Dual-network structured water-based composite binder, its preparation method and application in lithium ion battery

Abstract

This invention provides a dual-network structure aqueous composite binder, its preparation method, and its application in lithium-ion batteries. It comprises a water-soluble polymer, carboxymethyl cellulose, and a crosslinking agent, wherein the aqueous polymer accounts for 85-99.4 wt%, carboxymethyl cellulose accounts for 0.5-10 wt%, and the crosslinking agent accounts for 0.1%-5%. This invention also provides a negative electrode made from this dual-network structure aqueous composite binder and a lithium-ion battery containing this negative electrode. The water-soluble polymer and carboxymethyl cellulose have strong adhesion to the negative electrode material. The crosslinking agent and dendritic structure endow the binder with a dual-network structure, enhancing the binder's toughness and effectively adapting to the volume change effect of active material during battery charging and discharging, thus maintaining the cycle stability of the lithium-ion battery.

Description

Technical Field

[0001] This invention relates to the field of new energy and new materials technology, specifically to a dual-network structure aqueous composite binder, a lithium-ion battery negative electrode containing the dual-network structure aqueous composite binder, and a lithium-ion battery containing the lithium-ion battery negative electrode. Background Technology

[0002] Binders are crucial auxiliary functional materials in lithium-ion batteries, significantly impacting the mechanical properties of the battery electrodes and influencing both electrode manufacturing processes and electrochemical performance. Lithium-ion battery binders are polymeric adhesives, categorized into non-aqueous and aqueous binders. Non-aqueous binders primarily consist of polyvinylidene fluoride (PVDF), which requires the use of toxic organic solvents (such as N-methylpyrrolidone) during slurry preparation, hindering the development of environmentally friendly lithium-ion batteries. Furthermore, PVDF exhibits poor adhesion to the electrode active material, making it difficult to effectively suppress problems such as cracking, pulverization, and detachment of the electrode material due to volume changes during charge and discharge, resulting in poor cycle stability of the lithium-ion battery. Aqueous binders mainly include acrylic copolymers, sodium alginate, and carboxymethyl cellulose-styrene-butadiene rubber composites. Acrylic copolymers, sodium alginate, and carboxymethyl cellulose contain numerous polar functional groups such as carboxyl groups on their molecular chains, generating strong intermolecular forces with the active material, thus exhibiting good adhesion. Moreover, the preparation of aqueous binders does not require the use of toxic organic solvents, improving the environmental friendliness of lithium-ion batteries. However, aqueous binders are relatively rigid, and electrode sheets made from them are prone to surface cracking and pulverization when the volume of the active material changes, which also leads to poor cycle stability of lithium-ion batteries. Summary of the Invention

[0003] The purpose of this invention is to address the problem of insufficient cycle stability in existing lithium-ion batteries containing water-soluble binders by developing a novel water-soluble binder that can improve the cycle stability of lithium-ion batteries while maintaining good adhesion to active materials. Another objective of this invention is to develop an environmentally friendly lithium-ion battery with improved cycle stability.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] In a first aspect, the present invention provides a dual-network structure water-based composite adhesive comprising a water-soluble polymer, carboxymethyl cellulose, and a crosslinking agent. By weight, the water-soluble polymer comprises 85-99.4 wt%, the carboxymethyl cellulose comprises 0.5-10 wt%, and the crosslinking agent comprises 0.1%-5%. The dual-network structure water-based composite adhesive is formed by crosslinking the dendritic water-soluble polymer with the crosslinking agent to form a dual-network structure. In this dual-network structure water-based composite adhesive, carboxymethyl cellulose forms the main chain, and the water-soluble polymer forms the side chains, creating a network-like dendritic polymer. Simultaneously, the side-chain polymers form a crosslinked network through the crosslinking agent, thereby giving the entire adhesive a "dual-network structure" bonding effect.

[0006] Furthermore, the molecular weight M of this carboxymethyl cellulose W The value ranges from 50,000 to 300,000, with a degree of substitution of 0.5 to 1.5.

[0007] Furthermore, the water-soluble copolymer is an aqueous acrylic copolymer.

[0008] Furthermore, the crosslinking agent is an inorganic crosslinking agent or an organic crosslinking agent. Even further, the inorganic crosslinking agent is an inorganic metal cation Cu. 2+ 、Sr 2+ Ba 2+ Ca 2+ Co 2+ Fe 2+ Cd 2+ Mn 2+ Cr 3+ Fe 3+ Al 3+ One or more of the following are considered: organic crosslinking agents, which are combinations of organic peroxide crosslinking agents (e.g., dicumyl peroxide), silane coupling agents (e.g., γ-aminopropyltriethoxysilane), aziridine crosslinking agents (e.g., trifunctional aziridine crosslinking agents), carboimide crosslinking agents, and polyvinylpyrrolidone.

[0009] The aforementioned dual-network structure waterborne composite adhesive can be prepared by the method developed by the inventors. This preparation method includes the following steps:

[0010] The dual-network structure waterborne composite adhesive is prepared by polymerizing carboxymethyl cellulose with a first comonomer and / or a second comonomer and / or a third comonomer and a crosslinking agent in an oxygen-free aqueous system under the initiation of an initiator at pH 6-9 and temperature 40-120℃ for 4-10 hours. The first comonomer is one or more of methyl acrylate, acrylic acid, hydroxyethyl acrylate, and methacrylic acid; the second comonomer is one or more of acrylamide, N-hydroxymethylacrylamide, N,N-dimethylacrylamide, and 2-carboxypropyl methacrylate; and the third comonomer is one or more of methacrylamide, hydroxyethyl acrylate, N-hydroxymethylacrylamide, N-butoxymethylacrylamide, 2-hydroxyethyl methacrylate, and ethyl acrylate.

[0011] Furthermore, based on the solids content of the water-soluble polymer, the amount of the first comonomer is 0-50 wt%.

[0012] Furthermore, based on the solids content of the water-soluble polymer, the amount of the second comonomer is 0-50 wt%.

[0013] Furthermore, based on the solids content of the water-soluble polymer, the amount of the third comonomer is 0-50 wt%.

[0014] Furthermore, the initiator can be a commonly used initiator in copolymerization preparation. Preferably, the initiator is one or a combination of sodium persulfate, potassium persulfate, ammonium persulfate, and azobisisobutyramidine, and the amount of the initiator is 0.1-2.5 wt% based on the solids content of the water-soluble polymer.

[0015] It should be noted that the initiator can be added all at once or in stages. When the initiator is added all at once, it is added to the aqueous system containing carboxymethyl cellulose and a first comonomer and / or a second comonomer and / or a third comonomer, and then the polymerization reaction is carried out. When the initiator is added in stages, 0.1-2.4 wt% of the initiator, 0.5-9.5 wt% of carboxymethyl cellulose, and 0-50 wt% of the first comonomer and / or 0-50 wt% of the second comonomer and / or 0-50 wt% of the third comonomer are first subjected to polymerization in the aqueous system for 0.5-9.5 h, followed by further polymerization in the aqueous system for 0.1-2.4 wt% of the initiator, 0.5-9.5 wt% of carboxymethyl cellulose, and 0-50 wt% of the first comonomer and / or 0-50 wt% of the second comonomer and / or 0-50 wt% of the third comonomer.

[0016] Furthermore, the aqueous system can be adjusted to pH 6-9 using one or more of sodium bicarbonate, sodium hydroxide, lithium hydroxide, sodium carbonate, potassium hydroxide, potassium bicarbonate, potassium carbonate, ammonia, or acetic acid.

[0017] Furthermore, the aqueous system can be deoxygenated by evacuating the vacuum and then introducing nitrogen gas for 30-60 minutes.

[0018] In a second aspect, the present invention provides a lithium-ion battery negative electrode, the lithium-ion battery negative electrode comprising a negative electrode substrate and a negative electrode material coated on the negative electrode substrate, the negative electrode material comprising a negative electrode active material, a conductive agent and a dual-network structure aqueous composite binder of the first aspect of the present invention.

[0019] The negative electrode substrate can be any known lithium-ion battery negative electrode substrate, such as, but not limited to, copper foil. The negative electrode active material can be any known lithium-ion battery negative electrode active material, such as, but not limited to, graphite, soft carbon, hard carbon, lithium titanate, silicon, silicon-carbon, silicon-oxygen-carbon, silicon-tin alloy, tin, tin-carbon, or germanium. The conductive agent can be any known lithium-ion battery negative electrode conductive agent, such as, but not limited to, Super P, carbon nanotubes, or Ketjen Black.

[0020] The lithium-ion battery anode can be prepared as follows: Anode active material, conductive agent, and the dual-network structure aqueous composite binder are dissolved in an appropriate amount of water to form an electrode slurry, wherein the dual-network structure aqueous composite binder accounts for 1-20 wt% based on the solid content of the electrode slurry (i.e., based on the total weight of the anode material). The electrode slurry is then coated onto a cathode substrate and dried to form the lithium-ion battery anode.

[0021] In a third aspect, the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is the negative electrode of the lithium-ion battery of the second aspect of the present invention.

[0022] The beneficial effects of this invention are:

[0023] The dual-network polymer binder of this invention is made by crosslinking water-soluble dendritic polymers to form a dual-network molecular structure. The water-soluble polymer and carboxymethyl cellulose ensure the binder's adhesive properties, providing strong adhesion to the negative electrode material. The crosslinking agent and dendritic structure impart a dual-network structure to the binder, enhancing its toughness and effectively adapting to the volume change effect of the active material during battery charging and discharging. This buffers the stress generated by the expansion and contraction of the active material during charging and discharging, alleviates the damage to the electrode structure caused by the volume change of the active material, and maintains the integrity of the electrode structure during charging and discharging, thereby ensuring the cycle performance and rate performance of the lithium-ion battery. Therefore, the dual-network polymer binder of this invention plays a crucial role in the cycle stability of lithium-ion batteries. Using the dual-network polymer binder of this invention to prepare the lithium-ion battery negative electrode, and then manufacturing the lithium-ion battery, the resulting lithium-ion battery exhibits superior electrochemical performance. Furthermore, the manufacturing process of the dual-network polymer binder and the lithium-ion battery negative electrode of this invention is simple, easy to operate, and has high production efficiency. The solvent is water, which is environmentally friendly and suitable for widespread application. Attached Figure Description

[0024] Figure 1 The constant current charge-discharge cycle curves of the full cells prepared by the binder of Examples 1-5 and Comparative Example 1 are shown. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and are included within the protection scope of the present invention.

[0026] Example 1

[0027] In a 1L reactor, 5g carboxymethyl cellulose, 22g acrylic acid, 27g hydroxyethyl acrylate, 31g N-hydroxymethyl acrylamide, 2g calcium acetate, and 200mL deionized water were added. The pH was adjusted to 6-7 with sodium bicarbonate solution, and the mixture was stirred. After evacuation, nitrogen gas was introduced for 30 minutes, followed by the addition of 1.5g potassium persulfate. The mixture was then heated to 70℃ and reacted for 6 hours to obtain a water-based composite adhesive with a dual-network structure.

[0028] SiC650 (purchased from KELOD), conductive agent Super P (purchased from KELOD), and the prepared dual-network structure aqueous composite binder were mixed at a mass ratio of 95:1:4, and adjusted with an appropriate amount of deionized water to form a slurry. This slurry was coated onto copper foil and dried to prepare an electrode. In a glove box, a battery was assembled using the prepared electrode as the negative electrode and the NCM811 electrode as the positive electrode for constant current charge-discharge testing. The electrolyte was a mixed solution of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate (volume ratio 1:1:1) containing 1.0 mol / L lithium hexafluorophosphate and 5% fluoroethylene carbonate. After 10 repeated tests, the battery retained 76.45% of its capacity after 200 constant current charge-discharge cycles.

[0029] Example 2

[0030] In a 1L reactor, 42g of acrylic acid, 42g of N-butoxymethylacrylamide, 6g of carboxymethyl cellulose, and 200mL of deionized water were added. The pH was adjusted to 6-7 with sodium bicarbonate solution, and the mixture was stirred. After evacuation, nitrogen gas was introduced for 30 minutes, followed by the addition of 1.5g of ammonium persulfate. The mixture was heated to 70℃ and reacted for 8 hours, then further heated to 80℃ and reacted for 1 hour. After the reaction cooled to room temperature, 0.5g of a trifunctional aziridine crosslinking agent was added and stirred for 2 hours to obtain a dual-network structure waterborne composite adhesive.

[0031] SiC650, conductive agent Super P, and the prepared dual-network structure aqueous composite binder were mixed at a mass ratio of 95:1:4 and adjusted with an appropriate amount of deionized water to form a slurry. This slurry was coated onto copper foil and dried to prepare an electrode. In a glove box, a battery was assembled using the prepared electrode as the negative electrode and the NCM811 electrode as the positive electrode for constant current charge-discharge testing. The electrolyte was a mixed solution of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate (volume ratio 1:1:1) containing 1.0 mol / L lithium hexafluorophosphate and 5% fluoroethylene carbonate. After 10 repeated tests, the battery retained 76.98% of its capacity after 200 constant current charge-discharge cycles.

[0032] Example 3

[0033] In a 1L reactor, add 6g carboxymethyl cellulose, 0.8g potassium persulfate, and 100mL deionized water. After evacuation, purge with nitrogen at 70℃ for 30min. Then add 15g acrylic acid, 40g 2-carboxypropyl methacrylate, 5g methyl acrylate, and 100mL deionized water. Adjust the pH to neutral by adding 5% lithium hydroxide solution dropwise and react at 70℃ for 2h. Next, add a mixed solution of 20g acrylic acid, 3g γ-aminopropyltriethoxysilane, and 0.6g potassium persulfate dropwise, strictly controlling the adding rate, ensuring the mixed solution is added completely over 2h, and continue reacting for 3h. Finally, add 0.2g potassium persulfate solution and react for 2h. Remove the reactor and adjust the pH to neutral by adding 5% lithium hydroxide solution.

[0034] SiC650, conductive agent Super P, and the prepared dual-network structure aqueous composite binder were mixed at a mass ratio of 95:1:4 and adjusted with an appropriate amount of deionized water to form a slurry. This slurry was coated onto copper foil and dried to prepare an electrode. In a glove box, a battery was assembled using the prepared electrode as the negative electrode and the NCM811 electrode as the positive electrode for constant current charge-discharge testing. The electrolyte was a mixed solution of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate (volume ratio 1:1:1) containing 1.0 mol / L lithium hexafluorophosphate and 5% fluoroethylene carbonate. After 10 repeated tests, the battery retained 70.98% of its capacity after 200 constant current charge-discharge cycles.

[0035] Example 4

[0036] In a 1L reactor, 5g carboxymethyl cellulose, 40g acrylic acid, 36g hydroxyethyl acrylate, 7g ethyl acrylate, and 200mL deionized water were added. The pH was adjusted to 6-7 with sodium bicarbonate solution, and the mixture was stirred. After evacuation, nitrogen gas was introduced for 30 minutes, followed by the addition of 1.5g potassium persulfate. The mixture was then heated to 60℃ and reacted for 8 hours. Next, 4g calcium acetate solution was added, and the temperature was raised to 70℃ and reacted for another 1 hour to obtain a water-based composite adhesive with a dual-network structure.

[0037] SiC650, conductive agent Super P, and the prepared dual-network structure aqueous composite binder were mixed at a mass ratio of 95:1:4 and adjusted with an appropriate amount of deionized water to form a slurry. This slurry was coated onto copper foil and dried to prepare an electrode. In a glove box, a battery was assembled using the prepared electrode as the negative electrode and an NCM811 electrode as the positive electrode for constant current charge-discharge testing. The electrolyte was a mixed solution of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate (volume ratio 1:1:1) containing 1.0 mol / L lithium hexafluorophosphate and 5% fluoroethylene carbonate. After 10 repeated tests, the battery retained 61.10% of its capacity after 200 constant current charge-discharge cycles.

[0038] Example 5

[0039] In a 1L reactor, 8g of carboxymethyl cellulose, 40g of acrylic acid, 40g of N-hydroxymethylacrylamide, and 200mL of deionized water were added. The pH was adjusted to 6-7 with sodium bicarbonate solution, and the mixture was stirred. After evacuation, nitrogen gas was introduced for 30 minutes, followed by the addition of 1.5g of potassium persulfate. The mixture was then heated to 60℃ and reacted for 8 hours. Next, 4g of calcium acetate solution was added, and the mixture was further heated to 70℃ and reacted for 1 hour to obtain a water-based composite adhesive with a dual-network structure.

[0040] SiC650, conductive agent Super P, and the prepared dual-network structure aqueous composite binder were mixed at a mass ratio of 95:1:4 and adjusted with an appropriate amount of deionized water to form a slurry. This slurry was coated onto copper foil and dried to prepare an electrode. In a glove box, a battery was assembled using the prepared electrode as the negative electrode and the NCM811 electrode as the positive electrode for constant current charge-discharge testing. The electrolyte was a mixed solution of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate (volume ratio 1:1:1) containing 1.0 mol / L lithium hexafluorophosphate and 5% fluoroethylene carbonate. After 10 repeated tests, the battery retained 59.43% of its capacity after 200 constant current charge-discharge cycles.

[0041] Comparative Example 1

[0042] Comparative experiments were conducted using sodium carboxymethyl cellulose and styrene-butadiene rubber instead of the dual-network structure aqueous composite binder used in Examples 1-5. SiC650, conductive agent Super P, sodium carboxymethyl cellulose, and styrene-butadiene rubber were mixed in a mass ratio of 95:1:1.6:2.4 with an appropriate amount of deionized water to form a slurry. This slurry was coated onto copper foil and dried to prepare an electrode. In a glove box, a battery was assembled using the prepared electrode as the negative electrode and the NCM811 electrode as the positive electrode for constant current charge-discharge testing. The electrolyte was a mixed solution of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate (volume ratio 1:1:1) containing 1.0 mol / L lithium hexafluorophosphate and 5% fluoroethylene carbonate. After 10 repeated tests, the battery retained 49.48% of its capacity after 200 constant current charge-discharge cycles.

[0043] Figure 1 The constant current charge-discharge cycle curves of batteries prepared with the dual-network structure aqueous composite binder of Examples 1-5 and Comparative Example 1 are shown. Figure 1 As can be seen, after 200 cycles, the capacity retention rates of the batteries prepared with the dual-network structure aqueous composite binder of Examples 1-5 and Comparative Example 1 were 76.45%, 76.98%, 70.98%, 61.10%, 59.43%, and 49.48%, respectively. This demonstrates that the dual-network structure aqueous composite binder of the present invention can improve the cycle stability of the battery.

[0044] The above specific examples illustrate the present invention and are merely for the purpose of aiding understanding, not limiting the scope of the invention. Those skilled in the art can make various simple deductions, modifications, or substitutions based on the concept of the present invention. These deductions, modifications, or substitutions also fall within the scope of the claims of this invention.

Claims

1. A method for preparing a dual-network structure aqueous composite binder for lithium-ion batteries, characterized in that, The dual-network structure waterborne composite adhesive is composed of a water-soluble polymer, carboxymethyl cellulose, and a crosslinking agent. By total weight, the water-soluble polymer accounts for 85-99.4 wt%, the carboxymethyl cellulose accounts for 0.5-10 wt%, and the crosslinking agent accounts for 0.1-5 wt%. The carboxymethyl cellulose has a molecular weight of 50,000-300,000 and a degree of substitution of 0.5-1.

5. The dual-network structure is formed by the crosslinking agent connecting the carboxymethyl cellulose backbone to the water-soluble polymer side chains, creating a dendritic-network dual structure. The water-soluble polymer is a waterborne polyacrylic acid copolymer, and the crosslinking agent is an inorganic or organic crosslinking agent. The inorganic crosslinking agent is an inorganic metal cation Cu. 2+ 、Sr 2+ Ba 2+ Ca 2+ Co 2+ Fe 2+ Cd 2+ Mn 2+ Cr 3+ Fe 3+ Al 3+ The preparation method comprises one or more of the following: organic crosslinking agent is an organic peroxide crosslinking agent, a silane coupling agent, an aziridine crosslinking agent, a carboimide crosslinking agent, and polyvinylpyrrolidone; the preparation method includes the following steps: The dual-network structure waterborne composite adhesive is prepared by polymerizing carboxymethyl cellulose with a first comonomer, a second comonomer, a third comonomer, and a crosslinking agent in an oxygen-free aqueous system under the initiation of an initiator at pH 6-9 and temperature 40-120℃ for 4-10 h. The first comonomer is one or more of methyl acrylate, acrylic acid, hydroxyethyl acrylate, and methacrylic acid; the second comonomer is one or more of acrylamide, N-hydroxymethylacrylamide, N,N-dimethylacrylamide, and 2-carboxypropyl methacrylate; and the third comonomer is one or more of methacrylamide, hydroxyethyl acrylate, N-hydroxymethylacrylamide, N-butoxymethylacrylamide, 2-hydroxyethyl methacrylate, and ethyl acrylate.

2. The method for preparing a dual-network structure aqueous composite binder for lithium-ion batteries according to claim 1, characterized in that, The amount of the first comonomer is 0-50 wt%, based on the solids content of the water-soluble polymer. The amount of the second comonomer is 0-50 wt%, based on the solids content of the water-soluble polymer. The amount of the third comonomer is 0-50 wt%, based on the solids content of the water-soluble polymer. The initiator is one or more of sodium persulfate, potassium persulfate, ammonium persulfate, and azobisisobutyramidine, and the amount of the initiator is 0.1-2.5 wt% based on the solid content of the water-soluble polymer.

3. The method for preparing a dual-network structure aqueous composite binder for lithium-ion batteries according to claim 2, characterized in that, The initiator is added at once to the aqueous system containing carboxymethyl cellulose and the first comonomer, the second comonomer, and the third comonomer for polymerization; or, 0.1-2.4 wt% of the initiator, 0.5-9.5 wt% of carboxymethyl cellulose, 0-50 wt% of the first comonomer, 0-50 wt% of the second comonomer, and 0-50 wt% of the third comonomer are first subjected to polymerization in the aqueous system for 0.5-9.5 h, and then 0.1-2.4 wt% of the initiator, 0.5-9.5 wt% of carboxymethyl cellulose, 0-50 wt% of the first comonomer, 0-50 wt% of the second comonomer, and 0-50 wt% of the third comonomer are subjected to polymerization in the aqueous system for 0.5-9.5 h.

4. A lithium-ion battery, characterized in that, The battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode comprises a negative electrode substrate and a negative electrode material coated on the negative electrode substrate, wherein the negative electrode material comprises a negative electrode active material, a conductive agent, and the aqueous composite binder with a dual network structure prepared by any one of claims 1 to 3.

5. A lithium-ion battery according to claim 4, characterized in that, The dual-network structure aqueous composite binder accounts for 1-20 wt% of the total weight of the negative electrode material.

6. A lithium-ion battery according to claim 4, characterized in that, The negative electrode substrate is copper foil, the negative electrode active material is graphite, soft carbon, hard carbon, lithium titanate, silicon, silicon-carbon, silicon-oxygen-carbon, silicon-tin alloy, tin, tin-carbon or germanium, and the conductive agent is Super P, carbon nanotubes or Ketjen Black.

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