A method for preparing a multifunctional composite binder for silicon-based anodes

Abstract

A preparation method of a multifunctional composite binder for a silicon-based negative electrode, polyacrylic acid is dissolved in deionized water to obtain a polyacrylic acid solution; an alkaline solution is added to the polyacrylic acid solution to adjust the pH value to be alkaline, the polyacrylic acid molecular chain is deprotonated under alkaline conditions, and the mixture is uniformly mixed to obtain a deprotonated mixed solution; finally, gelatin is added to the mixed solution for compounding to obtain an aqueous composite binder. The advantages are: simple process, safety and environmental protection, enhanced mechanical toughness of the binder and anchoring capacity for silicon particles, to buffer the volume expansion of the silicon-based negative electrode, maintain the structural integrity of the electrode, and ensure the electrochemical performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries and relates to a method for preparing a multifunctional composite binder for silicon-based anodes, particularly a method for preparing a multifunctional composite binder for silicon-based anodes of lithium-ion batteries. Background Technology

[0002] Developing clean and sustainable energy has become a global consensus. To achieve the "dual carbon" goal and promote the development of green and low-carbon technologies, the development of high-energy-density energy storage systems is particularly crucial. Among numerous anode materials, silicon is considered one of the ideal anode materials for next-generation high-performance lithium-ion batteries due to its outstanding advantages such as extremely high theoretical specific capacity (approximately 4200 mAh / g), abundant reserves, and low cost.

[0003] However, the enormous volume expansion (>300%) that occurs during lithium insertion / extraction of silicon materials poses a fundamental challenge to their commercial application. This drastic volume fluctuation triggers a series of chain reactions: First, it directly leads to the breakage and pulverization of silicon particles, compromising the physical integrity of the electrodes; second, it causes the failure of electrical contact between the active material and the current collector, resulting in a break in the conductive network and a sharp increase in electrode impedance; more seriously, the continuous volume change triggers repeated rupture and regeneration of the surface solid electrolyte interphase (SEI). This process continuously consumes the limited electrolyte and thickens the interfacial layer, ultimately leading to a decrease in the battery's coulombic efficiency and a rapid decline in cycle life.

[0004] Currently, common research strategies mainly focus on modifying silicon materials themselves, such as nanostructuring, composite materials, and structural design. While these methods have achieved some success, they are often complex in process and costly, and fail to fundamentally solve the problems of stress management and structural integration at the electrode scale. Binders, as auxiliary materials with a small but crucial proportion in the electrode, hold promise for directly and effectively alleviating the problem of volume expansion in silicon anodes. A high-performance binder should not only enhance the bonding force between the active material, conductive agent, and current collector, maintaining the integrity of the electrode structure, but also possess excellent mechanical properties (such as elasticity and toughness) to buffer cyclic stress and inhibit active material shedding and excessive SEI film growth, thereby significantly improving the cycle stability and overall electrochemical performance of the battery. Therefore, developing novel high-performance binders suitable for silicon-based anodes has become one of the core technological breakthroughs driving the commercial application of high-specific-capacity silicon anodes.

[0005] Traditional polyvinylidene fluoride (PVDF) binders have two main limitations: firstly, their mechanical strength and adhesion are insufficient to effectively contain the massive volume expansion of silicon during cycling; secondly, they require N-methylpyrrolidone (NMP) as a solvent, which is not only hygroscopic but also releases volatile organic compounds that can affect operator health, leading to production safety and environmental pollution issues. To overcome the solvent problem of PVDF, water-based binder systems such as sodium carboxymethyl cellulose / styrene-butadiene rubber (CMC / SBR) have been widely used due to their environmental friendliness and low cost. However, this system still has significant drawbacks when dealing with extreme volume changes in silicon anodes: CMC and SBR are only physically blended, lacking stable chemical cross-linking, and are prone to phase separation during long-term cycling; more importantly, the predominantly rigid CMC network is prone to plastic deformation or brittle fracture under the stress of repeated and significant volume expansion of the silicon anode during long-term cycling, unable to buffer the expansion through sufficient elastic deformation, ultimately leading to electrode structure collapse and rapid capacity decay. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a multifunctional composite binder for silicon-based anodes. The process is simple, safe and environmentally friendly, and enhances the mechanical toughness of the binder and its anchoring ability to silicon particles, so as to buffer the volume expansion of silicon-based anodes, maintain the integrity of electrode structure, and ensure the electrochemical performance of the battery.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a multifunctional composite binder for silicon-based anodes, the specific steps of which are as follows: Step 1: Dissolve polyacrylic acid (PAA) in deionized water and stir until homogeneous to obtain a polyacrylic acid solution; Step 2: Add an alkaline solution to the polyacrylic acid solution to adjust the pH to alkaline. The polyacrylic acid molecular chains undergo deprotonation under alkaline conditions. Mix thoroughly to obtain a deprotonated mixed solution. Step 3: Finally, gelatin is added to the mixed solution to form a composite adhesive, thus obtaining the water-based composite adhesive.

[0008] Furthermore, the mass ratio of the polyacrylic acid to gelatin is 30:1-15:1.

[0009] Furthermore, the alkaline solution is a lithium hydroxide monohydrate solution.

[0010] Furthermore, the mass ratio of the polyacrylic acid to gelatin is 20:1.

[0011] Further preferably, the concentration of the lithium hydroxide monohydrate solution is 1 mol / L.

[0012] Furthermore, the molecular weight of the polyacrylic acid is 450,000 Mw.

[0013] Furthermore, the mass concentration of the polyacrylic acid solution is 5%.

[0014] Furthermore, the mass concentration of the gelatin aqueous solution is 5%.

[0015] Further, add an alkaline solution to adjust the pH to 5.

[0016] The multifunctional composite binder prepared by the above-mentioned preparation method is used as a binder in silicon-based anodes of lithium-ion batteries.

[0017] This invention provides a multifunctional composite binder for silicon-based anodes. It introduces gelatin biopolymers rich in various functional groups (-NH2, -OH) to form a multi-hydrogen bonded synergistic crosslinking network with PAA. This composite structure significantly enhances the binder's mechanical toughness and its anchoring ability to silicon particles, thereby effectively buffering volume expansion and maintaining the integrity of the electrode structure.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention constructs a three-dimensional network binder with both strong adhesion and high elasticity by combining polyacrylic acid (PAA) and gelatin. On the one hand, the abundant polar functional groups (-COOH, -NH2, -OH, etc.) on the molecular chains of polyacrylic acid and gelatin can form strong multidimensional hydrogen bonds between the active material, conductive agent, and current collector, achieving firm interfacial anchoring and providing excellent structural adhesion. On the other hand, the introduction of flexible gelatin segments and the presence of dynamic hydrogen bond crosslinking points enable the network to have good elastic deformation and stress dissipation capabilities, effectively buffering the huge volume expansion of silicon during cycling. This synergistic effect of "rigidity and flexibility" ensures the integrity of the electrode structure during long-term cycling, fundamentally inhibiting capacity decay caused by the pulverization and shedding of the active material.

[0019] 2. Based on the above-mentioned stabilizing effect on the electrode structure, this composite binder indirectly promotes the stability of the solid electrolyte interphase (SEI) film; its tough and elastic three-dimensional network can effectively constrain the volume change of silicon particles, reduce breakage, and thus avoid the continuous rupture and regeneration of the SEI film caused by repeated expansion and contraction of active materials; this helps to form a thin and dense stable SEI film on the electrode surface, significantly reducing the continuous decomposition of electrolyte and irreversible consumption of active lithium, thereby improving the long-term cycle stability and coulombic efficiency of the battery.

[0020] 3. All components of this composite adhesive have good water solubility, avoiding the dependence of traditional oil-based adhesive systems on toxic solvents (such as NMP); its slurry dispersibility is excellent, the preparation process is simple, it is environmentally friendly, and it shows good potential for large-scale industrial application. Attached Figure Description

[0021] Figure 1 This is a comparison chart of the first charge-discharge curves and long-cycle performance of the present invention (Comparative Examples 1-4 and Examples 1-4); Figure 2 The charge-discharge curves of the present invention (Comparative Examples 1-3 and Examples 1-4) at 1 C rate for the 1st, 5th, 10th, 30th, 50th, 70th and 100th cycles are shown. Figure 3 The rate performance diagram of the silicon anode of the present invention (Comparative Example 1, Comparative Example 3 and Examples 1-4); Figure 4 The following are EISNyquist curves of the present invention (Comparative Example 1 and Examples 1-4): (a) before cycling and (b) after 100 cycles at 1C. Figure 5 (a) Adhesion strength-displacement curve and (b) average peel force diagram of the present invention (Comparative Example 1 and Examples 2-4); Figure 6 The Fourier transform infrared spectra of the present invention (Comparative Example 1, Comparative Example 2 and Example 2); Figure 7 (a) Top-view SEM images of different electrodes in their original state for the present invention (Comparative Example 1 and Examples 1-4); (b) Top-view SEM images of different electrodes after 100 cycles. Figure 8 (a) Cross-sectional morphology of different electrodes in their original state for the present invention (Comparative Example 1 and Examples 1-4); (b) Cross-sectional morphology of different electrodes after 100 cycles. Figure 9 The XPS spectra of the present invention (Comparative Example 1 and Example 2) after 100 cycles are shown. Detailed Implementation

[0022] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0023] Example 1 This embodiment provides a method for preparing a multifunctional composite binder for silicon-based anodes, specifically including the following steps: Step 1: Weigh 0.25 g of polyacrylic acid (molecular weight 450,000 Mw) and dissolve it directly in 4.75 g of deionized water. Stir magnetically at room temperature at 30 r / min for 20 h until fully dissolved and crosslinked to obtain a polyacrylic acid solution with a mass concentration of 5 wt%, denoted as PAA. Step 2: Prepare a 1 mol / L lithium hydroxide monohydrate solution (LiOH·H2O); Step 3: Use a pipette to measure the prepared 1 mol / L lithium hydroxide monohydrate solution and add it dropwise to the polyacrylic acid solution to adjust the pH of the mixed solution to 5. Step 4: Weigh 0.25 g of gelatin and dissolve it directly in 4.75 g of deionized water. Stir magnetically in 40°C warm water until fully dissolved to obtain a gelatin solution with a mass concentration of 5 wt%, denoted as GEL. Step 5: Add the gelatin solution dropwise into the polyacrylic acid solution after adjusting the pH value in Step 3, so that the mass ratio of polyacrylic acid to gelatin is 15:1. After stirring evenly, a composite adhesive is obtained, which is denoted as PAA-GEL151.

[0024] Example 2 The difference in this embodiment is that the mass ratio of gelatin to polyacrylic acid added in step five is 1:20, while the rest is the same as in embodiment one.

[0025] Step 1: Weigh 0.25 g of polyacrylic acid (molecular weight 450,000 Mw) and dissolve it directly in 4.75 g of deionized water. Stir magnetically at room temperature at 30 r / min for 20 h until fully dissolved and crosslinked to obtain a polyacrylic acid solution with a mass concentration of 5 wt%, denoted as PAA. Step 2: Prepare a 1 mol / L lithium hydroxide monohydrate solution (LiOH·H2O); Step 3: Use a pipette to measure the prepared 1 mol / L lithium hydroxide monohydrate solution and add it dropwise to the polyacrylic acid solution to adjust the pH of the mixed solution to 5. Step 4: Weigh 0.25g of gelatin and dissolve it directly in 4.75g of deionized water. Stir magnetically in 40℃ warm water until fully dissolved to obtain a gelatin solution with a mass concentration of 5 wt%, denoted as GEL. Step 5: Add the gelatin solution dropwise into the polyacrylic acid solution after adjusting the pH value in Step 3, so that the mass ratio of polyacrylic acid to gelatin is 20:1. After stirring evenly, a composite adhesive is obtained, which is denoted as PAA-GEL201.

[0026] Example 3 The difference in this embodiment is that the mass ratio of gelatin to polyacrylic acid added in step five is 1:25, while the rest is the same as in embodiment one.

[0027] Step 1: Weigh 0.25 g of polyacrylic acid (molecular weight 450,000 Mw) and dissolve it directly in 4.75 g of deionized water. Stir magnetically at room temperature at 30 r / min for 20 h until fully dissolved and crosslinked to obtain an aqueous binder with a mass concentration of 5 wt%, denoted as PAA. Step 2: Prepare a 1 mol / L lithium hydroxide monohydrate solution (LiOH·H2O); Step 3: Use a pipette to measure the prepared 1 mol / L lithium hydroxide monohydrate solution and add it dropwise to the polyacrylic acid solution to adjust the pH of the mixed solution to 5. Step 4: Weigh 0.25 g of gelatin and dissolve it directly in 4.75 g of deionized water. Stir magnetically in 40°C warm water until fully dissolved to obtain a gelatin solution with a mass concentration of 5 wt%, denoted as GEL. Step 5: Add the gelatin solution dropwise into the polyacrylic acid solution after adjusting the pH value in Step 3, so that the mass ratio of polyacrylic acid to gelatin is 25:1. After stirring evenly, a composite adhesive is obtained, which is denoted as PAA-GEL251.

[0028] Example 4 The difference in this embodiment is that the mass ratio of gelatin to polyacrylic acid added in step five is 1:30, while the rest is the same as in embodiment one.

[0029] Step 1: Weigh 0.25 g of polyacrylic acid (molecular weight 450,000 Mw) and dissolve it directly in 4.75 g of deionized water. Stir magnetically at room temperature at 30 r / min for 20 h until fully dissolved and crosslinked to obtain a polyacrylic acid solution with a mass concentration of 5 wt%, denoted as PAA. Step 2: Prepare a 1 mol / L lithium hydroxide monohydrate solution (LiOH·H2O); Step 3: Use a pipette to measure and add a 1 mol / L lithium hydroxide solution dropwise to the polyacrylic acid solution, and adjust the pH of the mixed solution to 5. Step 4: Weigh 0.25 g of gelatin and dissolve it directly in 4.75 g of deionized water. Stir magnetically in 40°C warm water until fully dissolved to obtain a gelatin solution with a mass concentration of 5 wt%, denoted as GEL. Step 5: Add the gelatin solution dropwise into the polyacrylic acid solution after adjusting the pH value in Step 3, so that the mass ratio of polyacrylic acid to gelatin is 30:1. After stirring evenly, a composite adhesive is obtained, which is denoted as PAA-GEL301.

[0030] Comparative Example 1 Lithium-ion battery negative electrode binder: Only a 7 wt% polyacrylic acid (PAA) solution is used as the binder.

[0031] Comparative Example 2 Lithium-ion battery negative electrode binder: Only a 5 wt% gelatin (GEL) solution is used as the binder.

[0032] Comparative Example 3 The difference between this comparative example and Example 2 is that the alkaline solution prepared in step two is an ammonium hydroxide solution; otherwise, they are the same as in Example 2.

[0033] Step 1: Weigh 0.25 g of polyacrylic acid (molecular weight 450,000 Mw) and dissolve it directly in 4.75 g of deionized water. Stir magnetically at room temperature at 30 r / min for 20 h until fully dissolved and crosslinked to obtain a polyacrylic acid solution with a mass concentration of 5 wt%, denoted as PAA. Step 2: Prepare a 1 mol / L ammonium hydroxide solution; Step 3: Use a pipette to measure the prepared 1 mol / L ammonium hydroxide solution and add it dropwise to the polyacrylic acid solution to adjust the pH of the mixed solution to 5. Step 4: Weigh 0.25 g of gelatin and dissolve it directly in 4.75 g of deionized water. Stir magnetically in 40°C warm water until fully dissolved to obtain a gelatin solution with a mass concentration of 5 wt%, denoted as GEL. Step 5: Add the gelatin solution dropwise into the polyacrylic acid solution after adjusting the pH value in Step 3, so that the mass ratio of polyacrylic acid to gelatin is 20:1. After stirring evenly, a composite adhesive is obtained, which is denoted as PAA-GEL201.

[0034] Comparative Example 4 Comparative Example 4 introduces another animal-derived protein—serin—which is compounded with polyacrylic acid (PAA).

[0035] Step 1: Weigh 0.25 g of polyacrylic acid (molecular weight 450,000 Mw) and dissolve it directly in 4.75 g of deionized water. Stir magnetically at room temperature at 30 r / min for 20 h until fully dissolved and crosslinked to obtain a polyacrylic acid solution with a mass concentration of 5 wt%, denoted as PAA. Step 2: Weigh 0.25 g of sericin and dissolve it directly in 4.75 g of deionized water. Stir magnetically in 40°C warm water until fully dissolved to obtain a sericin solution with a mass concentration of 5 wt%, denoted as SJ. Step 3: Add the sericin solution dropwise into the polyacrylic acid solution in step 1, so that the mass ratio of polyacrylic acid to sericin is 20:1. After stirring evenly, a composite adhesive is obtained, which is denoted as PAA-SJ201.

[0036] Comparative Example 5 In the comparative experiments, it was found that the pH value of the composite system was a key factor determining its successful preparation. To verify and compare the effect of pH value on the composite system, in addition to pH=5 as specified in the examples, comparative samples with pH=3.0 and pH=7.0 were prepared according to the same material ratios and operating procedures. The preparation methods were completely consistent with the main example (steps one and two), only the endpoint of step three (pH adjustment) was changed.

[0037] Step 1: Weigh 0.25 g of polyacrylic acid (molecular weight 450,000 Mw) and dissolve it directly in 4.75 g of deionized water. Stir magnetically at room temperature at 30 r / min for 20 h until fully dissolved and crosslinked to obtain a polyacrylic acid solution with a mass concentration of 5 wt%, denoted as PAA. Step 2: Prepare a 1 mol / L lithium hydroxide monohydrate solution (LiOH·H2O); Step 3: Use a pipette to measure and add the 1 mol / L lithium hydroxide solution dropwise to the polyacrylic acid solution, and adjust the pH of the mixed solution to 3 and 7 respectively. Step 4: Weigh 0.25 g of gelatin and dissolve it directly in 4.75 g of deionized water. Stir magnetically in 40°C warm water until fully dissolved to obtain a gelatin solution with a mass concentration of 5 wt%, denoted as GEL. Step 5: Add the gelatin solution dropwise into the polyacrylic acid solution after adjusting the pH value in Step 3. If the pH is adjusted to 4.0 or 7.0, obvious flocculation or precipitation will appear in the system immediately or within a short period of time, proving that the composite system is highly sensitive to pH. If the pH value is exceeded, an effective binder cannot be obtained.

[0038] Application and performance testing The binder prepared using the above-described embodiments and comparative examples was used to prepare silicon anode materials as active materials for lithium-ion batteries to prepare electrode sheets (active material areal loading 0.4-0.6 mg / cm²). 2 Lithium-ion coin cells were prepared in a glove box, and their electrochemical performance was tested.

[0039] The comparison chart of the first charge-discharge curves and long-cycle performance of Comparative Examples 1-4 and Examples 1-4 of this invention is shown in the figure. Figure 1 As shown in the first charge-discharge curves of the batteries at 0.1 C, the first-charge specific capacities of Comparative Examples 1, 2, 3, and 4 are 2680.74, 2313.21, 2733.68, and 2564.28 mAh g, respectively. -1After 100 cycles, the capacity retention rates were 71%, 2%, 76%, and 41%, respectively. The initial charge specific capacities for Examples 1, 2, 3, and 4 were 2881.19, 3221.78, 2987.55, and 2959.48 mAhg, respectively. -1 The best performance was in Example 2, with a capacity retention rate of 81% after 100 cycles.

[0040] Table 1. Electrochemical performance of silicon-based anodes prepared with different binders The charge-discharge curves of Comparative Examples 1-3 and Examples 1-4 of this invention at 1 C rate for cycles 1, 5, 10, 30, 50, 70, and 100. Figure 2 As shown, from Figure 2 A noticeable decrease in battery charging specific capacity is observed, especially in the comparative example, where the specific capacity drops rapidly and significantly. After 30 cycles, the comparative example 2 exhibits the most severe degradation in charging specific capacity, decreasing from 848 mAh g⁻¹. -1 Reduced to 48 mAh g -1 Example 2 shows that the charging specific capacity is 2743 mAh g. -1 Reduced to 2221 mAh g -1 This demonstrates that Example 2 has better electrochemical performance than other negative electrodes.

[0041] Table 2. Battery Charging Capacity Attenuation Table The rate performance graphs of the silicon anodes of Comparative Example 1, Comparative Example 3, and Examples 1-4 of this invention are shown below. Figure 3 As shown, to verify the stability of its negative electrode under different current densities, the battery was tested at different current densities of 0.1 C, 0.2 C, 0.3 C, 0.5 C, 1 C, 2 C, 3 C, 5 C, 7 C, 10 C, and 0.1 C. The test results are shown below. Figure 3 As shown, Example 2 clearly demonstrates better rate performance, maintaining a higher specific capacity of 873 mA g even at 10 C. -1 When restored to 0.1 C, the capacity can be restored to 2933 mA g. -1 However, the proportional version cannot withstand a larger current, and its capacity drops to zero.

[0042] Table 3. Ratio of silicon-based anodes prepared with different binders The EISNyquist curves of Comparative Example 1 and Examples 1-4 of this invention are shown as follows: (a) before cycling and (b) after 100 cycles at 1C. Figure 4As shown, before the loop ( Figure 4 a) The Nyquist curve of Comparative Example 1 (pure PAA binder) shows a large semicircle in the high-frequency region, and its charge transfer resistance (Rct) is higher than that of Examples 2-4, but slightly lower than that of Example 1. This indicates that the binder described in this invention (Examples 2-4) can construct a better electrode interface in the initial state, which is beneficial for rapid charge transfer. After 100 cycles ( Figure 4 (b) In Comparative Example 1, the semicircle diameter increased significantly, and the Rct showed the largest increase. This is due to insufficient mechanical strength and adhesion of the PAA binder, which cannot effectively suppress particle separation and interface deterioration caused by changes in the volume of the active material during long-term cycling, resulting in a continuous increase in interfacial impedance. This result corresponds to the poor cycling stability and severe capacity decay of Comparative Example 1. In contrast, Example 2 exhibited the smallest semicircle diameter and the lowest Rct both before and after cycling, indicating that its electrode interface was the most stable and its charge transport kinetics were optimal. This is highly consistent with its excellent cycling performance and rate performance. The impedance characteristics of Examples 3 and 4 were also significantly better than those of Comparative Example 1, demonstrating the general advantage of the binder of this invention in improving electrode interface stability.

[0043] The (a) adhesion strength-displacement curves and (b) average peel force diagrams of Comparative Example 1 and Examples 1-4 of the present invention are shown below. Figure 5 As shown, the average adhesion force of Comparative Example 1 was 1.28 N, significantly lower than that of Examples 1, 2, 3, and 4. This indicates that the polymer network binder formed by gelatin and PAA can better allow Si particles to adhere to the current collector copper foil. Excellent adhesion and deformability help to better alleviate the enormous stress generated during the volume change of Si particles and maintain electrode integrity during battery cycling, thereby preserving battery capacity and extending battery life.

[0044] The Fourier transform infrared spectra of Comparative Example 1, Comparative Example 2, and Example 2 of this invention are as follows: Figure 6 As shown. The main characteristic absorption peaks of gelatin (GEL) include: amide I band (C=O stretching vibration) at 1632 cm⁻¹, amide II band (C–N stretching vibration and N–H bending vibration) at 1537 cm⁻¹, and amide III band (C–N stretching vibration and C–H / CH₂ deformation vibration) at 1236 cm⁻¹.

[0045] After crosslinking with polyacrylic acid (PAA), the following changes were observed in the composite material spectrum: the C=O stretching vibration peak of PAA shifted from 1704 cm⁻¹ to 1687 cm⁻¹, and its intensity decreased, indicating that hydrogen bonding interaction occurs between the carboxyl group of PAA and the amino or hydroxyl group of gelatin. Simultaneously, the characteristic peaks of PAA at 1247 cm⁻¹ and 1168 cm⁻¹ (attributed to the C–O stretching vibration in carboxylic acids and its coupling with the O–H in-plane bending vibration, respectively) significantly weakened and redshifted after composite formation, but did not completely disappear, further demonstrating the strong hydrogen bonding and ionic interaction between the carboxyl group (-COOH) of PAA and the amino / imino group of gelatin.

[0046] (a) Top-view SEM images of different electrodes in their original state in Comparative Example 1 and Examples 1-4 of this invention; (b) Top-view SEM images of different electrodes after 100 cycles. Figure 7 As shown, both the example and comparative electrode sheets exhibited good integrity and smooth surface morphology before cycling. However, after 100 cycles at 1 C, significant differences were observed between them. The electrodes of Examples 2-4 showed slight cracks and damage, while the electrode of Comparative Example 1 showed severe cracks and active material detachment. These results indicate that Example 2 is more suitable for mitigating the large volume expansion of Si and reducing electrode breakage.

[0047] (a) Cross-sectional morphology of different electrodes in their original state in Comparative Example 1 and Examples 1-4 of the present invention; (b) Cross-sectional morphology of different electrodes after 100 cycles as shown in Figure 1. Figure 8 As shown, a significant difference in electrode thickness can be clearly observed. After 100 cycles at a current density of 1C, the electrode thickness of Comparative Example 1 increased to 46.6 μm with an expansion rate of 281%, while the electrode thickness of Example 2 increased by 29.7 μm with an expansion rate of 266%. The PAA of Comparative Example 1 performed better than the PAA-GEL201 of Example 2 in mitigating the volume expansion of Si.

[0048] The XPS spectra of Comparative Example 1 and Example 2 after 100 cycles are shown below. Figure 9As shown in the O1s spectrum, both the Si-PAA electrode and the Si-PAAGEL201 electrode exhibited characteristic peaks primarily originating from electrolyte decomposition and SEI film formation. Comparison revealed that the peak area attributable to the organic components of the SEI in the O1s spectrum of the electrode of Example 2 was the smallest, indicating a lower accumulation of organic byproducts. This may be because the binder of Example 2 has higher bonding performance, helping to maintain the structural integrity of the silicon electrode, thereby reducing silicon particle breakage during cycling, inhibiting continuous exposure of the fresh surface, and thus reducing the repeated formation and accumulation of unstable SEI films. Furthermore, the F1s spectrum of the electrodes after cycling showed that the signal of fluorine-containing decomposition products such as LixPFyOz was the strongest in the spectrum of the electrode of Comparative Example 1, indicating a higher degree of electrolyte decomposition on the electrode surface. The corresponding signal of the electrode of Example 2 was weaker, further confirming that its interfacial side reactions were effectively suppressed.

[0049] In summary, the composite binder effectively binds the active particles, inhibits their shedding and isolates them, thereby maintaining the integrity of the electrode structure after cycling, with Example 2 being the best embodiment.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., 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 method for preparing a multifunctional composite binder for silicon-based anodes, characterized in that: Specific steps as follows: Step 1: Dissolve polyacrylic acid (PAA) in deionized water and stir until homogeneous to obtain a polyacrylic acid solution; Step 2: Add an alkaline solution to the polyacrylic acid solution to adjust the pH to alkaline. The polyacrylic acid molecular chains undergo deprotonation under alkaline conditions. Mix thoroughly to obtain a deprotonated mixed solution. Step 3: Finally, gelatin is added to the mixed solution to form a composite adhesive, thus obtaining the water-based composite adhesive.

2. The method for preparing the multifunctional composite binder for silicon-based anodes according to claim 1, characterized in that: The mass ratio of polyacrylic acid to gelatin is 30:1-15:

1.

3. The method for preparing the multifunctional composite binder for silicon-based anodes according to claim 1, characterized in that: The alkaline solution is a lithium hydroxide monohydrate solution.

4. The method for preparing the multifunctional composite binder for silicon-based anodes according to claim 1, characterized in that: The mass ratio of polyacrylic acid to gelatin is 20:

1.

5. The method for preparing the multifunctional composite binder for silicon-based anodes according to claim 3, characterized in that: The concentration of the lithium hydroxide monohydrate solution is 1 mol / L.

6. The method for preparing the multifunctional composite binder for silicon-based anodes according to claim 1, characterized in that: The molecular weight of the polyacrylic acid is 450,000 Mw.

7. The method for preparing the multifunctional composite binder for silicon-based anodes according to claim 1, characterized in that: The mass concentration of the polyacrylic acid solution is 5%.

8. The method for preparing the multifunctional composite binder for silicon-based anodes according to claim 1, characterized in that: The mass concentration of the gelatin aqueous solution is 5%.

9. The method for preparing the multifunctional composite binder for silicon-based anodes according to claim 1, characterized in that: Add an alkaline solution to adjust the pH to 5.

10. The application of a multifunctional composite binder prepared by the preparation method as described in claim 1 as a binder in a silicon-based anode of a lithium-ion battery.

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