An interpenetrating network-containing binder, an interpenetrating network and conductive network-containing binder, and preparation and use thereof

Abstract

The present application relates to a kind of interpenetrating network containing binder, interpenetrating network and the binder containing conductive network and preparation and application, binder includes: the polyvinyl alcohol, water-based polyurethane and water obtained by physical mixing, or the polyvinyl alcohol, water-based polyurethane, additive and water obtained by physical mixing;Wherein the additive is conductive additive or metal complex agent, the conductive additive is at least one selected from silver nanoparticles or silver nanowire;The metal complex agent is selected from Al 3+ Compared with the prior art, the present application realizes the mutual embedding between molecular chains by the compounding of polyvinyl alcohol and water-based polyurethane in different proportions, forms an interpenetrating network binder with multiple hydrogen bonding, which can produce strong van der Waals force with the surface of silicon-carbon material, enhance the adhesion between the current collector and the active material, effectively inhibit the volume expansion phenomenon of silicon in the active material, ensure the integrity of the electrode structure, and maintain the electrochemical stability during the cycle process.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and relates to an adhesive containing an interpenetrating network, an adhesive containing an interpenetrating network and a conductive network, and the preparation and application of the adhesive in silicon-carbon negative electrode lithium batteries. Background Art

[0002] Silicon is considered one of the most promising negative electrode materials for lithium-ion batteries due to its high theoretical specific capacity, low voltage platform, and abundant reserves. However, silicon materials have poor electrical conductivity and are prone to volume expansion during the charge and discharge process, resulting in pulverization of their own structure, which seriously reduces the battery capacity and service life, and hinders its commercialization process. Binders, as additives to silicon-based negative electrodes, can effectively inhibit the volume expansion of silicon materials and improve the conductivity of the electrode. The theoretical specific capacity of silicon-carbon materials depends on the addition ratio of silicon to carbon materials. The higher the addition ratio, the higher the theoretical specific capacity of the composite negative electrode, but the worse its cycle stability. Therefore, studying how to increase the addition ratio of silicon in silicon-carbon materials while ensuring long-term cycle stability and the process of application in high-power electrical appliances has broad research value.

[0003] Currently, the most common commercial binder is PVDF. PVDF binders have good electrochemical stability, but their conductivity is poor. They lack flexible structures and polar groups that can anchor to the surface of silicon materials. Therefore, they are not suitable for silicon-based anodes, which are prone to volume expansion and have poor conductivity. Although linear binders such as CMC, PAA, and PVA can form hydrogen bonds with the hydroxyl groups on the surface of silicon particles through the polar groups contained in their structures, their van der Waals forces are weak. After long-term charge and discharge cycles, silicon-based anodes will still face problems such as breakage and pulverization. Therefore, it is crucial to modify the basic binder and construct a three-dimensional network structure. The interpenetrating network is conducive to giving the silicon-based anode sufficient mechanical strength to withstand greater expansion stress. The conductive network binder helps to achieve high-performance electrodes because it can achieve mechanical and electronic integrity of the electrode.

[0004] Interpenetrating networks provide strong chemical interactions between binder chains. For example, high calcium cross-linked alginate hydrogels and some hybrid networks prepared by diffusion methods have been proposed as new binders for silicon-based and silicon-based anodes. Other strategies for preparing self-healing polymers through supramolecular interactions have also been adopted for silicon binders. These interpenetrating network designs have significantly improved the electrochemical performance of silicon. Wang et al. proposed an interpenetrating PAA-PVA highly absorbent gel binder for silicon anode, which can effectively alleviate the huge volume expansion during cycling due to the strong adhesion of the convertible network. Despite the significant improvement in electrochemical performance, the conductivity of the gel polymer binder is still limited by the insulating polymer chains, which may greatly hinder the transport of electrons. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a binder containing an interpenetrating and conductive network and its application in a silicon-carbon negative electrode lithium battery, so as to improve the cycle stability, rate performance and / or coulombic efficiency of the lithium battery.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] Currently, PEDOT:PSS is a conductive binder that significantly inhibits material dissolution and enhances conductivity through non-covalent electrostatic interactions with the sulfur atoms in DTT. However, due to the structural diversity of organic materials, the applicability of PEDOT:PSS to other organic electrodes remains unclear. Therefore, the combination of conductive additives with novel binders has demonstrated a viable approach to achieve both high conductivity and strong binding interactions, which helps to improve the achievable capacity and cycling stability of the electrode.

[0008] The present invention constructs an interpenetrating network structure binder with multiple dynamic hydrogen bonds through PVA and waterborne polyurethane (WPU), and introduces metal coordination bonds (metal ions) to strengthen the interpenetrating network effect, significantly enhancing the mechanical properties (peeling performance) of the binder system, and improving the adhesion between the current collector and the active material, effectively suppressing the volume expansion phenomenon of silicon in the active material, ensuring the integrity of the electrode structure, and improving the utilization rate and first effect of the active material. In addition, by introducing conductive additives (silver nanoparticles and silver nanowires) into the binder system, a conductive network is constructed, improving the long cycle performance and first coulomb efficiency of the silicon-carbon negative electrode, thereby improving the overall electrochemical performance of the battery.

[0009] A first aspect of the present invention provides an interpenetrating network-containing adhesive, comprising physically mixed polyvinyl alcohol, aqueous polyurethane and water, wherein the mass ratio of the polyvinyl alcohol to the aqueous polyurethane is (1-9):1.

[0010] The total content of the polyvinyl alcohol and waterborne polyurethane in the binder is 15-25 wt %.

[0011] The second aspect of the present invention provides a method for preparing an interpenetrating network-containing adhesive, comprising: stirring and mixing polyvinyl alcohol, water-based polyurethane and water.

[0012] The third aspect of the present invention provides an adhesive containing an interpenetrating network and a conductive network, comprising physically mixed polyvinyl alcohol, waterborne polyurethane, additives and water.

[0013] The mass ratio of the polyvinyl alcohol to the waterborne polyurethane is (1-9):1;

[0014] The additive is a conductive additive or a metal ligand, wherein the conductive additive is selected from at least one of silver nanoparticles or silver nanowires, and the metal ligand is selected from Al 3+ .

[0015] Furthermore, the amount of the silver nanoparticles is 1-2 mg / 5 g polyvinyl alcohol + aqueous polyurethane, and the amount of the silver nanowires is 1-2.5 mg / 5 g polyvinyl alcohol + aqueous polyurethane;

[0016] The metal coordination agent is selected from Al 3+ , the dosage is 1-2mmol / 1.5g water-based polyurethane.

[0017] A fourth aspect of the present invention provides a method for preparing an adhesive containing an interpenetrating network and a conductive network, comprising: stirring and mixing polyvinyl alcohol, waterborne polyurethane and water, and then adding additives to prepare the adhesive.

[0018] Furthermore, the preparation method of the waterborne polyurethane comprises:

[0019] Polyethylene glycol, dimethylol propionic acid, isophorone diisocyanate, and dibutyltin dilaurate are mixed and reacted, and then 2-hydroxyethyl methacrylate is added and stirred to react to obtain a polyurethane prepolymer;

[0020] Triethylamine was added to carry out neutralization reaction;

[0021] Add water to carry out emulsification reaction;

[0022] Ethylenediamine is added to carry out emulsion polymerization to obtain waterborne polyurethane.

[0023] Furthermore, the feeding ratio of the polyethylene glycol, dimethylolpropionic acid, isophorone diisocyanate, dibutyltin dilaurate, and 2-hydroxyethyl methacrylate is (20-30) g: (2-3) g: (9-13.5) g: (42-63) μL: (1-3) mL;

[0024] The mixing reaction comprises: first reacting polyethylene glycol and dimethylol propionic acid at 85-90° C. for 1-1.5 hours; then adding isophorone diisocyanate and dibutyltin dilaurate and reacting them at 80-85° C. for 2-2.5 hours;

[0025] During the stirring reaction, the reaction temperature is 80-85° C. and the reaction time is 1-1.5 h.

[0026] Furthermore, in the neutralization reaction, the amount of triethylamine added is (2-3) mL / mL 2-hydroxyethyl methacrylate; the reaction temperature is 40-45° C., and the reaction time is 0.5-1 h.

[0027] Furthermore, the amount of water added is (65-70) mL / mL 2-hydroxyethyl methacrylate; the reaction temperature is 85-90° C., and the reaction time is 0.25-0.3 h.

[0028] Furthermore, in the emulsion polymerization reaction, the amount of ethylenediamine added is 8-9 μL / μL dibutyltin dilaurate; the reaction temperature is 85-90° C., and the reaction time is 3-4 hours.

[0029] A fifth aspect of the present invention provides an application of a binder, including using the binder in preparing a lithium battery; more specifically, using the binder in preparing a negative electrode material, and then in preparing a lithium battery.

[0030] Furthermore, the negative electrode material is a silicon-carbon negative electrode material.

[0031] Furthermore, the positive electrode material of the lithium battery is lithium iron phosphate.

[0032] The present invention realizes the mutual interlocking between molecular chains by compounding polyvinyl alcohol (PVA) and waterborne polyurethane (WPU) in different proportions, forming an interpenetrating network binder (PVA-WPU) with multiple hydrogen bonds. This binder can generate strong van der Waals forces with the surface of silicon-carbon materials, enhance the adhesion between the current collector and the active material, effectively inhibit the volume expansion of silicon in the active material, ensure the integrity of the electrode structure, and thus maintain the electrochemical stability during the cycle. Further introduction of metal Al 3+ , to prepare PVA-Al 3+ -WPU binder, at this time the system forms a synergistic effect of multiple hydrogen bonds and metal coordination bonds, which strengthens the role of the interpenetrating network, and thus can significantly enhance the mechanical properties of the binder system, and improve the adhesion between the current collector and the active material, thereby improving the utilization rate and first effect of the active material. However, due to the weak conductivity of silicon materials, excellent performance binders not only need to provide sufficient mechanical strength for the active material, but also should focus on improving its conductive properties. Therefore, by introducing conductive additives into the binder system, that is, introducing Ag nanoparticles and Ag nanowires, a PVA-Ag-WPU binder is prepared, which can significantly improve the Li + The silicon-carbon negative electrode made of this binder is more likely to form a dense and stable SEI layer, reducing the occurrence of side reactions, thereby improving the overall electrochemical performance of the battery.

[0033] Compared with the prior art, the present invention has the following characteristics:

[0034] 1) The present invention forms an interpenetrating network binder (PVA-WPU) with multiple hydrogen bonds by physically blending WPU and PVA in different proportions. PVA-WPU enhances the interaction between the binder and the surface of the silicon-carbon material, while enhancing the adhesion between the current collector and the active material, effectively inhibiting the volume expansion of silicon in the active material, and improving the first effect and reversible capacity of the silicon-carbon negative electrode battery.

[0035] 2) Based on the optimal ratio of PVA-WPU binder, the present invention introduces a metal coordination bond (metal aluminum ion) with strong binding force to strengthen the role of the interpenetrating network, thereby improving the mechanical properties and bonding properties of the binder system, and preparing PVA-Al 3+ -WPU binder; by introducing conductive additives (silver nanoparticles and silver nanowires) with good dispersibility, the electrochemical performance of the silicon-carbon negative electrode is improved to prepare PVA-Ag-WPU binder.

[0036] 3) PVA-Ag-WPU and PVA-Al prepared by the present invention 3+ -WPU binder, through the synergistic effect of interpenetrating network and conductive network, not only effectively reduces the expansion stress of active materials during charging and discharging, but also forms a denser and thinner SEI film, constructs a new lithium ion transmission channel, and improves the transmission speed of Li+ in the battery, thereby improving the electrochemical reaction efficiency and active material utilization.

[0037] 4) Metal coordination bond PVA-Al prepared by the present invention 3+ -WPU binder and conductive additive PVA-Ag-WPU binder are assembled into lithium ion half-cells, which significantly improves the capacity retention rate and the first cycle coulombic efficiency. 3+ -The capacity retention rate of WPU binder increased from 70.90% to 82.15%, and the first-cycle coulombic efficiency increased from 80.96% to 85.24%;

[0038] 5) Chinese patent application CN118006253A discloses a composite binder, a negative electrode and a secondary battery, wherein the composite binder comprises carboxymethyl chitosan, an auxiliary binder and polyvinyl alcohol; the auxiliary binder comprises at least one of methyl hydroxypropyl cellulose, hydroxypropyl cellulose, polyurethane, polyanionic cellulose ether, hydroxypropyl starch ether and hydroxyethyl cellulose ether. The role of carboxymethyl chitosan in the above technical solution is to improve the dispersibility and adhesion of the slurry, solve the problem of cracking and shedding during coating, and have slurry moisture retention during coating, solve the problem of low peeling strength of the electrode and serious powder loss on the edges after winding, and improve the flexibility of the negative electrode. However, the PVA-WPU-73 slurry in the present invention will not have the problem of cracking and shedding during coating, and will not have the problem of powder loss after drying. Figure 11,It can also be seen that PVA-WPU-73 has a low swelling ratio and high peel strength, and ,the addition of carboxymethyl chitosan is unnecessary;

[0039] 6) The theoretical capacity of graphite negative electrode material is 372mAh / g, but the actual specific capacity is 330-370mAh / g. During the charge and discharge process, it easily reacts with the electrolyte to form an SEI film, which makes the initial coulombic efficiency of the lithium-ion battery low. In addition, the graphite negative electrode has poor compatibility with the electrolyte and is easily co-intercalated with the organic solvent in the electrolyte, which will cause the negative electrode graphite layer to expand and peel off, thereby reducing the cycle stability of the lithium-ion battery. The theoretical capacity of the silicon-carbon negative electrode selected in the present invention can reach 400-800mAh / g. The silicon-carbon negative electrode material combines the advantages of both silicon and carbon materials. It has both the high theoretical specific capacity of silicon and the good conductivity and cycle stability of carbon. Compared with the graphite negative electrode, it has more research significance. The improvement effect of the binder on the silicon-carbon negative electrode will be more meaningful than that of the graphite negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 FTIR spectra of WPU and PVA-WPU binders prepared in Example 1; (a) WPU; (b) PVA-WPU binders with different mass ratios;

[0041] Figure 2 : is the particle size distribution diagram of the WPU emulsion prepared in Example 1;

[0042] Figure 3 is the XRD pattern of SiC650;

[0043] Figure 4 SEM images of the silicon-carbon negative electrode SiC650 / PVA-WPU-73 prepared in Example 1; (a) high-resolution and (b) low-resolution original morphology characterizations; (c) Si and (d) C element distribution diagrams in the electrode piece;

[0044] Figure 5 XPS spectra of the silicon-carbon anode corresponding to the PVA-WPU-73 binder prepared in Example 1 after 100 cycles; (a) C1s and (b) F1s spectrum comparison;

[0045] Figure 6 CV curve of the silicon-carbon negative electrode SiC650 / PVA-WPU-73 prepared in Example 1;

[0046] Figure 7Impedance comparison of the SiC650 / PVA-WPU silicon-carbon anode prepared in Example 1 after 100 cycles; (a) Impedance comparison of the silicon-carbon anode corresponding to the PVA-WPU binder after 100 cycles; (b) Schematic diagram of the high-frequency region of the impedance curve of the PVA-WPU binder;

[0047] Figure 8 This is a comparison chart of the long cycle performance of the silicon-carbon negative electrodes SiC650 / PVA-WPU, SiC650 / PVA, and SiC650 / WPU prepared in Example 1;

[0048] Figure 9 This is a comparison chart of the rate performance of the silicon-carbon negative electrode SiC650 / PVA-WPU prepared in Example 1;

[0049] Figure 10 This is a comparison chart of the coulombic efficiency of the silicon-carbon negative electrode SiC650 / PVA-WPU, SiC650 / PVA, and SiC650 / WPU prepared in Example 1;

[0050] Figure 11 Comparison of (a) swelling ratio and (b) average peel force of different adhesives in Example 1;

[0051] Figure 12 The silicon-carbon negative electrode SiC650 / PVA-Ag-WPU (a) prepared in Example 2; SiC650 / PVA-Al 3+ -SEM image of WPU (b);

[0052] Figure 13 WPU (a) and PVA-WPU-73, PVA-Ag-WPU, PVA-Al prepared in Example 2 3+ - FTIR spectrum of WPU binder (b);

[0053] Figure 14 The PVA-Ag-WPU and PVA-Al prepared in Example 2 3+ -XPS spectra of the silicon-carbon anode corresponding to the WPU binder after 100 cycles; (ab) C1s and (cd) F1s spectrum comparison;

[0054] Figure 15 The silicon-carbon negative electrode SiC650 / PVA-Ag-WPU (a) prepared in Example 2; SiC650 / PVA-Al 3+ -CV curve of WPU (b);

[0055] Figure 16The silicon-carbon negative electrodes SiC650 / PVA-WPU-73, SiC650 / PVA-Ag-WPU, and SiC650 / PVA-Al prepared in Example 2 3+ - Impedance comparison chart of WPU after 100 cycles;

[0056] Figure 17 The silicon-carbon negative electrodes SiC650 / PVA-WPU-73, SiC650 / PVA-Ag-WPU, and SiC650 / PVA-Al prepared in Example 2 3+ -WPU long cycle capacity comparison chart;

[0057] Figure 18 The silicon-carbon negative electrodes SiC650 / PVA-WPU-73, SiC650 / PVA-Ag-WPU, and SiC650 / PVA-Al prepared in Example 2 3+ -WPU rate performance comparison chart;

[0058] Figure 19 The silicon-carbon negative electrodes SiC650 / PVA-WPU-73, SiC650 / PVA-Ag-WPU, and SiC650 / PVA-Al prepared in Example 2 3+ -Comparison of Coulombic efficiency of WPU;

[0059] Figure 20 XRD patterns of SiC650 and SiC950;

[0060] Figure 21 The silicon-carbon negative electrode SiC950 / PVA-WPU-73, SiC950 / PVA-Ag-WPU; SiC950 / PVA-Al 3+ -SEM images of WPU before and after cycling at 1C current density;

[0061] Figure 22 The silicon-carbon negative electrode SiC950 / PVA-Al prepared in Example 3 3+ -CV curve of WPU;

[0062] Figure 23 The silicon-carbon negative electrode SiC950 / PVA-WPU-73, SiC950 / PVA-Ag-WPU; SiC950 / PVA-Al 3+ -WPU long cycle capacity comparison chart;

[0063] Figure 24The silicon-carbon negative electrode SiC950 / PVA-WPU-73, SiC950 / PVA-Ag-WPU; SiC950 / PVA-Al 3+ -WPU rate performance comparison chart;

[0064] Figure 25 The silicon-carbon negative electrode SiC950 / PVA-WPU-73, SiC950 / PVA-Ag-WPU; SiC950 / PVA-Al 3+ - Coulombic efficiency comparison of WPU;

[0065] Figure 26 PVA-Al 3+ -WPU, PVA-Fe 3+ -WPU, PVA-Zn 2+ -WPU, PVA-Ni 2+ -Optical photograph of WPU adhesive. DETAILED DESCRIPTION

[0066] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0067] The silicon-carbon active material used in the following examples is SiC650 (theoretical specific capacity is 650 mAh g -1 ) and SiC950 (theoretical specific capacity is 950mAh·g -1 The required drugs are: polyethylene glycol 2000 (PEG 2000), dimethylolpropionic acid (DMPA), N,N-dimethylformamide (DMF), isophorone diisocyanate (IPDI), dibutyltin dilaurate (DBTDL), 2-hydroxyethyl methacrylate (HEMA), triethylamine (TEA), dimethyl sulfoxide, ethylenediamine, polyvinyl alcohol (PVA), nanosilver (nanoparticles and / or nanosilver wires) solution, aluminum trichloride, lithium hexafluorophosphate, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), lithium iron phosphate (LiFePO4), Super P, polyvinylidene fluoride (PVDF), N-methylpyrrolidone (NMP), and ultrapure water.

[0068]

[0069] 1. Synthesis of waterborne polyurethane WPU:

[0070] Take PEG 2000 and add it to a three-necked flask, maintain a vacuum environment, and stir for a certain period of time under oil bath heating conditions. Subsequently, dissolve the chain extender DMPA in DMF and react for several hours. Under a nitrogen-protected atmosphere, add IPDI and DBTDL to the flask and continue the reaction for a period of time. Continue to add HEMA to obtain a transparent polyurethane prepolymer. Add TEA to the flask for neutralization reaction. Add ultrapure water to the flask for rapid emulsification reaction. After the reaction is completed, add ethylenediamine solution to the mixed emulsion and carry out emulsion polymerization reaction for several hours to obtain the final product WPU emulsion. During the process, all drugs are added dropwise into the flask using a syringe to reduce the impact of moisture and oxygen in the air on the reaction atmosphere.

[0071] 2. Preparation of interpenetrating network adhesive PVA-WPU:

[0072] A certain amount of PVA gel and WPU emulsion were mixed, and then ultrapure water was added as a solvent. The mixture was stirred at a constant speed at room temperature for a certain period of time to produce a uniform PVA-WPU adhesive solution. By varying the added mass of PVA gel and WPU emulsion, interpenetrating network adhesives with composite mass ratios of PVA to WPU of 5:5, 6:4, 7:3, 8:2, and 9:1 were prepared.

[0073] 3. Preparation of conductive network adhesive:

[0074] Preparation of PVA-Ag-WPU adhesive: Take a certain amount of PVA gel and WPU emulsion, mix the two, add ultrapure water as a solvent, and stir at a constant speed at room temperature for a certain time to obtain a uniform and stable milky white adhesive solution. Continue to add nanosilver solution (silver nanoparticles and silver nanowires) and stir at a constant speed at room temperature for a certain time to ensure that the Ag nanoparticles are evenly dispersed to obtain a uniform PVA-Ag-WPU adhesive.

[0075] PVA-Al 3+ -WPU adhesive: The preparation method is basically the same as the above-mentioned PVA-Ag-WPU adhesive. After obtaining a uniform milky white adhesive solution, continue to add AlCl3 solution and stir at a constant speed for a certain period of time at room temperature to obtain a uniform PVA-Al 3 + -WPU binder.

[0076] 3. Preparation of silicon-carbon negative electrode:

[0077] SiC650, Super P, and PVA-WPU were mixed and ground in a mass ratio of 80:10:10, then dispersed in NMP and stirred overnight. The slurry was coated on aluminum foil and the resulting electrode was dried to remove the solvent.

[0078] 4. Preparation of lithium iron phosphate (LiFePO4) positive electrode:

[0079] LiFePO4, Super P, and PVDF were mixed and ground in a mass ratio of 80:10:10. The mixture was then dispersed in NMP and stirred overnight. The slurry was coated on aluminum foil, and the resulting electrode was dried to remove the solvent.

[0080] 5. Performance testing and battery assembly

[0081] The structures of WPU, PVA and composite binder were analyzed using Fourier transform infrared spectroscopy (FTIR).

[0082] The particle size of WPU was analyzed using a dynamic light scattering (DLS) particle size analyzer.

[0083] X-ray diffraction analysis (XRD) was used to characterize the crystal form and purity of SiC650 and SiC950.

[0084] Scanning electron microscopy (SEM) was used to characterize the microstructure of SiC650 and SiC950, as well as the microstructure and elemental analysis of silicon-carbon negative electrode sheets made with different binders.

[0085] X-ray photoelectron spectroscopy (XPS) was used to compare the compound content of the electrodes with different adhesives after cycling.

[0086] Cyclic voltammetry (CV) was performed using different electrode potential speeds to scan multiple times in the voltage range of 0.01-3 V at a rate of 0.1 mV·s -1 At a slow scanning speed, CV tests were performed on half-cells made with different binders to analyze the changes in the redox reactions corresponding to different batteries.

[0087] The test frequency range is 10 -2 -10 5 A 5mV disturbance voltage was applied within the scanning interval, and EIS tests were performed on half-cells made with different binders before and after cycling to analyze the changes in battery impedance caused by long cycling.

[0088] The binder's cycling performance was investigated through galvanostatic charge-discharge tests. Half-cells were tested over a voltage range of 0.01-2V at a current density of 1C for long-term cycling, while full-cells were tested over a voltage range of 2.5-3.9V at a current density of 0.5C for long-term cycling.

[0089] Charge and discharge tests were conducted to investigate key electrochemical properties of the binder, including rate capability, cycle life, discharge capacity, and coulombic efficiency. The voltage range for half-cells was 0.01-2V, and for full-cells was 2.5-3.9V.

[0090] The mechanical properties of the adhesive were determined by performing swelling performance characterization and 180° peeling tests on the electrodes corresponding to different adhesives.

[0091] Swelling performance test:

[0092]

[0093] The initial mass of the adhesive film is recorded as m1. After immersing in the electrolyte for 48 hours, take it out, wipe off the surface solvent and weigh it again. The mass is recorded as m2. The corresponding swelling rate can be calculated according to the above formula;

[0094] 180° Peel Test: Peel performance is tested using a universal material tester. The adhesive material is cut into 2.5cm x 15cm specimens. The specimens are then peeled from the flexible or rigid substrate at a 180° angle at a peel speed of 300mm / min.

[0095] Example 1

[0096] Preparation of WPU: 20g of PEG 2000 was added to a three-necked flask, maintained under vacuum, and stirred in an oil bath at 110°C for 2 hours. Subsequently, 2g of the chain extender DMPA was dissolved in DMF and added to the flask, reacting at 85°C for 1 hour. Under a nitrogen atmosphere, 9g of IPDI and 42μL of DBTDL were added to the flask, and the reaction continued at 80°C for 2 hours. 1mL of HEMA was then added and stirred for 1 hour to obtain a transparent polyurethane prepolymer. 2mL of TEA was added to the flask, and neutralization was carried out at 40°C for 0.5 hours. 65mL of ultrapure water was added to the flask, and a rapid emulsification reaction was carried out at 85°C for 15 minutes. After the reaction was completed, 350μL of ethylenediamine was added to the mixed emulsion, and emulsion polymerization was carried out at 85°C for 3 hours to obtain the final WPU emulsion. During the process, all drugs were added dropwise into the flask using a syringe to reduce the impact of moisture and oxygen in the air on the reaction atmosphere.

[0097] Preparation of PVA-WPU adhesive: Taking PVA-WPU-7:3 adhesive as an example (7:3 is the mass ratio of PVA to WPU), take 3.5g of PVA gel and WPU emulsion (containing 1.5g WPU), mix the two, add 2mL of ultrapure water as solvent, and stir at a constant speed for 12h at room temperature to prepare a uniform PVA-WPU-7:3 adhesive solution. The adhesive formulas of the other four mass ratios (9:1, 8:2, 6:4, 5:5, the total mass of PVA+WPU is 5g) only need to change the added mass of PVA gel and WPU emulsion. At the same time, set pure PVA and pure WPU as control groups.

[0098] Preparation of the silicon-carbon anode: SiC650, Super P, and PVA-WPU were mixed and ground in a mass ratio of 80:10:10. The mixture was then dispersed in NMP and stirred overnight. The slurry was coated on aluminum foil and dried to remove the solvent to produce the silicon-carbon anode sheet.

[0099] Preparation of the lithium iron phosphate (LiFePO4) cathode: LiFePO4, Super P, and PVDF were mixed and ground in a mass ratio of 80:10:10. The mixture was then dispersed in NMP and stirred overnight. The slurry was coated on aluminum foil and dried to remove the solvent to produce the lithium iron phosphate cathode sheet.

[0100] Performance testing and battery assembly:

[0101] A 2025 button-type battery case was selected for battery assembly, and the entire process was carried out in a glove box (H2O, O2 < 0.01 ppm).

[0102] The half-cell uses a silicon-carbon anode with a radius of 9mm as the positive electrode, a Celgaed 2400 polypropylene separator, and an 11mm radius pure lithium sheet as the negative electrode. The electrolyte is prepared by dissolving LiPF6 at a final concentration of 1.0M in a 1:1:1 volume ratio of EC, DEC, and DMC, with 5wt% FEC added as an electrolyte additive. Assembly is performed in the order of positive electrode casing, silicon-carbon anode, separator, electrolyte, lithium sheet, gasket, spring sheet, and negative electrode casing, ensuring that all components are centered between the positive and negative electrode casings.

[0103] Figure 1 The FTIR spectra of PVA-WPU binders with different ratios are shown in Figure 2. In the FTIR spectra of PVA binder, the wavelength of 3360 cm -1 The stretching vibration peak corresponding to the hydroxyl group appears at 1725cm, and in the PVA-WPU composite binder, the absorption peak shifts to the right. -1The intensity of the characteristic peak of carboxylic acid formate at 650-800 cm is significantly weakened, which indicates that hydrogen bonding is formed between the hydroxyl groups in PVA and the carboxylic acid formate and carboxyl groups in WPU, which changes the absorption peak position and intensity. -1 The corresponding primary amino group characteristic peak shows a significant weakening, which is due to the formation of hydrogen bonds between the hydroxyl groups in PVA and the amino groups in WPU. The test fully proves the successful synthesis of WPU and the formation of hydrogen bonds between PVA and WPU, which gives the binder good mechanical properties and can generate strong interaction with the silicon-carbon negative electrode surface.

[0104] Figure 2 This is the particle size distribution diagram in the WPU emulsion, which reflects that the particle size distribution uniformity between the particles in the emulsion is good, which is conducive to the subsequent uniform distribution in the composite adhesive.

[0105] Figure 3 This is the XRD spectrum of SiC650. No other impurity peaks were found, indicating that the material has high purity and is not prone to side reactions during the charge and discharge process, thereby improving the electrochemical stability of the silicon-carbon negative electrode.

[0106] Figure 4 SEM images of SiC650 / PVA-WPU-73, (a) high resolution, (b) low resolution original morphology characterization; (c) Si, (d) C element distribution in the electrode. Figures a and b show that the surface of the electrode is relatively flat. At low resolution (20 μm), there are some pores on the surface of the electrode, which is conducive to the electrode being fully infiltrated by the electrolyte and promotes Li during the charge and discharge process. + Figures c and d show that the Si and C elements in the electrode are evenly distributed without agglomeration.

[0107] Figure 5 This is the XPS spectrum of the silicon-carbon negative electrode corresponding to the PVA-WPU binder after 100 cycles, indicating that the higher the LiF component content, the tighter the SEI layer structure formed and the more stable the properties.

[0108] Figure 6 This is the CV curve of SiC650 / PVA-WPU-73. There are no mixed peaks, indicating that the redox reaction occurring inside the electrode is highly reversible, there is no interference from side reactions, and it has excellent electrochemical stability during the charge and discharge process.

[0109] Figure 7 The impedance comparison of the silicon-carbon negative electrode corresponding to the PVA-WPU type binder after 100 cycles shows that the Li + The diffusion speed is better than other silicon-carbon negative electrodes, which is conducive to the formation of a denser and thinner SEI layer and improves the electrochemical performance.

[0110] Figure 8 The long-cycle performance comparison of silicon-carbon anodes corresponding to different binders shows that the capacity retention rates of silicon-carbon anodes vary greatly with the different WPU introduction ratios. After 500 cycles, the corresponding capacity retention rates are 43.75%, 57.21%, 70.90%, 60.28% and 61.35%. Among them, SiC650 / PVA-WPU-73 has the highest capacity retention rate, with the highest specific capacity after activation being 503.8 mAh g -1 The discharge capacity corresponding to 500 cycles is 357.2 mAh g -1 .

[0111] Figure 9 The comparison of the rate performance of silicon-carbon anode corresponding to PVA-WPU type binder is shown. At the rates of 0.1C, 0.2C, 0.3C, 0.5C, 1C, and 3C, the lithium batteries assembled with different ratios of binders have a discharge capacity of 536.1 mAh g at a current density of 0.1C. -1 , 563.4mAh·g -1 、613.9mAh·g -1 、579.7mAh·g -1 and 541.2mAh·g -1 As the current density gradually increases, the discharge specific capacity gradually decreases, but in this process, the discharge specific capacity of the silicon-carbon negative electrode corresponding to the PVA-WPU-73 binder is always greater than that of other silicon-carbon negative electrodes.

[0112] Figure 10 The coulombic efficiency of silicon-carbon negative electrodes corresponding to different binders is compared. After 5 cycles of activation, the CE of the silicon-carbon negative electrode corresponding to the composite binder remains above 98%. The uniform and dense SEI film formed after activation effectively reduces the irreversible loss of capacity during the charge and discharge process and improves the capacity retention rate. In particular, SiC650 / PVA-WPU-73 performs best with an ICE of 80.96%.

[0113] Figure 11The swelling rate and average peeling force of different binders are compared. The swelling rate of the PVA-WPU-73 binder is the lowest, which can ensure the interaction between the electrolyte and effectively avoid affecting the properties of the binder itself, thereby maintaining sufficient electrical contact between the active material and the current collector and maintaining the cycle stability of the silicon-carbon negative electrode. Compared with the composite PVA-WPU binder, the average peeling force of the pure PVA binder and the pure PVA binder prepared electrode sheet is smaller (1.217 N, 1.366 N), and the two cannot play the unique advantages of the material. The average peeling force of the PVA-WPU-55, PVA-WPU-64, PVA-WPU-73, PVA-WPU-82 and PVA-WPU-91 binders is 2.725 N, 2.849 N, 3.013 N, 2.786 N and 2.691 N, respectively. The average peeling force corresponding to the PVA-WPU-73 binder is the highest. The best mixing concentration of PVA and WPU is 7:3, at this time, the hydrogen bond site utilization of the binder structure is the highest, so that the WPU molecular chain and the WPU molecular chain are intertwined with each other, the mechanical strength of the whole binder is improved, and the best bonding performance is played.

[0114] Example 2

[0115] The preparation of WPU is the same as that in Example 1.

[0116] The preparation of PVA-WPU binder is the same as that in Example 1, wherein the mass ratio of PVA to WPU is 7:3.

[0117] Preparation of PVA-Ag-WPU binder: take 3.5 g of PVA gel and WPU emulsion (containing 1.5 g of WPU), mix them, then add ultrapure water as a solvent, and stir at room temperature for 12 h to prepare a uniform and stable milky white binder solution. Continue to add 1 mL of 1 mg / mL silver nanoparticle solution (average particle size 12 nm), and stir at room temperature for 6 h to ensure uniform dispersion of Ag nanoparticles, and prepare a uniform PVA-Ag-WPU binder.

[0118] Preparation of PVA-Al 3+ -WPU binder: the preparation method is basically the same as that of the above PVA-Ag-WPU binder, except that after preparing a uniform milky white binder solution, 1 mL of 1 mol / L AlCl3 solution is continuously added, and stirred at room temperature for 6 h to prepare a uniform PVA-Al 3+ -WPU binder.

[0119] Preparation of PVA-M-WPU adhesive: The preparation method of the PVA-Ag-WPU adhesive is basically the same as that of the above-mentioned adhesive. The only difference is that after a uniform milky white adhesive solution (20 wt%) is obtained, 1 mL of AlCl3 solution (1 mol·L -1 ), stirred at room temperature for 6 h to ensure that Al 3+ Dispersed evenly in the system to obtain uniform PVA-Al 3+ -WPU binder. Under the same operating conditions, AlCl3 was replaced by FeCl3, ZnCl2, and NiCl2 to obtain PVA-Fe 3+ -WPU, PVA-Zn 2+ -WPU, PVA-Ni 2+ -WPU binder. Figure 26 As shown, PVA-Al 3+ -WPU binder is evenly dispersed, but PVA-Fe 3+ -WPU, PVA-Zn 2+ -WPU, PVA-Ni 2+ -WPU three kinds of binders showed obvious flocculation phenomenon, and Fe 3+ 、Zn 2+ 、Ni 2+ These three metal ions are not suitable for PVA-WPU binder system. 3+ -WPU adhesive expansion.

[0120] The preparation of the silicon-carbon negative electrode is the same as in Example 1;

[0121] The preparation of lithium iron phosphate (LiFePO4) positive electrode is the same as that in Example 1;

[0122] Figure 12 It is (a) SiC650 / PVA-Ag-WPU; (b) SiC650 / PVA-Al 3+ -WPU SEM images, Figures a and b show the distribution of Si, C, Ag, and Al in the two silicon-carbon negative electrodes. The various elements in the electrode are evenly distributed without any element agglomeration. Among them, the uniform distribution of Ag and Al is conducive to the construction of the conductive network in the electrode, promoting the lithium + The rapid transmission of the electrochemical reaction rate can promote the effective utilization of active materials during the cycle, thereby promoting the capacity stability during the charge and discharge process.

[0123] Figure 13 WPU and PVA-WPU, PVA-Ag-WPU, PVA-Al 3+-Comparison of FTIR spectra of WPU binder, the test fully proves the successful synthesis of WPU, at 3370cm -1 The peak range becomes significantly wider and tends to move to a lower peak position, proving that the introduction of metal coordination bonds and conductive additives interacts with carbamate groups and hydroxyl groups to form a conductive composite cross-linked network.

[0124] Figure 14 PVA-Ag-WPU, PVA-Al 3+ -XPS spectrum of the silicon-carbon negative electrode corresponding to the WPU binder after 100 cycles. The silicon-carbon negative electrode made with the binder modified by conductive properties is easier to form a dense and stable SEI film, and is not easy to cause side reactions during the charge and discharge process, thereby improving the cycle stability.

[0125] Figure 15 It is (a) SiC650 / PVA-Ag-WPU; (b) SiC650 / PVA-Al 3+ -WPU CV curve, there is no miscellaneous peak, indicating that the redox reaction inside the electrode is highly reversible, without interference from side reactions, and has excellent electrochemical stability during the charge and discharge process. In addition, during the negative scan process of the electrode, SiC650 / PVA-Al 3+ -WPU corresponding current value is higher than that of SiC650 / PVA-Ag-WPU, indicating that the introduction of metal coordination bonds is more effective in improving the electrochemical performance and can better stimulate the activity of electrochemical reactions.

[0126] Figure 16 Comparison of the impedance of silicon-carbon anodes with different binders after 100 cycles, SiC650 / PVA-Al 3+ -WPU, SiC650 / PVA-Ag-WPU have obvious linear slopes in the low-frequency region, indicating that Li + The diffusion rate is significantly improved, which is beneficial to increasing the electrochemical reaction rate and improving the effective capacity conversion rate of active substances, thereby improving the overall electrochemical performance.

[0127] Figure 17 Comparison of the long cycle capacity of silicon-carbon negative electrode corresponding to different binders, SiC650 / PVA-WPU, SiC650 / PVA-Ag-WPU and SiC650 / PVA-Al 3+ -WPU has a capacity retention rate of 70.90%, 72.67% and 82.15% after 500 cycles.

[0128] Figure 18The comparison of the rate performance of silicon-carbon anode corresponding to different binders is shown in Figure 2. At the rates of 0.1C, 0.2C, 0.3C, 0.5C, 1C, and 3C, the discharge specific capacities of lithium batteries assembled with different binder ratios at a current density of 0.1C are 613.9 mAh g -1 、619.3mAh·g -1 and 640.5mAh·g -1 , among which SiC650 / PVA-Al 3+ -WPU is almost close to the standard specific capacity of 650mAh g -1 At the same time, as the current density gradually increases, the discharge specific capacity of this silicon-carbon negative electrode is always greater than that of other silicon-carbon negative electrodes.

[0129] Figure 19 Comparison of the coulombic efficiency of silicon-carbon anode corresponding to different binders, SiC650 / PVA-WPU, SiC650 / PVA-Ag-WPU and SiC650 / PVA-Al 3+ The ICEs of the three binders (-WPU) were 80.96%, 83.20%, and 85.24%, respectively. The introduction of conductive additives and metal coordination bonds enhances the binder's conductivity. After five cycles of activation, the CEs of the silicon-carbon anodes corresponding to the three binders remained above 98%, indicating that a stable SEI layer has formed on the surface of the silicon-carbon anode, maintaining the stability of the electrochemical reaction and exhibiting good electrochemical reversibility.

[0130] Example 3

[0131] The preparation of WPU was the same as in Example 1;

[0132] The preparation of the PVA-WPU adhesive was the same as in Example 1, wherein the mass ratio of PVA to WPU was 7:3;

[0133] Preparation of PVA-Ag-WPU adhesive: Take 3.5g of PVA gel and WPU emulsion (containing 1.5g WPU), mix the two, add ultrapure water as a solvent, and stir uniformly at room temperature for 12h to obtain a uniform and stable milky white adhesive solution. Continue to add 0.2mL of 5mg / mL silver nanowire solution (diameter: 70nm, length: 45μm, purity: >99.5%), and stir uniformly at room temperature for 6h to obtain a uniform PVA-Ag-WPU adhesive.

[0134] PVA-Al 3+ - The preparation of WPU binder is the same as in Example 2;

[0135] Preparation of the silicon-carbon anode: SiC950, Super P, and PVA-WPU were mixed and ground in a mass ratio of 80:10:10. The mixture was then dispersed in NMP and stirred overnight. The slurry was coated on aluminum foil and dried to remove the solvent to produce the silicon-carbon anode sheet.

[0136] The preparation of lithium iron phosphate (LiFePO4) positive electrode is the same as that in Example 1.

[0137] Figure 20 The XRD patterns of SiC650 and SiC950 show no obvious impurity peaks, indicating that the purity of the two materials is high, which can effectively avoid the probability of side reactions caused by impurities during charge and discharge, thereby improving the efficiency of active materials and Li + utilization rate.

[0138] Figure 21 The SEM images of the silicon-carbon negative electrode before and after cycling at a current density of 1C show that there is no significant difference between the three types of electrodes before cycling, with a uniform surface and no agglomeration. After cycling, the electrodes show varying degrees of electrode damage due to the expansion of the silicon material. The cracks on the surface of SiC950 / PVA-WPU are long and deep, followed by SiC950 / PVA-Ag-WPU, and SiC950 / PVA-Al. 3+ -WPU surface cracks are the narrowest and have a small propagation range. Therefore, after the adhesive is modified with conductive properties, the charge transfer resistance is reduced, which greatly improves the Li + conductivity, promote the formation of a denser SEI film, and reduce electrode damage.

[0139] Figure 22 SiC950 / PVA-Al 3+ The CV curves for the -WPU show a high degree of overlap across the three test cycles, indicating that the redox reaction within the battery is highly reversible. The reduction peak at 0.15V corresponds to the lithium insertion reaction, while the oxidation peak at 0.53V corresponds to the formation of the SEI film. The absence of other peaks suggests minimal side reactions within the battery and high electrochemical stability.

[0140] Figure 23 Comparison of the long cycle capacity of silicon-carbon negative electrode corresponding to different binders, SiC650 / PVA-WPU, SiC650 / PVA-Ag-WPU and SiC650 / PVA-Al 3+ -WPU has a capacity retention rate of 72.69%, 79.43% and 82.28% after 300 cycles.

[0141] Figure 24Comparison of rate performance of silicon-carbon anode corresponding to different binders. At the rates of 0.1C, 0.2C, 0.3C, 0.5C, 1C, and 3C, SiC950 / PVA-WPU, SiC950 / PVA-Ag-WPU, and SiC950 / PVA-Al 3+ -WPU has a discharge capacity of 810.5 mAh g at a current density of 0.1 C. -1 、892.0mAh·g -1 and 930.9mAh·g -1 , among which SiC950 / PVA-Al 3+ -WPU's discharge specific capacity reaches 97.99% of the theoretical specific capacity. At the same time, as the current density gradually increases, the discharge specific capacity of this silicon-carbon negative electrode is always greater than that of other silicon-carbon negative electrodes.

[0142] Figure 25 Comparison of the coulombic efficiency of silicon-carbon anode corresponding to different binders, SiC950 / PVA-WPU, SiC950 / PVA-Ag-WPU and SiC950 / PVA-Al 3+ The ICEs of the three binders were 78.46%, 80.75%, and 81.91%, respectively. After five cycles of activation, the CEs of the silicon-carbon anodes made with the three binders all remained above 98%. This indicates that despite the increased silicon content in the active material and the increased volume effect, each electrode still formed a stable SEI layer, demonstrating good electrochemical activity and stability.

[0143] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. An adhesive containing an interpenetrating network and a conductive network, characterized in that: Including polyvinyl alcohol, water-based polyurethane, additives and water obtained by physical mixing, The mass ratio of the polyvinyl alcohol to the waterborne polyurethane is (1-9):1; The additive is a metal ligand, and the metal ligand is selected from Al 3+ .

2. A method for preparing an adhesive containing an interpenetrating network and a conductive network as claimed in claim 1, characterized in that: include: The polyvinyl alcohol, water-based polyurethane and water are stirred and mixed, and then additives are added.

3. The method for preparing the adhesive according to claim 2, wherein: The preparation method of the waterborne polyurethane comprises: Polyethylene glycol, dimethylol propionic acid, isophorone diisocyanate, and dibutyltin dilaurate are mixed and reacted, and then 2-hydroxyethyl methacrylate is added and stirred to react to obtain a polyurethane prepolymer; Triethylamine was added to carry out neutralization reaction; Add water to carry out emulsification reaction; Ethylenediamine is added to carry out emulsion polymerization to obtain waterborne polyurethane.

4. The method for preparing the adhesive according to claim 3, wherein: The feeding ratio of the polyethylene glycol, dihydroxymethylpropionic acid, isophorone diisocyanate, dibutyltin dilaurate, and 2-hydroxyethyl methacrylate is (20-30) g: (2-3) g: (9-13.5) g: (42-63) μL: (1-3) mL; The mixing reaction comprises: first reacting polyethylene glycol and dimethylol propionic acid at 85-90° C. for 1-1.5 hours; then adding isophorone diisocyanate and dibutyltin dilaurate and reacting them at 80-85° C. for 2-2.5 hours; During the stirring reaction, the reaction temperature is 80-85° C. and the reaction time is 1-1.5 h.

5. The method for preparing the adhesive according to claim 3, wherein: In the neutralization reaction, the amount of triethylamine added is (2-3) mL / mL 2-hydroxyethyl methacrylate; the reaction temperature is 40-45° C., and the reaction time is 0.5-1 h.

6. The method for preparing the adhesive according to claim 3, wherein: In the emulsification reaction, the amount of water added is (65-70) mL / mL 2-hydroxyethyl methacrylate; the reaction temperature is 85-90° C., and the reaction time is 0.25-0.3 h.

7. The method for preparing the adhesive according to claim 3, wherein: In the emulsion polymerization reaction, the amount of ethylenediamine added is 8-9 μL / μL dibutyltin dilaurate; the reaction temperature is 85-90° C., and the reaction time is 3-4 h.

8. A use of the adhesive according to claim 1, characterized in that: Binders are used in the preparation of lithium batteries.

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