A method for preparing silicon-based anode materials for lithium-ion batteries based on metal fluoride additives and its application.

Abstract

A method for preparing silicon-based anode materials for lithium-ion batteries based on metal fluoride additives and its application are disclosed. This method aims to address the technical problems of poor lithium-ion transport at the silicon-electrolyte interface and poor SEI mechanical properties in existing silicon anodes. The method involves dissolving a metal fluoride in a solvent, mixing it with silicon particles, adding resin, mixing thoroughly, evaporating to dryness, and then calcining to obtain the silicon-based anode material for lithium-ion batteries based on metal fluoride additives. This material retains a capacity of 1300–1450 mAh g after 200 cycles at a current of 0.2C and a voltage range of 0.01V–3V. ‑1 It can be used in lithium-ion applications.

Description

Technical Field

[0001] This invention relates to a method for preparing silicon-based anodes for lithium-ion batteries and their applications. Background Technology

[0002] Currently, widely used graphite-based anode materials have low specific capacity, and their capacity in batteries is nearing its theoretical limit, failing to meet the demands of higher-performance lithium-ion batteries. Therefore, developing novel anode materials with high specific capacity, high energy density, and high safety is crucial for future lithium-ion battery applications. Silicon (Si) materials, as anodes in lithium-ion batteries, have the following advantages: high theoretical specific capacity (4200 mAh g / g). -1 Li 22 Silicon (Si) anodes are more than 10 times more abundant than traditional graphite materials; their low operating voltage allows them to further improve battery energy density when matched with high-capacity, high-voltage NCM cathodes; they are abundant and widely available, being the second most abundant element in the Earth's crust at 26.3%, second only to oxygen; they are non-toxic and environmentally friendly. Therefore, silicon (Si) anodes are widely recognized in the industry as one of the preferred anode materials for developing next-generation high-energy-density lithium-ion batteries. However, compared to traditional commercial graphite anodes, silicon faces the problem of significant volume expansion. Several challenges of silicon anodes limit their further application: (1) Silicon anodes undergo large volume expansion / contraction during cycling, resulting in huge stress, which leads to silicon breakage and pulverization, ultimately resulting in loss of electrical contact and rapid capacity decay; (2) During cycling, the solid electrolyte membrane (SEI) of silicon anodes is constantly broken and reassembled, which leads to the SEI becoming thicker and thicker, accompanied by a large consumption of electrolyte and lithium ions; (3) In terms of the properties of the material itself, silicon is a common intrinsic semiconductor material with poor conductivity, which greatly limits the diffusion rate of lithium ions in silicon anodes and seriously affects the practical application of silicon anodes. Summary of the Invention

[0003] This invention aims to address the technical problems of poor lithium-ion transport at the silicon-electrolyte interface and poor SEI mechanical properties in existing silicon anodes. It provides a method for preparing silicon-based anode materials for lithium-ion batteries based on metal fluoride additives and their applications. This invention introduces a metal fluoride into micron-sized silicon, constructing an interface with fast ion transport and good mechanical properties on the silicon surface. Finally, carbon coating further enhances the material's conductivity while suppressing silicon volume expansion, thus solving the problems of poor lithium-ion transport at the silicon-electrolyte interface and poor SEI mechanical properties. This further improves the reaction kinetics of the silicon anode interface, suppresses volume effects, and stabilizes the interface.

[0004] The preparation method of the silicon-based anode material for lithium-ion batteries based on metal fluoride additives of the present invention is carried out according to the following steps:

[0005] 1. Dissolve the metal fluoride in a solvent, then add silicon particles and stir for 3-4 hours to obtain mixture A;

[0006] 2. Add the resin to mixture A and stir for 3-5 hours to obtain mixture B;

[0007] 3. The mixture B obtained in step 2 is heated in an oil bath to evaporate the solvent, resulting in a solid mixture;

[0008] IV. The solid mixture obtained in step III is placed in a tube furnace and calcined at 800–900°C for 2–3 hours under an argon atmosphere to obtain a silicon-based anode material for lithium-ion batteries based on metal fluoride additives, denoted as Si-M. x F y @C.

[0009] Furthermore, the metal fluoride mentioned in step one is one or a combination of several of MgF2, CaF2, ZnF2 and SnF2.

[0010] Furthermore, the silicon particles mentioned in step one have a particle size of 1–3 μm.

[0011] Furthermore, the solvent mentioned in step one is one or more of methanol, ethanol, and propanol.

[0012] Furthermore, the mass ratio of silicon to metal fluoride mentioned in step one is 1:(6-8).

[0013] Furthermore, the resin mentioned in step two is one or more of polyacrylonitrile, polyvinylpyrrolidone, and phenolic resin;

[0014] Furthermore, the evaporation temperature described in step three is 60℃~80℃.

[0015] The application of the silicon-based anode material for lithium-ion batteries prepared by the above method based on metal fluoride additives is to be used in lithium-ion batteries.

[0016] This invention uses metal fluorides as additives, dissolved in a solvent, and then mixed with silicon to coat the surface of micron-sized silicon with the metal fluorides. During the first cycle, this metal fluoride can form a fast lithium-ion conductor (LiF) / electron conductor (Li). x The M-mixed interface layer possesses high mechanical toughness, enhancing the interface stability of silicon. Finally, a carbon layer is formed through polymer pyrolysis, further improving reaction kinetics, suppressing volume effects, and stabilizing the interface, resulting in a silicon anode with significantly improved performance. The silicon-based lithium-ion battery anode material prepared in this invention underwent cycling tests at a current of 0.2C and a voltage range of 0.01V–3V, retaining a capacity of 1300–1450 mAh g after 200 cycles.-1 .

[0017] This invention modifies micron-sized silicon with metal fluorides, which effectively improves the interfacial reaction kinetics, increases the mechanical strength of the SEI layer, enhances the interfacial stability, effectively suppresses the volume expansion of micron-sized silicon particles, and solves the problems of poor lithium-ion transport between silicon and electrolyte and poor mechanical properties of SEI. The process is simple and easy to implement on a large scale. Attached Figure Description

[0018] Figure 1 This is the elemental analysis diagram of the silicon-based anode material for lithium-ion batteries prepared in Example 1;

[0019] Figure 2 These are scanning electron microscope images of the silicon-based anode material for lithium-ion batteries prepared in Example 1;

[0020] Figure 3 These are high-magnification scanning electron microscope images of the silicon-based anode material for lithium-ion batteries prepared in Example 1;

[0021] Figure 4 This is the XPS spectrum of the silicon-based anode material for lithium-ion batteries prepared in Example 1;

[0022] Figure 5 This is the GITT curve of the silicon-based anode material for lithium-ion batteries prepared in Example 1;

[0023] Figure 6 This is a cycle performance curve of the silicon-based anode material for lithium-ion batteries prepared in Example 1;

[0024] Figure 7 These are cycle performance curves of the silicon-based anode materials for lithium-ion batteries prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0025] Figure 8 This is a cycle performance curve of the silicon-based anode material for lithium-ion batteries prepared in Example 2. Detailed Implementation

[0026] The beneficial effects of the present invention will be verified using the following examples.

[0027] Example 1: The preparation method of the silicon-based anode material for lithium-ion batteries based on metal fluoride additives in this example is carried out according to the following steps:

[0028] 1. Add 0.05 g of SnF2 to 15 mL of ethanol, then add 0.35 g of silicon particles with an average particle size of 3 μm, stir for 3 h to obtain mixture A;

[0029] 2. Add 0.04 g of polyacrylonitrile resin to mixture A and stir for 3 h to obtain mixture B;

[0030] 3. The mixture B obtained in step 2 is heated in an oil bath at a temperature of 80°C to evaporate the solvent and obtain a solid mixture.

[0031] Fourth, place the solid mixture obtained in step three into a tube furnace and calcine it at 850°C for 2 hours under an argon atmosphere to obtain a silicon-based anode material for lithium-ion batteries based on metal fluoride additives, denoted as Si-SnF2@C.

[0032] The scanning electron microscope image of the silicon-based anode material for lithium-ion batteries obtained in this embodiment is shown below. Figure 1 As shown, from Figure 1 It can be seen that the metal fluoride SnF2 coating on the surface of silicon particles does not change the morphology of the silicon particles.

[0033] The high-magnification scanning electron microscope image of the silicon-based anode material for lithium-ion batteries obtained in this embodiment is shown below. Figure 2 As shown, from Figure 2 It can be seen that the silicon particles exhibit a certain degree of agglomeration.

[0034] The elemental analysis map of the silicon-based anode material for lithium-ion batteries obtained in this embodiment is as follows: Figure 3 As shown, from Figure 3 It can be seen that SnF2 is dispersed on the silicon surface.

[0035] The XPS test image of the silicon-based anode material for lithium-ion batteries obtained in this embodiment is as follows: Figure 4 As shown, from Figure 4 It can be seen that the metal fluoride on the surface of the silicon anode did not undergo a change in valence state, indicating that it exists stably.

[0036] The lithium-ion battery silicon-based anode material prepared in Example 1 was subjected to a constant current intermittent titration test with the silicon particles from Step 1. By controlling and setting the pulse current and relaxation time, the GITT curves of the lithium-ion battery silicon-based anode material and the original silicon particles are shown in the figure. Figure 5 As shown, from Figure 5 It can be seen that the introduction of metal fluorides significantly improves the ion transport rate, indicating that it improves the interfacial kinetics of silicon.

[0037] The silicon-based anode material for lithium-ion batteries prepared in Example 1 and the silicon particles from Step 1 were used as anode materials to prepare electrodes. A paste was prepared by mixing anode material, conductive carbon black, and binder in a ratio of 8:1:1, and then coated onto copper foil. After drying at 60°C for 6 hours, the paste was cut into 12mm anode sheets and assembled into half-cells. The cells were then tested at a current of 0.2C (1C = 4200mAh g / g). -1 The voltage range was 0.01V to 3V, and the activation current was 0.01C. Cyclic performance was tested, and the resulting cycle performance curves are shown in the figure. Figure 6 As shown, from Figure 6 It can be seen that the introduction of metal fluoride improves the interfacial stability of the silicon anode and suppresses the volume effect, thus improving the electrochemical performance of the silicon anode. After 200 cycles at 0.2C, the modified silicon anode still retains a capacity of 1446.6 mAh g⁻¹. -1 Compared to the original silicon anode, its cycle performance is significantly improved.

[0038] Comparative Example 1: This comparative example differs from Example 1 in that the operation in step one is replaced with:

[0039] 1. Add 0.05 g of SnF2 to 15 mL of ethanol, then add 0.45 g of silicon particles with an average particle size of 3 μm, stir for 3 h to obtain mixture A; other steps and parameters are the same as in Example 1.

[0040] Comparative Example 2: This comparative example differs from Example 1 in that the operation in step one is replaced with:

[0041] 1. Add 0.05 g of SnF2 to 15 mL of ethanol, then add 0.25 g of silicon particles with an average particle size of 3 μm, stir for 3 h to obtain mixture A; other steps and parameters are the same as in Example 1.

[0042] Compared to Example 1, Comparative Example 1, and Comparative Example 2, the difference lies in the ratio of silicon to metal fluoride. In Example 1, the mass ratio of SnF2 to silicon particles is 1:7; in Comparative Example 1, it is 1:9; and in Comparative Example 2, it is 1:5. The lithium-ion battery silicon-based anode materials prepared in Examples 1, 1, and 2 were used to fabricate electrodes. Specifically, a slurry was prepared by mixing anode material, conductive carbon black, and binder in a ratio of 8:1:1. This slurry was then coated onto copper foil, dried at 60°C for 6 hours, and subsequently cut into 12mm anode sheets. Half-cells were then assembled and tested at a current of 0.2C (1C = 4200 mAh g / g). -1 The voltage range was 0.01V to 3V, and the activation current was 0.01C. Cyclic performance was tested, and the resulting cycle performance curves are shown in the figure. Figure 7 As shown. From Figure 7 It can be seen that the capacity of the negative electrode material prepared in Comparative Example 1 is only 803.6 mAh g after 200 cycles. -1 The negative electrode material prepared in Comparative Example 2 had a capacity of only 165.6 mAh g after 200 cycles. -1 By comparing the materials obtained in Example 1 with those in Comparative Examples 1 and 2, it is shown that a mass ratio of metal fluoride to silicon of 1:7 can achieve good technical results.

[0043] Example 2: The preparation method of the silicon-based anode material for lithium-ion batteries based on metal fluoride additives in this example is carried out according to the following steps:

[0044] 1. Add 0.05 g of MgF2 to 15 mL of ethanol, then add 0.35 g of silicon particles with an average particle size of 3 μm, stir for 3 h to obtain mixture A;

[0045] 2. Add 0.04 g of phenolic resin to mixture A and stir for 3 h to obtain mixture B;

[0046] 3. The mixture B obtained in step 2 is heated in an oil bath at a temperature of 80°C to evaporate the solvent and obtain a solid mixture.

[0047] Fourth, place the solid mixture obtained in step three into a tube furnace and calcine it at 850°C for 2 hours under an argon atmosphere to obtain a silicon-based anode material for lithium-ion batteries based on metal fluoride additives, denoted as Si-MgF2@C.

[0048] The lithium-ion battery silicon-based anode material prepared in Example 2 was used to fabricate an electrode. Specifically, a slurry was prepared by mixing the anode material, conductive carbon black, and binder in a ratio of 8:1:1. This slurry was then coated onto copper foil and dried at 60°C for 6 hours. The slurry was then cut into 12mm anode sheets and assembled into a half-cell. The battery was tested at a current of 0.2C (1C = 4200mAh g / g). -1 The voltage range was 0.01V to 3V, and the activation current was 0.01C. Cyclic performance was tested, and the resulting cycle performance curves are shown in the figure. Figure 8 As shown. From Figure 8 It can be seen that the silicon-based anode material for lithium-ion batteries prepared using MgF2 retains a capacity of 1327.04 mAh g after 200 cycles. -1 .

Claims

1. A method for preparing a silicon-based anode material for lithium-ion batteries based on metal fluoride additives, characterized in that, This method is performed in the following steps:

1. Dissolve the metal fluoride in a solvent, then add silicon particles with a particle size of 1~3μm, stir for 3~4h to obtain mixture A; wherein the mass ratio of the metal fluoride to the silicon particles is 1:7; the solvent is one or more of methanol, ethanol and propanol.

2. Add the resin to mixture A and stir for 3-5 hours to obtain mixture B; 3. The mixture B obtained in step 2 is heated in an oil bath to evaporate the solvent, resulting in a solid mixture; IV. Place the solid mixture obtained in step III in a tube furnace and calcine it at 800-900℃ for 2-3 hours under an argon atmosphere to obtain a silicon-based anode material for lithium-ion batteries based on metal fluoride additives, denoted as Si-M. x F y @C.

2. The method for preparing a silicon-based anode material for lithium-ion batteries based on metal fluoride additives according to claim 1, characterized in that, The metal fluoride mentioned in step one is one or a combination of several of MgF2, CaF2, ZnF2 and SnF2.

3. A method for preparing a silicon-based anode material for lithium-ion batteries based on metal fluoride additives according to claim 1 or 2, characterized in that, The resin mentioned in step two is one or more of polyacrylonitrile, polyvinylpyrrolidone, and phenolic resin.

4. A method for preparing a silicon-based anode material for lithium-ion batteries based on metal fluoride additives according to claim 1 or 2, characterized in that, The oil bath heating temperature mentioned in step three is 60℃~80℃.

5. The application of the lithium-ion battery silicon-based anode material based on metal fluoride additives prepared by the method of claim 1, characterized in that... This application involves using silicon-based anode materials for lithium-ion batteries with metal fluoride additives.

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