Polyurethane adhesive and method of preparation and use thereof

Abstract

This invention discloses a polyurethane adhesive, its preparation method, and its applications, belonging to the field of secondary battery technology. It addresses the problems of existing adhesives' inability to adaptively repair electrode microcracks and their difficulty in long-term binding of highly expandable active materials, leading to short battery cycle life. The polyurethane adhesive of this application comprises aliphatic polymeric polyol, polyisocyanate, and chain extender in a molar ratio of 1:(1.5~2.5):(0.5~1.5); the chain extender includes aliphatic amino acid esters containing disulfide bonds or aliphatic polyols containing disulfide bonds. When the polyurethane adhesive of this invention is applied to electrodes containing highly expandable active materials, it can achieve long-term binding, thereby improving the cycle life of high-capacity batteries.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a polyurethane adhesive, its preparation method, and its applications. Background Technology

[0002] Binders are key auxiliary materials in lithium-ion battery electrodes. Although used in small quantities, they play a crucial role in maintaining the integrity of the electrode structure and ensuring electron and ion conduction pathways. Traditional binders, such as polyvinylidene fluoride (PVDF), rely on relatively weak van der Waals forces, have limited mechanical strength, and are processed in organic solvents. A more significant problem is that PVDF is an inert binder and cannot cope with the enormous volume changes of high-capacity electrode materials (such as silicon) during cycling (the volume expansion of silicon anodes can reach over 300%). This volume change leads to microcracks inside the electrode, causing a loss of electrical contact between the active material and the conductive agent and current collector, ultimately resulting in a sharp capacity decay and shortened cycle life.

[0003] To address this challenge, researchers have developed a variety of novel adhesives. For example, one study combined waterborne polyurethane (WPU) with tannic acid and bacterial cellulose, utilizing a hydrogen bond network to enhance bond strength and buffer volume expansion, and applied this to lithium-sulfur batteries. Another study introduced dynamic disulfide bonds into polymer electrolytes for use in solid-state lithium-sulfur batteries to repair solid-solid interface contact problems.

[0004] However, the combination of self-healing function and strong adhesion provided by existing adhesive technologies is insufficient: many materials that achieve self-healing through physical cross-linking (such as hydrogen bonding) often have insufficient mechanical strength and modulus, making it difficult to bind highly expandable active materials for a long time. On the other hand, some high-strength adhesives lack dynamic repair capabilities or have insufficient dynamic repair capabilities, making them unsuitable for electrode sheets containing high-capacity electrode materials. Summary of the Invention

[0005] This invention provides a polyurethane adhesive, its preparation method, and its uses, to solve the problems of existing adhesives being unable to adaptively repair electrode microcracks and unable to bind highly expanding active materials for a long time, resulting in short battery cycle life.

[0006] In a first aspect, this application provides a polyurethane adhesive, the raw materials of which include aliphatic polymeric polyol, polyisocyanate and chain extender, in a molar ratio of 1:(1.5~2.5):(0.5~1.5). The chain extender includes aliphatic amino acid esters containing disulfide bonds or aliphatic polyols containing disulfide bonds.

[0007] In one possible implementation, the chain extender includes one or more of cystine dimethyl ester (CDE), 2,2'-dihydroxyethyl disulfide (BHDS), and dithiodiethylene glycol; In one possible implementation, the aliphatic polymer polyol includes one or more of aliphatic polyether polyols and aliphatic polyester polyols; In one possible implementation, the polyisocyanate includes one or more of isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), and 4,4'-dicyclohexylmethane diisocyanate; In one possible implementation, the molecular weight Mn of the aliphatic polymer polyol is 1000~3000; In one possible implementation, the molar ratio of the aliphatic polymer polyol, polyisocyanate, and chain extender is 1:(1.8~2.2):(0.8~1.2).

[0008] In one possible implementation, the aliphatic polyether polyol includes one or more of polytetrahydrofuran ether diol (PTMG) and polypropylene glycol; In one possible implementation, the aliphatic polyester polyol comprises polycaprolactone diol (PCL).

[0009] Secondly, this application provides a method for preparing a polyurethane adhesive, comprising the following steps: S1. The polyisocyanate and aliphatic polymer polyol are mixed and subjected to a polymerization reaction to obtain a prepolymer; S2. The prepolymer is mixed with the chain extender to carry out a chain extension reaction, thereby obtaining the polyurethane adhesive.

[0010] In one possible implementation, the polymerization reaction is carried out at a temperature of 70-85°C for 2-4 hours. In one possible implementation, the polymerization reaction is carried out in the presence of a catalyst; In one possible implementation, the polymerization reaction is carried out in a protective atmosphere; In one possible implementation, the chain extension reaction is carried out at a temperature of 70-85°C for a time of 1-5 hours. In one possible implementation, in the step of mixing the prepolymer with the chain extender, the chain extender is first mixed with an organic solvent to prepare a chain extender solution, and then the chain extender solution is added dropwise to the prepolymer.

[0011] In one possible implementation, the catalyst comprises an organotin catalyst or a tertiary amine catalyst; Optionally, the organotin catalyst includes one or more of dibutyltin dilaurate and stannous octoate; In one possible implementation, the catalyst is used in an amount of 0.01% to 0.5% of the total mass of the polyisocyanate and the aliphatic polymer polyol. In one possible implementation, the protective atmosphere includes one or more of N2 and argon; In one possible implementation, the chain extender solution is added to the prepolymer over a period of 0.5 to 2 hours. In one possible implementation, the step of adding the chain extender solution dropwise to the prepolymer is performed at a temperature maintained at 70-85°C. In one possible implementation, the organic solvent includes one or more of N,N-dimethylformamide (DMF), N-methylpyrrolidone, and dimethyl sulfoxide.

[0012] Thirdly, this application provides the application of the polyurethane adhesive described herein or the polyurethane adhesive prepared according to the preparation method in an electrode.

[0013] Fourthly, this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material and a polyurethane adhesive. The polyurethane adhesive is the polyurethane adhesive described above or the polyurethane adhesive prepared according to the preparation method described above.

[0014] In one possible implementation, the negative electrode active material includes one or more of silicon carbon, silicon oxide, and nano-silicon powder; In one possible implementation, the mass ratio of the negative electrode active material to the polyurethane adhesive is (75~95):(1~15), preferably (80~90):(5~15).

[0015] Fifthly, this application provides a secondary battery, including the aforementioned negative electrode sheet.

[0016] The secondary battery also includes an electrolyte.

[0017] The technical solution of this invention has the following advantages: 1. The polyurethane adhesive raw materials provided by the present invention include polyisocyanate, aliphatic polymer polyol and chain extender, with a molar ratio of 1:(1.5~2.5):(0.5~1.5); the chain extender includes aliphatic amino acid ester containing disulfide bonds or aliphatic polyol containing disulfide bonds.

[0018] This invention's polyurethane adhesive contains covalent disulfide bonds, exhibiting a self-healing efficiency far exceeding that of physical hydrogen bonds, resulting in a stronger and more durable repair. In environments such as electrolytes that may disrupt hydrogen bonds, this invention relies on the exchange of aliphatic disulfide bonds, which exhibit higher activity under electrolyte swelling conditions, to achieve long-term self-healing under real-world battery operating conditions. The self-healing mechanism is more stable and reliable. This invention's polyurethane adhesive uses aliphatic polymer polyols to obtain flexible soft segments, which synergize with non-rigid aliphatic amino acid esters containing disulfide bonds or aliphatic polyol chain extenders containing disulfide bonds, endowing the entire dynamic network of the polyurethane adhesive with extremely high segment mobility. High segment mobility means that disulfide bonds have high exchange activity at room temperature. The repair, driven by internal micro-stress generated by electrode operation, is an adaptive process that requires no external conditions. The self-healing mechanism of this invention's polyurethane adhesive does not rely on environmentally sensitive physical forces and is specifically designed for complex electrochemical environments, achieving "no additional stimulation" in application scenarios. Furthermore, the flexible soft segments of the polyurethane adhesive of this invention, in synergy with aliphatic amino acid esters or aliphatic polyol chain extenders containing disulfide bonds, form a highly repairable network. When applied to electrodes containing highly expandable active materials, this network can achieve long-term binding, thereby improving the cycle life of high-capacity batteries.

[0019] This invention successfully combines high adhesive strength, excellent expansion suppression capability, and extremely high cycle stability, solving the industry pain points of traditional adhesives (PVDF) being unable to cope with volume expansion and conventional elastic adhesives (CPU) lacking long-term structural maintenance capability. The molecular design of this invention is specifically tailored to the mechano-electrochemical coupling requirements of lithium battery electrodes: strong adhesion, electrolyte resistance, and chain segment mobility adapted to electrode volume changes.

[0020] 2. The chain extender provided by this invention includes one or more of cystine dimethyl ester (CDE), 2,2'-dihydroxyethyl disulfide (BHDS), and dithiodiethylene glycol. Using CDE as a chain extender generates strongly polar urea bonds, significantly improving adhesion and strength, without introducing rigid aromatic rings. Using BHDS as a chain extender generates flexible segments, maintaining high elasticity.

[0021] 3. The preparation method of the polyurethane adhesive of the present invention includes the following steps: S1, mixing the polyisocyanate and the aliphatic polymer polyol and carrying out a polymerization reaction to obtain a prepolymer; S2, mixing the prepolymer with the chain extender and carrying out a chain extension reaction to obtain the polyurethane adhesive.

[0022] The preparation method of the adhesive of the present invention is simple and highly controllable.

[0023] The application of the adhesive of this invention in lithium-ion battery electrodes, especially in silicon-containing anodes, can significantly improve the cycle stability and capacity retention of the battery. Detailed Implementation

[0024] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0025] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0026] Example 1 This embodiment provides a polyurethane adhesive (SPU-1) with a raw material ratio (molar ratio) of polytetrahydrofuran ether diol (PTMG, Mn=2000): isophorone diisocyanate (IPDI): cystine dimethyl ester (CDE) = 1.0: 2.0: 1.0.

[0027] The preparation method of the polyurethane adhesive in this embodiment includes the following steps: 1. Add 0.01 mol PTMG (20.0 g) and 0.02 mol IPDI (4.44 g) to a dry three-necked flask, add 2 drops of DBTDL (dibutyltin dilaurate, about 0.1 g) catalyst, and react in an oil bath at 80 °C for 3 hours under nitrogen protection to obtain the prepolymer.

[0028] 2. Dissolve 0.01 mol CDE (2.10 g) in 20 mL of anhydrous DMF to prepare a CDE / DMF solution.

[0029] 3. Slowly add the CDE / DMF solution dropwise into the prepolymer obtained in step 1 using a constant pressure dropping funnel, and complete the dropwise addition within 1 hour, while maintaining the temperature at 80°C.

[0030] 4. After the addition is complete, continue the reaction for 4 hours. Take a small sample and monitor it using Fourier transform infrared spectroscopy (FTIR) until the -NCO characteristic peak (~2270 cm⁻¹) is reached. -1 )disappear.

[0031] 5. Pour the reaction solution obtained in step 4 onto a polytetrafluoroethylene plate and dry it in a vacuum oven at 80°C for 24 hours to obtain the elastomer film SPU-1.

[0032] Example 2 This embodiment provides a polyurethane adhesive (SPU-2), which is basically the same as that in Example 1, except that the raw material ratio (molar ratio) is PTMG (Mn=2000):IPDI:CDE=1.0:2.2:1.2.

[0033] This embodiment increases the ratio of IPDI to CDE to obtain a polymer network with higher crosslinking density and more disulfide bonds.

[0034] The preparation method of the polyurethane adhesive in this embodiment is the same as that in Example 1.

[0035] Example 3 This embodiment provides a polyurethane adhesive (SPU-3) with a raw material ratio (molar ratio) of PTMG (Mn=1000): hexamethylene diisocyanate (HDI): 2,2'-dihydroxyethyl disulfide (BHDS) as a chain extender, and a raw material molar ratio of 1.0:1.8:0.8.

[0036] The preparation method of the polyurethane adhesive in this embodiment is the same as that in Example 1.

[0037] Example 4 This embodiment provides a polyurethane adhesive (SPU-4), which is basically the same as that in Example 1, except that PTMG is replaced with an equimolar amount of polycaprolactone diol (PCL, Mn=2000), and the raw material molar ratio is PCL:IPDI:CDE=1.0:2.0:1.0.

[0038] The preparation method of the polyurethane adhesive in this embodiment is the same as that in Example 1.

[0039] Example 5 This embodiment provides a polyurethane adhesive (SPU-5), which is basically the same as that in Example 1, except that PTMG:IPDI:CDE = 1.0:2.5:1.5.

[0040] The preparation method of the polyurethane adhesive in this embodiment includes the following steps: 1. Add 0.01 mol PTMG (20.0 g) and 0.025 mol IPDI (5.56 g) to a dry three-necked flask, add DBTDL catalyst at a mass of about 0.1% of the total mass of PTMG and IPDI, and react in an oil bath at 80°C for 3.5 hours under nitrogen protection to obtain the prepolymer.

[0041] 2. Dissolve 0.015 mol CDE (3.15 g) in 25 mL of anhydrous DMF to prepare a CDE / DM solution.

[0042] 3. The CDE / DMF solution was slowly added dropwise to the prepolymer over 1.5 hours using a constant-pressure dropping funnel, while maintaining the temperature at 80°C. The viscosity of the system increased significantly during the dropwise addition process.

[0043] 4. After the addition is complete, continue the reaction for 5 hours. Take a small sample and monitor it using Fourier transform infrared spectroscopy (FTIR) until the -NCO characteristic peak (~2270 cm⁻¹) is reached. - ¹) Basically disappeared.

[0044] 5. The viscous reaction solution obtained in step 4 is poured onto a polytetrafluoroethylene plate and dried in a vacuum oven at 80°C for 24 hours to obtain a light yellow elastomer film, labeled as SPU-5.

[0045] Comparative Example 1 This comparative example uses commercial PVDF powder (HSV900) as a binder.

[0046] Comparative Example 2 This comparative example provides a polyurethane adhesive (CPU) that is essentially the same as that in Example 1, except that an equimolar amount of conventional chain extender 1,4-butanediol (BDO) is used instead of CDE, and the raw material molar ratio is PTMG (Mn=2000):IPDI:BDO=1.0:2.0:1.0.

[0047] The preparation method of this comparative polyurethane adhesive is the same as that of Example 1.

[0048] Comparative Example 3 This comparative example provides a polyurethane adhesive (CPU-D1) with a raw material ratio (molar ratio) of polytetrahydrofuran ether diol (PTMG, Mn=2000): isophorone diisocyanate (IPDI): 4,4'-diaminodiphenyl disulfide (DADPS) = 1.0: 2.2: 1.2.

[0049] The preparation method of the polyurethane adhesive in this embodiment is the same as that in Example 2.

[0050] Comparative Example 4 This comparative example provides a polyurethane adhesive with a raw material ratio (mass ratio) of polytetrahydrofuran ether diol (PTMG, Mn=2000): isophorone diisocyanate (IPDI): tannic acid (TA) = 20.0 g: 4.44 g: 2.00 g.

[0051] The preparation method of this comparative polyurethane adhesive includes: 1. Add 20.0 g PTMG (approximately 0.01 mol) and 4.44 g IPDI (0.02 mol) to a dry three-necked flask, add 2 drops of DBTDL catalyst, and react in an oil bath at 80°C for 3 hours under nitrogen protection to obtain the prepolymer.

[0052] 2. Dissolve 2.00 g of tannic acid in a mixed solvent of 20 mL of anhydrous DMF and 2 mL of anhydrous ethanol to prepare a tannic acid solution.

[0053] 3. Slowly add the tannic acid solution to the prepolymer using a constant pressure dropping funnel, completing the addition within 1 hour, while maintaining the temperature at 75°C (to prevent the tannic acid from partially decomposing due to excessive temperature).

[0054] 4. After the addition is complete, continue the reaction for 4 hours. Take a small sample and monitor it with FTIR until the -NCO characteristic peak disappears.

[0055] 5. The reaction solution obtained in step 4 is poured onto a polytetrafluoroethylene plate and dried in a vacuum oven at 60°C for 36 hours to obtain a dark brown, brittle solid film, labeled as CPU-TA.

[0056] Comparative Example 5 This comparative example provides a polyurethane adhesive with a raw material ratio (molar ratio) of polytetrahydrofuran ether diol (PTMG, Mn=2000): hexamethylene diisocyanate (HDI): cystamine dihydrochloride (Cystamine·2HCl) = 1.0: 2.2: 1.0.

[0057] The preparation method of this comparative polyurethane adhesive includes: 1. Add 0.01 mol PTMG (20.0 g) and 0.022 mol HDI (3.70 g) to a dry three-necked flask, add 2 drops of DBTDL catalyst, and react in an oil bath at 80°C for 3 hours under nitrogen protection to obtain the prepolymer.

[0058] 2. Dissolve 0.01 mol cystamine dihydrochloride (2.27 g) and 0.022 mol triethylamine (2.23 g, as an acid-binding agent) together in 25 mL of anhydrous DMF to prepare a solution.

[0059] 3. Slowly add the above mixed solution dropwise into the prepolymer using a constant pressure dropping funnel, completing the addition within 1 hour, while maintaining the temperature at 80°C. White fumes (triethylamine hydrochloride) will be generated during the addition process.

[0060] 4. After the addition is complete, continue the reaction for 5 hours. Take a small sample and monitor the reaction progress using FTIR until the -NCO characteristic peak disappears.

[0061] 5. Pour the reaction solution obtained in step 4 into a large amount of deionized water to precipitate, filter and wash the solid with water several times to remove salt byproducts, and finally place the solid in a vacuum oven at 60°C to dry for 48 hours to obtain a light yellow solid, labeled as CPU-Cys.

[0062] Comparative Example 6 This comparative example provides a polyurethane adhesive (SPU-F) with a raw material ratio (molar ratio) of polytetrahydrofuran ether diol (PTMG, Mn=2000): isophorone diisocyanate (IPDI): cystine dimethyl ester (CDE) = 1.0: 3.0: 1.8.

[0063] The preparation method of this comparative polyurethane adhesive is basically the same as that of Example 1, except that in step 3, the CDE / DMF solution is slowly added dropwise to the prepolymer obtained in step 1 using a constant pressure dropping funnel, with the addition time being 2 hours. In step 4, after the addition is complete, the reaction continues for 6 hours until the -NCO characteristic peak basically disappears. Because the viscosity of the reaction solution obtained in step 4 of this example is extremely high, in step 5, after casting and molding, it is vacuum dried at 80°C for 36 hours to obtain a hard and brittle deep yellow solid film, labeled as SPU-F.

[0064] The adhesives prepared using the respective examples and comparative examples were dissolved in N-methylpyrrolidone (NMP) to prepare an adhesive solution with a solid content of 8 wt%.

[0065] A silicon-carbon composite material (SiOx / C, the negative electrode active material), a conductive agent (Super P), and a binder were mixed at a mass ratio of 80:10:10, using NMP as a solvent, and thoroughly stirred in a planetary mixer until a homogeneous slurry was formed. The slurry was coated onto copper foil, dried under vacuum at 120°C for 12 hours, and then rolled and cut to obtain the negative electrode sheet. Using a lithium metal sheet as the counter electrode, Celgard 2400 as the separator, and 1M LiPF6 in EC / DEC / EMC (1:1:1 vol%) + 10% FEC as the electrolyte, a CR2032 coin cell was assembled in an argon glove box.

[0066] (1) The peel strength between the negative electrode active layer and the negative electrode current collector is tested according to ASTM D6862 (T-type peel).

[0067] (2) Tensile strength and elongation at break: The adhesive films obtained by casting in each embodiment and comparative example were tested according to GB / T 1040.

[0068] (3) Self-healing efficiency: The adhesive film obtained by casting is completely cut off, the cross-sections are in close contact and kept for a certain time (24h at room temperature), and then the tensile strength M1 after repair is tested and the tensile strength M0 of the original sample is tested. Self-healing efficiency = M1 / M0.

[0069] (4) Initial coulomb efficiency and capacity retention rate over 100 cycles: The electrochemical performance of the fabricated coin cell half-cells was tested using a Blue Electric Battery testing system: First, the cells were discharged at a constant current of 0.1C to 0.01 V and allowed to stand for 5 minutes; then, they were charged at the same constant current to 1.5 V and allowed to stand for 5 minutes. This process was repeated twice to stabilize the SEI film. Then, 100 charge-discharge cycles were performed at 0.5C and a voltage range of 0.01V to 1.5V.

[0070] Initial coulombic efficiency = (0.1C initial discharge capacity / 0.51C initial charge capacity) × 100%; Capacity retention rate over 100 cycles = Discharge capacity at 0.5C on the 100th cycle / Initial discharge capacity at 0.5C × 100%.

[0071] (5) Expansion rate of 100 electrode rings: After 100 cycles, disassemble the battery, remove the electrode plates, and clean and dry them. Use a micrometer or thickness gauge to measure the thickness of the electrode plates at multiple specific points, and compare it with the initial thickness before cycling to calculate the average expansion rate: [(thickness after cycling - thickness before cycling) / thickness before cycling] × 100%.

[0072] The test results are shown in Table 1.

[0073] Table 1

[0074] As shown in Table 1, the batteries using the polyurethane binders (SPU-1 to SPU-5) of the present invention can achieve stable repair in the electrolyte environment. Ultimately, in the harsh application scenario of silicon-carbon anode, they achieved comprehensive and significantly better overall performance than the comparative examples (high capacity retention and low electrode expansion rate).

[0075] Cycle stability (capacity retention): The capacity retention of this invention after 100 cycles is between 75.0% and 85.0%, significantly higher than that of the comparative example. Furthermore, a comparison of Examples 1-4 with Example 5 shows that when the molar ratio of aliphatic polymer polyol, polyisocyanate, and chain extender is in the range of 1:(1.8~2.2):(0.8~1.2), the capacity retention can be further improved, reaching between 79.0% and 85.0%. Among these, SPU-2 performed best (85.0%), with a retention rate 77% higher than that of PVDF. This directly proves that this invention can greatly extend battery life.

[0076] Electrode structure integrity (electrode expansion rate): The SPU series of this invention can effectively suppress the huge volume expansion of silicon anodes, controlling the electrode expansion rate after cycling to 19.7% to 26%, which is much lower than that of CPU (27.8%) and PVDF (38.2%). SPU-2 also performs best (19.7%). The significant reduction in expansion rate is the physical structural basis for the improved capacity retention.

[0077] Adhesion performance: The peel strength (18.5-24 N / m) of all SPU embodiments was several times that of PVDF (6.7 N / m), and was also generally higher than or comparable to that of CPU, demonstrating that the polyurethane substrate provided strong initial adhesion.

[0078] Comparative Example 2 (CPU) and SPU-1 have nearly identical polyurethane backbones, the only difference being whether dynamic disulfide bonds are introduced. A comparison between Comparative Example 2 and Example 1 shows that: 1. The self-healing efficiency of the CPU is 0%, while all SPU samples in this application show an efficiency of over 75%, proving that dynamic disulfide bonds are the chemical basis for the occurrence of reversible exchange reactions and the realization of the material's self-healing ability.

[0079] 2. A Qualitative Leap from "Buffering" to "Repair": While CPUs, due to their elasticity, can buffer some expansion compared to PVDF (expansion rate reduced from 38.2% to 27.8%), their capacity retention is limited (only up to 65.0%) because they cannot repair cracks. With the introduction of dynamic disulfide bonds, the SPU series further significantly reduces the expansion rate and increases the capacity retention to over 75% by repairing microscopic damage in real time. This demonstrates that dynamic disulfide bonds bring not just a simple "elasticity improvement," but a qualitative leap in functionality—"adaptive repair."

[0080] 3. Synergistic Effect: Taking the top-performing SPU-2 as an example, it simultaneously possesses the highest peel strength (23.5 N / m) and the lowest electrode expansion rate (19.7%). This indicates that the "tough polyurethane network" and the "dynamic disulfide bonds" produce a synergistic effect of 1+1>2: the strong network provides initial restraint, preventing material pulverization; the dynamic bonds repair the network immediately when it is damaged, preventing crack propagation. Together, they ensure the structural integrity of the electrode during long-term cycling.

[0081] The binder used in Comparative Example 3 exhibits characteristics of high rigidity (tensile strength 10.8 MPa), low elasticity (elongation at break 150%), slow repair, poor battery cycle life (capacity retention 68%), and severe electrode expansion (31.5%). The 4,4'-diaminodiphenyl disulfide used in Comparative Example 3 contains a rigid aromatic ring, causing the polymer hard segments to "freeze," resulting in poor chain mobility, low elongation at break, and slow repair speed (disulfide bond exchange is difficult). In the electrolyte environment, after its hydrogen bond network is disrupted, the slow repair speed leads to decreased adhesion (peel strength lower than SPU-1), failing to effectively bind silicon particles, resulting in a sharp increase in cycle expansion and low capacity retention.

[0082] Comparative Example 4 uses tannic acid to form a pure hydrogen bond system. Tannic acid provides abundant hydrogen bonds, but hydrogen bonds are weak and environmentally sensitive physical forces. In the electrolyte, the hydrogen bond network is easily solvated and broken down, leading to complete adhesion failure (peel strength of only 8.5 N / m). Simultaneously, it lacks covalent bond repair capabilities and cannot cope with cyclic stress, causing the electrode structure to rapidly deteriorate. This demonstrates that hydrogen bonds alone cannot solve the problem of electrode volume expansion.

[0083] In Comparative Example 5, the introduction of cystamine dihydrochloride led to the introduction of chloride ion impurities, which are difficult to completely remove. These impurities catalyze electrolyte decomposition and damage the SEI film during battery cycling. This directly resulted in higher irreversible capacity loss (reduced initial efficiency) and faster capacity decay. Although its mechanical properties are acceptable (due to its aliphatic disulfide bond system, similar to SPU-1), its poor electrochemical compatibility limits its ultimate application effectiveness.

[0084] In Comparative Example 6, excessive amounts of polyisocyanate and disulfide bond chain extenders lead to excessively high crosslinking density of the polymer network and loss of chain segment mobility, thereby impairing its self-healing ability and toughness required as a battery binder, resulting in a decline in overall electrochemical performance.

[0085] The data differences within the SPU series of this invention confirm the effectiveness of regulating performance through molecular design.

[0086] Table 2

[0087] This invention provides a highly tunable molecular platform that allows for the directional preparation of adhesives that emphasize high strength, high elasticity, or high repair efficiency by changing the chain extender, soft segment type, and crosslinking density. This adapts to electrode systems with different silicon contents and mechanical requirements, demonstrating strong application flexibility.

[0088] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A polyurethane adhesive, characterized by, The raw materials include aliphatic polymer polyols, polyisocyanates, and chain extenders, with a molar ratio of 1:(1.5~2.5):(0.5~1.5). The chain extender includes aliphatic amino acid esters containing disulfide bonds or aliphatic polyols containing disulfide bonds.

2. The polyurethane adhesive according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The chain extender includes one or more of cystine dimethyl ester, 2,2'-dihydroxyethyl disulfide, and dithiodiethylene glycol; (2) The aliphatic polymer polyol includes one or more of aliphatic polyether polyol and aliphatic polyester polyol; (3) The polyisocyanate includes one or more of isophorone diisocyanate, hexamethylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate; (4) The molecular weight Mn of the aliphatic polymer polyol is 1000~3000; (5) The molar ratio of the aliphatic polymer polyol, polyisocyanate and chain extender is 1:(1.8~2.2):(0.8~1.2).

3. The polyurethane adhesive according to claim 2, characterized in that The aliphatic polyether polyol includes one or more of polytetrahydrofuran ether diol and polypropylene glycol; And / or, the aliphatic polyester polyol includes polycaprolactone diol.

4. A process for the production of the polyurethane adhesive according to any one of claims 1 to 3, characterized in that Includes the following steps: S1. The polyisocyanate and aliphatic polymer polyol are mixed and subjected to a polymerization reaction to obtain a prepolymer; S2. The prepolymer is mixed with the chain extender to carry out a chain extension reaction, thereby obtaining the polyurethane adhesive.

5. The method for producing a polyurethane adhesive according to claim 4, characterized by, At least one of the following conditions must be met: (1) The polymerization reaction is carried out at a temperature of 70~85℃ for 2~4 hours; (2) The polymerization reaction is carried out in the presence of a catalyst; (3) The polymerization reaction is carried out in a protective atmosphere; (4) The chain extension reaction is carried out at a temperature of 70~85℃ for 1~5h; (5) In the step of mixing the prepolymer with the chain extender, the chain extender is first mixed with an organic solvent to prepare a chain extender solution, and then the chain extender solution is added dropwise to the prepolymer.

6. The method for producing a polyurethane adhesive according to claim 5, characterized by, At least one of the following conditions must be met: (1) The catalyst includes organotin catalysts or tertiary amine catalysts; (2) The amount of the catalyst used is 0.01% to 0.5% of the total mass of the polyisocyanate and aliphatic polymer polyol; (3) The protective atmosphere includes one or more of N2 and argon; (4) The chain extender solution is added to the prepolymer over a period of 0.5 to 2 hours; (5) The temperature is maintained at 70~85℃ during the step of adding the chain extender solution dropwise into the prepolymer; (6) The organic solvent includes one or more of N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.

7. The use of the polyurethane adhesive according to any one of claims 1-3 or the polyurethane adhesive prepared by the preparation method according to any one of claims 4-6 in an electrode.

8. A negative electrode sheet characterized by comprising: It includes a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material and a polyurethane adhesive; The polyurethane adhesive is the polyurethane adhesive according to any one of claims 1-3 or prepared according to the method of any one of claims 4-6.

9. The negative electrode sheet according to claim 8, characterized by, The negative electrode active material comprises one or more of silicon-carbon, silicon-oxygen, and nano-silicon powder. And / or The mass ratio of the negative electrode active material to the polyurethane adhesive is (75-95):(1-15).

10. A secondary battery characterized by comprising: The negative electrode sheet comprises the negative electrode active material according to claim 8 or 9.

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