Polymer, separator, and related secondary battery and electric device

Abstract

# imgabs0 #. The invention provides a polymer, an isolating membrane, a related secondary battery and a related electric device. The polymer comprises a first structural unit, a second structural unit and a third structural unit, the first structural unit comprises a structural unit shown as a formula (I), and in the formula (I), R1 comprises one or more of hydrogen atoms and substituted or unsubstituted C1-C5 alkyl groups; r2 comprises one or more of a substituted or unsubstituted alkyl group with 1 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group with 3 to 20 carbon atoms, and a substituted or unsubstituted hydroxyalkyl group with 1 to 20 carbon atoms; the second structural unit comprises a structural unit shown as a formula (II), and in the formula (II), R3 comprises one or more of hydrogen atoms and substituted or unsubstituted C1-C5 alkyl groups; the third structural unit comprises a structural unit as shown in a formula (III). The three structural units in the polymer can cooperate with one another to jointly improve the cohesiveness, stability, swelling resistance and thermal stability of the polymer.

Description

Polymers, separators and related secondary batteries and electrical devices Technical Field

[0001] The present application relates to the field of batteries, and in particular to a polymer, an isolation membrane, and related secondary batteries and electrical devices. Background Art

[0002] Secondary batteries have the characteristics of high capacity and long life, and are therefore widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric airplanes, electric boats, electric toy cars, electric toy boats, electric toy airplanes, and power tools, etc.

[0003] As the application range of batteries becomes wider and wider, the requirements for the safety performance of secondary batteries are becoming increasingly stringent. How to continuously improve the safety performance of secondary batteries remains an urgent problem to be solved by those skilled in the art.

[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, a separator, and related secondary batteries and electrical devices.

[0006] The first aspect of the present application provides a polymer, which includes a first structural unit, a second structural unit and a third structural unit; the first structural unit includes a structural unit represented by formula (I):

[0007]

[0008] In formula (I), R1 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group; alternatively, R1 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group; R2 includes one or more of a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, or a substituted or unsubstituted C1-C20 hydroxyalkyl group; alternatively, R2 includes one or more of a C1-C12 alkyl group, a C3-C12 cycloalkyl group, or a C1-C12 hydroxyalkyl group;

[0009] The second structural unit includes a structural unit represented by formula (II):

[0010]

[0011] In formula (II), R3 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group; alternatively, R3 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group;

[0012] The third structural unit includes a structural unit represented by formula (III):

[0013]

[0014] In formula (III), R4 to R 11 Each independently comprises a substituted or unsubstituted C1-C10 alkyl group, one or more structural units as shown in formula (III-1), and R4 to R 11 At least one of them includes a structural unit represented by formula (III-1),

[0015]

[0016] In formula (III-1), R 12 Including one or more of hydrogen atoms, substituted or unsubstituted C1-C5 alkyl groups; optionally, R 12 Including one or more of hydrogen atom, substituted or unsubstituted C1-C3 alkyl; R 13 Including substituted or unsubstituted C1-C10 alkyl; optionally, R 13 This includes substituted or unsubstituted C3-C10 alkyl groups.

[0017] Therefore, the first structural unit in this application can adjust the glass transition temperature of the polymer due to the flexible monomer segment in the molecular chain, improve the toughness and peel strength of the polymer, and contribute to good bonding. The second structural unit can produce excellent swelling resistance and high bonding properties, and help improve the ionic conductivity of the secondary battery. When the polymer is used in a separator, the polymer comes into contact with the electrolyte and is not easily swollen, thus having good swelling resistance. The third structural unit can give the polymer advantages in heat resistance and mechanical properties, ensuring the stability of the polymer during the long-term cycle charge and discharge of the secondary battery, effectively isolating the positive and negative pole pieces, thereby ensuring the safety performance of the secondary battery. The combination of the first structural unit and the third structural unit can play a synergistic role, improving the bonding and heat resistance of the polymer; the combination of the first structural unit and the second structural unit can play a synergistic role, improving the stability and swelling resistance of the polymer. The three structural units in the polymer work together to improve the bonding, stability, swelling resistance, and thermal stability of the polymer.

[0018] In some embodiments, R1 includes a hydrogen atom or a methyl group; and / or R2 includes a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an n-octyl group, an isooctyl group, a 2-ethylhexyl group, a dodecyl group, or an isobornyl group.

[0019] In some embodiments, R3 includes a hydrogen atom or a methyl group.

[0020] In some embodiments, R4 to R 11Each independently comprises a structural unit as shown in formula (III-1); optionally, R 12 including hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl or n-pentyl; and / or R 13 These include n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-octyl, isooctyl or 2-ethylhexyl.

[0021] In some embodiments, R4 to R 11 One of them includes a structural unit as shown in formula (III-1); optionally, R 12 including hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl or n-pentyl; and / or R 13 These include n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-octyl, isooctyl or 2-ethylhexyl.

[0022] In some embodiments, the molar content of the first structural unit, based on the total molar amount of the first structural unit, the second structural unit, and the third structural unit, is denoted as A%, with 60≤A<100; alternatively, 60≤A≤80. When the molar content of the first structural unit is within the above range, its proportion in the polymer is relatively large, which can improve the flexibility of the polymer and thus significantly enhance the adhesion of the polymer. When the polymer is used in a separator, it can enhance the bonding strength between the polymer and the separator substrate.

[0023] In some embodiments, the molar content of the second structural unit is expressed as B%, based on the total molar amount of the first structural unit, the second structural unit, and the third structural unit, where 0 < B ≤ 20; alternatively, 5 ≤ B ≤ 20. When the molar content of the second structural unit is within the above range, the stability of the polymer can be significantly improved.

[0024] In some embodiments, the molar content of the third structural unit, based on the total molar amount of the first structural unit, the second structural unit, and the third structural unit, is expressed as C%, where 0 < C ≤ 20; alternatively, 5 ≤ C ≤ 20. When the molar content of the third structural unit is within the above range, the heat resistance of the polymer can be guaranteed, and its relatively small proportion helps to increase the proportion of the first structural unit and the second structural unit, thereby improving the overall polymer properties such as adhesion, stability, and anti-swelling properties.

[0025] In some embodiments, based on the total molar amount of the first structural unit, the second structural unit, and the third structural unit, the molar content of the first structural unit is recorded as A%, the molar content of the second structural unit is recorded as B%, and the molar content of the third structural unit is recorded as C%. The polymer satisfies one or more of conditions (1) to (3): (1) 3≤A / B≤16; (2) 3≤A / C≤16; (3) A:B:C is (12 to 16): (1 to 4): (1 to 4). When the molar contents of the first structural unit, the second structural unit, and the third structural unit meet the above ratios, the three structural units cooperate with each other to further improve the adhesion, stability, anti-swelling and thermal stability of the polymer.

[0026] In some embodiments, the number average molecular weight of the polymer is 20,000 to 80,000, optionally 30,000 to 50,000. When the number average molecular weight of the polymer is within the above range, it is conducive to the formation of polymer particles with smaller particle size. When applied to the isolation membrane, it can achieve light and thin coating of the coating in the isolation membrane, reduce the overall thickness of the isolation membrane, and thus facilitate the improvement of the energy density of the secondary battery; and the particle size of the polymer particles formed by the polymer will not be too small, which can reduce the risk of polymer particles clogging the substrate in the isolation membrane and improve the overall air permeability and other properties of the isolation membrane. In some embodiments, the polymer is granular, and the polymer also meets one or more of conditions (I) to (III): (I) the morphology of the polymer includes spherical and / or quasi-spherical; (II) the volume distribution particle size Dv50 of the polymer meets: 0.1μm≤Dv50≤2.0μm; optionally, 0.5μm≤Dv50≤1.2μm; (III) the specific surface area of ​​the polymer is denoted as S, and its unit is m 2 When the polymer is in granular form and satisfies at least one of the above conditions, the polymer's adhesion, stability, anti-swelling and heat resistance can be further improved.

[0027] The second aspect of the present application provides a method for preparing a polymer, the method being used to prepare the polymer as described in any embodiment of the first aspect of the present application, the method comprising: providing a first monomer, a second monomer, and a third monomer; mixing the first monomer, the second monomer, and the third monomer, and performing a polymerization reaction under the action of an initiator to generate a polymer, wherein the first monomer comprises a compound represented by formula (IV),

[0028]

[0029] In formula (IV), R1 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group; alternatively, R1 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group; R2 includes one or more of a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, or a substituted or unsubstituted C1-C20 hydroxyalkyl group; alternatively, R2 includes one or more of a C1-C12 alkyl group, a C3-C12 cycloalkyl group, or a C1-C12 hydroxyalkyl group;

[0030] The second monomer includes a compound represented by formula (V),

[0031]

[0032] In formula (V), R3 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group; alternatively, R3 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group;

[0033] The third monomer includes a compound represented by formula (VI),

[0034]

[0035] In formula (VI), R 30 to R 37 Each independently comprises a substituted or unsubstituted C1-C10 alkyl group, one or more structural units as shown in formula (VI-1), and R 30 to R 37 At least one of them includes a structural unit represented by formula (VI-1),

[0036]

[0037] In formula (VI-1), R 12 Including one or more of hydrogen atoms, substituted or unsubstituted C1-C5 alkyl groups; optionally, R 12 including one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group;

[0038] R 13 Including substituted or unsubstituted C1-C10 alkyl; optionally, R 13 This includes substituted or unsubstituted C3-C10 alkyl groups.

[0039] In some embodiments, the step of mixing the first monomer, the second monomer, and the third monomer and causing a polymerization reaction to generate a polymer under the action of an initiator includes: adding the first monomer, the second monomer, and the third monomer to a solvent and an emulsifier and mixing them to form a mixed system; adding the initiator to the mixed system, and causing a polymerization reaction to generate the polymer under the action of the initiator.

[0040] In some embodiments, the first monomer includes one or more of methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.

[0041] In some embodiments, the second monomer includes acrylonitrile and / or methacrylonitrile.

[0042] In some embodiments, the third monomer includes one or more of methacryloxypropyl cage polysilsesquioxane, methacryloxypropyl heptaisobutyl polysilsesquioxane, methacryloxypropyl heptaoctyl polysilsesquioxane, acryloxypropyl cage polysilsesquioxane, acryloxypropyl heptaisobutyl polysilsesquioxane, and methacryloxypropyl heptaoctyl polysilsesquioxane.

[0043] The third aspect of the present application also provides an isolation membrane, comprising a substrate and a coating arranged on at least one surface of the substrate, wherein the coating comprises a polymer as described in any embodiment of the first aspect of the present application or a polymer prepared by the method as described in any embodiment of the second aspect of the present application.

[0044] In some embodiments, the mass percentage of the polymer, based on the mass of the coating, is m%, where m ≥ 70; alternatively, 80 ≤ m ≤ 95. When the mass percentage of the polymer is within the above range, the overall adhesion, stability, anti-swelling, and heat resistance of the separator can be further improved.

[0045] In some embodiments, the isolation film satisfies one or more of the following conditions (A) to (G):

[0046] (A) the longitudinal heat shrinkage of the isolation film at 150° C. for 1 hour is η1≤5.0%, optionally 0.5%≤η1≤3%;

[0047] (B) the transverse heat shrinkage of the isolation film at 150° C. for 1 hour is η2≤5.0%, optionally 0.5%≤η2≤2%;

[0048] (C) Longitudinal tensile strength R of the separator m1 ≥3000kg / cm 2 , optionally 3500kg / cm 2 ≤R m1 ≤4500kg / cm 2 ;

[0049] (D) Transverse tensile strength R of the separator m2 ≥3000kg / cm 2 , optionally 3500kg / cm 2 ≤R m2 ≤4500kg / cm 2 ;

[0050] (E) The air permeability of the isolation membrane is MAP ≤ 250 s / 100 mL, optionally 120 s / 100 mL ≤ MAP ≤ 180 s / 100 mL;

[0051] (F) The wetted length L of the isolation membrane is ≥ 30 mm, optionally, 30 mm ≤ L ≤ 80 mm;

[0052] (G) The wetting speed of the isolation film is u≥3 mm / s, optionally, 3 mm / s≤u≤10 mm / s.

[0053] The third aspect of the present application further provides a secondary battery comprising the isolation membrane of any embodiment of the second aspect of the present application.

[0054] The fourth aspect of the present application further provides an electrical device, comprising the secondary battery described in the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

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

[0057] FIG. 2 is an exploded schematic diagram of an embodiment of the secondary battery of FIG. 1 .

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

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

[0060] FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .

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

[0062] The drawings are not necessarily drawn to scale.

[0063] The following are the descriptions of the reference numerals:

[0064] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module;

[0065] 5. Secondary battery; 51. Housing; 52. Electrode assembly;

[0066] 53. Cover plate;

[0067] 6. Electrical equipment. DETAILED DESCRIPTION

[0068] The following detailed description specifically discloses embodiments of the polymer, separator, and related secondary battery and electrical device of the present application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid unnecessary length in the following description and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0069] " scope " 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 selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, 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 listed, and if the maximum range value 3,4 and 5 are listed, then the following scope can all be expected: 1-3,1-4,1-5,2-3,2-4 and 2-5.In the present application, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and 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.

[0070] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution. Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0071] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0072] 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 indicate that other components not listed may also be included or that only the listed components are included.

[0073] 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).

[0074] In this application, the terms "plurality", "multiple" and the like refer to two or more.

[0075] Unless otherwise specified, the terms used in this application have the common meanings that are commonly understood by those skilled in the art.

[0076] Unless otherwise stated, the numerical values ​​of the parameters mentioned in this application can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application.

[0077] The term "alkyl" encompasses both straight and branched chain alkyl groups. For example, the alkyl group may be a C1 to C50 alkyl group, a C1 to C40 alkyl group, a C1 to C30 alkyl group, a C1 to C20 alkyl group, a C1 to C12 alkyl group, a C1 to C10 alkyl group, a C1 to C6 alkyl group, a C1 to C5 alkyl group, or a C1 to C3 alkyl group. In some embodiments, the alkyl group includes a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, or the like. In addition, the alkyl group may be optionally substituted.

[0078] The term "cycloalkyl" refers to a ring structure having more than or equal to three carbon atoms. For example, cycloalkyl can be C3 to C50 cycloalkyl, C3 to C40 cycloalkyl, C3 to C30 cycloalkyl, C3 to C20 cycloalkyl, C3 to C12 cycloalkyl, C3 to C10 cycloalkyl, C3 to C6 cycloalkyl, C3 to C4 cycloalkyl. In certain embodiments, cycloalkyl includes cyclopropyl, cycloisopropyl, cyclobutyl, cycloisobutyl, tert-butyl ring, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl etc. In addition, cycloalkyl can be optionally substituted.

[0079] The term "hydroxyalkyl" refers to an alkyl group in which a hydrogen atom is replaced by a hydroxyl group. For example, a hydroxyalkyl group can be a C1 to C50 hydroxyalkyl group, a C1 to C40 hydroxyalkyl group, a C1 to C30 hydroxyalkyl group, a C1 to C20 hydroxyalkyl group, a C1 to C12 hydroxyalkyl group, a C1 to C10 hydroxyalkyl group, a C1 to C6 hydroxyalkyl group, a C1 to C5 hydroxyalkyl group, a C1 to C3 hydroxyalkyl group. In certain embodiments, an alkyl group includes a hydroxymethyl group, a hydroxyethyl group, a hydroxypropyl group, a hydroxyisopropyl group, a hydroxybutyl group, a hydroxyisobutyl group, a hydroxytert-butyl group, a hydroxypentyl group, a hydroxyhexyl group, a hydroxyheptyl group, a hydroxyoctyl group, etc. In addition, an alkyl group can be optionally substituted.

[0080] The term "hydrogen" refers to 1H (protium, H), 2H (deuterium, D), or 3H (tritium, T). In various embodiments, "hydrogen" may be 1H (protium, H).

[0081] In various places of this specification, the substituents of compounds are disclosed in groups or ranges. It is clearly expected that this description includes each individual subcombination of the members of these groups and ranges. For example, it is clearly expected that the term "C1 to C8 alkyl" discloses C1, C2, C3, C4, C5, C6, C7, C8, C1 to C8, C1 to C7, C1 to C6, C1 to C5, C1 to C4, C1 to C3, C1 to C2, C2 to C8, C2 to C7, C2 to C6, C2 to C5, C2 to C4, C2 to C3, C3 to C8, C3 to C7, C3 to C6, C3 to C5, C3 to C4, C4 to C8, C4 to C7, C4 to C6, C4 to C5, C5 to C8, C5 to C7, C5 to C6, C6 to C8, C6 to C7 and C7 to C8 alkyl.

[0082] As further examples, the integers in the range of 5 to 40 are specifically contemplated as individually disclosing 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, and 40; the integers in the range of 1 to 20 are specifically contemplated as individually disclosing 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20. Additional groups or ranges are expressly contemplated accordingly.

[0083] When the above groups are substituted, the substituent group may be a halogen atom or a heteroatom.

[0084] The term "halogen atom" refers to a fluorine atom, a chlorine atom, a bromine atom or the like.

[0085] The term "heteroatom" refers to a nitrogen atom, a sulfur atom, a phosphate atom, and the like.

[0086] Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is arranged between the positive electrode sheet and the negative electrode sheet. Its main function is to prevent the positive electrode sheet and the negative electrode sheet from short-circuiting, while allowing active ions to pass freely to form a loop.

[0087] With the application and promotion of secondary batteries, people have higher and higher requirements for the performance (such as safety performance) of secondary batteries. The separator is an important component of secondary batteries, and the safety performance of secondary batteries can be improved by improving the performance of the separator.

[0088] The inventors discovered that the isolation membranes in the related art have poor adhesion, and the isolation membranes have poor adhesion to the positive and negative electrode sheets. Usually, a coating containing a polymer is applied to the substrate to improve its adhesion; however, the polymer coating still has the problem of shrinkage at high temperatures. Specifically, the secondary battery releases heat during long-term cycle charge and discharge, and the heat causes the temperature inside the secondary battery to rise. The isolation membrane has poor heat resistance and a high shrinkage rate at high temperatures, making it impossible for the isolation membrane as a whole to play a good insulating role for the positive and negative electrode sheets, thereby deteriorating the safety performance of the secondary battery. In addition, the isolation membrane also needs to have good anti-swelling properties under the infiltration of the electrolyte. This is because if the isolation membrane is easy to swell, the volume of the isolation membrane increases significantly, which may cause squeezing of the positive and negative electrode sheets, causing adverse effects on the positive and negative electrode sheets. It can be seen that the isolation membranes in the related art are difficult to take into account adhesion, heat resistance and anti-swelling properties.

[0089] In order to solve the above problems, the inventors started from the perspective of improving the coating performance of the isolation membrane. The coating includes a polymer, which is formed by polymerizing monomers with multiple functions, thereby improving the performance of the isolation membrane. The technical solution of this application is described in detail below.

[0090] polymer

[0091] In a first aspect, the present application provides a polymer comprising a first structural unit, a second structural unit, and a third structural unit.

[0092] The first structural unit includes a structural unit represented by formula (I),

[0093]

[0094] In formula (I), R1 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group; alternatively, R1 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group;

[0095] R2 includes one or more of substituted or unsubstituted C1-C20 alkyl, substituted or unsubstituted C3-C20 cycloalkyl, substituted or unsubstituted C1-C20 hydroxyalkyl; alternatively, R2 includes one or more of C1-C12 alkyl, C3-C12 cycloalkyl, C1-C12 hydroxyalkyl.

[0096] The second structural unit includes a structural unit represented by formula (II),

[0097]

[0098] In formula (II), R3 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group; alternatively, R3 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group.

[0099] The third structural unit includes a structural unit represented by formula (III),

[0100]

[0101] In formula (III), R4 to R 11 Each independently comprises a substituted or unsubstituted C1-C10 alkyl group, one or more structural units as shown in formula (III-1), and R4 to R 11 At least one of them includes a structural unit represented by formula (III-1),

[0102]

[0103] In formula (III-1), R 12 Including one or more of hydrogen atoms, substituted or unsubstituted C1-C5 alkyl groups; optionally, R 12 Including one or more of hydrogen atom, substituted or unsubstituted C1-C3 alkyl; R 13 Including substituted or unsubstituted C1-C10 alkyl; optionally, R 13 This includes substituted or unsubstituted C3-C10 alkyl groups.

[0104] The polymer of the present application includes a first structural unit, a second structural unit and a third structural unit, and has good adhesion, stability, anti-swelling and heat resistance, etc.

[0105] Although the mechanism is not yet clear, the inventors of this application speculate that the possible reasons include the following:

[0106] The first structural unit can be formed by opening the carbon-carbon double bond of an acrylic ester monomer during the polymerization process. Since the flexible monomer segment in the molecular chain segment can adjust the glass transition temperature of the polymer, improve the toughness and peel strength of the polymer, it helps to exert a good bonding effect.

[0107] The second structural unit, formed by opening the carbon-carbon double bond of an acrylonitrile monomer during polymerization, exhibits excellent swelling resistance and high adhesion, helping to improve the ionic conductivity of secondary batteries. When the polymer is used in a separator, it comes into contact with the electrolyte, making it less susceptible to swelling and exhibiting good swelling resistance.

[0108] The third structural unit is formed by opening the carbon-carbon double bond of the substituted or unsubstituted acryloxy group of polysilsesquioxane during the polymerization process. Polysilsesquioxane can be considered as a material containing an organic-inorganic hybrid core-shell structure, wherein the internal inorganic framework serves as the core, i.e., a skeleton structure composed of Si-O-Si or Si-O bonds; the outer shell is composed of organic substituents (C1-C5 alkyl groups), which are wrapped around the skeleton structure and connected to the Si element of the skeleton structure. The core structure of polysilsesquioxane can give the polymer advantages in heat resistance and mechanical properties. Its poor shrinkage can ensure the stability of the polymer during the long-term cycle charge and discharge process of the secondary battery, effectively isolating the positive and negative electrodes, thereby ensuring the safety performance of the secondary battery. In addition, due to the small particle size and large specific surface area of ​​polysilsesquioxane, it is similar to most polymer chain segments in physical scale, which makes the atoms on the surface of polysilsesquioxane have high reactivity. The polymer modified with polysilsesquioxane has good heat resistance, flame retardancy and antioxidant properties.

[0109] While the above analysis is based on individual structural units, the synergistic effects between them cannot be ignored. Specifically, the first and third structural units work synergistically to enhance the polymer's adhesion and heat resistance; the first and second structural units work synergistically to improve the polymer's stability and anti-swelling properties.

[0110] In some embodiments, based on the total molar amount of the first structural unit, the second structural unit, and the third structural unit, the molar content of the first structural unit is recorded as A%, and 60≤A<100. When the molar content of the first structural unit is within the above range, its proportion in the polymer is relatively large, which can improve the flexibility of the polymer, thereby significantly improving the adhesion of the polymer; when the polymer is applied to an isolation membrane, it can improve the bonding strength between the polymer and the substrate of the isolation membrane. Optionally, 60≤A≤80. For example, the molar content of the first structural unit can be 60%, 65%, 70%, 75%, 80%, or a range consisting of any two of the above values.

[0111] In some embodiments, the molar content of the second structural unit, based on the total molar amount of the first structural unit, the second structural unit, and the third structural unit, is denoted as B%, where 0 < B ≤ 20. When the molar content of the second structural unit is within the above range, the stability of the polymer can be significantly improved. Alternatively, 5 ≤ B ≤ 20. For example, the molar content of the second structural unit can be 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, or a range consisting of any two of the above values.

[0112] In some embodiments, based on the total molar amount of the first structural unit, the second structural unit and the third structural unit, the molar content of the third structural unit is recorded as C%, 0<C≤20. When the molar content of the third structural unit is within the above range, the heat resistance of the polymer can be guaranteed, and its proportion is relatively small, which is beneficial to increase the proportion of the first structural unit and the second structural unit, and improve the overall adhesion, stability and anti-swelling properties of the polymer. Optionally, 5≤C≤20. For example, the molar content of the third structural unit can be 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20% or a range consisting of any two of the above values.

[0113] The polymer includes a first structural unit, which imparts good adhesion and flexibility to the polymer. However, since the polymer inevitably comes into contact with the electrolyte when applied to the separator, the swelling effect of the electrolyte can reduce the polymer's adhesion to a certain extent. The polymer also includes a second structural unit, and the cyano group in the second structural unit can synergize with the first structural unit to jointly improve the polymer's anti-swelling and adhesion properties. In particular, when the present application further satisfies 3≤A / B≤16, the first structural unit can further fully exert the synergistic effect with the second structural unit to improve the polymer's adhesion, stability, and anti-swelling properties. For example, A / B can be 3, 4, 5, 8, 10, 12, 15, 16, or a range consisting of any two of the above values.

[0114] The polymer includes a first structural unit, which imparts good adhesion to the polymer, but its own heat resistance is relatively poor. When the polymer is used in a separator, the temperature inside the secondary battery increases as the charge and discharge time of the secondary battery increases, which may cause damage to the first structural unit. The polymer also includes a third structural unit. The inorganic structure of the polysilsesquioxane in the third structural unit can synergize with the first structural unit to improve the overall heat resistance and adhesion properties of the polymer. In particular, when the present application further satisfies 3≤A / C≤16, the first structural unit can further fully exert the synergistic effect with the third structural unit to improve the adhesion and heat resistance of the polymer. For example, A / C can be 3, 4, 5, 8, 10, 12, 15, 16, or a range consisting of any two of the above values.

[0115] In some embodiments, A:B:C is (12 to 16): (1 to 4): (1 to 4). When the molar contents of the first structural unit, the second structural unit, and the third structural unit meet the above ratios, the three structural units in the polymer work together to improve the adhesion, stability, anti-swelling and thermal stability of the polymer. For example, A:B:C can be 12:4:4, 13:4:3, 14:4:2, 15:4:1, 16:3:1, 13:3:4 or 15:1:4. The first structural unit includes a variety of chemical structures, and the specific chemical structure of the first structural unit is described below.

[0116] In some embodiments, R1 includes a hydrogen atom or a methyl group.

[0117] In some embodiments, R2 comprises methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-octyl, isooctyl, 2-ethylhexyl, dodecyl, or isobornyl.

[0118] Illustratively, the first structural unit includes one or more of the structures represented by formula (I-1) to formula (I-8):

[0119]

[0120] The second structural unit includes a variety of chemical structures, and the specific chemical structure of the second structural unit is described below.

[0121] In some embodiments, R3 includes a hydrogen atom or a methyl group.

[0122] Illustratively, the second structural unit includes one or more of the structures represented by formula (II-1) to the structures represented by formula (II-4):

[0123]

[0124] The third structural unit includes a variety of chemical structures, and the specific chemical structure of the third structural unit is described below.

[0125] In some embodiments, R4 to R 11 Each independently comprises a structural unit as shown in formula (III-1); optionally, R 12 including hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl or n-pentyl; and / or R 13 These include n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-octyl, isooctyl or 2-ethylhexyl.

[0126] In some embodiments, R4 to R 11One of them includes a structural unit as shown in formula (III-1); optionally, R 12 including hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl or n-pentyl; and / or R 13 These include n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-octyl, isooctyl or 2-ethylhexyl.

[0127] The types of groups in the polymer can be measured using infrared spectroscopy. For example, the infrared spectrum of the material can be tested to determine the characteristic peaks contained therein, thereby determining the type of the modified group. Specifically, the material can be subjected to infrared spectroscopy analysis using instruments and methods well known in the art, for example, using an infrared spectrometer (such as the IS10 Fourier transform infrared spectrometer from Nicolet, USA), and tested according to GB / T 6040-2019 General Rules for Infrared Spectroscopy.

[0128] In some embodiments, the polymer has an infrared spectrum at 1750 cm -1 to 1735cm -1 , which indicates the presence of ester groups.

[0129] In some embodiments, the polymer has an infrared spectrum at 2260 cm -1 to 2220cm -1 , which indicates the presence of a cyano group.

[0130] In some embodiments, the polymer has an infrared spectrum of 1100 nm. -1 to 1120cm -1 The characteristic peaks of silsesquioxane are shown in FIG1 , which indicates the presence of the Si-O-Si skeleton of silsesquioxane.

[0131] The inventors found in further research that when the specific parameters of the polymer are within a specific range, the adhesion and stability of the polymer can be significantly improved.

[0132] In some embodiments, the number average molecular weight of the polymer is 20,000 to 80,000, optionally 30,000 to 50,000. For example, the number average molecular weight of the polymer can be 20,000, 25,000, 30,000, 35,000, 40,000, 45,000, 50,000, 55,000, 60,000, 65,000, 70,000, 75,000, 80,000, or a range consisting of any two of the above values. When the number average molecular weight of the polymer is within the above range, it is conducive to forming polymer particles with a smaller particle size. When applied to an isolation membrane, it can achieve a thin coating of the coating in the isolation membrane, reduce the overall thickness of the isolation membrane, and thus facilitate the improvement of the energy density of the secondary battery; and the particle size of the polymer particles formed by the polymer will not be too small, which can reduce the risk of polymer particles clogging the substrate in the isolation membrane and improve the overall air permeability and other properties of the isolation membrane.

[0133] The number average molecular weight of the polymer can be measured by gel permeation chromatography (GPC). Specifically, the measurement is performed using a GPC1515 instrument from Waters, USA. The sample is dissolved in tetrahydrofuran for more than 12 hours at a concentration of 4 mg / ml. The sample is filtered and tested at a temperature of 25°C and a flow rate of 1 ml / min.

[0134] The inventors have found in further studies that when the polymer is in a granular form and satisfies at least one of the following conditions, the polymer's adhesion, stability, anti-swelling and heat resistance can be further improved.

[0135] In some embodiments, the morphology of the polymer includes spherical and / or quasi-spherical shapes. When the polymer is applied to the separator, the polymer is in a granular form. The spherical and / or quasi-spherical granular form can ensure good overlap between the particles, and the presence of gaps between the particles is conducive to building a stable spatial network structure, thereby improving the ion transport properties and resistance to external force extrusion of the separator. In addition, the gaps between the spherical and / or quasi-spherical particles are large, which can reduce the effect of the coating on the air permeability of the substrate, further improve the overall air permeability and ion conductivity of the separator, and improve the dynamic performance of the secondary battery. Furthermore, the larger porosity between the spherical and / or quasi-spherical particles is conducive to improving the wettability of the separator to the electrolyte and the liquid retention rate and liquid retention rate of the separator, further improving the dynamic performance of the secondary battery; and the larger porosity can have a weight reduction effect, which is conducive to improving the energy density per unit weight of the secondary battery; and it can reduce the amount of polymer used in the coating, which is conducive to reducing the cost of the secondary battery.

[0136] The morphology of the polymer can be observed by a scanning electron microscope (SEM), for example, a JSM-5610LV scanning electron microscope produced by FEI Company of the United States is used to observe the morphology of the sample after vacuum gold spraying.

[0137] In some embodiments, the volume distribution particle size Dv50 of the polymer satisfies the following conditions: 0.1 μm ≤ Dv50 ≤ 2.0 μm; alternatively, 0.5 μm ≤ Dv50 ≤ 1.2 μm. The relatively small particle size of the polymer facilitates uniform dispersion of the polymer when applied to a separator, resulting in a more uniform film layer. For example, the volume distribution particle size Dv50 of the polymer can be 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.5 μm, 2.0 μm, or a range consisting of any two of the foregoing values.

[0138] The volume distribution particle size Dv50 of a polymer is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using a laser particle size analyzer (e.g., Master Size 3000) in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0139] In some embodiments, the specific surface area of ​​the polymer is denoted as S, and its unit is m 2 / g, 5.0≤S≤12.0; optionally, 6.0≤S≤10.0. When the specific surface area of ​​the polymer is within the above range, the specific surface area of ​​the polymer is relatively large, which is conducive to good overlap between particles, making it easier to form a pore structure between polymer particles, which is conducive to the migration of active ions. For example, the specific surface area of ​​the polymer can be 5.0m 2 / g, 5.5m 2 / g, 6.0m 2 / g, 7.0m 2 / g, 8.0m 2 / g, 9.0m 2 / g, 10.0m 2 / g, 11.0m 2 / g, 12.0m 2 / g or a range consisting of any two of the above values.

[0140] The specific surface area of ​​a polymer is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis method described in GB / T 19587-2017 and calculated using the BET (Brunauer-Emmett-Teller) method. Alternatively, the nitrogen adsorption specific surface area analysis can be performed using a Micromeritics Tri-Star 3020 specific surface area pore size analyzer.

[0141] Method for preparing polymers

[0142] In a second aspect, the present application provides a method for preparing a polymer, which can be used to prepare the polymer of any embodiment of the first aspect of the present application.

[0143] The method comprises:

[0144] Step S100, providing a first monomer, a second monomer and a third monomer;

[0145] In step S200 , the first monomer, the second monomer, and the third monomer are mixed and polymerized under the action of an initiator to generate a polymer.

[0146] In the present application, the first monomer, the second monomer and the third monomer are mixed and copolymerized, and the formed polymer is a copolymer of the three monomers.

[0147] The first monomer includes a compound represented by formula (IV),

[0148]

[0149] In formula (IV), R1 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group; alternatively, R1 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group;

[0150] R2 includes one or more of substituted or unsubstituted C1-C20 alkyl, substituted or unsubstituted C3-C20 cycloalkyl, substituted or unsubstituted C1-C20 hydroxyalkyl; alternatively, R2 includes one or more of C1-C12 alkyl, C3-C12 cycloalkyl, C1-C12 hydroxyalkyl.

[0151] The first monomer is an acrylic acid ester compound, and when it is polymerized, the carbon-carbon double bond opens to form a first structural unit.

[0152] Illustratively, the first monomer includes one or more of methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.

[0153] The second monomer includes a compound represented by formula (V),

[0154]

[0155] In formula (V), R3 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group; alternatively, R3 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group.

[0156] The second monomer is an acrylonitrile compound, and when it is polymerized, the carbon-carbon double bond opens to form a second structural unit.

[0157] Illustratively, the second monomer includes acrylonitrile and / or methacrylonitrile.

[0158] The third monomer includes a compound represented by formula (VI),

[0159]

[0160] In formula (VI), R 30 to R 37 Each independently comprises a substituted or unsubstituted C1-C10 alkyl group, one or more structural units as shown in formula (VI-1), and R 30 to R 37 At least one of them is a structural unit represented by formula (VI-1),

[0161]

[0162] In formula (VI-1), R 12 Including one or more of hydrogen atoms, substituted or unsubstituted C1-C5 alkyl groups; optionally, R 12 including one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group;

[0163] R 13 Including substituted or unsubstituted C1-C10 alkyl; optionally, R 13 This includes substituted or unsubstituted C3-C10 alkyl groups.

[0164] Illustratively, the third monomer includes one or more of methacryloxypropyl cage polysilsesquioxane, methacryloxypropyl heptaisobutyl polysilsesquioxane, methacryloxypropyl heptaoctyl polysilsesquioxane, acryloxypropyl cage polysilsesquioxane, acryloxypropyl heptaisobutyl polysilsesquioxane, and methacryloxypropyl heptaoctyl polysilsesquioxane.

[0165] In some embodiments, step S200 specifically includes:

[0166] Step S210, adding a first monomer, a second monomer, and a third monomer into a solvent and an emulsifier and mixing them to form a mixed system;

[0167] In step S220, an initiator is added to the mixed system, and a polymerization reaction occurs under the action of the initiator to generate a polymer.

[0168] The present application can copolymerize multiple monomers by emulsion polymerization, which is a simpler polymerization method. Of course, the present application can also adopt other polymerization methods, such as solution polymerization, suspension polymerization, etc. The process parameters used in the polymerization process can be selected from commonly used parameters in the field and will not be repeated here.

[0169] In some embodiments, the emulsifier includes one or more of sodium lauryl sulfate, sodium dodecylbenzene sulfonate, alkyl diphenyl oxide disulfonate, and ammonium ethoxylated alkylphenol sulfate.

[0170] In some embodiments, the ratio of the mass percentage of the emulsifier to the mass percentage of the first, second, and third monomers, based on the total mass of the mixed system, is 0.1% to 5%, i.e., the amount of the emulsifier used is 0.1% to 5% of the total mass of the three monomers. When the mass percentage of the emulsifier is within this range, the first, second, and third monomers can be emulsified and dispersed in the solvent to form a relatively uniform system.

[0171] In some embodiments, the initiator includes potassium persulfate and / or ammonium persulfate.

[0172] In some embodiments, the ratio of the mass percentage of the initiator to the mass percentage of the second monomer, the second monomer, and the third monomer, based on the total mass of the mixed system, is 0.15% to 1%. That is, the amount of the initiator used is 0.1% to 5% of the total mass of the three monomers. When the mass percentage of the initiator is within this range, sufficient polymerization can be ensured.

[0173] In some embodiments, the solvent may include water, such as deionized water.

[0174] As a specific embodiment, the method includes:

[0175] Preparation of prepolymer: deionized water, emulsifier, first polymerizable monomer, second polymerizable monomer and third polymerizable monomer are mixed and stirred uniformly to obtain a prepolymer;

[0176] Preparation of polymer: Add emulsifier and deionized water into the container and stir and emulsify for 30 to 60 minutes.

[0177] A uniform and stable emulsion is obtained; the prepolymer and initiator solution prepared in the previous step (the initiator potassium persulfate and / or ammonium persulfate is dissolved in deionized water to form a solution) are then slowly added dropwise. After the addition is completed, the temperature is raised to 90°C to 110°C and kept warm for reaction for 0.5h. The mixture is cooled to 40°C, the pH is adjusted to 7 to 8 with aqueous ammonia, filtered, discharged, and dried to obtain a polymer.

[0178] Isolation film

[0179] In a third aspect, the present application proposes an isolation membrane.

[0180] The isolation membrane includes a substrate and a coating disposed on at least one surface of the substrate, wherein the coating includes a polymer as described in any embodiment of the first aspect of the present application or a polymer prepared by the method described in any embodiment of the second aspect of the present application. Because the polymer has excellent adhesion, stability, swelling resistance, and heat resistance, when applied to the isolation membrane coating, it can significantly improve the adhesion, stability, swelling resistance, and heat resistance of the isolation membrane as a whole.

[0181] In some embodiments, based on the mass of the coating, the mass percentage of the polymer is m%, and m≥70;

[0182] Optionally, 80 ≤ m ≤ 95. When the polymer mass percentage is within the above range, the overall adhesion, stability, anti-swelling, and heat resistance of the separator can be further improved. The polymer mass percentage m% can be 70%, 80%, 85%, 86%, 88%, 90%, 92%, 95%, 98%, 99%, or a range consisting of any two of the above values.

[0183] The present application does not particularly limit the material of the substrate. Any known substrate with good chemical and mechanical stability may be selected, such as at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The substrate may be a single-layer film or a multi-layer composite film. When the substrate is a multi-layer composite film, the materials of each layer may be the same or different.

[0184] In some embodiments, the coating layer may further include a filler. Further, the filler may include at least one of inorganic particles and organic particles.

[0185] In some embodiments, the decomposition temperature of the filler may be above 200° C., so that the filler has good thermal stability and is not easily decomposed, thereby further improving the heat resistance of the isolation membrane.

[0186] The inorganic particles have the characteristics of high thermal stability and non-decomposability. In some embodiments, the inorganic particles may include at least one of inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of electrochemical reactions.

[0187] Optionally, the inorganic particles having a dielectric constant of 5 or more include boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O3 (abbreviated as PLZT, 0<m<1, 0<n<1), Pb(Mg3Nb 2 / 3 )O3-PbTiO3 (abbreviated as PMN-PT), and at least one of their respective modified inorganic particles. Optionally, the modification method of each inorganic particle may be chemical modification and / or physical modification. The chemical modification method includes coupling agent modification (for example, using silane coupling agent, titanate coupling agent, etc.), surfactant modification, polymer grafting modification, etc. The physical modification method may be mechanical force dispersion, ultrasonic dispersion, high energy treatment, etc. The modification treatment can reduce the agglomeration of inorganic particles, thereby enabling them to form a more stable and uniform spatial network structure with nanocellulose; in addition, by selecting coupling agents, surfactants or polymer-modified inorganic particles with specific functional groups, it is also helpful to improve the coating's wetting properties for the electrolyte and improve the bonding strength between the coating and the substrate.

[0188] Optionally, the inorganic particles having ion conductivity but not storing ions include Li3PO4, lithium titanium phosphate Li x1 Ti y1 (PO4)3, lithium aluminum titanium phosphate Li x2 Al y2 Ti z1 (PO4)3, (LiAlTiP) x3 O y3 Type glass, lanthanum lithium titanate Li x4 La y4 TiO3, lithium germanium thiophosphate Li x5 Ge y5 P z2 S w , lithium nitride Li x6 N y6 、SiS2 type glass Li x7 Si y7 S z3 and P2S5 glass Li x8 P y8 S z4At least one of the following: 0<x1<2, 0<y1<3, 0<x2<2, 0<y2<1, 0<z1<3, 0<x3<4, 0<y3<13, 0<x4<2, 0<y4<3, 0<x5<4, 0<y5<1, 0<z2<1, 0<w<5, 0<x6<4, 0<y6<2, 0<x7<3, 0<y7<2, 0<z3<4, 0<x8<3, 0<y8<3, 0<z4<7. This can further improve the ion transport properties of the isolation membrane.

[0189] Optionally, the inorganic particles capable of undergoing electrochemical reaction include at least one of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials and lithium-titanium compounds.

[0190] Organic particles have good thermal stability and are not easy to decompose, thereby improving the heat resistance of the isolation membrane; at the same time, when the internal temperature of the secondary battery reaches the melting point of the organic particles due to overcharge abuse, heat abuse, etc., the organic particles can also melt and be absorbed into the micropores of the substrate due to capillary action to play the role of closing the pores and breaking the circuit, which is beneficial to ensure that the secondary battery has high safety performance.

[0191] In some embodiments, the organic particles include but are not limited to at least one of polyethylene particles, polypropylene particles, polystyrene particles, melamine resin particles, phenolic resin particles, polyester particles (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, polyaryletherketone particles, and copolymers of butyl acrylate and ethyl methacrylate (e.g., cross-linked polymers of butyl acrylate and ethyl methacrylate).

[0192] In some embodiments, the glass transition temperature of the organic particles can optionally be above 130°C. Thus, when the internal temperature of the secondary battery reaches 130°C, the organic particles will not transition from a glassy state to a viscous flow state, thereby ensuring that the separator does not shrink dramatically. More optionally, the organic particles include, but are not limited to, at least one of melamine formaldehyde resin particles, phenolic resin particles, polyester particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, and polyaryletherketone particles.

[0193] In some embodiments, the coating further comprises a binder. The present application does not particularly limit the type of binder; any known material with good adhesive properties may be used. For example, the binder comprises at least one of an aqueous solution-based acrylic resin (e.g., a homopolymer of acrylic acid, methacrylic acid, or sodium acrylate, or a copolymer with other comonomers), polyvinyl alcohol, an isobutylene-maleic anhydride copolymer, and polyacrylamide.

[0194] Optionally, the content of the binder in the coating is less than 30%, based on the mass of the coating.

[0195] In some embodiments, the separator may further include an adhesive layer disposed on at least a portion of the coating, the adhesive layer comprising a binder. The adhesive layer not only prevents the coating from falling off, thereby improving the safety of the secondary battery, but also improves the interface between the separator and the electrode, thereby enhancing the cycling performance of the secondary battery.

[0196] Optionally, the binder includes at least one of an acrylate monomer homopolymer or copolymer, an acrylic acid monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer. The comonomer includes but is not limited to at least one of an acrylate monomer, an acrylic acid monomer, an olefin monomer, a halogen-containing olefin monomer, and a fluoroether monomer.

[0197] Alternatively, the binder includes a vinylidene fluoride based polymer, such as a homopolymer of vinylidene fluoride monomer (VDF) and / or a copolymer of vinylidene fluoride monomer and other comonomers. The other comonomers may be at least one of an olefin monomer, a fluorine-containing olefin monomer, a chlorine-containing olefin monomer, an acrylate monomer, an acrylic monomer, and a fluoroether monomer. Alternatively, the other comonomers may include trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-vinylidene fluoride, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro (alkyl vinyl) ether (such as perfluoro (methyl vinyl) ether PMVE, perfluoro (ethyl vinyl) ether PEVE, perfluoro (propyl vinyl) ether PPVE), perfluoro (1,3-dioxole) and perfluoro (2,2-dimethyl-1,3-dioxole) (PDD).

[0198] In some embodiments, the longitudinal heat shrinkage rate η1 of the isolation film at 150° C. for 1 hour is ≤5.0%, optionally, 0.5%≤η1≤3%.

[0199] In some embodiments, the transverse heat shrinkage rate η2 of the isolation film at 150° C. for 1 hour is ≤5.0%, optionally, 0.5%≤η2≤2%.

[0200] The separator of the present application has low thermal shrinkage in both the transverse and longitudinal directions at a high temperature of 150° C., thereby further improving the safety performance of the secondary battery.

[0201] In some embodiments, the longitudinal tensile strength R of the separator is m1 ≥3000kg / cm 2 , optionally, 3500kg / cm 2 ≤R m1 ≤4500kg / cm 2 .

[0202] In some embodiments, the transverse tensile strength R of the separator is m2 ≥3000kg / cm 2 , optionally, 3500kg / cm 2 ≤R m2 ≤4500kg / cm 2 .

[0203] The separator of the present application has high tensile strength in both the transverse and longitudinal directions. Therefore, when the secondary battery expands, the probability of the separator being damaged is low, thereby further improving the safety performance of the secondary battery.

[0204] In some embodiments, the air permeability of the isolation membrane is MAP≤250s / 100mL, optionally, 120s / 100mL≤MAP≤180s / 100mL. The isolation membrane of the present application has good air permeability, thereby improving ion transmission properties.

[0205] In some embodiments, the wetted length L of the isolation membrane is ≥ 30 mm, optionally, 30 mm ≤ L ≤ 80 mm.

[0206] In some embodiments, the wetting speed of the isolation film u≥3 mm / s, optionally, 3 mm / s≤u≤10 mm / s.

[0207] The separator of the present application has good electrolyte infiltration properties, thereby improving ion transport properties and secondary battery capacity.

[0208] The thermal shrinkage, tensile strength, and air permeability of the separator are all well-known in the art and can be measured using methods known in the art. For example, they can be tested in accordance with standard GB / T 36363-2018.

[0209] The wetting length and wetting speed of the isolation membrane have well-known meanings in the art and can be measured using methods known in the art. An exemplary test method is as follows: cut the isolation membrane into samples with a width of 5 mm and a length of 100 mm, fix the two ends of the sample and place it horizontally; take 0.5 mg of electrolyte and drop it in the center of the sample. After reaching the specified time (1 min in this application), take a picture and measure the length of the electrolyte diffusion, thereby obtaining the wetting length and wetting speed of the isolation membrane. In order to ensure the accuracy of the test results, multiple (for example, 5 to 10) samples can be taken for testing, and the test results are obtained by calculating the average value. The electrolyte can be prepared as follows: ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a mass ratio of 30:50:20 to obtain an organic solvent, and fully dried LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0210] It should be noted that the coating parameters (e.g., surface density, thickness, etc.) of the above-mentioned isolation film are the coating parameters of a single side of the substrate. When the coating is provided on both sides of the substrate, the coating parameters on either side that meet the requirements of this application are considered to fall within the scope of protection of this application.

[0211] Method for preparing isolation film

[0212] In a fourth aspect, the present application further provides a method for preparing an isolation membrane, which can be used to prepare the isolation membrane of any embodiment of the third aspect of the present application.

[0213] The method comprises:

[0214] Step S10, providing a substrate;

[0215] Step S20, preparing a coating slurry: mixing a polymer according to a predetermined mass in a solvent to prepare the coating slurry;

[0216] Step S30, coating: coating the coating slurry on at least one surface of the substrate to form a coating and drying the coating to obtain an isolation film, wherein the isolation film includes a substrate and a coating disposed on at least one surface of the substrate.

[0217] The polymer in step S20 can be the polymer of any embodiment of the first aspect of the present application, or a polymer prepared by the method described in any embodiment of the second aspect of the present application.

[0218] In some embodiments, in step S20, the solvent may be water, such as deionized water.

[0219] In some embodiments, in step S20, the coating slurry may further include other components, for example, a dispersant, a wetting agent, a binder, etc.

[0220] In some embodiments, in step S20, the solid content of the coating slurry can be controlled between 28% and 45%, for example, between 30% and 38%. When the solid content of the coating slurry is within the above range, it can effectively reduce film surface problems of the coating and reduce the probability of uneven coating, thereby further improving the energy density and safety performance of the secondary battery.

[0221] In some embodiments, in step S30, the coating is performed using a coating machine. The present application does not specifically limit the type of coating machine; for example, a commercially available coating machine may be used. The coating machine includes a gravure roller for transferring the coating slurry to the substrate.

[0222] In some embodiments, in step S30, the coating method may be transfer coating, spin spray coating, dip coating, etc.

[0223] In some embodiments, the method further comprises the following steps:

[0224] Step S40, secondary coating: coating a slurry containing a binder on at least a portion of the surface of the coating layer, and forming an adhesive layer after drying. Optionally, the coating method is rotary spraying.

[0225] The method for preparing the isolation membrane of the present application obtains the coating layer through one-time coating, which greatly simplifies the production process of the isolation membrane.

[0226] Some parameters such as raw materials and their contents used in the preparation method of the isolation membrane of the present application can refer to the isolation membrane of the first aspect of the embodiment of the present application, and will not be repeated here.

[0227] Unless otherwise specified, all raw materials used in the method for preparing the separator of the present application can be obtained commercially.

[0228] secondary batteries

[0229] In a fifth aspect, the present application also provides a secondary battery.

[0230] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after discharge to reactivate their active materials for continued use. Typically, a secondary battery comprises an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is positioned between the positive and negative electrodes to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0231] The present application has no particular limitation on the type of secondary battery. For example, the secondary battery may be a lithium-ion battery, a sodium-ion battery, etc. In particular, the secondary battery may be a lithium-ion secondary battery.

[0232] The secondary battery described in the present application includes a separator according to the third aspect of the present application or a separator prepared by the method according to the fourth aspect of the embodiment of the present application, wherein the separator is spaced between the positive electrode sheet and the negative electrode sheet. Optionally, at least one side of the separator close to the negative electrode sheet has a coating according to the present application. Furthermore, the side of the separator close to the positive electrode sheet has a coating according to the present application, and the side of the separator close to the negative electrode sheet also has a coating according to the present application; thereby, the secondary battery of the present application can improve its own safety performance.

[0233] [Positive electrode]

[0234] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector has two surfaces that oppose each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0235] When the secondary battery of the present application is a lithium-ion battery, the positive electrode active material may include, but is not limited to, at least one of a lithium-containing transition metal oxide, a lithium-containing phosphate, and their respective modified compounds. Examples of the lithium transition metal oxide may include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of the lithium-containing phosphate may include, but are not limited to, at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds.

[0236] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium ion battery may include a general formula of Li a Ni b Co c M d O e A f At least one of a lithium transition metal oxide and a modified compound thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes at least one of N, F, S and Cl.

[0237] As an example, the positive active material for lithium ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622),LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 At least one of O2, LiFePO4, and LiMnPO4.

[0238] When the secondary battery of the present application is a sodium ion battery, the positive electrode active material may include but is not limited to at least one of sodium-containing transition metal oxides, polyanion materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0239] As an example, the positive active material for sodium ion batteries may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, NaNi 1 / 2 Ti 1 / 2 O2、NaNi 1 / 2 Mn 1 / 2 O2、Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2、NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials, general formula X p M' q (PO4) r O x Y 3-x At least one of the materials. p M' q (PO4) r O x Y 3-x , 0<p≤4, 0<q≤2, 1≤r≤3, 0≤x≤2, X includes H + 、Li + 、Na +, K + and NH4 + At least one of , M' is a transition metal cation, optionally at least one of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halogen anion, optionally at least one of F, Cl and Br.

[0240] In the present application, the modified compounds of the above-mentioned positive electrode active materials may be the ones subjected to doping modification and / or surface coating modification on the positive electrode active materials.

[0241] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. This application does not particularly limit the type of the positive electrode conductive agent. By way of example, the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent is ≤5% based on the total mass of the positive electrode film layer.

[0242] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. This application does not particularly limit the type of the positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin. In some embodiments, based on the total mass of the positive electrode film layer, the mass percentage of the positive electrode binder is ≤5%.

[0243] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0244] The positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0245] [Negative electrode]

[0246] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0247] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. For example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material may include at least one of elemental tin, tin oxide, and a tin alloy.

[0248] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent. By way of example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent is ≤5% based on the total mass of the negative electrode film layer.

[0249] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. The present application does not particularly limit the type of the negative electrode binder. For example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), a water-soluble unsaturated resin SR-1B, a water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is ≤5% based on the total mass of the negative electrode film layer.

[0250] In some embodiments, the negative electrode film layer may optionally include other additives. For example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, or the like. In some embodiments, the weight percentage of the other additives is ≤ 2% based on the total weight of the negative electrode film layer.

[0251] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0252] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring until uniformly mixed. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0253] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate described herein further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode plate described herein further includes a protective layer covering the surface of the negative electrode film layer.

[0254] [Electrolyte]

[0255] During the charge and discharge process of a secondary battery, active ions are embedded and released back and forth between the positive and negative electrodes, and the electrolyte conducts the active ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected according to actual needs.

[0256] The electrolyte solution includes an electrolyte salt and a solvent. The types of the electrolyte salt and the solvent are not particularly limited and can be selected according to actual needs.

[0257] When the secondary battery of the present application is a lithium ion battery, as an example, the electrolyte salt may include but is not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0258] When the secondary battery of the present application is a sodium ion battery, as an example, the electrolyte salt may include but is not limited to at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalatoborate (NaDFOB), sodium dioxalatoborate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorobis(oxalatophosphate) (NaDFOP) and sodium tetrafluorooxalatophosphate (NaTFOP).

[0259] As an example, the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0260] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0261] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly through a winding process and / or a lamination process.

[0262] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0263] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0264] The present application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. FIG1 shows a secondary battery 5 with a square structure as an example.

[0265] In some embodiments, as shown in FIG2 , 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 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can be formed into an electrode assembly 52 through a winding process and / or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to demand.

[0266] The preparation method of the secondary battery of the present application is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, separator, and negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. The secondary battery is then vacuum packaged, allowed to stand, formed, and shaped.

[0267] In some embodiments of the present application, the secondary batteries according to the present application can be assembled into a battery module. The battery module can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0268] Figure 3 is a schematic diagram of an exemplary battery module 4. As shown in 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 using fasteners.

[0269] 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.

[0270] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0271] Figures 4 and 5 are schematic diagrams of an exemplary battery pack 1. As shown in 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 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0272] Electrical devices

[0273] The sixth aspect of the embodiment of the present application provides an electric device, which includes at least one of the secondary battery, battery module or battery pack of 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 can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0274] The electrical device may select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0275] Figure 6 is a schematic diagram of an exemplary 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 this device, a battery pack or battery module may be used.

[0276] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0277] Example

[0278] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are commercially available.

[0279] Preparation of polymers

[0280] Example A

[0281] Prepolymer preparation

[0282] 1400 g of deionized water and 7 g of sodium lauryl sulfate were added to a 5L three-necked flask, and the mixture was stirred and emulsified at a speed of 1500 r / min for 30 min to obtain a uniform and stable emulsion. Then, 645.68 g of methyl acrylate, 79.59 g of acrylonitrile and 663.50 g of methacryloyloxypropyl cage polysilsesquioxane (the molar content ratio of methyl acrylate, acrylonitrile and methacryloyloxypropyl cage polysilsesquioxane was 15:3:2) were added in sequence, and stirring was continued at a speed of 1500 r / min for 30 min to obtain a uniform prepolymer.

[0283] Polymer preparation

[0284] In a dry three-necked flask, add 3g of emulsifier and 1000g of deionized water, stir and emulsify at high speed for 30min to obtain a uniform and stable emulsion; then use a peristaltic pump to slowly drop the prepolymer and initiator solution prepared in the previous step (dissolve 3g of potassium persulfate as initiator in 30g of deionized water to form a solution), after the addition is completed, heat to 90°C and keep warm for 0.5h, cool to 40°C, adjust the pH to 7-8 with ammonia water, filter, discharge, and obtain a polymer through a drying process.

[0285] Example B to Example E

[0286] The polymer was prepared by a method similar to that of Example A. The difference from Example A was that at least one of the raw material components and contents was adjusted.

[0287] The relevant parameters for polymer preparation are shown in Tables 1 and 2.

[0288] Example 1

[0289] Preparation of isolation membrane

[0290] Provide PE substrate: thickness 7μm, porosity 40%, ion conductivity 1.20mS / cm.

[0291] Preparation of coating slurry: The polymer prepared in Example A and the binder aqueous solution type polyacrylic acid were mixed uniformly in a proper amount of solvent deionized water at a mass ratio of 90:10 to obtain coating slurry.

[0292] Coating: The prepared coating slurry is coated on both surfaces of the PE substrate using a coating machine, and then dried and cut to obtain a separator. The surface density of the coating on one side of the PE substrate is 0.9 g / m 2 , thickness is 0.45μm.

[0293] Preparation of positive electrode

[0294] The positive electrode active material LiNi 0.8 Co 0.1 Mn0.1 O2 (NCM811), conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in an appropriate amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 96.2:2.7:1.1 to obtain a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through drying, cold pressing, slitting, cutting and other processes. The surface density of the positive electrode sheet is 0.207mg / mm 2 , compacted density is 3.5g / cm 3 .

[0295] Preparation of negative electrode sheet

[0296] The negative electrode active material artificial graphite, conductive agent carbon black (Super P), binder styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) were mixed uniformly in an appropriate amount of deionized water as a solvent at a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry; the negative electrode slurry was coated on the negative electrode current collector copper foil, and the negative electrode sheet was obtained through drying, cold pressing, slitting and cutting processes. The surface density of the negative electrode sheet is 0.126mg / mm 2 , compacted density is 1.7g / cm 3 .

[0297] Preparation of electrolyte

[0298] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:70 to obtain an organic solvent, and fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0299] Preparation of secondary batteries

[0300] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly; the electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After vacuum packaging, standing, formation, shaping and other processes, a secondary battery is obtained.

[0301] Comparative Example, Example 2 to Example 15

[0302] The secondary battery was prepared using a method similar to that of Example 1, except that the preparation parameters of the isolation membrane were different. The specific parameters are shown in Table 3.

[0303] Example 16

[0304] The secondary battery was prepared by a method similar to that of Example 1, except that the coating slurry was prepared by mixing the polymer prepared in Example A, filler alumina (average particle size Dv50 of 300 nm), and binder aqueous solution type polyacrylic acid in a mass ratio of 80:15:5 in an appropriate amount of solvent deionized water to obtain a coating slurry with a solid content of 35 wt%.

[0305] Test section

[0306] 1. Test of the adhesion between the separator and the positive electrode

[0307] The battery's positive electrode sheet and separator were stacked together and placed on a hot press. Pressing parameters were set at 25°C, 10t pressure, and 30s. Bonded separator / positive electrode sheet samples were produced. The separator / electrode sheet samples were cut into 150×20mm rectangular strips. The positive electrode side of the strips was affixed to a steel plate using double-sided tape. At one end of the strips, the separator and positive electrode sheet were separated by 2cm along the length to produce the test specimens.

[0308] The steel plate was held horizontally and secured with the lower clamp of a universal testing machine (Xie Qiang Instrument Manufacturing (Shanghai) Co., Ltd., Model CTM2100). The peeled end of the separator, as described above, was secured with the upper clamp of the universal testing machine and connected to a tensile testing machine. The test conditions were set to a tensile rate of 20 mm / min and a horizontal pull of 10 cm. Once the tensile force stabilized, the tensile force was recorded. The ratio of the tensile force to the sample width was used to determine the adhesion strength between the separator and the electrode.

[0309] 2. Thermal shrinkage test of isolation film

[0310] Sample preparation: The isolation film prepared above was punched into samples with a width of 50 mm and a length of 100 mm using a punching machine. Five parallel samples were placed on A4 paper, and then the A4 paper containing the samples was placed on corrugated paper with a thickness of 1 mm to 5 mm.

[0311] Sample test: Set the temperature of the blast oven to 150°C. After the temperature reaches the set temperature and stabilizes for 30 minutes, place the A4 paper placed on the corrugated paper into the blast oven and start timing. After the set time (1 hour in this application) is reached, measure the length and width of the isolation film, and mark the values ​​as a and b respectively.

[0312] Calculation of thermal shrinkage: longitudinal (MD) thermal shrinkage = [(100-a) / 100] × 100%, transverse (TD) thermal shrinkage = [(50-b) / 50] × 100%, and the average value of 5 parallel samples is taken as the test result.

[0313] 3. Hot box test of secondary batteries

[0314] At 25°C, the secondary batteries were charged at a constant current of 1C to 4.2V. They were then charged at a constant voltage until the current reached ≤0.05C and allowed to rest for 5 minutes. Each secondary battery was then tested in a DHG-9070A DHG series high-temperature oven with a fixture. The temperature was raised from room temperature to 80±2°C at a rate of 5°C / min and held for 30 minutes. The temperature was then increased again at a rate of 5°C / min, with each 5°C increase lasting 30 minutes, until the secondary battery failed. The surface temperature of the secondary battery was monitored during the heating process. The oven temperature corresponding to the point at which the temperature began to rise sharply was the secondary battery's hot box failure temperature. A higher hot box failure temperature indicates better thermal safety.

[0315] Table 1

[0316]

[0317] Table 2

[0318]

[0319]

[0320] Table 3

[0321]

[0322] It can be seen from Tables 1 to 3 that the polymer of Comparative Example 1 includes a first structural unit and a second structural unit. When the isolation membrane adopts the polymer, its bonding performance is good, but the hot box failure temperature of the secondary battery is low, and thermal runaway is prone to occur; the polymer of Comparative Example 2 includes a first structural unit and a third structural unit. When the isolation membrane adopts the polymer, its heat resistance is improved to a certain extent, but the bonding performance of the isolation membrane is relatively poor.

[0323] The polymers of Examples 1 to 16 include a first structural unit, a second structural unit, and a third structural unit, which can improve the heat resistance, adhesion, and anti-swelling properties of the polymer. Adjusting the molar content of the three structural units can regulate the performance of the polymer to a certain extent, especially when 3≤A / B≤16, 3≤A / C≤16, and / or A:B:C is (12 to 16): (1 to 4): (1 to 4), the performance of the polymer can be further improved. In Examples 15 to 17, the polymers have good heat resistance, and when their content is relatively high, the heat resistance of the isolation membrane is better. Inorganic particles such as aluminum oxide can also be used as heat-resistant auxiliary materials to further improve the heat resistance of the isolation membrane.

[0324] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A polymer comprising a first structural unit, a second structural unit, and a third structural unit; The first structural unit includes a structural unit represented by formula (I): In formula (I), R1 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group; alternatively, R1 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group; R2 includes one or more of a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, or a substituted or unsubstituted C1-C20 hydroxyalkyl group; alternatively, R2 includes one or more of a C1-C12 alkyl group, a C3-C12 cycloalkyl group, or a C1-C12 hydroxyalkyl group; The second structural unit includes a structural unit represented by formula (II): In formula (II), R3 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group; alternatively, R3 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group; The third structural unit includes a structural unit represented by formula (III): In formula (III), R4 to R 11 Each independently comprises a substituted or unsubstituted C1-C10 alkyl group, one or more structural units as shown in formula (III-1), and R4 to R 11 At least one of them includes a structural unit represented by formula (III-1), In formula (III-1), R 12 Including one or more of hydrogen atoms, substituted or unsubstituted C1-C5 alkyl groups; optionally, R 12 including a hydrogen atom, or a substituted or unsubstituted C1-C3 alkyl group; R 13 Including substituted or unsubstituted C1-C10 alkyl; optionally, R 13 This includes substituted or unsubstituted C3-C10 alkyl groups.

2. The polymer according to claim 1, wherein R1 includes a hydrogen atom or a methyl group; and / or R2 includes methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-octyl, isooctyl, 2-ethylhexyl, dodecyl or isobornyl.

3. The polymer according to claim 1 or 2, wherein R3 includes a hydrogen atom or a methyl group.

4. The polymer according to any one of claims 1 to 3, wherein The R4 to R 11 Each independently comprises a structural unit as shown in formula (III-1); optionally, R 12 including hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl or n-pentyl; and / or R 13 including n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-octyl, isooctyl or 2-ethylhexyl; or The R4 to R 11 One of them includes a structural unit as shown in formula (III-1); optionally, R 12 including hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl or n-pentyl; and / or R 13 These include n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-octyl, isooctyl or 2-ethylhexyl.

5. The polymer according to any one of claims 1 to 4, wherein Based on the total molar amount of the first structural unit, the second structural unit and the third structural unit, the molar content of the first structural unit is recorded as A%, 60≤A<100; optionally, 60≤A≤80; and / or Based on the total molar amount of the first structural unit, the second structural unit and the third structural unit, the molar content of the second structural unit is recorded as B%, 0<B≤20; optionally, 5≤B≤20; and / or Based on the total molar amount of the first structural unit, the second structural unit and the third structural unit, the molar content of the third structural unit is recorded as C%, 0<C≤20; optionally, 5≤C≤20.

6. The polymer according to any one of claims 1 to 5, wherein Based on the total molar amount of the first structural unit, the second structural unit and the third structural unit, the molar content of the first structural unit is recorded as A%, the molar content of the second structural unit is recorded as B%, and the molar content of the third structural unit is recorded as C%. The polymer satisfies one or more of conditions (1) to (3): (1)3≤A / B≤16; (2)3≤A / C≤16; (3) A:B:C is (12 to 16):(1 to 4):(1 to 4).

7. The polymer according to any one of claims 1 to 6, wherein The number average molecular weight of the polymer is 20,000 to 80,000, and can be optionally 30,000 to 50,000.

8. The polymer according to any one of claims 1 to 7, wherein The polymer is in granular form and further satisfies one or more of conditions (I) to (III): (I) The morphology of the polymer includes spherical and / or spherical-like shapes; (II) the volume distribution particle size Dv50 of the polymer satisfies: 0.1 μm ≤ Dv50 ≤ 2.0 μm; optionally, 0.5 μm ≤ Dv50 ≤ 1.2 μm; (III) The specific surface area of ​​the polymer is denoted as S, and its unit is m 2 / g, 5.0≤S≤12.0; optionally, 6.0≤S≤10.

0.

9. A method for preparing a polymer, comprising: providing a first monomer, a second monomer, and a third monomer; The first monomer, the second monomer and the third monomer are mixed and polymerized under the action of an initiator to generate a polymer. Wherein, the first monomer includes a compound represented by formula (IV), In formula (IV), R1 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group; alternatively, R1 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group; R2 includes one or more of a substituted or unsubstituted C1-C20 alkyl group, a substituted or unsubstituted C3-C20 cycloalkyl group, or a substituted or unsubstituted C1-C20 hydroxyalkyl group; alternatively, R2 includes one or more of a C1-C12 alkyl group, a C3-C12 cycloalkyl group, or a C1-C12 hydroxyalkyl group; The second monomer includes a compound represented by formula (V), In formula (V), R3 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C5 alkyl group; alternatively, R3 includes one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group; The third monomer includes a compound represented by formula (VI), In formula (VI), R 30 to R 37 Each independently comprises a substituted or unsubstituted C1-C10 alkyl group, one or more structural units as shown in formula (VI-1), and R 30 to R 37 At least one of them includes a structural unit represented by formula (VI-1), In formula (VI-1), R 12 Including one or more of hydrogen atoms, substituted or unsubstituted C1-C5 alkyl groups; optionally, R 12 including one or more of a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group; R 13 Including substituted or unsubstituted C1-C10 alkyl; optionally, R 13 This includes substituted or unsubstituted C3-C10 alkyl groups.

10. The method according to claim 9, wherein: The step of mixing the first monomer, the second monomer and the third monomer and performing a polymerization reaction under the action of an initiator to generate a polymer comprises: adding the first monomer, the second monomer, and the third monomer into a solvent and an emulsifier and mixing them to form a mixed system; The initiator is added to the mixed system, and a polymerization reaction occurs under the action of the initiator to generate the polymer.

11. The method according to claim 9 or 10, wherein: The first monomer comprises one or more of methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-pentyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate and 2-hydroxypropyl methacrylate; and / or, The second monomer comprises acrylonitrile and / or methacrylonitrile; and / or The third monomer includes one or more of methacryloxypropyl cage polysilsesquioxane, methacryloxypropyl heptaisobutyl polysilsesquioxane, methacryloxypropyl heptaoctyl polysilsesquioxane, acryloxypropyl cage polysilsesquioxane, acryloxypropyl heptaisobutyl polysilsesquioxane and methacryloxypropyl heptaoctyl polysilsesquioxane.

12. A separator comprising a substrate and a coating disposed on at least one surface of the substrate, the coating comprising the polymer according to any one of claims 1 to 8 or the polymer prepared by the method according to any one of claims 9 to 11.

13. The isolation film according to claim 12, wherein Based on the mass of the coating, the mass percentage of the polymer is m%, where m≥70; optionally, 80≤m≤95.

14. The separator according to claim 12 or 13, wherein: The isolation film satisfies one or more of the following conditions (A) to (G): (A) the longitudinal heat shrinkage rate of the isolation film at 150° C. for 1 hour is η1≤5.0%, optionally, 0.5%≤η1≤3%; (B) the transverse heat shrinkage rate η2 of the isolation film at 150° C. for 1 hour is ≤5.0%, optionally, 0.5%≤η2≤2%; (C) Longitudinal tensile strength R of the separator m1 ≥3000kg / cm 2 , optionally, 3500kg / cm 2 ≤R m1 ≤4500kg / cm 2 ; (D) Transverse tensile strength R of the separator m2 ≥3000kg / cm 2 , optionally, 3500kg / cm 2 ≤R m2 ≤4500kg / cm 2 ; (E) The air permeability of the isolation membrane is MAP ≤ 250 s / 100 mL, optionally, 120 s / 100 mL ≤ MAP ≤ 180 s / 100 mL; (F) The wetted length L of the isolation membrane is ≥ 30 mm, optionally, 30 mm ≤ L ≤ 80 mm; (G) The wetting speed of the isolation film is u≥3 mm / s, optionally, 3 mm / s≤u≤10 mm / s. 15 . A secondary battery comprising the separator according to claim 12 .

16. An electric device comprising the secondary battery according to claim 15.

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