Lithium secondary battery and electrical apparatus

Abstract

The present application provides a lithium secondary battery and an electrical apparatus. 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 represented by formula I; the second additive comprises an isocyanate-based compound represented by formula II; 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 a good positive and negative electrode interface protection capability, reduces the side reactions on the surfaces of the positive and negative electrodes, reduces the impedance of a battery cell, and can improve the cycle performance and storage performance of the lithium secondary battery.

Description

Lithium secondary battery and electric device

[0001] Cross-reference to related applications

[0002] This application is based on Chinese Patent Application No. 202410864936.2, filed on June 28, 2024, entitled “Lithium secondary battery and electric device”, which is incorporated by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of secondary batteries, in particular to a lithium secondary battery and an electric device. BACKGROUND

[0004] Lithium secondary batteries have become the most popular energy storage system due to their high operating potential, long service life, and environmentally friendly characteristics, and have been widely used in pure electric vehicles, hybrid electric vehicles, smart grids, and other fields. With the increasing demand for battery cycle life, it is urgent to develop lithium ion battery systems with long cycle stability.

[0005] The electrolyte can have side reactions with the positive and negative electrodes of the secondary battery, damaging the structure of the positive and negative electrodes and degrading the cell impedance, thereby affecting the cycle life of the secondary battery. Typically, a film-forming additive can be added to the electrolyte to protect the positive and negative electrodes of the secondary battery. However, most of the existing film-forming additives are reduced to form a solid electrolyte interface (SEI) at the negative electrode during cell formation, and only a small amount of additives participate in the formation of a cathode electrolyte interphase (CEI) at the positive electrode, resulting in insufficient protection of the positive electrode interface and excessive protection of the negative electrode interface, ultimately affecting the cycle performance and storage performance of the battery.

[0006] Therefore, it is necessary to provide an electrolyte that can improve the protection of the positive and negative electrode interfaces of a lithium ion battery. SUMMARY

[0007] To solve the above problems, the present application provides a lithium secondary battery, which has stable positive and negative electrode surfaces and low cell impedance, and significantly improved cycle performance and storage performance.

[0008] A first aspect of the present application provides a lithium secondary battery, comprising a non-aqueous electrolyte, the non-aqueous electrolyte comprising a first additive, a second additive, and a non-aqueous solvent,

[0009] The first additive comprises a cyclic sulfate compound represented by Formula I,

[0010] R1, R2, R3, R4are each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C1-C3 alkyl, substituted or unsubstituted C1-C3 alkoxy, substituted or unsubstituted 5-6 membered saturated cyclic sulfonate group;

[0011] The second additive comprises an isocyanate-based compound shown in Formula II,

[0012] 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-C8 alkylene including saturated or unsaturated group, substituted or unsubstituted 5-6 membered alicyclic group, C1-C3 alkylene diphenyl;

[0013] The non-aqueous solvent comprises ethylene carbonate, and the mass content of the 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 by the present application, the cyclic sulfonate compound can react with residual alkali on the surface of the positive active material and participate in the formation of the positive CEI film. In addition, the cyclic sulfonate compound can also participate in the formation of the SEI film, reducing the side reaction of the non-aqueous electrolyte with the negative electrode plate. The isocyanate group in the isocyanate-based compound has strong electrophilicity, and preferentially reacts with water or acid in the electrolyte, thereby reducing the side reaction of the cyclic sulfonate compound with the electrolyte, and making it more participate in the interface film formation reaction. At the same time, the isocyanate-based compound also participates in the initial formation and stabilization process of the SEI film, improving the stability of the negative electrode material. Ethylene carbonate is prone to dehydrogenation and oxidation on the electrode surface to produce gas and water, and these decomposition products can react with the cyclic sulfonate compound and the isocyanate-based compound, consuming the first additive and the second additive, thereby affecting the film formation effect of the two on the positive and negative electrodes. Reducing the content of ethylene carbonate helps to reduce the side reaction of the first additive and the second additive, making them more participate in the interface film formation, thereby improving the positive and negative interface protection of the lithium secondary battery.

[0015] In any embodiment, one of R1and R2is selected from hydrogen, methyl, ethyl, fluoro, trifluoromethyl, cyano or and the other is selected from hydrogen; or, R1and R2are both selected from methyl; one of R3and R4is selected from hydrogen, methyl, ethyl, n-propyl, fluoro, ethoxy or and the other is selected from hydrogen; R5is selected from methylene, hexane group, 5-6 membered alicyclic group, wherein R 51 , R 52 , R 53 , R 54each occurrence is independently selected from hydrogen, halogen, methyl, ethyl.

[0016] In any embodiment, the mass content of ethylene carbonate 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 more participate in the interface film formation.

[0017] In any embodiment, the cyclic sulfate compound includes at least one of

[0018] The cyclic sulfate compound interacts with the residual alkali on the positive electrode surface, and one sulfate ring (or single ring) in the cyclic sulfate compound undergoes ring-opening reaction, and the single ring ring-opening product participates in the CEI film formation during the formation process and improves the film component. The sulfate group in the cyclic sulfate compound undergoes nucleophilic reaction with the oxygen atom on the surface of the positive active material, in-situ modifies the surface of the positive electrode particles, and improves the stability of the CEI film; at the same time, the cyclic sulfate compound can also participate in the formation of the negative SEI, reduce the reduction side reaction of the non-aqueous electrolyte with the surface of the negative electrode sheet and the damage of solvent co-intercalation to the stability of the negative electrode structure. The cyclic sulfate compound helps to improve the stability of the positive and negative electrodes, and reduce the impedance of the battery, thereby improving the cycle performance and storage performance of the lithium secondary battery.

[0019] In any embodiment, the isocyanate compound includes at least one of

[0020] The isocyanate group in the isocyanate compound can react with trace amounts of water and acid in the electrolyte, reduce the damage of the by-products generated by the reaction of the first additive and certain lithium salts (such as LiPF6) with water to the positive electrode interface film and the non-purpose consumption of the first additive, and promote the positive electrode to form a good CEI film. In addition, the isocyanate compound forms a thin and uniform SEI film on the negative electrode of the secondary battery, improves the film formation component, improves the stability of the negative electrode material while effectively reducing the consumption of active lithium, and further improves the storage performance of the battery.

[0021] In any embodiment, the non-aqueous electrolyte includes one of the following groups:

[0022] ​​(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, C1-16; and the second additive includes the isocyanate-based compound numbered as C2-17;

[0023] (2) the first additive includes the cyclic sulfate compound numbered as C1-16; and the second additive includes at least one of the isocyanate-based 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, C2-18.

[0024] By using the first additive and the second additive in combination, the consumption of the first additive can be reduced, and a stable and uniform interface film can be formed on both the positive electrode and the negative electrode of the secondary battery without using too much additive, thereby improving the positive and negative electrode interface protection and enhancing the cycle performance and storage performance of the lithium secondary battery.

[0025] In any of the embodiments, the non-aqueous electrolyte satisfies at least one of the following conditions:

[0026] (1) the mass content of the first additive is 0.05%-20% based on the total mass of the non-aqueous electrolyte;

[0027] (2) the mass content of the second additive is 0.01%-20% based on the total mass of the non-aqueous electrolyte;

[0028] (3) the mass ratio of the first additive to the second additive is 0.02-50.

[0029] In any of the embodiments, the non-aqueous electrolyte satisfies at least one of the following conditions:

[0030] (1) the mass content of the first additive is 0.05%-8% based on the total mass of the non-aqueous electrolyte;

[0031] (2) the mass content of the second additive is 0.1%-8% based on the total mass of the non-aqueous electrolyte;

[0032] (3) the mass ratio of the first additive to the second additive is 0.2-8;

[0033] (4) the mass content of ethylene carbonate is 15%-25% based on the total mass of the non-aqueous electrolyte.

[0034] The mass content of the first additive and the second additive in the non-aqueous electrolyte is in a suitable range, which helps to form SEI film and CEI film with suitable thickness for both positive and negative electrodes, reduces the side reaction of positive and negative electrodes, and does not excessively increase the impedance of the battery.

[0035] The mass ratio of the first additive and the second additive is in a suitable range, which can promote the synergistic effect of the two, reduce the side reaction of the first additive with the help of the second additive, make the first additive more involved in the film forming reaction of the positive electrode, and the second additive can still form an excellent SEI film for the negative electrode, so that the positive and negative electrodes have good interface protection, and the internal resistance of the battery is also moderate.

[0036] The mass content of ethylene carbonate in a suitable range helps to reduce the degree of dehydrogenation reaction on the surface of the positive electrode, slow down the dehydrogenation and oxidation side reaction, enhance the oxidation resistance of the non-aqueous electrolyte, reduce the damage of protons to the negative electrode, thereby prolonging the service life of the battery; it also helps to reduce the gas production of the secondary battery and improve the electrical and safety performance of the secondary battery.

[0037] In any embodiment, the water content of the non-aqueous electrolyte is 10 ppm to 100 ppm based on the total mass of the non-aqueous electrolyte.

[0038] In any embodiment, the water content of the non-aqueous electrolyte is 10 ppm to 50 ppm based on the total mass of the non-aqueous electrolyte.

[0039] The first additive and the second additive can undergo hydrolysis reaction to produce hydrolysis products with poor film forming effect, and the dissolution of the hydrolysis products in the non-aqueous electrolyte can affect the film forming effect of the positive electrode. The water content in the non-aqueous electrolyte is in a suitable range, which can reduce the hydrolysis of the first additive and the second additive and improve the interface protection of the positive and negative electrodes.

[0040] In any embodiment, the lithium secondary battery includes a positive electrode sheet, and the water content of the positive electrode sheet is 50 ppm to 150 ppm, which can be selected as 50 ppm to 100 ppm.

[0041] Controlling the water content of the positive electrode sheet in a suitable range can reduce the side reaction of the first additive and the second additive caused by the water in the electrode sheet entering the non-aqueous electrolyte, and help to improve the film forming effect of the positive and negative electrodes of the secondary battery.

[0042] In any embodiment, the positive electrode sheet includes a positive electrode active material, and the BET specific surface area of the positive electrode active material is less than or equal to 1.5 m 2 / g, which can be selected as 0.5 m 2 / g to 1 m 2 / g.

[0043] Controlling the BET specific surface area of the positive electrode active material within a suitable range helps to improve the degree of reaction between the first additive and the surface residual alkali of the positive electrode active material, and promotes the interfacial reaction of the first additive in the positive electrode. At the same time, the positive electrode active material surface has sufficient active sites for lithium ions to be embedded and extracted, which is beneficial to improve the cycle performance of the secondary battery.

[0044] In any embodiment, the positive electrode tab comprises a positive electrode active material, and the positive electrode active material comprises 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 comprises at least one of Ti, Al, Zr, Mg, Zn, Ba, Mo, B, which helps to improve the capacity and energy density of the secondary battery.

[0045] In any embodiment, the lithium secondary battery comprises a negative electrode tab, and the negative electrode tab comprises a negative electrode active material, wherein the BET specific surface area of the negative electrode active material is 0.5m 2 / g-2.0m 2 / g.

[0046] In any embodiment, the BET specific surface area of the negative electrode active material is 0.8m 2 / g-1.5m 2 / g.

[0047] In any embodiment, the Dv50 of the negative electrode active material is 5μm-30μm. In any embodiment, the Dv50 of the negative electrode active material is 7μm-25μm.

[0048] The BET specific surface area of the negative electrode active material within a suitable range can improve the acceptance of lithium ions by the negative electrode active material, reduce the deposition of lithium ions on the negative electrode surface; and also helps to control the interfacial reaction of the negative electrode, slow down the accumulation of negative electrode side reaction products and impedance increase. The Dv50 of the negative electrode active material within a suitable range can make the negative electrode have a good reaction rate, reduce the repeated damage of the SEI film and the consumption of active lithium, and improve the kinetic performance, capacity and cycle life of the secondary battery.

[0049] The second aspect of the present application provides a power device comprising the lithium secondary battery of the first aspect of the present application. The secondary battery provided by the present application has improved cycle performance and storage performance, and accordingly, the power device provided by the present application also has good performance. BRIEF DESCRIPTION OF DRAWINGS

[0050] FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0051] FIG. 2 is an exploded view of the secondary battery of the embodiment of the present application shown in FIG. 1;

[0052] FIG. 3 is a schematic view of a battery module of the embodiment of the present application;

[0053] FIG. 4 is a schematic view of a battery pack of the embodiment of the present application;

[0054] FIG. 5 is an exploded view of the battery pack of the embodiment of the present application shown in FIG. 4;

[0055] FIG. 6 is a schematic view of an electric device using the secondary battery of the embodiment of the present application as a power source.

[0056] Reference Signs: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0057] Hereinafter, the embodiments of the lithium secondary battery and the electric device of the present application are specifically disclosed with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed description is omitted. For example, there can be cases where detailed description of matters well known to those skilled in the art, repeated description of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0058] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., 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 particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. In addition, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" represents a shorthand manner of describing each and every numerical value that is contained in the range between "a" and "b," wherein "a" and "b" are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed herein, and "0-5" is merely a shorthand manner of describing each and every numerical value that is contained in the range between "0" and "5." In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0059] If not particularly specified, all the embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0060] If not particularly specified, all the technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0061] If not particularly specified, all the steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any order. For example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0062] If not particularly specified, the "comprise" and "include" mentioned in the present application are open-ended, and can also be closed. For example, the "comprise" and "include" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0063] If not particularly specified, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any one of the following conditions satisfies the condition "A or B": 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 A and B are both true (or exist).

[0064] Among the existing positive electrode materials, high-nickel positive electrode materials are considered to be the most promising lithium secondary battery positive electrode materials. However, in the process of charging and discharging, the active Ni 4+It has strong oxidizing property, which can accelerate the oxidative decomposition of electrolyte at the interface. This not only consumes electrolyte and leads to a decrease in conductivity, but also accumulates decomposition products on the electrode surface, increasing the interfacial resistance and further hindering charge transport. More seriously, continuous electrolyte decomposition can form an unstable interfacial film, leading to repeated growth and rupture of the interfacial film, consumption of active lithium, and a decrease in cycle capacity of the battery, affecting the service life of the battery. Film-forming additives are usually added to the electrolyte to provide protection for the electrode interface, but most of these additives are reduced to form a solid electrolyte interface film (SEI) at the negative electrode during the formation stage of the battery, and only a small amount of additives participate in the formation of a positive electrolyte interface film (CEI) at the positive electrode, resulting in insufficient protection of the positive electrode interface. At the same time, as a solvent component in the electrolyte, ethylene carbonate has excellent ionic conductivity and film-forming properties, but the proton hydrogen produced during its oxidation process can attack the lithium salt in the solvent, thereby damaging the SEI film and affecting the protection of the negative electrode interface. Therefore, the existing electrolyte has the problem of insufficient protection of the positive and negative electrode interfaces, thereby affecting the cycle performance and storage performance of the battery.

[0065] The present application provides a lithium secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a non-aqueous electrolyte and a separator. During the charging and discharging process of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0066] [Non-aqueous electrolyte]

[0067] The lithium secondary battery provided by the present application comprises a first additive, a second additive and a non-aqueous solvent, the first additive comprises a cyclic sulfate compound represented by formula I,

[0068] 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, and substituted or unsubstituted 5-6 membered saturated cyclic sulfate group;

[0069] The second additive comprises an isocyanate compound represented by formula II,

[0070] R5 is 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-C8 alkylene comprising saturated or unsaturated group, substituted or unsubstituted 5-6 membered cycloaliphatic, and C1-C3 alkylene diphenyl;

[0071] The nonaqueous solvent includes ethylene carbonate, and the mass content of the ethylene carbonate is greater than or equal to 10% and less than or equal to 50% based on the total mass of the nonaqueous electrolyte.

[0072] In the present text, the term "halogen" refers to the elements of group VIIA of the Periodic Table of the Elements, including fluorine, chlorine, bromine, iodine.

[0073] The term "C1-C3 alkyl" refers to a saturated hydrocarbon group consisting only of carbon and hydrogen atoms, containing from 1 to 3 carbon atoms, for example, methyl, ethyl, propyl.

[0074] The term "C1-C3 alkoxy" refers to an oxy group attached to a C1-C3 alkyl group.

[0075] The term "5-6 membered saturated cyclic sulfate" refers to a 5-6 membered saturated cyclic lactone containing a -OSO2O- group, which can be, for example,

[0076] The term "2 to 3 ring fused ring aralkylene" refers to an aralkylene group having two substitution sites, containing 2 to 3 benzene rings and being fused between the benzene rings by sharing two adjacent atoms, which includes, for example,

[0077] The term "C1-C8 alkylene" refers to a straight chain or branched chain saturated hydrocarbon group consisting only of carbon and hydrogen atoms, containing from 1 to 8 carbon atoms, which includes, for example, methylene, hexylene. Similarly, the term "C1-C3 alkylene" refers to a straight chain or branched chain saturated hydrocarbon group consisting only of carbon and hydrogen atoms, containing from 1 to 3 carbon atoms.

[0078] In the present text, the term "5 to 6 membered aliphatic group" refers to a general term for divalent groups obtained by removing two hydrogen atoms from an aliphatic hydrocarbon molecule containing 5-6 carbon atoms, which can be cycloalkylene, cycloalkenylene, etc., which includes, for example, cyclopentenylene, cyclohexenylene, cycloheptenylene, etc., but is not limited thereto.

[0079] The term "C1-C3 alkylene diphenyl" refers to a group formed by connecting two phenyl groups through an alkylene group containing 1-3 carbon atoms, which includes, for example,

[0080] The cyclic sulfate compound in the electrolyte can preferentially react with the residual alkali on the surface of the positive active material to form a monocyclic ring-opening product, which plays a role in situ modification on the surface of the positive electrode particles and participates in the formation of the positive electrode CEI film. As the concentration of cyclic sulfate compounds on the surface of the positive electrode decreases, the remaining cyclic sulfate compounds in the non-aqueous electrolyte are driven to the surface of the positive electrode, thereby playing a role in directing and anchoring the positive electrode before the formation of the battery. The organic matter in the monocyclic ring-opening product helps to improve the binding of the CEI film to the positive electrode surface, and the oxygen-sulfur bond in the sulfate group of the cyclic sulfate compound helps to improve the toughness of the CEI film, allowing the positive electrode to form a good CEI film. In addition, the cyclic sulfate compound can also participate in the formation of the SEI film, reduce the reduction side reaction of the non-aqueous electrolyte on the surface of the negative electrode, and reduce the damage of solvent co-intercalation to the stability of the negative electrode structure, thereby improving the stability of the negative electrode material.

[0081] The isocyanate group in the isocyanate compound has strong electrophilicity and is prone to react with oxygen-containing functional groups (such as -COOH, -OH, etc.) (for example: water, acid). This reaction tendency makes the isocyanate compound preferentially react with water and acid in the electrolyte, which not only reduces the damage of the by-products generated by the reaction of the cyclic sulfate compound with water to the positive and negative electrode interface film, but also allows the cyclic sulfate compound to participate more in the interface reaction to better form the interface film. In addition, the isocyanate compound can quickly form a film on the electrode surface, especially during the lithium ion intercalation process on the negative electrode surface, the isocyanate can participate in the initial formation and stabilization process of the SEI film, thereby improving the stability of the negative electrode material.

[0082] The non-aqueous solvent ethylene carbonate has a high dielectric constant (ε), which means it can be effectively polarized under the action of an electric field, thereby improving the ionic conductivity of the electrolyte, which can promote the rapid migration of lithium ions between the positive and negative electrodes, ensuring that the battery has good charge and discharge rate performance. However, it is prone to oxidative decomposition on the surface of the electrode, producing by-products such as lithium carbonate (Li2CO3), lithium fluoride (LiF), and ethylene carbonate (ECO). If these decomposition products cannot effectively integrate into the existing SEI film structure, or if their generation rate exceeds the self-repairing speed of the SEI film, it can cause local rupture or uneven thickening of the SEI film, thereby damaging the stability and integrity of the SEI film. In addition, the hydroxyl group (-OH) of the non-aqueous solvent ethylene carbonate is also prone to addition reaction with the isocyanate group in the isocyanate compound, consuming the second additive, thereby affecting the film formation effect of the first additive and the second additive on the positive and negative electrodes. By controlling the content of ethylene carbonate, the damage to the positive and negative electrode interface film can be reduced, thereby improving the cycle performance and storage performance of the lithium secondary battery.

[0083] By compounding the cyclic sulfate compound, the isocyanate-based compound, and the ethylene carbonate, side reactions of the cyclic sulfate compound and the isocyanate-based compound are reduced, and dehydrogenation and oxidation decomposition of the ethylene carbonate are reduced, damage to the positive and negative electrode interface is reduced, the positive and negative electrode interface is protected, the internal resistance of the battery cell is reduced, and the cycle performance and storage performance of the lithium secondary battery are improved.

[0084] In some embodiments, one of R1and R2is selected from hydrogen, methyl, ethyl, fluoro, trifluoromethyl, cyano, or and the other is selected from hydrogen.

[0085] In some embodiments, R1and R2are both selected from methyl.

[0086] In some embodiments, one of R3and R4is selected from hydrogen, methyl, ethyl, n-propyl, fluoro, ethoxy, or and the other is selected from hydrogen.

[0087] In some embodiments, the cyclic sulfate compound includes at least one of

[0088] The cyclic ester compound can preferentially react with residual alkali on the surface of the positive active material to form a monocyclic ring-opening product, play a role of in-situ modification on the surface of the positive electrode particles, and participate in the formation of the positive CEI film. With the decrease of the concentration of the cyclic sulfate compound on the surface of the positive electrode, the remaining cyclic sulfate compound in the non-aqueous electrolyte is driven to enrich on the surface of the positive electrode, thereby playing a role of being anchored on the positive electrode in advance before the formation of the battery cell. The organic matter in the monocyclic ring-opening product helps to improve the adhesion of the CEI film to the surface of the positive electrode, and the oxygen-sulfur bond in the sulfate group in the cyclic ester compound helps to improve the toughness of the CEI film, so that the positive electrode forms a good CEI film. In addition, the cyclic ester compound can also participate in the formation of the SEI film, reduce the reduction side reaction of the non-aqueous electrolyte on the surface of the negative electrode, and reduce the damage of solvent co-intercalation to the stability of the negative electrode structure. The cyclic ester compound helps to improve the stability of the positive and negative electrode materials, and improve the cycle performance and storage performance of the battery.

[0089] In some embodiments, the cyclic sulfate compound includes at least one of C1-12, C1-13, C1-14, C1-15, C1-16.

[0090] In some embodiments, the cyclic sulfate compound includes at least one of C1-12, C1-13, C1-14, C1-16.

[0091] ​The cyclic sulfate compound contains 3 or 4 sulfate groups, and the polycyclic structure can further improve the components of the positive and negative electrode interface film, improve the stability of the CEI film and SEI film, thereby reducing the consumption of active lithium and improving the cycle performance and storage performance of the battery. In addition, the number of sulfate groups makes the thickness of the CEI film and SEI film moderate, avoiding the increase of interface impedance and the deterioration of the performance of the battery due to the over-thickness of the interface film.

[0092] In some embodiments, the cyclic sulfate compound includes or is selected from C1-16. The cyclic sulfate compound has a proper number of sulfate groups and no alkyl, halogen atom or other substituent that increases the oxidation resistance of the non-aqueous electrolyte, which is helpful for the formation of the CEI film and SEI film.

[0093] In some embodiments, R5 is selected from methylene, hexylidene, 5- to 6-membered alicyclic group, wherein, R 51 , R 52 , R 53 , R 54 each occurrence is independently selected from hydrogen, halogen, methyl, ethyl; represents the connection site of the chemical group.

[0094] In some embodiments, in the second additive, R 51 , R 52 , R 53 , R 54 each occurrence is independently selected from hydrogen, fluorine, methyl, ethyl.

[0095] In some embodiments, R5 is selected from R 51 , R 52 , R 53 is hydrogen, R 54 is ethyl.

[0096] In some embodiments, R5 is selected from wherein, (1) R 52 , R 53 is hydrogen, R 51 , R 54 is methyl; (2) R 51 , R 52 is methyl, R 53 , R 54 is hydrogen; (3) R 51 , R 52 , R 53 , R 54 are all hydrogen, fluorine or methyl; or (4) R 51 , R53 is hydrogen, R 52 is hydrogen, R 54 is methyl.

[0097] In some embodiments, R5is selected from wherein (1) R 51 is hydrogen, R 52 is hydrogen, R 53 is hydrogen, R 54 is hydrogen; (2) R 51 is methyl, R 52 is hydrogen, R 53 is hydrogen, R 54 is hydrogen; (3) R 52 is methyl, R 51 is hydrogen, R 53 is hydrogen, R 54 is hydrogen.

[0098] In some embodiments, R5is selected from R 51 is hydrogen, R 52 is hydrogen, R 53 is hydrogen, R 54 is hydrogen

[0099] In some embodiments, the isocyanate-based compound comprises at least one of the following.

[0100] In some embodiments, the isocyanate-based compound comprises or is selected from C2-17.

[0101] During battery cycling, the SEI film can be damaged or dissolved to some extent. The isocyanate-based compound can continue to react with electrolyte components under conditions such as potential fluctuation or local overheating, supplement or repair the damaged SEI film, enhance its stability and integrity, and reduce the occurrence of side reactions. The thin and uniform SEI film formed by the isocyanate-based compound usually has good electrical insulation, ionic conductivity and mechanical stability. Such SEI film can effectively block electrons from crossing, allow lithium ions to pass smoothly, and at the same time resist the stress caused by volume change during charging and discharging of the battery, prolonging the cycle life of the battery. In addition, the optimized SEI film can also reduce the energy loss of lithium ions during intercalation / deintercalation and the consumption of active lithium, improving the charging and discharging efficiency of the battery. At the same time, the isocyanate-based compound can preferentially react with trace amounts of water and acid in the electrolyte over the cyclic sulfate compound, reducing the damage to the positive electrode interfacial film by the byproducts generated by the reaction of the first additive with water, improving the stability of the non-aqueous electrolyte, and improving the storage performance of the battery.

[0102] In some embodiments, the combination of additives in the non-aqueous electrolyte comprises one of the following groups: the first additive comprises 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, C1-16; the second additive comprises the isocyanate-based compound 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, C2-18.

[0103] In some embodiments, the combination of additives in the non-aqueous electrolyte comprises one of the following groups: the first additive comprises 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, C1-16; the second additive comprises the isocyanate-based compound numbered as C2-17.

[0104] In some embodiments, the combination of additives in the non-aqueous electrolyte comprises one of the following groups: the first additive comprises the cyclic sulfate compound numbered as C1-16; the second additive comprises at least one of the isocyanate-based 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, C2-18.

[0105] The use of the first additive and the second additive in combination, the second additive preferentially reacts with water and acid in the electrolyte, reduces the side reaction of the first additive, so that more first additive participates in the electrode interface film forming reaction, forms stable CEI film and SEI film, reduces the occurrence of side reaction, thereby improving the cycle performance and storage performance of the battery.

[0106] In some embodiments, the mass content of the ethylene carbonate is 15%-50%, 15%-40%, 15%-35%, 15%-30%, 15%-25%, 15%-20%, 20%-25%, based on the total mass of the non-aqueous electrolyte.

[0107] In some embodiments, the mass content of the ethylene carbonate is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or a range between any two of the aforementioned values or any value within the range, based on the total mass of the non-aqueous electrolyte.

[0108] A too low content of ethylene carbonate in the non-aqueous electrolyte can result in a too low conductivity of the electrolyte and a reduced lithium ion migration, which can affect the dynamic performance and cycle performance of the secondary battery. A too high content of ethylene carbonate in the non-aqueous electrolyte can result in a decomposition of the ethylene carbonate by dehydroxylation, which can damage the SEI film of the negative electrode and the performance of the battery; meanwhile, it can increase the consumption of the first and second additives and affect the film formation reaction of the first and second additives. Therefore, controlling the content of ethylene carbonate in the non-aqueous electrolyte within an appropriate range can take into account the ionic conductivity of the electrolyte and the formation of the positive CEI film and the negative SEI film, reduce the side reactions of the positive and negative electrodes, and improve the cycle performance of the lithium secondary battery.

[0109] 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%, 7%-18%, based on the total mass of the non-aqueous electrolyte.

[0110] In some embodiments, 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 between any two of the aforementioned values or any value within the range, based on the total mass of the non-aqueous electrolyte.

[0111] A too low mass content of the first additive in the non-aqueous electrolyte can be unfavorable for the formation of the positive CEI film, resulting in an insufficient protection of the positive electrode interface and an insignificant improvement effect on the performance of the battery; a too high mass content of the first additive can result in an excessive protection of the positive electrode interface and an increased impedance, which can be unfavorable for the improvement of the performance of the battery. Therefore, controlling the mass content of the first additive in the non-aqueous electrolyte within an appropriate range can form a good CEI film on the positive electrode and a good SEI film on the negative electrode at the same time, and the thickness of the CEI film and the SEI film is moderate, which can improve the protection of the positive and negative electrode interfaces while taking into account a moderate internal resistance of the battery, thereby improving the cycle performance and storage performance of the lithium secondary battery.

[0112] 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%, 0.5%-8% based on the total mass of the non-aqueous electrolyte.

[0113] In some embodiments, 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 aforementioned values or any value within the range based on the total mass of the non-aqueous electrolyte.

[0114] A mass content of the second additive in the non-aqueous electrolyte that is too low can result in insufficient reaction with water and acid, thereby causing hydrolysis of the first additive, affecting the subsequent film-forming effect of the first additive, causing insufficient protection of the positive and negative electrode interface, increasing side reactions, and not significantly improving the performance of the battery; a mass content of the second additive in the non-aqueous electrolyte that is too high can result in a too-thick SEI film, increasing the overall impedance of the battery, causing poor performance of the battery core, and affecting the storage performance of the battery.

[0115] In some embodiments, the electrolyte comprises: based on the total mass of the non-aqueous electrolyte, 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, C1-16, with a mass content of 0.2%-1%; the second additive includes the isocyanate-based compound numbered C2-17, with a mass content of 0.5%-1.5%; and ethylene carbonate, with a mass content of 15%-50%.

[0116] In some embodiments, the electrolyte comprises: based on the total mass of the non-aqueous electrolyte, the first additive includes the cyclic sulfate compound numbered C1-16, with a mass content of 0.2%-1%; the second additive includes at least one of the isocyanate-based 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, C2-18, with a mass content of 0.1%-8%; and ethylene carbonate, with a mass content of 15%-50%.

[0117] In some embodiments, the electrolyte comprises: the first additive comprises a cyclic sulfate compound numbered as C1-16 in an amount of 0.2%-1% by mass based on the total mass of the non-aqueous electrolyte; the second additive comprises an isocyanate compound numbered as C2-17 in an amount of 0.1%-8% by mass; and ethylene carbonate in an amount of 15%-40% by mass.

[0118] 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, 0.4-40.

[0119] 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 formed by any two of the above values or any value in the range.

[0120] The mass ratio of the first additive to the second additive in a suitable range can make the second additive preferentially react with water and acid, reduce the side reaction of the first additive with water and acid, and promote more 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 SEI film, so that 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.

[0121] In some embodiments, the non-aqueous electrolyte has a water content of 10-100 ppm by mass based on the total mass of the non-aqueous electrolyte. In some embodiments, the non-aqueous electrolyte has a water content of 10-50 ppm by mass based on the total mass of the non-aqueous electrolyte.

[0122] In some embodiments, the non-aqueous electrolyte has a water content of 10 ppm, 20 ppm, 40 ppm, 60 ppm, 80 ppm, 100 ppm by mass based on the total mass of the non-aqueous electrolyte, or a range formed by any two of the above values or any value in the range.

[0123] In this paper, the water content of the non-aqueous electrolyte is defined as known in the art, which can be measured by instruments and methods known in the art, for example, referring to the method for determining water content in GB / T 19282-2014. For example, the non-aqueous electrolyte is placed in a fully automatic moisture determination instrument measuring bottle, stirred until it is completely dissolved and uniform, and then the water content is measured.

[0124] The water content in the non-aqueous electrolyte that is too high can cause a large amount of the first additive to react with water, and the by-products generated dissolve in the electrolyte, resulting in poor film-forming effect of the first additive, thereby affecting the cycle performance and storage performance of the battery. The water content in the non-aqueous electrolyte within a suitable range can reduce the hydrolysis consumption of the first additive and the second additive, and improve the protection of the positive and negative electrode interfaces.

[0125] In some embodiments, the electrolyte includes an electrolyte salt and other solvents.

[0126] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0127] In some embodiments, the solvent can be selected from at least one of propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0128] In some embodiments, the electrolyte can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain performance of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature or low-temperature performance of the battery, etc.

[0129] [Positive electrode sheet]

[0130] The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer located on at least one side of the positive electrode current collector. The positive electrode material layer includes a positive electrode active material.

[0131] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode material layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0132] In some embodiments, the positive active material is a positive active material for a battery known in the art. As an example, the positive active material can include at least one of 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 a compound obtained by adding other transition metal or non-transition metal to the above compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive active material for a battery can also be used. These positive active materials can be used alone or in combination of two or more.

[0133] In some embodiments, the positive active material 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; and M includes at least one of Ti, Al, Zr, Mg, Zn, Ba, Mo, and B. The positive active material helps to improve the capacity and energy density of the secondary battery.

[0134] In some embodiments, the positive current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base such as a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0135] In some embodiments, the positive electrode sheet further includes a conductive agent, and the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0136] In some embodiments, the positive electrode sheet further includes a binder, and the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic ester resin.

[0137] In some embodiments, the positive electrode sheet can be prepared by dispersing the positive electrode active material in the above embodiments, the additive in the above embodiments, a binder, a conductive agent, and any other components in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying, cold pressing, etc., a positive electrode sheet is obtained.

[0138] In some embodiments, the water content of the positive electrode sheet is 50 ppm-150 ppm. In some embodiments, the water content of the positive electrode sheet is 50 ppm-145 ppm, 50 ppm-120 ppm, 50 ppm-100 ppm, 50 ppm-80 ppm.

[0139] In some embodiments, the water content of the positive electrode sheet is 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, 100 ppm, 110 ppm, 120 ppm, 130 ppm, 140 ppm, 150 ppm, or a range formed by any two of the above values or any value in the range.

[0140] In this document, the water content of the positive electrode sheet is defined in the art, and can be measured by instruments and methods known in the art, for example, the following method can be referred to: a test sample is placed in a solid water content analyzer device automatic sampling system, and during the test, the sample bottle is heated (the conventional heating temperature is 170°C, which can be adjusted according to the heat resistance of the sample) and dry gas is introduced, the gas in the sample bottle is blown into a titration cup for absorption titration, and the result is converted into the water content of the solid sample.

[0141] If the water content of the positive electrode sheet is too high, the water in the sheet will enter the electrolyte, causing the first additive in the electrolyte to directly hydrolyze, and further affecting the film forming effect of the positive and negative electrodes. Therefore, controlling the water content of the positive electrode sheet within a suitable range can reduce the hydrolysis of the first additive and the second additive, promote the formation of a stable interface film of the first additive and the second additive on the positive and negative electrodes, and thus improve the cycle performance and storage performance of the battery.

[0142] 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 m 2 / g. In some embodiments, the specific surface area of the positive electrode sheet is 0.1 m 2 / g-1.5 m 2 / g, 0.4 m 2 / g-1.5 m 2 / g, 0.3 m 2 / g-0.9 m 2 / g, 0.4 m 2 / g, 0.9 m 2 / g, 0.5 m 2 / g, 1 m 2 / g.

[0143] In some embodiments, the BET specific surface area of the positive active material in the positive electrode tab is 0.2 m 2 / g, 0.4 m 2 / g, 0.6 m 2 / g, 0.8 m 2 / g, 1 m 2 / g, 1.2 m 2 / g, 1.3 m 2 / g, 1.5 m 2 / g, or a range consisting of any two of the aforementioned values or any value within the range.

[0144] In this context, the BET specific surface area of the positive active material is defined as known in the art and can be determined using instruments and methods known in the art, for example, in accordance with GB / T 19587-2004 Gas Adsorption BET Method, after heating and degassing the sample, the amount of gas adsorbed on the surface of the solid at different adsorption pressures is determined at a constant low temperature, and 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 of the unit mass of the solid sample.

[0145] A too small BET specific surface area of the positive active material can increase the polarization of the battery and affect the storage performance of the battery. A too large specific surface area of the positive electrode tab can increase the contact area between the positive electrode tab and the non-aqueous electrolyte, increase the active reaction sites, increase the probability of the oxidative dehydrogenation of ethylene carbonate in the non-aqueous electrolyte, cause the generated proton hydrogen to attack the lithium salt in the solvent and thereby destroy the SEI film, and affect the cycle performance of the battery. Therefore, controlling the specific surface area of the positive electrode tab within an appropriate range can reduce the destruction of the SEI film and balance the capacity, cycle performance and kinetic performance of the battery.

[0146] [Positive electrode tab]

[0147] In some embodiments, the negative electrode tab includes a negative current collector and a negative film layer disposed on at least one surface of the negative current collector, the negative film layer including a negative active material.

[0148] As an example, the negative current collector has two opposite surfaces in the thickness direction of itself, and the negative film layer is disposed on any one or both of the two opposite surfaces of the negative current collector.

[0149] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base (e.g., a base of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0150] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination of two or more.

[0151] In some embodiments, the negative active material has a BET specific surface area of 0.5 m 2 / g to 2.0 m 2 / g. In some embodiments, the negative active material has a BET specific surface area of 0.7 m 2 / g to 2.0 m 2 / g, 0.8 m 2 / g to 1.5 m 2 / g, 0.8 m 2 / g to 2.0 m 2 / g, 1.0 m 2 / g to 1.8 m 2 / g, 0.5 m 2 / g to 1.5 m 2 / g.

[0152] In some embodiments, the negative active material has a BET specific surface area of 0.5 m 2 / g, 0.8 m 2 / g, 1.0 m 2 / g, 1.2 m 2 / g, 1.4 m 2 / g, 1.6 m 2 / g, 1.8 m 2 / g, 2.0 m 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 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.

[0154] 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.

[0155] In some embodiments, the D of the negative electrode active material V 50 represents 5μm-30μm.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] D of the negative active material V 50 can affect the number of reaction sites of the negative active material. D of the negative active material V 50 that is too small can result in too large specific surface area of the negative active material, too large contact area with electrolyte, which can result in intensified side reactions on the negative side of the battery, thus causing repeated damage of SEI film and increased consumption of lithium; D of the negative active material V 50 that is too large can not only result in too few reaction sites and slowed electrochemical reaction kinetics, but also can result in uneven surface of the negative active material during coating preparation of the electrode sheet, which can result in inconsistent compaction density due to uneven particle accumulation, thus affecting the electrical conductivity of the electrode and the energy density of the battery. Therefore, controlling D of the negative active material V 50 within a suitable range can reduce repeated damage of SEI film and consumption of active lithium, and improve the capacity, cycle life and kinetic performance of the battery.

[0160] In some embodiments, the negative film layer can further optionally include a binder. The binder can 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).

[0161] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super-conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0162] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0163] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative current collector, and after drying, cold pressing and the like, the negative electrode sheet can be obtained.

[0164] [Separator]

[0165] In some embodiments, the secondary battery further includes a separator. The type of the separator is not particularly limited in the present application, and any known porous structure separator with good chemical stability and mechanical stability can be selected.

[0166] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0167] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator film can be formed into an electrode assembly through a winding process or a stacking process.

[0168] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0169] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0170] The shape of the secondary battery is not particularly limited, and can be cylindrical, square, or any other shape. For example, FIG. 1 is a secondary battery 5 of a square structure as an example.

[0171] In some embodiments, referring to FIG. 2, the outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and a person skilled in the art can select according to the specific actual needs.

[0172] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0173] FIG. 4 is a battery module 3 as an example. Referring to FIG. 3, in the battery module 3, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 3. Of course, other arbitrary arrangements can also be made. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0174] Alternatively, the battery module 4 can further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0175] In some embodiments, the battery module described above can be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0176] FIGS. 4 and 5 are a battery pack 1 as an example. Referring to FIGS. 4 and 5, the battery pack 1 can include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery case includes an upper case 2 and a lower case 3, and the upper case 2 can be disposed on the lower case 3 to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery case in any manner.

[0177] In addition, the present application also provides a power consuming device including at least one of the secondary battery, the battery module, or the battery pack provided by the present application. The secondary battery, the battery module, or the battery pack can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0178] As the power consuming device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0179] FIG. 6 is a power consuming device as an example. The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of high power and high energy density of the secondary battery for the power consuming device, the battery pack or the battery module can be used.

[0180] As another example of the device, it can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thin and light, and the secondary battery can be used as a power source.

[0181] Embodiments

[0182] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are intended to explain the present application only, and should not be understood as limiting the present application. If a specific technique or condition is not mentioned in the embodiments, it is performed according to the technique or condition described in the literature in the art or according to the product manual. If the reagent or instrument used is not mentioned by the manufacturer, it is a conventional product that can be obtained by purchase on the market.

[0183] Compound and its abbreviated number:

[0184] I. Test method

[0185] 1. Water content of electrolyte

[0186] The water content in the electrolyte can be obtained by the method specified in GB / T 19282-2014.

[0187] 2. Water content of electrode sheet

[0188] The vial containing the electrode sheet test sample is placed into the automatic sample introduction system solid water content analyzer (Model: 874; Switzerland Mettler), and the vial is heated and dry gas is introduced during the test. The gas in the vial is blown into the titration cup for absorption titration. The ratio of the measured water content to the mass of the test sample is the water content of the electrode sheet.

[0189] 3. BET specific surface area

[0190] Referring to GB / T 19587-2004 gas adsorption BET method, after heating and degassing of the sample, the adsorption amount of gas on the surface of the solid under different adsorption pressures is measured at a constant low temperature (liquid nitrogen environment). Based on the BET multi-layer adsorption theory and its formula, the monolayer adsorption amount of the sample is obtained, and the specific surface area per unit mass of the test sample is calculated.

[0191] 4. Particle size test

[0192] Referring to GB / T 19077-2016 laser particle size analyzer diffraction method, the particle size distribution characteristics of the sample are determined.

[0193] 5. Battery performance test

[0194] (1) Battery normal temperature cycle performance test

[0195] At a constant temperature of 25℃, the lithium ion battery is charged at 0.5C constant current to a voltage of 4.4V, then charged at 4.4V constant voltage to a current ≤0.05C, and then discharged at 0.5C constant current to a voltage of 2.5V. This is one charge and discharge process. The discharge capacity at this time is recorded as the discharge capacity of the first cycle. Repeat the charging and discharging cycles, and calculate the cycle number when the capacity retention rate is 80%.

[0196] (2) Battery high temperature full charge storage performance test

[0197] The battery was charged at 0.33 C to 4.4 V and discharged at 0.33 C to 2.5 V at a constant temperature of 25 °C to test the discharge capacity D1; the battery was stored in a constant temperature environment of 60 °C, and every 30 days, the battery was taken out for testing, and the battery was cooled to 25 °C each time, and then the battery was charged at 0.33 C to 4.4 V and discharged at 0.33 C to 2.5 V to test the discharge capacity. The storage capacity retention decayed to 80% of the storage time was calculated.

[0198] II. Preparation method

[0199] Example 1

[0200] 1) Preparation of positive electrode sheet

[0201] The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2(BET specific surface area 0.61 m 2 / g), conductive agent acetylene black, and binder polyvinylidene fluoride were dissolved in a solvent N-methyl pyrrolidone at a mass ratio of 98:1:1, and after being fully stirred and mixed uniformly, a positive electrode film layer slurry was prepared. The positive electrode film layer slurry was coated on a positive electrode current collector aluminum foil, and then dried, cold-pressed, and cut to obtain a positive electrode sheet. The loading of the positive electrode active material on the single-sided aluminum foil of the positive electrode sheet was 0.016 g / cm 2 . The water content was 60.0 ppm.

[0202] 2) Preparation of negative electrode sheet

[0203] The negative electrode active material graphite (BET specific surface area 1.03 m 2 / g, Dv50 of 15.2 μm), conductive agent acetylene black, binder styrene-butadiene rubber, and thickening agent sodium carboxymethyl cellulose were fully stirred and mixed uniformly in deionized water at a weight ratio of 96:1:2:1 to obtain a negative electrode slurry. The negative electrode slurry was then coated on a copper foil, and then dried, cold-pressed, and cut to obtain a negative electrode sheet. The loading of the negative electrode active material graphite on the single-sided copper foil was 0.012 g / cm 2 .

[0204] 3) Separation film

[0205] A polypropylene film was used as the separation film.

[0206] 4) Preparation of electrolyte

[0207] In an argon-filled glove box (water content <0.1 ppm, oxygen content <0.1 ppm), lithium salt LiPF6, first additive (C1-1), second additive (C2-17) were added into non-aqueous solvents ethylene carbonate (EC) and methyl ethyl carbonate (EMC), and an electrolyte with a water content of 20.3 ppm was obtained after uniform mixing. 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%, and the mass content of the non-aqueous solvent ethylene carbonate (EC) was 20 wt%, the mass content of methyl ethyl carbonate (EMC) was 66 wt%, and the mass content of LiPF6 was 12.5 wt%.

[0208] 5) Preparation of the battery

[0209] The positive electrode sheet, the separator, and the negative electrode sheet were stacked in order, and an electric core was obtained after winding. The electric core was loaded into an outer package, the above-mentioned electrolyte was added, and a lithium secondary battery was obtained after packaging, standing, formation, aging, and other processes.

[0210] Example 2-44

[0211] The preparation method of Example 2-44 was similar to that of Example 1, and the mass content of EMC in the electrolyte was adaptively adjusted. The specific preparation parameters are shown in Table 1.

[0212] Comparative Example 1

[0213] Compared with Example 1, no first additive and second additive were added to the electrolyte.

[0214] Comparative Example 2

[0215] Compared with Example 40, the mass content of the second additive in the electrolyte was 25 wt%.

[0216] Comparative Example 3

[0217] Compared with Example 44, the mass content of ethylene carbonate in the non-aqueous electrolyte was 55 wt%.

[0218] Preparation parameters and performance test results of Examples 1-44 and Comparative Examples 1-3 are as follows:

[0219] As can be seen from Examples 1-41 and Comparative Examples 1-3, the combination of the cyclic sulfate compound and the isocyanate-based compound, 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 make the cycle number of the secondary battery at 25°C with a cycle capacity retention rate of 80% not less than 2100 cycles and the storage time of the secondary battery at 60°C with a storage capacity retention rate of 80% not less than 350 days.

[0220] As can be seen from Examples 1-16 and Examples 17-32, the combination of the cyclic sulfate compounds C1-1 to C1-16 with the isocyanate-based compound C2-17 or the combination of the cyclic sulfate compound C1-16 with the isocyanate-based compounds C2-1 to C2-18 can all improve the cycle performance and storage performance of the secondary battery.

[0221] As can be seen from Examples 34-36, when the mass content of the cyclic sulfate compound is in the range of 0.05wt% to 20wt%, the secondary battery has excellent cycle performance and storage performance. Compared with Comparative Example 1, the interface protection of the positive and negative electrodes is significantly improved.

[0222] As can be seen from Examples 37-40 and Comparative Example 2, when the mass content of the isocyanate-based compound is in the range of 0.01wt% to 20wt%, the cycle performance and storage performance of the secondary battery are significantly improved.

[0223] As can be seen from Examples 41-44 and Comparative Example 3, when the mass content of EC in the non-aqueous electrolyte is in the range of 15% to 50%, the cycle performance and storage performance of the secondary battery can be well balanced.

[0224] Examples 45-47

[0225] Examples 45-47 are similar to the preparation method of Example 16. In the preparation of the electrolyte, a small amount of water is added to the non-aqueous electrolyte to adjust the water content to 10.4ppm, 49.9ppm and 99.8ppm, respectively.

[0226] The performance test results of the secondary batteries of Examples 45-47 are as follows:

[0227] The above results show that the combination of the first additive C1-16 (0.5wt%), the second additive C2-17 (1wt%) and ethylene carbonate (20wt%) can provide good interface protection for the battery, improve the cycle number and storage time, and improve the cycle performance and storage performance of the battery when the water content in the non-aqueous electrolyte is in the range of 10ppm to 100ppm.

[0228] Examples 48-50

[0229] Examples 45-47 were prepared similarly to Example 16 by adjusting the cathode sheet drying parameters to adjust the cathode sheet moisture content to 50 ppm, 100 ppm, and 150 ppm, respectively.

[0230] The battery preparation and performance test results for Examples 45-47 are as follows:

[0231] The above results show 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 for secondary batteries in the range of 50 ppm to 150 ppm of cathode sheet moisture content.

[0232] Examples 51-53

[0233] Examples 51-53 were prepared similarly to Example 16, with the BET specific surface area of the cathode active material being 0.52 m 2 / g, 0.97 m 2 / g, and 1.48 m 2 / g, respectively. The battery preparation and performance test results are as follows:

[0234] The above results show that in the range of 0.5 m 2 / g to 1.5 m 2 / g, the active material particles have sufficient active sites, which is beneficial to improve the cycle performance of the secondary battery, and at the same time, have excellent storage performance.

[0235] Examples 54-57

[0236] Examples 54-57 were prepared similarly to Example 16, but the BET specific surface area and Dv50 of the anode active material were adjusted.

[0237] The battery preparation and performance test results are as follows:

[0238] The above results show that in the range of 0.5 m 2 / g to 2.0 m 2 / g, and the Dv50 is in the range of 5 μm to 30 μm, the secondary battery has excellent cycle performance and storage performance.

[0239] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. Furthermore, other modes constructed by applying various modifications to the embodiments, or by combining part of the configurations of the embodiments, which can be conceived by those skilled in the art, without departing from the spirit of the present application, are also included in the scope of the present application.

Claims

1. A lithium secondary battery, characterized in that, The electrolyte includes a non-aqueous electrolyte, which comprises a first additive, a second additive, and a non-aqueous solvent. The first additive comprises a cyclic sulfate compound represented by Formula I. 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. The second additive comprises an isocyanate-based compound as shown in Formula II. O=C=N——R5——N=C=O Equation II 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. 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.

2. The lithium secondary battery according to claim 1, characterized in that, 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, hexanediol, 5- to 6-membered alicyclic groups, Among them, R 51 R 52 R 53 R 54 Each time it appears, it is independently selected from hydrogen, halogen, methyl, and ethyl.

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

4. The lithium secondary battery according to any one of claims 1 to 3, characterized in that, The cyclic sulfate compound includes At least one of them; The isocyanate-based compound includes At least one of them.

5. The lithium secondary battery according to any one of claims 1 to 4, characterized in that, The non-aqueous electrolyte includes one of the following: (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; (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.

6. The lithium secondary battery according to any one of claims 1 to 5, characterized in that, The non-aqueous electrolyte meets at least one of the following conditions: (1) Based on the total mass of the non-aqueous electrolyte, the mass content of the first additive is 0.05%-20%; (2) Based on the total mass of the non-aqueous electrolyte, the mass content of the second additive is 0.01%-20%; (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 in that, The non-aqueous electrolyte meets at least one of the following conditions: (1) Based on the total mass of the non-aqueous electrolyte, the mass content of the first additive is 0.05%-8%; (2) Based on the total mass of the non-aqueous electrolyte, the mass content of the second additive is 0.1%-8%; (3) The mass ratio of the first additive to the second additive is 0.2-8; (4) Based on the total mass of the non-aqueous electrolyte, the mass content of the ethylene carbonate is 15%-25%.

8. The lithium secondary battery according to any one of claims 1 to 7, characterized in that, Based on the total mass of the non-aqueous electrolyte, the water content of the non-aqueous electrolyte is 10ppm-100ppm.

9. The lithium secondary battery according to any one of claims 1 to 8, characterized in that, Based on the total mass of the non-aqueous electrolyte, the water content of the non-aqueous electrolyte is 10ppm-50ppm.

10. The lithium secondary battery according to any one of claims 1 to 9, characterized in that, It includes a positive electrode sheet, wherein the water content of the positive electrode sheet is 50ppm-150ppm, and optionally 50ppm-100ppm.

11. The lithium secondary battery according to claim 9, characterized in that, The positive electrode sheet includes a positive active material, and 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-1.0m 2 / g.

12. The lithium secondary battery according to claim 10 or 11, characterized in that, Includes a negative electrode sheet, wherein 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 m². 2 / g-2.0m 2 / g; and / or The Dv50 of the negative electrode active material is 5μm-30μm.

13. The lithium secondary battery according to claim 12, characterized in that, The BET specific surface area of ​​the negative electrode active material is 0.8 m². 2 / g-1.5m 2 / g; and / or The Dv50 of the negative electrode active material is 7μm-25μm.

14. The lithium secondary battery according to any one of claims 10 to 13, characterized in that, The positive electrode sheet includes a positive electrode active material, which 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.

15. An electrical appliance, characterized in that, The lithium secondary battery includes any one of claims 1 to 14.

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