative electrode sheet, the negative electrode sheet including a negative electrode active material, wherein the BET specific surface area of ​​the negative electrode active material is 0.5 m². 2 / g-2.0m 2 / g. In any embodiment, the BET specific surface area of ​​the negative electrode active material is 0.8m². 2 / g-1.5m 2 / g.

[0049] In any embodiment, the Dv50 of the negative electrode active material is 5 μm-30 μm. In any embodiment, the Dv50 of the negative electrode active material is 7 μm-25 μm.

[0050] Within a suitable range, the BET specific surface area of ​​the negative electrode active material can enhance its lithium-ion acceptance capacity and reduce lithium-ion deposition on the negative electrode surface. It also helps control interfacial reactions at the negative electrode, mitigating the accumulation of by-reaction products and reducing impedance increases. Within a suitable range, the Dv50 of the negative electrode active material can ensure a good reaction rate, reducing repeated damage to the SEI film and the consumption of active lithium, thereby improving the kinetic performance, capacity, and cycle life of the secondary battery.

[0051] A third aspect of this application provides an electrical device including a lithium secondary battery as described in the second aspect of this application. The secondary battery provided by this application has improved cycle performance and storage performance; correspondingly, the electrical device provided by this application also has better performance. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0053] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of this application is shown;

[0054] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0055] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0056] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0057] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0058] Figure label:

[0059] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0060] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, its preparation method, and its power-consuming device. However, unnecessary details may be omitted. For example, detailed descriptions of well-known facts and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0061] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0062] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0063] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0064] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0065] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0066] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0067] Among existing cathode materials, high-nickel cathode materials are considered to have the greatest development potential for lithium-ion secondary battery cathode materials. However, during charge-discharge cycling, the active Ni in high-nickel cathode materials... 4+Exhibiting strong oxidizing properties, ethylene carbonate exacerbates the oxidative decomposition of the electrolyte at the interface. This not only consumes the electrolyte, leading to a decrease in conductivity, but also causes decomposition products to accumulate on the electrode surface, increasing interfacial resistance and further hindering charge transport. More seriously, continuous electrolyte decomposition forms an unstable interfacial film, leading to repeated growth and rupture of the interfacial film, consuming active lithium, causing battery cycle capacity decay, and affecting battery life. Film-forming additives are typically added to the electrolyte to provide electrode interface protection, but most of these additives are reduced to form a solid electrolyte interphase (SEI) film at the negative electrode during cell formation, with only a very small amount participating in the formation of a positive electrolyte interphase (CEI) film at the positive electrode, resulting in insufficient protection of the positive electrode interface. Simultaneously, ethylene carbonate, as a solvent component in the electrolyte, has excellent ionic conductivity and film-forming properties, but the protons generated during its oxidation process can attack lithium salts in the solvent, thereby damaging the SEI film and affecting the protection of the negative electrode interface. Therefore, existing electrolytes suffer from insufficient protection of the positive and negative electrode interfaces, thus affecting the battery's cycle performance and storage performance.

[0068] This application provides a lithium secondary battery, including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, disposed between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0069] [Non-aqueous electrolyte]

[0070] In the lithium secondary battery provided in this application, the non-aqueous electrolyte includes a first additive, a second additive, and a non-aqueous solvent. The first additive includes a cyclic sulfate compound represented by Formula I.

[0071]

[0072] R1, R2, R3 and R4 are each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C1-C3 alkyl, substituted or unsubstituted C1-C3 alkoxy, substituted or unsubstituted 5-6 member saturated cyclic sulfate ester group.

[0073] The second additive includes an isocyanate-based compound as shown in Formula II.

[0074]

[0075] R5 is selected from phenylene groups substituted with 0, 1, 2, 3 or 4 substituents selected from halogen, methyl, ethyl, alkylene groups, substituted or unsubstituted 2-3 cyclic fused-ring aromatic hydrocarbon groups, C1-C8 alkylene groups including saturated or unsaturated groups, substituted or unsubstituted 5-6 membered alicyclic groups, and C1-C3 alkylene diphenylene groups.

[0076] The non-aqueous solvent includes ethylene carbonate, and the mass content of ethylene carbonate is greater than or equal to 10% and less than or equal to 50% based on the total mass of the non-aqueous electrolyte.

[0077] In this article, the term "halogen" refers to elements in Group VIIA of the periodic table, including fluorine, chlorine, bromine, and iodine.

[0078] The term "C1-C3 alkyl" refers to a saturated hydrocarbon group consisting only of carbon and hydrogen atoms, containing 1-3 carbon atoms, such as methyl, ethyl, and propyl.

[0079] The term "C1-C3 alkoxy" refers to an oxygen group attached to a C1-C3 alkyl group.

[0080] The term "5-6 membered saturated cyclic sulfate group" refers to a 5-6 membered saturated cyclic lactone containing an -OSO2O- group. For example, it could be...

[0081] The term "2- to 3-cyclic fused-ring aromatic hydrocarbon group" refers to an aromatic hydrocarbon group containing 2 to 3 benzene rings fused together by sharing two adjacent atoms, having two substituent linkage sites. Examples include...

[0082] The term "C1-C8 alkylene" refers to a straight-chain or branched saturated alkylene group consisting only of carbon and hydrogen atoms, containing 1-8 carbon atoms, exemplarily including methylene and hexane. Similarly, the term "C1-C3 alkylene" refers to a straight-chain or branched saturated alkylene group consisting only of carbon and hydrogen atoms, containing 1-3 carbon atoms.

[0083] In this document, the term "5- to 6-membered alicyclic group" refers to the general term for the divalent group obtained by removing two hydrogen atoms from an alicyclic hydrocarbon molecule containing 5-6 carbon atoms. It can be a cycloalkyl group, a cycloalkenyl group, etc., and examples include cyclopentenyl, cyclohexenyl, cycloheptenyl, etc., but are not limited to these.

[0084] The term "C1-C3 alkylene diphenyl" refers to a group formed by linking two phenyl groups through an alkylene group containing 1-3 carbon atoms, exemplarily including...

[0085] Cyclic sulfate compounds in the electrolyte preferentially react with residual alkali on the surface of the positive electrode active material to form monocyclic ring-opening products, which act as in-situ modifications on the surface of the positive electrode particles and participate in the formation of the positive electrode CEI film. As the concentration of cyclic sulfate compounds on the positive electrode surface decreases, the remaining cyclic sulfate compounds in the non-aqueous electrolyte accumulate on the positive electrode surface under reaction-driven conditions, thus acting as a directional anchor to the positive electrode before cell formation. The organic matter in the monocyclic ring-opening products helps to improve the bonding between the CEI film and the positive electrode surface, and the oxygen-sulfur bonds in the sulfate groups of the cyclic sulfate compounds help to improve the toughness of the CEI film, enabling the positive electrode to form a good CEI film. In addition, the cyclic sulfate compounds can also participate in the formation of the SEI film, reducing the reduction side reactions of the non-aqueous electrolyte on the surface of the negative electrode and the damage to the structural stability of the negative electrode by solvent co-intercalation, thereby improving the stability of the negative electrode material.

[0086] The isocyanate groups in isocyanate-based compounds exhibit strong electrophilicity and readily react with oxygen-containing functional groups (such as -COOH, -OH, etc.) (e.g., water, acids). This reaction tendency causes isocyanate-based compounds to react preferentially with water and acids in the electrolyte compared to cyclic sulfate compounds. This reduces the damage to the positive and negative electrode interface film caused by byproducts generated from the reaction of cyclic sulfate compounds with water, and allows cyclic sulfate compounds to participate more in the interfacial reaction, resulting in better interfacial film formation. Furthermore, isocyanate-based compounds can rapidly form films on the electrode surface, especially during lithium-ion intercalation at the negative electrode surface. Isocyanates can participate in the initial formation and stabilization of the SEI film, improving the stability of the negative electrode material.

[0087] Ethylene carbonate, a non-aqueous solvent, has a high dielectric constant (ε), meaning it can be effectively polarized under an electric field, thereby improving the ionic conductivity of the electrolyte. This promotes the rapid migration of lithium ions between the positive and negative electrodes, ensuring good charge-discharge rate performance of the battery. However, it is prone to oxidative decomposition on the electrode surface, producing byproducts such as lithium carbonate (Li₂CO₃), lithium fluoride (LiF), and ethylene carbonate (ECO). If these decomposition products cannot effectively integrate into the original SEI film structure, or if their formation rate exceeds the self-repair rate of the SEI film, it can lead to localized cracking or uneven thickening of the SEI film, thus compromising its stability and integrity. Furthermore, the hydroxyl groups (-OH) of ethylene carbonate readily undergo addition reactions with the isocyanate groups in the isocyanate compounds, consuming the second additive and affecting the film-forming effect of the first and second additives at the positive and negative electrodes. By controlling the content of ethylene carbonate, its damage to the positive and negative electrode interface film can be reduced, thereby improving the cycle performance and storage performance of lithium secondary batteries.

[0088] By combining cyclic sulfate compounds, isocyanate compounds, and ethylene carbonate, side reactions of cyclic sulfate compounds and isocyanate compounds can be reduced, as well as the dehydrogenation and decomposition of ethylene carbonate. This reduces damage to the positive and negative electrode interfaces, improves the protection of the positive and negative electrode interfaces, lowers the internal resistance of the cell, and enhances the cycle performance and storage performance of lithium secondary batteries.

[0089] In some embodiments, one of R1 and R2 is selected from hydrogen, methyl, ethyl, fluorine, trifluoromethyl, cyano, or... The other one is selected from hydrogen.

[0090] In some embodiments, both R1 and R2 are selected from methyl groups.

[0091] In some embodiments, one of R3 and R4 is selected from hydrogen, methyl, ethyl, n-propyl, fluorine, ethoxy, or... The other one is selected from hydrogen.

[0092] In some embodiments, the cyclic sulfate compound includes

[0093] At least one of them.

[0094] The cyclic ester compounds preferentially react with residual alkali on the surface of the positive electrode active material to form monocyclic open-ring products, which act as in-situ modifications on the surface of the positive electrode particles and participate in the formation of the positive electrode CEI film. As the concentration of cyclic sulfate compounds on the positive electrode surface decreases, the remaining cyclic sulfate compounds in the non-aqueous electrolyte accumulate on the positive electrode surface under reaction-driven conditions, thus acting as a directional anchor to the positive electrode before cell formation. The organic matter in the monocyclic open-ring products helps improve the bonding between the CEI film and the positive electrode surface, and the oxygen-sulfur bonds in the sulfate groups of the cyclic ester compounds help improve the toughness of the CEI film, enabling the positive electrode to form a good CEI film. In addition, the cyclic ester compounds can also participate in the formation of the SEI film, reducing the reduction side reactions of the non-aqueous electrolyte on the surface of the negative electrode and the damage to the structural stability of the negative electrode by solvent co-intercalation. The cyclic ester compounds help improve the stability of the positive and negative electrode materials and improve the cycle performance and storage performance of the battery.

[0095] In some embodiments, the cyclic sulfate compound includes at least one of C1-12, C1-13, C1-14, C1-15, and C1-16.

[0096] In some embodiments, the cyclic sulfate compound includes at least one of C1-12, C1-13, C1-14, and C1-16.

[0097] The aforementioned cyclic sulfate compounds contain three or four sulfate groups. This polycyclic structure can further improve the composition of the positive and negative electrode interfacial films, enhance the stability of the CEI and SEI films, thereby reducing the consumption of active lithium and improving the battery's cycle and storage performance. Furthermore, the specified number of sulfate groups ensures that the CEI and SEI films have appropriate thicknesses, preventing excessively thick interfacial films from increasing interfacial impedance and degrading cell performance.

[0098] In some embodiments, the cyclic sulfate compound comprises or is selected from C1-16. This cyclic sulfate compound has a suitable number of sulfate groups and is free of alkyl, halogen atoms, or other substituents that increase the oxidation resistance of the non-aqueous electrolyte, thus contributing to the formation of CEI and SEI membranes.

[0099] In some embodiments, R5 is selected from methylene, hexane, 5- to 6-membered alicyclic groups,

[0100] Among them, R 51 R 52 R 53 R 54 Each time it appears, it is independently selected from hydrogen, halogen, methyl, and ethyl; Indicates the bonding site of a chemical group.

[0101] In some embodiments, in the second additive, R 51 R 52 R 53 R 54 Each time it appears, it is independently selected from hydrogen, fluorine, methyl, and ethyl.

[0102] In some implementations, R5 is selected from... R 51 R 52 R 53 For hydrogen, R 54 It is an ethyl group.

[0103] In some implementations, R5 is selected from... Among them, (1)R 52 R 53 For hydrogen, R 51 R 54 (2) R is methyl; 51 R 52 For methyl, R 53 R 54 (3)R is hydrogen; 51 R 52 R 53 R 54All are hydrogen, fluorine or methyl; or (4)R 51 R 53 For hydrogen, R 52 R 54 It is a methyl group.

[0104] In some implementations, R5 is selected from... Among them, (1)R 51 R 52 R 53 R 54 All are hydrogen; (2) R 51 For methyl, R 52 R 53 R 54 (3)R is hydrogen; 52 For methyl, R 51 R 53 R 54 It is hydrogen.

[0105] In some implementations, R5 is selected from... R 51 R 52 R 53 R 54 All are hydrogen

[0106] In some embodiments, the isocyanate-based compound includes

[0107]

[0108] At least one of them.

[0109] In some embodiments, the isocyanate group compound includes or is selected from C2-17.

[0110] During battery cycling, the SEI film may be damaged or dissolved to some extent. Isocyanate-based compounds can continue to react with electrolyte components under conditions such as potential fluctuations or local overheating, replenishing or repairing the damaged SEI film, enhancing its stability and integrity, and reducing the occurrence of side reactions. Thin and uniform SEI films formed with the participation of isocyanate-based compounds typically possess good electrical insulation, ionic conductivity, and mechanical stability. Such SEI films effectively block electron penetration, allowing lithium ions to pass smoothly, while resisting stress caused by volume changes during battery charging and discharging, thus extending the battery's cycle life. Furthermore, optimized SEI films can reduce energy loss and active lithium consumption during lithium ion insertion / extraction, improving battery charge / discharge efficiency. Simultaneously, isocyanate-based compounds preferentially react with trace amounts of water and acid in the electrolyte compared to cyclic sulfate compounds, reducing the damage to the positive electrode interface film caused by byproducts generated from the reaction of the first additive with water, improving the stability of the non-aqueous electrolyte, and enhancing the battery's storage performance.

[0111] In some embodiments, the combination of additives in the non-aqueous electrolyte includes one of the following: the first additive includes at least one of the cyclic sulfate compounds numbered C1-1, C1-2, C1-3, C1-4, C1-5, C1-6, C1-7, C1-8, C1-9, C1-10, C1-11, C1-12, C1-13, C1-14, C1-15, and C1-16; the second additive includes an isocyanate compound numbered C2-1, C2-2, C2-3, C2-4, C2-5, C2-6, C2-7, C2-8, C2-9, C2-10, C2-11, C2-12, C2-13, C2-14, C2-15, C2-16, C2-17, and C2-18.

[0112] In some embodiments, the combination of additives in the non-aqueous electrolyte includes one of the following: the first additive includes at least one of the cyclic sulfate compounds numbered C1-1, C1-2, C1-3, C1-4, C1-5, C1-6, C1-7, C1-8, C1-9, C1-10, C1-11, C1-12, C1-13, C1-14, C1-15, and C1-16; and the second additive includes isocyanate compounds numbered C2-17.

[0113] In some embodiments, the combination of additives in the non-aqueous electrolyte includes one of the following: the first additive includes cyclic sulfate compounds numbered C1-16; the second additive includes at least one of isocyanate compounds numbered C2-1, C2-2, C2-3, C2-4, C2-5, C2-6, C2-7, C2-8, C2-9, C2-10, C2-11, C2-12, C2-13, C2-14, C2-15, C2-16, C2-17, and C2-18.

[0114] The combined use of the first and second additives allows the second additive to react preferentially with water and acid in the electrolyte, reducing the side reactions of the first additive. This allows more of the first additive to participate in the electrode interface film-forming reaction, forming stable CEI and SEI films, reducing the occurrence of side reactions, and thus improving the battery's cycle performance and storage performance.

[0115] In some embodiments, the mass content of ethylene carbonate is 15%-50%, 15%-40%, 15%-35%, 15%-30%, 15%-25%, 15%-20%, or 20%-25% based on the total mass of the non-aqueous electrolyte.

[0116] In some embodiments, based on the total mass of the non-aqueous electrolyte, the mass content of the ethylene carbonate includes 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or a range consisting of any two of the above values ​​or any value within that range.

[0117] Insufficient ethylene carbonate content in non-aqueous electrolytes can lead to low electrolyte conductivity, reduced lithium-ion migration, and consequently, negatively impacted kinetic and cycle performance of the secondary battery. Excessive ethylene carbonate content, on the other hand, can cause dehydrogenation and decomposition, damaging the SEI film on the negative electrode and overall battery performance. It also increases the consumption of the first and second additives, affecting their film-forming reactions. Therefore, controlling the ethylene carbonate content in the non-aqueous electrolyte within a suitable range can balance electrolyte ionic conductivity with the formation of both the positive and negative CEI and SEI films, reducing side reactions at both electrodes and improving the cycle performance of lithium-ion secondary batteries.

[0118] In some embodiments, the mass content of the first additive is 0.05%-20% based on the total mass of the non-aqueous electrolyte. In some embodiments, the mass content of the first additive is 0.05%-15%, 0.05%-8%, 0.2%-15%, 0.2%-8%, 1%-20%, 1%-15%, 1%-8%, 5%-20%, or 7%-18% based on the total mass of the non-aqueous electrolyte.

[0119] In some embodiments, based on the total mass of the non-aqueous electrolyte, the mass content of the first additive is 0.05%, 0.2%, 0.5%, 1%, 3%, 5%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or a range consisting of any two of the above values ​​or any value within that range.

[0120] In non-aqueous electrolytes, excessively low levels of the first additive hinder the formation of the CEI film at the positive electrode, resulting in insufficient interface protection and minimal improvement in battery performance. Conversely, excessively high levels of the first additive can lead to over-protection at the positive electrode interface and increased impedance, also negatively impacting battery performance. Therefore, controlling the content of the first additive within a suitable range allows for the formation of a good CEI film at the positive electrode and a good SEI film at the negative electrode. The moderate thickness of both the CEI and SEI films enhances interface protection while maintaining appropriate internal resistance, thereby improving the cycle and storage performance of lithium-ion batteries.

[0121] In some embodiments, the mass content of the second additive is 0.01%-20% based on the total mass of the non-aqueous electrolyte. In some embodiments, the mass content of the second additive is 0.5%-20%, 0.5%-15%, 0.5%-1%, 0.1%-20%, 0.1%-8%, 1.0%-20%, 1.0%-15%, or 0.5%-8% based on the total mass of the non-aqueous electrolyte.

[0122] In some embodiments, based on the total mass of the non-aqueous electrolyte, the mass content of the second additive is 0.01%, 0.1%, 0.5%, 1%, 3%, 5%, 7%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, or a range consisting of any two of the above values ​​or any value within that range.

[0123] In non-aqueous electrolytes, an excessively low content of the second additive can lead to incomplete reaction with water and acid, resulting in the hydrolysis of the first additive. This affects the subsequent film-forming effect of the first additive, causing insufficient protection of the positive and negative electrode interfaces, increased side reactions, and insignificant improvement in battery performance. In contrast, an excessively high content of the second additive in non-aqueous electrolytes can result in an overly thick SEI film, increasing the overall impedance of the battery, leading to poor cell lifespan and affecting battery storage performance.

[0124] In some embodiments, the electrolyte comprises: based on the total mass of the non-aqueous electrolyte, a first additive comprising at least one of the cyclic sulfate compounds numbered C1-1, C1-2, C1-3, C1-4, C1-5, C1-6, C1-7, C1-8, C1-9, C1-10, C1-11, C1-12, C1-13, C1-14, C1-15, and C1-16 in a mass content of 0.2%-1%; a second additive comprising an isocyanate compound numbered C2-17 in a mass content of 0.5%-1.5%; and ethylene carbonate in a mass content of 15%-50%.

[0125] In some embodiments, the electrolyte comprises: based on the total mass of the non-aqueous electrolyte, a first additive comprising 0.2%-1% by mass of a cyclic sulfate compound numbered C1-16; a second additive comprising at least one of an isocyanate compound numbered C2-1, C2-2, C2-3, C2-4, C2-5, C2-6, C2-7, C2-8, C2-9, C2-10, C2-11, C2-12, C2-13, C2-14, C2-15, C2-16, C2-17, and C2-18 by mass of 0.1%-8%; and ethylene carbonate comprising 15%-50% by mass.

[0126] In some embodiments, the electrolyte comprises: based on the total mass of the non-aqueous electrolyte, a first additive comprising 0.2%-1% by mass of cyclic sulfate compounds numbered C1-16; a second additive comprising 0.1%-8% by mass of isocyanate compounds numbered C2-17; and 15%-40% by mass of ethylene carbonate.

[0127] In some embodiments, the mass ratio of the first additive to the second additive is 0.02-50. In some embodiments, the mass ratio of the first additive to the second additive is 0.2-8, 0.2-10, 0.2-20, 0.4-30, or 0.4-40.

[0128] In some embodiments, the mass ratio of the first additive to the second additive is 0.02, 0.2, 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or a range consisting of any two of the above values ​​or any value within that range.

[0129] When the mass ratio of the first additive to the second additive is within a suitable range, the second additive can preferentially react with water and acid, reducing the side reactions of the first additive with water and acid, and promoting more of the first additive to participate in the film-forming reaction of the positive and negative electrodes. At the same time, the second additive can still form an excellent negative electrode SEI film, so that both the positive and negative electrodes in the secondary battery have good interface protection and battery impedance, thereby improving the cycle performance and storage performance of the secondary battery.

[0130] In some embodiments, the water content of the non-aqueous electrolyte is 10 ppm to 100 ppm based on the total mass of the non-aqueous electrolyte. In some embodiments, the water content of the non-aqueous electrolyte is 10 ppm to 50 ppm based on the total mass of the non-aqueous electrolyte.

[0131] In some embodiments, based on the total mass of the non-aqueous electrolyte, the water content of the non-aqueous electrolyte is 10ppm, 20ppm, 40ppm, 60ppm, 80ppm, 100ppm, or a range consisting of any two of the above values ​​or any value within that range.

[0132] In this document, the water content of non-aqueous electrolytes is defined in the art and can be determined using instruments and methods known in the art, such as the method for water determination specified in GB / T 19282-2014. For example, the water content can be measured by placing the non-aqueous electrolyte into the testing bottle of an automated moisture analyzer, allowing it to dissolve completely, and then stirring it thoroughly.

[0133] Excessive water content in non-aqueous electrolytes can lead to a significant amount of the primary additive reacting with water. The resulting byproducts dissolve in the electrolyte, impairing the film-forming effect of the primary additive and thus affecting the battery's cycle and storage performance. Maintaining a suitable water content in the non-aqueous electrolyte can reduce the hydrolysis consumption of both the primary and secondary additives, improving the protection of the positive and negative electrode interfaces.

[0134] In some embodiments, the electrolyte includes electrolyte salts and other solvents.

[0135] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0136] In some embodiments, the solvent may be selected from at least one of propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0137] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0138] [Positive electrode plate]

[0139] The positive electrode includes a positive current collector and a positive electrode material layer located on at least one side of the positive current collector. The positive electrode material layer includes a positive electrode active material.

[0140] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0141] In some embodiments, the positive electrode active material is a known positive electrode active material for batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and compounds obtained by adding other transition metals or non-transition metals to the above compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0142] In some embodiments, the positive electrode active material includes LiNi. x Co y Mn z M 1-x-y-z O2, wherein x+y+z≤1, 0.5≤x≤1, 0≤y≤0.5, 0≤z≤0.5; M includes at least one of Ti, Al, Zr, Mg, Zn, Ba, Mo, and B. The positive electrode active material helps improve the capacity and energy density of the secondary battery.

[0143] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0144] In some embodiments, the positive electrode further includes a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0145] In some embodiments, the positive electrode sheet further includes a binder, which may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0146] In some embodiments, the positive electrode sheet can be prepared by dispersing the positive active material, additives, binders, conductive agents and any other components in the above embodiments in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0147] In some embodiments, the water content of the positive electrode is 50ppm-150ppm. In some embodiments, the water content of the positive electrode is 50ppm-145ppm, 50ppm-120ppm, 50ppm-100ppm, or 50ppm-80ppm.

[0148] In some embodiments, the water content of the positive electrode is 50ppm, 60ppm, 70ppm, 80ppm, 90ppm, 100ppm, 110ppm, 120ppm, 130ppm, 140ppm, 150ppm, or a range consisting of any two of the above values ​​or any value within that range.

[0149] In this paper, the water content of the positive electrode is defined in the art and can be determined using instruments and methods known in the art. For example, it can be tested as follows: Place the vial containing the sample into the automatic sample injection system of the solid water content analyzer. During the test, heat the vial containing the sample (the conventional heating temperature is 170°C, which can be adjusted according to the heat resistance temperature of the sample) and introduce dry gas. Purge the gas in the vial into the titration cup for absorption titration and convert the result into the water content of the solid sample.

[0150] If the moisture content of the positive electrode is too high, the water will enter the electrolyte, causing the primary additive in the electrolyte to hydrolyze directly, thus affecting the film formation effect of both the positive and negative electrodes. Therefore, controlling the moisture content of the positive electrode within a suitable range can reduce the hydrolysis of the primary and secondary additives, promote the formation of stable interfacial films between the primary and secondary additives on the positive and negative electrodes, and thereby improve the cycle performance and storage performance of the battery.

[0151] In some embodiments, the BET specific surface area of ​​the positive electrode active material in the positive electrode sheet is less than or equal to 1.5 m². 2 / g, optional 0.5m 2 / g-1m 2 / g. In some embodiments, the active specific surface area of ​​the positive electrode is 0.1m². 2 / g-1.5m 2 / g, 0.4m 2 / g-1.5m 2 / g, 0.3m 2 / g-0.9m 2 / g, 0.4m 2 / g-0.9m 2 / g.

[0152] In some embodiments, the BET specific surface area of ​​the positive electrode active material in the positive electrode sheet is 0.2 m². 2 / g, 0.4m 2 / g, 0.6m 2 / g, 0.8m 2 / g, 1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.5m 2 / g, or a range consisting of any two of the above values ​​or any value within that range.

[0153] In this paper, the BET specific surface area of ​​the positive electrode active material is a well-known definition in the art and can be measured using instruments and methods well-known in the art. For example, referring to GB / T 19587-2004 Gas Adsorption BET Method, after heating and degassing the sample, the amount of gas adsorbed on the solid surface under different adsorption pressures is measured at a constant low temperature. Based on the BET multilayer adsorption theory and its formula, the monolayer adsorption amount of the sample is obtained, thereby calculating the specific surface area per unit mass of solid sample.

[0154] A small BET specific surface area of ​​the positive electrode active material can increase battery polarization, affecting battery storage performance. Conversely, an excessively large active specific surface area of ​​the positive electrode can lead to an excessively large contact area between the electrode and the non-aqueous electrolyte, increasing the number of active reaction sites and raising the probability of ethylene carbonate oxidative dehydrogenation in the non-aqueous electrolyte. This results in protonated hydrogen atoms attacking lithium salts in the solvent, thereby damaging the SEI film and affecting battery cycle performance. Therefore, controlling the active specific surface area of ​​the positive electrode within a suitable range can reduce damage to the SEI film, balancing battery capacity, cycle performance, and kinetic performance.

[0155] [Negative electrode plate]

[0156] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0157] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0158] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0159] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0160] In some embodiments, the BET specific surface area of ​​the negative electrode active material is 0.5 m². 2 / g-2.0m 2 / g. In some embodiments, the BET specific surface area of ​​the negative electrode active material is 0.7m². 2 / g-2.0m 2 / g, 0.8m 2 / g-1.5m 2 / g, 0.8m 2 / g-2.0m 2 / g, 1.0m 2 / g-1.8m 2 / g, 0.5m 2 / g-1.5m 2 / g.

[0161] In some embodiments, the BET specific surface area of ​​the negative electrode active material is 0.5 m². 2 / g, 0.8m 2 / g, 1.0m 2 / g, 1.2m 2 / g, 1.4m 2 / g, 1.6m 2 / g, 1.8m 2 / g, 2.0m 2 / g, or a range consisting of any two of the above values ​​or any value within that range.

[0162] In this paper, the BET specific surface area of ​​the negative electrode active material is a well-known definition in the art and can be measured using instruments and methods well-known in the art. For example, referring to GB / T 19587-2004 Gas Adsorption BET Method, after heating and degassing the sample, the amount of gas adsorbed on the solid surface under different adsorption pressures is measured at a constant low temperature. Based on the BET multilayer adsorption theory and its formula, the amount of monolayer adsorption of the sample is obtained, thereby calculating the specific surface area per unit mass of solid sample.

[0163] The BET specific surface area of ​​the negative electrode active material can affect the number of reaction sites. If the BET specific surface area is too small, it can affect the lithium-ion insertion and extraction rates, resulting in poor lithium-ion acceptance and deposition on the negative electrode surface, increasing the battery's internal resistance. Conversely, if the BET specific surface area is too large, it can lead to an excessively large contact area between the negative electrode active material and the electrolyte, intensifying interfacial reactions and causing byproducts to accumulate at the interface, increasing the negative electrode impedance. Therefore, controlling the BET specific surface area of ​​the negative electrode active material within an appropriate range can reduce the consumption of active lithium ions, improve the battery's cycle performance and kinetic performance, while also maintaining good battery resistance.

[0164] In some embodiments, the D of the negative electrode active material V 50 represents 5μm-30μm.

[0165] In some embodiments, the D of the negative electrode active material V 50 is 5μm-28μm. In some embodiments, the D of the negative electrode active material... V 50 is 7μm-25μm, 5μm-25μm, 7μm-28μm, 10μm-25μm, 12μm-25μm.

[0166] In some embodiments, the D of the negative electrode active material V 50 can be 5μm, 10μm, 15μm, 20μm, 25μm, or 30μm, or a range consisting of any two of the above values ​​or any value within that range.

[0167] In this paper, the D of the negative electrode active material V 50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50%, which can be determined using instruments and methods known in the art. For example, referring to GB / T19077-2016 Laser Particle Size Analyzer Diffraction Method, take a clean beaker, add an appropriate amount of the sample to be tested, add a surfactant and then a dispersant. After thorough dispersion, use a laser particle size analyzer to determine the particle size distribution characteristics.

[0168] D of negative electrode active material V 50 can affect the number of reaction sites in the negative electrode active material. The D of the negative electrode active material... V A D50 value that is too small can lead to an excessively large specific surface area of ​​the negative electrode active material and an excessively large contact area with the electrolyte. This can intensify the side reactions on the negative electrode side of the battery, resulting in repeated damage to the SEI film and increased lithium consumption. VAn excessively high D50 not only leads to a insufficient number of reaction sites and slows down electrochemical reaction kinetics, but it can also cause uneven surface formation of the negative electrode active material during electrode preparation. This uneven particle packing can result in inconsistent compaction density, thus affecting the electrode conductivity and battery energy density. Therefore, controlling the D50 of the negative electrode active material is crucial. V Within a suitable range, 50 can reduce repeated damage to the SEI film and consumption of active lithium, thereby improving battery capacity, cycle life, and kinetic performance.

[0169] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0170] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0171] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0172] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0173] [Isolation membrane]

[0174] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0175] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0176] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0177] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0178] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0179] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0180] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0181] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0182] Figure 4 This is battery module 3, shown as an example. (See reference...) Figure 3 In battery module 3, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 3. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0183] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0184] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0185] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0186] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0187] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0188] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0189] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0190] Example

[0191] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0192] Compounds and their abbreviations:

[0193]

[0194]

[0195]

[0196] I. Testing Methods

[0197] 1. Electrolyte water content

[0198] The water content in the electrolyte can be obtained by referring to the method specified in GB / T 19282-2014.

[0199] 2. Moisture content of electrode sheets

[0200] Place the vial containing the electrode sample into the automatic sampling system of the solid water content analyzer (model: 874; Metrohm, Switzerland). During the test, heat the vial and pass dry gas through it. Purge the gas from the vial into the titration cup for absorption titration. The ratio of the measured water content to the mass of the sample is the water content of the electrode.

[0201] 3. BET specific surface area

[0202] Referring to GB / T 19587-2004 Gas Adsorption BET Method, after the sample is heated and degassed, the amount of gas adsorbed on the solid surface under different adsorption pressures is measured at a constant low temperature (liquid nitrogen environment). Based on the BET multilayer adsorption theory and its formula, the monolayer adsorption amount of the sample is obtained, and the specific surface area per unit mass of the sample is calculated.

[0203] 4. Particle size test

[0204] The particle size distribution characteristics of the samples were determined by laser particle size analyzer diffraction method according to GB / T19077-2016.

[0205] 5. Battery performance test

[0206] (1) Battery room temperature cycle performance test

[0207] Under a constant temperature environment of 25℃, the lithium-ion battery is charged at a constant current of 0.5C to a voltage of 4.4V, then charged at a constant voltage of 4.4V until the current is ≤0.05C, and then discharged at a constant current of 0.5C to a voltage of 2.5V. This constitutes one charge-discharge cycle, and the discharge capacity at this point is recorded as the discharge capacity of the battery in its first cycle. This charge-discharge cycle is repeated, and the number of cycles corresponding to when the battery retains 80% of its capacity is calculated.

[0208] (2) Battery high temperature full charge storage performance test

[0209] Under a constant temperature environment of 25℃, the battery was charged to 4.4V at 0.33C and then discharged to 2.5V at 0.33C. The discharge capacity D1 was then tested. The battery was stored in a constant temperature environment of 60℃, and tested every 30 days. For each test, the battery was cooled to 25℃, charged to 4.4V at 0.33C, and then discharged to 2.5V at 0.33C. The discharge capacity was then tested. The number of storage days required for the storage capacity retention rate to decay to 80% was calculated.

[0210] II. Preparation Method

[0211] Example 1

[0212] 1) Preparation of positive electrode sheet

[0213] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2 (BET specific surface area 0.61m²) 2 The positive electrode film slurry is prepared by dissolving the positive electrode active material (e.g., acetylene black, conductive agent, and polyvinylidene fluoride binder) in N-methylpyrrolidone at a mass ratio of 98:1:1. The mixture is thoroughly stirred and mixed to form a positive electrode film slurry. This slurry is then coated onto the positive electrode current collector aluminum foil, followed by drying, cold pressing, and slitting to obtain the positive electrode sheet. The loading of the positive electrode active material on one side of the aluminum foil on the positive electrode sheet is 0.016 g / cm³. 2 The water content is 60.0 ppm.

[0214] 2) Preparation of negative electrode sheet

[0215] The negative electrode active material is graphite (BET specific surface area 1.03m²). 2 The negative electrode slurry was prepared by thoroughly mixing a conductive agent (acetylene black), a binder (styrene-butadiene rubber), and a thickener (sodium carboxymethyl cellulose) in deionized water at a weight ratio of 96:1:2:1. The negative electrode slurry was then coated onto copper foil, followed by drying, cold pressing, and slitting to obtain the negative electrode sheet. The loading of graphite, the negative electrode active material, on a single side of the copper foil was 0.012 g / cm³. 2 .

[0216] 3) Separating membrane

[0217] Polypropylene film is used as the separator.

[0218] 4) Preparation of electrolyte

[0219] In an argon-filled glove box (water content <0.1 ppm, oxygen content <0.1 ppm), lithium salt LiPF6, first additive (C1-1), and second additive (C2-17) were added to non-aqueous solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC). After thorough mixing, an electrolyte with a water content of 20.3 ppm was obtained. Based on the total mass of the electrolyte, the mass content of the first additive was 0.5 wt%, the mass content of the second additive was 1 wt%, the mass content of the non-aqueous solvent ethylene carbonate (EC) was 20 wt%, the mass content of ethyl methyl carbonate (EMC) was 66 wt%, and the mass content of LiPF6 was 12.5 wt%.

[0220] 5) Battery manufacturing

[0221] The positive electrode, separator, and negative electrode are stacked in sequence and wound to obtain a battery cell. The battery cell is then placed in an outer packaging, and the electrolyte is added. After processes such as encapsulation, settling, formation, and aging, a lithium secondary battery is obtained.

[0222] Example 2-44

[0223] The preparation methods of Examples 2-44 are similar to those of Example 1, with the mass content of EMC in the electrolyte adjusted accordingly. The specific preparation parameters are shown in Table 1.

[0224] Comparative Example 1

[0225] Compared to Example 1, no first additive and second additive were added to the electrolyte.

[0226] Comparative Example 2

[0227] Compared to Example 40, the second additive has a mass content of 25 wt% in the electrolyte.

[0228] Comparative Example 3

[0229] Compared to Example 44, the mass content of ethylene carbonate in the non-aqueous electrolyte is 55 wt%.

[0230] The preparation parameters and performance test results of Examples 1-44 and Comparative Examples 1-3 are as follows:

[0231]

[0232]

[0233]

[0234] As can be seen from Examples 1-41 and Comparative Examples 1-3, the combination of cyclic sulfate compounds and isocyanate compounds, while controlling the mass content of ethylene carbonate in the non-aqueous electrolyte to be less than or equal to 50%, can effectively improve the interface protection of the positive and negative electrodes, significantly improve the cycle performance and storage performance of the secondary battery, and ensure that the secondary battery retains 80% of its cycle capacity for no less than 2100 cycles at 25°C and retains 80% of its storage capacity for no less than 350 days at 60°C.

[0235] As can be seen from Examples 1-16 and Examples 17-32, the combination of cyclic sulfate compounds C1-1 to C1-16 with isocyanate compounds C2-17, or the combination of cyclic sulfate compounds C1-16 with isocyanate compounds C2-1 to C2-18, respectively, is beneficial to improving the cycle performance and storage performance of secondary batteries.

[0236] As demonstrated in Examples 34-36, secondary batteries exhibiting excellent cycle performance and storage performance are achieved when the mass content of the cyclic sulfate compound ranges from 0.05 wt% to 20 wt%. Compared to Comparative Example 1, the protection of the positive and negative electrode interfaces is significantly improved.

[0237] As can be seen from Examples 37-40 and Comparative Example 2, when the mass content of isocyanate-based compounds is in the range of 0.01 wt% to 20%, the cycle performance and storage performance of the secondary battery are significantly improved.

[0238] As can be seen from Examples 41-44 and Comparative Example 3, EC can effectively balance the cycle performance and storage performance of secondary batteries when the mass content of non-aqueous electrolyte is in the range of 15%-50%.

[0239] Examples 45-47

[0240] Examples 45-47 are prepared in a similar manner to Example 16. During the preparation of the electrolyte, trace amounts of water are added to the non-aqueous electrolyte to adjust the water content to 10.4 ppm, 49.9 ppm, and 99.8 ppm, respectively.

[0241] The performance test results of the secondary batteries in Examples 45-47 are as follows:

[0242]

[0243] The above results indicate that the combination of the first additive C1-16 (0.5 wt%), the second additive C2-17 (1 wt%), and ethylene carbonate (20 wt%) can effectively provide interface protection for the battery, increase the number of cycles and storage days, and improve the battery's cycle performance and storage performance under conditions where the water content in the non-aqueous electrolyte is between 10 ppm and 100 ppm.

[0244] Examples 48-50

[0245] Examples 45-47 are prepared in a similar manner to Example 16, except that the moisture content of the positive electrode is adjusted to 50 ppm, 100 ppm, and 150 ppm by adjusting the drying parameters of the positive electrode.

[0246] The battery fabrication and performance test results of Examples 45-47 are as follows:

[0247]

[0248]

[0249] The above results indicate that the combination of the first additive C1-16 (0.5 wt%), the second additive C2-17 (1 wt%), and ethylene carbonate (20 wt%) can achieve both excellent cycle performance and storage performance in secondary batteries with a positive electrode water content of 50 ppm to 150 ppm.

[0250] Examples 51-53

[0251] Examples 51-53 were prepared using methods similar to those in Example 16, wherein the BET specific surface area of ​​the positive electrode active material was 0.52 m². 2 / g, 0.97m 2 / g, 1.48m 2 / g. The battery preparation and performance test results are as follows:

[0252]

[0253] The above results indicate that the positive electrode active material at 0.5m 2 / g-1.5m 2 Within the range of / g, the active material particles have sufficient active sites, which is beneficial to improving the cycle performance of secondary batteries and also has excellent storage performance.

[0254] Examples 54-57

[0255] Examples 54-57 are prepared in a similar manner to Example 16, but the BET specific surface area and Dv50 of the negative electrode active material are adjusted.

[0256] The battery fabrication and performance testing results are as follows:

[0257]

[0258] The above results indicate that the specific surface area of ​​the negative electrode active material is within 0.5 m². 2 / g-2.0m 2Within the range of / g, with Dv50 in the range of 5μm-30μm, the secondary battery exhibits excellent cycle performance and storage performance.

[0259] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A lithium secondary battery, characterized by comprising: The non-aqueous electrolyte includes a first additive, a second additive, and a non-aqueous solvent, The first additive includes a cyclic sulfate compound represented by Formula I, R1, R2, R3, and R4are each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C1-C3alkyl, substituted or unsubstituted C1-C3alkoxy, and substituted or unsubstituted 5-6 membered saturated cyclic sulfate group; The second additive includes an isocyanate compound represented by Formula II, O=C=N—R5—N=C=O Formula II R5is selected from phenylene substituted with 0, 1, 2, 3, or 4 substituents selected from halogen, methyl, ethyl, substituted or unsubstituted 2-3 ring fused ring aralkylene, C1-C8alkylene including saturated or unsaturated group, substituted or unsubstituted 5-6 membered cycloalkylene, and C1-C3alkylene diphenyl; The non-aqueous solvent includes ethylene carbonate in a mass content of 10% or more and 50% or less based on the total mass of the non-aqueous electrolyte.

2. The lithium secondary battery according to claim 1, characterized by one of said R1and R2is selected from hydrogen, methyl, ethyl, fluoro, trifluoromethyl, cyano or the other is selected from hydrogen; or, R1and R2are both selected from methyl; one of said R3and R4is selected from hydrogen, methyl, ethyl, n-propyl, fluoro, ethoxy or the other is selected from hydrogen; R5is selected from methylene, hexylidene, 5- to 6-membered cycloaliphatic, wherein R 51 , R 52 , R 53 , R 54 each occurrence is independently selected from hydrogen, halogen, methyl, ethyl.

3. The lithium secondary battery according to claim 1 or 2, characterized by The mass content of the ethylene carbonate is 15%-40% based on the total mass of the non-aqueous electrolyte.

4. The lithium secondary battery according to any one of claims 1 to 3, characterized by, The cyclic sulfate compound includes at least one of The isocyanate-based compound includes at least one of 5. The lithium secondary battery according to any one of claims 1 to 4, characterized by, The non-aqueous electrolyte includes one of the following groups: (1) The first additive includes at least one of the cyclic sulfate compounds numbered as C1-1, C1-2, C1-3, C1-4, C1-5, C1-6, C1-7, C1-8, C1-9, C1-10, C1-11, C1-12, C1-13, C1-14, C1-15, and C1-16; and the second additive includes the isocyanate compound numbered as C2-17; (2) The first additive includes the cyclic sulfate compound numbered as C1-16; and the second additive includes at least one of the isocyanate compounds numbered as C2-1, C2-2, C2-3, C2-4, C2-5, C2-6, C2-7, C2-8, C2-9, C2-10, C2-11, C2-12, C2-13, C2-14, C2-15, C2-16, C2-17, and C2-18.

6. The lithium secondary battery according to any one of claims 1 to 5, characterized by, The non-aqueous electrolyte satisfies at least one of the following conditions: (1) The mass content of the first additive is 0.05%-20% based on the total mass of the non-aqueous electrolyte; (2) The mass content of the second additive is 0.01%-20% based on the total mass of the non-aqueous electrolyte; (3) The mass ratio of the first additive to the second additive is 0.02-50.

7. The lithium secondary battery according to any one of claims 1 to 6, characterized by, The non-aqueous electrolyte satisfies at least one of the following conditions: (1) The mass content of the first additive is 0.05%-8% based on the total mass of the non-aqueous electrolyte; (2) The mass content of the second additive is 0.1%-8% based on the total mass of the non-aqueous electrolyte; (3) The mass ratio of the first additive to the second additive is 0.2-8; (4) The mass content of the ethylene carbonate is 15%-25% based on the total mass of the non-aqueous electrolyte.

8. The lithium secondary battery according to any one of claims 1 to 7, characterized by, The nonaqueous electrolyte has a water content of 10 ppm to 100 ppm based on the total mass of the nonaqueous electrolyte.

9. The lithium secondary battery according to any one of claims 1 to 8, characterized by, The nonaqueous electrolyte has a water content of 10 ppm to 50 ppm based on the total mass of the nonaqueous electrolyte.

10. The lithium secondary battery according to any one of claims 1 to 9, characterized by, The positive electrode sheet has a water content of 50 ppm to 150 ppm, and can be 50 ppm to 100 ppm.

11. The lithium secondary battery as claimed in claim 9, wherein the lithium secondary battery is a lithium secondary battery having a structure in which the cathode, the separator and the anode are sequentially stacked. The positive electrode plate comprises a positive electrode active material, the BET specific surface area of the positive electrode active material is less than or equal to 1.5 m 2 / g, which is optionally 0.5 m 2 / g-1.0 m 2 / g.

12. The lithium secondary battery according to claim 10 or 11, characterized by, The negative electrode sheet includes a negative electrode active material, wherein, The BET specific surface area of the negative electrode active material is 0.5 m 2 / g-2.0 m 2 / g; and / or The negative electrode active material has a Dv50 of 5 μm to 30 μm.

13. The lithium secondary battery according to claim 12, wherein The BET specific surface area of the negative electrode active material is 0.8 m 2 / g-1.5 m 2 / g; and / or The negative electrode active material has a Dv50 of 7 μm to 25 μm.

14. The lithium secondary battery according to any one of claims 10 to 13, characterized by, The positive electrode tab includes a positive electrode active material including LiNi x Co y Mn z M 1-x-y-z O2, wherein x+y+z≤1, 0.5≤x≤1, 0≤y≤0.5, 0≤z≤0.5; M includes at least one of Ti, Al, Zr, Mg, Zn, Ba, Mo, B.

15. An electrical device, comprising: The lithium secondary battery according to any one of claims 1 to 14.

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