Preparation method and application of multi-coating silicon-carbon negative electrode material
Through the preparation method of multi-clad silicon carbon anode material, a gradient cladding layer was constructed, which solved the volume expansion of silicon-based anode material, SEI film rupture and low conductivity problems in lithium-ion batteries, and achieved improvements in high capacity, stability and rate performance.
Patent Information
- Application Number
- CN202510293681.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-13
- Publication Date
- 2025-06-10
AI Technical Summary
The application of silicon-based anode materials in lithium-ion batteries faces problems such as structural deterioration caused by volume expansion, repeated rupture and regeneration of SEI films, and rate performance deterioration caused by low conductivity.
The preparation method of multi-clad silicon carbon negative electrode material is adopted to construct a gradient cladding layer to achieve synergistic effect between the conductive reinforcement layer and the mechanical buffer layer, suppress structural deterioration caused by volume deformation, and establish a stable electrode/electrolyte interface.
It effectively maintains the high capacity characteristics of silicon-based materials, suppresses structural degradation, establishes a stable electrode/electrolyte interface, and improves the application performance and stability of the battery.
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Figure CN120127129A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of battery materials, and more specifically, to a preparation method and application of a multi-coated silicon-carbon anode material. Background Art
[0002] Since its commercialization in the early 1990s, carbonaceous materials have formed a mature technical system as the anode of lithium-ion batteries. Carbon-based materials represented by natural graphite and artificial graphite have long dominated commercial applications with their stable electrochemical performance and reasonable cycle life. However, with the upgrading of the demand for energy density in large-scale energy storage application scenarios such as electric vehicles, the theoretical specific capacity (372 mAh / g) of traditional graphite anodes has approached its physical limit, which has prompted researchers to turn their attention to silicon-based material systems with a ten-fold theoretical capacity (4200 mAh / g).
[0003] While silicon-based anode materials exhibit significant capacity advantages, their industrial application still faces three core challenges: First, the volume expansion effect of up to 300% during lithiation causes the material structure to pulverize, resulting in the failure of electrical contact between the active material and the current collector; Second, the severe volume deformation causes the repeated rupture and regeneration of the solid electrolyte interface (SEI) film, which not only accelerates the consumption of the electrolyte, but also forms a continuously thickening passivation layer that hinders the transport of lithium ions; Finally, the low electrical conductivity (<0.001 S·cm-1) brought about by the intrinsic semiconductor characteristics severely restricts the charge transfer kinetics, leading to poor rate performance. These mutually coupled physical and chemical problems seriously damage the integrity and cycle stability of the electrode structure.
[0004] Current technological improvements mainly focus on four directions: 1. Micro-nano structure design alleviates mechanical stress through the size effect; 2. Porous structure construction reserves expansion space; 3. Alloying modification regulates volume changes; 4. Composite system construction enhances the conductive network. Among them, silicon / carbon composite materials are regarded as the most promising technical route for industrialization because they can synergistically play the advantages of graphite conductive matrix and high-capacity silicon. However, the existing composite systems still have significant defects: Although nanometerization treatment can improve the volume effect, it exacerbates the side reactions caused by the increase in specific surface area; The introduction of graphite components improves the conductivity, but its layered structure is prone to lithium dendrite growth during high-rate charge and discharge, making it difficult to meet the fast charging requirements of power batteries; The heterogeneous interface formed by traditional coating processes is difficult to effectively inhibit the excessive growth of the SEI film, all of which lead to phenomena such as capacity reduction and instability at the electrode / electrolyte interface when the anode material is applied, thus affecting the final battery efficiency. Summary of the Invention
[0005] Therefore, in order to effectively solve the above-mentioned existing problems, the present application provides a method for preparing a multi-coated silicon-carbon anode material. The finally obtained anode material can realize the synergistic effect of a conductive enhancement layer and a mechanical buffer layer by constructing a gradient coating layer. While maintaining the high-capacity characteristics of the silicon-based material, it can effectively inhibit the structural deterioration caused by volume deformation and establish a stable electrode / electrolyte interface, thereby effectively ensuring the application performance of the battery, meeting the high-performance requirements for battery materials in the existing technical field, and having broad application potential.
[0006] A method for preparing a multi-coated silicon-carbon anode material specifically includes the following steps:
[0007] S1: Mix graphite, a silicon source, dimethyl sulfoxide, and a hard carbon precursor and add them to a high-speed shear disperser, and stir and mix at a speed of 2000 - 3000 rpm for 30 - 60 min to form a uniformly mixed slurry;
[0008] S2: Add an acid material to the mixed slurry obtained in S1, place it in a water bath at 70 - 90 °C and heat and stir until the viscosity of the mixed slurry is 5000 - 10000 mPa·s to obtain a preheated slurry;
[0009] S3: Under an argon atmosphere, heat the preheated slurry obtained in S2 at a rate of 4 - 5 °C / min to 800 - 1200 °C, and anneal for 3 - 4 h to obtain a pre-product;
[0010] S4: Disperse the pre-product obtained in S3 in an organic solvent, add an organic coating agent and mix evenly, and heat in a water bath at 80 - 90 °C until the organic solvent completely evaporates to form a uniform coating layer;
[0011] S5: Anneal the product obtained in S4 for the second time under an argon atmosphere. After completion, sieve the product through a 200 - 300 mesh sieve, and use magnetic separation to remove metal impurities. Finally, a multi-coated silicon-carbon anode material is obtained.
[0012] As a preferred embodiment, in S1, the mass ratio of graphite, a silicon source, dimethyl sulfoxide, and a hard carbon precursor is (80 - 95):(5 - 20):(800 - 1500):(5 - 10).
[0013] As a more preferred embodiment, in S1, the mass ratio of graphite, a silicon source, dimethyl sulfoxide, and a hard carbon precursor is (90 - 95):(5 - 10):(800 - 1200):5.
[0014] As a preferred embodiment, the D50 average particle size of the graphite is 10 - 20 μm.
[0015] As a preferred embodiment, the specific surface area of the graphite is 2 - 5 m 2 / g.
[0016] As a preferred embodiment, the silicon source is spherical nano-silicon.
[0017] As a preferred embodiment, the D50 average particle size of the nano-silicon is 50 - 200 nm.
[0018] As a more preferred embodiment, the D50 average particle size of the nano-silicon is 60 - 120 nm.
[0019] As a preferred embodiment, the specific surface area of the nano-silicon is 30 - 50 m 2 / g.
[0020] As a preferred embodiment, the preparation method of the hard carbon precursor specifically includes the following steps:
[0021] S1: Mix phenol and formaldehyde solution in a reaction vessel, and adjust the pH of the system to 8 - 9 with sodium hydroxide, then raise the temperature to 75 - 85 °C and react for 2 - 4 h to obtain a prepolymer;
[0022] S2: Further mix the prepolymer with epichlorohydrin and melamine, then raise the temperature to 90 - 100 °C and keep the temperature for reaction for 2 - 3 h;
[0023] S3: After the product obtained in S2 is naturally cooled to room temperature, adjust the pH to 6.5 - 7.5 with acetic acid, then dehydrate the product, and vacuum dry it at 60 - 70 °C and crush it to an average particle size ≤10 μm.
[0024] As a preferred embodiment, the mass concentration of the formaldehyde solution is 30 - 40 wt%.
[0025] As a preferred embodiment, the mass ratio of phenol to formaldehyde solution is (90 - 100):(100 - 120).
[0026] As a preferred embodiment, the mass ratio of phenol, epichlorohydrin and melamine is (90 - 100):(10 - 15):(6 - 8).
[0027] The addition of the hard carbon precursor obtained through the above preparation can, while forming a hierarchical pore hard carbon framework and providing a fast diffusion channel (<2 nm) for lithium ions, accommodate the expansion of silicon particles and relieve macroscopic volume deformation, prompting the formed hard carbon pores to form a "cage-like encapsulation" of the silicon particles. Furthermore, when expanding, the pore walls can withstand mechanical stress. In addition, it can also absorb the expansion energy of silicon through elastic deformation via the porous structure, avoiding the expansion of electrode cracks. On the other hand, the melamine it contains generates a graphite nitrogen-doped structure during carbonization. While enhancing the conductivity of the hard carbon, the epoxy groups promote the interfacial fusion between the hard carbon and graphite particles, forming a three-dimensional continuous conductive network. Moreover, the presence of the epoxy groups can also react with the hydroxyl groups on the surface of silicon particles to enhance the interfacial bonding force, and its internal structure is more conducive to the formation of a more stable SEI film, significantly improving the stability and electrical properties of the silicon-carbon negative electrode.
[0028] As a preferred embodiment, the acid material is at least one of boric acid, phosphoric acid, amino acid, and ammonium phosphate.
[0029] As a more preferred embodiment, the acid material is boric acid or amino acid.
[0030] As a preferred embodiment, the mass ratio of the mixed slurry to the acid material is (85 - 95):(5 - 15).
[0031] As a more preferred embodiment, the mass ratio of the mixed slurry to the acid material is (90 - 95):(5 - 10).
[0032] As a preferred embodiment, the organic solvent is any one of dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran.
[0033] As a preferred embodiment, the mass ratio of the pre-product to the organic coating agent is (80 - 90):(10 - 20).
[0034] As a more preferred embodiment, the mass ratio of the pre-product to the organic coating agent is 90:10.
[0035] As a preferred embodiment, the organic coating agent is a composition of polyacrylonitrile and a modification aid.
[0036] As a preferred embodiment, the mass ratio of polyacrylonitrile to the modification aid is (7 - 10):(2 - 4).
[0037] As a more preferred embodiment, the mass ratio of polyacrylonitrile to the modification aid is (8 - 9):(2.5 - 3.5).
[0038] As a preferred embodiment, the preparation method of the modification aid specifically includes the following steps:
[0039] S1: After uniformly mixing polycaprolactone diol, maleic anhydride and acrylic acid in a reaction kettle, add ammonium persulfate and react at 90 - 120 °C for 3 - 4 h to obtain a grafted product;
[0040] S2: Continuously add epoxidized soybean oil and ethylenediamine to the grafted product, and raise the temperature to 90 - 100 °C and react for 2 - 3 h;
[0041] S3: Cool the product obtained in S2 to room temperature, wash it with ethanol to remove unreacted monomers, and dry it in vacuum at 60 - 70 °C and then crush it to an average particle size ≤ 15 μm.
[0042] As a preferred embodiment, the mass ratio of the polycaprolactone diol, maleic anhydride and acrylic acid is (95 - 100):(5 - 8):(12 - 16).
[0043] As a preferred embodiment, the mass ratio of the polycaprolactone diol, epoxidized soybean oil and ethylenediamine is (95 - 100):(15 - 20):(8 - 10).
[0044] By adding a compound organic coating agent, a cyclization reaction occurs during the low-temperature annealing stage, generating pyridine nitrogen. Its relatively high electronegativity can improve the conductivity of the negative electrode, and at the same time, it can increase additional lithium-ion binding active sites, having a good chemical reaction basis. Moreover, in the overall preparation method, after double coating, the obtained silicon-carbon negative electrode product has the characteristics of high cycle stability and good rate performance; on the other hand, the addition of the modification additive can effectively improve the binding force of the coating agent to the silicon source, and by introducing acid anhydride groups, improve the chemical inertness of the coating layer to the electrolyte. During coating, through the reaction with the aforementioned epoxy groups, a crosslinked network with a high crosslinking density is formed, endowing the coating layer with elasticity and thermal stability; in the coating system, the modification additive can also maintain high resilience, disperse local stress through characteristic chain segments, and through the preferential reaction effect, stabilize and optimize the interface of the SEI film, thereby improving the overall comprehensive performance of the negative electrode material.
[0045] As a preferred embodiment, the heating rate of the secondary annealing is 2.5 - 3 °C / min.
[0046] As a preferred embodiment, the temperature of the secondary annealing is 300 - 500 °C, and the holding time is 1 - 3 h.
[0047] This application further defines the application of the silicon-carbon negative electrode material prepared by the preparation method of the above-mentioned multi-layer coated silicon-carbon negative electrode material in portable electronic device batteries, power vehicle batteries and energy storage systems.
[0048] The beneficial effects of this application are:
[0049] 1. A multi-coated silicon-carbon anode material provided in this application can achieve the synergistic effect of a conductive enhancement layer and a mechanical buffer layer by constructing a gradient coating layer. While maintaining the high-capacity characteristics of the silicon-based material, it effectively inhibits the structural deterioration caused by volume deformation and establishes a stable electrode / electrolyte interface, thus effectively ensuring the application performance of the battery, meeting the high-performance requirements for battery materials in the existing technical field, and having broad application potential.
[0050] 2. A multi-coated silicon-carbon anode material provided in this application. The added hard carbon precursor can form a multi-stage pore hard carbon skeleton after carbonization, providing a fast lithium-ion diffusion channel (<2 nm) while accommodating the expansion of silicon particles and alleviating macroscopic volume deformation, avoiding the expansion of electrode cracks. On the other hand, the contained melamine generates a graphite nitrogen-doped structure during carbonization, enhancing the conductivity of hard carbon. At the same time, epoxy groups promote the interfacial fusion of hard carbon and graphite particles to form a three-dimensional continuous conductive network. The presence of epoxy groups can also react with the hydroxyl groups on the surface of silicon particles to enhance the interfacial binding force, and its internal structure is more conducive to the formation of a more stable SEI film, greatly improving the stability and electrical properties of the silicon-carbon anode.
[0051] 3. A multi-coated silicon-carbon anode material provided in this application. By adding a compound organic coating agent, a cyclization reaction occurs during the low-temperature annealing stage, generating pyridine nitrogen. Its good electronegativity can improve the conductivity of the anode and can also provide additional lithium-ion binding active sites, having a good chemical reaction basis. In the overall preparation method, after double coating, the obtained silicon-carbon anode product has the characteristics of high cycle stability and good rate performance. BRIEF DESCRIPTION OF THE DRAWINGS
[0052] Figure 1 It is a test chart of the battery cycle performance of Example 1.
[0053] Figure 2 It is a test chart of the battery cycle performance of Example 2.
[0054] Figure 3 It is a test chart of the battery cycle performance of Example 3.
[0055] Figure 4 It is a test chart of the battery cycle performance of Example 4. DETAILED DESCRIPTION OF THE INVENTION
[0056] In the detailed description, specific implementation cases will be used to more intuitively display and illustrate the content of the invention in this application.
[0057] Example 1
[0058] The preparation method of the multi-coated silicon-carbon anode material, in parts by mass, specifically includes the following steps:
[0059] S1: Mix 95 parts of graphite, 5 parts of silicon source, 800 parts of dimethyl sulfoxide and 5 parts of hard carbon precursor and add them to a high-speed shear disperser, stir and mix at a speed of 2400 rpm for 45 min to form a uniformly mixed slurry;
[0060] S2: Add 5 parts of amino acid to the 95 parts of mixed slurry obtained in S1, place it in a water bath at 85 °C and heat and stir until the viscosity of the mixed slurry is 5000 mPa·s to obtain a preheated slurry;
[0061] S3: Under an argon atmosphere, heat the preheated slurry obtained in S2 to 800 °C at a rate of 5 °C / min, hold for 4 h for annealing to obtain a pre-product;
[0062] S4: Disperse 90 parts of the pre-product obtained in S3 in 900 parts of tetrahydrofuran, add 10 parts of organic coating agent and mix evenly, heat in a water bath at 80 °C until dimethyl sulfoxide and tetrahydrofuran are completely evaporated to form a uniform coating layer;
[0063] S5: Anneal the product obtained in S4 for the second time under an argon atmosphere, with a heating rate of 2.5 °C / min, a temperature of 300 °C, and a holding time of 2 h. After completion, sieve the product through a 200-mesh sieve, remove metal impurities by magnetic separation, and finally obtain a silicon-carbon anode material with a multi-layer coating.
[0064] The average D50 particle size of graphite is 12.5 μm, and the specific surface area is 4.5 m 2 / g.
[0065] The silicon source is spherical nano-silicon, the average D50 particle size is 75 nm, and the specific surface area is 46 m 2 / g.
[0066] The preparation method of the hard carbon precursor, in terms of parts by mass, specifically includes the following steps:
[0067] S1: Mix 100 parts of phenol and 110 parts of formaldehyde solution in a reaction vessel, and adjust the pH of the system to 8.5 with sodium hydroxide, heat to 80 °C and react for 3 h to obtain a prepolymer;
[0068] S2: Further mix the prepolymer with 13 parts of epichlorohydrin and 6.5 parts of melamine, then heat to 100 °C and hold for 2.5 h;
[0069] S3: After the product obtained in S2 is naturally cooled to room temperature, adjust the pH to 6.8 with acetic acid, then dehydrate the product, and dry it in vacuum at 70 °C and crush it to an average particle size of 7.8 μm.
[0070] The mass concentration of the formaldehyde solution is 37 wt%.
[0071] The organic coating agent is a composition of polyacrylonitrile and a modifying aid, and the mass ratio is 8:3.
[0072] The polyacrylonitrile is purchased from the high-quality polyacrylonitrile product sold by Wuhan Smart Bio-Tech Co., Ltd.
[0073] The preparation method of the modifying aid, in parts by mass, specifically includes the following steps:
[0074] S1: Mix 98 parts of polycaprolactone diol, 7.5 parts of maleic anhydride and 14.6 parts of acrylic acid evenly in a reaction kettle, then add 1.8 parts of ammonium persulfate, and react at 115 °C for 3.5 h to obtain a grafted product;
[0075] S2: Continuously add 16.8 parts of epoxidized soybean oil and 9.5 parts of ethylenediamine to the grafted product, and raise the temperature to 100 °C and react for 2.5 h;
[0076] S3: Cool the product obtained in S2 to room temperature of 25 °C, wash it with ethanol to remove unreacted monomers, dry it in vacuum at 70 °C and then pulverize it to an average particle size of 9.2 μm.
[0077] The polycaprolactone diol is purchased from the PCL2000 model product sold by Wuhan Lanaibai Pharmaceutical Chemical Co., Ltd., China.
[0078] Example 2
[0079] This example is only different from Example 1 in the following aspects: The preparation method of the multi-coated silicon-carbon negative electrode material, in parts by mass, specifically includes the following steps:
[0080] S1: Mix 90 parts of graphite, 10 parts of silicon source, 1200 parts of dimethyl sulfoxide and 10 parts of hard carbon precursor and add them to a high-speed shear disperser, and stir and mix at a speed of 2400 rpm for 45 min to form a uniform mixed slurry;
[0081] S2: Add 10 parts of phosphoric acid to the 90 parts of mixed slurry obtained in S1, place it in a water bath at 85 °C and heat and stir until the viscosity of the mixed slurry is 8000 mPa·s to obtain a preheated slurry;
[0082] S3: Heat the preheated slurry obtained in S2 to 1000 °C at a rate of 5 °C / min under an argon atmosphere, and keep it at this temperature for 4 h for annealing to obtain a pre-product;
[0083] S4: Disperse the 90 parts of pre-product obtained in S3 in 1000 parts of dimethylformamide, add 10 parts of organic coating agent and mix evenly, and heat in a water bath at 80 °C until dimethyl sulfoxide and tetrahydrofuran are completely evaporated to form a uniform coating layer;
[0084] S5: The product obtained in S4 is annealed for the second time under an argon atmosphere, with a heating rate of 2.5 °C / min, a temperature of 300 °C, and a holding time of 2 h. After completion, the product is passed through a 200-mesh sieve, and metal impurities are removed by magnetic separation. Finally, the multi-coated silicon-carbon anode material is obtained.
[0085] Example 3
[0086] This example only differs from Example 1 in the following aspect: The preparation method of the multi-coated silicon-carbon anode material, in parts by mass, specifically includes the following steps:
[0087] S1: 80 parts of graphite, 20 parts of silicon source, 1200 parts of dimethyl sulfoxide, and 5 parts of hard carbon precursor are mixed and added to a high-speed shear disperser, and stirred and mixed at a speed of 2400 rpm for 45 min to form a uniform mixed slurry;
[0088] S2: 10 parts of boric acid are added to the 90 parts of mixed slurry obtained in S1, and placed in an 85 °C water bath and heated and stirred until the viscosity of the mixed slurry is 10000 mPa·s to obtain a preheated slurry;
[0089] S3: The preheated slurry obtained in S2 is heated to 1200 °C at a rate of 5 °C / min under an argon atmosphere, and annealed for 4 h to obtain a pre-product;
[0090] S4: The 90 parts of pre-product obtained in S3 are dispersed in 1100 parts of dimethyl sulfoxide, 10 parts of organic coating agent are added and mixed evenly, and heated in an 80 °C water bath until dimethyl sulfoxide and tetrahydrofuran are completely evaporated to form a uniform coating layer;
[0091] S5: The product obtained in S4 is annealed for the second time under an argon atmosphere, with a heating rate of 2.5 °C / min, a temperature of 300 °C, and a holding time of 2 h. After completion, the product is passed through a 200-mesh sieve, and metal impurities are removed by magnetic separation. Finally, the multi-coated silicon-carbon anode material is obtained.
[0092] Example 4
[0093] This example only differs from Example 1 in the following aspect: The preparation method of the multi-coated silicon-carbon anode material, in parts by mass, specifically includes the following steps:
[0094] S1: 90 parts of graphite, 10 parts of silicon source, 1500 parts of dimethyl sulfoxide, and 5 parts of hard carbon precursor are mixed and added to a high-speed shear disperser, and stirred and mixed at a speed of 2400 rpm for 45 min to form a uniform mixed slurry;
[0095] S2: 10 parts of boric acid are added to the 90 parts of mixed slurry obtained in S1, and placed in an 85 °C water bath and heated and stirred until the viscosity of the mixed slurry is 9000 mPa·s to obtain a preheated slurry;
[0096] S3: Heat the preheated slurry obtained in S2 to 1000 °C at a rate of 5 °C / min under an argon atmosphere, and anneal for 4 h to obtain a pre-product;
[0097] S4: Disperse 90 parts of the pre-product obtained in S3 in 1000 parts of dimethyl sulfoxide, add 10 parts of an organic coating agent and mix evenly, and heat in a water bath at 80 °C until dimethyl sulfoxide and tetrahydrofuran are completely evaporated to form a uniform coating layer;
[0098] S5: Anneal the product obtained in S4 for the second time under an argon atmosphere, with a heating rate of 2.5 °C / min, a temperature of 350 °C, and a holding time of 2.5 h. After completion, pass the product through a 200-mesh sieve and remove metal impurities by magnetic separation to finally obtain a multi-coated silicon-carbon anode material.
[0099] Comparative Example 1
[0100] This comparative example only differs from Example 1 in the following aspects: The preparation method of the multi-coated silicon-carbon anode material specifically includes the following steps in parts by mass:
[0101] S1: Mix 120 parts of graphite, 10 parts of a silicon source, 1200 parts of dimethyl sulfoxide, and 2.5 parts of a hard carbon precursor and add them to a high-speed shear disperser, and stir and mix at a speed of 2400 rpm for 45 min to form a uniform mixed slurry;
[0102] S2: Add 2.5 parts of an amino acid to 100 parts of the mixed slurry obtained in S1, place it in a water bath at 85 °C and heat and stir until the viscosity of the mixed slurry is 7000 mPa·s to obtain a preheated slurry;
[0103] S3: Heat the preheated slurry obtained in S2 to 800 °C at a rate of 5 °C / min under an argon atmosphere, and anneal for 4 h to obtain a pre-product;
[0104] S4: Disperse 90 parts of the pre-product obtained in S3 in 900 parts of tetrahydrofuran, add 5 parts of an organic coating agent and mix evenly, and heat in a water bath at 80 °C until dimethyl sulfoxide and tetrahydrofuran are completely evaporated to form a uniform coating layer;
[0105] S5: Anneal the product obtained in S4 for the second time under an argon atmosphere, with a heating rate of 2.5 °C / min, a temperature of 300 °C, and a holding time of 2 h. After completion, pass the product through a 200-mesh sieve and remove metal impurities by magnetic separation to finally obtain a multi-coated silicon-carbon anode material.
[0106] Comparative Example 2
[0107] This comparative example only differs from Example 1 in the following aspect: The organic coating agent is a composition of polyacrylonitrile and a modified additive, and the mass ratio is 9.5:0.5.
[0108] Comparative Example 3
[0109] This comparative example is only different from Example 1 in the following aspects: The organic coating agent is a composition of polyacrylonitrile and a modifying additive, and the mass ratio is 2:8.
[0110] Comparative Example 4
[0111] This comparative example is only different from Example 1 in the following aspects: The preparation method of the hard carbon precursor, in parts by mass, specifically includes the following steps:
[0112] S1: Mix 100 parts of phenol with 110 parts of formaldehyde solution in a reaction vessel, and adjust the pH of the system to 8.5 with sodium hydroxide, then raise the temperature to 80 °C and react for 3 h to obtain a prepolymer;
[0113] S2: Further mix the prepolymer with 5 parts of epichlorohydrin and 1.5 parts of melamine, then raise the temperature to 100 °C and keep the temperature for reaction for 2.5 h;
[0114] S3: After the product obtained in S2 is naturally cooled to room temperature, adjust the pH to 6.8 with acetic acid, then dehydrate the product, and pulverize it to an average particle size of 7.5 μm after vacuum drying at 70 °C.
[0115] The mass concentration of the formaldehyde solution is 37 wt%.
[0116] Comparative Example 5
[0117] This comparative example is only different from Example 1 in the following aspects: The preparation method of the modifying additive, in parts by mass, specifically includes the following steps:
[0118] S1: Mix 106 parts of polycaprolactone diol and 14.6 parts of acrylic acid evenly in a reaction kettle, then add 1.2 parts of ammonium persulfate, and react at 115 °C for 3.5 h to obtain a grafted product;
[0119] S2: Continuously add 8.5 parts of epoxidized soybean oil and 4.5 parts of ethylenediamine to the grafted product, and raise the temperature to 100 °C and react for 2.5 h;
[0120] S3: Cool the product obtained in S2 to room temperature of 25 °C, wash it with ethanol to remove unreacted monomers, and pulverize it to an average particle size of 11 μm after vacuum drying at 70 °C.
[0121] Comparative Example 6
[0122] This comparative example is only different from Example 1 in the following aspects: The preparation method of the modifying additive, in parts by mass, specifically includes the following steps:
[0123] S1: Mix 98 parts of polycaprolactone diol, 7.5 parts of maleic anhydride, and 5.5 parts of acrylic acid evenly in a reaction kettle, then add 1.8 parts of ammonium persulfate and react at 115 °C for 3.5 h to obtain a grafted product;
[0124] S2: Continuously add 25.5 parts of epoxidized soybean oil to the grafted product and raise the temperature to 100 °C for reaction for 2.5 h;
[0125] S3: Cool the product obtained in S2 to room temperature of 25 °C, wash it with ethanol to remove unreacted monomers, dry it in vacuum at 70 °C, and then crush it to an average particle size of 9.8 μm.
[0126] Performance evaluation
[0127] Weigh and mix the anode materials, SBR, CMC (binder), and carbon black (conductive agent) prepared in the above examples and comparative examples according to a mass ratio of 8:1:1, place them in a small mortar, add an appropriate amount of N-methylpyrrolidone (NMP), and grind them thoroughly for half an hour to make them evenly mixed. Then, prepare an anode electrode sheet and assemble it; the battery case model used for the button battery is CR2032, the lithium sheet is metallic lithium, and the electrolyte is LiPF6 with EC and DMC, DEC solvents in a volume ratio of 1:1:1; the battery performance test is carried out in a LAND test system, the test environment temperature is 25 °C, and the charge-discharge voltage range is 0.01 V to 1.5 V, that is, charging ends when the charging voltage ≥ 1.5 V, and discharging ends when the discharging voltage ≤ 0.01 V.
[0128] Test items:
[0129] 1. Initial discharge efficiency.
[0130] 2. Initial discharge specific capacity.
[0131] 3. Cycling performance: As Figures 1 to 4 shown are the cycling performance test result graphs of Examples 1 to 4 respectively, and the cycling performance test values (capacity retention rate after 200 cycles at a 1C current density) of the examples and comparative examples are recorded in Table 1.
[0132] Table 1 Performance evaluation table
[0133]
[0134] From the final performance test results of the examples and comparative examples, Comparative Examples 1-6 achieved worse performance results compared to the examples. Under a 1C current density, after 200 cycles, the examples still had a high capacity retention rate. The examples adopted a better technical solution to construct a gradient coating layer to achieve the synergistic effect of the conductive enhancement layer and the mechanical buffer layer. While maintaining the high-capacity characteristics of the silicon-based material, it effectively inhibited the structural deterioration caused by volume deformation and established a stable electrode / electrolyte interface, thus effectively ensuring the application performance of the battery.
Claims
1. A method for preparing a multi-layer silicon-carbon negative electrode material, characterized in that: The specific steps include: S1: adding graphite, silicon source, dimethyl sulfoxide and hard carbon precursor to a high-speed shear disperser, stirring and mixing at a speed of 2000-3000 rpm for 30-60 minutes to form a uniform mixed slurry; S2: adding an acid material to the mixed slurry obtained in S1, placing the mixture in a water bath at 70-90° C. and heating and stirring the mixture until the viscosity of the mixed slurry is 5000-10000 mPa·s, thereby obtaining a preheated slurry; S3: The preheated slurry obtained in S2 is heated to 800-1200° C. at a rate of 4-5° C. / min under an argon atmosphere, and annealed for 3-4 hours to obtain a pre-product; S4: dispersing the pre-product obtained in S3 in an organic solvent, adding an organic coating agent and mixing evenly, heating in a water bath at 80-90° C. until the organic solvent is completely evaporated to form a uniform coating layer; S5: annealing the product obtained in S4 twice in an argon atmosphere, and after completion, the product is sieved through a 200-300 mesh sieve and subjected to magnetic separation to remove metal impurities, thereby obtaining a multi-layer coated silicon-carbon negative electrode material; In the S1, the mass ratio of graphite, silicon source, dimethyl sulfoxide and hard carbon precursor is (80-95): (5-20): (800-1500): (5-10).
2. The method for preparing the multi-coated silicon-carbon negative electrode material according to claim 1, characterized in that: The graphite has an average particle size D50 of 10 to 20 μm and a specific surface area of 2 to 5 m 2 / g.
3. The method for preparing the multi-coated silicon-carbon negative electrode material according to claim 2, characterized in that: The silicon source is spherical nano-silicon, the average particle size D50 of the nano-silicon is 50-200nm, and the specific surface area is 30-50m 2 / g.
4. The method for preparing the multi-coated silicon-carbon negative electrode material according to claim 3, characterized in that: The method for preparing the hard carbon precursor specifically comprises the following steps: S1: Phenol and formaldehyde solution are mixed in a reaction container, and the pH of the system is adjusted to 8-9 with sodium hydroxide, and the temperature is raised to 75-85° C. for reaction for 2-4 hours to obtain a prepolymer; S2: further mixing the prepolymer with epichlorohydrin and melamine, then heating to 90-100° C. and keeping the temperature for reaction for 2-3 hours; S3: After the product obtained in S2 is naturally cooled to room temperature, acetic acid is added to adjust the pH to 6.5-7.5, and then the product is dehydrated and vacuum dried at 60-70° C. and crushed to an average particle size of ≤10 μm.
5. The method for preparing a multi-coated silicon-carbon negative electrode material according to claim 4, characterized in that: The mass concentration of the formaldehyde solution is 30-40wt%; the mass ratio of the phenol to the formaldehyde solution is (90-100):(100-120).
6. The method for preparing the multi-coated silicon-carbon negative electrode material according to claim 5, characterized in that: The mass ratio of phenol, epichlorohydrin and melamine is (90-100):(10-15):(6-8).
7. The method for preparing a multi-coated silicon-carbon negative electrode material according to claim 6, characterized in that: The acid material is boric acid or amino acid; the mass ratio of the mixed slurry to the acid material is (85-95):(5-15).
8. The method for preparing a multi-coated silicon-carbon negative electrode material according to claim 7, characterized in that: The organic coating agent is a composition of polyacrylonitrile and a modification auxiliary agent, and the mass ratio is (7-10): (2-4).
9. The method for preparing a multi-coated silicon-carbon negative electrode material according to claim 8, characterized in that: The preparation method of the modified auxiliary agent specifically comprises the following steps: S1: After polycaprolactone diol, maleic anhydride and acrylic acid are uniformly mixed in a reaction kettle, ammonium persulfate is added, and the mixture is reacted at 90-120° C. for 3-4 hours to obtain a grafted product; S2: Continue to add epoxidized soybean oil and ethylenediamine to the grafted product, raise the temperature to 90-100°C and react for 2-3h; S3: The product obtained in S2 is cooled to room temperature, washed with ethanol to remove unreacted monomers, dried in vacuum at 60-70°C, and then crushed to an average particle size of ≤15 μm; The mass ratio of the polycaprolactone diol, maleic anhydride and acrylic acid is (95-100):(5-8):(12-16).
10. Application of a negative electrode material obtained by the method for preparing a multi-coated silicon-carbon negative electrode material according to any one of claims 1 to 9 in portable electronic device batteries, power vehicle batteries and energy storage systems.