Preparation method of high-first-effect high-conductivity silicon monoxide negative electrode plate

Abstract

The invention relates to the technical field of lithium batteries, in particular to a preparation method of a high-first-efficiency and high-conductivity silicon monoxide negative pole piece, which comprises the following steps: 1, improving the conductivity of silicon monoxide powder in a fluorine-doped carbon coating manner, and enhancing the structural stability of an SEI film formed by the first charge and discharge of the silicon monoxide negative pole piece; 2, through a powder pre-lithiation mode, the lithium content of the silicon monoxide powder is improved, and the initial coulombic efficiency of the silicon monoxide negative electrode plate is enhanced; 3, by introducing a polymer binder containing a conjugated structure, the ion / electron conductivity of the silicon monoxide negative electrode plate is improved, the resistance of the negative electrode plate is reduced, and the volume expansion of silicon monoxide particles in the lithium intercalation and deintercalation process is buffered; and 4, mixing the powder prepared in the step 2 with the conductive polymer binder prepared in the step 3 to obtain the silicon monoxide negative pole piece. The negative pole piece prepared by the preparation method disclosed by the invention has relatively high first coulombic efficiency, relatively high conductivity and relatively high rate capability.

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-conductivity silicon monoxide negative electrode sheet. Background Art

[0002] With the growing demand for high energy density and long life lithium-ion batteries in energy storage projects, silicon-based materials have become the main candidate materials for the next generation of negative electrodes due to their low cost and high theoretical specific capacity. However, silicon-based negative electrodes face major challenges in commercialization, including volume expansion caused by lithium ion insertion, low intrinsic conductivity, and poor interfacial compatibility with the electrolyte, which can lead to a sharp drop in battery capacity or even failure. Silicon dioxide in silicon-based materials undergoes SiO2 degradation during the initial charge / discharge process. x +Li + →Li x Si y O z +LiO and Si+ x Li→Li x Si reacts with its inert products, which can act as a buffer layer to alleviate the volume expansion caused by silicon lithiation. Therefore, silicon oxide materials are generally considered to be feasible materials for designing high energy density negative electrodes.

[0003] However, in actual use, it is found that the first coulombic efficiency of silicon oxide negative electrode is low, and 20% of the active lithium in the battery is usually lost during the initial charge and discharge process. This is because silicon oxide has poor interfacial compatibility with the electrolyte, and the electrolyte and silicon oxide materials will undergo irreversible reactions. The irreversible formation of lithium silicates such as Li2O, LiSiO4 and Li6Si2O7 reduces the coulombic efficiency of the first cycle. In addition, another major loss of lithium ions is the lithium-containing SEI layer formed at the negative electrode-electrolyte interface. The loss of active lithium limits the performance of lithium-ion batteries. Therefore, it is usually necessary to add additional lithium sources to the negative electrode before the first charge and discharge cycle to form SEI, reduce the loss of active lithium caused by SEI formation during the initial charge process, and improve the performance of lithium-ion batteries.

[0004] Due to the poor intrinsic conductivity of silicon oxide materials, a large amount of conductive additives, such as acetylene black, are currently needed to ensure higher inter-particle conductivity. A large amount of additives will reduce the volume and lithium ion storage capacity, and there is no mechanical bonding force between the conductive additives. The stress generated by silicon oxide negative electrode materials during the lithiation process is an order of magnitude higher than that of graphite. The stress will destroy the connection between silicon oxide particles and the conductive additives. When the volume of silicon oxide expands after pre-lithiation, the conductive additives will be pushed away from the silicon oxide particles, resulting in a broken electrical connection. Summary of the invention

[0005] In view of the current problems of low first coulombic efficiency, low intrinsic conductivity and SEI structure stability caused by the loss of active lithium in silicon oxide negative electrode, the purpose of the present invention is to provide a new method for preparing silicon oxide negative electrode sheet to solve the above problems.

[0006] A method for preparing a high-initial-efficiency and high-conductivity silicon oxide negative electrode sheet, specifically comprising:

[0007] Step 1: Preparation of fluorine-doped carbon-coated silicon oxide particles: fluorine-doped carbon-coated silicon oxide particles are prepared by mixing fluorine-containing organic matter with silicon oxide particles and calcining them at high temperature. The fluorine-doped carbon coating is used to improve the conductivity of silicon oxide powder and enhance the structural stability of the SEI film formed by the first charge and discharge of the silicon oxide negative electrode plate;

[0008] Step 2: Preparation of lithium-rich fluorine-doped carbon-coated silicon oxide particles: The lithium-rich material is mixed with silicon oxide particles and calcined at high temperature to increase the lithium content of the silicon oxide powder and enhance the first coulombic efficiency of the silicon oxide negative electrode;

[0009] Step 3: Preparation of conductive polymer binder: partially lithiate a low elastic modulus polymer organic acid, mix it with a conductive polymer, and obtain the flexible part of the conductive polymer binder through hydrogen bonding; partially lithiate a high elastic modulus polymer organic acid, mix it with a conductive polymer, and obtain the rigid part of the conductive polymer binder through hydrogen bonding; the flexible-rigid part is mixed and prepared according to a set ratio to obtain a conductive polymer binder; by adding a conductive polymer and partially lithiated high elastic modulus polymer organic acid, a polymer binder containing a conjugated structure is introduced to improve the ionic / electronic conductivity of the silicon oxide negative electrode sheet, reduce the resistance of the negative electrode sheet, and buffer the volume expansion of silicon oxide particles during lithium insertion and extraction.

[0010] Step 4: Preparation of high first-efficiency and high-conductivity silicon oxide negative electrode sheet: Mix lithium-rich fluorine-doped carbon-coated silicon oxide particles, single-walled carbon nanotubes, and conductive polymer binder in a set proportion, add deionized water to dissolve and stir into a uniform slurry, and coat it on copper foil to prepare a high first-efficiency and high-conductivity silicon oxide negative electrode sheet.

[0011] It is further defined that the initial particle size D of silicon oxide in step 1 is 50 At 100-500nm, the fluorine-containing organic matter is selected from one or more of fluorinated polyolefins, such as polytetrafluoroethylene; fluorinated polyether polymers, such as perfluoroolefin ether; fluorinated polyurethane, such as perfluorochlorovinyl ester; fluorinated epoxy resins, such as perfluoroolefin epoxy resin; fluorinated polyesters, such as perfluoroterephthalate; and fluorinated polyethers, such as fluorinated polyether ketone.

[0012] It is further defined that in step 1, the fluorine-containing organic matter and silicon oxide particles are uniformly mixed by a liquid phase method. Add the fluorine-containing organic matter, such as 1,1,2-trifluoroethyl ether, to a beaker, stir magnetically, the magnetic stirring temperature is 50°C, the stirring speed is 400rpm, and silicon oxide particles are added in small batches during the stirring process, the mass ratio of 1,1,2-trifluoroethyl ether to silicon oxide is 0.3:1-0.5:1, the stirring temperature is 50-70°C, the stirring speed is 200-400rpm, and the stirring and dispersion time is 12-24h; the ultrasonic time is 20-40min; after the ultrasonication, add the mixture to a vacuum oven for drying to obtain uniformly mixed silicon oxide precursor particles, and adjust the vacuum oven temperature to 40-50°C during the drying process, and the drying time is 10-30min.

[0013] It is further defined that in step 1, the method of high-temperature pyrolysis in a tubular furnace is adopted to prepare fluorine-doped carbon-coated silicon oxide particles; first, the uniformly mixed silicon oxide precursor particles are placed in a tubular furnace, and the heating, high-temperature pyrolysis and cooling processes of the tubular furnace are protected by inert gas argon, the heating rate of the tubular furnace is 2 to 10°C / min, the reaction temperature is 500 to 700°C, the reaction time is 2 to 4h, and the fluorine-doped carbon-coated silicon oxide particles are obtained by natural cooling.

[0014] It is further defined that the lithium source in step 2 is a material capable of forming a Li-Si alloy, including one or more of lithium hydride, lithium borohydride, lithium powder, and lithium carbonate.

[0015] It is further defined that in step 2, the fluorine-doped carbon-coated silicon oxide and the lithium source are mixed evenly by mechanical ball milling, the mass ratio of fluorine-doped carbon-coated silicon oxide to the lithium source is 20:1-25:1, Si3N4 is selected as the ball milling medium, the mass ratio of the ball milling medium to the material is 5:5, and the ball milling tank is protected by inert gas; the ball milling speed is 100-200rpm, and the ball milling time is 2-4h. The evenly mixed fluorine-doped carbon-coated silicon oxide and lithium source are transferred to a tubular furnace, under a vacuum environment, the temperature of the tubular furnace is 400-550°C, and the reaction time is 3-5h. After cooling to room temperature, the particle size of the fluorine-doped carbon-coated lithium-rich silicon oxide particles is reduced by dry ball milling.

[0016] Further defined, in step 2, the dry ball milling reduces the particle size of the fluorine-doped carbon-coated lithium-rich silicon oxide particles, the ball milling medium is Si3N4, the mass ratio of the ball milling medium to the material is 4:1, the ball milling tank is protected by inert gas, the ball milling speed is 200-400rpm, the ball milling time is 1-2h, and the particle size D of the fluorine-doped carbon-coated lithium-rich silicon oxide particles after ball milling is 50 It is 400~800nm.

[0017] Further defined, the low elastic modulus polymer organic acid selected in the step 3 is a perfluorosulfonic acid (PFSA) polymer Nafion, and the high elastic modulus polymer organic acid is polyacrylic acid, polyvinyl acid, polymaleic acid or polyoxalic acid. It is configured into a solution by a magnetic stirring device, and the solvent for configuring the high elastic modulus polymer organic acid is deionized water, the polymer organic acid molecular weight is 100,000-180,000, the solute mass fraction is 20-30%, the magnetic stirring temperature is 50-60°C, the stirring speed is 500rpm, and a small amount is added multiple times to ensure full dispersion, and the dissolution and dispersion time is 2h, until the solution is uniform and transparent. The low elastic modulus polymer organic acid Nafion ionomer equivalent EW is 1000-1200. Affected by the fluorocarbon chain structure and the phenylsulfonic acid group, the solubility of Nafion in deionized water is low, so its solvent is selected from NMP and deionized water, and the mass fraction of Nafion: deionized water: NMP is 5:25:70.

[0018] It is further defined that the solvent for partially lithiation of the low elastic modulus organic acid and the high elastic modulus organic acid in step 3 is a lithium hydroxide solution. The mass fraction of the lithium hydroxide used is 14-18wt%, and the partial lithiation needs to retain part of the carboxyl group to form a hydrogen bond structure to ensure the hydrogen bond interaction with the conductive polymer polymer and the silicon oxide surface. The addition of lithium hydroxide is controlled by controlling the pH of the solution system, and the pH of the low elastic modulus organic polymer acid solution and the high elastic modulus organic polymer acid solution after partial lithiation is 4.0-4.5.

[0019] Further defined, the conductive polymer polymer in step 3 is selected from poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) composite material aqueous solution, with a mass fraction of 1.1wt%. The high elastic modulus polymer organic acid is added to the PEDOT:PSS solution, and the hydrogen bond network is uniformly mixed by magnetic stirring. The mass ratio of the PEDOT:PSS solution to the high elastic modulus polymer organic acid is 2.5:1 to 4.5:1, the magnetic stirring temperature is 40°C, the stirring speed is 600 to 800rpm, and the stirring time is 1 to 2h. Nafion is added to the PEDOT:PSS solution, and the hydrogen bond network is uniformly mixed by magnetic stirring. The mass ratio of the PEDOT:PSS solution to Nafion is 20:1 to 45:1, the magnetic stirring temperature is 40°C, the stirring speed is 600rpm, and the stirring time is 1 to 2h. Nafion mixed with conductive polymer and high modulus organic acid lithium salt mixed with conductive polymer are mixed in a mass ratio of 4:1 to 5:1. After mixing, the solution is subjected to magnetic stirring to improve the contact between the groups and construct a hydrogen bond network. The magnetic stirring temperature is 30°C, the stirring speed is 450rpm, and the stirring time is 12h.

[0020] It is further defined that in the step 4, the silicon oxide negative electrode is prepared, and the slurrying step is: the active material selected is lithium-rich fluorine-doped carbon-coated silicon oxide particles, the conductive agent is single-walled carbon nanotubes, and the binder is a conductive polymer binder. The solid mass ratio of lithium-rich silicon oxide particles: single-walled carbon nanotubes: conductive polymer binder is 80:10:10. The solvent is deionized water, the solid content is 40wt%, the slurry viscosity is 3400mPavs, 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 100um, 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 1.1-1.15g / cm 3 .

[0021] The technical principle of the present invention is: 1. Through Li x Si can effectively increase the lithium content in silicon oxide particles, ensuring that after the SEI formation process in the first cycle, there are still enough lithium ions in the entire battery system to carry the charge and shuttle between the positive and negative electrodes, ensuring the specific energy and energy density of the battery. x 1. Silicon oxide in Si will form gaps after delithiation, leaving space for the volume expansion of silicon oxide in the next pre-lithiation process. 2. Conductive polymer macromolecular binder provides molecular-level current branch on the surface of silicon oxide, and the rigid-flexible coexisting organic binder structure can make the silicon oxide particles still have stable electrical contact after delithiation, thereby improving the cycle life and conductivity of the silicon oxide negative electrode. 3. Introduce fluorine element. Since fluorine-containing elements will stably exist in the SEI layer, the contact point between the fluorocarbon layer and the silicon oxide particles has a high ionic conductivity, which can effectively promote Li + Uniform deposition of lithium ions can reduce the formation of lithium dendrites, stabilize the negative electrode material, and improve the cycle life.

[0022] The preparation method using the technical solution of the present invention has the following advantages:

[0023] 1. The fluorine-doped carbon coating prepared by the present invention can effectively improve the conductivity of silicon oxide. + The reaction can generate LiF, which has the advantages of high mechanical strength, low solubility, wide band gap and high voltage window. It is an important component to inhibit the failure of SEI structure, prevent material degradation and is conducive to the formation of a stable SEI structure.

[0024] 2. The lithium-rich silicon oxide particles of the present invention can effectively increase the lithium content of the powder particles. These nanoparticles can be processed in a slurry, are relatively stable in dry air and are compatible with existing industrial battery manufacturing processes.

[0025] 3. The conductive polymer binder prepared by the present invention has high mechanical properties and adhesion strength, and can alleviate the volume expansion of silicon dioxide particles during lithium embedding. By introducing conductive polymers, a layered flexible-rigid combined network and elastic electronic channels are constructed through interweaving interactions, thereby ensuring the integrity of the conductive path during lithium embedding of silicon dioxide particles and improving the cycle performance of silicon-based negative electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a schematic flow chart of a method for preparing a high-initial-efficiency and high-conductivity silicon oxide negative electrode sheet according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following is further described in detail through specific implementation methods:

[0028] A method for preparing a high-initial-efficiency and high-conductivity silicon oxide negative electrode sheet comprises the following steps:

[0029] Embodiment 1:

[0030] Step 1: Preparation of fluorine-doped carbon-coated silicon oxide particles:

[0031] D of silicon oxide particles 50 The particle size of the fluorinated organic compound is 100 nm, and the fluorinated ether solvent 1,1,2-trifluoroethyl ether is selected. The fluorinated organic compound and the silicon oxide particles are mixed evenly by a liquid phase method, and 1,1,2-trifluoroethyl ether is added to a beaker, and magnetic stirring is performed. The magnetic stirring temperature is 50°C and the stirring speed is 400rpm. During the stirring process, silicon oxide particles are added in small batches. The mass ratio of 1,1,2-trifluoroethyl ether to silicon oxide is 0.5:1, and the stirring and dispersion time is 12h. After the stirring, ultrasonication is performed for 30 minutes to ensure that the added silicon oxide is evenly dispersed. After ultrasonication, the mixture is added to a vacuum oven for drying to obtain uniformly mixed silicon oxide precursor particles. During the drying process, the vacuum oven temperature is adjusted to 40°C and the drying time is 10 minutes.

[0032] The dried mixture was transferred to a tube furnace, and the fluorine-doped carbon coating was obtained by high-temperature pyrolysis in the tube furnace. The heating, high-temperature pyrolysis, and cooling processes in the tube furnace all required inert gas argon protection. The heating rate of the tube furnace was 5°C / min, the reaction temperature was 600°C, the reaction time was 3h, and the fluorine-doped carbon-coated silicon oxide particles were prepared by natural cooling.

[0033] Step 2: Preparation of lithium-rich fluorine-doped carbon-coated silicon oxide particles:

[0034] The fluorine-doped carbon-coated silicon oxide and lithium hydride are evenly mixed by mechanical ball milling. The mass ratio of fluorine-doped carbon-coated silicon oxide to lithium hydride is 20:1. Si3N4 is used as the ball milling medium. The mass ratio of the ball milling medium to the material is 1:1. Inert gas is passed into the ball mill for protection. The ball milling speed is 200 rpm and the ball milling time is 2 h.

[0035] The uniformly mixed fluorine-doped carbon-coated silicon dioxide and lithium hydride were transferred into a tube furnace under vacuum at a temperature of 450°C for 5 hours and then cooled to room temperature.

[0036] The particle size of fluorine-doped carbon-coated lithium-rich silicon oxide particles was reduced by dry ball milling. Si3N4 was used as the ball milling medium. The mass ratio of the ball milling medium to the material was 4:1. The ball mill was protected by inert gas. The ball milling speed was 400 rpm and the ball milling time was 1 h.

[0037] Step 3: Preparation of highly conductive polymer binder:

[0038] The low elastic modulus polymer organic acid is selected from the perfluorosulfonic acid (PFSA) polymer Nafion, and the high elastic modulus polymer organic acid is selected from polyacrylic acid. It is configured into a solution by a magnetic stirring device, and the solvent for configuring high polyacrylic acid is deionized water, the molecular weight of polyacrylic acid is 150,000, the solute mass fraction is 25%, the magnetic stirring temperature is 50°C, the stirring speed is 500rpm, and a small amount is added multiple times to ensure full dispersion. The dissolution and dispersion time is 2 hours until the solution is uniform and transparent. The Nafion ionomer equivalent EW is 1000-1200, and its solvent is selected from NMP and deionized water, and the mass fraction of Nafion: deionized water: NMP is 5:25:70.

[0039] The solvent for partial lithiation of polyacrylic acid and Nafion is lithium hydroxide solution. The mass fraction of lithium hydroxide used is 14 wt %. The addition of lithium hydroxide is controlled by controlling the pH of the solution system. The pH of the polyacrylic acid solution and the Nafion solution after partial lithiation is 3.5.

[0040] The conductive polymer polymer is a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) composite material aqueous solution with a mass fraction of 1.1wt%, and the polyacrylic acid solution is mixed into the PEDOT:PSS solution and magnetically stirred, the mass ratio of the PEDOT:PSS solution to the polyacrylic acid solution is 4:1, the magnetic stirring temperature is 40°C, the stirring speed is 600rpm, and the stirring time is 1.5h. The Nafion solution is mixed into the PEDOT:PSS solution and magnetically stirred, the mass ratio of the PEDOT:PSS solution to the Nafion is 40:1, the magnetic stirring temperature is 40°C, the stirring speed is 600rpm, and the stirring time is 1.5h.

[0041] Nafion mixed with conductive polymer and high modulus organic acid lithium salt mixed with conductive polymer were mixed in a mass ratio of 4.5:1, and the magnetic stirring temperature was 30°C, the stirring speed was 450rpm, and the stirring time was 12h to obtain a conductive polymer binder with both flexibility and strength linked by hydrogen bonds. In this binder, due to the conjugated structure of PEDOT:PSS, it has high ionic conductivity, and the OH bond structure in PEDOT:PSS can construct a hydrogen bond structure with the OH bond between highly flexible Nafion and high-strength lithium polyacrylate, while improving the conductivity, constructing an organic network linked by hydrogen bonds, and limiting the volume expansion of silicon oxide particles during the lithium insertion process.

[0042] Step 4: Preparation of high initial efficiency and high conductivity silicon oxide negative electrode sheet:

[0043] Prepare silicon oxide negative electrode sheets, slurry preparation steps: solid mass ratio of lithium-rich silicon oxide particles: single-walled carbon nanotubes: conductive polymer binder is 80:10:10. The solvent is deionized water, the solid content is 40wt%, the slurry viscosity is 3400mPa·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 100um, and the electrode sheet is vacuum dried after coating, the oven temperature is 80℃, and the drying time is 12h. Rolling: The surface electrode sheet density is 1.10g / cm 3 .

[0044] Embodiment 2:

[0045] Step 1: Preparation of fluorine-doped carbon-coated silicon oxide particles:

[0046] D of silicon oxide particles 50 The diameter of the fluorinated organic compound is 250nm, and the fluorinated ether solvent 1,1,2-trifluoroethyl ether is selected. The fluorinated organic compound and silicon oxide particles are mixed evenly by a liquid phase method. 1,1,2-trifluoroethyl ether is added to a beaker and stirred magnetically at a temperature of 50°C and a stirring speed of 400rpm. During the stirring process, silicon oxide particles are added in small batches. The mass ratio of 1,1,2-trifluoroethyl ether to silicon oxide is 0.4:1, and the stirring and dispersion time is 12h. After the stirring, ultrasonication is performed for 30min to ensure that the added silicon oxide is evenly dispersed. After ultrasonication, the mixture is added to a vacuum oven for drying to obtain uniformly mixed silicon oxide precursor particles. During the drying process, the vacuum oven temperature is adjusted to 40°C and the drying time is 10min.

[0047] The dried mixture was transferred to a tube furnace, and the fluorine-doped carbon coating was obtained by high-temperature pyrolysis in the tube furnace. The heating, high-temperature pyrolysis, and cooling processes in the tube furnace all required inert gas argon protection. The heating rate of the tube furnace was 5°C / min, the reaction temperature was 600°C, the reaction time was 3h, and the fluorine-doped carbon-coated silicon oxide particles were prepared by natural cooling.

[0048] Step 2: Preparation of lithium-rich fluorine-doped carbon-coated silicon oxide particles:

[0049] The fluorine-doped carbon-coated silicon oxide and lithium hydride are evenly mixed by mechanical ball milling. The mass ratio of fluorine-doped carbon-coated silicon oxide to lithium hydride is 22.5:1. Si3N4 is used as the ball milling medium. The mass ratio of the ball milling medium to the material is 1:1. Inert gas is passed into the ball mill for protection. The ball milling speed is 200 rpm and the ball milling time is 2 h.

[0050] The uniformly mixed fluorine-doped carbon-coated silicon dioxide and lithium hydride were transferred into a tube furnace under vacuum at a temperature of 450°C for 5 hours and then cooled to room temperature.

[0051] The particle size of fluorine-doped carbon-coated lithium-rich silicon oxide particles was reduced by dry ball milling. Si3N4 was used as the ball milling medium. The mass ratio of the ball milling medium to the material was 4:1. The ball mill was protected by inert gas. The ball milling speed was 400 rpm and the ball milling time was 1 h.

[0052] Step 3: Preparation of highly conductive polymer binder:

[0053] The low elastic modulus polymer organic acid is selected from the perfluorosulfonic acid (PFSA) polymer Nafion, and the high elastic modulus polymer organic acid is selected from polyacrylic acid. It is configured into a solution through a magnetic stirring device, and the solvent for configuring the high polyvinyl acid is deionized water, the molecular weight of the polyvinyl acid is 10,000-50,000, the solute mass fraction is 25%, the magnetic stirring temperature is 50°C, the stirring speed is 500rpm, and a small amount is added multiple times to ensure full dispersion. The dissolution and dispersion time is 2 hours until the solution is uniform and transparent. The Nafion ionomer equivalent EW is 1000-1200, and its solvent is selected from NMP and deionized water, and the mass fraction of Nafion: deionized water: NMP is 5:25:70.

[0054] The solvent for partial lithiation of polyacrylic acid and Nafion is lithium hydroxide solution. The mass fraction of lithium hydroxide used is 14 wt %. The addition of lithium hydroxide is controlled by controlling the pH of the solution system. The pH of the polyacrylic acid solution and the Nafion solution after partial lithiation is 4.0.

[0055] The conductive polymer polymer is a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) composite material aqueous solution with a mass fraction of 1.1wt%, and the polyacrylic acid solution is mixed into the PEDOT:PSS solution and magnetically stirred, the mass ratio of the PEDOT:PSS solution to the polyacrylic acid solution is 4:1, the magnetic stirring temperature is 40°C, the stirring speed is 600rpm, and the stirring time is 1.5h. The Nafion solution is mixed into the PEDOT:PSS solution and magnetically stirred, the mass ratio of the PEDOT:PSS solution to the Nafion is 40:1, the magnetic stirring temperature is 40°C, the stirring speed is 600rpm, and the stirring time is 1.5h.

[0056] Nafion mixed with conductive polymer and high modulus organic acid lithium salt mixed with conductive polymer were mixed at a mass ratio of 4.5:1, with magnetic stirring at a temperature of 30° C., a stirring speed of 450 rpm, and a stirring time of 12 h.

[0057] Step 4: Preparation of high initial efficiency and high conductivity silicon oxide negative electrode sheet:

[0058] Prepare silicon oxide negative electrode sheets, slurry preparation steps: the selected active material is lithium-rich fluorine-doped carbon-coated silicon oxide particles, the conductive agent is single-walled carbon nanotubes, the binder is a conductive polymer binder, and the solid mass ratio of lithium-rich silicon oxide particles: single-walled carbon nanotubes: conductive polymer binder is 80:10:10. The solvent is deionized water, the solid content is 40wt%, the slurry viscosity is 3400mPa·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 100um, 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 1.10g / cm 3 .

[0059] Embodiment 3:

[0060] Step 1: Preparation of fluorine-doped carbon-coated silicon oxide particles:

[0061] D of silicon oxide particles 50 The diameter of the fluorinated organic compound is 500nm, and the fluorinated ether solvent 1,1,2-trifluoroethyl ether is selected. The fluorinated organic compound and silicon oxide particles are mixed evenly by a liquid phase method. 1,1,2-trifluoroethyl ether is added to a beaker and stirred magnetically. The magnetic stirring temperature is 50°C and the stirring speed is 400rpm. During the stirring process, silicon oxide particles are added in small batches. The mass ratio of 1,1,2-trifluoroethyl ether to silicon oxide is 3:1, and the stirring and dispersion time is 12h. After the stirring, ultrasonication is performed for 30min to ensure that the added silicon oxide is evenly dispersed. After ultrasonication, the mixture is added to a vacuum oven for drying to obtain uniformly mixed silicon oxide precursor particles. During the drying process, the vacuum oven temperature is adjusted to 40°C and the drying time is 10min.

[0062] The dried mixture was transferred to a tube furnace, and the fluorine-doped carbon coating was obtained by high-temperature pyrolysis in the tube furnace. The heating, high-temperature pyrolysis, and cooling processes in the tube furnace all required inert gas argon protection. The heating rate of the tube furnace was 5°C / min, the reaction temperature was 600°C, the reaction time was 3h, and the fluorine-doped carbon-coated silicon oxide particles were prepared by natural cooling.

[0063] Step 2: Preparation of lithium-rich fluorine-doped carbon-coated silicon oxide particles:

[0064] The fluorine-doped carbon-coated silicon oxide and lithium hydride are evenly mixed by mechanical ball milling. The mass ratio of fluorine-doped carbon-coated silicon oxide to lithium hydride is 25:1. Si3N4 is used as the ball milling medium. The mass ratio of the ball milling medium to the material is 1:1. The ball milling tank is protected by inert gas. The ball milling speed is 200 rpm and the ball milling time is 2 h.

[0065] The uniformly mixed fluorine-doped carbon-coated silicon dioxide and lithium hydride were transferred into a tube furnace under vacuum at a temperature of 450°C for 5 hours and then cooled to room temperature.

[0066] The particle size of fluorine-doped carbon-coated lithium-rich silicon oxide particles was reduced by dry ball milling. Si3N4 was used as the ball milling medium. The mass ratio of the ball milling medium to the material was 4:1. The ball mill was protected by inert gas. The ball milling speed was 400 rpm and the ball milling time was 1 h.

[0067] Step 3: Preparation of highly conductive polymer binder:

[0068] The low elastic modulus polymer organic acid is selected from the perfluorosulfonic acid (PFSA) polymer Nafion, and the high elastic modulus polymer organic acid is selected from polyacrylic acid. It is configured into a solution through a magnetic stirring device, and the solvent for preparing the high polyoxalic acid is deionized water, the molecular weight of the polyoxalic acid is 50,000-100,000, the solute mass fraction is 25%, the magnetic stirring temperature is 50°C, the stirring speed is 500rpm, and a small amount is added multiple times to ensure full dispersion. The dissolution and dispersion time is 2 hours until the solution is uniform and transparent. The Nafion ionomer equivalent EW is 1000-1200, and its solvent is selected from NMP and deionized water, and the mass fraction of Nafion: deionized water: NMP is 5:25:70.

[0069] The solvent for partial lithiation of polyacrylic acid and Nafion is lithium hydroxide solution. The mass fraction of lithium hydroxide used is 14 wt %. The addition of lithium hydroxide is controlled by controlling the pH of the solution system. The pH of the polyacrylic acid solution and the Nafion solution after partial lithiation is 4.5.

[0070] The conductive polymer polymer is a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) composite material aqueous solution with a mass fraction of 1.1wt%, and the polyacrylic acid solution is mixed into the PEDOT:PSS solution and magnetically stirred, the mass ratio of the PEDOT:PSS solution to the polyacrylic acid solution is 4:1, the magnetic stirring temperature is 40°C, the stirring speed is 600rpm, and the stirring time is 1.5h. The Nafion solution is mixed into the PEDOT:PSS solution and magnetically stirred, the mass ratio of the PEDOT:PSS solution to the Nafion is 40:1, the magnetic stirring temperature is 40°C, the stirring speed is 600rpm, and the stirring time is 1.5h.

[0071] Nafion mixed with conductive polymer and high modulus organic acid lithium salt mixed with conductive polymer were mixed at a mass ratio of 4.5:1, with magnetic stirring at a temperature of 30° C., a stirring speed of 450 rpm, and a stirring time of 12 h.

[0072] Step 4: Preparation of high initial efficiency and high conductivity silicon oxide negative electrode sheet:

[0073] Prepare silicon oxide negative electrode sheets, slurry preparation steps: the selected active material is lithium-rich fluorine-doped carbon-coated silicon oxide particles, the conductive agent is single-walled carbon nanotubes, the binder is a conductive polymer binder, and the solid mass ratio of lithium-rich silicon oxide particles: single-walled carbon nanotubes: conductive polymer binder is 80:10:10. The solvent is deionized water, the solid content is 40wt%, the slurry viscosity is 3400mPa·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 100um, 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 1.10g / cm 3 .

[0074] Comparative Example 1:

[0075] The difference from Example 1 is that the fluorine-doped carbon coating layer of the silicon dioxide particles is not constructed, that is, step 1 is missing, and the rest of the preparation method and parameters are consistent with Example 1.

[0076] Comparative Example 2:

[0077] The difference from Example 1 is that the silicon dioxide particles are not pre-lithiated, that is, step 2 is missing, and the rest of the preparation method and parameters are consistent with Example 1.

[0078] Comparative Example 3:

[0079] The difference from Example 1 is that no conductive polymer is introduced, that is, PEDOT:PSS is not added in step 3, and the rest of the preparation method and parameters are consistent with Example 1.

[0080] Comparative Example 4:

[0081] The difference from Example 1 is that in step 3, a slightly excess amount of LiOH is added to make the pH value 8, that is, all the sulfonic acid groups and carboxyl groups are converted into corresponding lithium salts, and the rest of the preparation method and parameters are consistent with Example 1.

[0082] The silicon-based negative electrode particles obtained in the above examples and comparative examples are further used to prepare negative electrodes, which specifically includes the following steps:

[0083] 1) Punch the rolled electrode sheet into a negative electrode sheet with a diameter of 10 mm.

[0084] 2) The prepared electrode was used as the positive electrode and metallic lithium was selected as the negative electrode to complete the button assembly process. The half-cell electrochemical performance test was performed on the assembled battery. The electrolyte used in the test was a mixture of 1.0M LiPF6, diethyl carbonate (DEC) and ethylene carbonate (EC) and 30wt% fluoroethylene carbonate (FEC) as an additive.

[0085] The performance of the silicon-based negative electrode prepared from the materials obtained in Examples 1-3 and Comparative Examples 1-3 was tested, and the test method was as follows:

[0086] (1) First coulombic efficiency test: voltage range 0.001 ~ 3V. Charge and discharge current: 0.1C, discharge first then charge. First coulombic efficiency calculation method: first charge capacity / first discharge capacity.

[0087] (2) Cyclic performance test method: Discharge at a rate of 0.5C and 2C, with a voltage range of 0.001-3V, for 200 cycles respectively, and test its capacity retention rate.

[0088] (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.

[0089] The electrical performance test results of the batteries prepared with the materials of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0090] Table 1 Battery performance test data

[0091]

[0092] It can be seen from Example 1, Example 2 and Example 3 combined with the comparative example that the silicon oxide negative electrode sheet prepared by the method of the present invention, when using the above-mentioned different N doping amounts, metal lithium content, high-strength polymer organic acid and pH value, the rate performance and capacity retention rate of the half-cell are greatly improved. It can be seen from Example 1 and Comparative Example 1 that the fluorine-doped carbon coating layer can significantly improve the cycle stability of the battery, and the improvement of the capacity retention rate under large current and small current is very obvious. It can be seen from Example 1 and Comparative Example 2 that the pre-lithium process can significantly improve the first coulomb efficiency of the battery. Since the number of lithium ions that can move freely during the battery charging and discharging process is maintained at a high level, the subsequent rate performance and capacity retention rate are better than the silicon oxide negative electrode sheet that has not been pre-lithiated. It can be seen from Example 1 and Comparative Example 3 that the conductive polymer on the surface of the silicon oxide negative electrode with a flexible-rigid coexisting binder can better maintain the integrity of the conductive network, and show excellent improvement ability in rate performance. The flexible-rigid coexisting structure can maintain the volume integrity of the silicon oxide particles during the lithium extraction process. It can be seen from Example 1 and Comparative Example 4 that due to the high physical and chemical degree of the binder system, there is a lack of effective hydrogen bond cross-linking between the binders, so there are few contact sites with the silicon oxide particles. During the lithium insertion process, the relatively low contact sites cannot inhibit the volume expansion of silicon oxide, resulting in the loss of binding sites between silicon oxide and the conductive binder, carbon layer, etc., becoming "dead silicon", losing the ability to de-insert lithium, and greatly reducing the battery's cycle efficiency and capacity retention rate. Therefore, it is very necessary to maintain a certain sulfonic acid group and carboxyl group to construct a hydrogen bond structure to alleviate the volume expansion of silicon oxide. In addition, the excellent solubility of the binder miscible with deionized water maintains the low toxicity and economy of the solvent. Therefore, Example 1 has a higher rate performance, cycle capacity retention rate and strong industrial promotion ability.

[0093] The present invention constructs a fluorine-doped carbon coating, the presence of which can enhance the pre-lithiation effect and effectively improve the integrity of the SEI structure, ensuring the integrity of the SEI structure during the battery charge and discharge process; the present invention uses lithium alloy pre-lithiation to allow silicon oxide particles to obtain a uniform local active lithium distribution, thereby achieving rapid pre-lithiation of silicon oxide anodes. By introducing a conductive polymer binder, the volume expansion of silicon oxide during lithium deintercalation can be effectively alleviated, the point-to-point contact between carbon black and silicon oxide particles will limit electron transmission, and the stress generated by high-capacity silicon oxide materials during the lithiation process will destroy the electrical decomposition and fracture between the conductive binder and the active material. The introduction of a flexible conductive polymer can maintain good electrical contact with silicon oxide, stabilize the cycle capacity of silicon oxide during the cycle, and enhance the conductivity of silicon oxide pole pieces.

[0094] 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 selecting other fluorinated organic substances such as fluorinated polyolefins, fluorinated polyether polymers, fluorinated polyurethanes, fluorinated epoxy resins, fluorinated polyesters, and fluorinated polyethers to replace 1,1,2-trifluoroethyl ether, simply changing the surface electrode density, etc. The effect can be expected and will not be repeated.

[0095] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is 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 the internal connection of two components. 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 in 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-conductivity silicon oxide negative electrode sheet, characterized in that: include: Step 1: Preparation of fluorine-doped carbon-coated silicon oxide particles: mixing silicon oxide and fluorine-containing organic matter evenly, and pyrolyzing the mixed particles at high temperature to obtain fluorine-doped carbon-coated silicon oxide particles; Step 2: Preparation of lithium-rich fluorine-doped carbon-coated silicon oxide particles: dry-mixing the fluorine-doped carbon-coated silicon oxide particles and the lithium source, and calcining the mixed particles at high temperature under a vacuum environment to obtain lithium-rich fluorine-doped carbon-coated silicon oxide particles; Step 3: Preparation of conductive polymer binder: partially lithiating a low elastic modulus polymer organic acid and mixing it with a conductive polymer, obtaining a flexible part of the conductive polymer binder through hydrogen bonding, partially lithiating a high elastic modulus polymer organic acid and mixing it with a conductive polymer, obtaining a rigid part of the conductive polymer binder through hydrogen bonding, and mixing the flexible and rigid parts according to a set ratio to obtain a conductive polymer binder; Step 4: Preparation of high first-efficiency and high-conductivity silicon oxide negative electrode sheet: Mix the lithium-rich fluorine-doped carbon-coated silicon oxide particles, single-walled carbon nanotubes, and conductive polymer binder obtained in step 2 according to a set ratio, add deionized water to dissolve and stir to form a uniform slurry, apply it on copper foil, dry and roll to prepare a high first-efficiency and high-conductivity silicon oxide negative electrode sheet.

2. The method for preparing a high-initial-efficiency and high-conductivity silicon oxide negative electrode sheet according to claim 1, characterized in that: The initial particle size D of silicon dioxide selected in step 1 50 The thickness of the nanostructured carbon fiber is 100 to 500 nm, and the fluorinated organic matter is selected from one or more of fluorinated polyolefins, fluorinated polyether polymers, fluorinated polyurethanes, fluorinated epoxy resins, fluorinated polyesters, and fluorinated polyethers.

3. The method for preparing a high-initial-efficiency and high-conductivity silicon oxide negative electrode sheet according to claim 1, characterized in that: In step 1, the fluorine-containing organic matter and silicon oxide particles are uniformly mixed by a liquid phase method; the method is to first stir the fluorine-containing organic matter, and add silicon oxide particles in small amounts in batches during the stirring process, and after the stirring is completed, ultrasonic vibration is performed to evenly disperse the added silicon oxide; after the ultrasonication, drying is performed to obtain uniformly mixed silicon oxide precursor particles; wherein the mass ratio of the fluorine-containing organic matter to silicon oxide is 0.3:1 to 0.5:

1.

4. The method for preparing a high initial efficiency and high conductivity silicon oxide negative electrode sheet according to claim 1, characterized in that: In step 1, a method of high-temperature pyrolysis in a tubular furnace is adopted to prepare fluorine-doped carbon-coated silicon oxide particles; first, the uniformly mixed silicon oxide precursor particles are placed in a tubular furnace, and the heating, high-temperature pyrolysis and cooling processes of the tubular furnace are protected by inert gas argon. The heating rate of the tubular furnace is 2 to 10°C / min, the reaction temperature is 500 to 700°C, the reaction time is 2 to 4h, and the fluorine-doped carbon-coated silicon oxide particles are obtained by natural cooling.

5. The method for preparing a high-initial-efficiency and high-conductivity silicon oxide negative electrode sheet according to claim 1, characterized in that: In step 2, the lithium source is selected from materials capable of forming Li-Si alloy, including one or more of lithium hydride, lithium borohydride, lithium powder, and lithium carbonate.

6. The method for preparing a high-initial-efficiency and high-conductivity silicon oxide negative electrode sheet according to claim 1, characterized in that: In the step 2, the fluorine-doped carbon-coated silicon oxide and the lithium source are uniformly mixed by mechanical ball milling, the mass ratio of the fluorine-doped carbon-coated silicon oxide to the lithium source is 20:1-25:1, Si3N4 is selected as the ball milling medium, the mass ratio of the ball milling medium to the material is 5:5, and the ball milling jar is protected by inert gas; in the step 2, the particle size of the fluorine-doped carbon-coated lithium-rich silicon oxide particles is reduced by dry ball milling, Si3N4 is selected as the ball milling medium, the mass ratio of the ball milling medium to the material is 4:1, and the ball milling jar is protected by inert gas. After ball milling, the particle size of the fluorine-doped carbon-coated lithium-rich silicon oxide particles is D 50 It is 400~800nm.

7. The method for preparing a high initial efficiency and high capacity silicon oxide negative electrode sheet according to claim 1, characterized in that: The low elastic modulus polymer organic acid selected in step 3 is a perfluorosulfonic acid polymer Nafion, and the high elastic modulus polymer organic acid is polyacrylic acid, polyvinyl acid, polymaleic acid or polyoxalic acid; it is configured into a solution by a magnetic stirring device, and the solvent for configuring the high elastic modulus polymer organic acid is deionized water, the molecular weight of the polymer organic acid is 100,000-180,000, the solute mass fraction is 20-30%, the low elastic modulus polymer organic acid Nafion ionomer equivalent EW is 1000-1200, the solvent is NMP and deionized water, and the mass fraction of Nafion: deionized water: NMP is 5:25:

70.

8. 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 3, the solvent for partially lithiation of the low elastic modulus organic polymer solution and the high elastic modulus organic polymer solution is a lithium hydroxide solution; the mass fraction of the lithium hydroxide used is 14-18wt%, and the addition of lithium hydroxide is controlled, and the pH of the low elastic modulus organic polymer acid solution and the high elastic modulus organic polymer acid solution after partial lithiation is 4.0-4.

5.

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 conductive polymer polymer in step 3 is selected from a PEDOT:PSS composite material aqueous solution with a mass fraction of 1.1wt%. First, a high elastic modulus polymer organic acid is added to the PEDOT:PSS composite material aqueous solution, and stirred to mix evenly to construct a hydrogen bond network. The mass ratio of the PEDOT:PSS solution to the high elastic modulus polymer organic acid is 2.5:1 to 4.5:1; then Nafion is added to the PEDOT:PSS solution, and stirred to mix evenly to construct a hydrogen bond network. The mass ratio of the PEDOT:PSS solution to Nafion is 20:1 to 45:1; finally, the Nafion mixed with the conductive polymer and the high modulus organic acid lithium salt mixed with the conductive polymer are mixed and stirred at a mass ratio of 4:1 to 5:1 to improve the contact between the groups.

10. 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 slurrying step in step 4: the mass ratio of lithium-rich fluorine-doped carbon-coated silicon dioxide particles, single-walled carbon nanotubes and conductive polymer binder is 80:10:10, the solvent is deionized water, the solid content is 30-40wt%, the slurry viscosity is 2800-3800mPa·s, the slurry is sieved through a 200-mesh sieve to remove particles; in the coating step: the coating substrate is copper foil, the coating seam width is 100um, and the electrode is vacuum dried after coating, the oven temperature is 80°C, and the drying time is 12h; in the rolling step, the surface electrode density is 1.1-1.15g / cm 3 .

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