A dual-network structured binder for silicon-based anodes of lithium-ion batteries and a preparation method and application thereof

Abstract

The application belongs to the technical field of lithium batteries, and discloses a double-network structure binder for a silicon-based negative electrode of a lithium ion battery and a preparation method and application thereof. The double-network structure binder is abbreviated as SGLT, wherein silk glue protein is dissolved in water, glutaraldehyde and an HCl solution are added to prepare an SG solution, then tannic acid and thioctic acid are added, in-situ polymerization is carried out at 120-180 DEG C, and the network LT is prepared based on the network SG formed by the tannic acid and the thioctic acid. The application first crosslinks to form a hard network SG, and then forms a network LT based on the network SG. The hard network SG serves as a stable skeleton and effectively inhibits the volume expansion of the electrode structure. The high-elasticity soft LT network serves as a buffer layer and relieves the stress generated by the volume expansion in the electrode. The binder has excellent mechanical properties, effectively inhibits the volume expansion of the SiO x negative electrode during the charge-discharge cycle process, and ensures the cycle stability of the electrode.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a dual-network structure binder for silicon-based anodes of lithium-ion batteries, its preparation method, and its application. Background Technology

[0002] With the development of new energy electric vehicles, the development of high-energy-density, high-power, and long-life anode materials has become one of the research hotspots for lithium-ion batteries. Currently, the main commercial lithium-ion battery anode material is graphite, with a theoretical specific capacity of only 372 mAh / g. Among these, silicon-oxygen (SiO₂) materials possess high theoretical specific capacity (2600 mAh / g) and low operating voltage. x Anode materials have attracted much attention. However, in the reversible delithiation and lithium insertion process, SiO₂... x The material will undergo significant volume expansion and form an unstable solid electrolyte interphase (SEI) film, leading to problems such as silicon oxide particle breakage, damage to the conductive network and battery capacity decay, which in turn affects the battery's cycle life and capacity.

[0003] Among numerous solutions, optimizing the binder has proven to be a cost-effective approach. Traditional binders, such as polyvinylidene fluoride (PVDF), are unsuitable for silicon-based anodes due to their weak van der Waals forces with silicon oxide, making them unable to withstand the significant volume expansion of the silicon oxide anode during charge and discharge. Furthermore, silicon-based anode binders with a single linear structure (such as linear polymer chains) are prone to irreversible slippage during continuous volume changes in the silicon oxide anode due to weak interchain interactions, leading to electrode cracking and decreased electrochemical performance. Elastic polymers are the preferred binders for silicon-based anodes because they undergo significant volume changes during charge and discharge. Soft elastic polymer binders lack sufficient stiffness, resulting in significant thickness changes in the silicon-based anode during charge and discharge. Plastic polymer binders can effectively constrain the volume changes of the silicon-based anode, stabilizing its thickness and maintaining the electrode structure. Therefore, designing binders with multi-network composite structures will effectively alleviate the problem of significant volume expansion of the silicon oxide anode during charge and discharge, ensuring the integrity of the electrode structure and thus guaranteeing the performance of SiO₂. x Electrochemical stability and cycling performance of the negative electrode. Summary of the Invention

[0004] This invention addresses the problem in existing technologies where "single linear silicon anode binders are linear polymer chains with weak inter-chain interactions, poor mechanical properties, and are prone to irreversible sliding during continuous volume changes in the silicon-oxygen anode, leading to electrode cracking and decreased electrochemical performance." The primary objective is to provide a dual-network structure binder for silicon-based anodes in lithium-ion batteries. This binder adds a complementary network to one network structure, forming a more complex and stable cross-linked structure, effectively mitigating the problems associated with SiO₂. x The volume expansion problem of the negative electrode during charging and discharging is addressed. The rigid SG network in the dual-network structure acts as a stabilizing framework, effectively suppressing the volume expansion of the electrode structure. The highly elastic soft LT network acts as a buffer layer, alleviating the stress caused by volume expansion within the electrode. The dual-network structure binder possesses excellent mechanical properties, thus effectively suppressing SiO₂ formation. x The volume expansion of the negative electrode during charge-discharge cycles ensures the cyclic stability of the electrode.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned dual-network structure binder for silicon-based anodes in lithium-ion batteries. This method forms a binder SGLT with a dual-network structure exhibiting elastic / plastic effects through hydrogen bonding crosslinking of SG and LT.

[0006] Another object of the present invention is to provide the application of the above-mentioned dual-network structure binder for silicon-based anodes of lithium-ion batteries.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A dual-network structure binder for silicon-based anodes in lithium-ion batteries, abbreviated as SGLT, is prepared by first dissolving sericin in water, adding glutaraldehyde and HCl solution to obtain SG solution, then adding tannic acid and lipoic acid, and performing in-situ polymerization at 120-180℃, whereby tannic acid and lipoic acid form network LT based on network SG.

[0009] Preferably, the mass ratio of the sericin, glutaraldehyde, tannic acid and lipoic acid is 1:(0.062-0.125):(0.2-1):(0.01-0.04); and the mass ratio of the glutaraldehyde and HCl solution is (2-6):1.

[0010] Preferably, the mass ratio of the sericin to water is 1:(20-50); the molecular weight of the sericin is 2000-100000; and the concentration of the HCl solution is 10-16 mol / L.

[0011] Preferably, the in-situ polymerization time is 2 to 4 hours.

[0012] The preparation method of the double-network structure binder for the silicon-based anode of a lithium-ion battery includes the following steps:

[0013] S1. Stir sericin in water, then add glutaraldehyde and a group activator to carry out a cross-linking reaction to obtain an SG solution;

[0014] S2. Add tannic acid and lipoic acid to the SG solution, and carry out in-situ polymerization at 120-180 °C. Tannic acid and lipoic acid form a network LT based on the network SG to obtain a binder with a double-network structure.

[0015] A negative electrode is prepared by mixing the double-network structure binder, an active substance SiO x , 0 < x < 2, a conductive agent and water, then stirring with water to obtain a uniformly dispersed electrode paste, coating the electrode paste on a copper foil, and carrying out in-situ polymerization at 120-180 °C and drying.

[0016] Preferably, the conductive agent is conductive carbon black, carbon nanotubes or conductive graphite; the mass ratio of the active substance SiO x , the conductive agent and the double-network structure binder is (7-8):(1-2):1; the stirring time is 6-8 h, the drying temperature is 60-80 °C, and the drying time is 12-36 h.

[0017] Application of the negative electrode in a lithium-ion battery.

[0018] Since sericin rich in polar amino acids has hydrophilicity and residue sites that are easily modified, it is relatively uniformly distributed when dissolved in water; glutaraldehyde is a homobifunctional cross-linking agent, which is easily soluble in water and can be used as a protein cross-linking agent. The cross-linking characteristics are high activity, fast reaction, high binding amount and stable product. Lipoic acid is a biomolecule with a special structure, including two types of dynamic bonds: the dynamic covalent disulfide bond in the five-membered ring and the non-covalent hydrogen bond of the carboxyl group. The double-network structure binder utilizes non-covalent interactions between molecules, such as hydrogen bonds, van der Waals forces and ionic interactions, etc., to achieve an efficient bonding effect. Through the hydrogen bond cross-linking of the SG network and the LT network, a binder SGLT with a double-network structure is formed, improving the mechanical strength of the binder and realizing the cycle stability of the silicon-based anode.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The binder SGLT of the present invention has a double-network structure with an elastic / plastic effect. This is because tannic acid and lipoic acid form a network LT based on the network SG, and a double-network structure is formed through a hydrogen bond cross-linking reaction. The interaction between the network SG and the network LT has higher mechanical properties, enabling the electrode to maintain good integrity during cycling.

[0021] 2. The dual-network structure binder of the present invention and SiO x The particles have abundant binding sites, allowing the binder to bind with SiO₂. x The particles have strong interfacial bonding ability, SiO x The negative electrode can better withstand volume changes during electrode charging and discharging. Furthermore, the two networks are cross-linked via hydrogen bonds. Therefore, due to the self-healing properties, bonding ability, and mechanical strength of this binder, it is suitable for use in SiO₂. x The negative electrode achieves stable long-cycle performance.

[0022] 3. The lipoic acid in the dual-network structure binder of the present invention contains reversible dynamic covalent disulfide bonds, which can reform after breaking. The dual-network structure, formed by cross-linking the two networks through hydrogen bonds, can maximize the mechanical properties of the binder and effectively suppress SiO2 during electrode charging and discharging. x The volume expansion of the negative electrode material causes SiO to... x The negative electrode exhibits good cycle stability.

[0023] 4. In this invention, tannic acid and lipoic acid crosslink to form a highly elastic soft network LT, which, together with sericin, glutaraldehyde solution, and hydrochloric acid, forms a hard network SG. The hard network SG acts as a stable framework, effectively suppressing the volume expansion problem of the electrode structure. The highly elastic soft network LT acts as a buffer layer, alleviating the stress caused by volume expansion inside the electrode. The dual-network structure binder has excellent mechanical properties, thereby effectively suppressing SiO2. x The volume expansion of the negative electrode during charge-discharge cycles ensures the cycle stability of the electrode. The dual-network structure binder not only provides stronger mechanical strength and elasticity, but also enhances the adhesion between the binder and silicon particles and current collectors, thereby significantly improving the cycle life and capacity retention of the battery. Attached Figure Description

[0024] Figure 1 This is a comparison graph of the cycle performance of the button cell in Application Example 1 and Application Comparative Example 1. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments, but these should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0026] Example 1

[0027] 1. Dissolve 0.15 g of sericin with a molecular weight of 2000 in 4.85 g of water by magnetic stirring, then add 0.0334 g of 50 wt% glutaraldehyde aqueous solution and 50 μL of 12 mol / L hydrochloric acid, and stir and react for 1 h to obtain a 5 wt% SG solution;

[0028] 2. Add 9.62 mg of lipoic acid and 0.38 mg of tannic acid to 200 mL of 5 wt% SG solution, and carry out in-situ polymerization at 150 °C for 2 h. Tannic acid and lipoic acid form a network LT based on the network SG to obtain a binder with a double network structure, abbreviated as SGLT.

[0029] Example 2

[0030] 1. Dissolve 0.25 g of sericin with a molecular weight of 2000 in 4.75 g of water by magnetic stirring, then add 0.05 g of 50 wt% glutaraldehyde aqueous solution and 50 μL of 12 mol / L hydrochloric acid, and stir and react for 1 h to obtain a 5 wt% network SG solution;

[0031] 2. Add 9.62 mg of lipoic acid and 0.38 mg of tannic acid to 200 mL of 5 wt% SG solution, and carry out in-situ polymerization at 150 °C for 2 h. Tannic acid and lipoic acid form a network LT based on the network SG to obtain a binder with a double network structure, abbreviated as SGLT.

[0032] Comparative Example 1

[0033] Add 0.15 g of sericin with a molecular weight of 2000 to 4.85 g of water, then add 0.05 g of 50 wt% glutaraldehyde aqueous solution and 50 μL of 12 mol / L hydrochloric acid, and stir and react for 1 h to obtain a 5 wt% SG binder.

[0034] Application Example 1

[0035] 1. Add 9.62 mg of lipoic acid and 0.38 mg of tannic acid in the preparation process of the binder SGLT in Example 1 to 200 mL of 5 wt% SG solution, and put it into a defoaming blender with the active substance SiO x (0 < x < 2) and the conductive agent Super P and stir to obtain a uniformly dispersed electrode paste;

[0036] 2. Coating the electrode paste on a copper foil and carrying out an in-situ cross-linking reaction at 150 °C for 2 h to obtain a pole piece with a binder having a double network structure.

[0037] 3. Cut the dried electrode from Example 1 into 12mm diameter circles to serve as the negative electrode. Transfer them into an argon-filled glove box. Use a lithium sheet as the counter electrode. The electrolyte consists of 10wt% fluoroethylene carbonate (FEC) and 1wt% vinylene carbonate (VC) as additives, with 1 mmol / L LiPF6 dissolved in ethylene carbonate (DEC) and diethyl carbonate (EC), where the volume ratio of DEC to EC is 1:1. Assemble a CR2032 coin cell, abbreviated as SGLT@SiO. x (0 <x<2)。

[0038] Application Example 2

[0039] 1. During the preparation of the SGLT binder in Example 2, 9.62 mg of lipoic acid and 0.38 mg of tannic acid were added to 200 mL of 5 wt% SG solution, and then reacted with the active material SiO2. x The conductive agent Super P was added to a degassing mixer and stirred to obtain a uniformly dispersed electrode slurry.

[0040] 2. The electrode paste was coated onto a copper foil and subjected to an in-situ crosslinking reaction at 150°C for 2 hours to obtain an electrode with a dual-network structure binder (SGLT).

[0041] Application Comparative Example 1

[0042] 1. Add active material SiO at a mass ratio of 7:2:1 x The conductive agent SuperP was mixed with 5 wt% of the SG binder of Comparative Example 1, and 200 μL of water was added. The mixture was stirred for 6 hours to obtain a uniformly dispersed electrode slurry.

[0043] 2. Coat the electrode paste onto copper foil, dry it under vacuum at 80°C for 12 hours, and cut it into circular electrode sheets with a diameter of 12 mm.

[0044] 3. Transfer the dried electrode to an argon-filled glove box. Using a lithium sheet as the counter electrode and an electrolyte (containing 10 wt% fluoroethylene carbonate (FEC) and 1 wt% vinylene carbonate (VC) as additives, with 1 mmol / L LiPF6 dissolved in ethylene carbonate (DEC) and diethyl carbonate (EC), where the volume ratio of DEC to EC is 1:1), assemble a CR2032 coin cell, abbreviated as SG@SiO. x (0 <x<2)。

[0045] The CR2032 coin cells assembled in Application Example 1 and Comparative Example 1 were left to stand at 28°C for 10 hours before their electrochemical performance was tested using a constant current test system in the Newway testing system. The test conditions were: current density 400 mA / g; voltage window 0.01-1.5 V. Figure 1This is a comparison graph showing the cycle performance of the CR2032 coin cells assembled in Application Example 1 and Comparative Example 1. Figure 1 It can be seen that the coin cell of Comparative Example 1, at a current density of 400 mA / g, exhibits a discharge capacity decay of 681 mAh / g after 100 cycles. In contrast, the coin cell of Application Example 1 has an initial discharge specific capacity exceeding 2100 mAh / g, an initial coulombic efficiency exceeding 60%, and maintains a capacity of 1061 mAh / g after 100 cycles, demonstrating higher discharge capacity and better cycle stability. These results indicate that the dual-network structure binder SGLT of this invention can enable SiO2... x The negative electrode exhibits good cycle stability. Furthermore, the dual-network structure binder not only provides greater mechanical strength and elasticity but also enhances the adhesion between the binder and the silicon particles and current collector, thereby significantly improving the battery's cycle life and capacity retention.

[0046] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A dual-network structure binder for silicon-based anodes in lithium-ion batteries, characterized in that, The dual-network structure adhesive, abbreviated as SGLT, is prepared by first dissolving sericin in water, adding glutaraldehyde and HCl solution to obtain SG solution, and then adding tannic acid and lipoic acid. In-situ polymerization is then carried out at 120-180℃, where tannic acid and lipoic acid form network LT based on the SG network. The mass ratio of sericin, glutaraldehyde, tannic acid, and lipoic acid is 1:(0.062-0.125):(0.2-1):(0.01-0.04); the mass ratio of glutaraldehyde to HCl solution is (2-6):1; the mass ratio of sericin to water is 1:(20-50); the molecular weight of sericin is 2000-100000; and the concentration of the HCl solution is 10-16 mol / L.

2. The dual-network structure binder for silicon-based anodes of lithium-ion batteries according to claim 1, characterized in that, The in-situ polymerization time is 2-4 hours.

3. The method for preparing the dual-network structure binder for silicon-based anodes of lithium-ion batteries according to claim 1 or 2, characterized in that, Includes the following steps: S1. Add water to sericin and stir, then add glutaraldehyde and a group activator to carry out a cross-linking reaction to obtain SG solution; S2. Tannic acid and lipoic acid are added to the SG solution and polymerized in situ at 120~180℃. Tannic acid and lipoic acid form a network LT based on the network SG and are cross-linked by hydrogen bonding to obtain a binder with a dual network structure.

4. A negative electrode, characterized in that, The negative electrode is made of the dual-network structure binder and active material SiO as described in claim 1 or 2. x ,0< x <2. The conductive agent and water are mixed, and then water is added and stirred to obtain a uniformly dispersed electrode slurry. The electrode slurry is coated onto a copper foil, polymerized in situ at 120~180℃, and then dried to obtain the final product.

5. The negative electrode according to claim 4, characterized in that, The conductive agent is conductive carbon black, carbon nanotubes, or conductive graphite; the active material is SiO₂. x The mass ratio of conductive agent and dual-network structure binder is (7~8):(1~2):1; the stirring time is 6~8 h, the drying temperature is 60~80 ℃, and the drying time is 12~36 h.

6. The application of the negative electrode according to claim 4 or 5 in a lithium-ion battery.

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