A lignin-based self-repairing adhesive, and a preparation method and application thereof

Abstract

The application discloses a lignin-based self-repairing binder and a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. The lignin-based self-repairing binder is prepared by the following steps: mixing polyacrylic acid, lignin sulfonate and a lithium-based thioctic acid material in a solution, and then performing heat treatment to obtain the lignin-based self-repairing binder; and the lithium-based thioctic acid material is lithium thioctic acid or lithium polythioctic acid crosslinked by itaconic acid. The binder obtained by the application has a three-dimensional network structure, lithiumated thioctic acid segments are introduced into the binder, and lignin sulfonate is used as a crosslinking network branch point, so that the binder has good adhesion. The introduction of lithium ions and crosslinked polythioctic acid improves the cycle performance and rate performance of the lithium ion battery under high current density.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a lignin-based self-healing binder, its preparation method, and its application. Background Technology

[0002] With the development of new energy vehicles, the demand for high-energy-density lithium-ion batteries is constantly increasing. However, the specific capacity of traditional graphite anodes (approximately 372 mAh / g) is nearing its limit and cannot meet future demands. Silicon-based anodes have become ideal candidate materials due to their extremely high theoretical specific capacity (approximately 4200 mAh / g), but their dramatic volume expansion during charge and discharge (up to 300% or more) can lead to material pulverization and repeated rupture of the SEI film, resulting in capacity decay and reduced cycle life, thus limiting their commercial application.

[0003] Binders play a crucial role in mitigating volume expansion and maintaining electrode structural stability. Traditional electrode binders, such as PVDF and CMC, have limited mechanical properties and are ill-suited to handle the volume changes in silicon-based materials. To address this, researchers are developing novel multifunctional binders, primarily including: three-dimensional cross-linked binders (enhancing mechanical strength), self-healing binders (repairing interfacial damage), and conductive binders (improving conductivity and reducing the amount of conductive agent required).

[0004] Lignin, with its multifunctional functional groups and natural structure, shows great potential in emerging fields such as battery binders. Its aromatic structure and rigid framework not only improve the cycle performance of lithium-sulfur batteries but also suppress volume expansion and the "shuttle effect," maintaining good performance even with low binder dosages. Chinese Patent (CN116804138B) discloses a method for preparing a silicon-based anode composite binder for lithium-ion batteries, which enhances the binder's bonding performance but still does not solve the problem of long-term cycle stability of the anode material under high current. Chinese Patent (CN113054193B) discloses a method for preparing a silicon-based anode self-healing polymer binder, which endows the binder with self-healing capabilities but does not solve the problem of low usable capacity of lithium-ion batteries under high current. Summary of the Invention

[0005] To address the problems existing in the prior art, the primary objective of this invention is to provide a method for preparing a lignin-based self-healing adhesive.

[0006] Another object of the present invention is to provide a lignin-based self-healing adhesive.

[0007] Another object of the present invention is to provide a negative electrode.

[0008] Another object of the present invention is to provide a lithium-ion battery.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A lignin-based self-healing adhesive, the preparation method of which includes the following steps: Polyacrylic acid, lignin sulfonate, and lithium thiocate-based materials are mixed in a solvent and then heat-treated to obtain the lignin-based self-healing adhesive. The mass ratio of polyacrylic acid, lignin sulfonate, and lithium thiocate-based material is 1~10:1~3:1~3. The lithium thiocate-based material is lithium thiocate or itaconic acid crosslinked polythiocate. The preparation method of itaconic acid crosslinked polythiocate includes: firstly polymerizing and crosslinking thiocate with itaconic acid, and then reacting it with lithium hydroxide to obtain the itaconic acid crosslinked polythiocate. The mass ratio of thiocate to itaconic acid is 1:(0.1~0.3).

[0010] This invention involves mixing and heat-treating a mixture of polyacrylic acid, lignin sulfonate, lithium thiocate, or itaconic acid-crosslinked lithium polythiocate to obtain a lignin-based self-healing adhesive. By introducing lithium-modified thiocate segments into the adhesive, the proportion of flexible segments is increased, preventing excessive rigidity and breakage. At high temperature, the disulfide bonds on thiocate undergo ring-opening polymerization to form metastable polythiocate. Based on this, itaconic acid, a biomass molecule with olefinic double bonds, is selected as a crosslinking agent or stabilizer. Its double bonds exhibit high activity and low steric hindrance, and its reactivity with thiocate is typically higher than that of other small biomass acids containing double bonds. Itaconic acid quenches the terminal sulfide groups of polythiocate through addition reactions, thereby preventing depolymerization and improving the stability of the crosslinked network.

[0011] This invention introduces lithium ions into the binder, which improves the binder's mechanical properties and ensures the integrity of its network structure. Compared to sodium ions, lithium ions can form coordination relationships with the hydroxyl and carboxyl groups on lignin, the carboxyl groups on polyacrylic acid, and the carboxyl groups on itaconic acid. This facilitates the migration of lithium ions in the electrolyte, promotes the hopping transport of lithium ions, reduces the volume expansion of silicon-based active materials, and thus improves the conductivity of silicon-based anode sheets and the rate performance of lithium-ion batteries.

[0012] Lignin molecules contain a large number of hydroxyl groups, which can undergo esterification with the carboxyl groups of polyacrylic acid to form covalent ester bonds. Furthermore, as a rigid structure in the cross-linking network, lignin can form hydrogen bonds with polyacrylic acid and lithium polylipoate.

[0013] Hydrogen bonds exist between polyacrylic acid, lignin sulfonate, and lithium thiocate or itaconic acid crosslinked lithium thiocate, which improves the stability of the binder.

[0014] During heat treatment, the carboxyl groups on polyacrylic acid undergo a thermal esterification reaction with the hydroxyl groups on lignin sulfonate, forming covalent ester bonds and constructing a rigid three-dimensional network. The long molecular chains in lithium polythiooctanoate can form molecular chain entanglements with the long molecular chains in the rigid three-dimensional network, further improving the stability of the network in the binder. Therefore, the lignin-based self-healing binder provided by this invention can improve the cycle performance and rate performance of silicon-based lithium-ion batteries at high current densities.

[0015] Heat treatment of the adhesive at 70~180℃ can improve the degree of cross-linking of the network structure, thereby improving the stability and structural integrity of the adhesive.

[0016] This invention utilizes lignin sulfonate, which, compared to other lignins, exhibits a higher Zeta potential. Increased lignin sulfonate content leads to a higher negative charge density, which helps improve the dispersibility between lignin molecules. Furthermore, lignin is a renewable biological resource, thus conserving resources and energy to a certain extent, in line with green and sustainable development goals.

[0017] Preferably, the mass ratio of lipoic acid to itaconic acid is 1:(0.15~0.25).

[0018] Preferably, the temperature of the heat treatment is 70~180℃.

[0019] More preferably, the temperature of the heat treatment is 100~180℃, even more preferably 120~180℃, and even more preferably 135~165℃.

[0020] Preferably, the heat treatment time is 1 to 3 hours.

[0021] Preferably, the mass ratio of the polyacrylic acid, lignin sulfonate, and lithium thiocate-based material is 4~10:1~3:1~3.

[0022] More preferably, the mass ratio of the polyacrylic acid, lignin sulfonate, and lithium thiocate-based material is 5~8:1~2:1~2.

[0023] More preferably, the mass ratio of the polyacrylic acid, lignin sulfonate, and lithium thiocate-based material is 5~8:1~1.5:1.5~2.

[0024] More preferably, the mass ratio of the polyacrylic acid, lignin sulfonate, and lithium thiocate-based material is 5~8:1:2.

[0025] Preferably, the polymerization crosslinking temperature is 100~200℃.

[0026] More preferably, the polymerization crosslinking temperature is 100~180℃, even more preferably 100~170℃, even more preferably 110~160℃, even more preferably 120~150℃, and even more preferably 130~140℃.

[0027] The carboxyl group on lipoic acid reacts with lithium hydroxide to generate a pre-lithiated flexible segment, which is then self-polymerized or copolymerized with itaconic acid under high temperature conditions to form a highly efficient lithium-conducting flexible segment.

[0028] More preferably, the polymerization crosslinking time is 0.5 to 2 hours.

[0029] More preferably, after polymerization and crosslinking, itaconic acid-crosslinked polythiooctanoic acid is obtained, wherein the mass ratio of itaconic acid-crosslinked polythiooctanoic acid to lithium hydroxide is 5~15:1~3.

[0030] More preferably, the mass ratio of the itaconic acid-crosslinked polythioctic acid to lithium hydroxide is 8~12:1~3.

[0031] Preferably, the method for preparing the lithium thiocate includes: mixing and reacting thiocic acid with lithium hydroxide to obtain the lithium thiocate.

[0032] More preferably, the mass ratio of thioctic acid to lithium hydroxide is 5~15:1~3.

[0033] More preferably, the mass ratio of thioctic acid to lithium hydroxide is 8~12:1~3.

[0034] The polyacrylic acid can be obtained by purchasing or making it in-house.

[0035] Preferably, the polyacrylic acid is synthesized by thermally initiated free radical polymerization.

[0036] More preferably, the method for preparing the polyacrylic acid includes: mixing acrylic acid with water, adding a thermal initiator, and reacting in an inert gas atmosphere to obtain the polyacrylic acid; the reaction temperature is 60~100℃, the reaction time is 2~8h, and the mass ratio of acrylic acid, water and thermal initiator is (100~400):(200~600):1.

[0037] More preferably, the thermal initiator for thermal initiation is ammonium persulfate.

[0038] Specifically, the lignin sulfonate is sodium lignin sulfonate or calcium lignin sulfonate.

[0039] Specifically, the solvent is at least one of deionized water, dioxane, and ethanol-water.

[0040] A silicon-based negative electrode sheet includes a negative electrode active material, a conductive agent, and a lignin-based self-healing binder.

[0041] Preferably, the method for preparing the silicon-based negative electrode includes: Polyacrylic acid, lignin sulfonate, and lithium thiocate-based materials are mixed in a solvent to obtain a first mixed solution; The negative electrode active material and the conductive agent are ball-milled and then mixed with the first mixed solution to obtain the negative electrode slurry. The negative electrode slurry is coated onto the surface of the current collector, and then heat-treated to obtain the silicon-based negative electrode sheet.

[0042] It should be noted that, in specific embodiments, in order to ensure that the negative electrode active material, conductive agent, and negative electrode binder are mixed evenly, and to construct an efficient conductive network and a stable binder crosslinking network in the negative electrode sheet, the negative electrode binder in the negative electrode slurry is a mixed solution before heat treatment, and the heat treatment step in the binder preparation is implemented in the negative electrode sheet preparation step.

[0043] High-temperature heat treatment during the preparation of negative electrode sheets helps to improve the stability of the negative electrode sheet structure and the integrity of the conductive network, reduces concentration polarization and ohmic polarization in lithium-ion batteries, and thus improves the cycle performance and rate performance of lithium-ion batteries at high current densities.

[0044] Specifically, the negative electrode active material is at least one of silicon, silicon suboxide, or silicon carbon.

[0045] Specifically, the conductive agent is at least one of conductive carbon black, graphite, acetylene black, Super P, Super S, graphene, carbon fiber, carbon nanotubes, or Ketjen black.

[0046] More preferably, the raw materials for the lignin-based self-healing binder are composed of polyacrylic acid, lignin sulfonate, and lithium thiocate-based materials, and the mass ratio of the negative electrode active material, conductive agent, and lignin-based self-healing binder raw materials in the negative electrode slurry is 1~10:1~3:1~3.

[0047] More preferably, in the negative electrode slurry, the mass ratio of the raw materials of the negative electrode active material, the conductive agent, and the lignin-based self-healing binder is 4~10:1~3:1~3.

[0048] More preferably, in the negative electrode slurry, the mass ratio of the raw materials of the negative electrode active material, the conductive agent, and the lignin-based self-healing binder is 5~8:1~2:1~2.

[0049] More preferably, the rotational speed of the ball mill is 100~1000 rpm.

[0050] More preferably, the ball milling time is 5 to 20 hours.

[0051] Ball milling not only reduces the particle size of active materials, making them finer, but also helps the conductive agent to be evenly distributed on the surface of the active material, thereby constructing a highly efficient conductive network.

[0052] More preferably, the mixing time is 1 to 10 hours.

[0053] In this invention, the current collector is at least one of copper foil, nickel foil, and carbon cloth.

[0054] Preferably, the loading of active material in the negative electrode is 1.0~2.5 mg / cm³. 2 .

[0055] A lithium-ion battery comprising the aforementioned silicon-based negative electrode.

[0056] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing a lignin-based self-healing binder. The method involves mixing polyacrylic acid, lignin sulfonate, lithium thiooctanoate, or itaconic acid-crosslinked lithium polythiooctanoate and then heat-treating the mixture to obtain the lignin-based self-healing binder. The covalent ester bond formed between lignin and polyacrylic acid acts as a rigid structure to suppress the expansion of the negative electrode material. The aromatic structure of lignin can create a certain degree of π-electron delocalization effect, reducing electron transport resistance, optimizing the electron network connection inside the electrode, and mitigating electrochemical polarization. The lithium-ionized polythiooctanoate can shorten the lithium-ion transport path, and the disulfide bonds can self-repair material cracks during cycling, ensuring the integrity of the conductive network and improving the stability of the crosslinked network. The synergistic effect of lignin and lithium polythiooctanoate promotes lithium-ion migration, thereby improving the rate performance of the battery. The binder obtained by this invention has a three-dimensional network structure. The introduction of lithium-ion thioctic acid segments into the binder increases the proportion of flexible segments, and lignin sulfonate is used as the crosslinking network fulcrum, so that the binder has good adhesion properties as well as self-healing properties, thereby improving the cycle performance and rate performance of lithium-ion batteries at high current densities.

[0057] This invention selects itaconic acid, a biomass molecule with olefin double bonds, as a crosslinking agent or stabilizer for polythiooctanoic acid. Itaconic acid double bonds have high activity and low steric hindrance. It quenches the terminal sulfur groups of polythiooctanoic acid through addition reaction to prevent polythiooctanoic acid depolymerization, thereby improving the stability of the crosslinking network and further improving the cycle performance and rate performance of lithium-ion batteries at high current densities. Attached Figure Description

[0058] Figure 1 The figures show the peeling performance of silicon-based anode sheets in Examples 4, 5 and Comparative Example 1.

[0059] Figure 2 This is a test diagram of the self-healing performance of Example 4.

[0060] Figure 3 The graph shows the cycling performance of lithium-ion batteries in Examples 4, 5 and Comparative Example 1 at a current density of 0.5 A / g.

[0061] Figure 4 The graph shows the cycle performance of the lithium-ion batteries in Examples 1-4 at a current density of 1 A / g.

[0062] Figure 5 The graphs show the rate performance of Examples 1, 4, 5 and Comparative Example 1 at different current densities. Detailed Implementation

[0063] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0064] Example 1 This embodiment provides a lignin-based self-healing adhesive, the preparation method of which includes the following steps: S0.1. Preparation of polyacrylic acid: The acrylic monomer was purified by chromatography to remove the polymerization inhibitor. 50g of purified acrylic acid and 100g of deionized water were placed in a three-necked flask, and 0.25g of ammonium persulfate (APS) was added. The reaction was carried out under a nitrogen atmosphere at 80℃ with high-speed stirring for 5 hours to obtain high-viscosity polyacrylic acid. The product was cut into small pieces, washed repeatedly with water, dissolved in water, and then freeze-dried to obtain polyacrylic acid.

[0065] S0.2. Preparation of lithium polythiooctanoate: 2 g of thioctic acid and 0.4 g of itaconic acid were reacted at 135 °C for 0.5 h, with a mass ratio of thioctic acid to itaconic acid of 1:0.2, to obtain itaconic acid crosslinked polythioctic acid; then 1 g of polythioctic acid and 0.1 g of lithium hydroxide were dissolved in ethanol and reacted for 2 h, centrifuged, washed, and freeze-dried to obtain itaconic acid crosslinked lithium polythiooctanoate.

[0066] S1. Dissolve polyacrylic acid, sodium lignosulfonate, and itaconic acid-crosslinked lithium polythiooctanoate in deionized water at a mass ratio of 7:1:2 and stir to obtain a mixed solution before heat treatment (i.e., the first mixed solution).

[0067] S2. The mixed solution before heat treatment is heat-treated in a high-temperature vacuum drying oven at 150°C for 2 hours to obtain the lignin-based self-healing adhesive.

[0068] To ensure uniform mixing of the negative electrode active material, conductive agent, and negative electrode binder, and to construct an efficient conductive network and a stable binder crosslinking network in the negative electrode sheet, the negative electrode binder in the negative electrode slurry is a mixed solution before heat treatment. The heat treatment step in the binder preparation is carried out in the negative electrode sheet preparation step. The preparation of the negative electrode slurry and the negative electrode sheet is as follows.

[0069] Methods for preparing negative electrode slurry include: The polyacrylic acid, sodium lignosulfonate, and itaconic acid crosslinked lithium thiooctanoate were dissolved in deionized water at a mass ratio of 7:1:2 and stirred to obtain a mixed solution before heat treatment (i.e., the first mixed solution).

[0070] Active material SiO and conductive carbon black were mixed at a mass ratio of 7:2, and a suitable mass was weighed into an agate ball mill jar, with the material volume not exceeding 1 / 2 of the jar. The mixture of SiO and conductive carbon black was ball milled at 400 r / min for 10 h. A lignin-based self-healing binder was prepared using polyacrylic acid, lignin sulfonate, and lithium thiocate as raw materials. A slurry was prepared by mixing the active material, conductive agent, and lignin-based self-healing binder raw materials at a mass ratio of 7:2:1. The ball-milled mixture was added to the pre-heat-treatment solution and stirred for 6 h to ensure thorough mixing, thus obtaining the negative electrode slurry.

[0071] The preparation method of the negative electrode sheet includes: scraping the negative electrode slurry on the copper foil with a doctor blade to obtain an active material loading of 1.0 mg / cm³. 2 The wetted electrode was placed in an 80°C forced-air drying oven for 1 hour to remove most of the solvent, followed by heat treatment in a 150°C high-temperature vacuum drying oven for 2 hours. The dried electrode sheet was then cut into 12 mm diameter electrode sheets using a slicer to obtain the negative electrode sheet.

[0072] The method for preparing a lithium-ion battery includes: using polypropylene as the battery separator, and a mixed electrolyte containing 1 mol of LiPF6, 10 wt% of fluoroethylene carbonate (FEC), 1 wt% of vinylene carbonate (VC), and ethylene carbonate (EC): diethyl carbonate (DEC) in a volume ratio of 1:1 as the battery electrolyte. A coin cell is assembled in an argon-filled glove box to obtain the lithium-ion battery.

[0073] Example 2 This embodiment provides a lignin-based self-healing adhesive. The difference from Embodiment 1 is that in step S2, 2 g of lipoic acid and 0.3 g of itaconic acid are reacted at 135°C for 0.5 h, and the mass ratio of lipoic acid to itaconic acid is 1:0.15 to obtain polylipoic acid crosslinked with itaconic acid. The rest is the same as in Embodiment 1.

[0074] Example 3 This embodiment provides a lignin-based self-healing adhesive. The difference from Embodiment 1 is that in step S2, 2 g of thioctic acid and 0.5 g of itaconic acid are reacted at 135°C for 0.5 h, and the mass ratio of thioctic acid to itaconic acid is 1:0.25 to obtain polythioctic acid crosslinked with itaconic acid. The rest is the same as in Embodiment 1.

[0075] Example 4 This embodiment provides a lignin-based self-healing adhesive, the preparation method of which includes the following steps: S1. Preparation of polyacrylic acid: Same as S1 in Example 1.

[0076] S2. Preparation of lithium lipoate: 2g of lipoic acid and 0.2g of lithium hydroxide were dissolved in ethanol respectively. While stirring, the lithium hydroxide-ethanol solution was poured into the lipoic acid-ethanol solution and reacted for 0.5h. After the reaction was completed, the solution was filtered, washed and freeze-dried to obtain lithium lipoate.

[0077] S3. Dissolve polyacrylic acid, sodium lignosulfonate, and lithium thiocate in deionized water at a mass ratio of 7:1:2 and stir to obtain a mixed solution before heat treatment.

[0078] S4. The mixed solution before heat treatment is heat-treated in a high-temperature vacuum drying oven at 150°C for 2 hours to obtain the lignin-based self-healing adhesive.

[0079] The preparation of the negative electrode slurry, negative electrode sheet and lithium-ion battery is the same as in Example 1, except that the mixed solution before heat treatment in step S3 of this example is used.

[0080] Example 5 This embodiment provides a lignin-based self-healing adhesive, which differs from Embodiment 4 in that, in step S3, the mass ratio of polyacrylic acid, sodium lignin sulfonate, and lithium thiocate is 7:2:1, while the rest is the same as in Embodiment 4.

[0081] Comparative Example 1 This comparative example provides a polyacrylic acid adhesive, the preparation method of which is the same as step S1 in Example 1.

[0082] Performance testing Peel performance test method: The 180° peel test was conducted using a microcomputer-controlled electronic universal testing machine CMT6203 from Shenzhen Sansi Experimental Instrument Co., Ltd. The negative electrode sheet was cut into a rectangle of 50mm×18mm, and 3M tape with a width of 18mm was attached to the coated surface of the electrode sheet. The 180° peel test was carried out at a peel rate of 100mm / min.

[0083] Constant current charge-discharge test: The constant current charge-discharge test records the battery's cycle performance and rate performance data under a constant current density. The test uses the Xinwei charge-discharge test system to test the battery's cycle performance and rate performance. The battery test conditions are a constant temperature of 25℃. Before cycling, the battery needs to be left to stand for 10 hours and activated with a small current for 3 cycles before the constant current charge-discharge test.

[0084] The peeling performance of Examples 1, 4, 5 and Comparative Example 1 is as follows: Figure 1 As shown in the figure, the average peel strength of the electrode prepared in Example 1 reached 6.25 N, the average peel strength of the electrode prepared in Example 5 reached 4.50 N, the average peel strength of Example 4 was 5.17 N, and the average peel strength of the electrode prepared from polyacrylic acid was only 3.27 N. Compared with Comparative Example 1, the improvement in peel strength of Examples 4 and 5 is mainly due to the thermal esterification reaction between polyacrylic acid and sodium lignosulfonate during heat treatment, forming a rigid three-dimensional network, and the molecular chains of lithium polythiooctanoate forming molecular chain entanglement with the molecular chains in the rigid three-dimensional network. The robust three-dimensional cross-linked network formed by the cross-linking of lithium polythiooctanoate with itaconic acid further improves the peel strength of Example 1.

[0085] The mixed solution obtained in step S3 of Example 4 was poured into a mold and heat-treated in a high-temperature vacuum drying oven at 150°C for 2 hours to obtain a film. The film was then cut into thin strips, and the middle of each strip was cut with a utility knife to ensure a smooth cut. The cut surfaces were then tightly bonded together and placed at room temperature for 8 hours. The results are as follows: Figure 2 As shown. The specimen of Example 4 exhibited self-healing ability at room temperature. When the repaired specimen was manually stretched using tweezers, it could withstand a certain tensile strength. This is due to the dynamic disulfide bonds in lithium polythiooctanoate and the abundant hydrogen bonds in the cross-linked network of the adhesive, which endow the adhesive with self-healing properties.

[0086] The cycling performance test results of Examples 4, 5 and Comparative Example 1 at a current density of 0.5 A / g are as follows: Figure 3 As shown in Table 1.

[0087] Table 1

[0088] Depend on Figure 3As shown in Table 1, at a current density of 0.5 A / g, Example 4 exhibits better cycling performance, retaining a discharge specific capacity of 909 mAh / g after 500 cycles, which is significantly better than Comparative Example 1. This indicates that the raw material ratio of the binder has a significant impact on the mechanical strength of the binder network. By changing the amount of sodium lignosulfonate and lithium thiocate added, the mechanical properties of the cross-linked network of the binder can be adjusted, while also altering the self-healing mechanical properties of the binder. A suitable ratio can provide the binder network with more appropriate mechanical properties and self-healing properties, thereby better maintaining the cycle life of the silicon-based anode.

[0089] The cycling performance test results of Examples 1-4 at a current density of 1 A / g are as follows: Figure 4 As shown in Table 2.

[0090] Table 2

[0091] Depend on Figure 4 As shown in Table 2, at a current density of 1 A / g, the reversible discharge specific capacity of Example 1 after 100 cycles is 1263 mAh / g, and after 1000 cycles is 854 mAh / g; the reversible discharge specific capacity of Example 2 after 100 cycles is 1320 mAh / g, and after 1000 cycles is 657 mAh / g; and the reversible discharge specific capacity of Example 3 after 100 cycles is 1335 mAh / g, and after 1000 cycles is 654 mAh / g. Compared with Example 4 (reversible discharge specific capacity after 100 cycles is 1109 mAh / g, and after 1000 cycles is 613 mAh / g), this indicates that the lithium-ion battery provided by the present invention has a higher capacity retention rate and reversible discharge specific capacity. This is attributed to the dual-monomer regulation of thioctic acid and itaconic acid, which improves the stability of the binder crosslinking network. Itaconic acid, a biomass molecule with olefin double bonds, is selected as a stabilizer, quenching the terminal sulfide groups of polythioctic acid through an addition reaction, thereby preventing polythioctic acid depolymerization and improving the stability of the crosslinking network. This indicates that the crosslinking network formed by the binder after heat treatment can alleviate the volume expansion of the silicon-based anode sheet during cyclic charging and discharging, thus improving the structural stability of the anode. Therefore, the silicon-based anode sheet provided by this invention can maintain long-term cycling stability under high current density, and the anode sheet provided by this invention can still maintain a high discharge specific capacity after high current density and long cycling.

[0092] The rate performance test results of Examples 1, 4, 5 and Comparative Example 1 at different current densities are as follows: Figure 5 As shown in Table 3.

[0093] Table 3

[0094] Depend on Figure 5 As shown in Table 3, the electrode of Example 1 exhibited the highest discharge capacity performance at all current densities. After five charge-discharge cycles at current densities of 0.1, 0.2, 0.5, 1, 2, and returning to 0.1 A / g, the discharge specific capacities for the last cycle at the corresponding current densities were 1725 mAh / g, 1543 mAh / g, 1439 mAh / g, 1333 mAh / g, 1120 mAh / g, and 1749 mAh / g, respectively. Notably, the electrode of Example 1 continued to exhibit a high discharge specific capacity of 1120 mAh / g at current densities as high as 2 A / g. Furthermore, when the current density returned to 0.1 A / g, the electrode of Example 1 easily recovered to 1749 mAh / g. This is attributed to the fact that the dicarboxylic acid crosslinking forms a moderately cross-linked three-dimensional structure in the binder network, preventing rigidity caused by excessive crosslinking while providing a continuous lithium-ion conduction pathway. The carboxylic acid groups can undergo reversible coordination dissociation with lithium ions, promoting hopping lithium-ion transport. For Example 1, the results show that the addition of itaconic acid significantly improves the rate performance and stability of the lithium-ion battery.

[0095] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lignin-based self-healing adhesive, characterized in that, Its preparation method includes the following steps: Polyacrylic acid, lignin sulfonate, and lithium thiocate-based materials are mixed in a solvent and then heat-treated to obtain the lignin-based self-healing adhesive. The mass ratio of polyacrylic acid, lignin sulfonate, and lithium thiocate-based material is 1~10:1~3:1~3; the lithium thiocate-based material is itaconic acid crosslinked lithium thiocate, and the preparation method of itaconic acid crosslinked lithium thiocate includes: firstly polymerizing and crosslinking thiocic acid with itaconic acid, and then reacting it with lithium hydroxide to obtain the itaconic acid crosslinked lithium thiocate, wherein the mass ratio of thiocic acid to itaconic acid is 1:(0.15~0.3).

2. The adhesive according to claim 1, characterized in that, The mass ratio of lipoic acid to itaconic acid is 1:(0.15~0.25).

3. The adhesive according to claim 1, characterized in that, The heat treatment temperature is 70~180℃.

4. The adhesive according to claim 1, characterized in that, The mass ratio of the polyacrylic acid, lignin sulfonate, and lithium thiocate-based material is 4~10:1~3:1~3.

5. The adhesive according to claim 1, characterized in that, The polymerization crosslinking temperature is 100~200℃.

6. The adhesive according to claim 1, characterized in that, The preparation method of the polyacrylic acid includes: mixing acrylic acid with water, adding a thermal initiator, and reacting in an inert gas atmosphere to obtain the polyacrylic acid; the reaction temperature is 60~100℃, the reaction time is 2~8h, and the mass ratio of acrylic acid, water and thermal initiator is (100~400):(200~600):

1.

7. A silicon-based negative electrode, characterized in that, Includes negative electrode active material, conductive agent, and lignin-based self-healing adhesive as described in any one of claims 1 to 6.

8. The silicon-based negative electrode according to claim 7, characterized in that, The method for preparing the silicon-based negative electrode includes: Polyacrylic acid, lignin sulfonate, and lithium thiocate-based materials are mixed in a solvent to obtain a first mixed solution; The negative electrode active material and the conductive agent are ball-milled and then mixed with the first mixed solution to obtain the negative electrode slurry. The negative electrode slurry is coated onto the current collector, and then heat-treated to obtain the silicon-based negative electrode sheet.

9. The silicon-based negative electrode according to claim 8, characterized in that, The raw materials for the lignin-based self-healing binder are composed of polyacrylic acid, lignin sulfonate, and lithium thiocate. In the negative electrode slurry, the mass ratio of the negative electrode active material, the conductive agent, and the raw materials of the lignin-based self-healing binder is 1~10:1~3:1~3.

10. A lithium-ion battery, characterized in that, Includes the silicon-based anode sheet as described in any one of claims 7 to 9.

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