Binder, preparation method therefor, and lithium ion battery

Abstract

The present application discloses a binder, a preparation method therefor, and a lithium ion battery. The binder is a polyamide polymer, comprising a repeating structural unit A as shown in a formula (I) and a repeating structural unit B as shown in a formula (II), wherein R1 comprises an aryl group containing neither an amide group nor an amino group; R2 comprises an aryl group containing at least one amide group or an aryl group containing at least one amino group; and the molar ratio of the repeating structural unit A to the repeating structural unit B is (2:1)-(6:1).

Description

A binder, its preparation method, and a lithium-ion battery

[0001] This application claims priority to Chinese Patent Application No. 2024104949103, filed with the Chinese Patent Office on April 23, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrode materials, specifically to a binder, its preparation method, and a lithium-ion battery. Background Technology

[0003] Currently, commercial lithium-ion batteries based on graphite anode materials have reached near their theoretical limits, making it difficult to meet the demands of today's information society for high-energy-density batteries. Silicon-based electrode materials are considered the most promising and competitive emerging electrode materials due to their relatively low discharge potential, high theoretical specific capacity, and abundant reserves. However, during charge and discharge, silicon-based anodes face repeated volume expansion and contraction, leading to degradation of their mechanical and electrical properties and resulting in capacity decay in silicon-based batteries. Therefore, developing polymer binders that can suppress the volume expansion of silicon particles and allow reversible volume expansion during cycling is crucial for the development of silicon-based batteries.

[0004] Currently, it is generally believed that polymer binders suitable for silicon anodes should possess the following key characteristics: strong intermolecular interactions between polymer chains to resist the volume expansion of Si particles; for example, aliphatic polymer binders, by introducing crosslinking or supramolecular structures, can suppress the volume expansion of Si particles. In related technical fields, there is an in-situ covalently crosslinked network polymer binder composed of PAA and carbonyl-terminated isocyanate-terminated polyurethane oligomers (PUOs), with 2-ureido-4-pyrimidinone (UPy) as a reversible quadruple hydrogen-bonded crosslinking agent for Si anodes in lithium-ion batteries. In related technical fields, polyrotaxane can also be used as a sliding motion crosslinked network polymer binder, integrating PAA as a linear polymer and cyclodextrin (CD) as a cyclic supramolecular structure. Technical issues

[0005] The aforementioned binders primarily rely on intermolecular forces. The backbone formed by the relatively weak cross-linking of polymers has low strength and limited ability to resist the volume expansion of Si particles. Aromatic polymers, however, possess a rigid and ordered polymer backbone structure due to the strong π-π bond interactions between them. This unique structure endows them with excellent tensile strength, capable of withstanding the large volume expansion of silicon particles and preventing the silicon particles from losing connection with the conductive network during charging and discharging. However, excessively high tensile strength will cause the binder to lose its elasticity and fail to perform its binding function. Technical solutions

[0006] In a first aspect, this application provides an adhesive, said adhesive being a polyamide polymer comprising repeating structural unit A as shown in formula (I) and repeating structural unit B as shown in formula (II):

[0007]

[0008] Formula (I)

[0009]

[0010] Equation (II),

[0011] Wherein, R1 includes an aryl group that does not contain an amide group or an amino group; R2 includes an aryl group that contains at least one amide group or an aryl group that contains at least one amino group;

[0012] The molar ratio of the repeating structural unit A to the repeating structural unit B is (2:1) to (6:1).

[0013] Secondly, this application provides a method for preparing an adhesive, comprising the following steps:

[0014] S1. Mix the aryl-containing diamine, the aryl-containing polyamine, and an organic solvent to prepare solution 1;

[0015] S2. Mix the diacid anhydride and the organic solvent to prepare solution 2;

[0016] S3. Mix and react the solutions 1 and 2 to obtain solution 3;

[0017] S4. Add an ether solvent, collect the precipitate, and obtain the binder;

[0018] The molar ratio of the aryl-containing diamine to the aryl-containing polyamine is (2:1) to (6:1).

[0019] Thirdly, this application provides a lithium-ion battery, including the binder. Beneficial effects

[0020] First, the binder in this application is a polyamide polymer, wherein the repeating structural unit B acts as a hard segment in the polyamide polymer backbone, and the relatively flexible repeating structural unit A acts as a soft segment in the polyamide polymer backbone. The molar ratio of the repeating structural unit A to the repeating structural unit B is (2:1) to (6:1). The molar ratio of the repeating structural unit A (soft segment) to the repeating structural unit B (hard segment) within this range can effectively improve the balance between the hardness and softness of the polyamide polymer binder, thereby effectively suppressing the volume expansion of Si particles while retaining elasticity and playing a bonding role. During cycling, the volume expansion / contraction recovery of the silicon-based negative electrode is achieved.

[0021] Secondly, the preparation method of the adhesive in this application involves first mixing an aryl-containing diamine, an aryl-containing polyamine, and an organic solvent to prepare a mixed solution 1 containing aryl-containing diamines and polyamines. Then, solution 1 is mixed with solution 2 containing diacid anhydrides to generate a polyamide adhesive. The mixing of aryl-containing diamines and polyamines to form solution 1 ensures that both react simultaneously with the diacid anhydrides. Even if the probability of reaction between these two amine compounds and the diacid anhydrides is essentially the same, this facilitates the formation of a copolymer of aryl-containing diamines and polyamines in stoichiometric proportions, achieving precise control of the soft-hard balance in the polyamide polymer adhesive. Furthermore, in step S4 of this application, an unsuitable solvent—an ether solvent—is used to precipitate and purify the polyamide adhesive obtained in step S3 by recrystallization. This purification method is simple and beneficial for large-scale production applications.

[0022] Third, the lithium-ion battery of this application includes the binder of this application. The binder of this application can effectively suppress the volume expansion of Si particles while retaining elasticity and playing a bonding role. During cycling, it can realize the volume expansion / contraction recovery of the silicon-based negative electrode, thereby improving the cycle performance of the lithium-ion battery of this application. Embodiments of the present invention

[0023] The molar ratio of repeating structural unit A and repeating structural unit B described in this application is (2:1) to (6:1), for example, it can be 2:1, 3:1, 4:1, 5:1, 6:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] In some embodiments, R2 comprises an aryl group containing at least one amino group.

[0025] R2 in this scheme includes an aryl group containing at least one amino group. The amino group on the end group of the polyamide polymer binder can form a strong bond with the Si particles. Since the polyamide polymer binder is a fused aromatic ring binder formed by repeating structural unit A and repeating structural unit B, after the amino group on the end group of the polyamide polymer binder strongly bonds with the Si particles, the interaction between the fused aromatic ring binder strongly bonded with the Si particles and the conductive agent increases. In essence, this enhances the interaction between the Si particles and the conductive agent, which can improve the bonding performance between silicon particles and the conductive agent and improve the electrical performance of silicon-containing negative electrodes.

[0026] In some embodiments, the number average molecular weight of the adhesive is 200,000 to 600,000 g / mol, for example, it can be 200,000, 300,000, 400,000, 500,000, or 600,000, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] The number-average molecular weight of the binder described in this scheme is 200,000~600,000 g / mol. When the number-average molecular weight of the polyamide polymer binder is within this range, it can make the binder easy to dissolve, have good dispersion with the conductive agent, ensure suitable viscosity of the slurry, and make it easy to coat evenly, which is beneficial to subsequent processing and production. It can also form a branched cross-linked bonding structure, improve the adhesion of the binder, form a good conductive network, and improve the electrical performance of the silicon-containing negative electrode.

[0028] In some embodiments, the aryl diamine providing the repeating structural unit A includes at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, and 3,4'-diaminodiphenyl ether.

[0029] In some embodiments, the aryl polyamine providing the repeating structural unit B includes at least one of 3,3'-diaminobenzidine, 1,2,4,5-phenyltetramine, and 3,3,4,4-tetraaminodiphenyl ether.

[0030] The molar ratio of the aryl-containing diamine and the aryl-containing polyamine described in this application is (2:1) to (6:1), for example, it can be 2:1, 3:1, 4:1, 5:1, 6:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] In some embodiments, the dicarboxylic anhydride includes at least one selected from pyromellitic dianhydride (PMDA), 4,4'-diphenyl ether dianhydride (ODPA), 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), 3,3',4,4'-diphenylsulfone tetracarboxylic acid dianhydride (DSDA), hexafluorodianhydride (6FDA), 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA), 4,4'-(4,4'-isopropylidene diphenoxy)bis(phthalic anhydride) (BPADA), and p-phenylene-bisphenyltrilate dianhydride (TAHQ).

[0032] In some embodiments, the organic solvent is a polar solvent.

[0033] In some embodiments, the polar solvent includes N,N-dimethylformamide.

[0034] In some embodiments, the molar ratio of the total amino groups in the aryl-containing diamine and the aryl-containing polyamine to the anhydride groups in the diacid anhydride is (3~6):1, for example, it can be 3:1, 4:1, 5:1, 6:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] The molar ratio of total amino groups in the aryl-containing diamines and polyamines to anhydride groups in the diacid anhydrides described in this scheme is (3~6):1. Within this range, the resulting polyamide polymer binder has sufficient amino groups to form a strong bond with Si particles, improving the adhesion performance to Si particles. It also forms a rich branched cross-linked structure. The increased interaction between the branched cross-linked binder and the conductive agent, which strongly bonds with Si particles, essentially enhances the interaction between Si particles and the conductive agent. This improves the bonding performance between silicon particles and the conductive agent, thereby improving the electrical performance of the silicon-containing negative electrode.

[0036] In some embodiments, in step S2, the temperature at which the dicarboxylic anhydride and the organic solvent are mixed is -30 to 5°C, for example, -30°C, -20°C, -10°C, 0°C, or 5°C, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] In some embodiments, in step S3, mixing solution 1 and solution 2 specifically involves adding solution 2 dropwise to solution 1.

[0038] In step S3 of this scheme, the mixing reaction of solution 1 and solution 2 specifically involves adding solution 2 dropwise to solution 1. By adopting the order of adding diacid anhydride to the mixed solution 1 containing aryl diamine and aryl polyamine, the conversion rate of diacid anhydride can be improved, thereby increasing the yield of branched crosslinked polymer binder. At the same time, by using the dropwise addition method, the aryl diamine and aryl polyamine can be fully polymerized and crosslinked with the diacid anhydride, thereby improving the soft-hard balance synthesis efficiency.

[0039] In some embodiments, in step S4, the ether solvent includes at least one of diethyl ether, propylene oxide, phenoxyethanol, dichlorodiethyl ether, dibenzyl ether, tetrahydropyran, cyclopentyl methyl ether, and trioxymethylene.

[0040] Example 1

[0041] S1. Add 40 mmol of 4,4-diaminodiphenyl ether and 10 mmol of 3,3-diaminobenzidine to a double-necked round-bottom flask, then add 30 mL of N,N-dimethylformamide solvent, and stir at room temperature until completely dissolved to obtain solution 1, which is ready for use.

[0042] S2. Take 15 mmol of benzoic acid dianhydride and dissolve it in 10 mL of N,N-dimethylformamide solvent at 0 °C to obtain solution 2, which is ready for use.

[0043] S3. Add solution 2 from step S2 dropwise to solution 1 from step S1, stir and react at room temperature for 15 h, and obtain mixed solution 3 after the reaction is completed, for later use;

[0044] S4. Take 30 mL of diethyl ether, add it to mixed solution 3, collect the polymer precipitate, then wash the polymer precipitate with deionized water, and then vacuum dry the polymer precipitate at room temperature to finally obtain the binder powder with a number average molecular weight of 210,000.

[0045] Example 2

[0046] S1. Take 20 mmol of p-phenylenediamine and 10 mmol of 1,2,4,5-phenyltetramine and add them to a double-necked round-bottom flask. Then add 15 mL of N,N-dimethylformamide solvent and stir at room temperature until completely dissolved to obtain solution 1 for later use.

[0047] S2. Take 13 mmol of 4,4'-biphenyl ether dianhydride and dissolve it in 11 mL of N,N-dimethylformamide solvent at 0 °C to obtain solution 2, which is ready for use.

[0048] S3. Add solution 2 from step S2 dropwise to solution 1 from step S1, stir and react at room temperature for 15 h, and obtain mixed solution 3 after the reaction is completed, for later use;

[0049] S4. Take 35 mL of diethyl ether, add it to mixed solution 3, collect the polymer precipitate, then wash the polymer precipitate with deionized water, and then vacuum dry the polymer precipitate at room temperature to finally obtain the binder powder with a number average molecular weight of 230,000.

[0050] Example 3

[0051] S1. Take 60 mmol of 3,4'-diaminodiphenyl ether and 10 mmol of 3,3,4,4-tetraaminodiphenyl ether and add them to a double-necked round-bottom flask. Then add 50 mL of N,N-dimethylformamide solvent and stir at room temperature until completely dissolved to obtain solution 1 for later use.

[0052] S2. Take 13 mmol of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and dissolve it in 12 mL of N,N-dimethylformamide solvent at 0 °C to obtain solution 2, which is ready for use.

[0053] S3. Add solution 2 from step S2 dropwise to solution 1 from step S1, stir and react at room temperature for 15 h, and obtain mixed solution 3 after the reaction is completed, for later use;

[0054] S4. Take 40 mL of diethyl ether, add it to mixed solution 3, collect the polymer precipitate, then wash the polymer precipitate with deionized water, and then vacuum dry the polymer precipitate at room temperature to finally obtain the binder powder with a number average molecular weight of 220,000.

[0055] Example 4

[0056] In this embodiment, step S2 is as follows: 120 mmol of benzoic acid dianhydride is dissolved in 80 mL of N,N-dimethylformamide solvent at 0°C to obtain solution 2, which is set aside. In step S4, 80 mL of diethyl ether is taken. The rest is the same as in Example 1, and the number-average molecular weight of the binder is 240,000.

[0057] Example 5

[0058] In step S3 of this embodiment, the reaction is stirred at room temperature for 1 hour. The rest is the same as in Example 1, and the number-average molecular weight of the binder is 190,000.

[0059] Example 6

[0060] S1. Add 40 mmol of 4,4-diaminodiphenyl ether to a two-necked round-bottom flask, then add 24 mL of N,N-dimethylformamide solvent, and stir at room temperature until it is completely dissolved to obtain solution 1, which is ready for use.

[0061] S2. Add 10 mmol of 3,3-diaminobenzidine to a double-necked round-bottom flask, then add 6 mL of N,N-dimethylformamide solvent, and stir at room temperature until it is completely dissolved to obtain solution 2, which is ready for use.

[0062] S3. Take 15 mmol of benzoic acid dianhydride and dissolve it in 10 mL of N,N-dimethylformamide solvent at 0 °C to obtain solution 3, which is ready for use.

[0063] S4. Add solution 3 from step S3 to solution 1 from step S1, stir and react at room temperature for 10 h, and obtain mixed solution 4 after the reaction is completed, for later use;

[0064] S5. Add solution 2 from step S2 dropwise to solution 4 from step S4, stir and react at room temperature for 10 h, and obtain mixed solution 5 after the reaction is completed, for later use;

[0065] S6. Take 30 mL of diethyl ether, add it to mixed solution 5, collect the polymer precipitate, then wash the polymer precipitate with deionized water, and then vacuum dry the polymer precipitate at room temperature to finally obtain the binder powder with a number average molecular weight of 210,000.

[0066] Comparative Example 1

[0067] S1. Add 40 mmol of 4,4-diaminodiphenyl ether to a two-necked round-bottom flask, then add 24 mL of N,N-dimethylformamide solvent, and stir at room temperature until it is completely dissolved to obtain solution 1, which is ready for use.

[0068] S2. Take 10 mmol of benzoic acid dianhydride and dissolve it in 7 mL of N,N-dimethylformamide solvent at 0 °C to obtain solution 2, which is ready for use.

[0069] S3. Add solution 2 from step S2 dropwise to solution 1 from step S1, stir and react at room temperature for 15 h, and obtain mixed solution 3 after the reaction is completed, for later use;

[0070] S4. Take 25 mL of diethyl ether, add it to mixed solution 3, collect the polymer precipitate, then wash the polymer precipitate with deionized water, and then vacuum dry the polymer precipitate at room temperature to finally obtain the binder powder with a number average molecular weight of 180,000.

[0071] Comparative Example 2

[0072] S1. Take 10 mmol of 3,3-diaminobenzidine and add it to a double-necked round-bottom flask. Then add 6 mL of N,N-dimethylformamide solvent and stir at room temperature until it is completely dissolved to obtain solution 1 for later use.

[0073] S2. Take 5 mmol of benzoic acid dianhydride and dissolve it in 4 mL of N,N-dimethylformamide solvent at 0 °C to obtain solution 2, which is ready for use.

[0074] S3. Add solution 2 from step S2 dropwise to solution 1 from step S1, stir and react at room temperature for 15 h, and obtain mixed solution 3 after the reaction is completed, for later use;

[0075] S4. Take 10 mL of diethyl ether, add it to mixed solution 3, collect the polymer precipitate, then wash the polymer precipitate with deionized water, and then vacuum dry the polymer precipitate at room temperature to finally obtain the binder powder with a number average molecular weight of 270,000.

[0076] Comparative Example 3

[0077] S1. Take 10 mmol of 4,4-diaminodiphenyl ether and 10 mmol of 3,3-diaminobenzidine and add them to a double-necked round-bottom flask. Then add 12 mL of N,N-dimethylformamide solvent and stir at room temperature until completely dissolved to obtain solution 1 for later use.

[0078] S2. Take 7.5 mmol of benzoic acid dianhydride and dissolve it in 6 mL of N,N-dimethylformamide solvent at 0 °C to obtain solution 2, which is ready for use.

[0079] S3. Add solution 2 from step S2 dropwise to solution 1 from step S1, stir and react at room temperature for 15 h, and obtain mixed solution 3 after the reaction is completed, for later use;

[0080] S4. Take 15 mL of diethyl ether, add it to mixed solution 3, collect the polymer precipitate, then wash the polymer precipitate with deionized water, and then vacuum dry the polymer precipitate at room temperature to finally obtain the binder powder with a number average molecular weight of 240,000.

[0081] Comparative Example 4

[0082] S1. Add 80 mmol of 4,4-diaminodiphenyl ether and 10 mmol of 3,3-diaminobenzidine to a double-necked round-bottom flask, then add 55 mL of N,N-dimethylformamide solvent, and stir at room temperature until completely dissolved to obtain solution 1, which is ready for use.

[0083] S2. Take 25 mmol of benzoic acid dianhydride and dissolve it in 17 mL of N,N-dimethylformamide solvent at 0 °C to obtain solution 2, which is ready for use.

[0084] S3. Add solution 2 from step S2 dropwise to solution 1 from step S1, stir and react at room temperature for 15 h, and obtain mixed solution 3 after the reaction is completed, for later use;

[0085] S4. Take 45 mL of diethyl ether, add it to mixed solution 3, collect the polymer precipitate, then wash the polymer precipitate with deionized water, and then vacuum dry the polymer precipitate at room temperature to finally obtain the binder powder with a number average molecular weight of 195,000.

[0086] Performance testing

[0087] 1. Preparation of lithium-ion batteries

[0088] Lithium-ion batteries are prepared according to the following process steps:

[0089] (1) Preparation of negative electrode

[0090] Using silicon carbon powder as the negative electrode active material, the binder prepared in the above examples and comparative examples was mixed with conductive agent acetylene black and thickener CMC (sodium carboxymethyl cellulose). The mass ratio of silicon carbon powder negative electrode active material, binder, conductive agent acetylene black and thickener CMC was 96.4:1.4:1:1.2. Deionized water was added as solvent, and the mixture was stirred under vacuum until the system was homogeneous. Then, it was sieved through a 150-mesh sieve to obtain a silicon negative electrode slurry with good uniformity.

[0091] Using copper foil as the current collector, the silicon anode slurry obtained above is coated onto both surfaces of the copper foil using an automatic coating machine. After drying at 85°C, it is rolled, and then the electrode is die-cut using an automatic die-cutting machine to obtain the silicon anode electrode sheet.

[0092] (2) Preparation of positive electrode sheet

[0093] Take ternary cathode material NCM (lithium nickel cobalt manganese oxide) powder, binder PVDF (polyvinylidene fluoride), and conductive agent acetylene black. According to the mass ratio, ternary cathode material NCM: conductive agent acetylene black: binder PVDF = 96:2:2; After mixing the above materials, add solvent N-methylpyrrolidone and stir under vacuum until the system is homogeneous. Then, sieve it through a 150-mesh sieve to obtain a cathode slurry with good uniformity.

[0094] Using Al foil as the current collector, the above-obtained positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil using an automatic coating machine. After drying at 120°C, it is rolled, and then the electrode sheet is die-cut by an automatic die-cutting machine to obtain the positive electrode sheet.

[0095] (3) Preparation of electrolyte

[0096] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0097] (4) Preparation of the separating membrane

[0098] Polyethylene film was chosen as the separator.

[0099] (5) Battery assembly

[0100] The negative electrode sheet, positive electrode sheet, and separator obtained above are stacked in a "Z" shape on a fully automatic stacking machine, with a stacking layer of 5 layers. Then, the positive and negative electrode tabs are pre-welded and refined using a laser spot welding machine. Subsequently, they are encapsulated with aluminum-plastic film, vacuum baked, and transferred to a dew point controlled environment. The electrolyte obtained above is then injected, and the battery is sealed to obtain a lithium-ion battery.

[0101] 1. Electrode performance testing

[0102] Adhesion test

[0103] Cut the negative electrode sheet into test specimens measuring 20mm × 100mm and set aside. Adhere one side of the negative electrode film to the electrode sheet with double-sided adhesive and press firmly with a roller to ensure complete adhesion between the adhesive and the electrode sheet. Adhere the other side of the double-sided adhesive to the stainless steel surface. Bend one end of the specimen in the opposite direction at a bending angle of 180°. Use a high-speed rail tensile testing machine. Fix one end of the stainless steel specimen to the lower clamp of the tensile testing machine, and fix the bent end of the specimen to the upper clamp. Adjust the specimen angle to ensure the upper and lower ends are vertical. Then, stretch the specimen at a speed of 50mm / min until the current collector is completely peeled off from the negative electrode film. Record the displacement and force during the process. Divide the force at equilibrium by the width of the electrode sheet adhered to the double-sided adhesive (the width direction of the electrode sheet is perpendicular to the peeling direction) as the adhesive force per unit length of the electrode sheet. In this test, the width of the electrode sheet was 20mm.

[0104] Thickness expansion rate

[0105] The lithium-ion battery was subjected to 100 repeated charge-discharge cycles at a current density of 0.1C within the charge-discharge range of 0.005V to 1.5V. The electrode thickness expansion rate after 100 cycles was obtained. Electrode thickness expansion rate = (negative electrode thickness after cycle - initial negative electrode thickness) / (initial negative electrode thickness) × 100%.

[0106] 2. Battery performance test

[0107] Cyclic performance test:

[0108] At 25℃, with the voltage range set to 2.5-4.3V, the prepared battery was charged and discharged at a 1C rate, and a full charge and discharge cycle test was performed for 1000 cycles. The capacity retention rate was recorded.

[0109] The performance test results of the above embodiments and comparative examples are shown in Table 1 below.

[0110] Table 1

[0111]

[0112] As shown in Table 1, the binders prepared in Examples 1-3 were used to prepare negative electrode sheets. Through the above-mentioned adhesion strength test, the adhesion strength was ≥2.4 N / m; through the above-mentioned negative electrode sheet thickness expansion rate test, the thickness expansion rate of the negative electrode sheets was ≤155%. The binders prepared in Examples 1-3 were used to prepare lithium-ion batteries. Through the above-mentioned cycle performance test, the cycle capacity retention rate was ≥88%. The technical effects of the binders prepared in Examples 1-3 fully demonstrate that the binders prepared in this application can achieve precise control of the soft-hard balance of polyamide polymer binders, thereby effectively suppressing the volume expansion of Si particles in the negative electrode active material, while retaining elasticity and playing a bonding role, achieving volume expansion / contraction recovery of the silicon-based negative electrode during cycling.

[0113] Compared to Example 1, in the preparation method of Example 4, the molar ratio of total amino groups in the aryl-containing diamine and polyamine to anhydride groups in the diacid anhydride was 1:2. During the polymerization reaction, the amino groups in the aryl-containing diamine and polyamine almost completely reacted, leaving almost no remaining amino groups to form a strong bond with the Si particles, thus reducing the adhesion performance to the Si particles and weakening the electrical performance of the silicon-containing anode. Specifically, the binder prepared in Example 4 was used to prepare the anode sheet. The adhesion strength test showed a value of 2.3 N / m (less than 2.5 N / m in Example 1); the thickness expansion rate of the anode sheet was 157% (greater than 150% in Example 1). The binder prepared in Example 4 was used to prepare a lithium-ion battery. The cycle performance test showed a cycle capacity retention rate of 87% (less than 90% in Example 1).

[0114] Compared to Example 1, the polymerization reaction time in the preparation method of Example 5 was 1 h, less than the 15 h in Example 1. The number-average molecular weight of the binder prepared in Example 5 was 190,000 (less than 210,000 in Example 1, and also less than the preferred range of 200,000-600,000 g / mol for the number-average molecular weight of the binder). The lower number-average molecular weight of the binder prepared in Example 5 resulted in fewer branched cross-linked bonding structures, reduced adhesive strength, poorer formation of conductive networks, and decreased electrical performance of the silicon-containing negative electrode. Specifically, the binder prepared in Example 5 was used to prepare the negative electrode sheet. The adhesive strength test showed a strength of 2.3 N / m (less than 2.5 N / m in Example 1); the thickness expansion rate of the negative electrode sheet was 156% (greater than 150% in Example 1). The binder prepared in Example 5 was used to prepare a lithium-ion battery. The cycle performance test showed a cycle capacity retention rate of 86% (less than 90% in Example 1).

[0115] Compared to Example 1, the preparation method of Example 6 differs from that of Example 1. In Example 6, the polymerization reaction involves first reacting 4,4-diaminodiphenyl ether (an aryl-containing diamine) with benzoic acid dianhydride (a diacid anhydride), followed by the addition of 3,3-diaminobenzidine (an aryl-containing polyamine). The preparation method of Example 6 results in different probabilities for the aryl-containing diamine—4,4-diaminodiphenyl ether—and the aryl-containing polyamine—3,3-diaminobenzidine—to participate in the reaction with the diacid anhydride—benzoic acid dianhydride. This makes it difficult to form a copolymer of aryl-containing diamines and aryl-containing polyamines according to the stoichiometric ratio of the raw materials, and makes it harder to achieve precise control of the soft-hard balance in polyamide polymer binders. The binder prepared in Example 6 was used to prepare the negative electrode sheet. The adhesion strength was 2.2 N / m (less than 2.5 N / m in Example 1) in the adhesion strength test. The thickness expansion rate of the negative electrode sheet was 158% (greater than 150% in Example 1) in the thickness expansion rate test. The binder prepared in Example 6 was used to prepare a lithium-ion battery. The cycle performance retention rate was 85% (less than 90% in Example 1) in the cycle performance test.

[0116] Compared to Example 1, the preparation method of Comparative Example 1 only used 4,4-diaminodiphenyl ether (an aryl-containing diamine). This means the binder prepared in Comparative Example 1 only has soft segments, resulting in a lower skeleton strength and limited resistance to the volume expansion of the Si particles, the negative electrode active material. Specifically, the binder prepared in Comparative Example 1 was used to prepare the negative electrode sheet. The adhesion strength test showed a value of 1.7 N / m (less than the 2.5 N / m in Example 1). The thickness expansion rate of the negative electrode sheet was 168% (greater than the 150% in Example 1). The binder prepared in Comparative Example 1 was used to prepare a lithium-ion battery. The cycle performance test showed a cycle capacity retention of 80% (less than the 90% in Example 1).

[0117] Compared to Example 1, the preparation method of Comparative Example 2 only used 3,3-diaminobenzidine (an aryl polyamine). This means the binder prepared in Comparative Example 2 only has hard segments. Aromatic polymers, due to their strong π-π bond interactions, possess a rigid and ordered polymer skeleton structure. This unique structure endows it with excellent tensile strength, which can withstand the large volume expansion of silicon particles and prevent the silicon particles from losing connection with the conductive network during charging and discharging. However, excessively high tensile strength will cause the binder to lose its elasticity and fail to perform its function. The binder prepared in Comparative Example 2 was used to prepare the negative electrode sheet. The adhesion strength test showed a strength of 1.6 N / m (less than 2.5 N / m in Example 1). The thickness expansion rate of the negative electrode sheet was 169% (greater than 150% in Example 1). The binder prepared in Comparative Example 2 was used to prepare a lithium-ion battery. The cycle performance test showed a cycle capacity retention of 79% (less than 90% in Example 1).

[0118] Compared to Example 1, Comparative Example 3 used less 4,4-diaminodiphenyl ether (an aryl-containing diamine) in its preparation method. This means the binder prepared in Comparative Example 3 has fewer soft segments and more hard segments, resulting in excellent tensile strength. This strength can withstand the large volume expansion of silicon particles and prevent the silicon particles from losing connection with the conductive network during charging and discharging. However, excessively high tensile strength can cause the binder to lose its elasticity and fail to perform its function. The binder prepared in Comparative Example 3 was used to prepare the negative electrode sheet. The adhesion strength test showed a value of 1.9 N / m (less than 2.5 N / m in Example 1). The thickness expansion rate of the negative electrode sheet was 158% (greater than 150% in Example 1). The binder prepared in Comparative Example 3 was used to prepare a lithium-ion battery. The cycle performance test showed a cycle capacity retention rate of 83% (less than 90% in Example 1).

[0119] Compared to Example 1, the preparation method of Comparative Example 4 used less 3,3-diaminobenzidine (an aryl-containing polyamine), meaning the binder prepared in Comparative Example 4 had fewer hard segments and more soft segments, resulting in a lower skeleton strength and limited resistance to the volume expansion of Si particles. Specifically, the binder prepared in Comparative Example 4 was used to prepare the negative electrode sheet, and the adhesion strength was 2.1 N / m (less than 2.5 N / m in Example 1) according to the adhesion strength test. The thickness expansion rate of the negative electrode sheet was 162% (greater than 150% in Example 1) according to the thickness expansion rate test. The binder prepared in Comparative Example 4 was used to prepare a lithium-ion battery, and the cycle performance retention rate was 82% (less than 90% in Example 1) according to the cycle performance test.

Claims

1. An adhesive, said adhesive being a polyamide polymer, comprising repeating structural unit A of formula (I) and repeating structural unit B of formula (II): Formula (I) Equation (II), in, R1 is an aryl group that does not contain an amide group or an amino group; R2 includes an aryl group containing at least one amide group or an aryl group containing at least one amino group; The molar ratio of the repeating structural unit A to the repeating structural unit B is (2:1) to (6:1).

2. The adhesive according to claim 1, wherein, The R2 includes an aryl group containing at least one amino group.

3. The adhesive according to claim 1, wherein, The number average molecular weight of the adhesive is 200,000-600,000 g / mol.

4. The adhesive according to claim 1, wherein, The aryl diamine providing the repeating structural unit A includes at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, and 3,4'-diaminodiphenyl ether.

5. The adhesive according to claim 1, wherein, The aryl polyamine providing the repeating structural unit B includes at least one of 3,3'-diaminobenzidine, 1,2,4,5-phenyltetramine, and 3,3,4,4-tetraaminodiphenyl ether.

6. A method for preparing an adhesive, comprising the following steps: S1. Mix the aryl-containing diamine, the aryl-containing polyamine, and an organic solvent to prepare solution 1; S2. Mix the diacid anhydride and the organic solvent to prepare solution 2; S3. Mix and react the solutions 1 and 2 to obtain solution 3; S4. Add an ether solvent, collect the precipitate, and obtain the binder; The molar ratio of the aryl-containing diamine to the aryl-containing polyamine is (2:1) to (6:1).

7. The method for preparing the adhesive according to claim 6, wherein, The dicarboxylic anhydride includes at least one of pyromellitic dianhydride, 4,4'-biphenyl ether dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic acid dianhydride, hexafluoro dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride, 4,4'-(4,4'-isopropylidene diphenoxy)bis(phthalic anhydride), and p-phenylene-bisphenyltriester dianhydride.

8. The method for preparing the adhesive according to claim 6, wherein, The molar ratio of the total amino groups in the aryl-containing diamine and polyamine to the anhydride groups in the diacid anhydride is (3~6):

1.

9. The method for preparing the adhesive according to claim 6, wherein, In step S2, the temperature at which the organic acid anhydride and the organic solvent are mixed is -30~5℃.

10. A lithium-ion battery comprising the binder as described in any one of claims 1 to 5 or the binder prepared by the preparation method described in any one of claims 6 to 9.

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