Negative electrode additive, negative electrode sheet, secondary battery, and electric device

Abstract

The application relates to a negative electrode additive, a negative electrode sheet, a secondary battery and a power utilization device. The negative electrode additive comprises at least one of a polymer A or a polymer B, the polymer A comprises a copolymer of A1 and A2, A1 comprises a homopolymer containing an acrylate structure, A2 comprises a homopolymer containing a cyclic carbonate structure, or A2 comprises a homopolymer containing a cyclic sulfate structure, or A2 comprises a copolymer containing a cyclic carbonate structure and a cyclic sulfate structure; the polymer B comprises a homopolymer of B1, B1 comprises an acrylate structure, and B1 further comprises a side chain containing a cyclic carbonate structure or a cyclic sulfate structure. The negative electrode additive can be used for forming an SEI film on the surface of a battery negative electrode material, improving the first charge-discharge efficiency and cycle stability of the battery.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a negative electrode additive, a negative electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0003] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant development of lithium-ion batteries, higher requirements have been placed on their energy density, cycle performance, and safety performance. The SEI film on the graphite surface plays a crucial role in the long-term cycle stability and safety performance of the battery cell. However, the formation of the SEI film consumes some lithium ions in the electrolyte, and these dead lithium ions lead to a decrease in the charge and discharge efficiency of the battery cell. Furthermore, the continuous aging of the SEI film during use causes solvent molecules to intercalate into the graphite, thereby damaging the electrode material and affecting the safety performance and lifespan of the battery cell.

[0004] Therefore, developing high-performance SEI interface films that are both practical and universal has always been one of the research hotspots in the industry. Summary of the Invention

[0005] This application provides a negative electrode additive, a negative electrode sheet, a secondary battery, and an electrical device. The negative electrode additive can form an SEI film on the surface of the negative electrode, thereby improving battery performance.

[0006] To achieve the above objectives, a first aspect of this application provides a negative electrode additive, comprising at least one of polymer A and polymer B.

[0007] Polymer A includes a copolymer of A1 and A2, wherein A1 includes a homopolymer containing an acrylate structure, and A2 includes a homopolymer containing a cyclic carbonate structure, or A2 includes a homopolymer containing a cyclic sulfate structure, or A2 includes a copolymer containing a cyclic carbonate structure and a cyclic sulfate structure.

[0008] Polymer B includes a homopolymer of B1, B1 comprising an acrylate structure, and B1 further comprising side chains containing a cyclic carbonate structure or a cyclic sulfate structure.

[0009] Therefore, the negative electrode additive of this application is obtained by copolymerization of polyacrylate segments combined with cyclic carbonate segments or cyclic sulfate segments, or by homopolymerization of polyacrylate structure combined with side chains containing cyclic carbonate structure or side chains containing cyclic sulfate structure, to obtain a water-soluble polymer that can be used to form an SEI film on the surface of battery negative electrode material, thereby improving the first charge-discharge efficiency and cycle stability of the battery.

[0010] In some embodiments of this application, A1 includes the structural formula shown in formula (1):

[0011]

[0012] In formula (1), a represents the degree of polymerization, R1 includes hydrogen or methyl, and R2 includes hydrogen or any one of the following groups:

[0013]

[0014] Where n1 to n4 are independently selected from positive integers from 1 to 4, and any "*" represents a connection site connected to an oxygen atom.

[0015] A2 includes one or more of the following structural formulas:

[0016]

[0017] Where b1 to b3 represent the degree of polymerization;

[0018] Optionally, A2 includes

[0019] Optionally, A2 includes

[0020] In some embodiments of the application, the mass percentage of the cyclic carbonate structure in polymer A is less than or equal to 50%, optionally 10% to 30%; and / or

[0021] The mass percentage of cyclic sulfate structures in polymer A is less than or equal to 30%, and can be selected as 10% to 20%.

[0022] In some embodiments of the application, B1 includes the structural formula shown in equation (2):

[0023]

[0024] In formula (2), c represents the degree of polymerization. Each occurrence of R3 independently includes either hydrogen or methyl groups, and each occurrence of R4 independently includes one or more of the following groups:

[0025]

[0026] Wherein, n5 to n6 are independently selected from positive integers from 1 to 4, R5 and R6 are independently selected from substituted or unsubstituted cyclic carbonate structural groups, or R5 and R6 are independently selected from substituted or unsubstituted cyclic sulfate structural groups, and any "*" indicates a linking site connected to an oxygen atom.

[0027] In some embodiments of this application, R5 and R6 are each independently selected from any one of the following groups:

[0028]

[0029] In this context, any "*" indicates a connection site that connects to an oxygen atom.

[0030] In some embodiments of this application, the mass percentage of the cyclic carbonate structure in polymer B is less than or equal to 100%, optionally 10% to 20%, and / or

[0031] The mass percentage of cyclic sulfate structures in polymer B is less than or equal to 50%, and can be selected as 5% to 10%.

[0032] In some embodiments of this application, the weight-average molecular weight of polymer A is 100,000 to 1,000,000, optionally 300,000 to 600,000; and / or,

[0033] The weight-average molecular weight of polymer B is 100,000 to 1,000,000, and can be selected as 300,000 to 600,000.

[0034] A second aspect of this application also provides a negative electrode sheet, including a current collector and a negative electrode active material layer disposed on at least one surface of the current collector, the negative electrode active material layer including the aforementioned negative electrode additive.

[0035] Therefore, this application improves the first charge-discharge efficiency and cycle stability of the battery by adding the above-mentioned negative electrode additive to the negative electrode sheet to participate in the formation of the SEI film.

[0036] In some embodiments of this application, the negative electrode additive has a mass percentage content of 0.3% to 1.3% in the negative electrode active material layer, and may be 0.3% to 0.8%.

[0037] A third aspect of this application provides a secondary battery, including the aforementioned negative electrode plate.

[0038] Therefore, the secondary battery provided in this application has high initial charge-discharge efficiency and cycle stability.

[0039] The fourth aspect of this application provides an electrical device including the secondary battery of the first aspect of this application.

[0040] The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery.

[0041] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0042] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0043] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0044] Figure 2 for Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0045] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0046] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0047] Figure 5 for Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0048] 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.

[0049] Explanation of reference numerals in the attached figures:

[0050] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Electrical device. Detailed Implementation

[0051] Hereinafter, some embodiments of the negative electrode additive, negative electrode sheet, secondary battery, and power-consuming device of this application are described in detail with appropriate reference to the accompanying drawings. However, some unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0052] The "range" disclosed in this application can be defined in the form of 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; any endpoint can be independently included or excluded, and they can be combined arbitrarily, meaning 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 ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also 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" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 for that parameter. For instance, when describing a parameter as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0053] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0054] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0055] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0056] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can 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.

[0057] In this application, open-ended technical features or solutions described using terms such as "containing," "comprising," or "including" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both the feature or solution that "A consists of a1, a2, and a3" and the feature or solution that "A includes not only a1, a2, and a3, but also other members." In this application, unless otherwise specified, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0058] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0059] In this application, terms such as "further," "even further," and "particularly" are used for descriptive purposes to indicate differences in content between different technical solutions, but should not be construed as limiting the scope of protection of this application.

[0060] In this application, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0061] Studies have shown that a stable and uniform SEI film is formed on the surface of the negative electrode active material, which has a stable and reversible lithium insertion / extraction capability during battery cycling, and can effectively improve the electrochemical performance of the battery. Currently, there are two main ways to construct the SEI film: (1) adding film-forming additives to the electrolyte. Common film-forming additives include unsaturated ester additives (VC vinylene carbonate, VEC vinylene carbonate, FEC fluoroethylene carbonate), sulfur-containing additives (PS 1,3-propane sulfonyl lactone, PES propylene-1,3 sulfonyl lactone, ES vinyl sulfite, DTD vinyl sulfate 1,3,2-dioxane-2,2-dioxide), lithium salt additives (LiBOB, LiPO2F2), and inorganic compound additives (Na2CO3, Na2SO3), etc.; (2) constructing artificial SEI films, such as CMC and SBR, which not only play a role in dispersing and bonding in the graphite negative electrode, but also help the formation of SEI during the first formation of graphite by coating the graphite surface.

[0062] In addition, traditional artificial SEIs focus on ionic cross-linked polymers and the development of novel electrolytes or electrode additives, but there are few reports on polymeric routes for film-forming additives, especially for aqueous or emulsion-type polymeric materials applied to graphite ends.

[0063] Based on this, one example of this application provides a negative electrode additive, including at least one of polymer A or polymer B.

[0064] Polymer A includes a copolymer of A1 and A2, wherein A1 includes a homopolymer containing an acrylate structure, and A2 includes a homopolymer containing a cyclic carbonate structure, or A2 includes a homopolymer containing a cyclic sulfate structure, or A2 includes a copolymer containing a cyclic carbonate structure and a cyclic sulfate structure.

[0065] Polymer B includes a homopolymer of B1, B1 comprising an acrylate structure, and B1 further comprising side chains containing a cyclic carbonate structure or a cyclic sulfate structure.

[0066] The hydrophilic polyacrylate segments or structures in the aforementioned polymers provide excellent adhesion, enabling them to coat the negative electrode material and form a film. This also gives the polymer good water solubility, resulting in better dispersion when added to the negative electrode film as an additive, thus achieving more uniform coating of the negative electrode material. Furthermore, the cyclic carbonate segments or cyclic sulfate segments, or cyclic carbonate side chains or side chains containing cyclic sulfate structures, exhibit good electrolyte wettability, improving the wetting of the coated negative electrode material with the electrolyte. They also serve as complexation sites for lithium ions, providing excellent ion transport pathways. Moreover, during battery cycling, the cyclic carbonate segments or cyclic sulfate segments, or cyclic carbonate side chains or side chains containing cyclic sulfate structures, preferably undergo ring-opening reactions, growing an SEI film in situ at the coating sites.

[0067] The structures of polymers A and B in the negative electrode additive of this application can be determined by conventional techniques in the art, such as infrared spectroscopy analysis of characteristic functional groups.

[0068] In some embodiments, A1 includes the structural formula shown in equation (1):

[0069]

[0070] In formula (1), a represents the degree of polymerization, R1 is selected from hydrogen or methyl, and R2 is selected from hydrogen or any one of the following groups:

[0071]

[0072] Where n1 to n4 are independently selected from positive integers from 1 to 4, and any "*" represents a connection site connected to an oxygen atom.

[0073] By adjusting the length and type of the R2 chain segments, the coating performance of the negative electrode additive on the negative electrode material can be further optimized. The longer the R2 chain, the better it is for improving the coating performance of the negative electrode binder on the negative electrode material.

[0074] In some alternative implementations, R2 is selected from...

[0075] In some implementations, A2 includes one or more of the following structural formulas:

[0076]

[0077] Where b1 to b3 represent the polymer degree. b1, b2, and b3 are each independently selected from any positive number, and they can be the same or different.

[0078] In some alternative implementations, A2 includes any two of the structures described above.

[0079] In some specific implementations, A2 includes

[0080] In some specific implementations, A2 includes

[0081] In some embodiments, the mass percentage of the cyclic carbonate structure in polymer A is less than or equal to 50%, optionally ranging from 10% to 30%. Understandably, the mass percentage of the cyclic carbonate structure in polymer A can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, and any value between them. Maintaining the mass percentage of the cyclic carbonate structure in polymer A within this range is more advantageous for controlling the water solubility of the synthesized polymer and its wettability with the electrolyte in the battery cell.

[0082] In some embodiments, the mass percentage of the cyclic sulfate structure in polymer A is less than or equal to 30%, optionally ranging from 10% to 20%. Understandably, the mass percentage of the cyclic sulfate structure in polymer A can be 0%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, and any value between them. The mass percentage of the cyclic sulfate structure in polymer A within this range is primarily to ensure the solubility of the monomers for the reaction. Solubility includes the miscibility of the cyclic sulfate monomers with the comonomers and their own solubility in the solvent, thereby ensuring the homogeneity of the monomer reaction.

[0083] The structural characteristics of polymer A, such as those of A1 and A2, and the mass percentages of cyclic carbonate structures and cyclic sulfate structures in polymer A can all be determined using conventional techniques in the art. For example, characteristic functional groups can be characterized by infrared spectroscopy, and the contents can be determined by carbon NMR and hydrogen NMR spectroscopy. Elemental analysis can then be used to determine the content of each element, and the content of each characteristic structure can be deduced in reverse. In some embodiments, the weight-average molecular weight of polymer A is 100,000 to 1,000,000, and can be selected as 300,000 to 600,000. Understandably, the weight-average molecular weight of polymer A can be 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, 800,000, 900,000, or 1,000,000.

[0084] The weight-average molecular weight of a polymer has a meaning well-known in the art and can be determined using instruments and methods well-known in the art. For example, the viscosity of its aqueous solution can be determined according to ASTM D 1439-03, and the molecular weight can be estimated from the viscosity of a standard polymer aqueous solution. According to one method, the molecular weight of the polymer can be estimated using the viscosity by the following formula:

[0085] η[Pa S]=8.91×10 -4 +1.30×10 -5 cM w 0.9 +5.33×10 -8 c 2 M w 1.8 +4.60×10 -15 c 4.34 M w 3.91 , where η is

[0086] Viscosity, c is the polymer concentration, M w It refers to molecular weight, as described by Kulicke in Polymer, Vol. 37, No. 13, pp. 2723-2731, 1996.

[0087] In some embodiments, B1 includes the structural formula shown in equation (2):

[0088]

[0089] In formula (2), c represents the degree of polymerization. Each group independently includes either hydrogen or methyl groups each time it appears. Each group independently includes one or more of the following groups each time R4 appears:

[0090]

[0091] Wherein, n5 to n6 are independently selected from positive integers from 1 to 4, R5 and R6 are independently selected from substituted or unsubstituted cyclic carbonate structural groups, or R5 and R6 are independently selected from substituted or unsubstituted cyclic sulfate structural groups, and any "*" indicates a linking site connected to an oxygen atom.

[0092] The larger the values ​​of n5 and n6, the longer the side chain of R4, which is more conducive to improving the coating performance of the negative electrode binder on the negative electrode material.

[0093] In some embodiments, R5 and R6 are each independently selected from any one of the following groups:

[0094]

[0095] In this context, any "*" indicates a connection site that connects to an oxygen atom.

[0096] In some embodiments, the mass percentage of the cyclic carbonate structure in polymer B is less than or equal to 100%, and can be selected as 10% to 20%. Understandably, the mass percentage of the cyclic carbonate structure in polymer B can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, and any value between them. A mass percentage of the cyclic carbonate structure in polymer B within this range is more beneficial to the wettability of the electrolyte. If the electrolyte solvent is a carbonate, the cyclic carbonate at the tail end is more likely to contact the electrolyte, thus preferentially reacting.

[0097] In some embodiments, the mass percentage of the cyclic sulfate structure in polymer B is less than or equal to 50%, optionally from 5% to 10%. Understandably, the mass percentage of the cyclic sulfate structure in polymer B can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, and any value between them.

[0098] The structural characteristics of polymer B, such as the characteristic functional groups, the mass percentage of cyclic carbonate structures and the mass percentage of cyclic sulfate structures in polymer B, can all be determined by conventional techniques in the field. For example, the characteristic functional groups can be characterized by infrared spectroscopy, and the contents can be determined by carbon NMR and hydrogen NMR spectroscopy. Then, the contents of each element can be determined by elemental analysis, and the contents of each characteristic structure can be deduced in reverse.

[0099] In some embodiments, the weight-average molecular weight of polymer B is 100,000 to 1,000,000, optionally 300,000 to 600,000. Understandably, the weight-average molecular weight of polymer B can be 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, 800,000, 900,000, or 1,000,000.

[0100] The weight-average molecular weight of a polymer has a meaning well-known in the art and can be determined using instruments and methods well-known in the art. For example, the viscosity of its aqueous solution can be determined according to ASTM D 1439-03, and the molecular weight can be estimated from the viscosity of a standard polymer aqueous solution. According to one method, the molecular weight of the polymer can be estimated using the viscosity by the following formula:

[0101] η[Pa S]=8.91×10 -4 +1.30×10 -5 cM w 0.9 +5.33×10 -8 c2 M w 1.8 +4.60×10 -15 c 4.34 M w 3.91 Where η is viscosity, c is polymer concentration, and M w It refers to molecular weight, as described by Kulicke in Polymer, Vol. 37, No. 13, pp. 2723-2731, 1996.

[0102] This application also provides an example of a method for preparing the polymer A described above. Polymer A can be synthesized from polymeric monomers via a free radical copolymerization reaction in the presence of an initiator. The polymeric monomers include a first monomer and a second monomer, wherein the first monomer is an acrylate monomer, and the second monomer is a monomer containing a cyclic carbonate structure or a monomer containing a cyclic sulfate structure.

[0103] In some embodiments, the polymerizing monomer includes acrylate monomers and monomers containing cyclic carbonate structures. In other embodiments, the polymerizing monomer includes acrylate monomers and monomers containing cyclic sulfate structures. In still other embodiments, the polymerizing monomer includes acrylate monomers, monomers containing cyclic carbonate structures, and monomers containing cyclic sulfate structures.

[0104] In some embodiments, the acrylate monomer is selected from any one of the compounds shown in formula (3):

[0105]

[0106] R1 and R2 are the same as described above, and will not be repeated here.

[0107] In some embodiments, the monomer containing the cyclic carbonate structure is selected from any one of the following formulas:

[0108]

[0109] In some embodiments, the monomer containing the cyclic sulfate structure is selected from:

[0110] In some embodiments, the first monomer includes any one of β-acryloyloxypropionic acid, methacrylic acid, acrylic acid, 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, Hydroxy-PEG3-acrylate (Chinese name 2-[2-(2-hydroxyethoxy)ethoxy]ethyl 2-acrylate), mono(2-acryloyloxyethyl ester) succinate, and β-acryloyloxypropionic acid.

[0111] In some embodiments, the second monomer comprises one or more of vinyl ethylene carbonate, vinylene carbonate, and propenyl-1,3-sulfonyl lactone. In some of these embodiments, the second monomer comprises vinylene carbonate and vinyl ethylene carbonate. In other embodiments, the second monomer comprises vinylene carbonate and propenyl-1,3-sulfonyl lactone.

[0112] The terms "first monomer" and "second monomer" used above are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Furthermore, "first monomer" and "second monomer" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0113] The initiator used in this application is not particularly limited and may be a persulfate initiator and / or an azo initiator. Specific examples of persulfate initiators include, but are not limited to, ammonium persulfate, sodium persulfate, potassium persulfate, and combinations thereof. Specific examples of azo initiators include, but are not limited to, azobisisobutyronitrile, azobisisoheptanenitrile, azobisisobutyric acid, and combinations thereof.

[0114] In some embodiments, the mass ratio of initiator to monomer is (0.01–2):100, optionally (0.01–0.5):100. Understandably, the mass ratio of initiator to monomer can also be 0.1:100, 0.2:100, 0.3:100, 0.4:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100, 1:100, 1.1:100, 1.2:100, 1.3:100, 1.4:100, 1.5:100, 1.6:100, 1.7:100, 1.8:100, 1.9:100, and any values ​​between them. Within this range of initiator-to-monomer mass ratio, polymer A has a more suitable number-average molecular weight, and the monomer conversion rate and reaction efficiency are higher.

[0115] This application also provides an example of a method for preparing the polymer B described above. Polymer B can be synthesized from the acrylate monomers via a free radical copolymerization reaction in the presence of an initiator to form polymer B1, and then, in the presence of a catalyst and a condensing agent, side chains containing cyclic carbonate structures or cyclic sulfate structures are grafted onto polymer B1 to obtain the polymer.

[0116] In some implementations, the graft monomer is any one of the following formulas:

[0117]

[0118] The grafting catalyst and condensing agent used in this application are not particularly limited. Specific examples of catalysts include, but are not limited to, 4-dimethylaminopyridine (DMAP), 4-pyrrolidinylpyridine (PPY), 9-azajulolidine (9-AJ), triethylamine, triethanolamine, and combinations thereof. Specific examples of condensing agents include, but are not limited to, dicyclohexylcarbodiimide (DCC), diisopropylcarbodiimide (DIC), 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC), and combinations thereof.

[0119] In some embodiments, the mass ratio of polymer:catalyst:condensing agent:graft monomer is 1:(0.1-0.2):(0.1-1):(0.01-1). Within this range of polymer-graft monomer mass ratio, polymer B has a more suitable grafting amount.

[0120] One example of this application provides a negative electrode sheet, including a current collector and a negative electrode active material layer disposed on at least one surface of the current collector, the negative electrode active material layer including the negative electrode additive of any of the above embodiments.

[0121] In some embodiments, the mass percentage of the negative electrode additive in the negative electrode active material layer is 0.3% to 1.3%, optionally 0.3% to 0.8%. Understandably, the mass percentage of the negative electrode additive in the negative electrode active material layer can be 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, and any value between them.

[0122] An example of this application also provides a secondary battery, including the negative electrode sheet described above.

[0123] An example of this application further provides an electrical device including at least one of the above-described secondary batteries.

[0124] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0125] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0126] Positive electrode sheet

[0127] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active material.

[0128] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0129] In some embodiments, the positive electrode 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on a polymeric material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0130] In some embodiments, the positive electrode active material may be a known positive electrode active material for batteries. As a non-limiting example, the positive electrode active material may include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified 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. Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxides (such as LiCoO2), lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium manganese iron phosphate and carbon composites. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.85 Co 0.15 Al 0.05 O2.

[0131] In some embodiments, the positive electrode active material layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0132] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0133] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000-25000 mPa·s. When coating the positive electrode slurry, the areal density per unit area of ​​the coating, based on dry weight (excluding solvent), can be 15-35 mg / cm³. 2The compaction density of the positive electrode sheet can be 3.0–3.6 g / cm³. 3 The concentration can be selected as 3.3–3.5 g / cm³. 3 .

[0134] Negative electrode sheet

[0135] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative active material layer of this application includes a negative active material and the negative additives described in any of the above examples or embodiments.

[0136] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0137] 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0138] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more 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.

[0139] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may include one or more 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).

[0140] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0141] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0142] 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 (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, and other processes. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000-10000 mPa·s. When coating the negative electrode slurry, the coating unit areal density (dry weight, minus solvent) can be 75-220 g / m². 2 The compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 ~1.8g / cm 3 .

[0143] electrolytes

[0144] Electrolytes function to conduct ions between the positive and negative electrodes. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid.

[0145] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0146] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0147] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethylene carbonate Fluoroethylene carbonate (FEC), 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.

[0148] 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.

[0149] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0150] Separating membrane

[0151] 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.

[0152] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0153] In some embodiments, the thickness of the isolation membrane is 6-40 μm, optionally 12-20 μm.

[0154] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0155] 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.

[0156] In some embodiments, the outer packaging of the secondary battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0157] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0158] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0159] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0160] In some of these embodiments, reference is made 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 number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs.

[0161] The secondary battery can be either battery module 4 or battery pack 1.

[0162] A battery module includes at least one battery cell. The number of battery cells in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0163] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0164] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0165] 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. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0166] 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.

[0167] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery 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, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0168] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0169] Figure 6 Here is an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0170] 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.

[0171] Example

[0172] 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 no specific technology or conditions are specified in the embodiments, they are performed according to the technology or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products, or products that can be synthesized using conventional methods from commercially available products.

[0173] In the following embodiments, unless otherwise specified, the temperature conditions are all room temperature, which refers to 20°C to 30°C, and further, it can be 25°C.

[0174] Unless otherwise specified, the raw materials used in the following examples are commercially available or can be prepared from commercially available raw materials through simple chemical modification. The intermediate and final products used in the synthesis, including the surfactants of this application, can be structurally identified by one or more of the following detection methods, including but not limited to: Fourier transform infrared (FT-IR) spectroscopy, ultraviolet spectroscopy, proton nuclear magnetic resonance (1H NMR), X-ray diffraction (XRD), gel permeation chromatography (GPC), high-performance liquid chromatography (HPLC), and mass spectrometry. The sample preparation and testing methods for these methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the specific structure and material properties of the compound. For those skilled in the art, given the structural formula of the target compound, the test results of the aforementioned methods can be used to determine whether a compound with the target structure has been synthesized. For example, with 1H NMR, structural identification can be performed based on parameters such as peak position, peak shape, and integral area ratio in the proton NMR spectrum to confirm whether a specific group has disappeared or appeared.

[0175] In the following examples, unless otherwise specified, DMAP is 4-dimethylaminopyridine and DCC is 1,3-dicyclohexylcarbodiimide.

[0176] Hydroxy-PEG3-acrylate (cas number: 16695-45-7) 1,2-Oxathiolan-4-ol,2,2-dioxide (cas number: 10200-48-3), 1,3,2-dioxathiolane-4-methanol 2-oxide (cas number: 13897-37-5).

[0177] Preparation Example 1

[0178] 150g of deionized water and 2g of sodium persulfate were added to a 1L four-necked flask and placed in a 70℃ water bath. The mixture was stirred and heated under nitrogen atmosphere. 5g of vinyl ethylene carbonate (first monomer) and 95g of β-acryloyloxypropionic acid (second monomer) were dissolved in 50g of DI water and then added dropwise to the flask over one hour. The reaction was carried out for 5 hours to obtain polymer A. The entire reaction was conducted under nitrogen protection.

[0179] The preparation methods for Preparation Examples 2-23 are similar to those for Preparation Example 1. The difference lies in the adjustment of parameters such as monomers, initiators, and their amounts. Specific parameters are detailed in Table 1 below.

[0180] Table 1

[0181]

[0182]

[0183] Preparation Example 24

[0184] 150g of tetrahydrofuran (THF) and 2g of azobisisobutyronitrile (AIBN) were added to a 1L four-necked flask and placed in a 70℃ water bath under nitrogen atmosphere with stirring and heating. 100g of β-acryloyloxypropionic acid was dissolved in 50g of THF and then added dropwise to the flask over one hour, reacting for 3 hours. The entire reaction was carried out under nitrogen protection. After the reaction was completed, the solvent was removed by vacuum drying to obtain polymer B1. 100g of polymer B1 and 100mL of N,N-dimethylformamide (DMF) were added to a 1L single-necked flask. After complete dissolution, 1g of DMAP, 10g of DCC, and 10g of 4-(hydroxymethyl)-5-methyl-[1,3]dioxane-2-one were added sequentially. The mixture was reacted at room temperature for 24 hours. Solid impurities were removed by filtration, and the product was dried under vacuum by vacuum distillation to obtain the solid product, polymer B.

[0185] The preparation methods for Preparation Examples 25–37 are similar to those for Preparation Example 24. The difference lies in the adjustment of parameters such as polymer B1, grafted monomers, and their amounts. Specific parameters are detailed in Table 2 below.

[0186] Table 2

[0187]

[0188]

[0189] Example 1

[0190] 1) Preparation of negative electrode sheet

[0191] The polymer prepared in Example 1, graphite (the negative electrode active material), carbon black (the conductive agent), sodium carboxymethyl cellulose (the thickener), and styrene-butadiene rubber (the binder) were mixed in a mass ratio of 0.3:97:0.4:0.3:1. Deionized water was added, and the mixture was stirred under vacuum to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto both sides of a copper foil. After the copper foil was dried at room temperature, it was transferred to a 120°C oven and dried for 1 hour. Then, it was cold-pressed and slit to obtain the negative electrode sheet, wherein the coating amount per unit area on both sides was 0.17 g / 1540.25 mm. 2 .

[0192] 2) Button assembly

[0193] The negative electrode sheet serves as the positive electrode, the lithium metal sheet as the negative electrode, nickel foam as the filler, and a PP film as the separator. A 1 mol / L LiPF6 solution with a combined solvent EC / DEC / DMC ratio of 1:1:1 (volume ratio) is used as the electrolyte. Assembly is performed using a CR2430 coin cell. The assembly sequence is: negative electrode shell - nickel foam - lithium sheet - electrolyte (30 μL) - separator - electrolyte (30 μL) - negative electrode sheet - positive electrode shell, and sealing is performed under 650 PSI pressure.

[0194] The secondary batteries in Examples 2 to 37 are prepared using methods similar to those in Example 1, but the polymers from the corresponding preparation examples are used.

[0195] Examples 38-40

[0196] The secondary batteries in Examples 38-40 were prepared in a similar manner to those in Example 1, except that the amount of polymer added to the negative electrode sheet (based on dry weight, excluding solvent) was 0.3%, 0.8%, and 1.4%, respectively.

[0197] Comparative Example 1

[0198] The preparation method of the secondary battery in Comparative Example 1 is similar to that in Example 1, except that no polymer is added to the negative electrode slurry, which only includes graphite as the negative electrode active material, carbon black as the conductive agent, sodium carboxymethyl cellulose as the thickener, and styrene-butadiene rubber as the binder.

[0199] Test methods

[0200] 1. Number-average molecular weight

[0201] The testing instrument was a Waters 1515 gel permeation chromatograph from PL (Platinum Corporation), equipped with a Waters 2695 separation unit, a Waters 2414 differential refractive index detector, and a CORTECS 2.7 μm column. The testing temperature was 20 °C. DIW was used as the mobile phase at a flow rate of 1.0 mL / min. The sample concentration was 10 mg / mL aqueous solution, filtered through a 0.22 μm polytetrafluoroethylene membrane before injection.

[0202] 2. Viscosity

[0203] The polymer synthesized in this patent was prepared into a 6% aqueous solution, and its specific viscosity was tested using an Anton Paar viscometer. The testing process was as follows: First, a #3 rotor was used for testing. If the viscosity at 12 rpm was <10000 mPa·s, the test result was adopted. If the viscosity at 12 rpm was >10000 mPa·s, the #4 rotor was used to continue measuring the viscosity at 12 rpm until the viscosity reached below 10000 mPa·s.

[0204] 3. Liquid absorption rate

[0205] The polymer described in this patent is cast into a film in a container. After it is completely dried, a certain weight (w0) of the film sample is placed in the above electrolyte solution and placed in an environment of 60°C for 7 days. Subsequently, the electrolyte adsorbed on the surface of the polymer film is removed, and the weight is recorded as (w1). The liquid absorption rate can be calculated as (w1-w0) / w0*100%.

[0206] 4. Battery Deduction Assessment

[0207] Button cell testing: The initial efficiency test was conducted using a 5V / 1mA blue-chip battery tester. The prepared button cells were placed in a constant temperature environment of 25℃ and allowed to stand for 5 hours. They were then discharged at a constant current of 0.05C to 0.005V, followed by a constant current discharge of 50uA to 0.005V, then allowed to stand for 5 minutes. Next, they were discharged at a constant current of 10uA to 0.005V, allowed to stand for 5 minutes, and then charged at a constant voltage of 0.1C to 2V. The test was then allowed to stand for 5 minutes. Initial coulombic efficiency = initial charge specific capacity / initial discharge specific capacity; specific capacity = capacity / mass of active material.

[0208] High-temperature cycling test of coin cells: The prepared coin cells were placed in a constant temperature environment of 25℃ for 3 hours, then charged to 2V at a constant current of 0.33C, 0.1C, and 100uA, and then placed to rest for 10 minutes. Next, they were discharged to 0.005V at a constant current of 0.33C, 0.1C, and 0.005V at a constant current of 0.05C, and then charged to 0.005V at a constant current of 50uA. After that, they were placed to rest for 10 minutes, charged to 2V at 0.33C, and placed to rest for 5 minutes. Then, the cycle was repeated 100 times, starting from the 0.33C constant current discharge to 0.005V step.

[0209] The test results are shown in Table 3:

[0210] Table 3

[0211]

[0212]

[0213]

[0214] As shown in the above embodiments, when the content of cyclic carbonate and cyclic sulfonate structures in the polymer of this application increases, that is, when the content of the second monomer and graft monomer increases, the molecular weight decreases under the same conditions. This is because the solubility and miscibility of the corresponding monomers decrease during the polymerization reaction. At the same time, when the content of cyclic carbonate and cyclic sulfonate structures in the polymer increases, its liquid absorption rate increases significantly. Meanwhile, the electrolyte discoloration can be observed, indicating that the polymer is insoluble in the electrolyte when the content of cyclic carbonate and cyclic sulfonate is low. When its content increases, the polymer wettability increases due to its structure similar to that of the electrolyte solvent, but there is also a risk of dissolution. Its cycle performance shows a significant decline (e.g., Example 12).

[0215] Secondly, when the content of the second monomer and graft monomer is low (that is, when the content of cyclic carbonate and cyclic sulfonate structures in the polymer is low), the effect on the initial efficiency and specific capacity is not significant. However, as their content increases, the initial efficiency of the graphite on the negative electrode side can be effectively improved. But after the content of cyclic carbonate structures in the polymer continues to increase to a certain extent, the initial efficiency decreases (as in Examples 8-12, the battery's initial efficiency increases with the increase of the mass content of the second monomer, but when the mass content of the second monomer reaches 20%, further increases in its content result in a decrease in the initial efficiency). This may be because with the increase of the cyclic carbonate structure content, the polymer dissolves in the electrolyte, and thus the SEI film at the graphite end continuously consumes lithium ions, leading to a decrease in the initial efficiency. Similar results can be obtained from the cycling data; the capacity cycle retention rate of polymers with high cyclic carbonate structure content shows a decreasing trend. It can be clearly seen from Examples 20-23 that high molecular weight polymers have little effect on initial efficiency and capacity, but for cycling, high molecular weight polymers may exhibit better adhesion and thus higher cycle retention rates. Comparing Comparative Example 1 with Examples 1-40, the initial coulombic efficiency of Examples 1-40 was higher than that of Comparative Example 1, which can effectively prove that the addition of polymer can improve the initial efficiency of graphite end materials.

[0216] It should be noted that, as shown in Table 3 above, the improvement in the initial coulombic efficiency of Example 4 compared to Comparative Example 1 is relatively low compared to other examples, but it still has a significant advantage in terms of cycle capacity retention.

[0217] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0218] 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 negative electrode additive, characterized in that, Including at least one of polymer A and polymer B, Polymer A includes a copolymer of A1 and A2, wherein A1 includes a homopolymer containing an acrylate structure, and A2 includes a homopolymer containing a cyclic carbonate structure, or A2 includes a homopolymer containing a cyclic sulfate structure, or A2 includes a copolymer containing a cyclic carbonate structure and a cyclic sulfate structure. Polymer B includes a homopolymer of B1, B1 includes an acrylate structure, and B1 also includes side chains containing a cyclic carbonate structure or a cyclic sulfate structure. A1 includes the structural formula shown in equation (1): ， In formula (1), a represents the degree of polymerization, R1 includes hydrogen or methyl, and R2 includes any one of the following groups: ， Where n1 to n4 are independently selected from positive integers from 1 to 4, and any "*" represents a connection site connected to an oxygen atom.

2. The negative electrode additive according to claim 1, characterized in that, A2 includes one or more of the following structural formulas: ， Where b1~b3 represent the degree of polymerization.

3. The negative electrode additive according to claim 2, characterized in that, A2 includes and .

4. The negative electrode additive according to claim 2, characterized in that, A2 includes and .

5. The negative electrode additive according to any one of claims 1 to 4, characterized in that, The mass percentage of cyclic carbonate structures in polymer A is less than or equal to 50%; and / or The mass percentage of cyclic sulfate ester structures in polymer A is less than or equal to 30%.

6. The negative electrode additive according to claim 5, characterized in that, The mass percentage of cyclic carbonate structures in polymer A is 10% to 30%; and / or The mass percentage of cyclic sulfate ester structures in polymer A is 10%~20%.

7. The negative electrode additive according to claim 1, characterized in that, B1 includes the structural formula shown in equation (2): ， In formula (2), c represents the degree of polymerization. Each occurrence of R3 independently includes either hydrogen or methyl groups, and each occurrence of R4 independently includes one or more of the following groups: Wherein, n5~n6 are each independently selected from positive integers from 1 to 4, R5 and R6 are each independently selected from substituted or unsubstituted cyclic carbonate structural groups, or R5 and R6 are each independently selected from substituted or unsubstituted cyclic sulfate structural groups, and any "*" indicates a linking site connected to an oxygen atom.

8. The negative electrode additive according to claim 7, characterized in that, R5 and R6 are each independently selected from any one of the following groups: ， In this context, any "*" indicates a connection site that connects to an oxygen atom.

9. The negative electrode additive according to claim 1, 7, or 8, characterized in that, The mass percentage of cyclic carbonate structures in polymer B is less than or equal to 100%, and / or The mass percentage of cyclic sulfate ester structures in polymer B is less than or equal to 50%.

10. The negative electrode additive according to claim 9, characterized in that, The mass percentage of cyclic carbonate structures in polymer B is 10%~20%, and / or The mass percentage of cyclic sulfate ester structures in polymer B is 5%~10%.

11. The negative electrode additive according to claim 1, characterized in that, Polymer A has a weight-average molecular weight of 100,000 to 1,000,000; and / or, The weight-average molecular weight of polymer B is 100,000 to 1,000,000.

12. The negative electrode additive according to claim 11, characterized in that, Polymer A has a weight-average molecular weight of 300,000 to 600,000; and / or, The weight-average molecular weight of polymer B is 300,000 to 600,000.

13. A negative electrode sheet, characterized in that, It includes a current collector and a negative electrode active material layer disposed on at least one surface of the current collector, the negative electrode active material layer including the negative electrode additive as described in any one of claims 1 to 12.

14. The negative electrode sheet according to claim 13, characterized in that, The negative electrode additive has a mass percentage content of 0.3% to 1.3% in the negative electrode active material layer.

15. The negative electrode sheet according to claim 14, characterized in that, The negative electrode additive has a mass percentage content of 0.3% to 0.8% in the negative electrode active material layer.

16. A secondary battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 13 to 15.

17. An electrical device, characterized in that, Includes at least one of the secondary batteries described in claim 16.

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