Preparation Method of a Novel Multifunctional Polymer Binder for Silicon-Based Anodes

Abstract

The present invention discloses a preparation method of a novel multifunctional polymer binder for a silicon-based anode of a lithium-ion battery. The polymer binder is prepared by a two-step method: In the first step, the carboxylic acid groups at both ends of 3,3'-dithiobispropionic acid and polyethylene glycol bis-carboxymethyl ether are converted into more reactive acyl chloride groups, and then the product is subjected to an interfacial polymerization reaction with [1,1'-biphenyl]-4,4'-diamino-2,2'-disulfonic acid to obtain a novel multifunctional polymer binder. The binder of the present invention can effectively inhibit the volume expansion of the silicon-based anode and improve the cycle stability and first-cycle Coulombic efficiency of the silicon-based lithium-ion battery. The method of the present invention is carried out at room temperature, with controllable cost and is suitable for large-scale application in silicon-based anodes.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion battery negative electrode binder, and in particular to a method for preparing a novel multifunctional polymer binder for silicon-based negative electrode. Background Art

[0002] Considering the actual demand for high energy density lithium-ion batteries, silicon (Si) has a high theoretical specific capacity (4200 mAhg -1 ), moderate voltage platform (< 0.5 V vs. Li + / Li) and abundant resource storage, it has become a promising new generation of lithium-ion battery negative electrode material. In addition to electrode material development and electrolyte optimization, binder design is considered to be a cost-effective strategy to improve the stability of silicon-based electrode structures. Traditional commercial polyvinylidene fluoride (PVDF) binders cannot alleviate the volume expansion of silicon particles during lithium insertion and delithiation due to weak van der Waals interactions, while some other commercial binders such as polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), etc. can improve the stability of silicon-based negative electrodes to a certain extent compared to PVDF, but the effect is limited. Therefore, it is of great significance to develop new and efficient silicon-based negative electrode polymer binders for lithium-ion batteries.

[0003] In the prior art, one patent document published in China, "a lithium-ion battery silicon-based negative electrode binder and a method for preparing a negative electrode sheet using the binder", has an authorization announcement number of CN109935832B, which includes a main binder and an auxiliary binder, the main binder is sodium alginate, and the auxiliary binder includes at least one of sodium carboxymethyl cellulose and styrene-butadiene rubber and gelatin; another patent document published in China, "a lithium-ion battery silicon-based negative electrode binder and a method for preparing a negative electrode sheet containing the binder", has an authorization announcement number of CN107959027B, and the binder is prepared by ultrasonically dispersing graphite oxide in water to obtain a graphene oxide (GO) aqueous dispersion, and then adding a modified SBR binder and stirring. The above two patents are still based on the modification of commercial binders, and the performance improvement of silicon-based negative electrodes is limited.

[0004] Although there are some reported cross-linked polymer binders with complex network structures that can form stronger connections with silicon, such as "Preparation Method of Silicon-Based Anode Binder for Lithium Batteries and the Binder, Authorization Publication No. CN109722190B", "Silicon-Based Anode Binder, Preparation Method Thereof and Application in Lithium-Ion Batteries, Authorization Publication No. CN110797538B" and "Silicon-Based Anode Binder for Lithium-Ion Batteries and Preparation Method and Application Thereof, Authorization Publication No. CN111785968B", etc., the single properties of these binders are not sufficient to simultaneously meet the various requirements of silicon electrodes, such as long-term cycling stability, fast ion conductivity, high first-cycle Coulombic efficiency and high mechanical strength, etc. Summary of the Invention

[0005] According to the defects and problems to be improved of the current silicon-based anode binder, the present invention proposes a preparation method of a novel multifunctional polymer binder for silicon-based anodes.

[0006] The principle of the present invention is to enhance the mechanical strength of the binder by constructing a hard phase with a cross-linked network to change the polymer structure, thereby alleviating the volume expansion of silicon in the lithiated state; using a representative substance of the soft phase, poly(ethylene oxide) (PEO)-based substance, to improve the ductility of the binder, thereby releasing the tensile stress in the lithiated state of the electrode; at the same time, the introduced PEO-based polyether monomer can provide an efficient charge transfer channel inside the electrode, thereby realizing the fast charge and discharge function for silicon-based lithium-ion batteries; prelithiation can provide an additional lithium source and improve the first-cycle Coulombic efficiency of the silicon-based anode.

[0007] The object of the present invention can be achieved by the following technical solutions:

[0008] A preparation method of a novel multifunctional polymer binder for silicon-based anodes, the preparation method of the polymer binder material is as follows: in the first step, 3,3'-dithiobis(propionic acid) (DPA), polyethylene glycol bis(carboxymethyl ether) (PEGCE) are reacted with a functional group-substituted chloride, and in the second step, the obtained product is subjected to an interfacial polymerization reaction with purified and lithiated [1,1'-biphenyl]-4,4'-diamine-2,2'-disulfonic acid (BDSA) to obtain the final polymer material, which is used as a binder to prepare a silicon-based anode for application in lithium-ion batteries. The preparation of this polymer includes the following steps:

[0009] (1) According to the molar amount, weigh 1-3 parts of DPA and 1-3 parts of PEGCE and disperse them in 10-50 ml of dichloromethane (DCM), add 6-18 parts of the functional group-substituted chloride and a catalyst, and react overnight at 50°C - 80°C. After the reaction is completed, remove the excess solvent by vacuum rotary evaporation, and then dissolve it in 50 ml of DCM again to obtain solution A.

[0010] (2) Weigh 2 - 6 parts of purified BDSA and 8 - 24 parts of lithium compound and dissolve them in 100 mL of deionized water to obtain solution B.

[0011] (3) The preparation method of solution C is to dissolve 2 - 6 parts of surfactant in 50 mL of DCM.

[0012] (4) The interfacial polymerization process is carried out in a high - speed stirrer. Before the reaction, nitrogen is blown into the high - speed stirrer in advance to protect the reaction. Mix solutions A, B, and C and stir at high speed at room temperature for 1 - 2 hours. After standing for 30 minutes, the solution is layered. Separate the aqueous solution and extract it twice with DCM. The extracted aqueous solution is subjected to vacuum rotary evaporation to increase the solution concentration, and then dropped into a poor solvent for precipitation. The precipitated product is vacuum - dried at 80 °C for 24 hours.

[0013] Preferably, in the preparation method of the novel multifunctional polymer binder for silicon - based anodes, the functional - group - substituted chloride is one or more of thionyl chloride (SOCl₂) or oxalyl chloride (COCl₂).

[0014] Preferably, in the preparation method of the novel multifunctional polymer binder for silicon - based anodes, the catalyst is one or more of N,N - dimethylformamide (DMF) or N,N - dimethylacetamide (DMAC).

[0015] Preferably, in the preparation method of the novel multifunctional polymer binder for silicon - based anodes, the lithium compound is one or more of lithium hydroxide hydrate (LiOH·H₂O), lithium bicarbonate (LiHCO₃), lithium oxalate (Li₂C₂O₄), or lithium carbonate (Li₂CO₃).

[0016] Preferably, in the preparation method of the novel multifunctional polymer binder for silicon - based anodes, the surfactant is one or more of PEG200, PEG300, PEG500 in the polyethylene glycol (PEG) series of substances.

[0017] Preferably, in the preparation method of the novel multifunctional polymer binder for silicon - based anodes, the poor solvent is a solvent that is miscible with water and has a polarity less than that of water, and can be one or more of acetone, tetrahydrofuran, N,N - dimethylformamide, ethanol, isopropanol.

[0018] The present invention coordinates the contradiction between high mechanical properties and good ionic conductivity through the autonomous design of a simple polymer structure. Novel polymers with high mechanical strength, good ionic conductivity, self-healing and extensibility are obtained by subjecting monomeric starting reactants with different functions to a two-step interfacial polymerization method. The polymer binder can inhibit the volume expansion of silicon-based materials, greatly improving the specific capacity, cycle stability, initial Coulombic efficiency and rate performance of silicon-based anodes. The preparation method of this multifunctional polymer binder is carried out at room temperature, with simple reactions and controllable costs, providing a cost-effective method for developing polymer binders for next-generation high-performance silicon-based anodes.

[0019] Advantages of the present invention:

[0020] The polymer binder in the present invention can effectively inhibit the volume expansion of the silicon-based anode during charge and discharge, maintain the mechanical stability of the silicon-based anode, and improve the initial cycle Coulombic efficiency of the electrode.

[0021] The polymer binder in the present invention improves the specific capacity, cycle stability and initial cycle Coulombic efficiency of the silicon-based anode.

[0022] The polymer binder in the present invention has a novel design and comprehensive functions, and is very suitable as a polymer binder for silicon-based anodes. Description of the Drawings

[0023] Figure 1 It is a comparative graph of the cycle performance of a lithium-ion half-cell of a silicon-based anode prepared with the polymer material prepared in Example 1 of the present invention and the commercially available PVDF purchased in Comparative Example 1 as a binder. Embodiments Examples

[0024] Weigh 1.5 parts of DPA and 1.5 parts of PEGCE and disperse them in 15 mL of DCM. Add 9 parts of SOCl2 and a drop of DMF as a catalyst and stir the reaction overnight at 50 °C. Rotavapor the solution under vacuum to remove the excess solvent, and then dissolve the remaining product after rotavaporation in 50 mL of DCM to obtain Solution A. Weigh 3 parts of purified BDSA and 12 parts of LiOH·H2O and dissolve them in 100 mL of deionized water to prepare Solution B. Weigh 3 parts of PEG 300 and dissolve them in 50 mL of DCM to obtain Solution C.

[0025] The interfacial polymerization process is carried out in a high-speed stirring container. Before the reaction, nitrogen is pre-injected into the high-speed stirring container to protect the reaction. Solutions A, B, and C are mixed and stirred at a speed of 8000 rpm for 1 hour at room temperature. After standing for 30 minutes, the solution is layered to obtain an aqueous solution, and the separated aqueous solution is extracted twice with DCM to remove the remaining reactive agents. The extracted aqueous solution is subjected to vacuum rotary evaporation to increase the solution concentration, and then the high-concentration product solution is dropped into acetone. The precipitated product is dried in vacuo at 80 °C for 24 hours.

[0026] Example 2

[0027] Weigh 2 parts of DPA and 1 part of PEGCE and disperse them in 20 mL of DCM. Add 9 parts of SOCl2 and a drop of DMCA as a catalyst and stir the reaction overnight at 50 °C. The solution is subjected to vacuum rotary evaporation to remove the excess solvent, and then the remaining product after rotary evaporation is dissolved in 50 mL of DCM to obtain solution A. Weigh 3 parts of purified BDSA and 12 parts of LiOH and dissolve them in 100 mL of deionized water to prepare solution B. Weigh 3 parts of PEG 300 and dissolve them in 50 mL of DCM to obtain solution C.

[0028] The interfacial polymerization process is carried out in a high-speed stirring container. Before the reaction, nitrogen is pre-injected into the high-speed stirring container to protect the reaction. Solutions A, B, and C are mixed and stirred at a speed of 8000 rpm for 1 hour at room temperature. After standing for 30 minutes, the solution is layered to obtain an aqueous solution, and the separated aqueous solution is extracted twice with DCM to remove the remaining reactive agents. The extracted aqueous solution is subjected to vacuum rotary evaporation to increase the solution concentration, and then the high-concentration product solution is dropped into acetone. The precipitated product is dried in vacuo at 80 °C for 24 hours.

[0029] Example 3

[0030] Weigh 1 part of DPA and 2 parts of PEGCE and disperse them in 30 mL of DCM. Add 9 parts of (COCl)2 and a drop of DMF as a catalyst and stir the reaction overnight at 50 °C. The solution is subjected to vacuum rotary evaporation to remove the excess solvent, and then the remaining product after rotary evaporation is dissolved in 50 mL of DCM to obtain solution A. Weigh 3 parts of purified BDSA and 12 parts of LiOH·H2O and dissolve them in 100 mL of deionized water to prepare solution B. Weigh 3 parts of PEG 200 and dissolve them in 50 mL of DCM to obtain solution C.

[0031] The interfacial polymerization process is carried out in a high-speed stirring container. Before the reaction, nitrogen is pre-injected into the high-speed stirring container to protect the reaction. Solutions A, B, and C are mixed and stirred at a speed of 8000 rpm at room temperature for 1 hour. After standing for 30 minutes, the solution is layered to obtain an aqueous solution, and the separated aqueous solution is extracted twice with DCM to remove the remaining reactive agents. The extracted aqueous solution is subjected to vacuum rotary evaporation to increase the solution concentration, and then the high-concentration product solution is dropped into acetone. The precipitated product is vacuum dried at 80 °C for 24 hours.

[0032] Example 4

[0033] Weigh 1.5 parts of DPA and 1.5 parts of PEGCE and disperse them in 50 mL of DCM. Add 9 parts of (COCl)2 and a drop of DMF as a catalyst and stir the reaction overnight at 50 °C. Vacuum rotary evaporate the solution to remove the excess solvent, and then dissolve the remaining product after rotary evaporation in 50 mL of DCM to obtain solution A. Weigh 3 parts of purified BDSA and 12 parts of lithium oxalate and dissolve them in 100 mL of deionized water to prepare solution B. Weigh 3 parts of PEG 300 and dissolve them in 50 mL of DCM to obtain solution C.

[0034] The interfacial polymerization process is carried out in a high-speed stirring container. Before the reaction, nitrogen is pre-injected into the high-speed stirring container to protect the reaction. Solutions A, B, and C are mixed and stirred at a speed of 8000 rpm at room temperature for 1 hour. After standing for 30 minutes, the solution is layered to obtain an aqueous solution, and the separated aqueous solution is extracted twice with DCM to remove the remaining reactive agents. The extracted aqueous solution is subjected to vacuum rotary evaporation to increase the solution concentration, and then the high-concentration product solution is dropped into tetrahydrofuran. The precipitated product is vacuum dried at 80 °C for 24 hours.

[0035] Example 5

[0036] Weigh 2 parts of DPA and 3 parts of PEGCE and disperse them in 50 mL of DCM. Add 15 parts of SOCl2 and a drop of DMF as a catalyst and stir the reaction overnight at 50 °C. Vacuum rotary evaporate the solution to remove the excess solvent, and then dissolve the remaining product after rotary evaporation in 50 mL of DCM to obtain solution A. Weigh 5 parts of purified BDSA and 10 parts of Li2CO3 and dissolve them in 100 mL of deionized water to prepare solution B. Weigh 5 parts of PEG 500 and dissolve them in 50 mL of DCM to obtain solution C.

[0037] The interfacial polymerization process is carried out in a high-speed stirring container. Before the reaction, nitrogen is pre-injected into the high-speed stirring container to protect the reaction. Solutions A, B, and C are mixed and stirred at a speed of 8000 rpm for 2 hours at room temperature. After standing for 30 minutes, the solution is layered to obtain an aqueous solution, and the separated aqueous solution is extracted twice with DCM to remove the remaining reactive surfactants. The extracted aqueous solution is subjected to vacuum rotary evaporation to increase the solution concentration, and then the high-concentration product solution is dropped into N,N-dimethylformamide. The precipitated product is vacuum dried at 80 °C for 24 hours.

[0038] Comparative Example 1

[0039] The comparative example in the present invention is a commercial PVDF binder (Mw = 53400) purchased from Sigma-Aldrich.

[0040] Test Example 1

[0041] The polymer material prepared in Example 1 and the commercial PVDF of Comparative Example 1 are used as binders and applied to the silicon negative electrode for electrochemical performance testing. The mass ratio of the components of the silicon negative electrode sheet is silicon nanoparticles: Super P: binder = 70:15:15 wt.%. The counter electrode of the lithium-ion half-cell is metallic lithium, and the separator is polyethylene PE.

[0042] The electrochemical performance tests include: constant current charge-discharge tests and rate performance tests. The electrochemical tests are carried out at room temperature (25 °C), the voltage range is 0.005 - 5 V, and the cycling current is 1 A g -1 .

[0043] The results are as follows:

[0044] The initial specific capacity of the silicon negative electrode prepared with the binder of Example 1 is 2567 mAh g -1 , and the specific capacity after 50 cycles is 1840 mAh g -1 , and the capacity retention rate is 72%.

[0045] The initial specific capacity of the silicon negative electrode prepared with the binder of Comparative Example 1 is 822 mAh g -1 , and the specific capacity after 50 cycles is 5.9 mAh g -1 , and the capacity retention rate is 7%.

[0046] It can be seen from the above test examples that the novel multifunctional polymer binder obtained in the present invention can effectively improve the electrochemical performance of silicon-based negative electrode lithium-ion batteries, increase the battery specific capacity, cycle stability, and discharge ability at high power.

[0047] The test results of the electrochemical cycling performance of the lithium-ion half-cells with silicon anodes assembled using Example 1 and Comparative Example 1 as binders are as Figure 1 shown.

[0048] The above description of the embodiments is provided to enable those of ordinary skill in the art to understand and apply the present invention. It is obvious that those skilled in the art can easily make various modifications to the embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the embodiments herein, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A preparation method of a multifunctional polymer binder for a silicon-based negative electrode, characterized in that, The preparation method of the polymer binder is as follows: In the first step, 3,3'-dithiobispropionic acid, polyethylene glycol bis(carboxymethyl) ether are reacted with a functional group-substituted chloride. In the second step, the obtained product is subjected to an interfacial polymerization reaction with purified and lithiated [1,1'-biphenyl]-4,4'-diamine-2,2'-disulfonic acid to obtain the final polymer material, which is used as a binder to prepare a silicon-based anode for use in a lithium-ion battery; the preparation of the polymer includes the following steps: (1) By molar parts, weigh 1-3 parts of 3,3'-dithiobispropionic acid and 1-3 parts of polyethylene glycol bis(carboxymethyl) ether, disperse them in 10-50 mL of dichloromethane, add 6-18 parts of the functional group-substituted chloride and a catalyst, react overnight at 50 °C - 80 °C, after the reaction is completed, remove the excess solvent by vacuum rotary evaporation, and then dissolve it again in 50 mL of dichloromethane to obtain solution A; (2) Weigh 2-6 parts of purified [1,1'-biphenyl]-4,4'-diamine-2,2'-disulfonic acid and 8-24 parts of a lithium compound, dissolve them in 100 mL of deionized water to obtain solution B; (3) Weigh 2-6 parts of a surfactant and dissolve it in 50 mL of dichloromethane to obtain solution C; (4) The interfacial polymerization process is carried out in a high-speed stirrer. Before the reaction, nitrogen is blown into the high-speed stirrer in advance to protect the reaction. Mix solution A, solution B and solution C, and stir at high speed at room temperature for 1-2 hours. After standing for 30 minutes, the solution is layered. Separate the aqueous solution and extract it twice with dichloromethane. Subject the extracted aqueous solution to vacuum rotary evaporation to increase the solution concentration, and then drop it into a poor solvent for precipitation. The precipitated product is dried in vacuo at 80 °C for 24 hours.

2. The preparation method of the multifunctional polymer binder for a silicon-based negative electrode according to claim 1, characterized in that, The functional group-substituted chloride is thionyl chloride and / or oxalyl chloride.

3. The preparation method of the multifunctional polymer binder for a silicon-based negative electrode according to claim 1, characterized in that, The catalyst is N,N-dimethylformamide and / or N,N-dimethylacetamide.

4. The preparation method of the multifunctional polymer binder for a silicon-based negative electrode according to claim 1, characterized in that, The lithium compound is lithium hydroxide hydrate, lithium bicarbonate, lithium oxalate or lithium carbonate.

5. The preparation method of the multifunctional polymer binder for a silicon-based negative electrode according to claim 1, characterized in that, The surfactant is a polyethylene glycol series substance with different molecular weights, including one or more of PEG-200, PEG-300, PEG-500.

6. The preparation method of the multifunctional polymer binder for a silicon-based negative electrode according to claim 1, characterized in that, The poor solvent is a solvent that is miscible with water and has a polarity less than that of water, including one or more of acetone, tetrahydrofuran, N,N-dimethylformamide, ethanol, isopropanol.

Images