Polymer, preparation method, negative pole piece, secondary battery and electric device

Abstract

The invention provides a polymer, a preparation method, a negative pole piece, a secondary battery and an electric device. The polymer contains a structural unit derived from an unsaturated carboxylic acid monomer, a structural unit derived from an unsaturated cyano monomer and a structural unit derived from a flexible monomer, and the glass transition temperature of the flexible monomer is-60 DEG C to 0 DEG C, and can be-55 DEG C to-15 DEG C. The polymer can reduce warping of a pole piece and widen a processing window of the pole piece.

Description

Polymer, preparation method, negative electrode sheet, secondary battery and electrical device Technical Field

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

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] Non-fluorinated polymer binders containing unsaturated carboxylic acid monomers are commonly used as negative electrode binders in secondary batteries due to their low cost, strong adhesion, and good water solubility. However, they suffer from a narrow processing window and difficulty meeting the requirements for high-performance active materials, which greatly limits their application. Therefore, existing polymer binders still need to be improved.

[0004] Summary of the Invention

[0005] The present application is made in view of the above-mentioned problems, and its purpose is to provide a polymer that can improve the warping phenomenon of the pole piece during the preparation process and widen the processing window of the pole piece.

[0006] In order to achieve the above-mentioned purpose, the present application provides a polymer, which contains structural units derived from unsaturated carboxylic acid monomers, structural units derived from unsaturated cyano monomers and structural units derived from flexible monomers, and the glass transition temperature of the flexible monomer is -60°C to 0°C, and can be optionally -55°C to -15°C.

[0007] The polymer contains structural units derived from unsaturated carboxylic acid monomers, which can improve the water solubility of the polymer and provide ion transmission channels for lithium ions, which is beneficial to the improvement of battery kinetic performance; the structural units derived from unsaturated cyano monomers can improve the bonding strength between the polymer and the active material and current collector; the structural units derived from flexible monomers can effectively lower the glass transition temperature of the polymer, improve the flexibility of the polymer, and reduce the uneven shrinkage and stress concentration of the polymer during the slurry drying process, thereby alleviating the degree of pole piece warping, widening the pole piece processing window, and improving the pole piece processability and quality stability.

[0008] In any embodiment, the flexible monomer comprises the structure shown in Formula I,

[0009] wherein R1, R2, and R3 are each independently hydrogen or substituted or unsubstituted C 1-5 Alkyl, R4 including C 1-5Hydroxyalkyl, C 1-5 Alkyl and C 1-5 One or more alkoxy groups.

[0010] In any embodiment, the unsaturated carboxylic acid monomer comprises a structure shown in Formula II, and the unsaturated cyano monomer comprises a structure shown in Formula III.

[0011] Among them, R5, R6, R7, R8, R9, R 10 Each independently includes hydrogen or substituted or unsubstituted C 1-5 alkyl.

[0012] In any embodiment, the polymer further comprises a structural unit derived from an unsaturated amide monomer, wherein the unsaturated amide monomer comprises a structure represented by Formula IV,

[0013] Among them, R 11 、R 12 、R 13 、R 14 、R 15 Each independently includes hydrogen or substituted or unsubstituted C 1-5 alkyl.

[0014] When the polymer contains structural units derived from unsaturated amide monomers, the amide groups in the polymer will dissociate after dissolving in water, making the polymer negatively charged. There is electrostatic repulsion between different chains in the polymer, which allows the polymer to stretch in the solution and allow the chains to entangle with each other, thereby improving the viscosity of the negative electrode slurry, enhancing the stability of the negative electrode slurry, and further optimizing the processing performance of the electrode.

[0015] In any embodiment, the flexible monomer includes one or more of hydroxyethyl acrylate, 4-hydroxybutyl acrylate, hydroxybutyl acrylate, ethyl acrylate, and n-butyl acrylate.

[0016] These flexible monomers possess both a low glass transition temperature and good compatibility with structural units derived from unsaturated carboxylic acid monomers and structural units derived from unsaturated cyano monomers, effectively lowering the polymer's glass transition temperature. Furthermore, these flexible monomers, through their ester, hydroxyl, and alkoxy groups, can effectively reduce the surface tension of the slurry, further minimizing electrode warpage and improving electrode processability and quality stability.

[0017] In any embodiment, the flexible monomer includes at least two of hydroxyethyl acrylate, 4-hydroxybutyl acrylate, hydroxybutyl acrylate, ethyl acrylate, and n-butyl acrylate.

[0018] By combining two different types of flexible monomers, it is possible to further improve the flexibility of the polymer, broaden the processing window and application scenarios of the polymer while taking into account the polymer bonding performance and suppressing the rebound of the electrode.

[0019] In any embodiment, the unsaturated carboxylic acid monomer includes one or more of acrylic acid, methacrylic acid, ethacrylic acid, and crotonic acid; the unsaturated cyano monomer includes one or more of acrylonitrile, crotonenitrile, methacrylonitrile, and ethacrylonitrile; and the unsaturated amide monomer includes one or more of acrylamide, methacrylamide, N,N-dimethylacrylamide, and N-methylacrylamide.

[0020] In any embodiment, based on the total molar number of all structural units in the polymer, the molar proportion of the structural unit derived from the flexible monomer is 5% to 50%, optionally 20% to 35%.

[0021] Polymers with a molar percentage of 5% to 50% of flexible monomer structural units have a lower glass transition temperature, which can alleviate pole piece warping and improve pole piece processing performance. Polymers with a molar percentage of 20% to 35% of flexible monomer structural units can balance the flexibility and adhesion of the polymer, reducing the risk of cold pressing and cracking of the pole piece during processing and wrinkling and debonding at the full charge interface, thereby improving production efficiency and yield rate. They can also maintain high adhesion and low rebound rate of the pole piece, thereby comprehensively improving the cycle stability of the battery.

[0022] In any embodiment, based on the total moles of all structural units in the polymer, the molar proportion of the structural units derived from the unsaturated carboxylic acid monomer is 10% to 60%, optionally 30% to 50%; and / or the molar proportion of the structural units derived from the unsaturated cyano monomer is 10% to 60%, optionally 15% to 45%; and / or the molar proportion of the structural units derived from the unsaturated amide monomer is 0% to 30%, optionally 5% to 20%.

[0023] The polymer having the structural unit within the above content range can improve flexibility while taking into account both adhesion and solubility.

[0024] In any embodiment, the glass transition temperature of the polymer is 40°C to 105°C, and optionally 40°C to 90°C.

[0025] When the polymer's glass transition temperature is between 40°C and 105°C, it exhibits excellent flexibility, resulting in low warpage and good processing performance for the electrode. Polymers with a glass transition temperature of 40°C to 90°C can further reduce edge cracking during battery rolling, further expanding the electrode processing window and improving its processing performance.

[0026] In any embodiment, the weight average molecular weight of the polymer is 500,000 to 2,000,000, and can be optionally 800,000 to 1,500,000.

[0027] When the weight-average molecular weight of the polymer is between 500,000 and 2,000,000, the viscosity of the aqueous solution at a certain solid content of the polymer is within an appropriate range, the electrode has good processing and bonding properties, and the battery has good cycle stability.

[0028] In any embodiment, the viscosity of an aqueous solution with a solid content of 6 wt % obtained by dissolving the polymer in deionized water is 8000 MPa·s to 30000 MPa·s, and can optionally be 10000 MPa·s to 20000 MPa·s.

[0029] When the viscosity of an aqueous solution with a solid content of 6 wt % prepared by dissolving the polymer in deionized water is within the above range, the slurry has stability and processability, the pole piece has excellent processability and bonding properties, and the battery has good cycle stability.

[0030] In any embodiment, the polymer includes at least one of acrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-hydroxyethyl acrylate copolymer, methacrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-methacrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-methacrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-hydroxybutyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-hydroxypropyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate-hydroxybutyl acrylate copolymer, and acrylic acid-acrylonitrile-hydroxyethyl acrylate-hydroxybutyl acrylate copolymer.

[0031] The second aspect of the present application provides a method for preparing a polymer, wherein raw materials including a flexible monomer, an unsaturated carboxylic acid monomer, and an unsaturated cyano monomer are polymerized under polymerizable conditions to prepare a polymer, wherein the glass transition temperature of the flexible monomer is -60°C to -0°C, and can be optionally -55°C to -15°C.

[0032] In any embodiment, the preparation method is specifically: polymerizing an initiator, a flexible monomer represented by formula I, an unsaturated carboxylic acid monomer represented by formula II, an unsaturated cyano monomer represented by formula III, and an unsaturated amide monomer represented by formula IV in an aqueous solvent;

[0033] Among them, R1, R2, R3, R5, R6, R7, R8, R9, R 10 、R 11 、R 12、R 13 、R 14 、R 15 Each independently includes hydrogen or substituted or unsubstituted C 1-5 Alkyl, R4 including C 1-5 Hydroxyalkyl, C 1-5 Alkyl and C 1-5 The solution polymerization method can be used to prepare the polymer, which can well control the reaction temperature and is conducive to the preparation of polymers with moderate molecular weight. In addition, the polymers synthesized by the solution polymerization method have good water solubility.

[0034] In any embodiment, the initiator comprises an inorganic peroxide initiator, and the inorganic peroxide initiator comprises any one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0035] In any embodiment, the mass of the initiator is 0.01% to 0.1% of the total mass of the flexible monomer, the unsaturated carboxylic acid monomer, the unsaturated cyano monomer, and the unsaturated amide monomer, and can be optionally 0.03% to 0.08%.

[0036] When the amount of the initiator is within the above range, the polymerization reaction rate is moderate, the system is heated evenly, the gel effect is weakened, and the polymer is polymerized evenly, thereby obtaining a polymer with a weight average molecular weight within an appropriate range.

[0037] In any embodiment, the polymerization reaction satisfies at least one of the following conditions:

[0038] (1) The reaction environment of the polymerization reaction is a water-insoluble gas atmosphere;

[0039] (2) The reaction temperature of the polymerization reaction is 60° C. to 100° C.;

[0040] (3) The stirring speed of the polymerization reaction is 200 rpm to 800 rpm;

[0041] (4) The reaction time of the polymerization reaction is 8 hours to 12 hours.

[0042] When the polymerization temperature is between 60°C and 100°C, the reactivity of free radicals in the solution is within an appropriate range, and the rates of chain transfer reaction and chain growth reaction are moderate, thereby making the molecular weight of the polymer within an appropriate range.

[0043] When the polymerization reaction time is 8 hours to 12 hours, the conversion rate of the monomer is within an appropriate range and the polymer has an appropriate weight average molecular weight.

[0044] In some embodiments, the water-insoluble gas is selected from one or more of nitrogen, oxygen, hydrogen, and methane.

[0045] A third aspect of the present application provides a negative electrode plate, comprising a negative electrode film layer, the negative electrode film layer comprising a binder, and the binder comprising a polymer in any embodiment or a polymer prepared by the preparation method in any embodiment.

[0046] In any embodiment, the binder accounts for 0.5% to 3% by mass, and optionally 1% to 2% by mass, based on the total mass of the negative electrode film layer.

[0047] Existing polymers containing unsaturated carboxylic acid monomers can cause severe warping and edge cracking in electrode plates at a 1% addition, making it difficult to meet production requirements. The polymers provided in the embodiments of this application can still achieve good processing properties in electrode plates at an addition level of up to 3%. Therefore, increasing the amount of binder can further improve the cycling stability of secondary batteries.

[0048] In any embodiment, the warping height of the negative electrode plate is 0 mm to 20 mm.

[0049] The polymer has a low glass transition temperature and high flexibility, which can effectively improve the uneven shrinkage and stress concentration of the polymer during the drying process and alleviate the warping of the electrode.

[0050] In any embodiment, the negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, and silicon-based materials.

[0051] Silicon-based materials have high capacity and can significantly increase the energy density of batteries. However, silicon-based materials have a large expansion rate during the cycle, which can easily cause uneven stress on the pole pieces, resulting in phenomena such as pole piece wrinkling. Since the stress at the inner corners of the battery cell is more severe, peeling, bubbling, cracking, and even membrane peeling may occur. The polymers provided in the embodiments of the present application can also be applied to silicon-based systems, reducing the uneven stress distribution of the pole pieces, effectively improving the peeling, bubbling, and cracking of the pole pieces when fully charged, and thus improving the cycle stability of the battery.

[0052] In any embodiment, the compacted density of the negative electrode sheet is 1.45 g / cm 3 ~1.95g / cm 3 .

[0053] Negative electrodes with high compaction density are more susceptible to brittle fracture during cycling, and even risk cracking during hot pressing after winding. The polymers provided in the embodiments of this application can also be applied to high-voltage dense electrodes, improving their flexibility and reducing the probability of cracking and brittle fracture during production and use.

[0054] The fourth aspect of the present application provides a secondary battery, comprising the negative electrode sheet of the third aspect of the present application.

[0055] A fifth aspect of the present application provides an electrical device comprising the secondary battery of the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0057] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .

[0058] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0059] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0060] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0061] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0062] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0063] Below, the embodiments of the polymer, preparation method, negative electrode plate, secondary battery and electrical device of the present application are described in detail with appropriate reference to the accompanying 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 structures 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 description 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.

[0064] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and 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 special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this 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 all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0065] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0066] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0067] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0068] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0069] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0070] Non-fluorinated polymers containing unsaturated carboxylic acid monomers have the advantages of low cost, strong adhesion, and good water solubility. In recent years, their application in secondary batteries has been widely studied. To meet the requirements for electrode adhesion, these binders often use large amounts of unsaturated carboxylic acid monomers and unsaturated monomers containing cyano groups as copolymer units, leveraging the interaction between the carboxyl and cyano groups and the current collector to improve electrode adhesion. However, practice has shown that slurries containing such polymers are prone to causing significant warping of the electrode during the coating and drying process, affecting the subsequent rolling and stability of the electrode quality.

[0071] [polymer]

[0072] Based on this, the present application provides a polymer, which contains structural units derived from unsaturated carboxylic acid monomers, structural units derived from unsaturated cyano monomers and structural units derived from flexible monomers, and the glass transition temperature of the flexible monomer is -60°C to 0°C, and can be optionally -55°C to -15°C.

[0073] As used herein, the term "polymer" includes, on the one hand, a collection of chemically homogeneous macromolecules prepared by polymerization, but differing in degree of polymerization, molar mass, and chain length. The term also includes derivatives of such collections of macromolecules formed by polymerization, i.e., compounds that can be obtained by reaction, for example, addition or substitution, of functional groups in the aforementioned macromolecules and that can be chemically homogeneous or chemically heterogeneous.

[0074] As used herein, the term "unsaturated carboxylic acid monomer" refers to an unsaturated monomer containing a -COOH group in the molecule.

[0075] As used herein, the term "unsaturated cyano monomer" refers to an unsaturated monomer containing a -CN group in the molecule.

[0076] In this article, the term "flexible monomer" refers to a monomer whose homopolymer has a low glass transition temperature and can improve the brittleness of the polymer and enhance the flexibility of the polymer.

[0077] In this article, the term "glass transition temperature" refers to the temperature at which a polymer transitions from a glassy state to a highly elastic state, abbreviated as Tg. The glass transition temperature of a flexible monomer is generally determined by measuring the glass transition temperature of the flexible monomer homopolymer or by consulting reference materials.

[0078] In some embodiments, the flexible monomer has a glass transition temperature of -60°C, -55°C, -50°C, -45°C, -40°C, -35°C, -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, or any value therebetween.

[0079] The polymer contains structural units derived from unsaturated carboxylic acid monomers, which can improve the water solubility of the polymer and provide ion transmission channels for lithium ions, which is beneficial to the improvement of battery kinetic performance; the structural units derived from unsaturated cyano monomers can improve the bonding strength between the polymer and the active material and current collector; the structural units derived from flexible monomers can effectively lower the glass transition temperature of the polymer, improve the flexibility of the polymer, and reduce the uneven shrinkage and stress concentration of the polymer during the slurry drying process, thereby alleviating the degree of pole piece warping, widening the pole piece processing window, and improving the pole piece processability and quality stability.

[0080] In some embodiments, the flexible monomer comprises a structure shown in Formula I,

[0081] wherein R1, R2, and R3 are each independently hydrogen or substituted or unsubstituted C 1-5 Alkyl, R4 including C 1-5 Hydroxyalkyl, C 1-5 Alkyl and C 1-5 One or more alkoxy groups.

[0082] As used herein, the term "substituted" refers to a compound or chemical moiety in which at least one hydrogen atom is replaced by another chemical moiety, wherein the substituents are each independently selected from the group consisting of hydroxyl, thiol, amino, cyano, nitro, aldehyde, halogen, alkenyl, alkynyl, aryl, heteroaryl, C 1-6 Alkyl, C 1-6 Alkoxy.

[0083] In this article, the term “C 1-5 "Hydroxyalkyl" refers to a group consisting of an alkyl group and a hydroxy group, with no unsaturation in the group, having from one to five carbon atoms, and attached to the rest of the molecule by a single bond, including but not limited to hydroxymethyl, hydroxyethyl, hydroxypropyl, and 4-hydroxybutyl.

[0084] In this article, the term “C 1-5 "Alkyl" refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, having from one to five carbon atoms, and attached to the remainder of the molecule by a single bond, including but not limited to methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, idenebutyl, and pentyl.

[0085] In this article, the term “C 1-5 "Alkoxy" refers to a group consisting of an alkyl group and an oxygen atom, has from one to five carbon atoms, and is attached to the rest of the molecule by a single bond. Common examples include methoxy (CH3O-), ethoxy (C2H5O-), propoxy (C3H7O-), etc.

[0086] In some embodiments, R1, R2, and R3 each independently comprise hydrogen or C 1-5 Alkyl, R4 includes C 1-4 Hydroxyalkyl.

[0087] In some embodiments, the flexible monomer includes one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, ethyl acrylate, and n-butyl acrylate.

[0088] In some embodiments, the flexible monomer includes one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, and 4-hydroxybutyl acrylate.

[0089] These flexible monomers possess both a low glass transition temperature and good compatibility with structural units derived from unsaturated carboxylic acid monomers and structural units derived from unsaturated cyano monomers, effectively lowering the polymer's glass transition temperature. Furthermore, these flexible monomers, through their ester, hydroxyl, and alkoxy groups, can effectively reduce the surface tension of the slurry, further minimizing electrode warpage and improving electrode processability and quality stability.

[0090] In some embodiments, the flexible monomer includes at least two of hydroxyethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, ethyl acrylate, and n-butyl acrylate.

[0091] In some embodiments, the flexible monomer includes at least two of hydroxyethyl acrylate, hydroxypropyl acrylate, and 4-hydroxybutyl acrylate.

[0092] By combining two different types of flexible monomers, it is possible to further improve the flexibility of the polymer, broaden the processing window and application scenarios of the polymer while taking into account the polymer bonding performance and suppressing the rebound of the electrode.

[0093] In some embodiments, the unsaturated carboxylic acid monomer comprises a structure shown in Formula II, and the unsaturated cyano monomer comprises a structure shown in Formula III.

[0094] Among them, R5, R6, R7, R8, R9, R 10 Each independently includes hydrogen or substituted or unsubstituted C 1-5 alkyl.

[0095] In some embodiments, the unsaturated carboxylic acid monomer includes one or more of acrylic acid, methacrylic acid, ethacrylic acid, and crotonic acid.

[0096] In some embodiments, the unsaturated cyano monomer comprises one or more of acrylonitrile, crotononitrile, methacrylonitrile, and ethacrylonitrile. In some embodiments, the polymer further comprises a structural unit derived from an unsaturated amide monomer, wherein the unsaturated amide monomer comprises a structure represented by Formula IV,

[0097] Among them, R 11 、R 12 、R 13 、R 14 、R 15 Each independently includes hydrogen or substituted or unsubstituted C 1-5 alkyl.

[0098] As used herein, the term "unsaturated amide monomer" refers to an unsaturated monomer containing -CO-N- in its molecule.

[0099] When the polymer contains structural units derived from unsaturated amide monomers, the amide groups in the polymer will dissociate after dissolving in water, making the polymer negatively charged. There is electrostatic repulsion between different chains in the polymer, which allows the polymer to stretch in the solution and allow the chains to entangle with each other, thereby improving the viscosity of the negative electrode slurry, enhancing the stability of the negative electrode slurry, and further optimizing the processing performance of the electrode.

[0100] In some embodiments, the unsaturated amide monomer includes one or more of acrylamide, methacrylamide, N,N-dimethylacrylamide, and N-methylacrylamide.

[0101] In some embodiments, based on the total molar number of all structural units in the polymer, the molar proportion of the structural unit derived from the flexible monomer is 5% to 50%, optionally 20% to 35%.

[0102] In some embodiments, the molar proportion of the structural unit derived from the flexible monomer based on the total moles of all structural units in the polymer is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any value therebetween.

[0103] Polymers with a molar percentage of 5% to 50% of flexible monomer structural units have a lower glass transition temperature, which can alleviate pole piece warping and improve pole piece processing performance. Polymers with a molar percentage of 20% to 35% of flexible monomer structural units can balance the flexibility and adhesion of the polymer, reducing the risk of cold pressing and cracking of the pole piece during processing and wrinkling and debonding at the full charge interface, thereby improving production efficiency and yield rate. They can also maintain high adhesion and low rebound rate of the pole piece, thereby comprehensively improving the cycle stability of the battery.

[0104] In some embodiments, based on the total moles of all structural units in the polymer, the molar proportion of the structural units derived from the unsaturated carboxylic acid monomer is 10% to 60%, optionally 30% to 50%; and / or the molar proportion of the structural units derived from the unsaturated cyano monomer is 10% to 60%, optionally 15% to 45%; and / or the molar proportion of the structural units derived from the unsaturated amide monomer is 0% to 30%, optionally 5% to 20%.

[0105] In some embodiments, the molar proportion of the structural units derived from the unsaturated carboxylic acid monomer is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or any value therebetween, based on the total moles of all structural units in the polymer.

[0106] In some embodiments, the molar proportion of the structural unit derived from the unsaturated cyano monomer based on the total moles of all structural units in the polymer is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or any value therebetween.

[0107] In some embodiments, the molar proportion of the structural unit derived from the unsaturated amide monomer is 0%, 5%, 10%, 15%, 20%, 25%, 30% or any value therebetween based on the total moles of all structural units in the polymer.

[0108] The polymer containing the structural unit within the above content range can improve flexibility while taking into account both adhesion and solubility. In some embodiments, the glass transition temperature of the polymer is 40°C to 105°C, and can be optionally 40°C to 90°C.

[0109] In this application, the glass transition temperature of a polymer can be tested using methods known in the art, such as a TA differential scanning calorimeter (Q1000). A 6-9 g polymer sample is heated from room temperature to 200°C at a heating rate of 10°C / min, then held at 200°C for 3 hours to eliminate thermal history. After cooling, the sample is heated again from room temperature to 200°C at a heating rate of 10°C / min. The differential scanning calorimetry curve obtained from this scan is analyzed to determine the polymer's glass transition temperature (in °C).

[0110] In some embodiments, the polymer has a glass transition temperature of 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 105°C, or any value therebetween.

[0111] When the polymer's glass transition temperature is within the above range, the polymer exhibits excellent flexibility, resulting in low warpage and good processing performance for the electrode. Polymers with a glass transition temperature of 40°C to 90°C can further reduce edge cracking during battery rolling, further expanding the electrode processing window and improving electrode processing performance.

[0112] In some embodiments, the weight average molecular weight of the polymer is 500,000 to 2,000,000, and can be optionally 800,000 to 1,500,000.

[0113] As used herein, the term "weight average molecular weight" refers to the sum of the weight fractions of molecules of different molecular weights in a polymer multiplied by their corresponding molecular weights.

[0114] In the present application, the weight-average molecular weight of the polymer can be tested using methods known in the art, such as gel chromatography, such as using a Waters 2695 Isocratic HPLC gel chromatograph (differential refractive index detector 2141). In some embodiments, the testing method is to use a polystyrene solution sample with a mass fraction of 3.0% as a reference and select a matching chromatographic column (oily: Styragel HT5DMF7.8*300mm+Styragel HT4). Use purified N-methylpyrrolidone (NMP) solvent to prepare a 3.0% polymer glue solution, and let the prepared solution stand for one day for use. During the test, first use a syringe to draw tetrahydrofuran, rinse, and repeat several times. Then draw 5 ml of the experimental solution, expel the air in the syringe, and wipe the needle tip dry. Finally, slowly inject the sample solution into the injection port. After the reading stabilizes, obtain the data and read the weight-average molecular weight.

[0115] In some embodiments, the weight average molecular weight of the polymer is 500,000, 700,000, 800,000, 900,000, 1,000,000, 1,200,000, 1,400,000, 1,500,000, 1,600,000, 1,800,000, 2,000,000, or any value therebetween.

[0116] When the weight average molecular weight of the polymer is within the above range, the viscosity of the aqueous solution at a certain solid content of the polymer is within an appropriate range, the electrode has good processing performance and bonding performance, and the battery has good cycle stability.

[0117] In some embodiments, the viscosity of an aqueous solution with a solid content of 6 wt % obtained by dissolving the polymer in deionized water is 8,000 MPa·s to 30,000 MPa·s, and can be optionally 10,000 MPa·s to 20,000 MPa·s.

[0118] In this application, the viscosity of the polymer solution can be tested using methods known in the art. For example, 24g of polymer and 376g of water are weighed separately in a 500ml beaker to prepare a 6% solids aqueous solution. The solution is then dispersed using a Lichen high-speed grinder at 800 rpm for 120 minutes, followed by ultrasonic vibration for 30 minutes to remove bubbles. A Lichen Technology NDJ-5S rotational viscometer is used, with a No. 64 rotor inserted into the aqueous solution until it is submerged. The viscosity is measured at 12 rpm and the viscosity reading is taken after 6 minutes.

[0119] In some embodiments, the viscosity of an aqueous solution of the polymer dissolved in deionized water with a solid content of 6 wt % is 8,000 MPa·s, 10,000 MPa·s, 15,000 MPa·s, 20,000 MPa·s, 25,000 MPa·s, 30,000 MPa·s, or any value therebetween.

[0120] When the viscosity of an aqueous solution with a solid content of 6 wt % prepared by dissolving the polymer in deionized water is within the above range, the slurry has stability and processability, the pole piece has excellent processability and bonding properties, and the battery has good cycle stability.

[0121] In some embodiments, the polymer includes at least one of acrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-hydroxyethyl acrylate copolymer, methacrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-methacrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-methacrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-hydroxybutyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-hydroxypropyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate-hydroxybutyl acrylate copolymer, and acrylic acid-acrylonitrile-hydroxyethyl acrylate-hydroxybutyl acrylate copolymer.

[0122] The second aspect of the present application provides a method for preparing a polymer, wherein raw materials including a flexible monomer, an unsaturated carboxylic acid monomer, and an unsaturated cyano monomer are polymerized under polymerizable conditions to prepare a polymer, wherein the glass transition temperature of the flexible monomer is -60°C to -0°C, and can be optionally -55°C to -15°C.

[0123] In some embodiments, the preparation method is specifically as follows: polymerizing an initiator, a flexible monomer represented by formula I, an unsaturated carboxylic acid monomer represented by formula II, an unsaturated cyano monomer represented by formula III, and an unsaturated amide monomer represented by formula IV in an aqueous solvent;

[0124] Among them, R1, R2, R3, R5, R6, R7, R8, R9, R 10 、R 11 、R 12 、R 13 、R 14 、R 15 Each independently includes hydrogen or substituted or unsubstituted C 1-5 Alkyl, R4 includes C 1-5 Hydroxyalkyl, C 1-5 Alkyl and C 1-5 One or more alkoxy groups.

[0125] The solution polymerization method can well control the reaction temperature when preparing polymers, which is conducive to the preparation of polymers with moderate molecular weight. In addition, the polymers synthesized by the solution polymerization method have good water solubility.

[0126] In some embodiments, the initiator comprises an inorganic peroxide initiator, and the inorganic peroxide initiator comprises any one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0127] In some embodiments, the mass of the initiator is 0.01% to 0.1% of the total mass of the flexible monomer, the unsaturated carboxylic acid monomer, the unsaturated cyano monomer, and the unsaturated amide monomer, and can be optionally 0.03% to 0.08%.

[0128] In some embodiments, the mass of the initiator is 0.01%, 0.03%, 0.05%, 0.08%, 0.1% or any value therebetween of the total mass of the flexible monomer, the unsaturated carboxylic acid monomer, the unsaturated cyano monomer, and the unsaturated amide monomer.

[0129] When the amount of the initiator is within the above range, the polymerization reaction rate is moderate, the system is heated evenly, the gel effect is weakened, and the polymer is polymerized evenly, thereby obtaining a polymer with a weight average molecular weight within an appropriate range.

[0130] In some embodiments, the polymerization reaction satisfies at least one of the following conditions:

[0131] (1) The reaction environment of the polymerization reaction is a water-insoluble gas atmosphere;

[0132] (2) The reaction temperature of the polymerization reaction is 60° C. to 100° C.;

[0133] (3) The stirring speed of the polymerization reaction is 200 rpm to 800 rpm;

[0134] (4) The reaction time of the polymerization reaction is 8 hours to 12 hours.

[0135] Water-insoluble gas refers to gas with solubility less than 0.1L. Gas solubility refers to the pressure of gas at 20℃ is 1.013×10 5 Pa, the volume of gas when it is dissolved in 1L of water to reach saturation.

[0136] In some embodiments, the water-insoluble gas is selected from one or more of nitrogen, oxygen, hydrogen, and methane.

[0137] In some embodiments, the polymerization reaction temperature is 60°C, 70°C, 80°C, 90°C, 100°C, or any value therebetween.

[0138] When the polymerization temperature is within the above range, the reactivity of free radicals in the solution is within an appropriate range, and the rates of chain transfer reaction and chain growth reaction are moderate, thereby making the weight average molecular weight of the polymer within an appropriate range.

[0139] In some embodiments, the stirring speed of the polymerization reaction is 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, or any value therebetween.

[0140] In some embodiments, the polymerization reaction time is 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, or any value therebetween.

[0141] When the reaction time of the polymerization reaction is within the above range, the conversion rate of the monomer is within an appropriate range and the polymer has an appropriate weight average molecular weight.

[0142] [Negative electrode]

[0143] In some embodiments, the negative electrode sheet includes a negative electrode film layer, the negative electrode film layer includes a binder, and the binder includes the polymer in any embodiment or the polymer prepared by the preparation method in any embodiment.

[0144] As used herein, the term "binder" refers to a chemical compound, polymer, or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.

[0145] In some embodiments, the dispersion medium of the binder is an aqueous solvent, such as water, that is, the binder is dissolved in the aqueous solvent.

[0146] In some embodiments, the binder accounts for 0.5% to 3% by mass, and optionally 1% to 2% by mass, based on the total mass of the negative electrode film layer.

[0147] In some embodiments, the binder accounts for 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or any value therebetween by mass, based on the total mass of the negative electrode film layer.

[0148] Existing polymers containing unsaturated carboxylic acid monomers can cause severe warping and edge cracking in electrode plates at a 1% addition, making it difficult to meet production requirements. The polymers provided in the embodiments of this application can still achieve good processing properties in electrode plates at an addition level of up to 3%. Therefore, increasing the amount of binder can further improve the cycling stability of secondary batteries.

[0149] In some embodiments, the warping height of the negative electrode plate is 0 mm to 20 mm.

[0150] In this application, the warpage height of the negative electrode sheet can be tested using methods known in the art. For example, the negative electrode slurry is applied to the negative electrode current collector and baked at 100°C for 1 minute to remove most of the water. The negative electrode sheet is then cut into 10 pieces of 4cm×4cm negative electrode sheets. The cut negative electrode sheets are then placed on a heating plate with a temperature stabilized at 120°C for 1 minute. The height of each negative electrode sheet raised from the plane of the heating plate is measured with a ruler, and recorded as h1, h2, h3, and h4 respectively. The average value of h1, h2, h3, and h4 corresponding to each negative electrode sheet is calculated and recorded as H. The average value H corresponding to the 10 negative electrode sheets is then averaged as the warpage height of the negative electrode sheet.

[0151] In some embodiments, the warping height of the negative electrode tab is 0 mm, 2 mm, 4 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, or any value therebetween.

[0152] The polymer has a low glass transition temperature and high flexibility, which can effectively improve the uneven shrinkage and stress concentration of the polymer during the drying process and alleviate the warping of the electrode.

[0153] In some embodiments, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, and silicon-based materials.

[0154] In some embodiments, the silicon-based material includes at least one of elemental silicon, nano-silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0155] Silicon-based materials have high capacity and can significantly increase the energy density of batteries. However, silicon-based materials have a large expansion rate during the cycle, which can easily cause uneven stress on the pole pieces, resulting in phenomena such as pole piece wrinkling. Since the stress at the inner corners of the battery cell is more severe, peeling, bubbling, cracking, and even membrane peeling may occur. The polymer provided in the embodiments of the present application can also be applied to silicon-based systems. While maintaining a low rebound rate of the pole piece, it can reduce the uneven stress distribution of the pole piece, effectively improve the peeling, bubbling, and cracking of the pole piece when fully charged, and thus improve the cycle stability of the battery.

[0156] In some embodiments, the negative electrode film layer includes a negative electrode active material and a binder, the negative electrode active material includes a silicon-based material, the binder includes a polymer, the polymer contains a structural unit derived from an unsaturated carboxylic acid monomer, a structural unit derived from an unsaturated cyano monomer, and a structural unit derived from a flexible monomer, the flexible monomer includes at least two of hydroxyethyl acrylate, hydroxypropyl acrylate, and 4-hydroxybutyl acrylate, and the glass transition temperature of the polymer is 40°C to 75°C.

[0157] In some embodiments, the compacted density of the negative electrode sheet is 1.45 g / cm 3 , 1.55g / cm 3 , 1.60g / cm 3 , 1.65g / cm 3 , 1.75g / cm 3 , 1.85g / cm 3 , 1.95g / cm 3 or any value in between.

[0158] Negative electrodes with high compaction density are more susceptible to brittle fracture during cycling, and even risk cracking during hot pressing after winding. The polymers provided in the embodiments of this application can also be applied to high-voltage dense electrodes, improving their flexibility while maintaining a low rebound rate, thereby reducing the probability of cracks and brittle fracture during production and use.

[0159] In some embodiments, the compacted density of the negative electrode sheet is 1.60 g / cm 3 ~1.95g / cm 3 The negative electrode film layer includes a binder, which includes a polymer. The polymer contains a structural unit derived from an unsaturated carboxylic acid monomer, a structural unit derived from an unsaturated cyano monomer, a structural unit derived from an unsaturated amide monomer, and a structural unit derived from a flexible monomer. The flexible monomer includes at least two of hydroxyethyl acrylate, hydroxypropyl acrylate, and 4-hydroxybutyl acrylate, and the glass transition temperature of the polymer is 40°C to 90°C.

[0160] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0161] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0162] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0163] In some embodiments, the negative electrode sheet can be prepared by the following method: 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 (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0164] [Positive electrode]

[0165] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0166] As an example, the positive electrode current collector has two surfaces facing each other in its own thickness direction.

[0167] The positive electrode film layer is arranged on either or both of the two opposite surfaces of the positive electrode current collector.

[0168] 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 polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0169] In some embodiments, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, 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. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 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 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0170] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0171] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0172] In some embodiments, the positive electrode sheet can be prepared by the following method: 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 (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0173] [Electrolytes]

[0174] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0175] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0176] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0177] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0178] In some embodiments, the electrolyte may further include additives. For example, the additives may include 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, and additives that improve battery high or low temperature performance.

[0179] [Isolation film]

[0180] 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 and mechanical stability can be selected.

[0181] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0182] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0183] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0184] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0185] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 having a square structure as an example. Optionally, the secondary battery is a lithium-ion battery or a sodium-ion battery.

[0186] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. 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 be formed into 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 secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0187] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0188] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0189] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0190] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0191] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0192] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0193] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0194] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0195] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0196] Example

[0197] Preparation method

[0198] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific 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. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0199] 1. Preparation method

[0200] Example 1

[0201] 1) Preparation of polymer

[0202] Hydroxyethyl acrylate (HEA), acrylic acid, acrylonitrile, and acrylamide were added to a three-necked flask equipped with a reflux condenser and a stirrer at a molar ratio of 35:30:25:10. Deionized water and 0.05% ammonium persulfate initiator (based on the total weight of the monomers) were added. The mixture was reacted at 80°C and 500 rpm under a nitrogen atmosphere for 8 hours to produce an acrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer. The copolymer had a weight-average molecular weight of 800,000, and a 6% solids content aqueous solution had a viscosity of 8,000 to 30,000 mPa.s.

[0203] 2) Preparation of positive electrode sheet

[0204] The positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), conductive carbon black, and polyvinylidene fluoride (PVDF) binder were mixed in a weight ratio of 92:4:4, then added to N-methylpyrrolidone and stirred to form a positive electrode slurry. The slurry was evenly coated on both surfaces of an aluminum foil positive current collector and dried to form a film. The film was then cold-pressed and slit to produce positive electrode sheets. The binder, PVDF with a weight-average molecular weight of 700,000, was purchased from Arkema France Ltd.

[0205] 3) Preparation of negative electrode sheet

[0206] The negative electrode active material ordinary graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), polymer prepared in Example 1, and thickener sodium hydroxymethyl cellulose (CMC-Na) were dissolved in deionized water at a weight ratio of 96.5:0.5:1:1:1, stirred at 1800 r / min and 25° C. for 3 h, and mixed uniformly to prepare a negative electrode slurry; the negative electrode slurry was uniformly coated on both surfaces of the negative electrode current collector copper foil once or multiple times, and the negative electrode sheet was obtained after drying, cold pressing, and slitting, with a compaction density of 1.5 g / cm 3 .

[0207] 4) Isolation film

[0208] Polypropylene film is used as the isolation film.

[0209] 5) Preparation of electrolyte

[0210] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3 / 7, LiPF6 lithium salt was dissolved in the organic solvent, and stirred evenly to prepare a 1M LiPF6 electrolyte.

[0211] 6) Preparation of batteries

[0212] The prepared positive electrode sheet, separator, and negative electrode sheet were stacked in order, with the separator positioned between the positive and negative electrode sheets to provide isolation. The cells were then wound to obtain a bare cell. The tabs were welded to the bare cell and placed in an aluminum shell. The cells were then baked at 80°C to remove moisture. The electrolyte was then injected and sealed to obtain an uncharged battery. The uncharged battery then underwent a series of steps, including resting, hot and cold pressing, formation, shaping, and capacity testing, to obtain the lithium-ion battery product of Example 1.

[0213] The batteries of Examples 2 to 13 were prepared similarly to the battery of Example 1, except that the molar ratios of acrylic acid, acrylonitrile, acrylamide, and hydroxyethyl acrylate monomers were adjusted, and the amount of initiator used was changed accordingly. The specific parameters are shown in Table 1.

[0214] The batteries of Examples 14 to 16 were prepared similarly to the battery of Example 1, except that the mass fraction of the polymer was adjusted. Based on the total mass of the negative electrode film layer, the mass of the negative electrode active material changed accordingly. The specific parameters are shown in Table 1.

[0215] The batteries of Examples 17 to 20 were prepared similarly to the battery of Example 11, except that the amount of initiator used was adjusted to 0.1%, 0.05%, 0.03%, and 0.03% of the total mass of the monomer, respectively, and the reaction times were 8 hours, 10 hours, 10 hours, and 12 hours, respectively, thereby adjusting the molecular weight of the polymer. The specific parameters are shown in Table 1.

[0216] The preparation method of the battery of Example 21 is similar to that of the battery of Example 1, except that the hydroxyethyl acrylate monomer is replaced with 4-hydroxybutyl acrylate (4-HBA) monomer, and the molar ratio remains unchanged. The specific parameters are shown in Table 1.

[0217] The battery of Example 22 is prepared in a similar manner to that of Example 1, except that the hydroxyethyl acrylate monomer is replaced with a hydroxypropyl acrylate monomer with a molar ratio of 25%, and the molar ratio of the acrylic acid monomer is changed accordingly. The specific parameters are shown in Table 1.

[0218] The battery of Example 23 was prepared in a similar manner to the battery of Example 1, except that the acrylic acid monomer was replaced with a methacrylic acid monomer. The specific parameters are shown in Table 1.

[0219] The preparation method of the battery of Example 24 is similar to that of the battery of Example 1, except that the acrylonitrile monomer is replaced with a methacrylonitrile monomer, and the molar ratio remains unchanged. The specific parameters are shown in Table 1.

[0220] The preparation method of the battery of Example 25 is similar to that of the battery of Example 1, except that the acrylamide monomer is replaced by a methacrylamide monomer with the molar ratio remaining unchanged. The specific parameters are shown in Table 1.

[0221] Example 26

[0222] 1) Preparation of polymer

[0223] Hydroxyethyl acrylate, 4-hydroxybutyl acrylate, acrylic acid, acrylonitrile, and acrylamide were added to a three-necked flask equipped with a reflux condenser and a stirrer at a molar ratio of 5:15:35:40:5. Deionized water and 0.05% ammonium persulfate initiator (based on the total weight of the monomers) were added. The mixture was reacted at 80°C and 500 rpm under a nitrogen atmosphere for 8 hours to produce an acrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate-hydroxybutyl acrylate copolymer. The copolymer had a weight-average molecular weight of 800,000.

[0224] 2) Preparation of positive electrode sheet

[0225] The positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), conductive carbon black, and polyvinylidene fluoride (PVDF) binder were mixed in a weight ratio of 92:4:4, then added to N-methylpyrrolidone and stirred to form a positive electrode slurry. The slurry was evenly coated on both surfaces of an aluminum foil positive current collector and dried to form a film. The film was then cold-pressed and slit to produce positive electrode sheets. The binder, PVDF with a weight-average molecular weight of 700,000, was purchased from Arkema France Ltd.

[0226] 3) Preparation of negative electrode sheet

[0227] The negative electrode active material high-density graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), polymer prepared in Example 1, and thickener sodium hydroxymethyl cellulose (CMC-Na) were dissolved in deionized water at a weight ratio of 96.5:0.5:1:1:1, stirred at 1800 r / min and 25° C. for 3 h, and mixed uniformly to prepare a negative electrode slurry; the negative electrode slurry was uniformly coated on both surfaces of the negative electrode current collector copper foil once or multiple times, and the negative electrode sheet was obtained after drying, cold pressing, and slitting, with a compaction density of 1.75 g / cm 3 .

[0228] 4) Isolation film

[0229] Polypropylene film is used as the isolation film.

[0230] 5) Preparation of electrolyte

[0231] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3 / 7, LiPF6 lithium salt was dissolved in the organic solvent, stirred evenly, and a 1M LiPF6EC / EMC solution was prepared to obtain an electrolyte.

[0232] 6) Preparation of batteries

[0233] The positive electrode sheet, separator, and negative electrode sheet were stacked in order, with the separator positioned between the positive and negative electrode sheets to provide isolation. The cells were then wound to obtain a bare cell. The tabs were welded to the bare cell and placed in an aluminum casing. The cells were then baked at 80°C to remove moisture. The electrolyte was then injected and sealed to obtain an uncharged battery. The uncharged battery then underwent a series of steps, including resting, hot and cold pressing, formation, shaping, and capacity testing, to obtain the lithium-ion battery product of Example 26.

[0234] The preparation method of the batteries of Examples 27-28 is similar to that of the battery of Example 26, except that the molar ratio of hydroxyethyl acrylate and 4-hydroxybutyl acrylate is adjusted. The specific parameters are shown in Table 3.

[0235] Example 29

[0236] 1) Preparation of polymer

[0237] Hydroxyethyl acrylate, 4-hydroxybutyl acrylate, acrylic acid, and acrylonitrile were added to a three-necked flask equipped with a reflux condenser and a stirrer at a molar ratio of 20:20:40:20. Deionized water and 0.05% ammonium persulfate initiator (based on the total weight of the monomers) were added. The mixture was reacted at 80°C and 500 rpm under a nitrogen atmosphere for 8 hours to produce an acrylic acid-acrylonitrile-hydroxyethyl acrylate-hydroxybutyl acrylate copolymer. The copolymer had a weight-average molecular weight of 800,000.

[0238] 2) Preparation of positive electrode sheet

[0239] The positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2O2 (NCM622), conductive carbon black, and polyvinylidene fluoride (PVDF) binder were mixed in a weight ratio of 92:4:4 with N-methylpyrrolidone to create a positive electrode slurry. The slurry was evenly coated on both surfaces of an aluminum foil positive current collector and dried to form a film. The positive electrode sheets were then cold-pressed and slit. The binder, PVDF with a weight-average molecular weight of 700,000, was purchased from Arkema France Ltd.

[0240] 3) Preparation of negative electrode sheet

[0241] The negative electrode active material ordinary graphite material, silicon carbon material, conductive agent carbon black, binder styrene butadiene rubber (SBR), polymer prepared in Example 1, and thickener sodium hydroxymethyl cellulose (CMC-Na) were dissolved in deionized water according to a weight ratio of 66.5:30:0.5:1:1:1, stirred at 1800 r / min and 25°C for 3 hours, and mixed uniformly to prepare a negative electrode slurry; the negative electrode slurry was evenly coated on both surfaces of the negative electrode current collector copper foil once or multiple times, and the negative electrode sheet was obtained after drying, cold pressing, and slitting, with a compaction density of 1.50 g / cm 3 .

[0242] 4) Isolation film

[0243] Polypropylene film is used as the isolation film.

[0244] 5) Preparation of electrolyte

[0245] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3 / 7, LiPF6 lithium salt was dissolved in the organic solvent, stirred evenly, and a 1M LiPF6EC / EMC solution was prepared to obtain an electrolyte.

[0246] 6) Preparation of batteries

[0247] The positive electrode sheet, separator, and negative electrode sheet were stacked in order, with the separator positioned between the positive and negative electrode sheets to provide isolation. The cells were then wound to obtain a bare cell. The tabs were welded to the bare cell and placed in an aluminum casing. The cells were then baked at 80°C to remove moisture. The electrolyte was then injected and sealed to obtain an uncharged battery. The uncharged battery then underwent a series of steps, including resting, hot and cold pressing, formation, shaping, and capacity testing, to obtain the lithium-ion battery product of Example 29.

[0248] The preparation method of the battery of Example 30-31 is similar to that of the battery of Example 30, except that the molar ratio of hydroxyethyl acrylate and 4-hydroxybutyl acrylate is adjusted. The specific parameters are shown in Table 3.

[0249] The battery of Comparative Example 1 was prepared in a similar manner to that of Example 1. The binder used for the negative electrode was a polyacrylic acid binder with a weight-average molecular weight of 800,000, purchased from Indole, LA133. The specific parameters are shown in Table 1.

[0250] The battery of Comparative Example 2 was prepared in a similar manner to that of Example 1, but the polymerization monomers were only acrylic acid, acrylonitrile, and acrylamide monomers. The specific parameters are shown in Table 1.

[0251] The battery of Comparative Example 3 was prepared in a similar manner to the battery of Example 26. The binder used for the negative electrode was a polyacrylic acid binder with a weight-average molecular weight of 800,000, purchased from Indole, LA133. The specific parameters are shown in Table 3.

[0252] The battery of Comparative Example 4 was prepared in a similar manner to the battery of Example 26, but the polymerization monomers were only acrylic acid, acrylonitrile, and acrylamide monomers. The specific parameters are shown in Table 3.

[0253] The battery of Comparative Example 5 was prepared in a similar manner to the battery of Example 29. The binder used for the negative electrode was a polyacrylic acid binder with a weight-average molecular weight of 800,000, purchased from Indole, LA133. The specific parameters are shown in Table 3.

[0254] The battery of Comparative Example 6 was prepared in a similar manner to the battery of Example 29, but the polymerization monomers were only acrylic acid, acrylonitrile, and acrylamide monomers. The specific parameters are shown in Table 3.

[0255] 2. Test Method

[0256] 1. Polymer property test

[0257] 1) Glass transition temperature test

[0258] Glass transition temperature (Tg) measurements were performed using a TA differential scanning calorimeter (Q1000). A 6-9 g polymer sample was heated from room temperature to 200°C at a heating rate of 10°C / min. The sample was then held at 200°C for 3 hours to eliminate thermal history. After cooling, the sample was heated again from room temperature to 200°C at a heating rate of 10°C / min. The Tg of the polymer was determined by analyzing the Tg curve obtained from this scan (unit: °C).

[0259] 2) Weight average molecular weight test

[0260] A Waters 2695 Isocratic HPLC gel chromatography instrument (differential refractive index detector 2141) was used. A 3.0% polystyrene solution sample was used as a reference, and a matching chromatographic column was selected (oil-based: Styragel HT5DMF7.8*300mm+Styragel HT4). A 3.0% polymer gel was prepared using purified N-methylpyrrolidone (NMP) solvent. The prepared solution was allowed to stand for one day before use. During testing, tetrahydrofuran was first drawn into a syringe and rinsed several times. Then, 5 ml of the experimental solution was drawn, the air in the syringe was expelled, and the needle tip was wiped dry. Finally, the sample solution was slowly injected into the injection port. After the reading stabilized, the data was acquired and the weight-average molecular weight was read.

[0261] 3) Viscosity of 6 wt% solid content aqueous solution

[0262] Weigh 24g of polymer and 376g of water in a 500ml beaker to create a 6% solids aqueous solution. Stir and disperse the solution using a Lichen high-speed grinder at 800 rpm for 120 minutes, then ultrasonically vibrate for 30 minutes to remove air bubbles. Use a Lichen Technology NDJ-5S rotational viscometer with a #64 rotor inserted into the aqueous solution until it submerges the scale line. Test the viscosity at 12 rpm and read the viscosity after 6 minutes.

[0263] 2. Performance test of negative electrode

[0264] 1) Test whether the roller is cracked

[0265] Place the electrode after coating the slurry on a roller press, adjust the thickness of the roller gap and the rolling pressure to appropriate values, and then roll it. Observe whether the film layer of the electrode and the current collector are cracked at the junction. If there is no crack, it is determined that there is no edge burst. If there is crack, it is determined that an edge burst has occurred.

[0266] 2) Electrode rebound rate 48 hours after rolling.

[0267] The thickness of the negative electrode sheet is measured using a vernier caliper. The initial thickness D0 of the negative electrode sheet after rolling is used as the benchmark. The thickness of the negative electrode sheet after 48 hours of standing after rolling is D1. The rebound rate of the sheet 48 hours after rolling = [(D1-D0) / D0]×100%.

[0268] 3) Warping height

[0269] The negative electrode slurry was applied to the negative electrode current collector and baked at 100°C for 1 minute to remove most of the water. The negative electrode slurry was then cut into 10 4cm x 4cm negative electrode sheets. The cut negative electrode sheets were then placed on a 120°C heating plate for 1 minute. The height of each negative electrode sheet raised from the heating plate plane was measured using a ruler, and recorded as h1, h2, h3, and h4. The average value of h1, h2, h3, and h4 for each negative electrode sheet was calculated and recorded as H. The average value H corresponding to the 10 negative electrode sheets was then taken as the warpage height of the negative electrode sheet.

[0270] 4) Bending times test

[0271] Cut the cold pressed negative electrode into 20*100mm 2 Fold the test specimen in the forward direction, flatten it with a 2kg roller, unfold it and check against the light to see if there is any light transmittance. If there is no light transmittance, fold it in the reverse direction, flatten it with a 2kg roller, and check against the light again. Repeat this process until there is light transmittance. Record the number of folds. Repeat the test three times and take the average value as the number of bending times of the electrode.

[0272] 5) Corner demoulding test

[0273] After the capacity test, the battery cell is disassembled in a fully charged state to observe whether there is film shedding and powder falling at the convex corner of the negative electrode. If only powder falling occurs, it is recorded as Level 1; if demolding occurs, it is recorded as Level 2; if peeling and bubbling occur, it is recorded as Level 3.

[0274] 6) Pole piece adhesion test

[0275] Referring to the national standard "Adhesive 180° Peel Strength Test Method", the adhesion test process is as follows:

[0276] Use a razor blade to cut a sample with a width of 30mm and a length of 100-160mm. Apply special double-sided tape to the steel plate with a width of 20mm and a length of 90-150mm. Attach the electrode sample cut earlier to the double-sided tape with the test surface facing down. Finally, use a roller to roll it three times in the same direction.

[0277] Insert a paper tape with a width equal to that of the electrode and a length 80 to 200 mm greater than the length of the sample under the electrode and secure it with wrinkle glue.

[0278] Turn on the Sansi tensile testing machine (sensitivity set to 1N) and wait for the indicator light to illuminate. Adjust the limit block to the appropriate position and secure the end of the steel plate without the electrode to the lower clamp. Fold the paper tape upward and secure it with the upper clamp. Use the "up" and "down" buttons on the manual controller included with the tensile testing machine to adjust the position of the upper clamp. Then perform the test and read the value.

[0279] 3. Battery performance test

[0280] 1) Battery capacity retention test

[0281] At 25°C, the battery was charged at a constant current of 1 / 3C to 4.25V, then charged at a constant voltage of 4.25V to a current of 0.05C, left for 5 minutes, and then discharged at 1 / 3C to 2.8V. The obtained capacity was recorded as the initial capacity C0. The above steps were repeated for the same battery, and the discharge capacity Cn of the battery after the nth cycle was recorded at the same time. The battery capacity retention rate after each cycle is Pn = Cn / C0*100%, and the battery cycle capacity retention rate after 500 cycles was recorded.

[0282] 3. Analysis of test results of various embodiments and comparative examples

[0283] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in the table below.

[0284] Table 1

[0285] Table 2

[0286] Table 3

[0287] Table 4

[0288] The glass transition temperature of hydroxyethyl acrylate is -15°C, the glass transition temperature of hydroxypropyl acrylate is -30°C, and the glass transition temperature of 4-hydroxybutyl acrylate is -55°C. As can be seen from Tables 1-4, the polymers in Examples 1-31 all contain structural units derived from unsaturated carboxylic acid monomers, structural units derived from unsaturated cyano monomers, and structural units derived from flexible monomers, and the glass transition temperature of the flexible monomers is between -60°C and 0°C, and can optionally be between -55°C and -15°C.

[0289] As can be seen from Tables 1 and 2, when the negative electrode plate includes the above polymer, the plate binder has low cohesive force, so that the negative electrode plate has a low warpage height and good molding quality.

[0290] As shown in Table 1, a polymer glass transition temperature of 40°C to 105°C results in low warpage and excellent molding quality for the negative electrode sheet. A glass transition temperature of 40°C to 90°C prevents edge cracking during roll pressing, significantly improving production efficiency and quality.

[0291] As shown in Examples 1-5 in Table 1, when the molar percentage of structural units derived from hydroxyethyl acrylate is 5% to 50%, based on the total molar number of all structural units in the polymer, the electrode warpage height is reduced and the electrode has excellent molding stability. When the molar percentage is 20% to 35%, the negative electrode electrode does not break during roller pressing, improving production efficiency; it also maintains high electrode adhesion and low electrode rebound rate, thereby comprehensively improving the battery's cycling stability.

[0292] As can be seen from Examples 1 and 6-13 in Table 1, based on the total molar number of all structural units in the polymer, the molar proportion of the structural units derived from the unsaturated cyano monomer is 10% to 45%, the electrode has good bonding performance, and the battery has excellent cycle stability.

[0293] It can be seen from Examples 1 and 10-13 in Table 1 that when the molar content of the structural unit derived from the unsaturated amide monomer is 0% to 30% based on the total molar number of all structural units in the polymer, the negative electrode slurry has a suitable viscosity, which is conducive to slurry coating and molding, and improves the quality of the negative electrode sheet.

[0294] As can be seen from Examples 1 and 14-16, the mass content of the polymer is 0.5% to 3% based on the total mass of the negative electrode film layer. The negative electrode sheet has both low warpage height and good bonding performance, and the battery has excellent cycle stability.

[0295] It can be seen from Example 1 and Examples 17-20 that when the weight average molecular weight of the polymer is 500,000 to 2,000,000, the negative electrode sheet has both low warpage height and good bonding performance, and the battery has excellent cycle stability.

[0296] From the comparison of the examples and comparative examples in Table 3, it can be seen that the polymer provided in the present application is also suitable for use in high-pressure dense graphite negative electrode plate systems to reduce the warping height of the electrode plates.

[0297] When the polymer includes two flexible monomers, hydroxyethyl acrylate and hydroxybutyl acrylate, the polymer can improve the flexibility of the high-voltage dense negative electrode while taking into account the high adhesion and low rebound rate of the electrode, increase the number of bending times of the electrode, meet the use requirements of the high-voltage dense negative electrode system, and improve the cycle stability of the battery through comprehensive effects.

[0298] From the comparison of the examples and comparative examples in Table 3, it can be seen that the polymer provided in the present application is also applicable to the silicon negative electrode system and reduces the warping height of the electrode.

[0299] When the polymer includes two flexible monomers, hydroxyethyl acrylate and hydroxybutyl acrylate, the polymer can achieve high adhesion and low rebound rate while reducing the occurrence of silicon negative electrode corner demolding, meeting the use requirements of the silicon negative electrode system, and improving the cycle stability of the battery through comprehensive effects.

[0300] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A polymer, characterized in that The polymer contains structural units derived from unsaturated carboxylic acid monomers, structural units derived from unsaturated cyano monomers and structural units derived from flexible monomers, and the glass transition temperature of the flexible monomers is -60°C to 0°C, and can be optionally -55°C to -15°C.

2. The polymer according to claim 1, characterized in that The flexible monomer comprises a structure shown in Formula I, wherein R1, R2, and R3 are independently hydrogen or substituted or unsubstituted C 1-5 Alkyl, R4 includes C 1-5 Hydroxyalkyl, C 1-5 Alkyl and C 1-5 One or more of alkoxy groups.

3. The polymer according to claim 1 or 2, characterized in that The unsaturated carboxylic acid monomer includes a structure shown in Formula II, The unsaturated cyano monomer includes a structure shown in formula III, Among them, R5, R6, R7, R8, R9, R 10 Each independently includes hydrogen or substituted or unsubstituted C 1-5 alkyl.

4. The polymer according to any one of claims 1 to 3, characterized in that The polymer further comprises a structural unit derived from an unsaturated amide monomer, wherein the unsaturated amide monomer comprises a structure represented by Formula IV, Among them, R 11 , R 12 , R 13 , R 14 , R 15 Each independently comprises hydrogen or substituted or unsubstituted C 1-5 alkyl.

5. The polymer according to any one of claims 1 to 4, characterized in that The flexible monomer includes one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, ethyl acrylate, and n-butyl acrylate.

6. The polymer according to any one of claims 1 to 4, characterized in that The flexible monomer includes at least two of hydroxyethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, ethyl acrylate, and n-butyl acrylate.

7. The polymer according to any one of claims 4 to 6, characterized in that The unsaturated carboxylic acid monomer includes one or more of acrylic acid, methacrylic acid, ethacrylic acid, and crotonic acid; the unsaturated cyano monomer includes one or more of acrylonitrile, crotonic acid, methacrylonitrile, and ethacrylonitrile; the unsaturated amide monomer includes one or more of acrylamide, methacrylamide, N,N-dimethylacrylamide, and N-methylacrylamide.

8. The polymer according to any one of claims 1 to 7, characterized in that Based on the total molar number of all structural units in the polymer, the molar proportion of the structural unit derived from the flexible monomer is 5% to 50%, and can be optionally 20% to 35%.

9. The polymer according to any one of claims 4 to 8, characterized in that Based on the total molar number of all structural units in the polymer, the molar proportion of the structural units derived from the unsaturated carboxylic acid monomer is 10% to 60%, optionally 30% to 50%, and / or The molar proportion of the structural unit derived from the unsaturated cyano monomer is 10% to 60%, optionally 15% to 45%, and / or The molar proportion of the structural unit derived from the unsaturated amide monomer is 0% to 30%, and can be optionally 5% to 20%.

10. The polymer according to any one of claims 1 to 9, characterized in that The glass transition temperature of the polymer is 40°C to 105°C, and can be optionally 40°C to 90°C.

11. The polymer according to any one of claims 1 to 10, characterized in that The weight average molecular weight of the polymer is 500,000 to 2,000,000, and can be 800,000 to 1,500,000.

12. The polymer according to any one of claims 1 to 11, characterized in that The viscosity of the aqueous solution with a solid content of 6 wt % obtained by dissolving the polymer in deionized water is 8000 mPa·s to 30000 mPa·s, and can be optionally 10000 mPa·s to 20000 mPa·s.

13. The polymer according to any one of claims 1 to 12, characterized in that The polymer includes at least one of acrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-hydroxyethyl acrylate copolymer, methacrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-methacrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-methacrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-hydroxybutyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-hydroxypropyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate-hydroxybutyl acrylate copolymer, and acrylic acid-acrylonitrile-hydroxyethyl acrylate-hydroxybutyl acrylate copolymer.

14. A method for preparing a polymer, characterized in that: The following steps are involved: Under polymerizable conditions, raw materials including flexible monomers, unsaturated carboxylic acid monomers and unsaturated cyano monomers are polymerized to prepare polymers, wherein the glass transition temperature of the flexible monomers is -60°C to 0°C, and can be optionally -55°C to -15°C.

15. The preparation method according to claim 14, characterized in that: The preparation method is specifically: The initiator, the flexible monomer shown in formula I, the unsaturated carboxylic acid monomer shown in formula II, the unsaturated cyano monomer shown in formula III, and the unsaturated amide monomer shown in formula IV are subjected to polymerization reaction in a water solvent; Among them, R1, R2, R3, R5, R6, R7, R8, R9, R 10 , R 11 , R 12 , R 13 , R 14 , R 15 Each independently comprises hydrogen or substituted or unsubstituted C 1-5 Alkyl, R4 includes C 1-5 Hydroxyalkyl, C 1-5 Alkyl and C 1-5 One or more of alkoxy groups.

16. The preparation method according to claim 15, characterized in that: The initiator includes an inorganic peroxide initiator, and the inorganic peroxide initiator includes any one of ammonium persulfate, potassium persulfate, and sodium persulfate.

17. The preparation method according to claim 15 or 16, characterized in that: The mass of the initiator is 0.01% to 0.1% of the total mass of the flexible monomer, the unsaturated carboxylic acid monomer, the unsaturated cyano monomer and the unsaturated amide monomer, and can be optionally 0.03% to 0.08%.

18. The preparation method according to any one of claims 14 to 17, characterized in that: The polymerization reaction satisfies at least one of the following conditions: (1) The reaction environment of the polymerization reaction is a water-insoluble gas atmosphere; (2) The reaction temperature of the polymerization reaction is 60° C. to 100° C.; (3) The stirring speed of the polymerization reaction is 200 rpm to 800 rpm; (4) The reaction time of the polymerization reaction is 8 to 12 hours.

19. The preparation method according to claim 18, characterized in that: The water-insoluble gas includes one or more of nitrogen, oxygen, hydrogen and methane.

20. A negative electrode plate, characterized in that: The negative electrode plate includes a negative electrode film layer, the negative electrode film layer includes a binder, and the binder includes a polymer as described in any one of claims 1 to 13 or a polymer prepared by the preparation method as described in any one of claims 14 to 19.

21. The negative electrode sheet according to claim 20, characterized in that: The mass proportion of the binder is 0.5% to 3%, and can be 1% to 2%, based on the total mass of the negative electrode film layer.

22. The negative electrode sheet according to claim 20 or 21, characterized in that: The warping height of the negative electrode plate is 0 mm to 20 mm.

23. The negative electrode sheet according to any one of claims 20 to 22, characterized in that: The negative electrode plate includes a negative electrode active material, and the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, and silicon-based materials.

24. The negative electrode sheet according to any one of claims 20 to 23, characterized in that: The compaction density of the negative electrode plate is 1.45 g / cm 3 ~1.95g / cm 3 .

25. A secondary battery, characterized in that: A negative electrode sheet comprising the negative electrode sheet according to any one of claims 20 to 24.

26. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 25.

Images