Polyphenol polyurethane / polyacrylic acid binder as well as preparation method and application thereof

Abstract

The invention discloses a polyphenol polyurethane / polyacrylic acid binder as well as a preparation method and application thereof. The binder provided by the invention is obtained by compounding the polyphenol polyurethane and the polyacrylic acid, and the polyphenol polyurethane / polyacrylic acid binder with good mechanical properties and lithium ion conductivity is obtained by controlling the addition amount of the polyphenol polyurethane and the polyacrylic acid and the preparation parameters of the polyphenol polyurethane. The silicon negative electrode half-cell prepared from the binder has high rate performance and high cycle stability, specifically, the initial specific discharge capacity at 2C rate is 1430 mAh / g or above, the capacity retention ratio is 70.6% or above, the ion diffusion rate is 1.73 * 10 <-10 > cm < 2 > / s or above, and the cycle performance is good. The problem that an existing lithium ion battery binder is insufficient in improving the cycling stability and rate capability of a lithium ion battery is solved.

Description

Technical Field

[0001] This invention relates to the field of battery adhesive technology, and more specifically, to a polyphenol polyurethane / polyacrylic acid adhesive, its preparation method, and its application. Background Technology

[0002] Improving the driving range of new energy electric vehicles urgently requires lithium-ion batteries with higher energy density. Silicon-based anodes, with their ultra-high theoretical capacity (4200 mAh / g), are considered key materials for breaking through the energy density bottleneck. However, problems such as structural damage due to massive volume expansion, SEI instability, and poor cycle life severely hinder their large-scale commercial application. Currently, the mainstream low-silicon-content silicon-carbon anodes offer limited capacity improvements; while high-silicon solutions (50%) are under research and initial application, they still require complex material design. Against this backdrop, binders, as a key component of the battery, have a significant impact on the performance of silicon-based batteries.

[0003] Currently, polyacrylic acid (PAA) has become a commonly used binder in commercial lithium-ion batteries due to the strong interaction between its carboxyl groups and silanol groups (Si-OH). However, PAA binders suffer from excessively rigid molecular chains and a lack of flexible segments, making it difficult to effectively buffer the volume changes of silicon materials during charge and discharge. This results in an inability to maintain the stability of the electrode-electrolyte interface, leading to increased interfacial impedance and decreased cycle stability of lithium-ion batteries. Furthermore, PAA is prone to localized gelation at high concentrations, which not only affects the uniformity of slurry dispersion but also hinders lithium-ion transport kinetics, thus impacting the high-rate performance of lithium-ion batteries.

[0004] Therefore, it is particularly important to study a binder that can effectively improve the cycle stability and rate performance of silicon-based anode lithium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem that existing lithium-ion battery binders are not effective in improving the cycle stability and rate performance of lithium-ion batteries, and to provide a polyphenol polyurethane / polyacrylic acid binder. This binder has good mechanical properties and lithium-ion conductivity, can effectively alleviate the volume deformation caused by lithium-ion batteries during charging and discharging, and can enhance the electronic conductivity of electrode materials, thereby solving the problem that existing lithium-ion battery binders are not effective in improving the cycle stability and rate performance of lithium-ion batteries.

[0006] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: A polyphenolic polyurethane / polyacrylic acid adhesive, said adhesive comprising the following components in parts by weight, totaling 100 parts: 40-90 parts of polyacrylic acid; 10-60 parts of polyphenolic polyurethane; The polyphenol polyurethane is prepared from the following raw materials: polytetrahydrofuran, tannic acid, and isocyanate monomer; the molar ratio of polytetrahydrofuran to isocyanate monomer to tannic acid is 1:1.1~2.5:0.1~1.5.

[0007] First, when polyphenolic polyurethane (PPP) and polyacrylic acid (PAA) are used in combination, PAA exhibits high bonding strength, providing stronger interfacial stability than PPP and reducing the peeling of silicone-based fillers. Simultaneously, PPP's excellent elasticity improves PAA's toughness, preventing electrode cracking due to excessive brittleness. PPP contains phenolic hydroxyl groups (-OH) and ether oxygen bonds (-O-), which form a dynamically reversible and dense network of strong hydrogen bonds (PU-PAA hydrogen bonds) with the carboxyl groups (-COOH) of PAA. Under stress, these hydrogen bonds break, dissipating energy and improving the electrode material's toughness; after stress relief, the hydrogen bonds recombine to restore the material's elasticity, further enhancing its resistance to cyclic stress.

[0008] Secondly, the polyphenolic polyurethane contains tannic acid groups, which provide abundant phenolic hydroxyl groups to bond with the hydroxyl groups (-OH) on the silicon surface, forming stable Si-OC covalent bonds, thereby strengthening the anchoring interface. The phenolic hydroxyl groups have strong reducing properties and can participate in the formation of SEI during the first charge-discharge cycle and chelate Fe in the electrolyte. 3+ Cu 2+ Plasma reduces electrolyte damage to the SEI film, thereby improving the electrode's electronic conductivity and mechanical strength. Simultaneously, phenolic hydroxyl groups efficiently remove highly reactive substances generated during battery cycling, protecting the binder molecular chains from oxidative degradation. Furthermore, polyphenolic polyurethanes contain ether oxygen bonds (-O-), which possess lithium-philic properties and effectively promote macroscopic Li-... + The transport of these components allows polyphenolic polyurethane / polyacrylic acid binders to improve the rate performance of lithium-ion batteries.

[0009] Preferably, the polyphenol polyurethane / polyacrylic acid adhesive is prepared by compounding the following components in parts by weight: 40-55 parts polyacrylic acid and 45-60 parts polyphenol polyurethane.

[0010] Preferably, the polyphenol polyurethane / polyacrylic acid adhesive is prepared by compounding the following components in parts by weight: 50 parts polyacrylic acid and 50 parts polyphenol polyurethane.

[0011] Excessive acrylic acid content in polyphenol polyurethane / polyacrylic acid adhesives weakens the adhesive's flexibility and elasticity, making the polymer film brittle and prone to cracking. This negatively impacts the stability between silicon particles and the conductive agent under cyclic stress, and excessive polyacrylic acid chains hinder lithium-ion transport. Conversely, insufficient acrylic acid content fails to provide enough PU-PAA hydrogen bond crosslinking sites, weakening the network reinforcement effect and resulting in inadequate anchoring properties.

[0012] Preferably, the molar ratio of polytetrahydrofuran to isocyanate monomer to tannic acid is 1:1.5~2:0.5~1.

[0013] Preferably, the number-average molecular weight of the polytetrahydrofuran is 1000-2000.

[0014] Preferably, the polyacrylic acid has a number-average molecular weight of 300,000 to 1,250,000.

[0015] More preferably, the polyacrylic acid has a number-average molecular weight of 400,000 to 600,000.

[0016] The preparation method of the above-mentioned polyphenol polyurethane / polyacrylic acid adhesive is also within the scope of protection of this invention, and includes the following steps: S1. Dissolve polytetrahydrofuran and isocyanate monomers in a solvent, stir to carry out a prepolymerization reaction, then add tannic acid to carry out a chain extension reaction, and dry after the reaction to obtain polyphenolic polyurethane. S2. Dissolve polyphenolic polyurethane and polyacrylic acid in a solvent, stir and mix until uniform and clear, to obtain the polyphenolic polyurethane / polyacrylic acid adhesive.

[0017] Preferably, the isocyanate monomer can be a commonly used isocyanate monomer in the art, such as one or more of 1,6-hexanediisocyanate, toluenediisocyanate, 4,4-diphenylmethanediisocyanate, 1,5-naphthalenediisocyanate, 3,3'-dimethyl-4,4'-biphenyldiisocyanate, phenylene diisocyanate, tetramethylene diisocyanate, terephthalene diisocyanate, and hexamethylene diisocyanate.

[0018] Preferably, the solvent is one or more of N-methylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and tetrahydrofuran.

[0019] As is well known in the art, catalysts can be added to increase the reaction rate during the preparation of polyurethane. Preferably, the catalyst is one or more of dibutyltin dilaurate, dibutyltin diacetate, dimethyltin diolate, stannous octoate, di(dodecylthio)dibutyltin, and monobutyltin oxide.

[0020] Preferably, the temperature of the prepolymerization reaction in step S1 is 60~100℃.

[0021] Preferably, the prepolymerization reaction in step S1 takes 3 to 8 hours.

[0022] Preferably, the prepolymerization reaction in step S1 is carried out under an inert atmosphere.

[0023] Preferably, the temperature of the chain extension reaction in step S1 is 60~100℃.

[0024] Preferably, the chain extension reaction in step S1 takes 8 to 24 hours.

[0025] Preferably, the chain extension reaction in step S1 is carried out under an inert atmosphere.

[0026] Preferably, the temperature for compounding in step S2 is 20~130℃.

[0027] More preferably, the temperature for compounding in step S2 is 60~90℃.

[0028] Preferably, the solvent in step S2 can be a polar organic solvent commonly used in the art, such as one or more of dimethyl sulfoxide, N,N-dimethylformamide, N-methylpyrrolidone, N,N-dimethylacetamide, acetone, and tetrahydrofuran.

[0029] Preferably, in step S2, the total mass ratio of polyphenol polyurethane and polyacrylic acid to solvent is 0.04~0.05g:25mL.

[0030] The application of the aforementioned polyphenol polyurethane / polyacrylic acid binder in the preparation of silicon-based anodes is also within the scope of protection of this invention.

[0031] This invention provides a silicon anode sheet, comprising the following components in parts by mass: 50-70 parts of silicon-active material; 15-25 parts of conductive additive; 15-25 parts of the above-mentioned polyphenol polyurethane / polyacrylic acid adhesive.

[0032] Preferably, the silicon active material is one or more of elemental silicon, silicon suboxide, silicon-carbon composite material, and silicon alloy material.

[0033] Preferably, the size of the silicon active material is 50 nm to 3 μm.

[0034] Preferably, the specific surface area of ​​the conductive additive is >1000m². 2 / g.

[0035] Preferably, the conductive additive can be a commonly used conductive additive in the art, such as one or more of carbon nanotubes, graphite, graphene, and carbon black.

[0036] The present invention provides a silicon anode half-cell, wherein the silicon anode half-cell includes the aforementioned silicon anode sheet.

[0037] The preparation method of the aforementioned silicon anode sheet and silicon anode half-cell is also within the scope of protection of this invention, and includes the following steps: S1. Dissolve the silicon active material, conductive additive and the above-mentioned polyphenol polyurethane / polyacrylic acid binder in a solvent, mix them evenly, and dry them to form a film to obtain the silicon anode sheet; S2. Vacuum dry the silicon anode sheet, cut and assemble the sheets to obtain the silicon anode half cell.

[0038] Preferably, the solvent is dimethyl sulfoxide.

[0039] Compared with the prior art, the beneficial effects of the present invention include: This invention provides a polyphenol polyurethane / polyacrylic acid binder, obtained by compounding polyphenol polyurethane and polyacrylic acid. This binder possesses a rich, dynamically reversible, and dense network of strong hydrogen bonds (PU-PAA hydrogen bonds), effectively mitigating the volume deformation of silicon active materials during charge and discharge, thereby maintaining the mechanical stability of the electrode structure. Simultaneously, this binder provides binding sites for silicon active materials and electrolytes, and participates in the first-cycle SEI formation during lithium-ion battery charge-discharge cycles, improving the electronic conductivity of the electrode material. This binder exhibits excellent mechanical properties and lithium-ion conductivity, resulting in silicon anode half-cells with high rate performance and high cycle stability. Specifically, at 2C rate, the initial discharge specific capacity is above 1430 mAh / g, the capacity retention is above 70.6%, and the ion diffusion rate is 1.73 × 10⁻⁶. -10 cm 2 This invention addresses the problem of insufficient improvement in cycle stability and rate performance of lithium-ion batteries by using existing lithium-ion battery binders at speeds of 1000 m / s or higher. Furthermore, it was unexpectedly discovered that the polyphenolic polyurethane / polyacrylic acid binder provided by this invention possesses excellent self-healing capabilities, effectively repairing micro-stress cracks caused by volume changes during electrode cycling and inhibiting their propagation. Attached Figure Description

[0040] Figure 1 Fourier transform infrared spectra of isophorone diisocyanate, tannic acid, and the polyphenolic polyurethane obtained in Example 1 of this invention.

[0041] Figure 2 This is a diagram illustrating the self-healing effect of the polyphenol polyurethane / polyacrylic acid adhesive provided in Example 1 of the present invention.

[0042] Figure 3The graphs show the long-cycle test results of silicon anode half-cells assembled with polyphenol polyurethane / polyacrylic acid binders according to Examples 1, 18 and Comparative Example 9 of the present invention at a 2C rate. Detailed Implementation

[0043] The present invention will be further described below with reference to embodiments and comparative examples. These embodiments are merely typical descriptions of the present invention, but the present invention is not limited thereto. Unless otherwise specified, the test methods used in the following embodiments and comparative examples are conventional methods, and the raw materials and reagents used are commercially available from conventional commercial sources.

[0044] Example 1 This embodiment provides a method for preparing a polyphenolic polyurethane / polyacrylic acid adhesive. The adhesive comprises the following components in parts by weight: 50 parts polyphenolic polyurethane and 50 parts polyacrylic acid. The polyphenolic polyurethane is prepared from raw materials in the following molar ratio: the molar ratio of polytetrahydrofuran to isophorone diisocyanate to tannic acid is 1:1.5:0.5.

[0045] A method for preparing a polyphenol polyurethane / polyacrylic acid adhesive, specifically including the following steps: S1. Add 5g of polytetrahydrofuran (M w =2000) was dissolved in 10 mL of N-methylformamide solvent, and 0.834 g of isophorone diisocyanate and dibutyltin dilaurate catalyst were added and stirred to carry out prepolymerization reaction for 4 h. Then, 2.13 g of tannic acid and 20 mL of N-methylformamide solvent were added and stirred to carry out chain extension reaction for 16 h. After the reaction was completed, the reaction product was placed in a forced-air drying oven to dry the solvent and obtain polyphenol polyurethane. S2. Mix 50g of the polyphenol polyurethane obtained in step S1 with 50g of polyacrylic acid (M w =450,000) is dissolved in dimethyl sulfoxide and mixed at 80°C until homogeneous and clear to obtain polyphenolic polyurethane / polyacrylic acid adhesive.

[0046] Fourier transform infrared characterization was performed on isophorone diisocyanate, tannic acid, and the polyphenolic polyurethane obtained in this example: Small amounts of liquid isophorone diisocyanate, tannic acid powder, and polyphenol polyurethane film were placed on a diamond-based sample stage. For non-liquid samples, the fixing valves were tightened. Fourier transform infrared (FTIR) measurements were performed in ATR mode, with a measurement range of 4000-500 cm⁻¹. -1 The result after processing is as follows Figure 1 As shown.

[0047] Depend on Figure 1 It can be seen that isophorone diisocyanate at 2200cm -1There is a distinct -N=C=O characteristic absorption peak at 2200 cm⁻¹. Polyphenolic polyurethane shows a peak at 2200 cm⁻¹. -1 The characteristic absorption peak at -N=C=O completely disappeared at 1540 cm⁻¹. -1 A bending vibration peak appears in the CNH plane at 1720 cm⁻¹. -1 The appearance of a carbonyl C=O stretching vibration peak at 1440 cm⁻¹ indicates that the isocyanate group has completely undergone an addition reaction with the phenolic hydroxyl group of tannic acid to form a carbamate bond. -1 With 1600cm -1 The appearance of an aromatic C=C skeleton stretching vibration peak at 3100-3400 cm⁻¹ indicates that the benzene ring structure of tannic acid has been successfully incorporated into the polyurethane network. Due to the overlap and hydrogen bond interaction between the NH stretching vibration peak of the polyphenolic polyurethane and the phenolic hydroxyl absorption peak of tannic acid, a peak appears in the 3100-3400 cm⁻¹ range. -1 A broad peak appears at this point.

[0048] Self-healing tests were conducted on the polyphenolic polyurethane / polyacrylic acid adhesive obtained in this embodiment: The polyphenol polyurethane / polyacrylic acid adhesive film was cut into circular pieces with a diameter of 14 cm and cut in half along the diameter direction. The two semicircles were then tightly spliced ​​together along the cut in air or in an electrolyte environment and left to stand for four hours without applying additional stress. The recovery of the cut seam was then observed.

[0049] Depend on Figure 2 It is evident that the polyphenol polyurethane / polyacrylic acid adhesive provided in this embodiment can undergo self-healing under both air and electrolyte immersion conditions. This indicates that the polyphenol polyurethane / polyacrylic acid adhesive provided in this embodiment possesses excellent self-healing capabilities.

[0050] Examples 2-18 Examples 2-18 provide different methods for preparing polyphenol polyurethane / polyacrylic acid adhesives, and the differences from Example 1 are shown in Table 1 below: Table 1. Parameters for the preparation method of polyphenol polyurethane / polyacrylic acid adhesives in Examples 1-18

[0051] Example 19 This embodiment provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive, which differs from Example 1 only in the compounding temperature in step S2, specifically 120°C.

[0052] Example 20 This embodiment provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive, which differs from Example 1 only in the compounding temperature in step S2, specifically 25°C.

[0053] Example 21 This embodiment provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is that the hard segment reactive monomer used to prepare the polyphenol polyurethane in step S1 is different, specifically, isophorone diisocyanate is replaced with diphenylmethane diisocyanate.

[0054] Example 22 This embodiment provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is that the hard segment reactive monomer used to prepare the polyphenol polyurethane in step S1 is different, specifically, isophorone diisocyanate is replaced with hexamethylene diisocyanate.

[0055] Example 23 This embodiment provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is that the number-average molecular weight of the polytetrahydrofuran used in step S1 is different, specifically 1000.

[0056] Example 24 This embodiment provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is that the number-average molecular weight of the polyacrylic acid used in step S2 is different, specifically 300,000.

[0057] Example 25 This embodiment provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is that the number-average molecular weight of the polyacrylic acid used in step S2 is different, specifically 600,000.

[0058] Example 26 This embodiment provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is that the number-average molecular weight of the polyacrylic acid used in step S2 is different, specifically 1,250,000.

[0059] Comparative Example 1 This comparative example provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is that the weight parts of polyphenol polyurethane and polyacrylic acid are different in step S2. Specifically, the polyacrylic acid is 100 parts and the polyphenol polyurethane is 0 parts.

[0060] Comparative Example 2 This comparative example provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is that the weight parts of polyphenol polyurethane and polyacrylic acid are different in step S2. Specifically, the polyacrylic acid is 0 parts and the polyphenol polyurethane is 100 parts.

[0061] Comparative Example 3 This comparative example provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is the weight ratio of polyphenol polyurethane and polyacrylic acid in step S2. Specifically, the polyacrylic acid is 10 parts and the polyphenol polyurethane is 90 parts.

[0062] Comparative Example 4 This comparative example provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is the weight ratio of polyphenol polyurethane and polyacrylic acid in step S2. Specifically, the polyacrylic acid is 20 parts and the polyphenol polyurethane is 80 parts.

[0063] Comparative Example 5 This comparative example provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is the weight ratio of polyphenol polyurethane and polyacrylic acid in step S2. Specifically, the polyacrylic acid is 30 parts and the polyphenol polyurethane is 70 parts.

[0064] Comparative Example 6 This comparative example provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is that the soft segment reactive monomer used to prepare the polyphenol polyurethane in step S1 is different. Specifically, polytetrahydrofuran (M... w =2000) was replaced with polyethylene glycol (M w =2000).

[0065] Comparative Example 7 This comparative example provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is that the soft segment reactive monomer used to prepare the polyphenol polyurethane in step S1 is different. Specifically, polytetrahydrofuran (M... w =2000) was replaced with polycarbonate diol (M w =2000).

[0066] Comparative Example 8 This comparative example provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is the molar ratio of the reactants used to prepare the polyphenol polyurethane in step S1, specifically polytetrahydrofuran (M... w =2000) with the molar ratio of isophorone diisocyanate to tannic acid is 1:3:2.

[0067] Comparative Example 9 This comparative example provides a method for preparing a polyphenol polyurethane / polyacrylic acid adhesive. The only difference from Example 1 is the molar ratio of the reactants used to prepare the polyphenol polyurethane in step S1, specifically polytetrahydrofuran (M... w =2000) with the molar ratio of isophorone diisocyanate to tannic acid is 1:1.02:0.02.

[0068] Silicon anode half-cell preparation The polyphenol polyurethane / polyacrylic acid binders prepared in Examples 1-26 and Comparative Examples 1-9 were respectively used to prepare flexible self-supporting silicon anode sheets and assembled into silicon anode half-cells. The specific preparation methods are as follows: S1. Weigh 0.15g of elemental silicon (1 micrometer in size) and 0.05g of single-walled carbon nanotubes (1000 m² in specific surface area). 2 / g), 0.05g of polyphenol polyurethane / polyacrylic acid binder is dissolved in dimethyl sulfoxide and mixed by ultrasonic treatment to obtain a uniform slurry. The mixed slurry is poured into a mold with polytetrafluoroethylene or polyethylene terephthalate as the substrate, dried to form a film, and then peeled off to obtain a flexible self-supporting silicon anode sheet; S2. The flexible self-supporting silicon anode sheet obtained in step S1 is vacuum dried, cut, weighed, and assembled to obtain a silicon anode half-cell.

[0069] Performance testing of flexible self-supporting silicon anode sheets 1. Tensile property determination: The flexible self-supporting silicon anode sample was cut into rectangular strips (50 mm in length and 5 mm in width) before the test. During the test, the initial gauge length of the sample clamping distance was set to 3 cm, the tensile rate was kept at 2 mm / min, the stress-strain curve was measured, and the tensile strength at break (MPa) was read.

[0070] Silicon anode half-cell performance test 1. Calculation of lithium-ion diffusion coefficient: The AC impedance spectrum of the battery was tested at room temperature, with a frequency range of 0.1-1MHz.

[0071] The lithium-ion diffusion coefficient is calculated based on the linear relationship between peak current and the square root of the scan rate, according to the Randles-Sevcik formula:

[0072] Among them, I P Where is the peak current (A), n is the number of electrons transferred in each lithium ion during the electrochemical reaction, and A is the active area of ​​the electrode (cm²). 2 ),D Li The diffusion coefficient of lithium ions in the electrode (cm) 2 / s), C0 is the molar concentration of lithium ions, and V is the scan rate (V / s).

[0073] 2. Initial capacity determination of charge-discharge cycles: The initial capacity of the battery during charge-discharge cycles was tested at a voltage range of 0.01-1.5V and a 2C rate.

[0074] 3. Charge-discharge cycle retention rate determination: The charge-discharge cycle performance of the battery is tested at a voltage range of 0.01-1.5V and a 2C rate, and the capacity retention rate is expressed as the capacity retention rate after 100 cycles.

[0075] The performance test results of Examples 1-26 and Comparative Examples 1-9 are shown in Table 2 below.

[0076] Table 2 Performance test results of Examples 1-26 and Comparative Examples 1-9

[0077] As can be seen from the data in Examples 1-26, the silicon anode half-cell made with the polyphenol polyurethane / polyacrylic acid binder provided by the present invention has an initial cycling capacity of over 1430 mAh / g at 2C rate, a cycle capacity retention of over 70.6%, and a lithium-ion diffusion coefficient of 1.73 × 10⁻⁶. -10 cm 2 / s or more. When the weight ratio of polyacrylic acid to polyphenolic polyurethane in the polyphenolic polyurethane / polyacrylic acid binder is 40~80:20~60 and the molar ratio of polytetrahydrofuran to isocyanate monomer to tannic acid is 1:1.5~2:0.5~1, the prepared silicon anode half-cell has an initial cycling capacity of over 1815 mAh / g at 2C rate, a cycling capacity retention of over 90.1%, and a lithium-ion diffusion coefficient of over 2.62×10. -10 cm 2 / s or more.

[0078] As can be seen from Example 1 and Comparative Example 1, the silicon anode half-cell made with the polyphenol polyurethane / polyacrylic acid binder provided by the present invention exhibits superior initial capacity and capacity retention at 2C rate compared to the polyacrylic acid binder. This is because the polyphenol polyurethane possesses excellent elasticity, which improves the toughness of the polyacrylic acid and prevents the electrode from cracking due to excessive brittleness. The polyphenol polyurethane and polyacrylic acid form a dynamically reversible and dense strong hydrogen bond (PU-PAA hydrogen bond) network, effectively mitigating the volume deformation of the silicon active material during charging and discharging, thus enabling the silicon anode half-cell to exhibit excellent rate performance and cycle stability.

[0079] As can be seen from Examples 1-5 and Comparative Examples 2-5, when the weight percentage of polyacrylic acid in the polyphenol polyurethane / polyacrylic acid binder is less than 30 parts, the prepared silicon anode half-cell exhibits lower rate performance and poorer cycle stability. Specifically, the initial cycle capacity at 2C rate is only 940-1502 mAh / g, and the cycle capacity retention is only 58.1%-65.6%. This is because the low acrylic acid content cannot provide sufficient hydrogen bond crosslinking sites, resulting in a decrease in anchoring effect. Consequently, the binder cannot have a stable network structure and cannot effectively alleviate the volume deformation caused by the silicon active material during charging and discharging, thus causing the silicon anode half-cell to exhibit lower rate performance and poorer cycle stability.

[0080] As can be seen from Examples 1 and Comparative Examples 6 and 7, the selection of the polyphenol polyurethane soft segment reactive monomer in the polyphenol polyurethane / polyacrylic acid binder has a decisive influence on the binder's performance. Compared with polyethylene glycol and polycarbonate glycol, polytetrahydrofuran soft segments, with their superior low-temperature flexibility and elastic modulus, can efficiently absorb and disperse the volume expansion stress of silicon particles during charge-discharge cycles, thereby maintaining the integrity of the electrode structure. Simultaneously, the polytetrahydrofuran soft segment molecular chain does not contain easily hydrolyzed ester or carbonate groups, but only stable ether bonds (-CH2-CH2-O-), reducing the risk of electrolyte swelling and effectively preventing the binder's adhesive strength from weakening and ion transport resistance from increasing. Furthermore, the polytetrahydrofuran soft segment is hydrophobic, preventing moisture from entering the binder and avoiding the hydrolysis of LiPF6 to generate HF, thus protecting the stability of the SEI film on the silicon surface. In summary, the polyphenol polyurethane / polyacrylic acid binder provided by this invention has both high mechanical robustness and electrochemical compatibility, which can endow lithium-ion batteries with better initial cycle capacity and cycle capacity retention, solving the problem that existing lithium-ion battery binders are insufficient in improving the cycle stability and rate performance of lithium-ion batteries.

[0081] As can be seen from Examples 1, 6, 11, 17, 18 and Comparative Examples 8, 9, when the molar ratio of polytetrahydrofuran to isocyanate monomer to tannic acid in the polyphenol polyurethane / polyacrylic acid binder is not within the range of 1:1.1~2.5:0.1~1.5, the prepared polyphenol polyurethane / polyacrylic acid binder will fail to achieve efficient lithium-ion transport and effective stress dispersion due to improper separation of the polyphenol polyurethane microphase. This results in the prepared silicon anode half-cell exhibiting low rate performance and poor cycle stability, specifically, an initial cycle capacity of only 600~750 mAh / g at 2C rate and a cycle capacity retention of only 46.7%~48.4%. Figure 3 As shown, Examples 1 and 18 exhibited better initial capacity and capacity retention at 2C high magnification compared to Comparative Example 9.

[0082] As can be seen from Examples 1 and Comparative Examples 1 and 9, the polyphenolic polyurethane hard segment structure composed of isocyanate and tannic acid can endow the adhesive with self-healing ability. This is due to the phenolic hydroxyl groups in the hard segment structure synergistically forming a multiple dynamic and reversible hydrogen bond network with polyacrylic acid, while the polytetrahydrofuran soft segment provides the necessary molecular chain segment mobility, significantly improving the fluidity of the entire system, breaking the rigid frozen state of the polyacrylic acid molecular chain, and allowing the dynamic hydrogen bond network to quickly recombine at the damaged interface, thereby achieving a self-healing effect.

Claims

1. A polyphenolic polyurethane / polyacrylic acid adhesive, characterized in that, The adhesive comprises the following components in parts by weight, totaling 100 parts: 40-90 parts of polyacrylic acid; 10-60 parts of polyphenolic polyurethane; The polyphenol polyurethane is prepared from the following raw materials: polytetrahydrofuran, tannic acid, and isocyanate monomer; the molar ratio of polytetrahydrofuran to isocyanate monomer to tannic acid is 1:1.1~2.5:0.1~1.

5.

2. The polyphenol polyurethane / polyacrylic acid adhesive according to claim 1, characterized in that, The adhesive comprises the following components in parts by weight, totaling 100 parts: 40-55 parts of polyacrylic acid; 45-60 parts of polyphenolic polyurethane.

3. The polyphenol polyurethane / polyacrylic acid adhesive according to claim 1, characterized in that, The molar ratio of polytetrahydrofuran to isocyanate monomer to tannic acid is 1:1.5~2:0.5~1.

4. The polyphenol polyurethane / polyacrylic acid adhesive according to any one of claims 1 to 3, characterized in that, The polytetrahydrofuran has a number-average molecular weight of 1000-2000.

5. The polyphenol polyurethane / polyacrylic acid adhesive according to any one of claims 1 to 3, characterized in that, The polyacrylic acid has a number average molecular weight of 300,000 to 1,250,000.

6. The method for preparing the polyphenol polyurethane / polyacrylic acid adhesive according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Dissolve polytetrahydrofuran and isocyanate monomers in a solvent, stir to carry out a prepolymerization reaction, then add tannic acid to carry out a chain extension reaction, and dry after the reaction to obtain polyphenolic polyurethane. S2. Dissolve polyphenolic polyurethane and polyacrylic acid in a solvent, stir and mix until uniform and clear, to obtain the polyphenolic polyurethane / polyacrylic acid adhesive.

7. The use of the polyphenol polyurethane / polyacrylic acid binder according to any one of claims 1 to 5 in the preparation of silicon-based anodes.

8. A silicon anode sheet, characterized in that, The components include the following parts by mass: 50-70 parts of silicon-active material; 15-25 parts of conductive additive; 15-25 parts of the polyphenol polyurethane / polyacrylic acid adhesive according to any one of claims 1 to 5.

9. The silicon anode sheet according to claim 8, characterized in that, The silicon-active material is one or more of elemental silicon, silicon suboxide, silicon-carbon composite materials, and silicon alloy materials.

10. The method for preparing the silicon anode sheet according to any one of claims 8 to 9, characterized in that, The process includes the following steps: dissolving the silicon active material, conductive additive, and any of the polyphenol polyurethane / polyacrylic acid binders described in claims 1 to 5 in a solvent, mixing them evenly, and drying them to form a film, thereby obtaining a silicon anode sheet.

Images