Silicon-carbon negative electrode binder material having self-healing performance, preparation method therefor, and use thereof

Abstract

Disclosed in the present invention are a silicon-carbon negative electrode binder material having self-healing performance, a preparation method therefor, and the use thereof. The preparation method for the silicon-carbon negative electrode binder material comprises the following steps: (1) dissolving guar gum in water, and performing a hydrolysis reaction at 30-100℃ under a stirring condition to obtain a guar gum solution; and then dissolving citric acid in water and performing a hydrolysis reaction under a stirring condition to obtain a citric acid solution; and (2) mixing the guar gum solution and the citric acid solution, adding glycerol, and performing a re-hydrolysis reaction on same to obtain the silicon-carbon negative electrode binder material having self-healing performance. The present invention uses glycerol as a plasticizer to promote the condensation reaction between guar gum and citric acid; meanwhile, a large number of hydrogen bonds in said binder material promotes the self-healing function thereof, thereby relieving volumetric expansion of negative electrode sheets during charging and discharging processes, and further improving the capacity retention rate and cycle stability of batteries.

Description

A silicon-carbon negative electrode binder material with self-healing properties and its preparation method and application Technical Field

[0001] The present invention belongs to the technical field of energy storage materials, and in particular relates to a silicon-carbon negative electrode binder material with self-healing properties, and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) are a mature technology used as a power source in a wide range of applications. However, emerging applications, such as electric vehicles, are challenging key electrochemical properties. Batteries are currently widely used in portable electrochemical energy storage applications, including electric vehicles, mobile phones, laptops, and smart wearable devices. Market demands for lithium-ion batteries' energy density, safety, reliability, fast charging, and cycling stability continue to increase. To achieve high energy conversion efficiency and energy density, high-performance electrochemical energy storage technologies have become a research hotspot.

[0003] The theoretical lithium storage capacity of silicon is 4200 mAh g -1 Among all elements that can be alloyed and store lithium, silicon has the highest specific capacity. Furthermore, its voltage platform is slightly higher than that of graphite (approximately 0.4V), making it less likely to cause surface lithium deposition during low-temperature charging or rapid charging (lithium insertion), and its safety performance is better than that of graphite. Furthermore, silicon reserves are abundant, accounting for approximately 25.7% of the total weight of the Earth's crust. Furthermore, the cost of using silicon as a negative electrode material for batteries is low, and it is environmentally friendly and non-toxic. However, there are also some drawbacks when using silicon as a negative electrode material. When silicon particles are intercalated with lithium, a huge volume effect occurs, which can cause the electrode material to crack after multiple charge and discharge cycles. Subsequently, strong mechanical stress is induced, resulting in loss of contact between the electrode active material and the current collector, and the active silicon also pulverizes, leading to rapid attenuation of the electrode capacity.

[0004] When silicon is electrochemically stored for lithium, a solid electrolyte interface film, or SEI film, is produced. When de-lithiation occurs, the silicon particles become smaller, causing the SEI film to rupture, exposing new silicon surfaces and contacting the electrolyte. During subsequent multiple cycles, new SEI films are produced on the newly exposed silicon surfaces. These SEI films are electronic insulators (conductors for lithium ions), which have a significant impact on cycle performance and can cause the impedance of the material to increase. This reduces the electrochemical activity of the electrode material.

[0005] Currently, the most commonly used binder in commercial batteries is polyvinylidene fluoride (PVDF). However, when used as a binder, PVDF molecules can only be connected by van der Waals forces, making it prone to breakage. This ineffective bonding force for silicon-based materials, which have a significant volume expansion effect, can lead to easy detachment of the electrode material, resulting in unstable battery cycling and rapid capacity decay. In recent years, biomass binders have seen rapid development. Commonly used biomass binders include sodium alginate, gum arabic, guar gum, and xanthan gum. However, guar gum currently suffers from low initial coulombic efficiency, poor cycling stability, and rapid capacity decay. Currently designed binders primarily utilize ester bonds formed through a condensation reaction between hydroxyl and carboxyl groups to form cross-linked binders. Therefore, developing binders with superior performance, simple preparation, and low cost is a current research goal.

[0006] Summary of the Invention

[0007] The primary purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for preparing a silicon-carbon negative electrode binder material with self-healing properties.

[0008] Another object of the present invention is to provide a silicon-carbon negative electrode binder material with self-healing properties prepared by the method.

[0009] Another object of the present invention is to provide an application of the silicon-carbon negative electrode binder material with self-healing properties.

[0010] The purpose of the present invention is achieved through the following technical solutions:

[0011] A method for preparing a silicon-carbon negative electrode binder material with self-healing properties comprises the following steps:

[0012] (1) Hydrolysis treatment: dissolving guar gum in water and performing a hydrolysis reaction at 30-100° C. under stirring to obtain a guar gum solution; dissolving citric acid in water and performing a hydrolysis reaction under stirring to obtain a citric acid solution;

[0013] (2) Rehydrolysis treatment: guar gum solution and citric acid solution are mixed and then glycerol is added to obtain a reaction solution; the reaction solution is then subjected to a rehydrolysis reaction under stirring conditions to obtain a silicon-carbon negative electrode binder material with self-healing properties.

[0014] The concentration of the guar gum solution in step (1) is 5-15 mg / ml, preferably 10 mg / ml.

[0015] The citric acid described in step (1) is preferably citric acid monohydrate.

[0016] The dosage of the citric acid monohydrate is calculated based on 15 to 45 mg of citric acid monohydrate per milliliter of water; preferably, it is calculated based on 30 mg of citric acid monohydrate per milliliter of water.

[0017] The water described in step (1) is preferably deionized water.

[0018] In step (1), the temperature of the guar gum hydrolysis reaction is preferably 40-90°C; more preferably 40-80°C; and even more preferably 60°C.

[0019] The hydrolysis reaction time in step (1) is 2 to 3 hours, preferably 3 hours.

[0020] The concentration of guar gum in the reaction solution in step (2) is 0.1-10% by mass; preferably 0.1-5% by mass; further 0.6-0.7% by mass; and further preferably 0.65% by mass.

[0021] The concentration of citric acid in the reaction solution in step (2) is 0.1-10% by mass; preferably 0.1-5% by mass; further 0.6-0.7% by mass; and further preferably 0.65% by mass.

[0022] The concentration of glycerol in the reaction solution in step (2) is 4 to 50% by mass; preferably 4.5 to 20% by mass; further 4.6 to 11.1% by mass; and further preferably 11.1% by mass.

[0023] The re-hydrolysis reaction time in step (2) is 2 to 3 hours, preferably 3 hours.

[0024] A silicon-carbon negative electrode binder material with self-healing properties is prepared by any of the methods described above.

[0025] Application of the silicon-carbon negative electrode binder material with self-healing properties in the preparation of negative electrode materials for lithium-ion batteries.

[0026] The lithium-ion battery negative electrode material includes a lithium-ion battery negative electrode sheet and the like.

[0027] A lithium-ion battery negative electrode sheet comprises active material nano-silicon, a conductive agent and the above-mentioned silicon-carbon negative electrode binder material with self-healing properties.

[0028] The silicon-carbon negative electrode binder material with self-healing properties accounts for 10 to 20% of the total mass of the active material nano-silicon, the conductive agent and the silicon-carbon negative electrode binder material with self-healing properties; preferably, it accounts for 10% of the total mass of the active material nano-silicon, the conductive agent and the silicon-carbon negative electrode binder material with self-healing properties.

[0029] The silicon nanoparticles account for 80-90% of the total mass of the active material nano-silicon, the conductive agent and the silicon-carbon negative electrode binder material with self-healing properties; preferably account for 85% of the total mass of the active material nano-silicon, the conductive agent and the silicon-carbon negative electrode binder material with self-healing properties.

[0030] The conductive agent accounts for 5-10% of the total mass of the active material nano-silicon, the conductive agent and the silicon-carbon negative electrode binder material with self-healing properties; preferably 5% of the total mass of the active material nano-silicon, the conductive agent and the silicon-carbon negative electrode binder material with self-healing properties.

[0031] The particle size of the active material nano silicon is 20-60nm.

[0032] The conductive agent is one or more of conductive carbon black, poly (3,4-ethylenedioxythiophene) - polystyrene sulfonic acid (PEDOT / PSS), carbon nanotubes and graphene; preferably conductive carbon black and carbon nanotubes; more preferably a conductive agent obtained by mixing conductive carbon black and carbon nanotubes in a mass ratio of 9.7:0.1.

[0033] The method for preparing the negative electrode sheet of a lithium-ion battery comprises stirring and mixing silicon nanoparticles, a conductive agent, the above-mentioned silicon-carbon negative electrode binder material with self-healing properties, and water to obtain a battery electrode slurry; then coating the battery electrode slurry into a film, placing it under vacuum drying at 60-120°C, and then rolling (stamping) to obtain the negative electrode sheet of a lithium-ion battery.

[0034] The stirring time is 6 to 8 hours, preferably 6 hours.

[0035] The vacuum drying temperature is preferably 60-80°C, more preferably 60°C.

[0036] The vacuum drying time is 10 to 24 hours, preferably 12 hours.

[0037] The thickness of the lithium-ion battery negative electrode sheet can be selected according to actual needs; preferably, it is 70 to 140 microns; more preferably, it is 80 microns.

[0038] Application of the silicon-carbon negative electrode binder material with self-healing properties and / or the lithium-ion battery negative electrode sheet in the preparation of lithium-ion batteries.

[0039] The lithium-ion battery is preferably a button cell; more preferably a 2032 button half cell.

[0040] A button battery comprises the lithium ion battery negative electrode sheet, positive electrode sheet, electrolyte and diaphragm.

[0041] The positive electrode sheet is preferably a lithium sheet.

[0042] The electrolyte is a conventional lithium-ion battery electrolyte; preferably a LiPF6 electrolyte, which is prepared by the following method: adding LiPF6 to a solvent obtained by mixing EC (ethylene carbonate), EMC (ethyl methyl carbonate) and DMC (dimethyl carbonate) in a volume ratio of 1:1:1 to obtain a LiPF6 electrolyte.

[0043] The concentration of the LiPF6 electrolyte is preferably 1 mol / L.

[0044] The separator is a conventional lithium-ion battery separator; preferably, it is a polypropylene microporous membrane Celgard-2400.

[0045] The electrode binder of the present invention uses guar gum (GG), citric acid (CA) and glycerol (Gly) as raw materials. The modified guar gum obtained by hydrolyzing guar gum contains guar gum (GG), which is produced from guar seeds and consists of linear (1→4)-β-D-mannopyranosyl units with (1→6) bonded α-D-galactopyranose units. It is a low-cost, highly environmentally friendly and biorenewable polysaccharide polymer. The GG molecule contains a large number of polar hydroxyl groups that can provide more connection sites to form hydrogen bonds with the silicon surface. However, due to the large number of hydroxyl groups contained in the GG molecule, it is easy to agglomerate, making the binder solution gel-like and having extremely poor fluidity, which increases the difficulty of the coating process and affects the various components in the electrode. Glycerol is a kind of glycerol with a large number of -OH polar groups, which form hydrogen bonds between molecules. The molecular chains with strong polar groups have strong forces, while the molecular chains with non-polar groups have small forces. The polar groups of glycerol will interact with the polar groups of the polymer, weakening the attraction between the polymers, making the polymers with strong polar groups easy to shape, improving the flexibility of the guar gum molecular chains, thereby improving the flexibility of the guar gum, and promoting the more flexible guar gum molecular chains to expose more hydroxyl sites, which can react with citric acid molecules to shrink, forming hydrogen bonds stronger than van der Waals forces, thereby promoting the self-healing effect, thereby inhibiting the volume expansion effect, and thus improving the capacity retention rate and cycle stability of the battery.

[0046] The present invention has the following advantages and effects compared to the prior art:

[0047] 1. The present invention provides a guar gum binder with self-healing function. It is discovered for the first time that glycerol as a small molecule has a significant effect on promoting the self-healing function. Therefore, the present invention uses glycerol as a plasticizer to promote the condensation reaction between guar gum and citric acid. Glycerol as a small molecule plasticizer molecule is inserted between polymer molecular chains, weakening the interaction force between polymer molecular chains, thereby increasing the mobility of polymer molecular chains, enhancing the flexibility of guar gum polymer, and exposing more hydroxyl sites to combine with citric acid molecules, causing condensation reaction, and forming a three-dimensional network cross-linked by hydrogen bonds; at the same time, the large number of hydrogen bonds contained inside promote its self-healing function, and it has the ability to self-repair after fracture, can repair cracks generated in silicon electrodes during charging and discharging, and promote the improvement of electrochemical performance.

[0048] 2. The present invention mainly weakens the van der Waals force between polymers through the plasticization and self-healing effect of glycerol, and then forms strong hydrogen bonds through condensation reaction between hydroxyl and carboxyl groups. The self-repair function of the three-dimensional space skeleton is formed by the extension of the molecular chain to cope with the severe volume expansion effect of silicon-based materials. The prepared binder has excellent performance. The self-healing property promoted by glycerol can effectively alleviate the volume expansion of the negative electrode during the charging and discharging process, and improve the capacity retention rate and cycle stability of the battery.

[0049] 3. The preparation process of the present invention is simple, easy to operate, low in cost, has good product uniformity, is environmentally friendly, and is suitable for industrial-scale production.

[0050] 4. The lithium battery prepared by the invention has the advantages of high specific capacity, stable cycle performance and good rate performance. It solves the problems of large irreversible capacity, poor conductivity, cycle stability and poor rate performance in the actual preparation and application of existing silicon-based negative electrode materials. It can meet the needs of high-capacity and long-life electronic devices and expand the application range of lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] FIG1 is an FTIR spectrum of the binder prepared in Example 1, as well as guar gum, citric acid monohydrate and glycerol.

[0052] FIG2 is a contact angle diagram of the adhesives prepared in Example 1 and Comparative Examples 2-3.

[0053] FIG3 is an impedance diagram of the negative electrode sheets of lithium-ion batteries prepared in Example 1 and Comparative Examples 1-2.

[0054] FIG4 is a graph showing cycle data of the negative electrode sheets of lithium ion batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 2 (at a current density of 0.5 A / g).

[0055] FIG5 is a rate performance cycle curve diagram of the lithium ion battery negative electrode sheets prepared in Examples 1 to 3 and Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0056] The present invention will be described in further detail below in conjunction with the examples, but embodiments of the present invention are not limited thereto. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art. The test methods in the following examples where specific experimental conditions are not specified are generally based on conventional experimental conditions. Unless otherwise specified, the reagents and raw materials used in the present invention can be obtained commercially.

[0057] In the following examples and comparative examples of the present invention, the raw active material nanosilicon used has a purity of 99.9% and a particle size of 20 to 60 nm; guar gum (GG), citric acid monohydrate (CA, purity ≥99.5%), glycerol (also known as glycerol, GLY, analytical grade AR), carbon nanotubes (CNTs), and current collector copper foil (thickness 9 μm) were all purchased from Aladdin's official website.

[0058] In the following examples and comparative examples of the present invention, the microscopic properties of the electrode materials were tested using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Microscopic morphology of electrode material samples with different binders was tested. FTIR and XPS can determine the molecular structure of substances and identify compounds.

[0059] In the following examples and comparative examples of the present invention, the electrochemical performance testing steps of the electrode materials are as follows:

[0060] The electrode sheet was cut into an electrode sheet with a diameter of Φ = 12 nm, and the required materials were placed in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), and a button battery was assembled according to the negative electrode shell, spring, 2032 gasket, lithium sheet (counter electrode), diaphragm, electrode sheet, and positive electrode shell. Then, the electrochemical performance of the button batteries assembled with the electrode materials of the embodiment and the comparative example was tested using the Neware electrochemical test system; wherein, the positive electrode was a lithium sheet, and the electrolyte was a 1 mol / L LiPF6 solution ( That is, LiPF6 is dissolved in a solvent obtained by mixing EC (ethylene carbonate) / EMC (ethyl methyl carbonate) / DMC (dimethyl carbonate) in a volume ratio of 1:1:1 to form an electrolyte with a final concentration of 1 mol / L), the diaphragm is a polypropylene microporous membrane Celgard-2400, and button batteries are assembled in an argon-filled glove box. Subsequently, electrochemical performance tests are performed in the voltage range of 0.01-1V to obtain the corresponding capacity-time relationship graph, thereby studying the lithium storage performance of the electrode material. The button battery is subjected to impedance testing using the German Zahner IM-6 model electrochemical workstation, with a frequency scan range of 0.01-106HZ and a perturbation voltage amplitude of 5mV. The button battery is subjected to electrochemical reaction testing of the electrode using the German Zahner IM-6 model electrochemical workstation, with a scan voltage range of 0.01-3V and a scan rate of 0.05mV / s. The performance tests are repeated three times.

[0061] Example 1

[0062] A method for preparing a lithium-ion battery silicon composite electrode (Si@GG-CA-GLY electrode) comprises the following steps:

[0063] (1) Hydrolysis treatment: 10 mg of guar gum raw material was dissolved in 1 ml of deionized water and stirred at 60° C. for 3 hours to hydrolyze the guar gum solution; 10 mg of citric acid raw material (i.e., citric acid monohydrate) was dissolved in 0.333 ml of deionized water and stirred for 3 hours to hydrolyze the citric acid to obtain a citric acid solution;

[0064] (2) Re-hydrolysis treatment: The guar gum solution obtained by hydrolysis and the citric acid solution were stirred and mixed, and then 130 μL of glycerol was added and stirred for 3 hours for hydrolysis treatment;

[0065] (3) Preparation of a binder: The product obtained by hydrolysis in step (2) is used as a binder, that is, as a lithium ion battery binder (GG-CA-GLY), which contains a large number of hydroxyl groups and carboxyl groups.

[0066] (4) Preparation of lithium-ion battery negative electrode: 170 mg of active material nano-silicon, 9.6 mg of conductive carbon black, and 25 mg of 0.4 wt% carbon nanotubes (CNT) were taken in an agate mortar and ground into a uniform powder. Then, the powder was added to 20 mg of the above-mentioned binder and stirred at room temperature for 6 hours to prepare a battery electrode slurry. The slurry was evenly coated on the current collector copper foil with a 0.9 mm thick scraper (i.e., the slurry coating thickness was 0.9 mm, the same below), and dried in a vacuum drying oven at 60°C for 12 hours. The dried electrode was punched into a small disc with a diameter of 12 mm to obtain a Si@GG-CA-GLY electrode (thickness 80 microns).

[0067] Example 2

[0068] (1) Hydrolysis treatment: 10 mg of guar gum raw material was dissolved in 1 ml of deionized water and stirred at 60° C. for 3 hours to hydrolyze the guar gum solution; 10 mg of citric acid raw material (i.e., citric acid monohydrate) was dissolved in 0.333 ml of deionized water and stirred for 3 hours to hydrolyze the citric acid to obtain a citric acid solution;

[0069] (2) Re-hydrolysis treatment: The guar gum solution obtained by hydrolysis and the citric acid solution were stirred and mixed, and then 100 μL of glycerol was added and stirred for 3 hours for hydrolysis treatment;

[0070] (3) Preparation of a binder: The product obtained by hydrolysis in step (2) is directly used as a binder, that is, as a lithium ion battery binder (GG-CA-GLY), which contains a large number of hydroxyl groups and carboxyl groups.

[0071] (4) Preparation of lithium-ion battery negative electrode: 170 mg of active material nano-silicon, 9.6 mg of conductive carbon black, and 25 mg of 0.4 wt% CNT were taken in an agate mortar and ground into a uniform powder. Then, they were added to 20 mg of the above-mentioned binder and stirred at room temperature for 6 hours to prepare a battery electrode slurry. The slurry was evenly coated on the current collector copper foil with a 0.9 mm thick scraper and dried in a vacuum drying oven at 60°C for 12 hours. The dried electrode was punched into small discs with a diameter of 12 mm to obtain Si@GG-CA-GLY electrode (thickness of 80 microns).

[0072] Example 3

[0073] (1) Hydrolysis treatment: 10 mg of guar gum raw material was dissolved in 1 ml of deionized water and stirred at 60° C. for 3 hours to hydrolyze the guar gum solution; 10 mg of citric acid raw material (i.e., citric acid monohydrate) was dissolved in 0.333 ml of deionized water and stirred for 3 hours to hydrolyze the citric acid to obtain a citric acid solution;

[0074] (2) Re-hydrolysis treatment: The guar gum solution obtained by hydrolysis and the citric acid solution were stirred and mixed, and then 50 μL of glycerol was added and stirred for 3 hours for hydrolysis treatment;

[0075] (3) Preparation of a binder: The product obtained by hydrolysis in step (2) is directly used as a binder, that is, as a lithium ion battery binder (GG-CA-GLY), which contains a large number of hydroxyl groups and carboxyl groups.

[0076] (4) Preparation of lithium-ion battery negative electrode: 170 mg of active material nano-silicon, 9.6 mg of conductive carbon black, and 25 mg of 0.4 wt% CNT were taken in an agate mortar and ground into a uniform powder. Then, they were added to 20 mg of the above-mentioned binder and stirred at room temperature for 6 hours to prepare a battery electrode slurry. The slurry was evenly coated on the current collector copper foil with a 0.9 mm thick scraper and dried in a vacuum drying oven at 60°C for 12 hours. The dried electrode was punched into small discs with a diameter of 12 mm to obtain Si@GG-CA-GLY electrode (thickness of 80 microns).

[0077] Comparative Example 1

[0078] (1) Hydrolysis treatment: 10 mg of guar gum raw material was dissolved in 1 ml of deionized water and stirred at 60° C. for 3 hours to hydrolyze the guar gum solution; 10 mg of citric acid raw material (i.e., citric acid monohydrate) was dissolved in 0.333 ml of deionized water and stirred for 3 hours to hydrolyze the citric acid to obtain a citric acid solution;

[0079] (2) Re-hydrolysis treatment: The guar gum solution obtained by hydrolysis was mixed with the citric acid solution, and then 0 μL of glycerol was added and stirred for 3 hours for hydrolysis treatment;

[0080] (3) Preparation of a binder: The product obtained by hydrolysis in step (2) is directly used as a binder, that is, as a lithium ion battery binder (GG-CA-GLY), which contains a large number of hydroxyl groups and carboxyl groups.

[0081] (4) Preparation of lithium-ion battery negative electrode: 170 mg of active material nano-silicon, 9.6 mg of conductive carbon black, and 25 mg of 0.4 wt% CNT were taken in an agate mortar and ground into a uniform powder. The powder was then added to 20 mg of the binder in step (3) and stirred at room temperature for 6 h to prepare a battery electrode slurry. The slurry was evenly coated on the current collector copper foil with a 0.9 mm thick scraper and dried in a vacuum drying oven at 60°C for 12 h. The dried electrode was punched into small discs with a diameter of 12 mm to obtain Si@GG-CA-GLY electrode (80 μm thick).

[0082] Comparative Example 2

[0083] The negative electrode of the lithium-ion battery was prepared using CMC binder: 80 mg of active material nanosilicon, 10 mg of sodium carboxycellulose (neutral, USP GRADE, purchased from Aladdin's official website), and 10 mg of conductive carbon black were respectively ground into uniform powder in an agate mortar, and then stirred in a reagent bottle with 0.8 g of ultrapure water for 24 hours to obtain the CMC binder; then the slurry was evenly coated on the current collector copper foil with a 0.9 mm thick scraper and baked in a vacuum oven at 60°C for 12 hours to obtain the SiNPs@CMC electrode (thickness 80 microns).

[0084] Comparative Example 3

[0085] The negative electrode of a lithium-ion battery was prepared using PVDF binder: 80 mg of active material nanosilicon, 10 mg of polyvinylidene fluoride, and 10 mg of conductive carbon black were respectively ground into a uniform powder in an agate mortar, and then stirred for 6 hours in a reagent bottle with 1.2 g of N-methylpyrrolidone (analytical grade, purchased from Aladdin's official website) to obtain the PVDF binder; the slurry was then evenly coated on the current collector copper foil with a 0.9 mm thick scraper and baked in a vacuum oven at 60°C for 12 hours to obtain the SiNPs@PVDF electrode (80 microns thick).

[0086] Effect embodiment

[0087] Lithium-ion battery negative electrodes were prepared using the binder solutions of Examples 1-3 and Comparative Examples 1-3 and assembled into button cells as follows: Following the methods described in the Examples and Comparative Examples, the active material nanosilicon, conductive additive, and binder were weighed and mixed in a mass ratio of 8:1:1. Deionized water was added and stirred at room temperature for 6 hours to form a battery electrode slurry. The slurry was then evenly coated onto a current collector copper foil using a 0.9 mm spatula and dried in a vacuum drying oven at 80°C for 12 hours. The dried electrode was punched into small discs with a diameter of 12 mm. In an argon-filled glove box, the negative electrode, separator, electrolyte, lithium sheet, spring, and 2032 gasket were packaged in positive and negative electrode housings to produce a 2032 button cell. The electrolyte was a 1 mol / L LiPF6 solution (using ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) (volume ratio 1:1:1) as solvent). Test method and conditions: The constant current method was used to test the cycle stability and rate performance of the battery, with a potential window of 0.01-1.5V.

[0088] The test results are shown in Figures 1 to 5. From Figures 1 to 5, we can see that:

[0089] Figure 1 is the FTIR spectrum of the GG-CA-GLY binder (GGC for short), GG (guar gum), CA (citric acid monohydrate), and GLY (glycerol) prepared in Example 1. As can be seen from the figure, the infrared characteristic absorption peaks of GG are at 1637 cm-1 and 1160 cm-1, the characteristic absorption peak of -COOH of CA is at 1693 cm-1, and the -C=O position of GG-CA-GLY is shifted to the high beam at 1715 cm-1 due to the addition of CA. -1 The ester bond of GG-CA-GLY is mainly due to the condensation reaction of hydroxyl and carboxyl groups. All adhesives are in the range of 3600-2750cm -1 The infrared absorption peak at is mainly caused by the stretching vibration and deformation vibration of the hydroxyl groups and free -OH groups on the carboxylic acids on each binder. The formation of ester bonds indicates that the GG-CA-GLY binder has been successfully synthesized and used as a binder in silicon negative electrode lithium-ion batteries.

[0090] Figure 2 shows the contact angle test results of the GG-CA-GLY binder (GGC for short) prepared in Example 1 and the CMC and PVDF binders prepared in Comparative Examples 2 and 3 (tested using a video optical contact angle meter, Dataphysics OCAPro 15). The contact angles with the silicon surface are 29.3 degrees, 71 degrees, and 47.9 degrees, respectively. It can be concluded that the prepared GG-CA-GLY binder has a larger contact area with the silicon surface, can better wrap silicon particles, and can better buffer the volume expansion of silicon, resulting in superior electrochemical performance.

[0091] Figure 3 shows the impedance test results of the Si@GG-CA-GLY electrode prepared in Example 1, the Si@GG-CA-GLY electrode prepared in Comparative Example 1, and the SiNPs@CMC electrode prepared in Comparative Example 2. It can be seen that the Si@GG-CA-GLY electrode prepared in Example 1 has the smallest charge transfer impedance and lithium ion diffusion resistance. The semicircular area in the high-frequency region represents the charge transfer impedance of the electrode surface, and the slope of the oblique line in the low-frequency region represents the lithium ion diffusion resistance inside the electrode material.

[0092] Figure 4 shows the cycle data of the electrode sheets obtained in Examples 1 to 3 and Comparative Examples 1 to 2 at a current density of 0.5 A / g. The results show that under the same test conditions, glycerol significantly promotes the self-healing properties of the electrode sheets using different binders. There is a significant difference in electrochemical performance between Comparative Example 1 without glycerol and Examples 1 to 3. Compared with traditional binders (Comparative Examples 2 and 3), the capacity of CMC and PVDF binders is significantly lower than that of GG-CA-GLY, and their capacity decay is larger in the subsequent cycle process. It can be seen that the performance of GG-CA-GLY binder is significantly better than that of CMC and PVDF binder (due to the poor performance of PVDF binder, it is not marked in the figure). At a current density of 0.5 A / g, the electrode containing GG-CA-GLY binder still retains a high capacity of 2300 mAh / g after 120 cycles, and its cycle stability is good.

[0093] Figure 5 is the electrochemical performance test results of the electrodes prepared in Examples 1 to 3 and Comparative Examples 1 to 3. The results show that the Si@GG-CA-GLY electrode prepared by the present invention has good cycle performance and good rate performance, and is much higher than the SiNPs@CMC electrode and SiNPs@PVDF electrode in Comparative Examples 2 and 3.

[0094] The above results show that the GG-CA-GLY binder synthesized by the method of the present invention has certain self-healing properties and flexibility, effectively improves the volume expansion problem of silicon particles during continuous charging and discharging, and improves the electrochemical performance of the binder in silicon negative electrode lithium ion batteries.

[0095] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon negative electrode binder material with self-healing properties, characterized in that: The steps include: (1) Hydrolysis treatment: dissolving guar gum in water, and performing a hydrolysis reaction at 30 to 100° C. under stirring to obtain a guar gum solution; dissolving citric acid in water, and performing a hydrolysis reaction under stirring to obtain a citric acid solution; (2) Rehydrolysis treatment: guar gum solution and citric acid solution are mixed and then glycerol is added to obtain a reaction solution; the reaction solution is then subjected to a rehydrolysis reaction under stirring conditions to obtain a silicon-carbon negative electrode binder material with self-healing properties.

2. The method for preparing the silicon-carbon negative electrode binder material with self-healing properties according to claim 1, characterized in that: In step (1), the temperature of the guar gum hydrolysis reaction is 40 to 90° C.; The concentration of guar gum in the reaction solution in step (2) is 0.1 to 10% by mass; The concentration of citric acid in the reaction solution in step (2) is 0.1 to 10% by mass; The concentration of glycerol in the reaction solution in step (2) is 4 to 50% by mass.

3. The method for preparing the silicon-carbon negative electrode binder material with self-healing properties according to claim 2, characterized in that: In step (1), the temperature of the guar gum hydrolysis reaction is 40 to 80° C.; The concentration of guar gum in the reaction solution in step (2) is 0.1 to 5% by mass; The concentration of citric acid in the reaction solution in step (2) is 0.1 to 5% by mass; The concentration of glycerol in the reaction solution in step (2) is 4.5-20% by mass.

4. The method for preparing the silicon-carbon negative electrode binder material with self-healing properties according to claim 3, characterized in that: In step (1), the temperature of the guar gum hydrolysis reaction is 60° C.; The concentration of guar gum in the reaction solution in step (2) is 0.6-0.7% by mass; The concentration of citric acid in the reaction solution in step (2) is 0.6-0.7% by mass; The concentration of glycerol in the reaction solution in step (2) is 4.6-11.1% by mass.

5. The method for preparing the silicon-carbon negative electrode binder material with self-healing properties according to claim 1, characterized in that: The concentration of the guar gum solution in step (1) is 5-15 mg / ml; The citric acid described in step (1) is citric acid monohydrate; The dosage of the citric acid monohydrate is calculated based on 15-45 mg of citric acid monohydrate per ml of water; The hydrolysis reaction time in step (1) is 2 to 3 hours; The time of the re-hydrolysis reaction in step (2) is 2 to 3 hours.

6. A silicon-carbon negative electrode binder material with self-healing properties, characterized in that: It is prepared by the method according to any one of claims 1 to 5.

7. Use of the silicon-carbon negative electrode binder material with self-healing properties as claimed in claim 6 in the preparation of negative electrode materials for lithium-ion batteries.

8. A negative electrode sheet for a lithium-ion battery, characterized in that: It comprises active material nano-silicon, a conductive agent and the silicon-carbon negative electrode binder material with self-healing properties as claimed in claim 6; The particle size of the active material nano-silicon is 20 to 60 nm; The conductive agent is one or more of conductive carbon black, poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid, carbon nanotubes and graphene; The silicon-carbon negative electrode binder material with self-healing properties accounts for 10-20% of the total mass of the active material nano-silicon, the conductive agent and the silicon-carbon negative electrode binder material with self-healing properties; The silicon nanoparticles account for 80-90% of the total mass of the active material nano-silicon, the conductive agent and the silicon-carbon negative electrode binder material with self-healing properties; The conductive agent accounts for 5-10% of the total mass of the active material nano silicon, the conductive agent and the silicon-carbon negative electrode binder material with self-healing performance.

9. Use of the silicon-carbon negative electrode binder material with self-healing properties as claimed in claim 6 and / or the lithium ion battery negative electrode sheet as claimed in claim 8 in the preparation of lithium ion batteries.

10. A button battery, characterized in that: The lithium-ion battery comprises a negative electrode sheet, a positive electrode sheet, an electrolyte and a separator as claimed in claim 8; The positive electrode sheet is a lithium sheet; The electrolyte is LiPF6 electrolyte; The diaphragm is a polypropylene microporous membrane Celgard-2400.

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