Negative electrode additive, negative electrode pole piece, secondary battery and electric device

Abstract

The invention relates to a negative electrode additive, a negative electrode pole piece, a secondary battery and an electric 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 copolymer containing 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, and the first charge-discharge efficiency and the cycle stability of a battery are improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a negative electrode additive, a negative electrode plate, a secondary battery and an electrical device. Background Art

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] In recent years, as the application scope of lithium-ion batteries becomes wider and wider, lithium-ion batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As lithium-ion batteries have made great progress, higher requirements have been put forward for their energy density, cycle performance and safety performance. The SEI film on the surface of graphite plays a vital role in the long-term cycle stability and safety performance of the battery cell. However, the SEI film will consume some lithium ions in the electrolyte during its formation. This part of dead lithium will cause the charge and discharge efficiency of the battery cell to decrease. In addition, the continuous aging of the SEI film during use causes the embedding of solvent molecules into the graphite, thereby damaging the electrode material and having a certain impact on the safety performance and service life of the battery cell.

[0004] Therefore, the development of 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] The present application provides a negative electrode additive, a negative electrode plate, a secondary battery and an electrical device. The negative electrode additive can form a SEI film on the surface of the negative electrode to improve battery performance.

[0006] In order to achieve the above object, the first aspect of the present application provides a negative electrode additive, including at least one of polymer A and polymer B,

[0007] 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;

[0008] The polymer B includes a homopolymer of B1, B1 includes an acrylate structure, and B1 further includes a side chain containing a cyclic carbonate structure or a cyclic sulfate structure.

[0009] Thus, the negative electrode additive of the present application is obtained in the form of a copolymerization of a polyacrylate segment with a cyclic carbonate segment or a cyclic sulfate segment, or in the form of a homopolymerization of a polyacrylate structure with a side chain containing a cyclic carbonate structure or a side chain containing a cyclic sulfate structure, to obtain a water-soluble high molecular polymer, which can be used for the formation of an SEI film on the surface of a negative electrode material of a battery, thereby improving the initial charge and discharge efficiency and cycle stability of the battery.

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

[0011]

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

[0013]

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

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

[0016]

[0017] Among them, b1~b3 are the polymerization degrees;

[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%, and can be optionally 10% to 30%; and / or

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

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

[0023]

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

[0025]

[0026] Wherein, n5~n6 are independently selected from positive integers of 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 "*" represents a connection site to an oxygen atom.

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

[0028]

[0029] Wherein, any "*" indicates a linking site to an oxygen atom.

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

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

[0032] In some embodiments of the present application, the weight average molecular weight of polymer A is 100,000 to 1,000,000, and can be 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 from 300,000 to 600,000.

[0034] The second aspect of the present application further provides a negative electrode plate, comprising a current collector and a negative electrode active material layer disposed on at least one surface of the current collector, wherein the negative electrode active material layer comprises the negative electrode additive.

[0035] Therefore, the present application improves the initial charge and discharge efficiency and cycle stability of the battery by adding the above-mentioned negative electrode additives to the negative electrode plate to participate in the formation of the SEI film.

[0036] In some embodiments of the present application, the mass percentage of the negative electrode additive in the negative electrode active material layer is 0.3% to 1.3%, and can be optionally 0.3% to 0.8%.

[0037] The third aspect of the present application provides a secondary battery, comprising the negative electrode plate.

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

[0039] A fourth aspect of the present application provides an electrical device, comprising the secondary battery of the first aspect of the present application.

[0040] The electric device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0041] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0043] Figure 1 It is a schematic diagram of a battery cell according to an embodiment of the present application.

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

[0045] Figure 3 It is a schematic diagram of a battery module according to one embodiment of the present application.

[0046] Figure 4 A schematic diagram of a battery pack according to an embodiment of the present application.

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

[0048] Figure 6 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0049] Description of reference numerals:

[0050] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0051] Below, some embodiments of the negative electrode additive, negative electrode plate, secondary battery and electric device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0052] "Scope" disclosed in the present application can be limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or excluding end values, and any end value can be included or not included independently, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 listed, and if the maximum range values ​​3,4 and 5 are also listed, the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation for these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed 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 the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0054] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0055] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0056] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0057] In the present application, in the open technical features or technical solutions described by the words "contain", "include", "comprise", etc., unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A not only includes a1, a2 and a3, but also includes other members". In the present application, unless otherwise specified, A (such as B) means 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", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

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

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

[0061] According to research, a stable and uniform SEI film is formed on the surface of the negative electrode active material, which has the ability to stably and reversibly insert / extract lithium during the battery cycle, and can effectively improve the electrochemical performance of the battery. At present, there are two main ways to construct the SEI film: (1) adding film-forming additives to the electrolyte. The common film-forming additives are mainly unsaturated ester additives (VC vinylene carbonate, VEC vinyl ethylene carbonate, FEC fluoroethylene carbonate), sulfur-containing additives (PS1,3-propane sultone, PES propylene-1,3 sultone, ES vinyl sulfite, DTD vinyl sulfate 1,3,2-dioxathiolane-2,2-dioxide), lithium salt additives (LiBOB, LiPO2F2) and inorganic compound additives (Na2CO3, Na2SO3), etc.; (2) constructing an artificial SEI film, such as CMC and SBR, which not only play a role in dispersion and bonding on the graphite negative electrode, but also help the formation of SEI when coated on the graphite surface during the first formation period.

[0062] In addition, traditional artificial SEI focuses on ionic cross-linked polymers and the development of new electrolytes or electrode additives, but there are few reports on the polymer route of film-forming additives, especially water-based or emulsion-based polymer materials applied to graphite ends.

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

[0064] 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;

[0065] The polymer B includes a homopolymer of B1, B1 includes an acrylate structure, and B1 further includes a side chain containing a cyclic carbonate structure or a cyclic sulfate structure.

[0066] The hydrophilic polyacrylate segment or hydrophilic polyacrylate structure in the above polymer can provide good bonding effect, play a role in coating and filming the negative electrode material, and make the geopolymer have good water solubility, and when added to the negative electrode film layer as a negative electrode additive, the dispersion is better, and the negative electrode material can be coated more evenly. The cyclic carbonate segment or cyclic sulfate segment, or the cyclic carbonate structure side chain or the side chain containing the cyclic sulfate structure, has good electrolyte wettability, which can improve the infiltration of the coated negative electrode material with the electrolyte, and further, it can also provide a good ion transmission path as a complexing site for lithium ions. Furthermore, during the battery cycle charge and discharge process, the cyclic carbonate segment or cyclic sulfate segment, or the cyclic carbonate structure side chain or the side chain containing the cyclic sulfate structure, can preferably undergo a ring-opening reaction, and grow in situ at the coating site to form an SEI film.

[0067] The structures of polymer A and polymer B in the negative electrode additive of the present application can be determined by conventional technical means in the art, for example, by infrared spectroscopy analysis of characteristic functional groups.

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

[0069]

[0070] In formula (1), a is 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] Wherein, n1 to n4 are independently selected from positive integers of 1 to 4, and any "*" represents a connection site to an oxygen atom.

[0073] By adjusting the length and type of the above R2 chain segment, the coating performance of the negative electrode additive on the negative electrode material can be further optimized. The longer the R2 chain length, the more conducive it is to improving the coating performance of the negative electrode binder on the negative electrode material.

[0074] In some optional embodiments, R2 is selected from

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

[0076]

[0077] b1 to b3 are the degrees of polymerization. b1, b2, and b3 are each independently selected from any positive number and may be the same or different.

[0078] In some optional embodiments, A2 includes any two of the above structures.

[0079] In some embodiments, A2 comprises

[0080] In some embodiments, A2 comprises

[0081] In some embodiments, the mass percentage of the cyclic carbonate structure in polymer A is less than or equal to 50%, and can be optionally 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 therebetween. The mass percentage of the cyclic carbonate structure in polymer A within this range is more conducive to regulating the water solubility of the synthetic polymer and the wettability of 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%, and can be optionally 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 therebetween. The mass percentage of the cyclic sulfate structure in polymer A is within this range, mainly to ensure the solubility of the monomer for reaction, and the solubility includes the mutual solubility of the cyclic sulfate monomer and the comonomer and the solubility of the cyclic sulfate monomer in the solvent, thereby ensuring the homogeneity of the monomer for reaction.

[0083] The structural features of the above-mentioned polymer A, such as the structural features of A1 and the structural features of A2, the mass percentage of the cyclic carbonate structure in polymer A, and the mass percentage of the cyclic sulfate structure can all be determined by conventional technical means in the art, such as characterizing the characteristic functional groups by infrared spectroscopy, determining the content by nuclear magnetic carbon spectrum and nuclear magnetic hydrogen spectrum, and then determining the content of each element by elemental analysis, and then reversely deriving the content of each characteristic structure. In some embodiments, the weight average molecular weight of polymer A is 100000 to 1000000, and can be optionally 300000 to 600000. Understandably, the weight average molecular weight of polymer A can be 100000, 200000, 300000, 400000, 500000, 600000, 700000, 800000, 900000, 1000000.

[0084] The weight average molecular weight of a polymer has a meaning known in the art and can be measured using instruments and methods known in the art, for example, the viscosity of its aqueous solution can be measured 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 a polymer can be estimated using the viscosity by the following formula:

[0085] η[Pa S]=8.91×10 -4 +1.30×10 -5 C 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 concentration of the polymer, M w is the molecular weight as described by Kulicke in Polymer, Vol. 37, No. 13, pp. 2723-2731, 1996.

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

[0088]

[0089] In formula (2), c is the degree of polymerization, each occurrence of each group independently includes hydrogen or methyl, and each occurrence of R4 independently includes one or more of the following groups:

[0090]

[0091] Wherein, n5~n6 are independently selected from positive integers of 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 "*" represents a connection site to an oxygen atom.

[0092] The larger the values ​​of n5 and n6 are, the longer the side chain branch of R4 is, 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 independently selected from any one of the following groups:

[0094]

[0095] Wherein, any "*" indicates a linking site 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 optionally 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 therebetween. The mass percentage of the cyclic carbonate structure in polymer B is within this range, which is more conducive to the wettability of the electrolyte. If the electrolyte solvent is carbonate, the cyclic carbonate at the tail end is more conducive to contact with the electrolyte, thereby preferentially reacting.

[0097] In some embodiments, the mass percentage of the cyclic sulfate structure in polymer B is less than or equal to 50%, and can be 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 therebetween.

[0098] The structural characteristics of the above-mentioned polymer B, such as the characteristic functional groups, the mass percentage of the cyclic carbonate structure in polymer B, and the mass percentage of the cyclic sulfate structure, can all be determined by conventional technical means in the art, such as characterizing the characteristic functional groups by infrared spectroscopy, determining the appropriate content by nuclear magnetic resonance carbon spectrum and nuclear magnetic resonance hydrogen spectrum, and then combining elemental analysis to determine the content of each element, and then reversely deduce the content of each characteristic structure.

[0099] In some embodiments, the weight average molecular weight of polymer B is 100000 to 1000000, and can be 300000 to 600000. Understandably, the weight average molecular weight of polymer B can be 100000, 200000, 300000, 400000, 500000, 600000, 700000, 800000, 900000, 1000000.

[0100] The weight average molecular weight of a polymer has a meaning known in the art and can be measured using instruments and methods known in the art, for example, the viscosity of its aqueous solution can be measured 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 a polymer can be estimated using the viscosity by the following formula:

[0101] η[Pa S]=8.91×10 -4 +1.30×10 -5 C 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 the viscosity, c is the concentration of the polymer, M w is the molecular weight as described by Kulicke in Polymer, Vol. 37, No. 13, pp. 2723-2731, 1996.

[0102] An example of the present application also provides a method for preparing the above-mentioned polymer A. The polymer A can be synthesized by free radical copolymerization of polymerizable monomers in the presence of an initiator. The polymerizable monomers include a first monomer and a second monomer, 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 polymerized monomers include acrylate monomers and monomers containing cyclic carbonate structures. In other embodiments, the polymerized monomers include acrylate monomers and monomers containing cyclic sulfate structures. In yet other embodiments, the polymerized monomers include 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 represented by the following formula (3):

[0105]

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

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

[0108]

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

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

[0111] In some embodiments, the second monomer includes one or more of vinyl carbonate, vinylene carbonate, and prop-1-enyl-1,3-sultone. In some embodiments, the second monomer includes vinylene carbonate and vinyl carbonate. In other embodiments, the second monomer includes vinylene carbonate and prop-1-enyl-1,3-sultone.

[0112] The above-mentioned "first monomer" and "second monomer" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first monomer" and "second monomer" only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

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

[0114] In some embodiments, the mass ratio of the initiator to the polymerization monomer is (0.01-2):100, optionally (0.01-0.5):100. Understandably, the mass ratio of the initiator to the polymerization 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 value therebetween. When the mass ratio of the initiator to the polymerization monomer is within this range, the polymer A has a more suitable number average molecular weight, and the polymerization monomer conversion rate and reaction efficiency are higher.

[0115] An example of the present application also provides a method for preparing the above polymer B. Polymer B can be obtained by synthesizing polymer B1 by free radical copolymerization of the above acrylate monomer in the presence of an initiator, and grafting a side chain containing a cyclic carbonate structure or a cyclic sulfate structure onto polymer B1 in the presence of a catalyst and a condensation agent.

[0116] In some embodiments, the grafting monomer is any one of the following formulae:

[0117]

[0118] The grafting catalyst and condensing agent of the present application are not particularly limited. Specific examples of catalysts may include, but are not limited to, 4-dimethylaminopyridine (DMAP), 4-pyrrolidinopyridine (PPY), 9-azajulolidine (9-AJ), triethylamine, triethanolamine, and combinations thereof. Specific examples of condensing agents may 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: condensation agent: grafting monomer is 1: (0.1-0.2): (0.1-1): (0.01-1). When the mass ratio of polymer to grafting monomer is within this range, polymer B has a more suitable grafting amount.

[0120] An example of the present application further provides a negative electrode plate, including a current collector and a negative electrode active material layer arranged on at least one surface of the current collector, and the negative electrode active material layer includes 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%, and can be 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 therebetween.

[0122] An example of the present application also provides a secondary battery, including the above-mentioned negative electrode plate.

[0123] An example of the present application further provides an electrical device, comprising at least one of the above-mentioned secondary batteries.

[0124] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0125] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0126] Positive electrode

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

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

[0129] In some of the 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 polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0130] In some of the embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional 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. Among them, examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. 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 referred to as NCM 333 )、LiNi 0.5 Co0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.85 Co 0.15 Al 0.05 O2.

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

[0132] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, 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 of the embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode 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 5000-25000mPa·s. When applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15-35 mg / cm 2The compaction density of the positive electrode sheet can be 3.0 to 3.6 g / cm 3 , can be selected as 3.3~3.5g / cm 3 .

[0134] Negative electrode

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

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

[0137] In some of the embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0138] In some of the embodiments, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. 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, lithium titanate, etc. The silicon-based material may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional 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 further 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 further include a conductive agent, which 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 of the embodiments, the negative electrode active material layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0142] In some of the embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the surface of the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode collector coated with the negative electrode slurry can be on a single surface of the negative electrode collector or on both surfaces of the negative electrode 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 2000-10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75-220g / m 2 The compaction density of the negative electrode sheet can be 1.0g / cm 3 ~1.8g / cm 3 .

[0143] Electrolytes

[0144] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The present application has no particular restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid.

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

[0146] In some of the 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 difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0147] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethylene carbonate One or more of fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0148] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high 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), trifluoromethylethylene carbonate (TFPC), and the like.

[0150] Isolation film

[0151] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0152] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane 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 isolation film has a thickness of 6-40 μm, and optionally 12-20 μm.

[0154] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0155] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0156] In some embodiments, the outer packaging of the secondary battery can be a hard 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 package, such as a bag-type soft package. The material of the soft package can be plastic, and further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

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

[0158] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0159] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The battery cell 5 is a square structure as an example.

[0160] In some of these embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may 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 shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0161] The secondary battery may be a battery module 4 or a battery pack 1 .

[0162] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0163] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0164] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0165] In some of the embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0166] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0167] In addition, the present application also provides an electrical device, which includes a secondary battery provided by the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, 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., but are not limited thereto.

[0168] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0169] Figure 6 The power consumption device 6 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0170] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0171] Example

[0172] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where the techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Where the manufacturers are not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially, or can be synthesized in a conventional manner by commercially available products.

[0173] In the following examples, the temperature conditions not specifically stated are all room temperature, which refers to 20°C to 30°C, and further, may be 25°C.

[0174] In the following examples, unless otherwise specified, the following raw materials can be obtained commercially or can be prepared by simple chemical modification of commercially available raw materials. The intermediate and final products synthesized in each example, including the surfactant of the present application, can be structurally identified by one or more of the following detection methods, including but not limited to: Fourier infrared (FT-IR) spectroscopy, ultraviolet spectroscopy, hydrogen spectrum nuclear magnetic resonance (1H NMR) method, X-ray diffraction (XRD) method, gel permeation chromatography (GPC) method, high performance liquid chromatography (HPLC) method, mass spectrometry, etc. The sample preparation methods and test methods of these test 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 target compound structural formula, it is possible to combine the test results of the aforementioned test methods to determine whether the compound of the target structure has been synthesized. Taking 1H NMR as an example, the structure can be identified according to the peak position, peak shape, integrated area ratio and other parameters in the hydrogen spectrum nuclear magnetic spectrum to confirm whether a specific group disappears or appears.

[0175] In the following examples, unless otherwise specified, DMAP is 4-dimethylaminopyridine, 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°C water bath, and heated with stirring under a nitrogen atmosphere. 5g of vinyl carbonate (the first monomer) and 95g of β-acryloxypropionic acid (the second monomer) were dissolved in 50g of DI water, and then added dropwise to the flask within one hour, and reacted for 5h to obtain polymer A. The entire reaction was placed under a nitrogen atmosphere.

[0179] The preparation methods of Preparation Examples 2 to 23 are similar to the preparation method of Preparation Example 1. The difference is that the relevant parameters such as the monomer, initiator and its amount are adjusted. The specific parameters are shown 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°C water bath. The mixture was stirred and heated under nitrogen. 100g of β-acryloxypropionic acid was dissolved in 50g of THF and then added dropwise to the flask within one hour for 3h. The reaction was carried out under nitrogen protection. After the reaction was completed, the mixture was dried under vacuum and the solvent was removed 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]dioxol-2-one were added in sequence. The mixture was reacted at room temperature for 24h, solid impurities were removed by filtration, vacuum distillation was performed, and vacuum drying was performed to obtain a solid product, namely polymer B.

[0185] The preparation methods of Preparation Examples 25 to 37 are similar to the preparation method of Preparation Example 24. The difference is that the relevant parameters such as polymer B1, grafting monomer and its amount are adjusted. The specific parameters are shown 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 as a negative electrode active material, carbon black as a conductive agent, sodium carboxymethyl cellulose as a thickener, and styrene-butadiene rubber as an adhesive were mixed in a mass ratio of 0.3:97:0.4:0.3:1, and deionized water was added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry was evenly coated on both sides of the copper foil; the copper foil was dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then supercooled pressed and cut to obtain a negative electrode sheet, wherein the coating amount per unit area on both sides was 0.17 g / 1540.25 mm 2 .

[0192] 2) Snap-on assembly

[0193] The negative electrode sheet is used as the positive electrode, the metal lithium sheet is used as the negative electrode, the nickel foam is used as the filler, the PP film is used as the separator, 1 mol / l LiPF6, and the combined solvent EC / DEC / DMC=1:1:1 (volume ratio) are used as the electrolyte, and the CR2430 button battery shell is used for assembly. The assembly is carried out according to the negative electrode shell-nickel foam-lithium sheet-electrolyte (30uL)-separator-electrolyte (30uL)-negative electrode sheet-positive electrode shell, and sealed with 650PSI pressure.

[0194] The secondary batteries of Examples 2 to 37 were prepared in a similar manner to the secondary battery of Example 1, but the polymers of the corresponding preparation examples were used.

[0195] Embodiments 38 to 40

[0196] The preparation methods of the secondary batteries of Examples 38 to 40 are similar to those of the secondary battery of Example 1, except that the amounts of polymer added to the negative electrode plates (based on dry weight, excluding solvent) are 0.3%, 0.8%, and 1.4%, respectively.

[0197] Comparative Example 1

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

[0199] Test Method

[0200] 1. Number average molecular weight

[0201] The test instrument is a Waters 1515 gel permeation chromatograph from PL Corporation of the United States, equipped with a Waters 2695 separation unit, a Waters 2414 differential refractometer and a CORTECS 2.7 μm chromatographic column, and the test temperature is 20°C. DIW is used as the mobile phase, the flow rate is 1.0 mL / min, and the sample concentration is 10 mg / mL of aqueous solution, which is filtered through a 0.22 μm polytetrafluoroethylene membrane before injection.

[0202] 2. Viscosity

[0203] The polymer synthesized in this patent is prepared into a 6% aqueous solution, and the specific viscosity is tested using an Anton Paar viscometer. The test process is as follows: first use the 3# rotor to test. If the viscosity is <10000mPa.s at 12rpm, use the test result. If the viscosity is >10000mPa.s at 12rpm, continue to use the 4# rotor to measure the viscosity at a speed of 12rpm until the viscosity reaches below 10000mPa.s.

[0204] 3. Liquid absorption rate

[0205] The polymer described in this patent is cast into a film in a container. After complete drying, a certain weight (w0) of the film sample is placed in the above-mentioned 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 weighed as (w1). The liquid absorption rate can be calculated as (w1-w0) / w0*100%.

[0206] 4. Power withholding assessment

[0207] Button test: Use 5V / 1mA blue electric tester to conduct the first efficiency test. Place the prepared button battery in a constant temperature environment of 25℃ for 5 hours, discharge to 0.005V at 0.05C constant current, discharge to 0.005V at 50uA constant current, then stand for 5 minutes, discharge to 0.005V at 10uA constant current, stand for 5 minutes, charge to 2V at 0.1C constant voltage, stand for 5 minutes, and then the test ends. First coulomb efficiency = first charge gram capacity / first discharge gram capacity, gram capacity = capacity / mass of active material.

[0208] Button power high temperature cycle test: The prepared button battery was placed in a constant temperature environment of 25℃ for 3 hours, charged to 2V at 0.33C constant current, charged to 2V at 0.1C constant current, charged to 2V at 100uA constant current, then allowed to stand for 10 minutes, discharged to 0.005V at 0.33C constant current, discharged to 0.005V at 0.1C constant current, charged to 0.005V at 0.05C constant current, charged to 0.005V at 50uA constant current, then allowed to stand for 10 minutes, charged to 2V at 0.33C, allowed to stand for 5 minutes, and then cycled 100 times from the step of discharging at 0.33C constant current to 0.005V.

[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 the cyclic carbonate structure and the cyclic sulfonate structure in the polymer of the present application increases, that is, when the content of the second monomer and the grafted monomer increases, the molecular weight under the same conditions decreases. This is due to the decrease in the solubility and miscibility of the corresponding monomers during the polymerization reaction. At the same time, when the content of the cyclic carbonate structure and the cyclic sulfonate structure in the polymer increases, its liquid absorption rate increases significantly, and the color change of the electrolyte can be observed, indicating that the polymer is insoluble in the electrolyte when the content of the cyclic carbonate and the cyclic sulfonate is low, and when its content increases, due to the structure similar to the electrolyte solvent, the polymer wettability increases, but there is also a risk of dissolution, and its cycle performance shows a significant attenuation (for example, Example 12).

[0215] Secondly, when the content of the second monomer and the grafted monomer is low (that is, when the content of the cyclic carbonate structure and the cyclic sulfonate structure in the polymer is low), the effect on the first effect and the change in gram capacity is not significant, and with the increase of its content, the first effect of the graphite on the negative electrode side can be effectively improved, but the first effect of the cyclic carbonate structure content in the polymer decreases after continuing to increase to a certain extent (such as Examples 8 to 12, with the increase of the mass content of the second monomer, the first effect value of the battery increases, and when the mass content of the second monomer reaches 20%, the first effect value decreases when its content increases further). This may be due to the increase in the content of the cyclic carbonate structure, and its polymer is dissolved in the electrolyte, so the SEI film formation at the graphite end has been consuming lithium ions, resulting in a decrease in the first effect. Similar results can be obtained from the cycle data. The capacity cycle retention rate of the polymer with a high cyclic carbonate structure content shows a decreasing trend. It can be clearly seen from Examples 20 to 23 that high molecular weight polymers have little effect on the first effect and capacity, and for cycles, high molecular weight polymers may show better bonding ability, so the cycle retention rate is higher. Comparing Comparative Example 1 with Examples 1-40, the first coulombic efficiencies of Examples 1 to 40 are all higher than those of Comparative Example 1, which can effectively prove that the addition of polymer can improve the first efficiency of the graphite end material.

[0216] It should be noted that the data in Table 3 above show that the improvement in the first coulombic efficiency of Example 4 compared with the first coulombic efficiency of Comparative Example 1 is lower than that of other embodiments, but it still has great advantages in terms of cycle capacity retention rate.

[0217] The above description of various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced to each other, and for the sake of brevity, they will not be repeated herein.

[0218] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode additive, characterized in that: comprising at least one of polymer A and polymer B, 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 includes a homopolymer of B1, B1 includes an acrylate structure, and B1 further includes a side chain containing a cyclic carbonate structure or a cyclic sulfate structure.

2. The negative electrode additive according to claim 1, characterized in that A1 includes the structural formula shown in formula (1): In formula (1), a is the degree of polymerization, R1 includes hydrogen or methyl, and R2 includes hydrogen or any one of the following groups: Wherein, n1-n4 are independently selected from positive integers of 1-4, and any "*" represents a connection site to an oxygen atom.

3. The negative electrode additive according to claim 1 or 2, characterized in that: A2 includes one or more of the following structural formulas: Among them, b1~b3 are the polymerization degrees; Optionally, A2 includes Optionally, A2 includes 4. The negative electrode additive according to any one of claims 1 to 3, characterized in that: The mass percentage of the cyclic carbonate structure in polymer A is less than or equal to 50%, and can be optionally 10% to 30%; and / or The mass percentage of the cyclic sulfate structure in polymer A is less than or equal to 30%, and can be optionally 10% to 20%.

5. The negative electrode additive according to claim 1, characterized in that: B1 includes the structural formula shown in formula (2): In formula (2), c is the degree of polymerization, each occurrence of R3 independently includes hydrogen or methyl, and each occurrence of R4 independently includes one or more of the following groups: Wherein, n5-n6 are independently selected from positive integers of 1-4, 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 "*" represents a connection site to an oxygen atom.

6. The negative electrode additive according to claim 5, characterized in that: R5 and R6 are independently selected from any one of the following groups: Wherein, any "*" indicates a connection site to an oxygen atom.

7. The negative electrode additive according to claim 1, 5 or 6, characterized in that: The mass percentage of the cyclic carbonate structure in polymer B is less than or equal to 100%, and can be 10% to 20%, and / or The mass percentage of the cyclic sulfate structure in polymer B is less than or equal to 50%, and can be optionally 5% to 10%.

8. The negative electrode additive according to claim 1, characterized in that: The weight average molecular weight of polymer A is 100,000 to 1,000,000, and can be 300,000 to 600,000; and / or, The weight average molecular weight of polymer B is 100,000 to 1,000,000, and can be selected from 300,000 to 600,000.

9. A negative electrode plate, characterized in that: The invention comprises a current collector and a negative electrode active material layer arranged on at least one surface of the current collector, wherein the negative electrode active material layer comprises the negative electrode additive according to any one of claims 1 to 8.

10. The negative electrode sheet according to claim 9, characterized in that: The mass percentage of the negative electrode additive in the negative electrode active material layer is 0.3% to 1.3%, and can be optionally 0.3% to 0.8%.

11. A secondary battery, characterized in that: Including the negative electrode sheet as described in claim 9 or 10.

12. An electrical device, characterized in that: Comprising at least one of the secondary batteries described in claim 11.

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