Binder compound, conductive binder, and secondary battery including the same

Abstract

The present application provides a binder compound, a conductive binder, and a secondary battery containing the same. The binder compound of the present application has a structure of formula (I), wherein R 1 、R 2 Each independently represents a linear or branched C 1‑12 Alkyl; R 3 Represents halogen or cyano; R 4 represents hydroxymethyl or amino; Z represents a linear or branched C 1‑12 Alkylene; and m represents an integer ranging from 7600 to 47000. The binder compound and conductive binder of the present application can improve the storage and cycle performance of secondary batteries. #imgabs0#

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a binder compound, a conductive binder, and a preparation method thereof, as well as a secondary battery, a battery module, a battery pack, and an electrical device comprising the conductive binder. Background Art

[0002] In recent years, with the widespread application of secondary batteries, people's requirements for battery performance have become increasingly higher.

[0003] The internal resistance, storage, and cycle performance of secondary batteries are affected by many factors, including the dispersion of the conductive agent in the electrode material. However, since conductive agents (such as carbon black) tend to agglomerate during the preparation of battery electrodes, achieving uniform distribution is difficult.

[0004] Currently, the industry mainly alleviates the agglomeration problem of conductive agents (such as carbon black) by adding dispersants, but the addition of dispersants will bring some negative effects to the battery.

[0005] Therefore, there is a need in the art for a technical solution to solve the problem of conductive agent agglomeration and improve battery performance. Summary of the Invention

[0006] Technical problem to be solved by the invention

[0007] The present application is made in view of the above-mentioned problems, and its purpose is to solve the problem of agglomeration of the conductive agent during the stirring process, thereby avoiding the deterioration of battery performance caused by the agglomeration.

[0008] Technical solutions to solve problems

[0009] In order to achieve the above-mentioned object, the first aspect of the present application provides a binder compound having a structure of formula (I):

[0010]

[0011] Among them, R 1 、R 2 Each independently represents a linear or branched C 1-12 Alkyl; R 3 Represents halogen or cyano; R 4 represents hydroxymethyl or amino; Z represents a linear or branched C 1-12alkylene; and m represents an integer selected from 7600-47000, optionally selected from 7600-23100, more optionally selected from 19000-21000, and even more optionally selected from 19600-20500. The binder compound of the present application can be used to perform surface grafting modification on carbon-based conductive agent particles, thereby improving the problem of easy agglomeration of the carbon-based conductive agent during slurry stirring, thereby improving at least one of the storage and cycling properties without compromising the overall performance of the secondary battery.

[0012] In any embodiment, R 1 、R 2 Each independently represents a linear or branched C 2-8 Alkyl, optionally linear or branched C 2-6 Alkyl; and / or, R 3 represents a cyano group; and / or, Z represents a linear or branched C 2-8 Alkylene, optionally linear or branched C 2-6 Alkylene.

[0013] In any embodiment, the binder compound of the present application has the following structure:

[0014]

[0015] By selecting the structure of the binder compound, its bonding ability to the current collector and the electrode material, its chemical modification ability to the carbon-based conductive agent, and its ability to improve the agglomeration of the conductive agent can be further improved.

[0016] A second aspect of the present application further provides a method for preparing a binder compound, comprising the following steps:

[0017] (i) in the presence of an initiator, causing a chain transfer agent of formula (II) to undergo polymerization reaction with a vinylidene fluoride monomer in a solvent:

[0018]

[0019] Among them, R 1 、R 2 Each independently represents a linear or branched C 1-12 Alkyl, R 3 represents halogen or cyano, Z represents a linear or branched C 1-12 alkylene;

[0020] (ii) reacting the reaction product obtained in step (i) with a reducing agent in a solvent to obtain a compound of the following formula (I); or

[0021] (iii) reacting the reaction product obtained in step (i) with an aminating agent in a solvent;

[0022] (iv) reacting the reaction product obtained in step (iii) with an oxidizing agent under alkaline conditions to obtain a binder compound of the following formula (I),

[0023]

[0024] Among them, R 1 -R 3 and Z are as defined above; R 4 represents a hydroxymethyl group or an amino group; and m represents an integer selected from 7600-47000, alternatively selected from 7600-23100, more alternatively selected from 18000-21000, and even more alternatively 19600-20500.

[0025] Therefore, the present application provides a method for preparing the binder compound of the first aspect of the present application.

[0026] In any embodiment, step (i) is carried out at 60-80° C., optionally 65-75° C., more optionally 70° C. The temperature is selected so that the above steps proceed at an ideal reaction rate to avoid low molecular weight of the polymer or implosion.

[0027] In any embodiment, the mass ratio of the chain transfer agent to the vinylidene fluoride monomer in step (i) is 1:1783-11029; alternatively, 1:1783-5421; more alternatively, 1:4400-5000; and even more preferably, 1:4600-4800. By selecting the mass ratio of the chain transfer agent to the vinylidene fluoride monomer, the degree of polymerization (or molecular weight) of the resulting binder compound can be controlled.

[0028] In any embodiment, the chain transfer agent in step (i) is 4-cyano-4-(propylthiocarbonyl)thiopentanoic acid of formula (II-1):

[0029]

[0030] By selecting the chain transfer agent, the vinylidene fluoride monomer can be polymerized in a desired manner to obtain the binder compound, and the binder compound thus obtained can effectively perform graft modification on the conductive agent.

[0031] In any embodiment, step (ii) is performed at -10-10°C, alternatively at -5-5°C, more alternatively at -5-0°C, and even more alternatively at 0°C.

[0032] In any embodiment, step (iii) is performed at 35-60°C, alternatively at 40-45°C, more alternatively at 45°C.

[0033] In any embodiment, step (iv) is performed at 15-50°C, alternatively at 20-45°C, more alternatively at 25-35°C, and even more alternatively at 25°C.

[0034] Controlling the above steps within the above temperature range is beneficial to controlling the reaction and preventing the formation of by-products.

[0035] The third aspect of the present application provides a conductive adhesive, which comprises a carbon-based conductive agent portion and a binder portion covalently linked to the carbon-based conductive agent portion, wherein the binder portion has a structure of formula (III):

[0036]

[0037] Among them, R 1 、R 2 Each independently represents a linear or branched C 1-12 Alkyl; R 3 Represents halogen or cyano; R 4 represents hydroxymethyl or amino; Z represents a linear or branched C 1-12 Alkylene; and m represents an integer selected from 7600-47000, alternatively selected from 7600-23100, more alternatively selected from 19000-21000, and more alternatively selected from 19600-20500, R 5 represents #-CH2OC(O)-* or #-NHC(O)-*, wherein # represents the position of connection to Z and * represents the position of covalent connection to the carbon-based conductive agent. The conductive adhesive of the present application has both adhesiveness and conductivity, and improves the dispersibility of conventional carbon-based conductive agents to avoid agglomeration.

[0038] In any embodiment, the binder portion has the following structure:

[0039]

[0040] Wherein * represents the position where the carbon-based conductive agent portion is covalently connected. The conductive adhesive having the binder portion having the above structure can better achieve the effect of improving the aggregation of the conductive agent.

[0041] In any embodiment, the mass ratio of the binder portion to the carbon-based conductive agent portion is 0.1-5:1, optionally 0.3-1:1. The mass ratio of the binder portion to the carbon-based conductive agent portion is selected to achieve a good balance of bonding properties, conductive properties, and agglomeration-improving properties in the resulting conductive adhesive.

[0042] In any embodiment, the specific surface area of the carbon-based conductive agent portion is 1-3000m 2 / g, optionally 10-1200m2 / g, more preferably 20-800m 2 When the specific surface area of the carbon-based conductive agent is within this range, a good balance between adhesion and conductivity can be achieved, which is more conducive to improving battery performance.

[0043] In any embodiment, the carbon-based conductive agent is selected from one or more of superconducting carbon, carbon black SP, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; optionally, carbon black SP. Further selection of the carbon-based conductive agent can further enhance battery performance.

[0044] A fourth aspect of the present application provides a method for preparing a conductive adhesive, comprising the following steps:

[0045] The binder compound of formula (I), a carbon-based conductive agent, and a catalyst are reacted in a solvent to obtain a conductive binder:

[0046]

[0047] Among them, R 1 、R 2 Each independently represents a linear or branched C 1-12 Alkyl; R 3 Represents halogen or cyano; R 4 represents hydroxymethyl or amino; Z represents a linear or branched C 1-12 and m represents an integer selected from 7600-47000, alternatively selected from 7600-23100, more alternatively selected from 19000-21000, and even more alternatively selected from 19600-20500.

[0048] In any embodiment, R 1 、R 2 Each independently represents a linear or branched C 2-8 Alkyl, optionally linear or branched C 2-6 Alkyl; and / or, R 3 represents a cyano group; and / or, Z represents a linear or branched C 2-8 Alkylene, optionally linear or branched C 2-6 Alkylene.

[0049] In any embodiment, the binder compound of formula (I) has the following structure:

[0050]

[0051]

[0052] In any embodiment, the reaction is carried out at a temperature of -5-5° C., optionally -5-0° C., and more optionally 0° C. By controlling the reaction temperature within the above range, the reaction rate can be easily controlled.

[0053] In any embodiment, the mass ratio of the binder compound to the carbon-based conductive agent is 0.1-5:1, optionally 0.3-1:1. By controlling the mass ratio of the binder compound to the carbon-based conductive agent during the reaction, the resulting conductive binder can achieve a good balance in terms of adhesion, conductivity, and improved agglomeration, further improving battery performance.

[0054] In any embodiment, the carbon-based conductive agent is selected from one or more of superconducting carbon, carbon black SP, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, and may be carbon black SP. By selecting a suitable carbon-based conductive agent, the performance of the battery can be further improved.

[0055] In any embodiment, the specific surface area of the carbon-based conductive agent is 1-3000m 2 / g, optionally 10-1200m 2 / g, more preferably 20-800m 2 By selecting the specific surface area of the carbon-based conductive agent within the above range, the resulting conductive binder can achieve a balance between conductivity and improved agglomeration, which is beneficial to improving battery performance.

[0056] The fifth aspect of the present application provides use of the conductive adhesive of the third aspect of the present application or the conductive adhesive prepared by the preparation method of the fourth aspect of the present application in a secondary battery.

[0057] A sixth aspect of the present application provides a positive electrode sheet comprising a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode material layer comprises the conductive binder of the third aspect of the present application or the conductive binder prepared by the preparation method of the fourth aspect of the present application. The conductive agent in the positive electrode material layer of the positive electrode sheet of the present application can be uniformly distributed without agglomeration, thereby improving battery performance.

[0058] In any embodiment, the positive electrode material layer includes 1-10% by weight, and optionally 3-6% by weight, of the conductive binder, based on the total weight of the positive electrode material layer. By controlling the content of the conductive binder in the positive electrode material layer within the above range, at least one of the cycle performance and storage performance of the battery can be improved.

[0059] The seventh aspect of the present application provides a secondary battery, which includes the positive electrode sheet of the sixth aspect of the present application.

[0060] An eighth aspect of the present application provides a battery module, which includes the secondary battery according to the seventh aspect of the present application.

[0061] The ninth aspect of the present application provides a battery pack, which includes the battery module of the eighth aspect of the present application.

[0062] The tenth aspect of the present application provides an electrical device, which includes at least one selected from the secondary battery of the seventh aspect of the present application, the battery module of the eighth aspect of the present application, or the battery pack of the ninth aspect of the present application.

[0063] Compared with the prior art, the present application has at least the following beneficial effects: the binder compound of the present application can chemically combine with the carbon-based conductive agent and be grafted on its surface, thereby avoiding the agglomeration of the conductive agent during the preparation of the electrode, thereby improving at least one of the storage performance and cycle performance without losing the comprehensive performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 This is an infrared spectrum of the conductive adhesive of Example 1;

[0065] Figure 2 Scanning electron microscope photos showing the cross-sectional morphology of the positive electrode fragments of Example 1 and Comparative Example C1;

[0066] Figure 3 is a schematic diagram of a secondary battery according to one embodiment of the present application;

[0067] Figure 4 yes Figure 3 An exploded view of a secondary battery according to an embodiment of the present application is shown;

[0068] Figure 5 is a schematic diagram of a battery module according to one embodiment of the present application;

[0069] Figure 6 is a schematic diagram of a battery pack according to one embodiment of the present application;

[0070] Figure 7 yes Figure 6 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0071] Figure 8 Schematic diagram of an electric device using the secondary battery according to one embodiment of the present application as a power source.

[0072] Description of reference numerals:

[0073] 1-battery pack; 2-upper box; 3-lower box; 4-battery module; 5-secondary battery; 51-housing; 52-pole assembly; 53-top cover assembly. DETAILED DESCRIPTION

[0074] Before describing the adhesive compounds, conductive adhesives, methods of preparing the same, and uses thereof, it should be understood that the present application is not limited to the specific materials, methods, and experimental conditions described, as these may vary. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting, as the scope of the present application will be limited only by the appended claims.

[0075] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Any methods and materials similar or equivalent to those described herein may be used in the practice or testing of this application, and it should be understood that modifications and variations are encompassed within the spirit and scope of this disclosure.

[0076] For the sake of clarity, this application specifically discloses certain numerical ranges. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0077] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0078] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0079] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0080] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0081] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0082] 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).

[0083] With the rapid development of new energy vehicles in recent years, people have higher and higher requirements for the performance of secondary batteries. Therefore, how to further improve the performance of secondary batteries has always been the focus of secondary battery research and development.

[0084] The internal resistance, storage performance and cycle performance of secondary batteries are affected by many factors, such as the material and thickness of the current collector, the material, compaction, moisture content, coating thickness of the electrode, diaphragm, conductive agent, electrolyte and preparation process, etc. In addition, the internal resistance, storage and cycle performance of secondary batteries are also affected by the dispersion of the conductive agent in the electrode. Generally speaking, the more uniform the distribution of the conductive agent in the electrode material, the better the performance of the secondary battery. However, since the conductive agent (usually carbon black) is easy to agglomerate during the electrode preparation process, it is difficult to achieve uniform distribution in production practice.

[0085] At present, the industry mainly adds dispersants to the electrode material slurry, which alleviates the agglomeration problem to a certain extent. However, at the same time, the addition of dispersants also brings some negative effects: on the one hand, dispersants have no positive contribution to battery performance, and even because of a large amount of residue in the electrode material, they reduce the proportion of active materials in it, thereby reducing the energy density of the battery; on the other hand, the addition of dispersants will also complicate the electrode preparation process and increase costs.

[0086] To address the aforementioned issues, the present application provides a binder compound that chemically reacts with groups (such as carboxyl groups) present on the surface of carbon-based conductive agents (such as carbon black) particles, thereby grafting onto the surface of the carbon-based conductive agent. Furthermore, the present application provides a conductive binder formed by the reaction of the binder compound of the present application with the carbon-based conductive agent. The conductive binder comprises a carbon-based conductive agent portion and a binder portion, thereby possessing both bonding and conductive functions. Furthermore, the conductive binder is less likely to agglomerate when mixed with other materials to prepare electrode slurry, thereby enabling uniform distribution within the electrode material layer, thereby improving battery performance.

[0087] Binder compound

[0088] In a first aspect, the present application provides a binder compound having a structure of formula (I):

[0089]

[0090] Among them, R 1 、R 2 Each independently represents a linear or branched C 1-12 Alkyl; R 3 Represents halogen or cyano; R 4 represents hydroxymethyl or amino; Z represents a linear or branched C 1-12 and m represents an integer selected from 7600-47000, alternatively selected from 7600-23100, more alternatively selected from 19000-21000, and even more alternatively selected from 19600-20500.

[0091] The adhesive compound of the present application has a reactive group (such as a hydroxyl group or an amino group) at the end. While having the desired bonding properties, it can graft and modify the surface of the carbon-based conductive agent particles through covalent bonding to form a conductive adhesive, thereby improving the agglomeration problem of the carbon-based conductive agent.

[0092] When the m value is within the above range, the binder compound has strong bonding ability, moderate reactivity and reaction rate with the carbon-based conductive agent, strong anti-agglomeration ability after grafting with the carbon-based conductive agent, good solubility, and good slurry stability during cathode slurry preparation, thereby making the electrode material evenly distributed, and the secondary battery prepared therefrom has good cycle and storage performance.

[0093] In some embodiments, in the above formula (I), R 1 、R 2 Each independently represents a linear or branched C 2-8 Alkyl, optionally linear or branched C 2-6 Alkyl; and / or, R 3 represents a cyano group; and / or, Z represents a linear or branched C 2-8 Alkylene, optionally linear or branched C 2-6 Alkylene.

[0094] In some embodiments, the binder compound of the present application has the following structure:

[0095]

[0096] By selecting the structure of the binder compound, the binder's ability to bind to the current collector and the electrode material, its ability to chemically modify the conductive agent, and its ability to improve the agglomeration of the conductive agent can be further improved.

[0097] In some embodiments, the number average molecular weight (Mn) of the binder compound of the present application is 500,000-3,000,000, and optionally 500,000-1,500,000. When the molecular weight of the binder compound is within the above-mentioned suitable range, it can have appropriate solubility and adhesion. In other words, controlling the molecular weight within the above-mentioned range can better balance the two.

[0098] A second aspect of the present application provides a method for preparing a binder compound, comprising the following steps:

[0099] (i) in the presence of an initiator, causing a chain transfer agent of formula (II) to undergo polymerization reaction with a vinylidene fluoride monomer in a solvent:

[0100]

[0101] Among them, R 1 、R 2 Each independently represents a linear or branched C 1-12 Alkyl, R 3 represents halogen or cyano, Z represents a linear or branched C 1-12 alkylene;

[0102] (ii) reacting the reaction product obtained in step (i) with a reducing agent in a solvent to obtain a compound of the following formula (I); or

[0103] (iii) reacting the reaction product obtained in step (i) with an aminating agent in a solvent;

[0104] (iv) reacting the reaction product obtained in step (iii) with an oxidizing agent under alkaline conditions to obtain a binder compound of the following formula (I),

[0105]

[0106] Among them, R 1 -R 3 and Z are as defined above; R 4 represents a hydroxymethyl group or an amino group; and m represents an integer selected from 7600-47000, alternatively selected from 7600-23100, more alternatively selected from 19000-21000, and even more alternatively selected from 19600-20500.

[0107] By the above method, the desired binder compound can be prepared.

[0108] In some embodiments, in the above method, step (i) is performed at 60-80° C., optionally 65-75° C., and more optionally 70° C. Controlling the temperature within this range can achieve an appropriate reaction rate to avoid low molecular weight or implosion.

[0109] In some embodiments, the reaction of step (i) is carried out under oxygen-free conditions. In some embodiments, the reaction of step (i) is optionally carried out in an inert gas atmosphere. In some embodiments, the reaction of step (i) is optionally carried out in an N2 atmosphere. Thus, oxidation of free radicals can be avoided, the reaction is carried out as desired, and side reactions are reduced.

[0110] In some embodiments, the initiator in step (i) is an initiator known in the art that can be used for the reaction. In some embodiments, the initiator is azobisisobutyronitrile (AIBN) or dibenzoyl peroxide (BPO). Alternatively, in some embodiments, the initiator is azobisisobutyronitrile.

[0111] In some embodiments, the solvent in step (i) is tetrahydrofuran (THF), dimethylformamide (DMF) or dimethyl sulfoxide (DMSO); alternatively, the solvent in step (i) is tetrahydrofuran.

[0112] In some embodiments, the mass ratio of the chain transfer agent to the vinylidene fluoride monomer in step (i) is 1:1783-11029, alternatively 1:1783-5421, more alternatively 1:4400-5000, and even more preferably 1:4600-4800. By selecting the mass ratio of the chain transfer agent to the vinylidene fluoride monomer used in the method, the degree of polymerization (or molecular weight) of the resulting binder compound can be controlled.

[0113] In some embodiments, the chain transfer agent in step (i) is 4-cyano-4-(propylthiocarbonyl)thiopentanoic acid (CPP) of formula (II-1):

[0114]

[0115] The inventors have discovered that by adopting a chain transfer agent of formula (II), optionally a chain transfer agent of formula (II-1), the method of the present application can cause the vinylidene fluoride monomer to polymerize in a manner with a fast polymerization rate, high controllability of the polymerization molecular weight, and good molecular weight consistency (that is, a small polymer dispersibility index (PDI)) to obtain the binder compound of the present application, and the binder compound thus obtained can effectively carry out graft modification of the conductive agent.

[0116] In some embodiments, the solvent in step (ii) is tetrahydrofuran, dimethylformamide, or dimethyl sulfoxide; alternatively, the solvent in step (ii) is tetrahydrofuran. In some embodiments, the reducing agent in step (ii) is LiAlH4. In some embodiments, step (ii) is carried out at -10-10°C, alternatively at -5-5°C, more alternatively at -5-0°C, and even more alternatively at 0°C.

[0117] In some embodiments, the solvent in step (iii) is methanol. In some embodiments, the aminating agent in step (iii) is ammonia. In some embodiments, step (iii) is performed at 35-60°C, optionally at 40-45°C, more optionally at 45°C.

[0118] In some embodiments, the oxidizing agent in step (iv) is sodium hypochlorite. In some embodiments, step (iv) is carried out in the presence of NaOH. In some embodiments, step (iv) is carried out at 15-50°C, optionally at 20-45°C, more optionally at 25-35°C, and even more optionally at 25°C. Using the above reaction conditions, the reaction can be easily controlled and the formation of by-products can be prevented.

[0119] In some embodiments, the method of the present application may also optionally include a post-processing step. As will be appreciated by those skilled in the art, the post-processing step may include conventional post-processing methods selected based on product properties, such as filtering, washing, drying, and the like.

[0120] Conductive adhesive

[0121] In a third aspect, the present application provides a conductive adhesive comprising a carbon-based conductive agent portion and a binder portion covalently linked to the carbon-based conductive agent portion, wherein the binder portion has a structure of formula (III):

[0122]

[0123] Among them, R 1 、R 2 Each independently represents a linear or branched C 1-12 Alkyl; R 3 Represents halogen or cyano; R 4 represents hydroxymethyl or amino; Z represents a linear or branched C 1-12 Alkylene; m represents an integer selected from 7600-47000, optionally selected from 7600-23100, more optionally selected from 19000-21000, and more optionally selected from 19600-20500; R 5 represents #-CH2OC(O)-* or #-NHC(O)-*, and # represents the position to which Z is bonded, and * represents the position to which the carbon-based conductive agent portion is covalently bonded.

[0124] The conductive binder of this application combines both adhesiveness and conductivity, and improves the dispersibility of conventional carbon-based conductive agents, preventing agglomeration. Therefore, in the preparation of positive electrode slurry, using the conductive binder of this application to replace the binder and conductive agent added separately in the prior art can fundamentally solve the problem of conductive agent agglomeration during stirring, which can deteriorate battery performance.

[0125] In addition, it is easy for those skilled in the art to understand that by using the conductive adhesive of the present application to replace the adhesive and the conductive agent added in separate feeding steps, the working efficiency can be improved.

[0126] As used herein, the terms "covalently linked" or "covalently bound" or "covalently linked" and similar expressions are used interchangeably to mean that atoms, molecules or parts of molecules are linked together by covalent bonds.

[0127] In some embodiments, in the conductive adhesive of the present application, the adhesive portion has the following structure:

[0128]

[0129] where * indicates the position of covalent attachment to the carbon-based conductive agent moiety.

[0130] In some embodiments, the mass ratio of the binder portion to the carbon-based conductive agent portion in the conductive binder is 0.1-5:1, optionally 0.3-1:1.

[0131] In the conductive binder of the present application, the mass ratio of the binder portion to the carbon-based conductive agent portion affects its bonding and conductivity, which in turn affects battery performance. When the mass ratio of the binder portion to the carbon-based conductive agent portion is within the range of 0.1-5:1, and optionally within the range of 0.3-1:1, the conductive binder exhibits excellent bonding strength and conductivity, thereby achieving good conductivity in the electrode. Furthermore, due to the presence of an appropriate amount of the binder portion grafted onto the surface of the conductive agent particles, agglomeration is significantly improved, thereby improving the cycling and storage performance of secondary batteries containing the conductive binder or electrode of the present application.

[0132] In some embodiments, the specific surface area of the carbon-based conductive agent portion is 1-3000 m 2 / g, optionally 10-1200m 2 / g, more preferably 20-800m 2 / g.

[0133] The specific surface area of the carbon-based conductive agent directly affects the conductivity of the electrode. When the carbon-based conductive agent portion of the conductive binder has a specific surface area within the above range, the conductive binder can desirably mitigate or prevent agglomeration while maintaining good adhesion and conductivity. This results in a strong bond between the electrode material layers and good conductivity, which is beneficial for improving battery performance.

[0134] The carbon-based conductive agent portion of the present application can be selected from various carbon-based conductive agents conventional in the art. In some embodiments, the carbon-based conductive agent portion is selected from, but not limited to, one or more of superconducting carbon, carbon black (such as carbon black SP, acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene and carbon nanofibers. In some embodiments, optionally, the carbon-based conductive agent is carbon black. As carbon black, various commercially available carbon blacks, such as furnace black carbon black, can be used. In some embodiments, more optionally, the carbon-based conductive agent portion is carbon black SP. By further selecting the carbon-based conductive agent portion, the performance of the battery can be further improved.

[0135] A fourth aspect of the present application provides a method for preparing a conductive adhesive, comprising the following steps:

[0136] The binder compound of formula (I), a carbon-based conductive agent, and a catalyst are reacted in a solvent to obtain a conductive binder:

[0137]

[0138] Among them, R 1 、R 2 Each independently represents a linear or branched C 1-12 Alkyl; R 3 Represents halogen or cyano; R 4 represents hydroxymethyl or amino; Z represents a linear or branched C1-12 and m represents an integer selected from 7600-47000, alternatively selected from 7600-23100, more alternatively selected from 19000-21000, and even more alternatively selected from 19600-20500.

[0139] In some embodiments, in formula (I), R 1 、R 2 Each independently represents a linear or branched C 2-8 Alkyl, optionally linear or branched C 2-6 Alkyl; and / or, R 3 represents a cyano group; and / or, Z represents a linear or branched C 2-8 Alkylene, optionally linear or branched C 2-6 Alkylene.

[0140] In some embodiments, the binder compound of formula (I) has the following structure:

[0141]

[0142] In some embodiments, in the above method, the solvent is tetrahydrofuran (THF), dimethylformamide (DMF), dimethyl sulfoxide (DMSO) or pyridine; alternatively, the solvent is tetrahydrofuran or pyridine. More alternatively, in the above method, if the binder compound of formula (I-1) is used, the solvent is tetrahydrofuran. More alternatively, in the above method, if the binder compound of formula (I-2) is used, the solvent is pyridine.

[0143] In some embodiments, the above method uses low temperature conditions. In some embodiments, the reaction is carried out at a temperature of -5-5°C, optionally -5-0°C, and more optionally 0°C. When the reaction temperature is within this range, the reaction rate can be easily controlled and other side reactions can be avoided.

[0144] In some embodiments, this step is performed in the presence of a catalyst. When the terminal group of the binder compound is a hydroxyl group, the catalyst may be, for example, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), N-hydroxysuccinimide (NHS), or the like; when the terminal group of the binder compound is an amino group, the catalyst may be, for example, thionyl chloride (SOCl2).

[0145] When the terminal group of the binder compound is an amino group, in some embodiments, the method steps can be performed under a basic environment. The basic environment can be achieved by adding a basic substance to the solvent, such as triethylamine.

[0146] In some embodiments, in the above method, the reaction is carried out under stirring.

[0147] In some embodiments, the mass ratio of the binder compound to the carbon-based conductive agent is 0.1-5:1, and optionally 0.3-1:1. By controlling the mass ratio of the binder compound to the carbon-based conductive agent during the reaction, the resulting conductive binder can achieve a balance in terms of adhesion, conductivity, and improved agglomeration, thereby further improving battery performance.

[0148] In some embodiments, the carbon-based conductive agent is selected from one or more of superconducting carbon, carbon black (such as carbon black SP, acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the carbon-based conductive agent is optionally carbon black. In some embodiments, more optionally, the carbon-based conductive agent is optionally carbon black SP. By selecting an appropriate carbon-based conductive agent, the performance of the battery can be further improved.

[0149] In some embodiments, the specific surface area of the carbon-based conductive agent is 1-3000 m 2 / g, optionally 10-1200m 2 / g, more preferably 20-800m 2 By selecting the specific surface area of the carbon-based conductive agent within the above range, the resulting conductive binder can achieve a balance between conductivity and improved agglomeration, which is beneficial to improving battery performance.

[0150] The conductive adhesive of the present application can be used for preparing positive electrode sheets in secondary batteries.

[0151] Positive electrode

[0152] In a sixth aspect, the present application provides a positive electrode sheet comprising a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode material layer comprises the conductive binder of the third aspect of the present application or the conductive binder prepared by the preparation method of the fourth aspect of the present application. The conductive agent in the positive electrode material layer of the positive electrode sheet of the present application can be uniformly distributed without agglomeration, thereby improving battery performance.

[0153] In some embodiments, the positive electrode material layer includes 1-10 weight %, preferably 3-6 weight % of the conductive binder based on the total weight of the positive electrode material layer. When the content of the conductive binder in the positive electrode material layer of the present application is within the above range, the conductivity of the electrode sheet is good, the impedance is small, the overall polarization of the battery cell is small, and the cycle and storage properties of the secondary battery are significantly improved. After the content of the conductive binder in the positive electrode material layer reaches 6 weight %, the cycle and storage performance of the battery do not improve much with the increase in content. When the content of the conductive binder exceeds 10 weight %, the storage and cycle performance of the battery do not show a clear trend of further improvement compared to when the content does not exceed 10 weight %, but the battery capacity is reduced because the load of the positive electrode active material in the electrode sheet is sacrificed at this time. Therefore, when the positive electrode material layer of the electrode sheet contains 1-10 weight %, optionally 3-6 weight % of the conductive binder, the secondary battery obtained from such an electrode sheet has the best comprehensive performance, that is, it has improved storage and cycle performance and good capacity at the same time.

[0154] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode material layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0155] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0156] The positive electrode material layer also contains a positive electrode active material. In some embodiments, the positive electrode active material may be a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3Mn1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0157] In some embodiments, the positive electrode material layer may further optionally include other binders. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF) binders conventional in the art, polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0158] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0159] secondary batteries

[0160] The seventh aspect of the present application provides a secondary battery, which includes the positive electrode sheet of the sixth aspect of the present application. Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0161] In some embodiments, the secondary battery is a lithium-ion secondary battery.

[0162] [Negative electrode]

[0163] The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode material layer includes a negative electrode active material.

[0164] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0165] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0166] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0167] In some embodiments, the negative electrode material layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0168] In some embodiments, the negative electrode material layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0169] In some embodiments, the negative electrode material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0170] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0171] [Electrolytes]

[0172] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0173] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0174] The electrolyte salt may be an electrolyte salt for secondary batteries known in the art. In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0175] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0176] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0177] [Isolation film]

[0178] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0179] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0180] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0181] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0182] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0183] The present application has no particular restrictions on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, Figure 3 The secondary battery 5 is a square structure as an example.

[0184] In some embodiments, reference Figure 4 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0185] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0186] Figure 5 4 is an example of a battery module. Figure 5 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of secondary batteries 5 may further be fixed by fasteners.

[0187] 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.

[0188] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0189] Figure 6 and Figure 7 The battery pack 1 is used as an example. Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0190] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0191] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0192] Figure 8This is an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0193] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0194] Example

[0195] The following describes embodiments of the present application. The embodiments described below are exemplary and are only used to explain the present application, and should not be understood as limiting the present application.

[0196] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the art or the product instructions shall be followed.

[0197] All reagents and instruments used without manufacturer indication are commercially available conventional products.

[0198] Test Method

[0199] Infrared spectrum test

[0200] According to the infrared spectrum analysis method of GB / T6040-2002, the structure and composition of the conductive adhesive of the embodiment were measured using a Nicolet IS10 Fourier transform infrared spectrometer. The test wave number range is 600 to 4000 cm -1 .

[0201] Number average molecular weight (Mn) test

[0202] The number average molecular weight (Mn) of the binder compound obtained in each example was measured using a HLC-8320GPC gel permeation chromatograph (GPC) produced by Tosoh Corporation of Japan, a SuperMultiporeHZ series semi-micro SEC column, and standard PS polystyrene.

[0203] Test method: Dissolve 2 mg of the test substance in 2 mL of GPC-specific dimethylformamide (DMF) solvent, inject 2.5 μL, and test with the following parameters:

[0204] Pump flow rate: 0.05 mL / min;

[0205] Filling volume: 200μL;

[0206] Temperature control range: 45℃;

[0207] Data acquisition frequency: 100Hz.

[0208] Battery capacity test

[0209] The battery capacity was tested using a Hepu CHT3568 battery capacity tester at 25°C, a current of 0.33C, and a voltage of 2.8-4.35V.

[0210] Pole adhesion test

[0211] Take the electrode and cut it into a test sample with a length of 100 mm and a width of 10 mm. Take a stainless steel plate with a width of 25 mm, stick double-sided tape (width 11 mm), stick the side of the test sample coated with the positive electrode material on the double-sided tape on the stainless steel plate, and use a 2000g roller to roll back and forth on its surface three times at a speed of 300 mm / min. Bend one end of the test sample 180 degrees, manually peel off the positive electrode material layer and the current collector of the test sample along the length direction by 25 mm, and then fix the test sample on the INSTRON 336 testing machine so that the peeling surface is consistent with the force line of the testing machine (that is, parallel to the movement direction of the testing machine when peeling). Continue to use the testing machine to continuously peel the test sample at a speed of 30 mm / min. The peeling force curve obtained is taken as the average value of the stable section within the range of 10-50 mm on the curve (that is, the section on the peeling force curve that no longer increases monotonically) as the peeling force F0. Then the bonding force F between the positive electrode material layer and the current collector in the test sample = F0 / width of the test sample (the unit of F is N / m).

[0212] Electrode resistance test

[0213] According to the standard GB / T1410-2006, the Hioki BT3563S resistance meter is used to take the electrode to be tested and place it on the resistance meter test bench under ambient temperature and humidity for testing. The area of the test electrode sample is 1540.25mm 2 , test voltage: 0.00001V, test pressure ≥0.4 tons (T), time interval 10s.

[0214] Battery cycle performance test

[0215] At 25°C, charge the secondary battery under test at a constant current rate of 1C to a charge cutoff voltage of 4.30V. Then, charge it at a constant voltage to a current of ≤0.05C, let it rest for 10 minutes, and then discharge it at a constant current rate of 1C to a discharge cutoff voltage of 3.3V, let it rest for 10 minutes. This is considered one charge and discharge cycle (i.e., one cycle (cls)). Perform this charge and discharge cycle test on the battery for 1000 cycles. The percentage of the discharge capacity in the last cycle to the discharge capacity in the third cycle is the cycle capacity retention rate.

[0216] Battery high temperature storage performance test

[0217] At 25°C, the secondary battery to be tested is charged at a constant current rate of 0.33C to a charge cut-off voltage of 4.35V, then charged at a constant voltage to a current of ≤0.05C, left to stand for 10 minutes, and then discharged at a constant current rate of 0.33C to a discharge cut-off voltage of 2.8V. The measured discharge capacity is the first-cycle discharge capacity C0. The battery is then charged at a constant current rate of 0.33C to a charge cut-off voltage of 4.30V, and then charged at a constant voltage to a current of ≤0.05C. Then, the battery was stored at 60°C for 30 days (d), and then discharged at a constant current of 0.33C to a discharge cut-off voltage of 2.8V, allowed to stand for 10min, and then charged at a constant current of 0.33C to a charge cut-off voltage of 4.35V, and then charged at a constant voltage to a current ≤ 0.05C, allowed to stand for 10min, and then discharged at a constant current of 0.33C to a discharge cut-off voltage of 2.8V. The discharge capacity measured in this way is the reversible capacity C1 stored at 60°C for 15 days, which is one storage cycle. The battery was stored for 180 days (i.e., 12 cycles) according to this method, and the percentage of the reversible capacity C12 stored at 60°C for 180 days to the first cycle discharge capacity C0 was the high temperature storage capacity retention rate.

[0218] Example 1

[0219] (1) Preparation of binder compound:

[0220] In a three-necked flask, add 6.5g of vinylidene fluoride monomer and chain transfer agent CPP to a mass ratio of 1:4744. Dissolve the mixture in 200mL of tetrahydrofuran, evacuate, and continuously flow with nitrogen. Add 0.05g of azobisisobutyronitrile initiator, heat to 70°C, and stir at 70°C for 12 hours. Pour the reaction mixture into 0°C icy ether, allow to settle, and dry to obtain a solid powder.

[0221] The above solid powder was completely dissolved in 200 mL of tetrahydrofuran, 0.5 g of LiAlH4 was added, and the mixture was stirred in an ice-water bath at 0°C for 4 hours, and then poured into ice ether at 0°C and allowed to settle again to obtain a binder compound.

[0222]

[0223] (2) Preparation of conductive adhesive:

[0224] Weigh 10g of the specific surface area of 80m 2 / g of conductive carbon black SP was dissolved in 100ml of tetrahydrofuran. 6.4g of the binder compound obtained in step (1), 0.002g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) as a catalyst, and 0.002g of N-hydroxysuccinimide (NHS) were added and mixed uniformly. The mixture was stirred at 0°C for 5 hours and then filtered. The resulting solid was transferred to a beaker, washed with an appropriate amount of dichloromethane, stirred for 30 minutes, and then filtered and dried to obtain a conductive adhesive powder.

[0225] The reaction formula is as follows (the dark circles represent conductive agent carbon black SP particles, and the same applies below):

[0226]

[0227] Figure 1 The infrared spectrum of the conductive adhesive obtained in this embodiment is shown. -1 is the stretching vibration peak of CH, 1405 cm -1 is CH2 bending vibration, 1186cm -1 , 879cm -1 CC skeleton vibration, 615cm -1 , 530cm -1 CF2 vibration peak, 1592cm -1 and 1406cm -1 The peaks at 2883 cm are the characteristic peaks of symmetrical stretching vibration and asymmetrical stretching vibration of COO-. -1 is the stretching vibration peak of CH, 1405 cm -1 is CH2 bending vibration, 1186cm -1 , 879cm -1 CC skeleton vibration, 615cm -1 , 530cm -1 is the CF2 vibration peak; from the infrared spectrum it can be seen that the binder compound of the present application has been successfully grafted onto the SP surface.

[0228] (3) Preparation of positive electrode sheet:

[0229] The positive electrode active material lithium iron phosphate (LiFePO4) and the conductive binder prepared in the above step (2) were mixed in a mass ratio of 96:4, and then solvent NMP was added to adjust the solid content to 70% to 80% by weight. After stirring, the positive electrode slurry was obtained. 2 The electrode loading is coated on the current collector aluminum foil, and then dried, cold pressed and cut into positive electrode sheets.

[0230] (4) Preparation of negative electrode sheet:

[0231] After dry mixing graphite, conductive agent and sodium carboxymethyl cellulose (CMC-Na), deionized water was added to adjust the solid content to 45% to 55% by weight, and then styrene-butadiene rubber (SBR) was added as a binder. The mass ratio of graphite, conductive agent, CMC-Na and SBR was 96.5:1:1:1.5. After stirring evenly, the negative electrode slurry was obtained, and then the mixture was heated to 11.4 mg / cm 2 The electrode load is coated on the copper foil, and then dried, cold pressed and cut into negative electrode sheets.

[0232] (5) Preparation of secondary batteries:

[0233] The electrode and diaphragm obtained in step (3) and step (4) are wound into a battery cell, and then encapsulated into a dry battery cell with an aluminum-plastic film. After liquid injection (the electrolyte is a solution with a concentration of 1 mol / L obtained by dissolving LiPF6 in ethylene carbonate (EC) / dimethyl carbonate (DMC) with a mass ratio of 1:1), formation, aging and other processes, a secondary battery is prepared.

[0234] Example 2

[0235] (1) Preparation of binder compound:

[0236] In a three-necked flask, add 6.5 g of vinylidene fluoride monomer and chain transfer agent CPP so that the mass ratio of chain transfer agent to vinylidene fluoride monomer is 1:4657; dissolve in 200 mL of tetrahydrofuran, evacuate, and then continuously introduce N2, add 0.05 g of azobisisobutyronitrile initiator, heat to 70°C, stir and react at 70°C for 12 hours, then pour the reaction mixture into 0°C ice ether for sedimentation and dry to obtain solid powder.

[0237] The above solid powder was transferred to a three-necked flask, 200 mL of methanol was added, ammonia was introduced at a reaction temperature of 45°C, and after reacting for 10 hours, the mixture was poured into 0°C ice ether for precipitation to obtain a solid.

[0238] The above solid was transferred to a round-bottom flask, 2 g of sodium hypochlorite was added, and the mixture was dissolved in 200 mL of methanol. Then, 50 mL of 0.05 mol / L sodium hydroxide was added, and the mixture was stirred and reacted at 25°C for 6 hours. Finally, the obtained product was poured into 0°C ice ether for precipitation to obtain the binder compound.

[0239] The reaction formula is as follows:

[0240]

[0241] (2) Preparation of conductive adhesive:

[0242] Weigh 10g of the conductive carbon black SP and dissolve it in 100ml of pyridine. Then add 6.4g of the binder compound prepared in step (1), 0.002g of SOCl2 (sulfonyl chloride) as a catalyst, and 0.1mg of triethylamine. Mix thoroughly, stir at 0°C for 3 hours, and filter. The resulting solid is transferred to a beaker, washed with an appropriate amount of dichloromethane, stirred for 30 minutes, and then filtered and dried to obtain the conductive adhesive powder of the present application.

[0243]

[0244] The conductive adhesive obtained in this embodiment was subjected to infrared spectrum test, wherein 2883 cm -1 is the stretching vibration peak of CH, 1405 cm -1 is CH2 bending vibration, 1186cm -1 , 879cm -1 CC skeleton vibration, 615cm -1 , 530cm -1 CF2 vibration peak, 3650cm -1 is the stretching vibration peak of NH; 1680cm -1 is a C=O vibration peak; from the infrared spectrum, it can be seen that the binder compound of the present application has been successfully grafted onto the SP surface.

[0245] The conductive adhesive was used to prepare the electrode and battery in the same manner as in steps (3) to (5) in Example 1.

[0246] Examples 3-8

[0247] In Examples 3-8, except for the different mass ratios of the chain transfer agent to the vinylidene fluoride monomer in step 1) and the different mass ratios of the binder compound to the conductive carbon black SP in step 2), other conditions are the same as those in Example 1.

[0248] The amount of conductive carbon black SP added in step 2) is shown in Table 1.

[0249] Table 1 Mass ratio of binder compound to conductive carbon black SP in Examples 1-8

[0250]

[0251] The performance test values of the binder compounds, pole pieces and batteries obtained in the above examples are shown in Table 5 below.

[0252] Examples 9-14

[0253] In Examples 9-14, except for the different mass ratios of the chain transfer agent to the vinylidene fluoride monomer in step 1) and the different specific surface areas of the conductive carbon black SP in step 2), other conditions are the same as those in Example 1.

[0254] The specific surface area of the conductive carbon black SP in each embodiment in step 2) is shown in Table 2.

[0255] Table 2 Specific surface area of conductive carbon black SP

[0256]

[0257] The performance test values of the binder compounds, pole pieces and batteries obtained in the above examples are shown in Table 5 below.

[0258] Examples 15-20

[0259] In Examples 15-20, except for the different mass ratios of the chain transfer agent to the vinylidene fluoride monomer in step 1) and the different amounts of the conductive adhesive added in step 3), the other conditions are the same as those in Example 1.

[0260] When preparing the electrode sheets in each embodiment, the weight percentage of the conductive binder contained in the positive electrode material layer is shown in Table 3.

[0261] Table 3 Weight percentage of conductive binder contained in the positive electrode material layer (wt%)

[0262] Example 1 15 16 17 18 19 20 weight% 4 0.5 1 3 6 10 12

[0263] The performance test values of the electrodes and batteries obtained in the above embodiments are shown in Table 5 below.

[0264] Comparative Example C1

[0265] Positive electrode preparation:

[0266] The positive electrode active material (lithium iron phosphate (LiFePO4)) with a specific surface area of 580m 2 / g conductive carbon black SP and binder polyvinylidene fluoride (PVDF) were added and mixed in a mass ratio of 96:2.5:1.5, and then solvent NMP was added to adjust the solid content to 70 wt%-80 wt%. After stirring, the positive electrode slurry was obtained, and then 20 mg / cm 2 The positive electrode sheet loading is coated on aluminum foil, and then dried, cold pressed and cut into positive electrode sheets;

[0267] Thereafter, a secondary battery was prepared in the same manner as in steps (4) to (5) of Example 1.

[0268] Relevant performance test data are shown in Table 5 below. Figure 2Scanning electron microscope images of the cross-sectional morphology of the positive electrode segments of Example 1 and Comparative Example C1 are shown. As can be seen in the image, at a magnification of 500x, the conductive agent in the positive electrode segment of Comparative Example C1 exhibits significant agglomeration and uneven distribution. At a magnification of 1000x, the conductive agent in the positive electrode segment of Example 1 exhibits virtually no agglomeration and a significantly more uniform distribution.

[0269] The pole pieces and batteries prepared in the above-mentioned embodiments and comparative examples were tested. Table 5 shows the performance test results of the pole pieces and batteries prepared in the above-mentioned embodiments 1-20 and comparative example C1:

[0270] Table 5. Binder compound molecular weight Mn and unit number m as well as electrode and battery performance data

[0271]

[0272]

[0273] As shown in Examples 1 and 3-8, when the mass ratio of the binder portion to the carbon-based conductive agent portion in the conductive binder is between 0.1 and 5:1, the conductive binder exhibits excellent bonding and conductivity, and the storage and cycling performance of the secondary batteries prepared therefrom are improved compared to Comparative Example C1. In particular, within the range of 0.3 to 1:1, the bonding and conductivity of the conductive binder, as well as the storage and cycling performance of the battery, are significantly improved.

[0274] It can be seen from Examples 1 and 9-14 that when the specific surface area of the carbon black used is 1-3000m 2 / g range, optionally in the range of 10-1200m 2 / g range, more particularly in the 20-800m 2 / g range, the conductive binder has good adhesion and conductivity, and the storage and cycle performance of the battery are also significantly improved compared with comparative example C1.

[0275] It can be seen from Examples 1 and 16-20 that when the conductive binder contained in the positive electrode material layer is in the range of 1-10 wt %, especially in the range of 3-6 wt %, the cycle and storage performance of the battery are significantly improved compared with Comparative Example C1.

[0276] As the proportion of conductive binder in the positive electrode material layer increases, the proportion of active material therein decreases accordingly, which leads to a decrease in battery capacity. In Example 1, the conductive binder content is 4% by weight, and the battery capacity is 2.5Ah after testing; when the conductive binder content is increased to 12% by weight, the battery capacity of Example 20 drops to 2.0Ah. Those skilled in the art will know that if the conductive binder content continues to increase, the content of active material continues to decrease accordingly, and the battery capacity will continue to decrease. Therefore, controlling the content of conductive binder in the positive electrode material layer to 1-10% by weight can obtain a battery with better overall performance.

[0277] In summary, the conductive adhesive, electrode sheet, and battery of the present application, compared with Comparative Example C1, can enable the secondary battery to obtain balanced and improved storage and cycle performance.

[0278] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A binder compound, characterized in that Having the structure of formula (I): Among them, R 1 、R 2 Each independently represents a linear or branched C 1-12 Alkyl; R 3 Represents halogen or cyano; R 4 represents hydroxymethyl or amino; Z represents a linear or branched C 1-12 an alkylene group; and m represents an integer selected from 7,600 to 47,000.

2. The binder compound according to claim 1, characterized in that m represents an integer selected from 7600-23100.

3. The binder compound according to claim 2, characterized in that m represents an integer selected from 19,000-21,000.

4. The binder compound according to claim 3, characterized in that m represents an integer selected from 19600-20500.

5. The binder compound according to claim 1, characterized in that R 1 、R 2 Each independently represents a linear or branched C 2-8 Alkyl; and / or, R 3 represents a cyano group; and / or, Z represents a linear or branched C 2-8 Alkylene.

6. The binder compound according to claim 5, characterized in that R 1 、R 2 Each independently represents a linear or branched C 2-6 alkyl.

7. The binder compound according to claim 5, characterized in that Z represents a linear or branched C 2-6 Alkylene.

8. The binder compound according to any one of claims 1 to 7, characterized in that Has the following structure:

9. A method for preparing a binder compound, characterized in that: The following steps are involved: (i) in the presence of an initiator, causing a chain transfer agent of formula (II) to undergo polymerization reaction with a vinylidene fluoride monomer in a solvent: Among them, R 1 、R 2 Each independently represents a linear or branched C 1-12 Alkyl, R 3 represents halogen or cyano, Z represents a linear or branched C 1-12 alkylene; (ii) reacting the reaction product obtained in step (i) with a reducing agent in a solvent to obtain a compound of the following formula (I); or (iii) reacting the reaction product obtained in step (i) with an aminating agent in a solvent; (iv) reacting the reaction product obtained in step (iii) with an oxidizing agent under alkaline conditions to obtain a binder compound of the following formula (I), Among them, R 1 -R 3 and Z are as defined above; R 4 represents a hydroxymethyl group or an amino group; and m represents an integer selected from 7,600 to 47,000.

10. The method according to claim 9, characterized in that m represents an integer selected from 7600-23100.

11. The method according to claim 10, characterized in that m represents an integer selected from 19,000-21,000.

12. The method according to claim 11, characterized in that m represents an integer selected from 19600-20500.

13. The method according to claim 9, characterized in that Step (i) is carried out at 60-80°C.

14. The method according to claim 13, characterized in that Step (i) is carried out at 65-75°C.

15. The method according to claim 14, characterized in that Step (i) was carried out at 70°C.

16. The method according to claim 9, characterized in that The mass ratio of the chain transfer agent to the vinylidene fluoride monomer in step (i) is 1:1783-11029.

17. The method according to claim 16, characterized in that The mass ratio of the chain transfer agent to the vinylidene fluoride monomer in step (i) is 1:1783-5421.

18. The method according to claim 17, characterized in that The mass ratio of the chain transfer agent to the vinylidene fluoride monomer in step (i) is 1:4400-5000.

19. The method according to claim 18, characterized in that The mass ratio of the chain transfer agent to the vinylidene fluoride monomer in step (i) is 1:4600-4800.

20. The method according to any one of claims 9 to 19, characterized in that The chain transfer agent in step (i) is 4-cyano-4-(propylthiocarbonyl)thiopentanoic acid of formula (II-1):

21. The method according to any one of claims 9 to 19, wherein: Step (ii) is carried out at -10-10°C.

22. The method according to claim 21, characterized in that Step (ii) is carried out at -5-5°C.

23. The method according to claim 22, characterized in that Step (ii) is carried out at -5-0°C.

24. The method according to claim 23, wherein Step (ii) was carried out at 0°C.

25. The method according to any one of claims 9 to 19, characterized in that Step (iii) is carried out at 35-60°C.

26. The method according to claim 25, characterized in that Step (iii) is carried out at 40-45°C.

27. The method according to claim 26, characterized in that Step (iii) was carried out at 45°C.

28. The method according to any one of claims 9 to 19, characterized in that Step (iv) is carried out at 15-50°C.

29. The method according to claim 28, characterized in that Step (iv) is carried out at 20-45°C.

30. The method according to claim 29, wherein Step (iv) is carried out at 25-35°C.

31. The method according to claim 30, wherein Step (iv) was carried out at 25°C.

32. A conductive adhesive, characterized in that: The present invention comprises a carbon-based conductive agent portion and a binder portion covalently linked to the carbon-based conductive agent portion, wherein the binder portion has a structure of formula (III): Among them, R 1 、R 2 Each independently represents a linear or branched C 1-12 Alkyl; R 3 Represents halogen or cyano; R 4 represents hydroxymethyl or amino; Z represents a linear or branched C 1-12 Alkylene; m represents a number selected from 7600-47000; R 5 represents #-CH2OC(O)-* or #-NHC(O)-*, and # represents the position to which Z is bonded, and * represents the position to which the carbon-based conductive agent portion is covalently bonded.

33. The conductive adhesive according to claim 32, wherein m represents an integer selected from 7600-23100.

34. The conductive adhesive according to claim 33, wherein m represents an integer selected from 19,000-21,000.

35. The conductive adhesive according to claim 34, wherein m represents an integer selected from 19600-20500.

36. The conductive adhesive according to claim 32, wherein The binder portion has the following structure: where * indicates the position of covalent attachment to the carbon-based conductive agent moiety.

37. The conductive adhesive according to any one of claims 32 to 36, characterized in that: The mass ratio of the binder part to the carbon-based conductive agent part is 0.1-5:

1.

38. The conductive adhesive according to claim 37, wherein The mass ratio of the binder part to the carbon-based conductive agent part is 0.3-1:

1.

39. The conductive adhesive according to any one of claims 32 to 36, characterized in that The specific surface area of the carbon-based conductive agent is 1-3000m 2 / g.

40. The conductive adhesive according to claim 39, wherein The specific surface area of the carbon-based conductive agent is 10-1200m 2 / g.

41. The conductive adhesive according to claim 40, characterized in that The specific surface area of the carbon-based conductive agent is 20-800 m 2 / g.

42. The conductive adhesive according to any one of claims 32 to 36, characterized in that The carbon-based conductive agent is partially selected from one or more of superconducting carbon, carbon black SP, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

43. The conductive adhesive according to claim 42, wherein The carbon-based conductive agent is partially selected from carbon black SP.

44. A method for preparing a conductive adhesive, characterized in that: The following steps are involved: The binder compound of formula (I), a carbon-based conductive agent, and a catalyst are reacted in a solvent to obtain a conductive binder: Among them, R 1 、R 2 Each independently represents a linear or branched C 1-12 Alkyl; R 3 Represents halogen or cyano; R 4 represents hydroxymethyl or amino; Z represents a linear or branched C 1-12 an alkylene group; and m represents an integer selected from 7,600 to 47,000.

45. The method according to claim 44, wherein m represents an integer selected from 7600-23100.

46. The method according to claim 45, characterized in that m represents an integer selected from 19,000-21,000.

47. The method according to claim 46, wherein m represents an integer selected from 19600-20500.

48. The preparation method according to claim 44, characterized in that R 1 、R 2 Each independently represents a linear or branched C 2-8 Alkyl; and / or, R 3 represents a cyano group; and / or, Z represents a linear or branched C 2-8 Alkylene.

49. The preparation method according to claim 48, characterized in that R 1 、R 2 Each independently represents a linear or branched C 2-6 alkyl.

50. The preparation method according to claim 48, characterized in that Z represents a linear or branched C 2-6 Alkylene.

51. The preparation method according to claim 44, characterized in that The binder compound of formula (I) has the following structure:

52. The preparation method according to any one of claims 44 to 51, characterized in that The reaction is carried out at a temperature of -5-5°C.

53. The preparation method according to claim 52, characterized in that The reaction is carried out at a temperature of -5-0°C.

54. The preparation method according to claim 53, characterized in that The reaction was carried out at a temperature of 0°C.

55. The preparation method according to any one of claims 44 to 51, characterized in that The mass ratio of the binder compound to the carbon-based conductive agent is 0.1-5:

1.

56. The preparation method according to claim 55, characterized in that The mass ratio of the binder compound to the carbon-based conductive agent is 0.3-1:

1.

57. The preparation method according to any one of claims 44 to 51, characterized in that The carbon-based conductive agent is selected from one or more of superconducting carbon, carbon black SP, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

58. The preparation method according to claim 57, characterized in that The carbon-based conductive agent is selected from carbon black SP.

59. The preparation method according to any one of claims 44 to 51, characterized in that The specific surface area of the carbon-based conductive agent is 1-3000m 2 / g.

60. The preparation method according to claim 59, characterized in that The specific surface area of the carbon-based conductive agent is 10-1200m 2 / g.

61. The preparation method according to claim 60, characterized in that The specific surface area of the carbon-based conductive agent is 20-800m 2 / g.

62. Use of the conductive adhesive according to any one of claims 32 to 43 or the conductive adhesive prepared by the preparation method according to any one of claims 44 to 61 in a secondary battery.

63. A positive electrode plate, characterized in that The invention comprises a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode material layer comprises the conductive binder according to any one of claims 32 to 43 or a conductive binder prepared by the preparation method according to any one of claims 44 to 61.

64. The positive electrode sheet according to claim 63, characterized in that The positive electrode material layer includes 1-10 wt % of the conductive binder based on the total weight of the positive electrode material layer.

65. The positive electrode plate according to claim 64, characterized in that The positive electrode material layer includes 3-6 weight % of the conductive binder based on the total weight of the positive electrode material layer.

66. A secondary battery, characterized in that Includes the positive electrode sheet according to any one of claims 63-65.

67. A battery module, characterized in that: Includes the secondary battery as described in claim 66.

68. A battery pack, characterized in that: A battery module comprising the battery module of claim 67.

69. An electrical device, characterized in that: Includes at least one selected from the secondary battery of claim 66, the battery module of claim 67, or the battery pack of claim 68.

Images