A chitosan-based self-repairing polymer binder, a preparation method and application thereof

Abstract

The application provides a chitosan-based self-repairing polymer binder, a preparation method thereof and application thereof in a silicon-based negative electrode. The chitosan-based self-repairing polymer binder is prepared by using carboxymethyl chitosan and polyacrylic acid as raw materials, heating and stirring the two in a solvent to cause a cross-linking reaction based on ionic bonding, and constructing a polymer binder with a stable macromolecular structure, which presents excellent structural stability and a wide electrochemical window, and also has excellent self-repairing performance and ionic conductivity. The synthesis process is safe, simple, convenient and environmentally friendly, has industrial batch production potential, and the abundant carboxyl groups in the chitosan-based self-repairing polymer binder form a covalent bond with the surface hydroxyl groups of the silicon-based negative electrode material to form a stable silicon-based negative electrode interface, so that the silicon-based negative electrode prepared by using the chitosan-based self-repairing polymer binder has the advantages of high active material proportion, high loading, high specific capacity, good rate performance and cycle stability.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to chitosan-based self-healing polymer binders and their preparation methods, and their application as binders in silicon-based anodes. Background Technology

[0002] In lithium-ion battery electrodes, the main function of the binder is to bond the active material, conductive agent, and current collector together and maintain the stability of the conductive network structure. Traditional binders, such as polyvinylidene fluoride (PVDF), are bonded to the active material by van der Waals forces, which are relatively weak and cannot withstand large stresses. Other commonly used binders, such as CMC / SBR, often suffer from poor mechanical properties due to their high brittleness, high stiffness, and low ductility, making them unable to withstand the large volume changes of the active material during cycling. This results in physical blockages between active material particles and between the active material and the conductive agent and current collector, leading to capacity decay and rapid capacity drops. Furthermore, the binder hinders lithium-ion diffusion, creating high charge transport impedance at the interface, which affects the battery's cycle life and safety.

[0003] Silicon, as an anode material, is abundant in nature and has a high theoretical specific capacity (4200 mAh g). -1 It is considered the most promising high-energy-density lithium-ion battery anode material, and its electrochemical reaction depends on a relatively complex alloying process, as shown in formulas (1)-(4):

[0004] Si (crystalline) + x Li + + xe - →Li x Si (amorphous state) (1)

[0005] Li x Si (amorphous) + (3.75-x)Li + + (3.75-x) e - →Li 15 Si4 (crystalline state) (2)

[0006] Part of Li 15 Si4 (crystalline) → Li x Si (amorphous) + γ Li + + γ e - (3)

[0007] Li x Si (amorphous) → Si (amorphous) + x Li + + xe - (4)

[0008] During the complex and repetitive alloying reaction process, the volume change of silicon reaches 300% or more, which极易 leads to the rupture and pulverization of active particles and the mechanical peeling of the electrode sheet from the current collector. Silicon monoxide (SiO x , 0 < x ≤ 2) negative electrode material generates Li x Si during the first alloying process. At the same time, the in-situ generated Li4SiO4 and Li2O inert phases isolate the contact between the active particles and the electrolyte, which can play a role in buffering the volume effect and maintaining the electrochemical activity of the material. However, with the cycle, the electrochemically active lithium storage phase (Si amorphous) of SiO x continuously decreases, and the irreversible phases Li2O and Li4SiO4 gradually increase, resulting in serious capacity attenuation. Moreover, the uncontrollable growth of the silicon-based negative electrode / electrolyte interface layer causes rapid attenuation of the battery capacity; the poor electronic conductivity (10 -3 S cm -1 ) and lithium ion diffusion coefficient (10 -12 cm 2 S -1 ) of the silicon-based material result in slow charge transfer kinetics, leading to a low initial Coulomb efficiency and restricting its capacity performance at high current densities. Therefore, there are still problems to be solved urgently in the large-scale commercial application of silicon-based negative electrode materials.

[0009] In recent years, functional supramolecular polymers with self-repairing properties have been developed and have received extensive attention for their application as adhesives. Patent CN117080449A provides a self-repairing binder for batteries, which consists of a binder, an auxiliary agent, a solvent, and a self-repairing agent. The self-repairing agent can be encapsulated by polymer microcapsules to achieve the automatic release of the repair binder when the battery suffers minor damage. However, due to the limited microcapsules in the material and the inability to replenish them again, the repair cycle is limited, reducing its application value. Patent CN110061238A provides a water-soluble self-healing polyacrylic acid-based binder PAA-UPy, which has good self-healing performance because it has a quadruple hydrogen bond with good reversibility in its molecular structure and can reversibly break under external stimuli such as external force or temperature and regenerate after the external stimulus disappears. However, polyacrylic acid has poor mechanical toughness and is prone to brittle fracture during the process of resisting the volume change of the electrode material.

[0010] Developing novel self-healing binders while simultaneously improving the mechanical properties of the binder, such as ductility and elastic modulus, while maintaining the structural stability of the polymer, presents significant technical challenges. This is particularly important for enhancing the stress threshold that binders can withstand during volume expansion / contraction, thus meeting the demands of commercial applications. Furthermore, considering the specific requirements of binders in high-energy-density electrode materials, exemplified by silicon-based anodes, there is an urgent need to endow polymer binders with more functions through molecular design, such as ionic or electronic conductivity. This would assist in constructing continuous ionic and electronic conductive networks on the electrode, enabling the fabrication of high-capacity thick electrodes, improving the structural stability of the electrode during cycling, and reducing interfacial carrier transport impedance. Therefore, the development of next-generation lithium-ion batteries, especially high-energy-density rechargeable batteries, urgently requires the design of binder systems that meet the requirements of good structural and electrochemical stability, excellent mechanical and self-healing properties, and high ionic conductivity. Summary of the Invention

[0011] The purpose of this invention is to provide a chitosan-based self-healing polymer binder, its preparation method, and its application in silicon-based anodes, all exhibiting good structural and electrochemical stability, excellent mechanical and self-healing properties, and high ionic conductivity. This invention not only boasts a low-cost, safe, simple, and environmentally friendly synthesis process with potential for industrial mass production, but also produces silicon-based anodes with high active material loading, high specific capacity, good rate performance, and excellent structural and electrochemical stability.

[0012] To achieve the above objectives, the present invention adopts the following technical solution.

[0013] A chitosan-based self-healing polymer adhesive, comprising a reaction product of carboxymethyl chitosan and polyacrylic acid, exists stably in a cross-linked network structure, and its general structural formula is shown below:

[0014]

[0015] (Where: R=H, CH2COOH)

[0016] A method for preparing a chitosan-based self-healing polymer adhesive, comprising the reaction of carboxymethyl chitosan with polyacrylic acid, and the preparation process including the following steps:

[0017] (1) Dissolve carboxymethyl chitosan in a solvent at a ratio of 1 to 5 wt% to prepare solution a; the molecular weight of the carboxymethyl chitosan is 150,000 to 600,000, the degree of carboxylation is ≥80%, and the solubility difference between the solvent and the carboxymethyl chitosan is ≤1.7-2.

[0018] (2) Dissolve polyacrylic acid in a solvent at a ratio of 1 to 5 wt% to prepare solution b; the molecular weight of the polyacrylic acid is 6000 to 8000.

[0019] (3) Add solution b dropwise to the above-prepared solution a, so that the mass ratio of carboxymethyl chitosan to polyacrylic acid reaches 1~6:1, and beige micelles are precipitated. After heating and stirring, the micelles are dissolved into solution c.

[0020] (4) Dry the solution c prepared in the above steps to obtain a transparent polymer, namely chitosan-based self-healing polymer adhesive.

[0021] Further, the solvent mentioned in steps (1) and (2) is any one of deionized water, N-methylpyrrolidone, N,N-dimethylformamide, and tetrahydrofuran.

[0022] Furthermore, the heating and stirring described in step (3) is carried out at 60 ℃-80 ℃ for 3-12 h, and the speed is 600-1000 rpm.

[0023] Furthermore, the drying described in step (4) is performed by forced air drying or vacuum drying at 60℃-80℃ for 24-48 hours.

[0024] A silicon-based anode using a chitosan-based self-healing polymer binder includes a silicon-based anode active material, a conductive agent, and a chitosan-based self-healing polymer binder. The mass ratio of the silicon-based anode active material, the conductive agent, and the chitosan-based self-healing polymer binder is 60-80: 20-10: 20-10. The silicon-based anode active material includes, but is not limited to, at least one of silicon, silicon suboxide, and silicon carbide compounds. The conductive agent includes at least one of conductive carbon black, carbon nanotubes, graphene, modified graphene, and graphite oxide. The conductive carbon black includes at least one of Super P, acetylene black, and Ketjen black.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] This invention relates to a chitosan-based self-healing polymer adhesive prepared from carboxymethyl chitosan and polyacrylic acid. The adhesive undergoes a crosslinking reaction based on ion bonding in a solvent through heating and stirring. Carboxymethyl chitosan, rich in amino groups, acts as crosslinking sites, reacting with the abundant carboxyl groups in polyacrylic acid to form a stable crosslinked network structure. Simultaneously, the abundant carboxyl and hydroxyl groups in carboxymethyl chitosan form hydrogen bonds through inter-component interactions, endowing the adhesive with excellent self-healing properties. Furthermore, the abundant carboxyl groups in the adhesive matrix can form covalent bonds with groups on the surface of silicon-based anode active materials, resulting in greater bonding strength and more stable adhesion compared to traditional adhesives that rely on van der Waals forces. Moreover, this adhesive also exhibits excellent ionic conductivity, assisting in the construction of a continuous ionic electronic conductivity network on the electrode, improving the structural stability of the electrode during cycling and reducing interfacial carrier transport impedance. The synthesis process of this adhesive is safe, simple, and environmentally friendly, possessing potential for industrial mass production. The silicon-based anode sheet prepared with this chitosan-based self-healing polymer binder can still have high specific capacity, good rate performance, and good interfacial structural stability and electrochemical stability, even with high active material loading. Attached Figure Description

[0027] Figure 1 The Fourier transform infrared spectrum of the chitosan-based self-healing polymer adhesive obtained in Example 1 is shown.

[0028] Figure 2 The image shows a test photograph of the self-healing performance of the chitosan-based self-healing polymer adhesive obtained in Example 2.

[0029] Figure 3 The results show the thermal stability test results of the chitosan-based self-healing polymer adhesive obtained in Example 3.

[0030] Figure 4 The results are the electrochemical window test results of the chitosan-based self-healing polymer adhesive obtained in Example 3.

[0031] Figure 5 The electrochemical impedance spectroscopy is the result of room temperature ionic conductivity testing of the chitosan-based self-healing polymer adhesive obtained in Example 4.

[0032] Figure 6 The nanoindentation curves of the silicon-based anodes obtained in Example 5, Comparative Example 2, and Comparative Example 3 are shown.

[0033] Figure 7 The bar chart shows the reduced modulus and hardness of the silicon-based anodes obtained in Example 5, Comparative Example 2, and Comparative Example 3, as obtained by nanoindentation testing.

[0034] Figure 8 The peeling test curves are for the silicon-based anodes obtained in Comparative Examples 2, 3, and 6.

[0035] Figure 9 This is a rate performance test chart for the battery in Example 7.

[0036] Figure 10 The images shown are electron microscope (EM) images of the surface and cross-section of the battery before and after cycling in Example 7.

[0037] Figure 11 This is a long-cycle test diagram of the battery in Example 8.

[0038] Figure 12 This is a graph showing the trend of coulombic efficiency variation during the long-cycle process of the battery in Example 8. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0040] Example 1:

[0041] 0.30 g of carboxymethyl chitosan was dissolved in 5.70 g of deionized water to prepare solution a, wherein the molecular weight of carboxymethyl chitosan was 150,000 and the degree of carboxylation was 80%. 0.05 g of polyacrylic acid was dissolved in 0.95 g of deionized water to prepare solution b, wherein the molecular weight of polyacrylic acid was 6000. 1.00 g of solution b was added dropwise to 6.00 g of solution a, wherein the mass ratio of carboxymethyl chitosan to polyacrylic acid was 6:1. Beige micelles precipitated. The micelles were dissolved by stirring at 80°C for 3 hours at 1000 rpm to prepare solution c. Solution c prepared in the above steps was dried at 80°C for 48 hours to obtain a yellow transparent polymer, which is a chitosan-based self-healing polymer adhesive. Its molecular structure is shown below:

[0042]

[0043] (Where: R=H, CH2COOH)

[0044] The Fourier transform infrared spectrum of the chitosan-based self-healing polymer adhesive obtained in Example 1 is shown below. Figure 1 As shown in the figure, it can be clearly seen that the wavenumber of polyacrylic acid is 1451 cm⁻¹. -1 and 1165 cm -1The absorption peaks around 3295 cm⁻¹ are due to the disappearance of the C-OH stretching vibration peak. -1 -NH3 appears on both the left and right sides. + The stretching vibration absorption peak, which belongs to carboxymethyl chitosan, has a wavenumber of 1587 cm⁻¹. -1 and 1412 cm -1 The absorption peaks on the left and right are due to the stretching vibration peaks of C=O, which have shifted position. Infrared spectroscopy results confirm that carboxymethyl chitosan and polyacrylic acid form a cross-linked network composed of numerous ionic bonds through a complexation reaction, yielding the target product, a chitosan-based self-healing polymer adhesive, and that hydrogen bonding interactions exist between the adhesive components.

[0045] Comparative Example 1:

[0046] 0.05 g of carboxymethyl chitosan was dissolved in 1.20 g of deionized water to prepare solution a, wherein the molecular weight of carboxymethyl chitosan was 300,000 and the degree of carboxylation was 90%. 0.15 g of polyacrylic acid was dissolved in 7.35 g of deionized water to prepare solution b, wherein the molecular weight of polyacrylic acid was 7000. 7.35 g of solution b was added dropwise to the 1.25 g solution a, wherein the mass ratio of carboxymethyl chitosan to polyacrylic acid was 0.5:1. A flocculent white precipitate formed. The mixture was stirred at 80°C for 4 hours at 800 rpm.

[0047] The product obtained in Comparative Example 1 was a flocculent white precipitate that could not be dissolved into a solution even after heating and stirring. The results of Comparative Example 1 verify that the mass ratio of carboxymethyl chitosan to polyacrylic acid significantly affects the crosslinking reaction, making it impossible to obtain the target product, chitosan-based self-healing polymer binder.

[0048] Example 2:

[0049] 0.30 g of carboxymethyl chitosan was dissolved in 7.20 g of N-methylpyrrolidone to prepare solution a, wherein the molecular weight of carboxymethyl chitosan was 300,000 and the degree of carboxylation was 90%. 0.30 g of polyacrylic acid was dissolved in 7.20 g of N-methylpyrrolidone to prepare solution b, wherein the molecular weight of polyacrylic acid was 7000. 7.50 g of solution b was added dropwise to 7.50 g of solution a, wherein the mass ratio of carboxymethyl chitosan to polyacrylic acid was 1:1. Beige micelles precipitated. The micelles were dissolved by stirring at 80°C for 3 hours at 1000 rpm to prepare solution c. Solution c prepared in the above steps was uniformly coated and dried at 80°C for 48 hours to obtain a transparent polymer, which is a chitosan-based self-healing polymer adhesive.

[0050] The self-healing performance test photos of the chitosan-based self-healing polymer adhesive obtained in Example 2 are shown below. Figure 2 As shown in the figure, it can be clearly seen that after the chitosan-based self-healing polymer adhesive is cut into two parts and the fracture surfaces are brought back into contact, rapid reassembly of the fracture surfaces is achieved through self-healing under the condition of contact for 1 min at 25 °C, and it can withstand further tensile testing. The initial elongation at break of the chitosan-based self-healing polymer adhesive reaches 758.3%, and after undergoing the self-healing performance test, its elongation at break can still recover to 733.3%, with a self-healing efficiency of 96.7%, further demonstrating that the chitosan-based self-healing polymer adhesive has both excellent mechanical properties and self-healing properties.

[0051] Example 3:

[0052] 0.30 g of carboxymethyl chitosan was dissolved in 29.70 g of desN,N-dimethylformamide to prepare solution a, wherein the molecular weight of carboxymethyl chitosan was 150,000 and the degree of carboxylation was 90%. 0.10 g of polyacrylic acid was dissolved in 9.90 g of desN,N-dimethylformamide to prepare solution b, wherein the molecular weight of polyacrylic acid was 6000. 10.00 g of solution b was added dropwise to 30.0 g of solution a, wherein the mass ratio of carboxymethyl chitosan to polyacrylic acid was 3:1. Beige micelles precipitated. The micelles were dissolved by stirring at 60°C for 12 hours at 600 rpm to prepare solution c. Solution c prepared in the above steps was vacuum dried at 60°C for 24 hours to obtain a transparent polymer, which is a chitosan-based self-healing polymer adhesive.

[0053] The thermal stability test results of the chitosan-based self-healing polymer adhesive obtained in Example 3 are as follows: Figure 3 As shown in the figure, it can be clearly seen that the obtained chitosan-based self-healing polymer binder has the lowest polymer side chain decomposition temperature (239.4 °C) and macromolecular backbone cleavage temperature (323.4 °C), indicating that the macromolecular structure constructed by the chitosan-based self-healing polymer binder through ionic bonding exhibits excellent structural stability.

[0054] The electrochemical window test results of the chitosan-based self-healing polymer adhesive obtained in Example 3 are as follows: Figure 4 As shown in the figure, it can be clearly seen that the obtained chitosan-based self-healing polymer binder has a wide electrochemical window (4.8V), indicating that the chitosan-based self-healing polymer binder exhibits excellent electrochemical stability.

[0055] Example 4:

[0056] 0.30 g of carboxymethyl chitosan was dissolved in 7.20 g of tetrahydrofuran to prepare solution a, wherein the molecular weight of carboxymethyl chitosan was 600,000 and the degree of carboxylation was 90%. 0.05 g of polyacrylic acid was dissolved in 2.45 g of tetrahydrofuran to prepare solution b, wherein the molecular weight of polyacrylic acid was 8000. 2.50 g of solution b was added dropwise to the 7.50 g of solution a, wherein the mass ratio of carboxymethyl chitosan to polyacrylic acid was 6:1. Beige micelles precipitated. The micelles were dissolved by stirring at 60°C for 12 hours at 600 rpm to prepare solution c. Solution c prepared in the above steps was uniformly coated and vacuum dried at 60°C for 24 hours to obtain a transparent polymer, which is a chitosan-based self-healing polymer adhesive.

[0057] The electrochemical impedance spectroscopy of the chitosan-based self-healing polymer adhesive obtained in Example 4, based on room temperature ionic conductivity testing, is shown below. Figure 5 As shown in the figure, the ionic conductivity of carboxymethyl chitosan and polyacrylic acid at 25 °C is 1.45 × 10⁻⁶, respectively. -4 S cm -1 With 6.33×10 -5 S cm -1 In comparison, the obtained chitosan-based self-healing polymer binder exhibits the highest room temperature ionic conductivity (2.89 × 10⁻⁶). -4 S cm -1 ).

[0058] Example 5:

[0059] A negative electrode slurry was prepared by combining the chitosan-based self-healing polymer binder prepared in Example 1, silica suboxide, graphene, and solvent, wherein the mass ratio of silica suboxide, graphene, and chitosan-based self-healing polymer binder was 80:10:10. The negative electrode slurry was coated onto a current collector, dried, and rolled to form a silicon-based negative electrode sheet. The coating thickness of the negative electrode slurry on the current collector was 200 μm. The drying step involved vacuum drying at 60 °C for 24 h, resulting in an electrode sheet with an active material loading of 2.0 mg / cm³. 2 .

[0060] Comparative Example 2:

[0061] The binder used in this comparative example is only carboxymethyl chitosan. A negative electrode slurry was prepared by mixing carboxymethyl chitosan, silica, conductive carbon black Super P, and a solvent, with a mass ratio of silica, conductive carbon black Super P, and carboxymethyl chitosan of 60:20:20. The negative electrode slurry was coated onto a current collector, dried, and rolled to form a silicon-based negative electrode sheet. The coating thickness of the negative electrode slurry on the current collector was 150 μm. The drying step involved vacuum drying at 80 °C for 24 h, resulting in an electrode sheet with an active material loading of 0.5 mg / cm³. 2 .

[0062] Comparative Example 3:

[0063] The binder used in this comparative example is only polyacrylic acid. A negative electrode slurry was prepared by mixing polyacrylic acid, silica, conductive carbon black SuperP, and a solvent, with a mass ratio of silica, conductive carbon black SuperP, and polyacrylic acid of 60:20:20. The negative electrode slurry was coated onto a current collector, dried, and rolled to form a silicon-based negative electrode sheet. The coating thickness of the negative electrode slurry on the current collector was 150 μm. The drying step involved vacuum drying at 80 °C for 24 h, resulting in an active material loading of 0.5 mg / cm³. 2 .

[0064] The nanoindentation curves of the silicon-based anodes obtained in Example 5, Comparative Example 2, and Comparative Example 3 are shown below. Figure 6 As shown in the figure, it can be clearly seen that under a certain load, the nanoindentation depth of Example 5, Comparative Example 3, and Comparative Example 2 gradually increases. This indicates that even with a high loading of silicon-based anode active material, the silicon suboxide anode particles bonded with the chitosan-based self-healing polymer binder used in Example 5 exhibit the strongest bonding force among the three binder systems. Furthermore, the silicon-based anode sample of Example 5 showed the smallest deformation under maximum load during the test, indicating that the thick silicon-based anode prepared with the chitosan-based self-healing polymer binder exhibits minimal irreversible deformation after undergoing the loading and unloading process.

[0065] The bar charts of the reduced modulus and hardness of the silicon-based anode sheets obtained by nanoindentation testing in Examples 5, 2, and 3 are shown below. Figure 7 As shown in the figure, it can be clearly seen that the silicon-based anode sheet of Example 5 has the highest folded modulus and hardness, indicating that the use of chitosan-based self-healing polymer binder can effectively enhance the mechanical properties of the silicon-based anode.

[0066] Example 6:

[0067] A negative electrode slurry was prepared by combining the chitosan-based self-healing polymer binder prepared in Example 1, silica, conductive carbon black Super P, and solvent, wherein the mass ratio of silica, conductive carbon black Super P, and chitosan-based self-healing polymer binder was 60:20:20. The negative electrode slurry was coated onto a current collector, dried, and rolled to form a silicon-based negative electrode sheet. The coating thickness of the negative electrode slurry on the current collector was 150 μm. The drying process involved vacuum drying at 80 °C for 12 h, resulting in an electrode sheet with an active material loading of 0.7 mg / cm³. 2 .

[0068] The peeling test curves of the silicon-based anode sheets obtained in Comparative Examples 2, 3, and 6 are shown below. Figure 8 As shown in the figure, the average adhesion force of the silicon-based negative electrode obtained in Comparative Example 2, which uses only carboxymethyl chitosan as a binder, is 0.66 N, and the average adhesion force of the silicon-based negative electrode obtained in Comparative Example 3, which uses only polyacrylic acid as a binder, is 1.71 N. In contrast, the average adhesion force of the silicon-based negative electrode obtained in Example 6, which uses a chitosan-based self-healing polymer binder, is significantly increased to 3.69 N, indicating that the synthesized chitosan-based self-healing polymer binder has excellent adhesion properties.

[0069] Example 7:

[0070] The silicon-based negative electrode obtained in Example 5 was used to assemble a CR2032 coin cell with a lithium metal sheet. The main components of the electrolyte used were lithium salt and organic solvent. The lithium salt was selected from at least one of the following substances: LiPF6, LiClO4, LiBF4, LiAsF6, LiAlCl4, LiCF3SO3, LiN(SO2CF3)2, LiBOB, LiSbF6, LiSCN, LiSnF6, LiGeF6, and LiTaF6. The organic solvent is selected from at least one of the following substances: ethylene carbonate, propylene carbonate, butene carbonate, vinylene carbonate, ethylene sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, methyl acetate, ethyl acetate, ethyl propionate, ethyl butyrate, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, dioxolane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, acetonitrile, dimethyl sulfoxide, acetone, N,N-dimethylformamide, sulfolane, and dimethyl sulfone.

[0071] The rate performance test results of the battery obtained in Example 7 are as follows: Figure 9 As shown in the figure, the battery with high active material loading prepared in Example 7 exhibits good rate performance at 0.05 A g. -1The initial discharge specific capacity is 1779.1 mA hg. -1 The Coulomb efficiency is 79.5%, even at 2 Ag. -1 The discharge specific capacity can still reach 891.4 mA hg. -1 After cycling at different current densities, the capacity retention rate was 98.0%.

[0072] Example 7: SEM images of the battery before and after cycling (surface / section). Figure 10 As shown in the figure, the number of cracks on the electrode surface of the battery in Example 7 during cycling is small, and the existing cracks are significantly thinner and shallower, and their distribution is relatively uniform. This indicates that the negative electrode using chitosan-based self-healing polymer binder is subjected to uniform stress and suffers less damage. Furthermore, the volume expansion rate of the negative electrode after cycling is only 33.3%, indicating that the chitosan-based self-healing binder has excellent mechanical-electrochemical stability, ensuring the volume stability of the negative electrode during cycling.

[0073] Example 8:

[0074] The silicon-based anode obtained in Example 6 was used to assemble a CR2032 coin cell with a lithium metal sheet, and the rest of the process was the same as in Example 7.

[0075] Example 8: Long-cycle test diagram of the battery (as shown in Figure 8). Figure 11 As shown in the figure. It can be seen from the figure that the battery of Example 8 operates at 1 Ag... -1 The capacity retention rate was 91% after 400 cycles, and the cycle length exceeded 500 cycles. The trend of coulombic efficiency during long-cycle processes is as follows: Figure 12 As shown in the figure, the coulombic efficiency of the battery in Example 8 remained at ~100% during long-term cycling, indicating that the silicon-based anode using chitosan-based self-healing polymer binder maintained structural stability during cycling, ensuring interfacial charge transport.

[0076] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A chitosan-based self-healing polymeric binder, characterized in that, The adhesive is composed of a crosslinking reaction product of carboxymethyl chitosan and polyacrylic acid, and its structure is as follows: ； Wherein: R = H, CH2COOH; The carboxymethyl chitosan has a molecular weight of 150,000 to 600,000 and a degree of carboxylation of ≥80%; the polyacrylic acid has a molecular weight of 6,000 to 8,000; and the mass ratio of carboxymethyl chitosan to polyacrylic acid is 1 to 6:

1.

2. A process for the preparation of the chitosan-based self-healing polymeric binder of claim 1, characterized by, Prepared by crosslinking carboxymethyl chitosan with polyacrylic acid, the preparation process includes the following steps: (1) Dissolve carboxymethyl chitosan in a solvent at a ratio of 1 to 5 wt% to prepare solution a; the molecular weight of the carboxymethyl chitosan is 150,000 to 600,000, the degree of carboxylation is ≥80%, and the solubility difference between the solvent and the carboxymethyl chitosan is ≤1.7-2. (2) Dissolve polyacrylic acid in a solvent at a ratio of 1 to 5 wt% to prepare solution b; the molecular weight of the polyacrylic acid is 6000 to 8000. (3) Add solution b dropwise to the above-prepared solution a, so that the mass ratio of carboxymethyl chitosan to polyacrylic acid reaches 1~6:1, and beige micelles are precipitated. After stirring at a temperature range of 60 ℃ to 80 ℃ for 3 to 12 h at a speed of 600 to 1000 rpm, the micelles are dissolved into solution c. (4) Dry the solution c prepared in the above steps to obtain a transparent polymer, namely chitosan-based self-healing polymer adhesive.

3. The method for preparing the chitosan-based self-healing polymer adhesive according to claim 2, characterized in that, The solvents mentioned in steps (1) and (2) are any one of deionized water, N-methylpyrrolidone, N,N-dimethylformamide, and tetrahydrofuran.

4. The method for preparing the chitosan-based self-healing polymer adhesive according to claim 2, characterized in that, The drying process described in step (4) involves blowing or vacuum drying at 60℃-80℃ for 24-48 hours.

5. A silicon-based negative electrode using a chitosan-based self-healing polymer binder prepared by the method according to any one of claims 2-4, characterized in that, It includes silicon-based anode active material, conductive agent, and chitosan-based self-healing polymer binder, with the mass ratio of silicon-based anode active material, conductive agent, and chitosan-based self-healing polymer binder being 60~80: 20~10: 20~10; The silicon-based anode active material includes at least one of silicon, silicon suboxide, and silicon carbide. The conductive agent includes at least one of conductive carbon black, carbon nanotubes, graphene, modified graphene, and graphite oxide. The conductive carbon black includes at least one of Super P, acetylene black, and Ketjen black.

Images