A binder having a crosslinked network structure, and a method for preparing and using the same

Abstract

This invention provides an adhesive with a cross-linked network structure. The invention utilizes piperidine derivatives to modify olefin derivatives to generate non-conjugated free radical compounds. These non-conjugated free radical compounds are then polymerized with vinylaniline to generate a highly conductive polymer A. Acrylic monomers, acrylate monomers, and L-aspartic acid are polymerized to generate a flexible polymer B with multiple hydrogen bonds. These two polymers are then cross-linked to form a cross-linked network structure, ultimately preparing the adhesive. Compared to traditional PAA-type adhesives, the adhesive of this invention contains multiple functional groups, possessing flexibility, strength, and conductivity. The cross-linked network structure helps alleviate the volume expansion problem of silicon electrode materials during battery charging and discharging, extending battery life and maintaining battery stability.

Description

Technical Field

[0001] This invention relates to the field of battery material binder technology, and more specifically, to a binder with a cross-linked network structure, its preparation method, and its application. Technical Background

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and environmental friendliness. With technological advancements and increasing market demand, the performance requirements for lithium-ion batteries are also rising. Silicon-based anode materials have attracted significant attention due to their extremely high theoretical specific capacity. Compared to traditional graphite anode materials, silicon-based anode materials hold the promise of significantly improving the energy density of lithium-ion batteries.

[0003] Binders are polymeric compounds that adhere the positive and negative electrode active materials to the current collector. Their main function is to bond the active materials and maintain the stability of the electrode structure and electrochemical performance during battery production and use, effectively addressing battery energy density issues. Currently, commonly used binders for lithium-ion batteries include polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polyacrylic acid (PAA). Among these, polyacrylic acid (PAA) is a water-soluble polymer, also known as acrylic homopolymer, and is weakly acidic. It exhibits advantages such as low swelling, stable electrode structure during charging and discharging, relatively uniform coating, the ability to form a dense film that increases the contact area between the active material and the current collector, high tensile strength, and ease of processing. Studies have shown that PAA has a higher carboxyl content, making it more suitable for silicon-containing negative electrodes. PAA not only forms strong hydrogen bonds with Si but also forms a coating layer similar to an SEI film on the Si surface, inhibiting electrolyte decomposition and exhibiting superior electrochemical performance in Si electrode materials. However, PAA contains a large number of carboxyl groups, which easily cause agglomeration, making the binder solution gel-like with extremely poor fluidity. This increases the difficulty of the coating process, affects the uniform distribution of each component in the electrode, and has poor mechanical properties, being brittle when cold and sticky when hot. Furthermore, the single functional group in the binder molecule has limited interfacial strengthening effect in multi-interface electrode systems. Therefore, it cannot meet the requirements for long-cycle use of high-expansion silicon-based anodes.

[0004] Although silicon-based anode materials possess excellent theoretical specific capacity, they face a series of challenges in practical applications. Silicon undergoes significant volume changes during charge and discharge (up to 300% or more), easily leading to electrode structure damage, active material shedding, and rapid capacity decay. Furthermore, silicon's poor conductivity further limits its performance under high-rate charge and discharge conditions. Therefore, developing high-performance binders to alleviate the volume expansion problem of silicon anodes and improve their conductivity has become a current research hotspot. Summary of the Invention

[0005] This invention provides an adhesive with a cross-linked network structure. The invention utilizes piperidine derivatives to modify olefin derivatives to generate non-conjugated free radical compounds. These non-conjugated free radical compounds are then polymerized with vinylaniline to generate a highly conductive polymer A. Acrylic monomers, acrylate monomers, and L-aspartic acid are polymerized to generate a flexible polymer B with multiple hydrogen bonds. These two polymers are then cross-linked to form a cross-linked network structure. Compared to traditional PAA-type adhesives, the adhesive of this invention contains multiple functional groups, combining flexibility, strength, and conductivity. The cross-linked network structure helps alleviate the volume expansion problem of silicon electrode materials during battery charging and discharging, extending battery life and maintaining battery stability.

[0006] The technical solution of the present invention is as follows:

[0007] A polymer with a cross-linked network structure is a cross-linked polymer formed by polymerizing a non-conjugated free radical compound as shown in formula (1) with vinyl aniline to generate a highly conductive polymer A, which is then cross-linked with a multi-hydrogen bond flexible polymer B.

[0008] The multi-hydrogen bond flexible polymer B is a polymer formed by copolymerizing acrylic monomers shown in B-1, acrylate monomers shown in B-2, and L-aspartic acid.

[0009]

[0010] Among them, R1, R2, R3, R4, R5, and R6 may be the same or different, and are independently selected from hydrogen, halogen, and C. 1-20 Alkyl, Halogenated C 1-20 Alkyl, C 3-20 cycloalkyl or halogenated C 3-20 cycloalkyl;

[0011] R7, R8, R9, R 10 Whether the elements are the same or different, they are independently selected from hydrogen, halogens, and carbon. 1-20 Alkyl, Halogenated C 1-20 Alkyl, C 3-20 cycloalkyl or halogenated C 3-20 cycloalkyl;

[0012] R 11 Selected from -COORa; Ra selected from C 1-20 Alkyl, Halogenated C 1-20 Alkyl or C 1-20Alkylene-OH; x and y are the molar percentages of the non-conjugated radical compound of monomer formula (1) and vinyl aniline, respectively, for preparing conductive polymer A, satisfying: 0.4≤x≤0.7, 0.3≤y≤0.6, x+y=1; for example, 0.5≤x≤0.6, 0.4≤y≤0.5, x+y=1;

[0013] m, n, and z are the molar percentages of the acrylic monomer (B-1), acrylate monomer (B-2), and L-aspartic acid monomer, respectively, used to prepare the multi-hydrogen-bonded flexible polymer. The three monomers satisfy the following conditions: 0.3≤m≤0.5, 0.2≤n≤0.4, 0.1≤z≤0.5, m+n+z=1. For example, 0.35≤m≤0.45, 0.25≤n≤0.35, 0.15≤z≤0.45, m+n+z=1.

[0014] According to an embodiment of the present invention, in the multi-hydrogen bonded flexible polymer B, (m+z) represents the molar percentage of the acrylic monomer shown in monomer B-1 to the acrylic monomer shown in B-1 and the acrylate monomer shown in B-2 constituting the multi-hydrogen bonded flexible polymer B, while n represents the molar percentage of the acrylate monomer shown in monomer B-2 to the acrylic monomer shown in B-1 and the acrylate monomer shown in B-2 constituting the multi-hydrogen bonded flexible polymer B; and z represents the molar percentage of L-aspartic acid to the acrylic monomer shown in B-1 and the acrylate monomer shown in B-2 constituting the multi-hydrogen bonded flexible polymer B. Furthermore, although the structure of the multi-hydrogen bonded flexible polymer B is as shown in formula (B), it does not represent the linkage mode disclosed in formula (B), and it can be a block copolymer or a random copolymer.

[0015] According to an embodiment of the present invention, the mass ratio of the conductive polymer A to the multi-hydrogen bonded flexible polymer B is 1:(1 to 10), for example 1:(1 to 4), or even 1:(1 to 3).

[0016] According to embodiments of the present invention, R1, R2, R3, R4, R5, and R6 may be the same or different, and are independently selected from hydrogen, halogen, and C. 1-12 Alkyl, Halogenated C 1-12 Alkyl, C 3-12 cycloalkyl or halogenated C 3-12 cycloalkyl;

[0017] According to an embodiment of the present invention, R7, R8, R9, R 10 Whether the elements are the same or different, they are independently selected from hydrogen, halogens, and carbon. 1-12 Alkyl, Halogenated C 1-12 Alkyl, C 3-12 cycloalkyl or halogenated C 3-12 cycloalkyl;

[0018] According to an embodiment of the present invention, R 11 Selected from -COORa; Ra selected from C 1-12 Alkyl, Halogenated C 1-12 Alkyl or -C 1-12 Alkylene-OH.

[0019] In some embodiments of the present invention, R1, R2, R3, R4, R5, and R6 may be the same or different, and are each independently selected from hydrogen or C. 1-6 alkyl;

[0020] In some embodiments of the present invention, R7, R8, R9, R 10 Whether the two are the same or different, they are independently selected from hydrogen or C. 1-6 alkyl;

[0021] In some embodiments of the present invention, R 11 Selected from -COORa; Ra selected from C 1-6 Alkyl or -C 1-6 Alkylene-OH.

[0022] As an example, R1, R2, R7, R8, R9, R 10 For H;

[0023] As an example, R3, R4, R5, and R6 are methyl or ethyl;

[0024] As an example, R 11 Selected from -COORa; Ra is selected from methyl, ethyl, propyl, -methylene-OH or -ethylene-OH.

[0025] The present invention also provides an ionic polymer with a cross-linked network structure, which is prepared by adjusting the pH of the system to 7-10 using an alkali metal salt as described above.

[0026] According to an embodiment of the present invention, the alkali metal salt is selected from at least one of alkali metal hydroxides, alkali metal carbonates, or alkali metal bicarbonates.

[0027] According to an embodiment of the present invention, the alkali metal hydroxide is selected from sodium hydroxide and potassium hydroxide.

[0028] According to an embodiment of the present invention, the alkali metal carbonate is selected from sodium carbonate and potassium carbonate.

[0029] According to an embodiment of the present invention, the alkali metal bicarbonate is selected from sodium bicarbonate and potassium bicarbonate.

[0030] The present invention also provides a method for preparing a polymer having a cross-linked network structure as described above, comprising the following steps:

[0031] The highly conductive polymer A, as described above, is cross-linked with the flexible polymer B with multiple hydrogen bonds.

[0032] According to an embodiment of the present invention, the crosslinking polymerization reaction of the highly conductive polymer A and the multi-hydrogen-bonded flexible polymer B is carried out in water.

[0033] According to an embodiment of the present invention, the mass ratio of the highly conductive polymer A to the multi-hydrogen bonded flexible polymer B is 1:(1 to 10), for example 1:(1 to 4), or even 1:(1 to 3).

[0034] According to an embodiment of the present invention, the temperature of the crosslinking polymerization reaction is 35-60°C, for example 40-55°C; and the reaction time is 1-24 hours, for example 3-12 hours.

[0035] According to an embodiment of the present invention, the highly conductive polymer A is prepared by the following method:

[0036]

[0037] Among them, R1, R2, R3, R4, R5, and R6 have the definitions described above;

[0038] The compound shown in Formula (I) is mixed with thionyl chloride and halogenated to prepare the acyl chloride compound shown in Formula (II); the acyl chloride compound shown in Formula (II) is then mixed with the compound shown in Formula (III) and substituted to prepare the non-conjugated radical compound shown in Formula (1); the non-conjugated radical compound shown in Formula (1) is then polymerized with 4-vinylaniline in the presence of an initiator to prepare a highly conductive polymer A;

[0039] In some embodiments of the present invention, the conductive polymer A is prepared by the following method: the compound shown in formula (I) and thionyl chloride are mixed in a molar ratio of 1:(1-4), the reaction temperature is 0-40℃, and the reaction time is 0.5-5h, to prepare the acyl chloride compound shown in formula (II) by halogenation; the acyl chloride compound shown in formula (II) and the compound shown in formula (III) are then mixed in a molar ratio of (1-4):1, the reaction temperature is 50-70℃, and the reaction time is 1-48h, to prepare the non-conjugated radical compound shown in formula (1) by substitution; the non-conjugated radical compound shown in formula (1) is then mixed with 4-vinylaniline and an initiator, the molar ratio of the non-conjugated radical compound shown in formula (1) to 4-vinylaniline is 1:(0.5-3), the reaction temperature is 50-70℃, and the reaction time is 9-15h, to prepare the highly conductive polymer A.

[0040] According to an embodiment of the present invention, the initiator is a free radical polymerization initiator, which includes a water-soluble redox polymerization initiator; the oxidant is selected from at least one of potassium persulfate, sodium persulfate, ammonium persulfate, benzoyl peroxide, tert-butyl hydroperoxide, acetyl peroxide, and dicumyl hydroperoxide; when the free radical polymerization initiator is selected from a water-soluble redox polymerization initiator, a reducing agent is also required for the reaction, which is selected from at least one of isoascorbic acid, ferrous ion salt, sodium sulfite, and sodium bisulfite.

[0041] According to an embodiment of the present invention, the initiator, or the total amount of initiator and reducing agent added, accounts for 0.001-1% of the monomer mass, for example, 0.01-0.5%.

[0042] In some embodiments of the present invention, the multi-hydrogen-bonded flexible polymer B is prepared by the following method:

[0043] 1) Mix the acrylic monomers shown in B-1 and the acrylate monomers shown in B-2 at a molar ratio of 1:(0.1-0.6) with water to prepare a solution A with a mass concentration of 5-30%, and adjust the pH value to 3-4; the pH adjuster is selected from at least one of inorganic bases, such as sodium carbonate, sodium bicarbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide.

[0044] 2) Prepare a solution B with a mass concentration of 0.01-30% by mixing the initiator with water; the initiator is the same as the free radical polymerization initiator mentioned above, and its addition amount is 0.001-1% of the monomer mass;

[0045] 3) Take 1 / 20 to 1 / 5 of the volume of solution A, add 1 / 20 to 1 / 5 of the volume of solution B, heat to 60-70℃, and continue for more than half an hour to obtain solution C;

[0046] 4) Divide the remaining solution A into two parts, labeled A1 and A2, and the remaining solution B into two parts, labeled B1 and B2. First, slowly add A1 and B1 dropwise into solution C, controlling the time to complete the addition within 1-2 hours, keeping the temperature at 60-70℃. After the addition is complete, keep the temperature and react for more than 2 hours to obtain solution D.

[0047] 5) Add the remaining A2 and B2 solutions dropwise into solution D, and add L-aspartic acid dropwise. Control the time to complete the addition within 3-5 hours, keep the temperature at 35-50℃, and keep the reaction at this temperature for more than 5 hours after the addition is complete to obtain the multi-hydrogen bond flexible polymer B.

[0048] The present invention also provides the use of polymers having cross-linked network structures as described above for preparing ionic polymers having cross-linked network structures as described above.

[0049] The present invention also provides a method for preparing an ionic polymer having a cross-linked network structure as described above, comprising: reacting the polymer having a cross-linked network structure as described above with an alkali metal salt to a system pH of 7-10, for example 7-8.

[0050] According to an embodiment of the present invention, the alkali metal salt is selected from at least one of alkali metal hydroxides, alkali metal carbonates, or alkali metal bicarbonates.

[0051] According to an embodiment of the present invention, the alkali metal hydroxide is selected from sodium hydroxide and potassium hydroxide.

[0052] According to an embodiment of the present invention, the alkali metal carbonate is selected from sodium carbonate and potassium carbonate.

[0053] According to an embodiment of the present invention, the alkali metal bicarbonate is selected from sodium bicarbonate and potassium bicarbonate.

[0054] The present invention also provides the use of ionic polymers having a cross-linked network structure as described above as binders, such as negative electrode binders.

[0055] According to an embodiment of the present invention, the adhesive comprises an ionic polymer having a cross-linked network structure as described above and water.

[0056] According to an embodiment of the present invention, the solid content of the adhesive is 1-20%, for example 3-10%.

[0057] According to an embodiment of the present invention, the binder is a conductive silicon-based negative electrode binder, such as a conductive silicon-based negative electrode binder for lithium-ion batteries.

[0058] Beneficial effects:

[0059] 1. In the binder preparation process of this invention, the introduction of non-conjugated free radical structures and conjugated structures into the highly conductive polymer A significantly improves the conductivity of the binder. The introduction of L-aspartic acid increases the density of active groups (carboxyl, hydroxyl, and amino groups) in the main chain structure of the multi-hydrogen-bonded flexible polymer B, providing cross-linking reaction sites. The highly conductive polymer A and the multi-hydrogen-bonded flexible polymer B form covalent and non-covalent hydrogen bonds through the condensation reaction of amino and carboxyl groups, thereby improving the peel strength of the electrode, suppressing the expansion of the silicon-oxygen anode during cycling, improving the lithium-ion transport capacity, reducing the internal resistance of the lithium-ion battery, and thus improving the rate performance and cycle stability of the battery.

[0060] 2. The cross-linked network structure of the binder of the present invention can significantly enhance the mechanical properties of the binder, such as tensile strength, fracture toughness and impact resistance, thereby improving the durability and stability of the electrode.

[0061] 3. The adhesive of the present invention can also effectively improve the compatibility between different polymers. Polymer B provides hydrophilicity and viscosity, and its molecular backbone contains alkane structure, which has good flexibility. It works synergistically with polymer A to improve the elasticity of the adhesive to a certain extent, which is beneficial to improving the uniformity and stability of the material.

[0062] Terminology Definitions and Explanations

[0063] The term "halogen" refers to F, Cl, Br, and I. In other words, F, Cl, Br, and I can be described as "halogens" in this specification.

[0064] Term "C" 1-20 "alkyl" should be understood to refer to a straight-chain or branched saturated monovalent hydrocarbon group having 1-20 carbon atoms, preferably C14. 1-6 Alkyl group. "C" 1-6 "Alkyl" should be understood to mean a straight-chain or branched saturated monovalent hydrocarbon group having 1, 2, 3, 4, 5, or 6 carbon atoms. The alkyl group is, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, 2-methylbutyl, 1-methylbutyl, 1-ethylpropyl, 1,2-dimethylpropyl, neopentyl, 1,1-dimethylpropyl, 4-methylpentyl, 3-methylpentyl, 2-methylpentyl, 1-methylpentyl, 2-ethylbutyl, 1-ethylbutyl, 3,3-dimethylbutyl, 2,2-dimethylbutyl, 1,1-dimethylbutyl, 2,3-dimethylbutyl, 1,3-dimethylbutyl, or 1,2-dimethylbutyl, or their isomers.

[0065] The term "halogenated C" 1-20 "alkyl" should be understood as the "C" mentioned above. 1-20 An alkyl group is a group formed by substituting at least one hydrogen atom, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 hydrogen atoms, with a halogen. For example, a halogenated C... 1-12 Alkyl or halogenated C 1-6 alkyl".

[0066] Term "C" 3-20 "Cycloalkyl" should be understood as representing a saturated monovalent monocyclic, bicyclic, or polycyclic hydrocarbon ring (also called a fused ring hydrocarbon ring) with 3-20 carbon atoms. Bicyclic or polycyclic cycloalkyl includes fused cycloalkyl, bridged cycloalkyl, and spirocyclic cycloalkyl; fused ring refers to a fused ring structure formed by two or more cyclic structures sharing two adjacent ring atoms (i.e., sharing a bond). Bridged ring refers to a fused ring structure formed by two or more cyclic structures sharing two non-adjacent ring atoms. Spirocyclic refers to a fused ring structure formed by two or more cyclic structures sharing a single ring atom. For example, the C 3-20 Cycloalkyl groups can be C3-8 Monocyclic cycloalkyl groups, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, or C 7-12 Circoalkyl, such as decahydronaphthalene ring; or C 7-12 Bridged cycloalkyl groups, such as norbornene, adamantane, and bicyclo[2,2,2]octane.

[0067] The term "halogenated C" 3-20 "Cycloalkyl" should be understood as the "C" mentioned above. 3-20 A cycloalkyl group is a group formed by substituting at least one hydrogen atom, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 hydrogen atoms, with a halogen. For example, a halogenated C... 3-12 "Cycloalkyl" or "halogenated C" 3-6 Cycloalkyl. Detailed Implementation

[0068] To better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to the embodiments.

[0069] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0070] Example 1

[0071] Under nitrogen protection, 10 mL of LDM and 1 g of anhydrous calcium chloride were added to a flask. 7.2 g (0.1 mol) of acrylic acid was added to the flask, followed by 11.9 g (0.1 mol) of thionyl chloride. The mixture was reacted at room temperature for 2 h. 14.1 g (0.1 mol) of 2,2,6,6-tetramethyl-4-hydroxypiperidine was dissolved in 20 mL of tetrahydrofuran and added to the above solution. The mixture was heated to 60 °C and refluxed for 24 h. After the reaction was completed, the temperature was lowered, and the reaction product was added to 200 mL of dichloromethane to precipitate, yielding 21.1 g (0.1 mol) of 2,2,6,6-tetramethylpiperidine-4-yl acrylate.

[0072] Nitrogen gas was introduced into a 500ml three-necked flask equipped with a stirrer and a condenser. 390g of deionized water was added, and the temperature was raised to 60℃. 13g (0.06mol) of 2,2,6,6-tetramethylpiperidin-4-yl acrylate and 12g (0.1mol) of 4-vinylaniline, as well as 0.04g (0.38mmol) of sodium bisulfite and 0.08g (0.34mmol) of sodium persulfate were slowly added dropwise. The temperature was maintained until all the monomers were added. The polymerization reaction was stopped after 12 hours, yielding a mixture of polymer A and water with a solid content of 6%.

[0073] Weigh 15g (0.21mol) of acrylic acid and 11g (0.095mol) of hydroxyethyl acrylate, add 234g of water and mix to prepare solution A. Add 6g (0.057mol) of sodium carbonate and adjust the pH to 4. Weigh 0.04g (0.380mmol) of sodium bisulfite and 0.08g (0.340mmol) of sodium persulfate, add 20g of water and mix to prepare solution B.

[0074] Nitrogen gas was introduced into a 500ml three-necked flask equipped with a stirrer and a condenser. 100g of deionized water was added, and the temperature was raised to 60℃. 1 / 20 volume of solution A and 1 / 20 volume of solution B were added, and the mixture was kept at this temperature for 1 hour.

[0075] The remaining solution A is divided into two equal parts, labeled A1 and A2. At the same time, the remaining solution B is divided into two equal parts, labeled B1 and B2. First, A1 and B1 are slowly added dropwise into the three-necked flask, and the addition is completed within 1-2 hours. The temperature is maintained at 60℃. After the addition is completed, the temperature is maintained for 2 hours for the reaction to proceed.

[0076] The remaining solutions A2 and B2 were added dropwise to a three-necked flask, followed by 24 g (0.18 mol) of L-aspartic acid. The addition was completed over 3-5 hours, while maintaining the temperature above 45°C. After the addition was complete, the reaction was maintained at this temperature for at least 5 hours to obtain a mixture of polymer B and water with a solid content of 6%.

[0077] Polymer A and polymer B were blended at a mass ratio of 1:1, and the reaction was carried out at 40°C for 8 hours with continuous stirring. After cooling to room temperature, the pH was adjusted to 7-8 to obtain the binder.

[0078] Example 2 (different monomer ratios in component A and component B)

[0079] Nitrogen gas was introduced into a 500ml three-necked flask equipped with a stirrer and a condenser. 380g of deionized water was added, and the temperature was raised to 60°C. 17.5g (0.083mol) of 2,2,6,6-tetramethylpiperidin-4-acrylate and 7g (0.059mol) of 4-vinylaniline, along with 0.04g (0.38mmol) of sodium bisulfite and 0.07g (0.294mmol) of sodium persulfate were slowly added dropwise. The temperature was maintained until all the monomers were added. The polymerization reaction was stopped after 12 hours, yielding a mixture of polymer A and water with a solid content of 6%.

[0080] Weigh 14g (0.190mol) of acrylic acid and 8g (0.070mol) of hydroxyethyl acrylate, add 198g of water and mix to prepare solution A. Then add 5.6g (0.053mol) of sodium carbonate and adjust the pH to 4. Weigh 0.04g (0.380mmol) of sodium bisulfite and 0.07g (0.294mmol) of sodium persulfate, add 20g of water and mix to prepare solution B.

[0081] Nitrogen gas was introduced into a 500ml three-necked flask equipped with a stirrer and a condenser. 100g of deionized water was added, and the temperature was raised to 60℃. 1 / 20 volume of solution A and 1 / 20 volume of solution B were added, and the temperature was maintained for 1 hour.

[0082] The remaining solution A is divided into two equal parts, labeled A1 and A2. At the same time, solution B is divided into two equal parts, labeled B1 and B2. First, A1 and B1 are slowly added dropwise into the three-necked flask, and the addition is completed within 1-2 hours. The temperature is maintained at 60℃. After the addition is completed, the temperature is maintained for 2 hours for the reaction to proceed.

[0083] The remaining solutions A2 and B2 were added dropwise to a three-necked flask, followed by 16 g (0.120 mol) of L-aspartic acid. The addition was completed over 3-5 hours, while maintaining the temperature at 45°C. After the addition was complete, the reaction was maintained at this temperature for at least 5 hours to obtain a mixture of polymer B and water with a solid content of 6%.

[0084] Polymer A and polymer B were blended at a mass ratio of 1:1, and the reaction was carried out at 40°C for 8 hours with continuous stirring. After cooling to room temperature, the pH was adjusted to 7-8 to obtain the binder.

[0085] Example 3 (Polymers A and B have different mass ratios)

[0086] Polymer A and polymer B from Example 1 were mixed at a mass ratio of 1:2, stirred continuously at 40°C for 8 hours, and then cooled to room temperature. The pH was then adjusted to 7-8 to obtain the binder.

[0087] Example 4 (Polymers A and B have different mass ratios)

[0088] Polymer A and polymer B from Example 1 were mixed at a mass ratio of 1:3, stirred continuously at 40°C for 8 hours, and then cooled to room temperature. The pH was then adjusted to 7-8 to obtain the binder.

[0089] Comparative Example 1 (Commonly Used Adhesives in the Existing Technology)

[0090] Composed of CMC (sodium carboxymethyl cellulose) and SBR (styrene-butadiene rubber), with a CMC:SBR ratio of 1:2 (based on solid weight). The CMC (sodium carboxymethyl cellulose) was purchased from Aladdin Reagent Co., Ltd., with a weight-average molecular weight of approximately 250,000; the SBR (styrene-butadiene rubber) was purchased from Kelude New Energy Technology Co., Ltd., and was a 48% styrene-butadiene rubber (SBR) emulsion.

[0091] Comparative Example 2 (Polymer B is used alone as a binder; Polymer A cannot be used as a binder)

[0092] Take polymer B from Example 1, adjust the pH to 7-8, and obtain the binder.

[0093] Comparative Example 3 (the mass ratio of polymer A to B is smaller than the preferred range)

[0094] Polymer A and polymer B from Example 1 were mixed at a mass ratio of 1:4, stirred continuously at 40°C for 8 hours, and then cooled to room temperature. The pH was then adjusted to 7-8 to obtain the binder.

[0095] Comparative Example 4 (the mass ratio of polymer A to B is larger than the preferred range)

[0096] Polymer A and polymer B from Example 1 were mixed at a mass ratio of 2:1, stirred continuously at 40°C for 8 hours, and then cooled to room temperature. The pH was then adjusted to 7-8 to obtain the binder.

[0097] Performance testing:

[0098] Peel strength test method

[0099] ① Take 96.5 wt% silicon-carbon anode (capacity 600mAh / g), 1.0 wt% conductive carbon black (super p), and 2.5 wt% silicon-based anode binder (based on solid content) obtained in the examples and comparative examples, with the remainder being deionized water. After stirring and dispersing the mixture in a homogenizer for 3-10 hours, a negative electrode slurry is prepared. The slurry is then coated onto a copper foil using a 150μm doctor blade and baked at 80℃ for 12 hours. The negative electrode sheet is then cut into strips with a length of 170mm and a width of 20mm using a flat paper cutter. Finally, the strips are wiped clean with a lint-free paper to remove any stains or dust.

[0100] ② Cut a piece of 3M 468MP double-sided tape, 20mm wide and 120mm long, and stick it on the unmarked steel ruler, centering it in the middle;

[0101] ③ Place the side of the cut electrode sheet with active material onto the double-sided tape, with the ends flush. Use a pressure roller (2kg) with a diameter of 84mm and a height of 45mm to roll back and forth on the surface of the negative electrode sheet 3 times.

[0102] ④ After folding the free end of the negative electrode sheet in the test sample 180°, clamp it on the upper clamp of the tensile tester, and clamp the ungraded steel ruler on the lower clamp. Under the conditions of 22-28℃ and humidity less than 25%, prepare several negative electrode sheets with a width of 20mm. The electrode sheet is stretched at a speed of 200mm / min. The average value of the stretching distance is taken as 25-80mm (total stretching distance 100mm). Peel the negative electrode sheet. When the copper foil and coating are completely separated, read the test result of the peel strength of the electrode sheet coating (adhesive).

[0103] Ionic conductivity testing methods

[0104] ① Apply the adhesive to the Celgard 2500 diaphragm and bake it under vacuum at 85°C for 24 hours to remove the solvent from the adhesive.

[0105] ② Cut the diaphragm coated with adhesive (film thickness 20-200μm) into round pieces with a diameter of 18mm for later use.

[0106] ③ Assemble two sets of button cells, one set with a separator without adhesive (blank set) and the other set with a separator coated with adhesive and dried (test set). Inject the two sets of separators into an electrolyte prepared by mixing 1M LiPF6, ethylene carbonate EC, methyl ethyl carbonate EMC, and diethyl carbonate DMC in a mass ratio of 1:1:1 and let stand for 24 hours.

[0107] ④ Perform EIS testing on coin cells using an electrochemical workstation. Test frequency: 0.1~1MHz, amplitude: 5mV, test temperature: room temperature.

[0108] ⑤ Calculate the ionic conductivity of the adhesive using the following formula:

[0109] σ b =L / (ΔR) ct A)

[0110] R ct --charge transfer impedance

[0111] A -- Area of ​​the binder film

[0112] L -- Thickness of the binder film

[0113] ΔR ct =RawR ct R0, RawR ct R0 can be obtained from the intersection of the EIS test curve and the X-axis.

[0114] Mechanical property testing methods

[0115] The stress-strain curve of the adhesive film was tested using a multi-functional tensile testing machine. The dried adhesive film (prepared by pouring the adhesive liquid into a polytetrafluoroethylene mold, and then sequentially placing it at room temperature for 24 hours, in a drying oven at 60°C for 4 hours, and in a drying oven at 80°C for 2 hours to remove the solvent, thus forming the adhesive film) was cut into strips of 50 mm × 15 mm. After measuring the thickness using a micrometer, the stress-strain curve was tested at a tensile speed of 20 mm / min.

[0116] Stability test

[0117] Graphite and binder (net content) were mixed at a mass ratio of 97:3 for testing (the binder's water content was 6%). Specifically, 97 parts graphite, 25 parts binder (actual binder was 1.5 parts solid), and 40 parts water were thoroughly dispersed and kneaded using a double planetary mixer. Then, 25 parts binder (actual binder was 1.5 parts solid) and 13 parts water were added and thoroughly stirred to obtain a negative electrode slurry with a solid content of 50% (all "parts" refer to parts by weight). The viscosity was tested using a rotational viscometer (rotor No. 4, 30 rpm, 25°C) both when the binder was discharged and after standing at room temperature for 24 hours.

[0118] The test results are shown in Tables 1 and 2.

[0119] Table 1

[0120] Adhesive source Peel strength N / m Ionic conductivity mS / cm Tensile strength (MPa) Example 1 25 <![CDATA[8*10 -4 ]]> 10.1 Example 2 17 <![CDATA[7*10 -4 ]]> 9.6 Example 3 28 <![CDATA[5*10 -4 ]]> 11.1 Example 4 30 <![CDATA[4*10 -4 ]]> 11.7 Comparative Example 1 7 <![CDATA[1*10 -4 ]]> 6.4 Comparative Example 2 13 <![CDATA[6*10 -5 ]]> 7.7 Comparative Example 3 15 <![CDATA[3*10 -4 ]]> 12.2 Comparative Example 4 5 <![CDATA[9*10 -4 ]]> 6.8

[0121] Comparing the performance test results of the adhesives prepared in Examples 1, 2, 3, and 4 with those in Comparative Example 1, it can be seen that the introduction of conductive groups into the adhesive of this application can increase the density of active sites, thereby effectively improving the conductivity, peel strength, and tensile strength of the adhesive. Comparing the performance test results of the adhesives prepared in Examples 1 and 2, it can be seen that the proportion of polymer B in Example 2 is lower, resulting in a decrease in the peel strength and tensile strength of the adhesive. Comparing the test results of the adhesives in Examples 1 and 2, it can be seen that the adhesive in Example 1, after forming a cross-linked network structure compared to Comparative Example 2, also exhibits increased peel strength and tensile strength. Comparing the performance test results of the adhesives prepared in Examples 1, 3, and 4, it can be found that when the content of conductive polymer A in the adhesive is reduced, the conductivity of the adhesive decreases. Comparing the test results of the adhesives in Examples 1 and 3, it can be seen that when there is too much polymer B in the adhesive in Comparative Example 3, its tensile strength increases, but its peel strength decreases, and its conductivity is poor. Comparing the test results of the adhesives in Example 1 and Comparative Example 4, it can be seen that the adhesive in Comparative Example 4 has a higher content of conductive polymer A, which improves its conductivity, but its peel strength and tensile strength are lower.

[0122] Table 2

[0123] Adhesive source Discharge viscosity (mPa·s) Viscosity after standing for 24 hours (mPa·s) Example 1 4268 4668 Example 2 4648 4912 Example 3 4835 5218 Example 4 5187 5650 Comparative Example 1 5171 10387 Comparative Example 2 9840 16073 Comparative Example 3 6710 12087 Comparative Example 4 2457 3180

[0124] Comparing the viscosity test results of the adhesives prepared in Examples 1, 3, and 4, it can be found that when the amount of polymer B added to the adhesive is higher, the viscosity of the adhesive is greater, and the viscosity of the slurry increases slightly after standing for 24 hours. The adhesive slurries prepared in Comparative Examples 1 and 2 show a greater increase in viscosity after standing for 24 hours. Comparing the viscosity test results of the adhesives prepared in Example 1 and Comparative Example 3, it can be seen that when the amount of polymer B added to the adhesive in Comparative Example 3 is too high, the viscosity of the adhesive slurry increases more after standing, indicating that the amount of polymer B added should not be too high. The adhesive prepared in Comparative Example 4 has a low discharge viscosity and poor slurry stability, indicating that the amount of polymer B added should not be too low either.

[0125] The technical solutions provided in this application have been described in detail above. The descriptions of the embodiments above are only for the purpose of helping to understand the methods and core ideas of this application; at the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A polymer having a cross-linked network structure, which is a cross-linked polymer formed by polymerizing a non-conjugated free radical compound as shown in formula (1) with vinyl aniline to generate a highly conductive polymer A, and then cross-linking it with a multi-hydrogen bond flexible polymer B; in, The multi-hydrogen bond flexible polymer B is a polymer formed by copolymerizing acrylic monomers shown in B-1, acrylate monomers shown in B-2, and L-aspartic acid. Among them, R1, R2, R3, R4, R5, and R6 may be the same or different, and are independently selected from hydrogen, halogen, and C. 1-20 Alkyl, Halogenated C 1-20 Alkyl, C 3-20 cycloalkyl or halogenated C 3-20 cycloalkyl; R7, R8, R9, R 10 Whether the elements are the same or different, they are independently selected from hydrogen, halogens, and carbon. 1-20 Alkyl, Halogenated C 1-20 Alkyl, C 3-20 cycloalkyl or halogenated C 3-20 cycloalkyl; R 11 Selected from -COORa; Ra selected from C 1-20 Alkyl, Halogenated C 1-20 Alkyl or C 1-20 alkylene-OH; x and y are the molar percentages of the non-conjugated free radical compound of monomer formula (1) and vinyl aniline, respectively, used to prepare conductive polymer A. The two satisfy the following conditions: 0.4≤x≤0.7, 0.3≤y≤0.6, x+y=1; m, n, and z are the molar percentages of the acrylic monomer shown in B-1, the acrylate monomer shown in B-2, and the L-aspartic acid monomer, respectively, used to prepare the multi-hydrogen bonded flexible polymer. The three satisfy the following conditions: 0.3≤m≤0.5, 0.2≤n≤0.4, 0.1≤z≤0.5, and m+n+z=1.

2. The polymer with a cross-linked network structure according to claim 1, wherein, The mass ratio of the conductive polymer A to the multi-hydrogen bond flexible polymer B is 1:(1-10), for example 1:(1-4), or even 1:(1-3). Preferably, R1, R2, R3, R4, R5, and R6 may be the same or different, and are independently selected from hydrogen, halogen, and carbon. 1-12 Alkyl, Halogenated C 1-12 Alkyl, C 3-12 cycloalkyl or halogenated C 3-12 cycloalkyl; Preferably, R7, R8, R9, R 10 Whether the elements are the same or different, they are independently selected from hydrogen, halogens, and carbon. 1-12 Alkyl, Halogenated C 1-12 Alkyl, C 3-12 cycloalkyl or halogenated C 3-12 cycloalkyl; Preferably, R 11 Selected from -COORa; Ra selected from C 1-12 Alkyl, Halogenated C 1-12 Alkyl or -C 1-12 Alkylene-OH.

3. The polymer having a cross-linked network structure according to claim 1 or 2, wherein, R1, R2, R3, R4, R5, and R6 may be the same or different, and are independently selected from hydrogen or C. 1-6 alkyl; Preferably, R7, R8, R9, R 10 Whether the two are the same or different, they are independently selected from hydrogen or C. 1-6 alkyl; Preferably, R 11 Selected from -COORa; Ra selected from C 1-6 Alkyl or -C 1-6 Alkylene-OH.

4. The polymer having a cross-linked network structure according to any one of claims 1-3, wherein, R1, R2, R7, R8, R9, R 10 For H; Preferably, R3, R4, R5, and R6 are methyl or ethyl; Preferably, R 11 Selected from -COORa; Ra is selected from methyl, ethyl, propyl, -methylene-OH or -ethylene-OH.

5. A method for preparing the polymer having a cross-linked network structure according to any one of claims 1-4, wherein, Includes the following steps: The highly conductive polymer A described in any one of claims 1-4 is subjected to a crosslinking polymerization reaction with the flexible polymer B with multiple hydrogen bonds.

6. An ionic polymer having a cross-linked network structure, which is prepared by adjusting the pH of the system to 7-10 using an alkali metal salt, as described in any one of claims 1-4.

7. The ionic polymer with a cross-linked network structure according to claim 6, wherein, The alkali metal salt is selected from at least one of alkali metal hydroxides, alkali metal carbonates, or alkali metal bicarbonates.

8. A method for preparing the ionic polymer having a cross-linked network structure as described in claim 6 or 7, comprising: The polymer with a cross-linked network structure as described in any one of claims 1-4 is prepared by reacting it with an alkali metal salt until the pH of the system is 7-10.

9. Use of the ionic polymer having a cross-linked network structure as described in claim 6 or 7 as a binder, such as a negative electrode binder.

10. The use according to claim 9, wherein, The binder is a conductive silicon-based negative electrode binder, such as a conductive silicon-based negative electrode binder for lithium-ion batteries.

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