Preparation method of high-first-effect high-capacity silicon monoxide negative pole piece

Abstract

The invention relates to the technical field of lithium batteries, in particular to a preparation method of a high-first-efficiency high-capacity silicon monoxide negative pole piece, which comprises the following steps: 1, improving the lithium content of silicon monoxide powder by adopting a powder pre-lithiation mode; 2, through the lithium-rich high-conductivity polymer binder, the lithium content in the silicon monoxide negative electrode plate is further improved, the conductivity of the silicon monoxide negative electrode plate is enhanced, the ratio of active substances in a solid is increased, and the surface density of the active substances is increased; and 3, mixing the powder prepared in the step 1 with the lithium-rich high-conductivity polymer binder prepared in the step 2 to obtain the silicon monoxide negative pole piece. According to the negative electrode prepared by the method, the lithium content is increased through powder pre-lithiation and slurry pre-lithiation, and the negative electrode has relatively high first coulombic efficiency. And meanwhile, the lithium-rich good conductive binder improves the ionic conductivity of the silicon monoxide negative electrode and reduces the weight of the silicon monoxide coated carbon layer, so that the silicon monoxide negative electrode plate has extremely high surface density and mass capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a method for preparing a high-initial-efficiency and high-capacity silicon monoxide negative electrode sheet. Background Art

[0002] Due to the widespread use of fossil fuels, which has led to global warming and frequent extreme weather events, countries are actively developing renewable, clean energy sources to reduce fossil fuel consumption. This development relies heavily on rechargeable batteries, as wind and solar power generation is intermittent and random, requiring them to balance power supply and consumption. Currently, lithium-ion batteries are the most common rechargeable battery, and improving their energy density and cycle life is crucial for further developing the new energy industry.

[0003] A typical lithium-ion battery consists of a positive electrode, a negative electrode, a current collector, a separator, and an electrolyte. Its charge and discharge behavior is based on the transfer of lithium ions between the positive and negative electrodes. Therefore, the amount of lithium ions that can be transferred determines the battery's capacity. In batteries that use silicon-based materials instead of traditional negative electrodes, such as those using silicon oxide negative electrodes, all the transferable lithium ions in the battery come from the positive electrode material. Side reactions between the anode and electrolyte, the formation of a solid electrolyte interface (SEI) on the anode surface, SEI growth, and lithium deposition during cycling can lead to the irreversible consumption of approximately 6%-15% of the lithium ions in the positive electrode material. Therefore, pre-lithiation, which introduces additional active lithium ions into the battery to compensate for this lithium loss, is crucial. Pre-lithiation not only increases the battery's specific capacity but also offers additional benefits, such as increasing the battery voltage, improving the stability of the SEI during deep discharge, and extending the cycle life. In the lithium-ion battery industry, pre-lithiation can increase the battery's energy density by 5-10% and increase the cycle life by 3-5 times. Therefore, it is very important to develop cheap and efficient pre-lithiation technology.

[0004] Currently commonly used pre-lithiation methods include: external electrochemical pre-lithiation, liquid chemical pre-lithiation and contact pre-lithiation. Among them, external electrochemical pre-lithiation requires interruption of battery manufacturing steps and has poor compatibility with existing processes; liquid chemistry is still in the laboratory stage because the pre-lithiation solvent used has strong adhesion to the electrode and is difficult to remove; dead lithium that loses electronic conductivity during contact pre-lithiation accumulates around the anode interface, hindering the proton / charge transfer reaction and reducing the utilization rate of lithium. In other words, these methods cannot compensate for the loss of active lithium ions well, and thus cannot solve the problems of insufficient cycle performance and low first coulombic efficiency of silicon monoxide negative electrode. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a silicon monoxide negative electrode sheet to solve the technical problems of insufficient cycle stability and area capacity and low first coulombic efficiency of silicon monoxide negative electrodes in the prior art.

[0006] To achieve the above-mentioned object, the present invention provides a method for preparing a high-initial-efficiency and high-capacity silicon oxide negative electrode sheet, comprising:

[0007] Step 1: Preparation of lithium-rich silicon oxide particles: Silicon oxide and lithium source are mixed evenly and sintered at high temperature under an inert gas protection environment to obtain a lithium-silicon alloy pre-embedded with lithium;

[0008] Step 2: Preparation of a lithium-rich conductive polymer binder: Mixing a highly flexible polymer organic acid, a high-strength polymer organic acid, and lithium hydroxide to obtain a partially pre-lithiated, hydrogen-bonded flexible-rigid organic acid lithium polymer binder;

[0009] Step 3: Preparation of high-initial-efficiency and high-capacity silicon dioxide negative electrode sheet: The lithium-rich silicon dioxide particles, single-walled carbon nanotubes, and lithium-rich conductive polymer binder obtained in step 1 are mixed in a certain proportion, added and dissolved and stirred into a uniform slurry, and coated on copper foil to prepare a high-initial-efficiency and high-capacity silicon dioxide negative electrode sheet.

[0010] It is further defined that the initial particle size D of silicon dioxide in step 1 is 50 At 100-200 nm, the lithium source is selected from one or more of lithium hydride, lithium borohydride, lithium powder, and lithium carbonate to form a Li-Si or Li-Si-O alloy material.

[0011] It is further defined that in step 1, silicon oxide and the lithium source are evenly mixed by mechanical ball milling, the mass ratio of silicon oxide to lithium source is 15:1 to 20:1, Si3N4 is selected as the ball milling medium, the mass ratio of ball milling medium to material is 7:3, and the ball mill is protected by inert gas; the ball mill speed is 200 to 500 rpm, and the ball milling time is 1 to 2 hours; the evenly mixed silicon oxide and lithium source are transferred to a tubular furnace, under inert gas protection, the tubular furnace temperature is 500 to 600°C, the reaction time is 4 to 6 hours, and after cooling to room temperature, the particle size is reduced by sand milling-spray drying.

[0012] Further defined, the solvent selected in the sand grinding process in step 1 is ultrapure water (conductivity <0.055uS / cm, resistivity <18.2MΩ·cm), the filling rate of the sand grinding zirconium beads is 70-80%, and the particle size of the sand grinding zirconium beads is D 50 The size of lithium-rich silicon oxide particles after sand grinding is 0.02 mm, the sand grinding time is 0.5 to 1 h, and the size of lithium-rich silicon oxide particles after sand grinding is D 50The lithium-rich silicon oxide slurry was spray-dried to remove the solvent, with the spray drying feed temperature being 100°C, the outlet air temperature being 80°C, and the argon flow rate being 2 m / s.

[0013] Further defined, the high-strength polymer organic acid selected in step 2 can be polyacrylic acid, polylactic acid, polymalic acid, polysuccinic acid, etc.; the high-flexibility polymer organic acid is a perfluorosulfonic acid (PFSA) polymer or a sulfonated tetrafluoroethylene fluorinated polymer-copolymer, such as Nafion (produced by DuPont), Aciplex (produced by Asahi Kasei Corporation), Flemion F (produced by Asahi Glass Co., Ltd.), etc. The molecular weight of the high-strength polymer organic acid depends on the organic acid selected. Generally, the molecular weight (MW) of the high-strength polymer organic acid is 10,000 to 250,000. It is prepared into a solution by magnetic stirring. The solvent is deionized water with a mass fraction of 20 to 28%. The magnetic stirring temperature is 40 to 48 ° C. and the stirring speed is 300 to 400 rpm. It is added in small batches to ensure that it is fully dispersed after each addition. Continue to add. The dissolution and dispersion time is 1 to 2 hours until the solution is uniform and transparent. The highly flexible polymer organic acid uses a long side chain (LSC) ionomer with an ionomer equivalent weight (EW) of 800-1100. The solvent of the highly flexible polymer organic acid solution uses anhydrous ethanol and deionized water. The mass fraction of the highly flexible polymer organic acid: deionized water: anhydrous ethanol is 5:15-20:80-75.

[0014] Further defined, the reagent for lithiating the high-strength polymer organic acid in step 2 is a lithium hydroxide solution, and the mass fraction of lithium hydroxide is 8-12wt%. The lithiation process needs to reserve some carboxyl groups to ensure their hydrogen bond interaction with the hydroxyl groups on the surface of silicon oxide, so the addition of lithium hydroxide needs to be controlled to a pH of 4.5-5.5. The reagent for lithiating the high-flexibility polymer organic acid is lithium hydroxide. Since the sulfonic acid group of the high-flexibility polymer is a terminal group, the mass fraction of lithium hydroxide added is 0.15-0.25wt%. Like the high-strength polymer lithium salt, the lithiation process needs to reserve some sulfonic acid groups, so the addition of lithium hydroxide needs to be controlled to a pH of 4.5-5.5. A high-strength polymer organic acid lithium salt is mixed with a high-flexibility polymer organic acid lithium salt in a mass ratio of 8:2 to 9.5:0.5. The unlithiated carboxyl groups and sulfonic acid groups interact with each other through hydrogen bonds to form a high-strength-high-flexibility adhesive network. After mixing, the solution is magnetically stirred to increase the contact between the groups. The magnetic stirring temperature is 30 to 50°C, the stirring speed is 300 to 500 rpm, and the stirring time is 12 to 24 hours.

[0015] It is further defined that in the step 3, silicon dioxide negative electrode sheets are prepared, and the slurrying step is: the active material selected is lithium-rich silicon dioxide particles, the conductive agent is single-walled carbon nanotubes, and the binder is a lithium-rich good conductive polymer binder, and the solid mass ratio of lithium-rich silicon dioxide particles: single-walled carbon nanotubes: lithium-rich good conductive polymer binder is 85:5:10. The solvent is deionized water, the solid content is 45wt%, the slurry viscosity is 4000mPa·s, and the slurry is sieved through a 200-mesh sieve to remove particles. Coating: The coating substrate is copper foil, the coating seam width is 180um, and the electrode is vacuum dried after coating, the oven temperature is 80°C, and the drying time is 12h. Rolling: The surface electrode density is 1.12g / cm 3 .

[0016] The technical principles of the present invention are as follows: 1. By pre-lithiation of lithium alloy, LixSi is used to effectively improve the specific energy and energy density of the battery. Nano-sized LixSi particles can provide uniform local lithium distribution to achieve rapid pre-lithiation of the silicon oxide anode. The smaller particle size is less likely to disrupt the structure of the electrode. In addition, the silicon oxide with LixSi will form voids after delithiation, leaving space for the volume expansion of the silicon oxide in the next pre-lithiation process. 2. A highly flexible polymer organic acid and a high-strength polymer organic acid are mixed with lithium hydroxide to obtain a partially pre-lithiated and hydrogen-bonded flexible-rigid organic acid lithium polymer binder, thereby constructing a three-dimensional network binder with both high strength and high flexibility. In this binder, the partially lithiated high-strength polymer organic acid, such as polypropylene, has high viscosity and high mechanical properties, and the partially lithiated high-flexibility polymer organic acid, such as Flemion F, can serve as a buffer structure for the volume expansion of silicon oxide, thereby enhancing the cycle performance of the silicon oxide negative electrode. 3. Due to the ionic conductivity of the polymer binder, the movement of localized solvated ions in the polymer chain can promote the transfer of lithium ions to the carboxylic acid and sulfonic acid groups on the binder through partial pre-lithiation, thereby enhancing the conductivity of lithium ions.

[0017] The preparation method using the technical solution of the present invention has the following advantages:

[0018] 1. The lithium-rich silicon oxide particles prepared by the present invention can effectively increase the lithium content of powder particles. These nanoparticles are produced by a thermal alloying process, can be processed in a slurry, are stable in dry air, and are compatible with existing industrial battery manufacturing processes;

[0019] 2. The lithium-rich conductive polymer binder prepared by the present invention has high mechanical properties and adhesion strength, can effectively buffer the volume expansion of silicon oxide particles, improve cycle life, and at the same time, partially pre-lithiation process, can increase the lithium content and conductivity of the negative electrode plate as a whole;

[0020] 3. The present invention introduces active lithium in two dimensions, namely powder and additive, through multiple pre-lithiation processes, which can significantly improve the initial coulombic efficiency of the battery, enhance the stability of the SEI structure and extend the cycle life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The figure is a flow chart of a method for preparing a high-initial-efficiency and high-capacity silicon monoxide negative electrode sheet according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The following is further described in detail through specific implementation methods:

[0023] A method for preparing a high-initial-efficiency and high-capacity silicon oxide negative electrode sheet comprises the following steps:

[0024] Example 1:

[0025] Step 1: Preparation of lithium-rich silicon oxide particles:

[0026] D 50 =100nm silicon dioxide and lithium borohydride were uniformly mixed by mechanical ball milling. The mass ratio of silicon dioxide to lithium source was 18:1. Si3N4 was used as the ball milling medium. The mass ratio of ball milling medium to material was 7:3. Inert gas was introduced into the ball milling jar for protection. The ball milling speed was 300 rpm and the ball milling time was 1.5 hours.

[0027] The uniformly mixed silicon oxide and lithium source were transferred to a tube furnace under inert gas protection at a temperature of 550°C for 5.5 hours to obtain a lithium-silicon alloy pre-embedded with lithium.

[0028] After the reaction temperature dropped to room temperature, the particles were reduced in size by sand milling and spray drying. Ultrapure water (conductivity <0.055 μS / cm, resistivity <18.2 MΩ·cm) was used as the sand milling solvent. The zirconium bead filling ratio was 80%, the particle size (D50) was 0.02 mm, and the sand milling time was 0.5 h. The D50 size of the lithium-rich silica particles after sand milling was approximately 200 nm, thus preparing a slurry. The solvent was then removed from the lithium-rich silica slurry by spray drying. The spray drying feed temperature was 100°C, the outlet air temperature was 80°C, and the argon flow rate was 2 m / s.

[0029] Step 2: Preparation of lithium conductive polymer binder:

[0030] A high-strength, high-flexibility polymeric organic acid solution was prepared: polyacrylic acid was used as the high-strength polymeric organic acid; Flemion F, a perfluorosulfonic acid (PFSA) polymer, was used as the high-flexibility polymeric organic acid. The molecular weight (MW) of the high-strength polymeric organic acid was 200,000-250,000. The solution was prepared by magnetic stirring. Deionized water (28% by mass) was used as the solvent. The stirring temperature was 45°C and the stirring speed was 400 rpm. Small amounts were added in batches, ensuring thorough dispersion after each addition. Continued additions were made for 2 hours until the solution was homogeneous and transparent. The high-flexibility polymeric organic acid was a long side chain (LSC) ionomer with an ionomer equivalent weight (EW) of 830. Anhydrous ethanol and deionized water were used as the solvents for the high-flexibility polymeric organic acid solution. The mass ratio of the high-flexibility polymeric organic acid: deionized water: anhydrous ethanol was 5:20:75.

[0031] Preparation of a partially pre-lithiated, hydrogen-bonded flexible-rigid organic acid polymer binder: The reagent for lithiating the high-strength polymer organic acid is a lithium hydroxide solution with a mass fraction of 12wt%. The lithiation process requires the reservation of some carboxyl groups to ensure hydrogen bonding interactions with the hydroxyl groups on the surface of silicon oxide, so the addition of lithium hydroxide needs to be controlled to a pH of 5.0. The reagent for lithiating the high-flexibility polymer organic acid is lithium hydroxide. Since the sulfonic acid group of the high-flexibility polymer is a terminal group, the mass fraction of lithium hydroxide added is 0.18wt%. Similar to the high-strength polymer lithium salt, the lithiation process requires the reservation of some sulfonic acid groups, so the addition of lithium hydroxide needs to be controlled to a pH of 5.0. High-strength polymer organic acid lithium salt and high-flexibility polymer organic acid lithium salt are mixed in a mass ratio of 8:2. The unlithiated carboxyl groups and sulfonic acid groups interact with each other through hydrogen bonds to form a high-strength-high-flexibility adhesive network. After mixing, the solution is magnetically stirred to improve the contact between the groups. The magnetic stirring temperature is 40°C, the stirring speed is 400 rpm, and the stirring time is 12 hours.

[0032] Step 3: Preparation of high initial efficiency and high capacity silicon oxide negative electrode:

[0033] The active material used is lithium-rich silicon oxide particles, the conductive agent is single-walled carbon nanotubes, and the binder is lithium-rich good conductive polymer binder. The solid mass ratio of lithium-rich silicon oxide particles: single-walled carbon nanotubes: lithium-rich good conductive polymer binder is 85:5:10. The solvent is deionized water, the solid content is 45wt%, the slurry viscosity is 4000mPa·s, and the slurry is sieved through a 200-mesh sieve to remove particles. Coating: The coating substrate is copper foil, the coating seam width is 180um, and the electrode is vacuum dried after coating. The oven temperature is 80°C and the drying time is 12h. Rolling: The surface electrode density is 1.12g / cm 3 .

[0034] Example 2:

[0035] Step 1: Preparation of lithium-rich silicon oxide particles:

[0036] D 50 =150nm silicon dioxide and lithium borohydride were mixed uniformly by mechanical ball milling. The mass ratio of silicon dioxide to lithium source was 18:1. Si3N4 was used as the ball milling medium. The mass ratio of ball milling medium to material was 7:3. Inert gas was introduced into the ball milling jar for protection. The ball milling speed was 300 rpm and the ball milling time was 1.5 hours.

[0037] The uniformly mixed silicon oxide and lithium source were transferred to a tube furnace under inert gas protection at a temperature of 550°C for 5.5 hours to obtain a lithium-silicon alloy pre-embedded with lithium.

[0038] After the reaction temperature dropped to room temperature, the particles were reduced in size by sand milling and spray drying. Ultrapure water (conductivity <0.055 μS / cm, resistivity <18.2 MΩ·cm) was used as the sand milling solvent. The zirconium bead filling ratio was 80%, the particle size (D50) was 0.02 mm, and the sand milling time was 0.5 h. The D50 size of the lithium-rich silica particles after sand milling was approximately 200 nm, thus preparing a slurry. The solvent was then removed from the lithium-rich silica slurry by spray drying. The spray drying feed temperature was 100°C, the outlet air temperature was 80°C, and the argon flow rate was 2 m / s.

[0039] Step 2: Preparation of lithium conductive polymer binder:

[0040] A high-strength, high-flexibility polymeric organic acid solution was prepared: polylactic acid (PLA) was used as the high-strength polymeric organic acid; Aciplex, a perfluorosulfonic acid (PFSA) polymer, was used as the high-flexibility polymeric organic acid. The molecular weight (MW) of the high-strength polymeric organic acid ranged from 50,000 to 100,000. The solution was prepared by magnetic stirring. Deionized water (28% by mass) was used as the solvent. The stirring temperature was 45°C and the stirring speed was 400 rpm. Small amounts were added in batches, ensuring thorough dispersion after each addition. Continued additions were made for 2 hours until the solution was homogeneous and transparent. The high-flexibility polymeric organic acid was a long side chain (LSC) ionomer with an ionomer equivalent weight (EW) of 850. Anhydrous ethanol and deionized water were used as the solvents for the high-flexibility polymeric organic acid solution. The mass ratio of the high-flexibility polymeric organic acid: deionized water: anhydrous ethanol was 5:20:75.

[0041] Preparation of a partially pre-lithiated, hydrogen-bonded flexible-rigid organic acid polymer binder: The reagent for lithiating the high-strength polymer organic acid is a lithium hydroxide solution with a mass fraction of 12wt%. The lithiation process requires the reservation of some carboxyl groups to ensure hydrogen bonding interactions with the hydroxyl groups on the surface of silicon oxide, so the addition of lithium hydroxide needs to be controlled to a pH of 4.5. The reagent for lithiating the high-flexibility polymer organic acid is lithium hydroxide. Since the sulfonic acid group of the high-flexibility polymer is a terminal group, the mass fraction of lithium hydroxide added is 0.18wt%. Similar to the high-strength polymer lithium salt, the lithiation process requires the reservation of some sulfonic acid groups, so the addition of lithium hydroxide needs to be controlled to a pH of 4.5. High-strength polymer organic acid lithium salt and high-flexibility polymer organic acid lithium salt are mixed in a mass ratio of 8:2. The unlithiated carboxyl groups and sulfonic acid groups interact with each other through hydrogen bonds to form a high-strength-high-flexibility adhesive network. After mixing, the solution is magnetically stirred to improve the contact between the groups. The magnetic stirring temperature is 40°C, the stirring speed is 400 rpm, and the stirring time is 12 hours.

[0042] Step 3: Preparation of high initial efficiency and high capacity silicon oxide negative electrode:

[0043] The active material used is lithium-rich silicon oxide particles, the conductive agent is single-walled carbon nanotubes, and the binder is lithium-rich good conductive polymer binder. The solid mass ratio of lithium-rich silicon oxide particles: single-walled carbon nanotubes: lithium-rich good conductive polymer binder is 85:5:10. The solvent is deionized water, the solid content is 45wt%, the slurry viscosity is 4000mPa·s, and the slurry is sieved through a 200-mesh sieve to remove particles. Coating: The coating substrate is copper foil, the coating seam width is 180um, and the electrode is vacuum dried after coating. The oven temperature is 80°C and the drying time is 12h. Rolling: The surface electrode density is 1.12g / cm 3 .

[0044] Example 3:

[0045] Step 1: Preparation of lithium-rich silicon oxide particles:

[0046] D 50 = 200nm silicon dioxide and lithium borohydride were mixed uniformly by mechanical ball milling. The mass ratio of silicon dioxide to lithium source was 18:1. Si3N4 was used as the ball milling medium. The mass ratio of ball milling medium to material was 7:3. Inert gas was introduced into the ball milling jar for protection. The ball milling speed was 300 rpm and the ball milling time was 1.5 hours.

[0047] The uniformly mixed silicon oxide and lithium source were transferred to a tube furnace under inert gas protection at a temperature of 550°C for 5.5 hours to obtain a lithium-silicon alloy pre-embedded with lithium.

[0048] After the reaction temperature dropped to room temperature, the particles were reduced in size by sand milling and spray drying. Ultrapure water (conductivity <0.055 μS / cm, resistivity <18.2 MΩ·cm) was used as the sand milling solvent. The zirconium bead filling ratio was 80%, the particle size (D50) was 0.02 mm, and the sand milling time was 0.5 h. The D50 size of the lithium-rich silica particles after sand milling was approximately 200 nm, thus preparing a slurry. The solvent was then removed from the lithium-rich silica slurry by spray drying. The spray drying feed temperature was 100°C, the outlet air temperature was 80°C, and the argon flow rate was 2 m / s.

[0049] Step 2: Preparation of lithium conductive polymer binder:

[0050] A high-strength, high-flexibility polymeric organic acid solution was prepared: polymalic acid was used as the high-strength polymeric organic acid; Nafion, a perfluorosulfonic acid (PFSA) polymer, was used as the high-flexibility polymeric organic acid. The molecular weight (MW) of the high-strength polymeric organic acid ranged from 20,000 to 50,000. The solution was prepared by magnetic stirring in deionized water at a mass fraction of 28%. The magnetic stirring temperature was 45°C and the stirring speed was 400 rpm. Small amounts were added in batches, ensuring thorough dispersion after each addition. Continued additions were made for 2 hours until the solution was homogeneous and transparent. The high-flexibility polymeric organic acid was a long side chain (LSC) ionomer with an ionomer equivalent weight (EW) of 1100. The solvents for the high-flexibility polymeric organic acid solution were anhydrous ethanol and deionized water, with a mass ratio of 5:20:75 for the high-flexibility polymeric organic acid:deionized water:anhydrous ethanol.

[0051] Preparation of a partially pre-lithiated, hydrogen-bonded flexible-rigid organic acid polymer binder: The reagent for lithiating the high-strength polymer organic acid is a lithium hydroxide solution with a mass fraction of 12wt%. The lithiation process requires the reservation of some carboxyl groups to ensure hydrogen bonding interactions with the hydroxyl groups on the surface of silicon oxide, so the addition of lithium hydroxide needs to be controlled to a pH of 5.5. The reagent for lithiating the high-flexibility polymer organic acid is lithium hydroxide. Since the sulfonic acid group of the high-flexibility polymer is a terminal group, the mass fraction of lithium hydroxide added is 0.18wt%. Similar to the high-strength polymer lithium salt, the lithiation process requires the reservation of some sulfonic acid groups, so the addition of lithium hydroxide needs to be controlled to a pH of 5.5. High-strength polymer organic acid lithium salt and high-flexibility polymer organic acid lithium salt are mixed in a mass ratio of 8:2. The unlithiated carboxyl groups and sulfonic acid groups interact with each other through hydrogen bonds to form a high-strength-high-flexibility adhesive network. After mixing, the solution is magnetically stirred to improve the contact between the groups. The magnetic stirring temperature is 40°C, the stirring speed is 400 rpm, and the stirring time is 12 hours.

[0052] Step 3: Preparation of high initial efficiency and high capacity silicon oxide negative electrode:

[0053] The active material used is lithium-rich silicon oxide particles, the conductive agent is single-walled carbon nanotubes, and the binder is lithium-rich good conductive polymer binder. The solid mass ratio of lithium-rich silicon oxide particles: single-walled carbon nanotubes: lithium-rich good conductive polymer binder is 85:5:10. The solvent is deionized water, the solid content is 45wt%, the slurry viscosity is 4000mPa·s, and the slurry is sieved through a 200-mesh sieve to remove particles. Coating: The coating substrate is copper foil, the coating seam width is 180um, and the electrode is vacuum dried after coating. The oven temperature is 80°C and the drying time is 12h. Rolling: The surface electrode density is 1.12g / cm 3 .

[0054] Comparative Example 1:

[0055] The difference from Example 1 is that the silicon dioxide particles are not pre-lithiated, that is, step 1 is missing, and the rest of the preparation method and parameters are consistent with Example 1.

[0056] Comparative Example 2:

[0057] The difference from Example 1 is that no high-mechanical-performance, high-viscosity high-molecular-weight polymer is introduced, that is, no partially lithiated polyacrylic acid is added in step 2. The remaining preparation methods and parameters remain the same as those in Example 1.

[0058] Comparative Example 3:

[0059] The difference from Example 1 is that no highly flexible polymer is introduced, that is, no partially lithiated Flemion F is introduced in step 2). The rest of the preparation method and parameters are consistent with Example 1.

[0060] Comparative Example 4:

[0061] The difference from Example 1 is that the pH of the highly flexible polymer and the high-strength polymer after lithiation is adjusted to pH = 9, and an excess of LiOH is added in step 2. That is, all sulfonic acid groups and carboxyl groups are converted into corresponding lithium salts. The rest of the preparation method remains the same as Example 1.

[0062] The silicon-based negative electrode particles obtained in the above examples and comparative examples are further used to prepare a negative electrode, which specifically includes the following steps:

[0063] 1) Punch the rolled electrode into a negative electrode with a diameter of 10 mm.

[0064] 2) Using the prepared electrode as the positive electrode and metallic lithium as the negative electrode, the button battery assembly process is completed, and the half-cell electrochemical performance test of the assembled battery is performed, and the electrolyte used is tested.

[0065] The performance of the silicon-based negative electrodes prepared from the materials obtained in Examples 1-3 and Comparative Examples 1-3 was tested using the following method:

[0066] (1) Area capacity: Weigh the mass of the negative electrode and calculate the mass of the active material by the proportion of active material. The theoretical capacity of silicon monoxide is 2100 mAh / g.

[0067] (2) Initial Coulombic Efficiency Test: Voltage range 0.001-3 V. Charge and discharge current: 0.1 C, discharge first, then charge. Initial Coulombic Efficiency calculation method: initial charge capacity / initial discharge capacity.

[0068] (3) Rate performance test method: charge and discharge at rates of 0.1C, 0.2C, 0.4C, 0.8C, and 1.6C, with a voltage range of 0.001-3V, for 10 cycles each time, and discharge at a rate of 0.2C for 100 cycles to test its capacity retention rate.

[0069] (4) Cyclic performance test method: Discharge at a rate of 0.5C and 2C, with a voltage range of 0.001-3V, and cycle 200 times to test its capacity retention rate.

[0070] The electrical performance test results of the batteries prepared using the materials of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0071] Table 1 Battery performance test data

[0072]

[0073] It can be seen from Example 1, Example 2 and Example 3 in combination with the comparative example that the silicon oxide negative electrode sheet prepared by the method of the present invention using the above-mentioned high-strength polymer organic acid and high-flexibility polymer organic acid has greatly improved the rate performance and capacity retention of the half-cell. It can be seen from Example 1 and Comparative Example 1 that the pre-lithiation process can significantly improve the first coulombic efficiency and cycle performance of the battery, and the improvement in the capacity retention under high current is extremely obvious. It can be seen from Example 1 and Comparative Example 2 and Comparative Example 3 that the high-strength and high-flexibility coexisting three-dimensional network structure binder on the surface of the silicon oxide negative electrode has both a high-strength polyacrylic acid framework and a high-flexibility soft Flemion F as a buffer structure, has strong adhesion to the silicon oxide negative electrode and the current collector, can adapt to the huge volume change during the lithium insertion process of the silicon oxide negative electrode, and maintain the integrity of the silicon oxide negative electrode structure. It can be seen from the examples and comparative example 4 that due to the high degree of lithiation of the binder system and the lack of hydrogen bond cross-linking between the binders, the binder is still a linear structure rather than a coated network structure, with few contact sites with silicon oxide, large volume collisions during lithium insertion, and linear binder slippage, which cannot play a role in inhibiting volume expansion. Therefore, Example 1 has a higher cycle capacity retention rate, while the rate performance and capacity retention rate of comparative example 4 are lower. Therefore, maintaining a certain degree of lithiation not only increases the content of active lithium in the slurry to ensure that lithium ions can be transferred through the physical and chemical groups of the binder, thereby improving the conductivity of the silicon oxide negative electrode, but also retains certain sulfonic acid and carboxyl groups. These groups construct a robust three-dimensional conductive network between the binder and the binder, and between the binder and the silicon oxide active particles, which plays an important role in stabilizing the volume expansion of silicon oxide. Therefore, Example 1 has better rate performance.

[0074] The present invention uses lithium alloy pre-lithiation to achieve a uniform local distribution of active lithium at the silicon oxide negative electrode, thereby realizing rapid pre-lithiation of the silicon oxide anode. A lithium-rich, highly conductive polymer binder: partially lithiated lithium polyacrylate and Flemion F construct a three-dimensional network binder with both high strength and high flexibility. In this binder, the high viscosity and high mechanical properties of partially lithiated polypropylene maintain good contact between silicon oxide and the current collector. The highly flexible Flemion F can buffer the volume expansion of silicon oxide during the lithium insertion process, ensuring the integrity of the silicon oxide particle structure. Due to the ionic conductivity of the polymer binder, the movement of localized solvated ions in the polymer chain causes lithium ions to transfer to the carboxylic acid and sulfonic acid groups on the binder, enhancing the conductivity of the silicon oxide electrode.

[0075] It should be pointed out that those skilled in the art can use or adjust other reagents with similar properties and similar process parameters mentioned in this application according to actual conditions, such as simply changing the high-strength polymer organic acid, simply changing the high-flexibility polymer organic acid, or simply changing similar process parameters, such as simply adjusting the mass ratio of silicon oxide to lithium source, simply adjusting the surface electrode density, simply changing the reaction time, etc. These effects can be expected and will not be repeated.

[0076] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, several variations and improvements can be made without departing from the technical solution of the present invention. In the present invention, unless otherwise clearly specified and limited, the terms "install", "connect", "connect", "fix" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. The scope of protection claimed by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a high-initial-efficiency and high-capacity silicon oxide negative electrode sheet, characterized in that: include: Step 1: Preparation of lithium-rich silicon oxide particles: Silicon oxide and lithium source are mixed evenly, and sintered at high temperature under an inert gas protection environment to obtain a lithium-silicon alloy pre-embedded with lithium; Step 2: Preparation of lithium-rich conductive polymer binder: mixing a high-flexibility polymer organic acid, a high-strength polymer organic acid and lithium hydroxide to obtain a partially pre-lithiated and hydrogen-bonded flexible-rigid organic acid lithium polymer binder; Step 3: Preparation of high-initial-efficiency and high-capacity silicon oxide negative electrode sheet: The lithium-rich silicon oxide particles, single-walled carbon nanotubes, and lithium-rich conductive polymer binder obtained in step 1 are mixed according to a set ratio, added to dissolve and stirred into a uniform slurry, coated on copper foil, dried and rolled to prepare a high-initial-efficiency and high-capacity silicon oxide negative electrode sheet.

2. The method for preparing a high initial efficiency and high capacity silicon oxide negative electrode sheet according to claim 2, characterized in that: The initial particle size D of silicon dioxide in step 1 50 At 100-200 nm, the lithium source is selected from one or more of lithium hydride, lithium borohydride, lithium powder, and lithium carbonate.

3. The method for preparing a high initial efficiency and high capacity silicon oxide negative electrode sheet according to claim 1, characterized in that: In the step 1, silicon dioxide and the lithium source are uniformly mixed by mechanical ball milling, the mass ratio of silicon dioxide to the lithium source is 15:1-20:1, Si3N4 is selected as the ball milling medium, an inert gas is passed into the ball milling jar for protection, and the ball milling time is 1-2 hours; the uniformly mixed silicon dioxide and lithium source are transferred to a tubular furnace, reacted under the protection of inert gas, the temperature of the tubular furnace is 500-600°C, and the reaction time is 4-6 hours.

4. The method for preparing a high initial efficiency and high capacity silicon oxide negative electrode sheet according to claim 3, characterized in that: In the step 1, the temperature is cooled to room temperature after the reaction in the tubular furnace, and then the particle size is reduced by sand milling-spray drying.

5. The method for preparing a high initial efficiency and high capacity silicon oxide negative electrode sheet according to claim 4, characterized in that: The solvent used in the sand grinding process in step 1 is ultrapure water, the filling rate of the sand grinding zirconium beads is 70-80%, and the particle size of the sand grinding zirconium beads is D 50 The size of lithium-rich silicon oxide particles after sand grinding is 0.02 mm. 50 The particle size is 200-400 nm, and then the slurry is prepared and the solvent is removed by spray drying. The feed temperature of the spray drying is 100° C., the outlet air temperature is 80° C., and the argon flow rate is 2 m / s.

6. The method for preparing a high initial efficiency and high capacity silicon oxide negative electrode sheet according to claim 1, characterized in that: The high-strength polymer organic acid selected in step 2 is polyacrylic acid, polylactic acid, polymalic acid or polysuccinic acid, which is added in small amounts in batches into deionized water and stirred to form a solution, ensuring that it is fully dispersed after each addition, and then continuing to add until the solution is uniform and transparent, and the mass fraction of the solution is 20-28%; the high-flexibility polymer organic acid is a perfluorosulfonic acid polymer, which is configured into a solution, the solvent is anhydrous ethanol and deionized water, and the mass ratio of the high-flexibility polymer organic acid, deionized water and anhydrous ethanol is 5:15-20:80-75.

7. The method for preparing a high initial efficiency and high capacity silicon oxide negative electrode sheet according to claim 1, characterized in that: In the step 2, the mass fraction of lithium hydroxide in the lithiated high-strength polymer organic acid is 8-12wt%, and the addition of lithium hydroxide is controlled to a pH of 4.5-5.5; the mass fraction of lithium hydroxide in the lithiated high-flexibility polymer organic acid is 0.15-0.25wt%, and the addition of lithium hydroxide is controlled to a pH of 4.5-5.5; the high-strength polymer organic acid lithium salt and the high-flexibility polymer organic acid lithium salt are mixed in a mass ratio of 8:2-9.5:0.5 to form a high-strength-high-flexibility adhesive network.

8. The method for preparing a high initial efficiency and high capacity silicon oxide negative electrode sheet according to claim 7, characterized in that: The high-strength polymer organic acid lithium salt and the high-flexibility polymer organic acid lithium salt are mixed and then magnetically stirred at a temperature of 30 to 50° C., a stirring speed of 300 to 500 rpm, and a stirring time of 12 to 24 hours.

9. The method for preparing a high initial efficiency and high capacity silicon oxide negative electrode sheet according to claim 1, characterized in that: The slurry in step 3 meets the following requirements: lithium-rich silicon oxide particles, single-walled carbon nanotubes, and lithium-rich conductive polymer binder are mixed in a mass ratio of 85:5:10, deionized water is used as the solvent, the solid content is 45wt%, the slurry viscosity is 4000mPa·s, and the slurry is sieved through a 200-mesh sieve to remove particles.

10. The method for preparing a high initial efficiency and high capacity silicon oxide negative electrode sheet according to claim 1, characterized in that: The coating, drying and rolling in step 3 include: the coating substrate is copper foil, the coating gap width is 180um, the electrode is vacuum dried after coating, the oven temperature is 80°C, the drying time is 12h, and the rolling: the surface electrode density is 1.1-1.15g / cm 3 .

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