A bipolar binder for silicon-based anodes of lithium-ion batteries and a method for its preparation and use

Abstract

The application belongs to the technical field of lithium batteries, and discloses a bipolar binder for a silicon-based negative electrode of a lithium ion battery and a preparation method and application thereof, wherein the bipolar binder is abbreviated as PLT-Y, lipoic acid and tannic acid are heated and stirred at 120-150 DEG C under a nitrogen atmosphere, the obtained mixed solution is dissolved in N, N-dimethylformamide, and then benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate, triethylamine and 1-pyrenemethylammonium hydrochloride are sequentially added, the amidation reaction is carried out at room temperature, the obtained solution is poured into deionized water to precipitate, and finally freeze-drying is carried out to obtain the bipolar binder. The bipolar binder has the advantages of good dispersibility and strong adhesion for the silicon-based material, can effectively inhibit the volume expansion of the silicon-carbon negative electrode material in the charging and discharging process of the electrode, makes the silicon-carbon negative electrode exhibit good cycle stability, and thus improves the electrochemical performance of the silicon-based negative electrode of the lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium batteries, and particularly relates to a dual-adhesion binder for a silicon-based negative electrode of a lithium ion battery, and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have the advantages of high capacity, no memory effect, fast reversible charge and discharge, and high coulomb efficiency. Lithium ion batteries have been widely used in commercial products, such as mobile phones, notebook computers, digital cameras, new energy vehicles, etc. Graphite is a common negative electrode material for lithium ion batteries. However, as the energy density of lithium ion batteries continues to increase, the graphite negative electrode with a theoretical capacity of only 372 mAh / g cannot meet the current demand. Therefore, it is urgent to find a high-capacity negative electrode material to replace graphite. Among the many new negative electrode materials, silicon is considered to be the most promising new generation of negative electrode material, with a theoretical specific capacity of up to 4200 mAh / g. However, due to the huge volume change (about 300%) and low first coulomb efficiency of silicon-based negative electrode materials, their commercialization is seriously hindered. Silicon-carbon materials with better cycle performance and higher coulomb efficiency are currently the focus of commercialization of silicon-based materials. However, silicon-carbon materials still have certain volume expansion problems, which result in poor long cycle stability and rate performance.

[0003] Currently, the main methods to solve the volume expansion problem of silicon-carbon negative electrodes are nanocrystallization and structuring. However, due to the complexity of the synthesis process, the cumbersome steps and high cost, it is difficult to achieve commercialization. Through research and investigation, optimizing the binder is one of the most economical and effective methods to solve the volume expansion problem of silicon-carbon negative electrodes. The main functions of the negative electrode binder are: binding the negative electrode material and the current collector to stabilize the structure; acting as a dispersant during the preparation of the negative electrode slurry to reduce material agglomeration. Due to the complexity of silicon-carbon materials, the commonly used negative electrode binders (CMC and SBR) have difficulty in dispersing silicon-carbon materials during the slurry process. In addition, due to the poor adhesion, the material is easy to fall off the copper foil. Therefore, the current commercial binders are not suitable for silicon-carbon negative electrodes. In recent years, researchers have made great efforts in designing and preparing silicon-carbon binders to improve the electrochemical performance of silicon-carbon negative electrodes. SUMMARY

[0004] In order to solve the above-mentioned problems and shortcomings of the prior art, the primary purpose of the present application is to provide a dual-adhesion binder for a silicon-based negative electrode of a lithium ion battery. The binder has good dispersibility and strong adhesion to silicon-carbon materials, can effectively inhibit the volume expansion of silicon-carbon negative electrode materials during the charging and discharging process of the electrode, and can make the silicon-carbon negative electrode exhibit good cycle stability, thereby significantly improving the electrochemical performance of the silicon-based negative electrode of the lithium ion battery.

[0005] Another object of the present application is to provide a preparation method of the above-mentioned amphiphilic binder for silicon-based anodes of lithium ion batteries.

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

[0007] The object of the present application is achieved by the following technical solutions:

[0008] An amphiphilic binder for silicon-based anodes of lithium ion batteries, which is abbreviated as PLT-Y, is prepared by heating and stirring lipoic acid and tannic acid at 120-150 DEG C under a nitrogen atmosphere, dissolving the obtained mixture in N,N-dimethylformamide, then sequentially adding benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate (PyBOP), triethylamine and 1-pyrenemethylammonium hydrochloride, precipitating the product by pouring into deionized water after amidation reaction at room temperature, and finally freeze-drying.

[0009] Preferably, the mass ratio of the lipoic acid, tannic acid, benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate and 1-pyrenemethylammonium hydrochloride is 1:(0.04-0.12):(0.2-0.36):(0.12-0.4); and the mass of the lipoic acid and the volume of the triethylamine are 1g:(0.08-0.15)mL.

[0010] Preferably, the heating and stirring time is 0.5-2h, the amidation reaction time is 6-36h, and the freeze-drying time is 12-36h.

[0011] The preparation method of the amphiphilic binder for silicon-based anodes of lithium ion batteries comprises the following steps:

[0012] S1. Heating and stirring lipoic acid at 120-150 DEG C under a nitrogen atmosphere, then adding tannic acid to perform cross-linking reaction, cooling at room temperature, dissolving in N,N-dimethylformamide, and preparing a mixed solution;

[0013] S2. Sequentially adding benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate, triethylamine and 1-pyrenemethylammonium hydrochloride to the above-mentioned mixed solution, performing amidation reaction at room temperature, precipitating the product by pouring into deionized water, and finally freeze-drying to obtain the amphiphilic binder.

[0014] A kind of negative electrode is that active material silicon carbon, conductive agent is mixed with the amphiphilic binder, after stirring after adding N-methyl pyrrolidone, electrode slurry of uniform dispersion is obtained, the electrode slurry is coated on copper foil, and is prepared by vacuum drying.

[0015] Preferably, the conductive agent is conductive carbon black, carbon nanotube, special conductive carbon black or conductive graphite;The mass ratio of the active material silicon carbon, conductive agent and amphiphilic binder is (7-8) :(1-2) :1.

[0016] Preferably, the stirring time is 6-8h, the temperature of vacuum drying is 100-120℃, and the time of vacuum drying is 12-36h.

[0017] The application of the negative electrode in lithium ion battery. Dry electrode piece is transferred into glove box filled with argon for battery assembly. Lithium piece is used as counter electrode in the battery, 1.2mmol / L of LiPF6 is used as solute in electrolyte, the volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) is 1:1, fluoroethylene carbonate (FEC) and 1wt% of ethylene carbonate (VC) are used as additives, and CR2032 button cell is assembled.

[0018] Preferably, the negative material of the lithium ion battery is silicon-carbon composite material.

[0019] The present application is obtained by polyphenol-sulfur radical addition reaction of lipoic acid and tannic acid, and then acylated reaction with 1-pyrene methyl amine hydrochloride to synthesize the amphiphilic binder. Tannic acid has abundant catechol and o-benzene triol groups, as well as good biocompatibility and strong adhesion. Lipoic acid has a special structure of biomolecules, including two types of dynamic bonds: dynamic covalent disulfide bond in five-membered ring and non-covalent hydrogen bond of carboxyl group. 1-pyrene methyl amine hydrochloride has a polycyclic aromatic hydrocarbon structure with a good conjugated system. The modified amphiphilic binder by tannic acid and 1-pyrene methyl amine hydrochloride improves the mechanical strength of the binder and realizes the cycle stability of the silicon-carbon negative electrode.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] 1. The PLT-Y amphiphilic binder of the present application is obtained by polyphenol-sulfur radical addition reaction of natural biological small molecules lipoic acid and tannic acid without solvent, and then acylated reaction with 1-pyrene methyl amine hydrochloride. The obtained amphiphilic binder has a three-dimensional network structure, which is conducive to the transmission of electrons and ions, greatly improves the mechanical properties of the binder, and makes the electrode maintain good integrity during the cycle process.

[0022] 2.The PLT-Y amphiphilic binder of the present application has good affinity to graphite, conductive carbon black and silicon materials, because the large number of carboxyl and catechol groups of the lipoic acid and tannic acid have good affinity to silicon, and the 1-pyrene methanamine hydrochloride contains a large number of benzene ring functional groups, which are easy to form π-π conjugation with the graphite structure, and the combination of the two is conducive to the formation of a coating layer on the surface of the silicon-carbon material.

[0023] 3.The PLT-Y amphiphilic binder of the present application has the advantages of good dispersibility and strong adhesion to silicon-carbon materials. It can effectively protect the active material from the influence of the electrolyte, reduce the generation of SEI film, and significantly improve the electrochemical performance of the silicon-carbon negative electrode of the lithium ion battery.

[0024] 4.The lipoic acid-tannic acid polymeric by the reaction of lipoic acid and tannic acid in the present application contains reversible dynamic covalent disulfide bonds, which can be reformed after breaking, and the binder is a three-dimensional network structure, which can effectively inhibit the volume expansion of the silicon-carbon negative material during the charging and discharging process of the electrode, so that the silicon-carbon negative electrode exhibits good cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The 180° peeling curve of the silicon-carbon negative electrode made of the amphiphilic binder (PLT-Y) in Application Example 1 and the sodium carboxymethyl cellulose (CMC) in Comparative Example 1.

[0026] Figure 2 The cycle performance graph of the Li∥Si / C950@PLT-Y button cell composed of the composition of Application Example 1.

[0027] Figure 3 The comparison graph of the cycle performance of the Li∥Si / C950@PLT-Y button cell composed of the composition of Application Example 1 and the Li∥Si / C950@CMC button cell composed of the composition of Comparative Example 1. DETAILED DESCRIPTION

[0028] The content of the present application will be further illustrated below in combination with specific examples, but should not be understood as a limitation of the present application. If not specifically indicated, the technical means used in the examples are conventional means known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field.

[0029] Example 1

[0030] Under nitrogen atmosphere, 1.25 g of lipoic acid was added into a three-necked flask, heated to 150°C and magnetically stirred for 10 min, then 0.05 g of tannic acid was added for crosslinking reaction for 0.5 h, the liquid mixture was dissolved in 30 mL of N,N-dimethylformamide solution, 0.2 g of PyBOP, 0.11 mL of triethylamine and 0.05 g of 1-pyrenemethylammonium hydrochloride were added in turn, amidation reaction was carried out at room temperature for 36 h, then the precipitate was separated by pouring into 200 mL of deionized water, and then freeze-dried for 24 h to obtain the amphiphilic binder, which was abbreviated as PLT-Y.

[0031] Example 2

[0032] Under nitrogen atmosphere, 4 g of lipoic acid was added into a three-necked flask, heated to 120°C and magnetically stirred for 10 min, then 0.24 g of tannic acid was added for crosslinking reaction for 1 h, the liquid mixture was dissolved in 80 mL of N,N-dimethylformamide solution, 0.6 g of PyBOP, 0.4 mL of triethylamine and 0.2 g of 1-pyrenemethylammonium hydrochloride were added in turn, amidation reaction was carried out at room temperature for 36 h, then the precipitate was separated by pouring into 500 mL of deionized water, and then freeze-dried for 24 h to obtain the amphiphilic binder, which was abbreviated as PLT-Y.

[0033] Application Example 1

[0034] 1. The active material silicon carbon, conductive agent Super P and the amphiphilic binder of Example 1 were dissolved in N-methyl pyrrolidone to obtain a 5 wt% solution of the amphiphilic binder, which was mixed with a mass ratio of 8:1:1, then 100-1000 mL of N-methyl pyrrolidone was added and stirred in a deaerating stirrer to obtain a uniformly dispersed electrode slurry, which was coated on a copper foil, vacuum dried at 120°C for 12 h, and cut into a circular negative electrode sheet with a diameter of 12 mm.

[0035] 2. The dried negative electrode sheet was transferred into an argon-filled glove box, a lithium sheet was used as the counter electrode, the electrolyte used the solute LiPF6 with a concentration of 1.2 mmol / L, the solvent was a volume ratio of 1:1 of ethylene carbonate (EC) and diethyl carbonate (DEC), 10 wt% fluoroethylene carbonate (FEC) and 1 wt% vinyl carbonate (VC) as additives, assembled into a CR2032 button cell, which was abbreviated as Li∥Si / C950@PLT-Y, and then left for 10 h. The standing battery was subjected to constant current test for electrochemical performance in a Neware test system.

[0036] Figure 1 The 180° peeling curve of the silicon carbon negative electrode made of the amphiphilic binder (PLT-Y) in Application Example 1 and the sodium carboxymethyl cellulose (CMC) in Comparative Example 1. From the Figure 1It can be seen that the PLT-Y binder has stronger adhesion to the silicon-carbon material, which is beneficial to alleviate the volume expansion of the silicon-carbon material during the lithium extraction process and maintain the structural integrity of the electrode. Figure 2 The cycle performance graph of the Li∥Si / C950@PLT-Y button cell composed of Example 1 is shown in Figure 2. Figure 2 It can be seen that the Li∥Si / C950@PLT button cell composed of the parent binder (PLT-Y) has a first discharge specific capacity of more than 1100 mAh / g at a current density of 285 mA / g, a first coulombic efficiency of 79%, and a capacity of 819 mAh / g after 100 cycles, showing excellent cycle stability.

[0037] Comparative Example 1

[0038] 1. 0.5 g of sodium carboxymethyl cellulose (commercially available, abbreviated as CMC) powder was added to 9.5 g of deionized water to obtain a 5 wt% binder.

[0039] 2. The active material silicon-carbon, the conductive agent SupperP, and the 5 wt% binder were mixed in a mass ratio of 8:1:1, and after adding 100-1000 mL of deionized water, the mixture was stirred for 6-8 h to obtain a uniformly dispersed electrode slurry. The electrode slurry was coated onto a copper foil, vacuum dried at 120°C for 12 h, and cut into a circular electrode with a diameter of 12 mm.

[0040] 3. The electrode was transferred into an argon-filled glove box for battery assembly. Lithium foil was used as the counter electrode in the battery, and 1.2 mmol / L LiPF6 was used as the solute in the electrolyte, with a volume ratio of 1:1 of ethylene carbonate (EC) and diethyl carbonate (DEC) as the solvent, 10 wt% fluoroethylene carbonate (FEC) and 1 wt% vinyl carbonate (VC) as additives, to assemble a CR2032 button cell, abbreviated as Li∥Si / C950@CMC.

[0041] The CR2032 button cells assembled in Example 1 and Comparative Example 1 were placed at 28°C for 10 h and then subjected to constant current test electrochemical performance in a Neware test system. The test conditions were: current density 285 mA / g; voltage window 0.01-1.5 V. Figure 3 The cycle performance comparison graph of the CR2032 button cells prepared in Example 1 and Comparative Example 1 is shown in Figure 2. Figure 3It can be known that the capacity attenuation of the Li||Si / C950@CMC button cell prepared by the comparative example 1 is 635mAh / g after 100 cycles at a current density of 285mA / g, the capacity of the Li||Si / C950@PLT-Y button cell prepared by the application example 1 is maintained at more than 819mAh / g, and the button cell has higher discharge capacity and better cycle stability. It can be known that the dual parent binder (PLT-Y) of the application can make the silicon-carbon negative electrode exhibit good cycle stability, thereby improving the electrochemical performance of the silicon-based negative electrode of the lithium ion battery.

[0042] The above examples are the preferred embodiments of the application, but the embodiments of the application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the application should be equivalent replacement methods and should be included in the protection scope of the application.

Claims

1. A bipolar binder for silicon-based anodes of lithium-ion batteries, characterized in that, The amphiphilic binder is abbreviated as PLT-Y, lipoic acid and tannic acid are heated and stirred under a nitrogen atmosphere at 120-150°C, the obtained mixture is dissolved in N,N-dimethylformamide, then benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate, triethylamine and 1-pyrenemethylammonium chloride hydrochloride are added in sequence, after amidation reaction at room temperature, the product is poured into deionized water to precipitate, and finally freeze-drying is performed to obtain the product.

2. The amphiphilic binder for silicon-based anodes of lithium-ion batteries according to claim 1, characterized in that, The mass ratio of lipoic acid, tannic acid, benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate and 1-pyrenemethylammonium chloride hydrochloride is 1:(0.04-0.12):(0.2-0.36):(0.12-0.4); the mass of lipoic acid and the volume of triethylamine are 1g:(0.08-0.15)mL.

3. The amphiphilic binder for silicon-based anodes of lithium-ion batteries according to claim 1, characterized in that, The heating and stirring time is 0.5-2h, the amidation reaction time is 6-36h, and the freeze-drying time is 12-36h.

4. The process for the preparation of a biocompatible binder for silicon-based anodes for lithium-ion batteries according to any one of claims 1-3, characterized in that, The method comprises the following steps: S1. lipoic acid is heated and stirred under a nitrogen atmosphere at 120-150°C, then tannic acid is added to perform crosslinking reaction, and the product is cooled at room temperature and dissolved in N,N-dimethylformamide to obtain a mixed solution; S2. benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate, triethylamine and 1-pyrenemethylammonium chloride hydrochloride are added in the above mixed solution, amidation reaction is performed at room temperature, the product is poured into deionized water to precipitate, and finally freeze-drying is performed to obtain the amphiphilic binder.

5. A negative electrode characterized by comprising: The negative electrode is prepared by mixing active material silicon carbon, conductive agent and the amphiphilic binder according to any one of claims 1-3, then adding N-methylpyrrolidone and stirring to obtain a uniformly dispersed electrode slurry, coating the electrode slurry on a copper foil, and performing vacuum drying to obtain the negative electrode.

6. The negative electrode according to claim 5, characterized by The conductive agent is conductive carbon black, carbon nanotube, special conductive carbon black or conductive graphite; the mass ratio of the active material silicon carbon, conductive agent and amphiphilic binder is (7-8):(1-2):

1.

7. The negative electrode according to claim 5, wherein The stirring time is 6-8h, the vacuum drying temperature is 100-120°C, and the vacuum drying time is 12-36h.

8. Application of the negative electrode according to any one of claims 5-7 in a lithium ion battery.

9. Use of the negative electrode according to claim 8 in a lithium-ion battery, characterized in that, The negative electrode material of the lithium ion battery is silicon carbon composite material.

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