Preparation method of fluorine-doped lithium-rich silicon-based anode binder with good conductivity

Abstract

The invention belongs to the technical field of energy storage, and particularly relates to a preparation method of a fluorine-doped lithium-rich silicon-based anode binder with good conductivity, which comprises the following steps: 1, preparing a lithium-rich organic polymer to improve the initial coulombic efficiency of a silicon-based anode material; 2, a macromolecular structure is formed through the reaction among organic matters, and a three-dimensional network cross-linking reaction is formed through the traffic reaction among macromolecules, so that the mechanical property of the silicon-based negative electrode material is improved; 3, fluorine-containing organic macromolecules are added, crosslinking is formed between macromolecules far away from each other while the fluorine element is supplemented, and the three-dimensional network structure is consolidated; 4, introducing a polymer containing a conjugated double bond structure; the fluorine-doped lithium-rich silicon-based anode binder with good conductivity is prepared by the method, the problem of volume expansion of a silicon-based anode in the charging and discharging process is effectively relieved, a stable solid electrolyte interface is constructed, the conductivity of the silicon-based anode is enhanced, and the service life of the silicon-based anode is prolonged. Therefore, the first coulombic efficiency, the large-current voltage resistance and the long-period stability of the silicon-based anode are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage, and particularly relates to a preparation method of a fluorine-doped highly conductive lithium-rich silicon-based anode binder. Background Art

[0002] In the era of growing energy demand and accelerating technological advancement, the performance of lithium-ion batteries urgently needs to be improved by leaps and bounds to meet the requirements of high energy density, long cycle life, and environmental sustainability. The unique performance advantages of silicon-based materials not only bring new breakthroughs to battery technology but also provide an important direction for the research and development of next-generation storage devices. The specific advantages are as follows: 1. High theoretical specific capacity. Silicon-based materials have a theoretical specific capacity far exceeding that of traditional high-performance materials. The theoretical specific capacity of silicon is 4200 mAh / g, and that of SiO is 2600 mAh / g. The higher specific capacity enables silicon-based high-performance batteries to store more electrical energy under the same mass, significantly improving the energy density of the batteries. 2. High safety. Metallic lithium is prone to form lithium dendrites, which may lead to battery short circuits or thermal runaway. The structure and reactivity of silicon-based anodes are more stable than those of metallic lithium, which gives silicon-based high-performance batteries greater advantages in terms of safety and reduces the risk of battery overheating, fire, or explosion. 3. Abundant resources and environmentally friendly. Silicon, as the most abundant element on Earth, mainly exists in sand and ores, with extremely rich reserves. Compared with rare metals (such as cobalt and lithium), the extraction and processing costs of silicon are lower and its impact on the environment is smaller, meeting the requirements of large-scale production regulation and conforming to the sustainable development goal.

[0003] Silicon-based high-performance anodes have become an important direction for the development of lithium-ion batteries due to their ultra-high specific capacity, high safety, abundant resources, etc., and have important applications in fields such as electric vehicles, energy storage systems, portable electronic devices, drones and power tools, medical devices, aerospace, and military. Despite the significant advantages of silicon-based anode materials, their development still faces the following challenges: 1. Volume expansion. During the lithium intercalation process, the volume of silicon expands by up to ~300%. The huge volume expansion will cause particle pulverization and destruction of the electrolyte structure. After the lithium deintercalation process, the silicon-based anode will expose a fresh silicon surface. When lithium is intercalated again, the newly exposed silicon surface will capture more lithium to form a new solid electrolyte interface film (SEI), consuming lithium ions and electrolyte in the electrode material. 2. Low cycle stability. The volume change causes the SEI film to break and reconstruct repeatedly, gradually reducing the available lithium ions in the battery and exacerbating the battery capacity decay. At the same time, the continuous formation and rupture of the SEI film lead to contact between the battery electrolyte and the silicon-based anode, resulting in continuous side reactions, a gradual decrease in the lithium salt concentration, a decrease in the battery conductivity, an increase in the internal resistance, and in severe cases, the gas generated during the reaction may cause safety problems such as battery swelling or thermal runaway, seriously affecting the battery performance. 3. High initial irreversible capacity. Silicon-based materials consume a large amount of lithium ions during the first cycle, reducing the first Coulombic efficiency. Summary of the Invention

[0004] The present invention aims to provide a new method for preparing a silicon-based anode polymer material to alleviate the volume expansion problem of the silicon-based anode during charge and discharge, construct a stable solid electrolyte interface, and enhance the conductivity of the silicon-based anode, thereby improving the first Coulomb efficiency, high current withstand voltage, and long-cycle stability of the silicon-based anode.

[0005] To achieve the above object, the present invention provides a preparation method of a fluorine-doped highly conductive lithium-rich silicon-based anode binder, including:

[0006] Step 1: Preparation of lithium-rich organic polymer: Using a mixed solvent of NMP and GBL, prepare a LiOH solution with a mass concentration of 15 - 20 wt% and a high-polymer organic acid solution with a mass fraction of 8 - 15 wt% respectively. The weight ratio of the LiOH solution to the high-polymer organic acid solution is 0.24 - 0.3:1. Control the temperature and stir and mix the two evenly to obtain a lithium salt solution of the organic acid. Perform rotary evaporation to remove part of the solvent to increase the solution viscosity.

[0007] Step 2: Preparation of polyester three-dimensional network polymer: Put a certain concentration of polymer polyether polyol or polyester polyol into a flask to cross-link with isocyanate trimer to produce a polyurethane prepolymer. Appropriately introduce a catalyst to accelerate the reaction rate. Add a dihydroxy organic compound containing a disulfide bond to the reaction system and continue the reaction to obtain a structurally stable network polymer.

[0008] Step 3: Preparation of highly fluorinated and highly stressed cross-linked network polymer: Add fluorinated polyether diol (fluorinated organic compound) to the network polymer material obtained in Step 2 to cross-link the exposed isocyanate groups, build a bridge between chain structures with a relatively large distance, and construct branched chains.

[0009] Step 4: Introduction of a polymer containing a conjugated double bond structure: Dissolve polyaniline with a hydroxyl substituent in a solution, stir until fully dissolved, mix it with the prepared highly fluorinated and highly stressed cross-linked network polymer, introduce a conjugated double bond structure after building a bridge between the chain polymers, and improve the conductivity of the polymer material.

[0010] Further limitation: In the preparation of the LiOH solution in Step 1, the mass ratio of the solvent NMP to GBL is 1.5:1. NMP enhances the polarity of the solvent, and GBL improves the solubility of the polymer in the solvent. LiOH needs to be vacuum dried to remove water before use. The drying temperature is 100 °C and the drying time is 12 h to obtain a LiOH solution with a mass concentration of 18 wt%. During the preparation of the organic acid solution, the mass ratio of the solvent NMP to GBL is 1.5:1 to ensure efficient miscibility with the LiOH solution. The high-polymer organic acid is poly(methacrylic acid) (PMAA), and the molecular weight of poly(methacrylic acid) is 2000. It needs to be vacuum dried to remove water before use. The drying temperature is 100 °C and the drying time is 12 h to prepare an organic acid solution with a mass fraction of 12 wt%. The weight ratio of the LiOH solution to the high-polymer organic acid solution is 0.25:1.

[0011] Further limitation: When preparing the lithiated organic acid solution in Step 1, the alkali solution and the organic acid are uniformly mixed. The stirring temperature is 50 °C, the stirring speed is 500 rpm, and the reaction duration is 3 h. The reaction solution is transferred to the rotating flask of a rotary evaporator. The temperature of the heating water bath is controlled at 80 °C, the vacuum degree is 120 mbr, the rotation speed is 120 rpm, and it is cooled with tap water.

[0012] Further limitation: The polyether polyol or polyester polyol in Step 2 includes but is not limited to polypropylene glycol, polyethylene glycol, or polyether diol. It is vacuum dried before use. The drying temperature is 100 - 120 °C and the drying time is 2 - 4 h. A low-degree-of-polymerization tris(isocyanate) polyester is selected, with a degree of polymerization of 10 - 50. It needs to be vacuum dried before use. The drying temperature is 40 - 60 °C and the drying time is 4 - 8 h. A catalyst needs to be added for the high-polymer reaction to increase the reaction rate. The catalyst can be an ammonium catalyst such as triethylamine, dimethylaminobenzoic acid, N,N-dimethylcyclohexylamine, etc. or a tin catalyst such as dibutyltin dilaurate (DBTDL), stannous octoate (EGT). The purity of the catalyst is above 99%. The catalyst needs to be vacuum dried before use. The drying temperature is 40 - 60 °C and the drying time is 2 - 4 h.

[0013] Further limitation: The reaction for generating polyurethane in Step 2 includes two steps: dissolution and reaction. In the first step, the low-degree-of-polymerization tris(isocyanate) polyester and the tin catalyst are dissolved in a mixed solvent of NMP and GBL. The mass ratio of NMP to GBL is 1.5:1. The mixing process requires protection by an argon atmosphere and magnetic stirring. The temperature is 60 °C and the stirring speed is 600 rpm to ensure that the reactants and the catalyst can be fully dissolved. In the second step, under the protection of an argon environment, PPG is added to the mixed solution, and magnetic stirring is continued. The reaction temperature is raised to 80 °C, the stirring speed is 1000, and the reaction time is 3 h. The mass ratio of the polyol, tris(isocyanate) polyester, and the catalyst is 1:0.6:6×10 -4 。

[0014] Further limitation: The organic compound with disulfide bond and dihydroxy group in step 2 includes 2-hydroxyethyl disulfide, 3,3`-dihydroxydiphenyl disulfide or 4-hydroxyphenyl disulfide; before use, it is dried in vacuum, the drying temperature is 40-60°C, and the drying time is 8-12h. The organic compound with disulfide bond and dihydroxy group is dissolved in a mixed solution of NMP:GBL with a mass ratio of 1.5:1, the temperature is 60°C, and the stirring speed is 600rpm to ensure its full dissolution. The solution of the organic compound with disulfide bond and dihydroxy group is added into a magnetic stirrer, and the reaction continues. The reaction temperature is reduced to 30-50°C, the reaction time is 2-4h, and the mass ratio of the organic compound with disulfide bond and dihydroxy group to isocyanic acid tripolyester is 1:4.8-5.6.

[0015] Further limitation: The organic compounds selected in the process of constructing the fluorinated side chain in step 3 include 2,2-difluoro-1,3-propanediol, 2,2,3,3-tetrafluoro-1,4-butanediol, etc. Before use, it needs to be dried in vacuum, the drying temperature is 40-60°C, the vacuum degree is controlled at 80-100mbar, and the drying time is 8-12h. The organic compound with fluorinated side chain and dihydroxy group is dissolved in a mixed solution of NMP:GBL with a mass ratio of 1.5:1, the temperature is 60°C, and the stirring speed is 600rpm to ensure its full dissolution. The solution of the fluorinated organic compound is added into a magnetic stirrer, and the reaction continues. The reaction temperature is 25-40°C, the reaction duration is 1-2h, and the mass ratio of the fluorinated organic compound to isocyanic acid tripolyester is 1:10.8-12.5.

[0016] Further limitation: For the polymer with conjugated structure introduced in step 4, first, the pH of the solution needs to be adjusted. The NMP solution of p-toluenesulfonic acid is added to adjust the pH. p-Toluenesulfonic acid is dissolved in NMP, and magnetic stirring is carried out. The temperature of magnetic stirring is 40-60°C, and the time is 1-2h. After adding the p-toluenesulfonic acid solution, the pH range is 3-4. The polyhydroxyaniline solution is added. The molecular weight of polyhydroxyaniline is 10,000-100,000. Polyaniline is dissolved in a mixed solution of NMP and ethanol, and the mass ratio of NMP:ethanol is 1-4:20. It is added into a magnetic stirrer, and the reaction continues. The reaction temperature is 40-60°C, and the reaction duration is 4-6h. The mass ratio of the added amount of polyhydroxyaniline to isocyanic acid tripolyester is 0.2-1:0.12. Subsequently, the solution is poured into a rotary evaporator. The water bath temperature is 40-60°C, the reduced pressure is -0.08-0.1MPa, and the rotation speed is 100-150rpm. The solvent is evaporated to solidify the polymer, and a fluorine-doped highly conductive lithium-rich silicon-based anode binder is obtained.

[0017] The present invention also provides a silicon monoxide negative electrode sheet, which includes a negative electrode current collector and a silicon monoxide negative electrode active material layer coated on the surface of the negative electrode current collector. The negative electrode active material layer includes the above-mentioned fluorine-doped lithium-rich silicon-based anode binder with good conductivity and a silicon monoxide negative electrode active material.

[0018] The technical principle of the new silicon-based anode polymer material prepared by the present invention to improve the silicon-based anode is as follows: During the lithium insertion and extraction process of the silicon-based anode, the drastic volume expansion reduces the stability of the interface structure, promotes side reactions such as electrolyte decomposition, reduces the lithium ion concentration, and thus reduces the cycle performance of the battery. The present invention constructs a new type of polymer binder to alleviate the volume expansion of the silicon-based anode during the lithium insertion and extraction process. The soft three-dimensional polyurethane polymer elastic network can play a buffering role, alleviate the volume change of the silicon-based anode, reduce the damage caused by volume expansion, and improve the cycle life; the fluorine-containing polymer layer with a rigid structure can promote the rapid migration of electrons / ions, regulate the composition of the SEI formed on the surface of SiO particles, make it rich in high-stress fluorine-containing substances, improve the mechanical stability of the SEI, reduce the irreversible lithium loss caused by the repeated rupture and regeneration of the SEI film, and inhibit the fragmentation of SiO particles. The conductive polymer can form a conductive network on the silicon-based anode, make the electron transport more efficient, significantly improve the charge-discharge efficiency and power density of the battery. Moreover, the conductive polymer material has good thermal stability and chemical stability, can provide additional safety protection for the silicon-based anode, reduce the decomposition of the electrolyte and the occurrence of side reactions, and reduce thermal runaway and other safety risks. The lithium polymethacrylate prepared by the method of the present application can effectively improve the first Coulomb efficiency of the silicon-based anode, introduce lithium ions into the anode in advance, reduce the loss of lithium ions during the first discharge, and optimize the formation process of the SEI film by adding lithium polymethacrylate, making it more uniform and having good mechanical stability.

[0019] The preparation method of the present invention and the obtained binder have the following advantages:

[0020] 1. The fluorine-doped lithium-rich silicon-based anode binder with good conductivity prepared by the present invention can improve the interface stability by introducing fluorine-containing polymers. Fluorine doping can enhance the chemical compatibility between the silicon-based anode and the electrolyte. Lithium polymethacrylate and fluorine-containing organic polymers help to form a stable and dense electrolyte interface on the electrode surface. The dense SEI film has good chemical stability and low ion migration torque, effectively reducing the electrolyte decomposition and side reactions at the electrolyte interface, and improving the first Coulomb efficiency and long-term cycle stability of the battery.

[0021] 2. The conductive polymer introduced into the fluorine-doped lithium-rich silicon-based anode binder with good conductivity prepared by the present invention can improve the conductivity, which is beneficial to reducing the internal resistance of the material, improving the efficiency of the silicon-based anode, ensuring the continuity of the conductive network, reducing the dead zone of the active material, and preventing some active materials from losing their functions; the high conductivity and interface stability can ensure the capacity output of the battery at high rates, and improve the battery density and power density;

[0022] 3. In the fluorine-doped lithium-rich silicon-based anode binder with good conductivity prepared by the present invention, the constructed polyurethane flexible polymer matrix can effectively buffer the volume expansion and contraction during the lithium insertion and extraction process of the silicon-based anode, disperse local stress, avoid the formation of stress concentration regions in the silicon-based anode, reduce the risk of mechanical damage, and improve the cycling performance of the silicon-based anode. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic flow chart of the preparation of a new fluorine-doped lithium-rich silicon-based anode binder with good conductivity according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The following is a further detailed description through specific embodiments: The present invention is of great necessity for improving the high-performance materials and properties of silicon-based anodes and promoting the development of the next generation of high-energy-density lithium-ion batteries. This binder addresses the specific core problems encountered by silicon-based anode materials in practical applications from multiple aspects. The fluorine-doped lithium-rich silicon-based anode binder can reduce the volume expansion of the silicon-based anode, improve the conductivity of the silicon-based anode, enhance the stability of the SEI film, meet the high-energy-density requirements of the silicon-based anode, improve the rate performance, meet the fast charge and discharge requirements, and provide multi-faceted support for the improvement of the overall performance of lithium-ion batteries. Its specific preparation method is as shown in the appendix Figure 1 as follows.

[0025] Example 1:

[0026] Step 1: Prepare a lithium-rich organic polymer:

[0027] Prepare a LiOH solution with a certain concentration and a high-polymer organic acid solution with a certain concentration. Control the temperature to mix the two evenly, stir magnetically for a certain time to obtain a lithium salt solution of the organic acid, and perform rotary evaporation to remove part of the solvent to increase the solution viscosity;

[0028] Step 11: Prepare a LiOH solution with a certain concentration. LiOH needs to be vacuum dried to remove water before use. The drying temperature is 100 °C and the drying time is 12 h. The solvent uses a mixed solvent of NMP and GBL, with the mass ratio of NMP:GBL being 1.5:1. The mass concentration of the prepared LiOH solution is 18 wt%, and the total amount of the solution is 125 g.

[0029] Step 12: Prepare a poly(methacrylic acid) (PMAA) solution with a certain concentration. The molecular weight of poly(methacrylic acid) is 2000. It needs to be vacuum dried to remove water before use. The drying temperature is 100 °C and the drying time is 12 h. The mass fraction of the prepared organic acid solution is 12 wt%, and the total amount of the prepared organic acid solution is controlled at 500 g.

[0030] Step 13: Uniformly mix the lye and organic acid, with a magnetic stirring temperature of 50°C, a stirring speed of 500 rpm, and a reaction duration of 3 h. Transfer the reacted solution to the rotary flask of a rotary evaporator, control the temperature of the heating water bath at 80°C, the vacuum degree at 120 mbr, the rotation speed at 120 rpm, and cool with tap water.

[0031] Step 2: Preparation of polyester three-dimensional network polymer:

[0032] Put a certain concentration of high molecular polyether polyol or polyester polyol into a flask to undergo a cross-linking reaction with isocyanate trimer to produce a polyurethane prepolymer, and appropriately introduce a catalyst to accelerate the reaction rate. Add a dihydroxy organic compound containing a disulfide bond to the reaction system and continue the reaction to obtain a structurally stable network polymer high molecule;

[0033] Step 21: The polyether polyol used is polypropylene glycol (PPG), and the molecular weight of polypropylene glycol is 500. PPG needs to be vacuum dried before use, with a drying temperature of 40°C and a drying time of 4 h. Select a low-polymerization-degree isocyanate triester, which needs to be vacuum dried before use, with a drying temperature of 40°C and a drying time of 4 h. A catalyst needs to be added for the high molecular reaction, and the catalyst selected is dibutyltin dilaurate (DBTDL). The purity of the DBTDL catalyst is above 99%, and it needs to be vacuum dried before use, with a drying temperature of 40°C and a drying time of 4 h.

[0034] Step 22: Dissolution process: Dissolve the low-polymerization-degree isocyanate triester and the tin-based catalyst in a mixed solvent of NMP and GBL, with the mass ratio of NMP:GBL being 1.5:1. The mixing process requires argon gas atmosphere protection and magnetic stirring, with a temperature of 60°C and a stirring speed of 600 rpm to ensure that the reactants and the catalyst can be fully dissolved.

[0035] Step 23: Reaction stage: Under the protection of argon gas environment, add PPG to the mixed solution, continuously stir magnetically, raise the reaction temperature to 80°C, the stirring speed to 1000, and the reaction time to 3 h. The mass ratio of polyol:isocyanate triester:catalyst is 1:0.6:6x10 -4 。

[0036] Step 24: Introduce a disulfide bond, which can improve the anti-fatigue performance of the silicon-based anode, enhance the cross-linking density and the stability of the high molecular network. The dihydroxy organic compound containing a disulfide bond selected in this patent is 2-hydroxyethyl disulfide. It needs to be vacuum dried before use, with a drying temperature of 40°C and a drying time of 8 h. Dissolve 2-hydroxyethyl disulfide in a mixed solution with a mass ratio of NMP:GBL of 1.5:1, at a temperature of 60°C and a stirring speed of 600 rpm to ensure its full dissolution. Add the 2-hydroxyethyl disulfide solution to a magnetic stirrer and continue the reaction. The reaction temperature is reduced to 45°C, and the reaction time is 4 h. The mass ratio of 2-hydroxyethyl disulfide to isocyanate triester is 1:5.

[0037] Step 3: Preparation of highly fluorinated and highly stressed cross-linked polymer: Add fluorinated polyether diol to the polymer material obtained in Step 2 to cross-link the exposed isocyanate groups, bridge between chain structures that are far apart, and construct branched chains.

[0038] The organic compound selected in this patent for constructing the fluorinated branched chain is 2,2-difluoro-1,3-propanediol. It needs to be vacuum dried before use, with a drying temperature of 40 °C and a drying time of 8 h. Dissolve 2,2-difluoro-1,3-propanediol in a mixed solution of NMP:GBL with a mass ratio of 1.5:1, at a temperature of 60 °C and a stirring speed of 600 rpm to ensure complete dissolution. Add the fluorinated organic compound solution to a magnetic stirrer and continue the reaction at a reaction temperature of 30 °C for a reaction duration of 2 h. The mass ratio of 2,2-difluoro-1,3-propanediol to isocyanuric acid triester is 1:12.

[0039] Step 4: Introduce a polymer with a conjugated double bond structure: Dissolve polyaniline with a hydroxyl substituent in a solution, stir magnetically to dissolve it completely, mix it with the prepared highly fluorinated and highly stressed cross-linked polymer, bridge between the chain polymers, and introduce a conjugated double bond structure to improve the conductivity of the polymer material.

[0040] Step 41: Adjust the pH of the solution: Add an NMP solution of p-toluenesulfonic acid to adjust the pH. p-Toluenesulfonic acid is dissolved in NMP, stir magnetically at a temperature of 40 °C for 1 h. After adding the p-toluenesulfonic acid solution, the pH is 3.2.

[0041] Step 42: Add a conductive polymer: Add a polyhydroxyaniline solution. The molecular weight of polyhydroxyaniline is 10,000. Polyaniline is dissolved in a mixed solution of NMP and ethanol, with a mass ratio of NMP:ethanol of 1:4. Add it to a magnetic stirrer and continue the reaction at a reaction temperature of 45 °C for a reaction duration of 4 h. The mass ratio of the added polyhydroxyaniline to isocyanuric acid triester is 1:0.12.

[0042] Step 43: Pour the solution into a rotary evaporator, with a water bath temperature of 60 °C, a reduced pressure of 0.1 MPa, and a rotation speed of 150 rpm. Evaporate the solvent to solidify the polymer and obtain a fluorine-doped lithium-rich silicon-based anode binder with good conductivity.

[0043] Example 2:

[0044] Step 1: Prepare a lithium-rich organic polymer:

[0045] Prepare a LiOH solution with a certain concentration and a high-polymer organic acid solution with a certain concentration. Control the temperature to mix the two evenly, stir magnetically for a certain time to obtain a lithium salt solution of the organic acid, and perform rotary evaporation to remove part of the solvent to increase the viscosity of the solution.

[0046] Step 11: Prepare a LiOH solution with a certain concentration. LiOH needs to be vacuum dried to remove water before use. The drying temperature is 100 °C and the drying time is 12 h. The solvent uses a mixed solvent of NMP and GBL, with the mass ratio of NMP:GBL being 2:1. The mass concentration of the prepared LiOH solution is 15 wt%, and the total amount of the solution is 120 g.

[0047] Step 12: Prepare a polyacrylic acid solution with a certain concentration. It needs to be vacuum dried to remove water before use. The drying temperature is 100 °C and the drying time is 12 h. The mass fraction of the prepared organic acid solution is 8 wt%, and the total amount of the prepared organic acid solution is controlled at 500 g.

[0048] Step 13: Uniformly mix the alkali solution and the organic acid. The magnetic stirring temperature is 50 °C, the stirring speed is 500 rpm, and the reaction duration is 3 h. Transfer the reacted solution to the rotary flask of a rotary evaporator, control the temperature of the heating water bath at 80 °C, the vacuum degree at 120 mbr, and the rotation speed at 120 rpm, and cool it with tap water.

[0049] Step 2: Preparation of polyester three-dimensional network polymer:

[0050] Put a certain concentration of high molecular polyether polyol or polyester polyol into a flask to react with isocyanate trimer to produce a polyurethane prepolymer. Appropriately introduce a catalyst to accelerate the reaction rate. Add a dihydroxy organic compound containing a disulfide bond to the reaction system and continue the reaction to obtain a structurally stable network polymer high molecule;

[0051] Step 21: The polyether polyol used is polyethylene glycol. PPG needs to be vacuum dried before use. The drying temperature is 40 °C and the drying time is 4 h. Select a low degree of polymerization isocyanuric acid trimer, which needs to be vacuum dried before use. The drying temperature is 40 °C and the drying time is 4 h. A catalyst needs to be added for the high molecular reaction. The catalyst selected is dibutyltin dilaurate (DBTDL). The purity of the DBTDL catalyst is above 99%. It needs to be vacuum dried before use. The drying temperature is 40 °C and the drying time is 4 h.

[0052] Step 22: Dissolution process: Dissolve the low degree of polymerization isocyanuric acid trimer and the tin-based catalyst in a mixed solvent of NMP and GBL, with the mass ratio of NMP:GBL being 2:1. The mixing process needs to be protected by an argon atmosphere and magnetically stirred at a temperature of 60 °C and a stirring speed of 600 rpm to ensure that the reactants and the catalyst can be fully dissolved.

[0053] Step 23: Reaction stage: Protect with an argon environment. Add PPG to the mixed solution, continuously magnetically stir, raise the reaction temperature to 80 °C, the stirring speed is 1000, the reaction time is 3 h, and the mass ratio of polyol:isocyanuric acid trimer:catalyst is 1:0.6:6×10 -4 。

[0054] Step 24: Introduce disulfide bonds, which can improve the anti-fatigue performance of silicon-based anodes, enhance the crosslinking density and the stability of the polymer network. The disulfide bond-containing dihydroxy organic compound selected in this patent is 2-hydroxyethyl disulfide. It needs to be vacuum-dried before use, with a drying temperature of 40 °C and a drying time of 8 h. Dissolve 2-hydroxyethyl disulfide in a mixed solution of NMP:GBL with a mass ratio of 2:1, at a temperature of 60 °C and a stirring speed of 600 rpm to ensure complete dissolution. Add the 2-hydroxyethyl disulfide solution to a magnetic stirrer and continue the reaction. The reaction temperature is reduced to 45 °C, and the reaction time is 4 h. The mass ratio of 2-hydroxyethyl disulfide to triisocyanate polyester is 1:5.

[0055] Step 3: Preparation of highly fluorinated and highly stressed crosslinked polymer network: Add fluorinated polyether diol to the polymer material obtained in Step 2 to crosslink the exposed isocyanate groups, bridge between chain structures that are far apart, and construct branched chains;

[0056] The organic compound selected in this patent for constructing fluorinated branched chains is 2,2-difluoro-1,3-propanediol. It needs to be vacuum-dried before use, with a drying temperature of 40 °C and a drying time of 8 h. Dissolve 2,2-difluoro-1,3-propanediol in a mixed solution of NMP:GBL with a mass ratio of 2:1, at a temperature of 60 °C and a stirring speed of 600 rpm to ensure complete dissolution. Add the fluorinated organic compound solution to a magnetic stirrer and continue the reaction. The reaction temperature is 30 °C, and the reaction duration is 2 h. The mass ratio of 2,2-difluoro-1,3-propanediol to triisocyanate polyester is 1:10.8.

[0057] Step 4: Introduce a polymer containing a conjugated double bond structure: Dissolve polyaniline with a hydroxyl substituent in a solution, stir magnetically to ensure complete dissolution, and mix it with the prepared highly fluorinated and highly stressed crosslinked polymer network. After bridging between chain polymers, introduce a conjugated double bond structure to improve the conductivity of the polymer material.

[0058] Step 41: Adjust the pH of the solution: Add an NMP solution of p-toluenesulfonic acid to adjust the pH. p-Toluenesulfonic acid is dissolved in NMP, stir magnetically, with a magnetic stirring temperature of 40 °C and a time of 1 h. The pH is 3.2 after adding the p-toluenesulfonic acid solution.

[0059] Step 42: Add a conductive polymer: Add a polyhydroxyaniline solution. The molecular weight of polyhydroxyaniline is 10,000. Polyaniline is dissolved in a mixed solution of NMP and ethanol, with a mass ratio of NMP:ethanol of 1:4. Add it to a magnetic stirrer and continue the reaction. The reaction temperature is 45 °C, and the reaction duration is 4 h. The mass ratio of the added polyhydroxyaniline to triisocyanate polyester is 0.5:0.12.

[0060] Step 43: Pour the solution into a rotary evaporator. The water bath temperature is 60°C, the pressure is reduced to 0.1 MPa, and the rotation speed is 150 rpm. Evaporate the solvent to solidify the polymer, obtaining a fluorine-doped lithium-rich silicon-based anode binder with good conductivity.

[0061] Example 3:

[0062] Step 1: Prepare a lithium-rich organic polymer:

[0063] Prepare a LiOH solution with a certain concentration and a high-polymer organic acid solution with a certain concentration. Control the temperature to mix the two evenly, stir magnetically for a certain time to obtain a lithium salt solution of the organic acid, and perform rotary evaporation to remove part of the solvent and increase the solution viscosity.

[0064] Step 11: Prepare a LiOH solution with a certain concentration. LiOH needs to be vacuum dried to remove water before use. The drying temperature is 100°C, and the drying time is 12 h. The solvent uses a mixed solvent of NMP and GBL, with the mass ratio of NMP:GBL being 1:1. The mass concentration of the prepared LiOH solution is 20 wt%, and the total amount of the solution is 150 g.

[0065] Step 12: Prepare a poly(lactic-co-glycolic acid) copolymer solution with a certain concentration. It needs to be vacuum dried to remove water before use. The drying temperature is 100°C, and the drying time is 12 h. The mass fraction of the prepared organic acid solution is 15 wt%, and the total amount of the prepared organic acid solution is controlled at 500 g.

[0066] Step 13: Uniformly mix the alkali solution and the organic acid, stir magnetically at a temperature of 50°C and a stirring speed of 500 rpm for 3 h. Transfer the reacted solution to the rotary flask of the rotary evaporator, control the temperature of the heating water bath to 80°C, the vacuum degree to 120 mbr, and the rotation speed to 120 rpm, and cool with tap water.

[0067] Step 2: Preparation of a polyester three-dimensional network polymer:

[0068] Put a certain concentration of polyether polyol or polyester polyol into a flask to react with isocyanate trimer to produce a polyurethane prepolymer. Appropriately introduce a catalyst to accelerate the reaction speed. Add a dihydroxy organic compound containing a disulfide bond to the reaction system and continue the reaction to obtain a structurally stable network polymer.

[0069] Step 21: The polyether polyol used is polyether diol. PPG needs to be vacuum dried before use. The drying temperature is 40°C, and the drying time is 4 h. Select a low-polymerization-degree isocyanate triester, which needs to be vacuum dried before use. The drying temperature is 40°C, and the drying time is 4 h. A catalyst needs to be added for the polymer reaction. The catalyst selected is spray tin (EGT), with the purity of the EGT catalyst being above 99%. It needs to be vacuum dried before use. The drying temperature is 40°C, and the drying time is 4 h.

[0070] Step 22: Dissolution process: Dissolve low-polymerization-degree isocyanuric acid triester and tin catalyst in the mixed solvent of NMP and GBL, with the mass ratio of NMP:GBL being 1:1. The mixing process requires protection under an argon atmosphere and magnetic stirring at a temperature of 60 °C and a stirring speed of 600 rpm to ensure that the reactants and the catalyst can be fully dissolved.

[0071] Step 23: Reaction stage: Under the protection of an argon environment, add PPG to the mixed solution, continue magnetic stirring, raise the reaction temperature to 80 °C, with a stirring speed of 1000, and a reaction time of 3 h. The mass ratio of polyol:isocyanuric acid triester:catalyst is 1:0.6:6×10 -4 。

[0072] Step 24: Introduce disulfide bonds, which can improve the anti-fatigue performance of the silicon-based anode, enhance the crosslinking density and the stability of the polymer network. The disulfide bond-containing dihydroxy organic compound selected in this patent is 2-hydroxyethyl disulfide. It needs to be vacuum dried before use at a drying temperature of 40 °C and a drying time of 8 h. Dissolve 2-hydroxyethyl disulfide in the mixed solution with a mass ratio of NMP:GBL of 1:1 at a temperature of 60 °C and a stirring speed of 600 rpm to ensure its full dissolution. Add the 2-hydroxyethyl disulfide solution to the magnetic stirrer and continue the reaction. The reaction temperature is reduced to 45 °C, and the reaction time is 4 h. The mass ratio of 2-hydroxyethyl disulfide to isocyanuric acid triester is 1:5.

[0073] Step 3: Preparation of highly fluorinated and highly stressed crosslinked polymer: Add fluorinated polyether diol to the polymer material obtained in Step 2 to crosslink the exposed isocyanate groups, build bridges between chain structures that are far apart, and construct branched chains;

[0074] The organic compound selected in this patent for constructing the fluorinated branched chain is 2,2,3,3-tetrafluoro-1,4-butanediol. It needs to be vacuum dried before use at a drying temperature of 40 °C and a drying time of 8 h. Dissolve 2,2,3,3-tetrafluoro-1,4-butanediol in the mixed solution with a mass ratio of NMP:GBL of 1:1 at a temperature of 60 °C and a stirring speed of 600 rpm to ensure its full dissolution. Add the fluorinated organic compound solution to the magnetic stirrer and continue the reaction. The reaction temperature is 30 °C, and the reaction duration is 2 h. The mass ratio of 2,2,3,3-tetrafluoro-1,4-butanediol to isocyanuric acid triester is 1:12.5.

[0075] Step 4: Introduce a polymer containing a conjugated double bond structure: Dissolve polyaniline with a hydroxyl substituent in the solution, stir magnetically to fully dissolve it, and mix it with the prepared highly fluorinated and highly stressed crosslinked polymer. After bridging between the chain polymers, introduce a conjugated double bond structure to improve the conductivity of the polymer material.

[0076] Step 41: Adjust the pH of the solution: Add a p-toluenesulfonic acid NMP solution to adjust the pH. p-Toluenesulfonic acid is dissolved in NMP, and magnetic stirring is carried out at a temperature of 40 °C for 1 h. After adding the p-toluenesulfonic acid solution, the pH is 3.2.

[0077] Step 42: Add a conductive polymer: Add a polyhydroxyaniline solution. The molecular weight of polyhydroxyaniline is 10,000. Polyaniline is dissolved in a mixed solution of NMP and ethanol, and the mass ratio of NMP to ethanol is 1:4. Add it to a magnetic stirrer and continue the reaction at a reaction temperature of 45 °C for 4 h. The addition ratio of the reacted polyhydroxyaniline to the mass of the isocyanic acid tripolyester is 0.2:0.12.

[0078] Step 43: Pour the solution into a rotary evaporator, with a water bath temperature of 60 °C, a reduced pressure of 0.1 MPa, and a rotation speed of 150 rpm. Evaporate the solvent to solidify the polymer, and obtain a fluorine-doped lithium-rich silicon-based anode binder with good conductivity.

[0079] Comparative Example 1:

[0080] The difference from Example 1 is that the lithium-rich organic polymer was not prepared, that is, Step 1 was missing, and the remaining preparation methods and parameters were the same as those in Example 1.

[0081] Comparative Example 2:

[0082] The difference from Example 1 is that the organic polymer containing a disulfide bond was not introduced, that is, Step 2.4) was missing, and the remaining preparation methods and parameters were the same as those in Example 1.

[0083] Comparative Example 3:

[0084] The difference from Example 1 is that the fluorine-containing organic polymer was not introduced, that is, Step 3) was missing, and the remaining preparation methods and parameters were the same as those in Example 1.

[0085] Comparative Example 4:

[0086] The difference from Example 1 is that the polyaniline containing a hydroxyl substituent with a conjugated double bond structure was not introduced, that is, Step 4) was missing, and the remaining preparation methods and parameters were the same as those in Example 1.

[0087] Continue to prepare the negative electrode with the silicon-based negative electrode particles obtained from the above examples and comparative examples, which specifically includes the following steps:

[0088] 1) Prepare a slurry by mixing silicon monoxide particles, acetylene black, and a fluorine-doped lithium-rich silicon-based binder with good electrical conductivity in a mass ratio of 8:0.5:1.5. The solvent is a mixed solvent of NMP and GBL, and the mass ratio of the two is 1.5:1, to obtain a uniform slurry with a viscosity of 4000 mPa·S. Filter the slurry and evenly coat it on a Cu foil. The temperature during the coating process is 80°C, and the vacuum drying oven is kept at a constant temperature of 80°C for 1 h. After rolling, punch it into a negative electrode sheet with a diameter of 14 mm.

[0089] 2) Use the prepared electrode sheet as the negative electrode and select NCM811 ternary material as the positive electrode to complete the button cell assembly process, and conduct electrochemical performance tests on the assembled battery.

[0090] Perform performance tests on the silicon-based negative electrodes prepared from the materials of Examples 1-3 and Comparative Examples 1-4. The test methods are as follows:

[0091] (1) DC impedance: Test standard: D at room temperature (25°C), battery capacity state 50%, 2C, discharge for 20 s to obtain DCR (DC impedance).

[0092] (2) First Coulomb efficiency test: Voltage range 0.001 - 3V. Charge and discharge current: 0.1C, first discharge then charge. Calculation method of first Coulomb efficiency: First charge capacity / First discharge capacity.

[0093] (3) Rate performance test method: Charge and discharge at rates of 0.1C, 0.2C, 0.4C, 0.8C, and 1.6C, voltage range 0.001 - 3V, 10 cycles each time, discharge at a rate of 0.2C, and cycle 100 times to test its capacity retention rate.

[0094] (4) Cycle performance test method: Discharge at rates of 0.5C and 2C, voltage range 0.001 - 3V, cycle 800 times to test its capacity retention rate.

[0095] The test results of the electrical performance of the batteries prepared from the materials of Examples 1-3 and Comparative Examples 1-4 are shown in Table 1.

[0096] Table 1 Battery performance test data

[0097]

[0098] As can be seen from Example 1 and Comparative Example 1, the addition of lithium polymethacrylate supplements part of the active lithium, reduces the first irreversible lithium loss, and thus significantly improves the first Coulombic efficiency and the energy output performance of the battery. As can be seen from Example 1 and Comparative Example 2, as a kind of dynamic covalent bond, disulfide bonds can undergo specific cleavage and recombination during the lithium insertion and extraction process. This property enables the polymer binder to have a self-healing function, which can significantly improve the mechanical properties of the material, making the network structure not easily damaged during the lithium insertion process, and thus endowing the silicon-based anode with good cycling performance and rate performance. As can be seen from Example 1 and Comparative Example 3, doping with fluorine helps to form an SEI containing a large amount of LiF components on the electrode surface. This structure is chemically stable and has a high lithium ion mobility, which can effectively isolate the contact between the electrolyte and the silicon-based anode and reduce the side reactions on the battery surface. It has an important impact on stabilizing the structure of the silicon-based anode. Therefore, the rate performance, the retention rate of the large current cycling capacity, and the retention rate of the small current cycling of Comparative Example 3 are all relatively low. As can be seen from Example 1 and Comparative Example 4, the introduction of conductive polymers can form a conductive network in the silicon-based anode, enabling efficient electron transport, improving the overall conductivity of the silicon-based anode, and enhancing the charge and discharge efficiency and power density of the battery.

[0099] The fluorine-doped lithium-rich silicon-based anode binder with good conductivity prepared by the present invention combines multiple functions such as a binder, a lithium supplement agent, and a conductive agent. Lithium polymethacrylate can introduce active lithium at the initial stage of charge and discharge, reduce the irreversible loss of lithium ions during the first discharge, enable the silicon-based anode to reach a stable state faster, reduce the capacity loss caused by volume change, and improve the first Coulombic efficiency; the flexible polyurethane polymer structure can effectively buffer the volume expansion of the silicon-based anode, provide mechanical support for the deformation of the silicon-based anode, reduce the pulverization of the silicon-based anode, and improve the cycle life of the silicon-based anode; the introduction of fluorine-containing organic compounds enhances the mechanical stability of the SEI, reduces the rupture of the SEI caused by the volume expansion of the silicon-based anode, prevents the overgrowth of the SEI, reduces the consumption of lithium ions, and improves the cycle stability of the battery; the introduction of conductive polymers effectively improves the conductivity of the silicon-based anode and ensures the capacity of the silicon-based anode during high-current charge and discharge.

[0100] For other reagents with similar properties and the selection of similar reaction parameters, those skilled in the art can determine them according to common knowledge. The above are only examples of the present invention. Common knowledge such as specific structures, characteristics, and reactant ratios known in the art is not described in detail here. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can be made, such as simply adjusting the parameter selection within or near the specified parameter range. These should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application should be based on the content of its claims, and the specific implementation manners described in the specification can be used to explain the content of the claims.

Claims

1. A method for preparing a fluorine-doped good conductive lithium-rich silicon-based anode binder, characterized in that: include: Step 1: preparing lithium-rich organic polymer: using NMP and GBL mixed solvent, respectively preparing LiOH solution with a mass concentration of 15-20wt% and polymer organic acid solution with a mass fraction of 8-15wt%, the weight ratio of LiOH solution to polymer organic acid solution is 0.24-0.3:1, controlling the temperature to stir and mix the two to obtain a lithium salt solution of organic acid, and concentrating the solution by rotary evaporation; Step 2: Preparation of polyester three-dimensional network polymer: Put high molecular weight polyether polyol or polyester polyol into a flask to react with isocyanate trimer to produce polyurethane prepolymer, add dihydroxy organic matter containing disulfide bonds into the reaction system, continue the reaction, and obtain a network polymer with stable structure; Step 3: Preparation of high-fluorine high-stress cross-linked network polymer: Add fluorine-containing organic matter to the network polymer material obtained in step 2 to cross-link the exposed isocyanate groups, bridge the chain structures at a distance, and construct branched chains to obtain a high-fluorine high-stress cross-linked network polymer; Step 4: Introducing polymers containing conjugated double bond structures: dissolve polyaniline containing hydroxyl substituents in the solution, stir until fully dissolved, mix with the high-fluorine high-stress cross-linked network polymer prepared in step 3, and introduce conjugated double bond structures after bridging between chain polymers.

2. The method for preparing a fluorine-doped good conductive lithium-rich silicon-based anode binder according to claim 1, characterized in that: In the LiOH solution prepared in step 1, the mass ratio of NMP to GBL is 2:1 to 1:1, and LiOH is vacuum dried to remove water before use, and the mass concentration of the prepared LiOH solution is 18 wt %.

3. The method for preparing a fluorine-doped good conductive lithium-rich silicon-based anode binder according to claim 1, characterized in that: In the process of preparing the polymer organic acid solution in step 1, the mass ratio of NMP to GBL is 2:1-1:1, the molecular weight of the polymer organic acid is 2000-3000, including polyacrylic acid, polymethacrylic acid, polylactic acid-glycolic acid copolymer or polymaleic acid and its derivatives, the organic acid is vacuum dried to remove water before use, and the mass fraction of the prepared organic acid solution is controlled at 12wt%.

4. The method for preparing a fluorine-doped good conductive lithium-rich silicon-based anode binder according to claim 1, characterized in that: When preparing the lithiated organic acid solution in step 1, the LiOH solution and the organic acid are uniformly mixed, the stirring temperature is 40-80° C., and the reaction time is 2-3 hours; the solution after the reaction is transferred to a rotary bottle of a rotary evaporator, the temperature of the heating water bath is controlled to be 80-90° C., the vacuum degree is 100-150 mbr, the rotation speed is 100-150 rpm, and the tap water is used for cooling.

5. The method for preparing a fluorine-doped good conductive lithium-rich silicon-based anode binder according to claim 1, characterized in that: The polyether polyol or polyester polyol in step 2 has a molecular weight of 200 to 1000, including polypropylene glycol, polyethylene glycol or polyether glycol; a catalyst is also introduced into the cross-linking reaction in step 2, and the catalyst is an ammonium catalyst or a tin catalyst with a purity of more than 99%, and the catalyst is vacuum dried before use.

6. The method for preparing a fluorine-doped good conductive lithium-rich silicon-based anode binder according to claim 5, characterized in that: The reaction of generating polyurethane in step 2 includes two steps of dissolution and reaction. In the first step, low-polymerization degree isocyanate trimer and tin catalyst are dissolved in a mixed solvent of NMP and GBL, wherein the mass ratio of NMP to GBL is 1.5:

1. During the mixing process, argon atmosphere is used for protection and magnetic stirring is performed at a temperature of 60 to 80°C to ensure that the reactants and the catalyst are fully dissolved. In the second step, argon environment is used for protection, polyether polyol is added to the mixed solution, magnetic stirring is continued, the reaction temperature is 60 to 80°C, the reaction time is 2 to 3h, and the mass ratio of polyether polyol, isocyanate trimer and catalyst is 1:0.6 to 0.7:1.6x10 -4 ~8.4x10 -4 .

7. The method for preparing a fluorine-doped good conductive lithium-rich silicon-based anode binder according to claim 1, characterized in that: The disulfide-bond-containing dihydroxy organic matter in step 2 includes 2-hydroxyethyl disulfide, 3,3'-dihydroxydiphenyl disulfide or 4-hydroxyphenyl disulfide; vacuum drying is performed before use; the disulfide-bond-containing dihydroxy organic matter is dissolved in a mixed solution of NMP:GBL with a mass ratio of 1.5:1, the temperature is 60°C, and the stirring speed is 600rpm to ensure that it can be fully dissolved; then the solution of the disulfide-bond-containing dihydroxy organic matter is added to a magnetic stirrer, and the reaction is continued, the reaction temperature is reduced to 30-50°C, the reaction time is 2-4h, and the mass ratio of the disulfide-bond-containing dihydroxy organic matter to isocyanate trimer is 1:4.8-5.

6.

8. The method for preparing a fluorine-doped good conductive lithium-rich silicon-based anode binder according to claim 1, characterized in that: The fluorinated organic matter selected in the process of constructing the fluorinated side chain in step 3 includes 2,2-difluoro-1,3-propylene glycol or 2,2,3,3-tetrafluoro-1,4-butanediol; vacuum drying is performed before use; the dihydroxy organic matter containing the fluorinated side chain is dissolved in a mixed solution of NMP:GBL with a mass ratio of 1.5:1, the temperature is 60°C, and the stirring speed is 600rpm to ensure that it can be fully dissolved; the fluorinated organic matter solution is added to a magnetic stirrer and the reaction is continued at a reaction temperature of 25 to 40°C and a reaction time of 1 to 2 hours, and the mass ratio of the fluorinated organic matter to isocyanate trisester is 1:10.8 to 12.

5.

9. The method for preparing a fluorine-doped good conductive lithium-rich silicon-based anode binder according to claim 1, characterized in that: In the step 4, a conjugated polymer is introduced. First, p-toluenesulfonic acid is added to the NMP solution to adjust the pH to 3-4, and the p-toluenesulfonic acid is dissolved in the NMP by stirring. Then, a polyhydroxyaniline solution is added, wherein the molecular weight of the polyhydroxyaniline is 10,000-100,000, and the polyaniline is dissolved in a mixed solution of NMP and ethanol, wherein the mass ratio of NMP to ethanol is 1-4:20, and the reaction is continued by stirring. The reaction temperature is 40-60° C., and the reaction time is 4-6 hours. The mass ratio of the added amount of polyhydroxyaniline to isocyanate trimer is 0.2-1:0.

12. The solution is then poured into a rotary evaporator, the water bath temperature is 40-60° C., the pressure is reduced by -0.08-0.1 MPa, and the solvent is evaporated to solidify the polymer to obtain a fluorine-doped good conductive lithium-rich silicon-based anode binder.

10. A silicon oxide negative electrode plate, characterized in that: It comprises a negative electrode current collector and a silicon oxide negative electrode active material layer coated on the surface of the negative electrode current collector, wherein the negative electrode active material layer comprises silicon oxide negative electrode active material and a fluorine-doped good conductive lithium-rich silicon-based anode binder obtained according to the preparation method of claim 1.

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