Preparation method and application of lithium-ion battery composite material with honeycomb structure

Abstract

A preparation method and application of a lithium-ion battery composite material with a honeycomb structure, which relates to the preparation and application of a lithium-ion battery negative electrode. It is intended to solve the technical problems of mechanical failure and poor conductivity caused by the volume expansion of silicon materials in existing high-energy-density lithium batteries. Preparation method: first add phytic acid solution to the solvent and stir, then add water and continue stirring, then add carbon matrix, stir evenly to obtain a carbon dispersion; then drop silane reagent into the carbon dispersion, let it stand to obtain a gel; finally, sinter the gel to obtain a lithium-ion battery composite material with a honeycomb structure. The half-cell assembled with the negative electrode prepared by this material has a voltage range of 0.01V~3V and a current density of 2Ag ‑1 The initial capacity is 339~423mAh g ‑1 The capacity retention rate after 500 cycles is 87% to 95.4%, which can be used in lithium batteries.

Description

Technical Field

[0001] The invention discloses a method for preparing a negative electrode of a lithium ion battery. Background Art

[0002] The negative electrode is an important component of lithium-ion batteries. Using high-capacity negative electrode materials can effectively improve the energy density of the entire battery. The actual specific capacity of the most commonly used graphite material can reach 360-365mAh g -1 , which is very close to the theoretical specific capacity (372mAh g -1 ), further improvement of the performance of graphite negative electrode has very limited effect on the performance of lithium-ion batteries, and is far from meeting the current requirements for high-capacity batteries. The specific capacity of silicon-based negative electrode can reach 4200mAh g -1 , which is more than 10 times that of traditional graphite negative electrodes. The new silicon-based lithium battery has the advantages of high specific energy, good safety, and long life. Therefore, it is one of the recognized directions in the industry to use silicon-based negative electrodes to replace the current graphite negative electrodes to improve the energy density of lithium batteries. Although the single silicon material has a high specific capacity, its volume expansion and contraction changes by 320% during the charge and discharge process, which will generate large mechanical stress. After multiple cycles, the silicon particles will break and pulverize, causing the negative electrode to fail. In addition, the contact between silicon and the conductive agent and the negative electrode binder is poor, resulting in poor overall conductivity of the electrode. These problems limit the application of silicon-based negative electrodes. Summary of the Invention

[0003] The present invention aims to solve the technical problems of mechanical failure and poor conductivity caused by the volume expansion of silicon materials in existing high-energy-density lithium batteries, and provides a preparation method and application of a lithium-ion battery composite material with a honeycomb structure. The present invention combines the principles of bionics with the field of battery materials through the design and preparation of a silicon-carbon negative electrode bionic structure, and prepares a lithium-ion battery composite material with a honeycomb structure, thereby obtaining a lithium battery with high energy density, long cycle life and high safety.

[0004] The method for preparing the lithium ion battery composite material having a honeycomb structure of the present invention is carried out according to the following steps:

[0005] 1. Preparation of carbon matrix: After uniformly mixing high molecular organic matter and low molecular organic matter, grinding to obtain mixed powder; then sintering the mixed powder in a high temperature furnace to obtain carbon matrix; wherein the high molecular organic matter is polyvinyl pyrrolidone or polyacrylonitrile; the low molecular organic matter is melamine or urea;

[0006] 2. Weigh the carbon substrate, phytic acid solution, silane reagent and solvent; wherein the silane reagent is 3-aminopropyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltriethoxysilane or 3-aminopropyltriethoxysilane; and the solvent is dimethyl sulfoxide or N,N-dimethylformamide;

[0007] 3. Under stirring conditions, add the phytic acid solution to the solvent and stir for 10 to 15 minutes, then add water and continue stirring for 10 to 20 minutes; the volume of the water added is 1% to 2% of the volume of the solvent; then add the carbon matrix and stir evenly to obtain a carbon dispersion; finally, add the silane reagent dropwise, stir for 1 to 2 minutes after the addition is complete, and then let it stand for 8 to 12 hours to obtain a gel;

[0008] Fourth, the gel is placed in a tubular furnace, heated to 800-900°C in an argon atmosphere and maintained for 2 hours for sintering to obtain a lithium-ion battery composite material with a honeycomb structure.

[0009] Furthermore, the mass ratio of the high molecular organic matter to the low molecular organic matter in step 1 is 1:(2-3).

[0010] Furthermore, the sintering in step 1 is carried out at a temperature of 800-900° C. for 1.5-2 hours.

[0011] Furthermore, the ratio of the mass of the carbon matrix described in step 2 to the volume of the phytic acid solution is 1g:(0.5~2)mL; the ratio of the mass of the carbon matrix to the volume of the silane reagent is 1g:(1~6)mL, and the ratio of the mass of the carbon matrix to the volume of the solvent is 1g:(10~40)mL.

[0012] The application of the lithium-ion battery composite material having the honeycomb structure is to use the composite material in lithium-ion batteries.

[0013] The present invention uses a bionic structure design method to prepare a silicon-carbon composite material with a three-dimensional nanoscale bionic honeycomb structure. Through the integrated structural design of the "buffer skeleton" and the micro-nano structure, it solves the problem of severe volume expansion of traditional silicon-based negative electrodes during charging, which leads to collapse and failure of the electrode structure and poor conductivity.

[0014] The present invention uses the product of sintering a mixture of organic and inorganic substances as a carbon matrix, then introduces it into a silane solution that can be in-situ polymerized in a solvent environment, and finally sintering the polymerized gel to obtain a honeycomb-shaped lithium-ion battery SiO x C composite material. This material's porous structure provides space for the volume expansion gradient of silicon oxide and relieves stress, effectively preventing the silicon-based anode from shattering due to volume expansion during cycling. Furthermore, its large specific surface area and porous structure allow for electrolyte infiltration, shortening the lithium ion transmission path and enhancing the composite material's reactivity.

[0015] The present invention has a honeycomb lithium ion battery SiO xC composite material, prepared as negative electrode, assembled half-cell, in the voltage range of 0.01V ~ 3V, current density of 2Ag -1 The initial capacity is 339~423mAh g -1 The capacity retention rate after 500 cycles is 87% to 95.4%. Its performance is better than that of traditional graphite negative electrode. It has the characteristics of high energy density, long cycle life and high safety, and can be used in lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The lithium ion battery composite material PM@SiO with honeycomb structure prepared in Example 1 x / SEM photograph of C;

[0017] Figure 2 The lithium ion battery composite material PM@SiO with honeycomb structure prepared in Example 1 x High-magnification scanning electron microscope photograph of / C;

[0018] Figure 3 The carbon matrix PM prepared by step 1 of Example 1 and the PM@SiO prepared by step 4 are x / C and SiO prepared in Comparative Example 1 x XRD spectrum of / C;

[0019] Figure 4 PM@SiO prepared in Example 1 x / C and SiO prepared in Comparative Example 1 x Thermogravimetric analysis curve of / C;

[0020] Figure 5 The carbon matrix PM prepared by step 1 of Example 1 and the PM@SiO prepared by step 4 are x / C and SiO prepared in Comparative Example 1 x / C pore size distribution diagram;

[0021] Figure 6 PM@SiO prepared in Example 1 x / C and SiO prepared in Comparative Example 1 x / C cycle performance diagram;

[0022] Figure 7 PU@SiO prepared in Example 2 x / C cycle performance diagram. DETAILED DESCRIPTION

[0023] The beneficial effects of the present invention are demonstrated with the following examples.

[0024] Example 1: PM@SiO composite material for lithium-ion batteries with a honeycomb structurex The preparation method of / C is carried out according to the following steps:

[0025] 1. Preparation of carbon matrix (PM): 8 g of polyvinyl pyrrolidone and 4 g of melamine were mixed and then ground for 5 minutes to obtain a mixed powder. The mixed powder was then placed in a muffle furnace and heated to 800°C for 2 hours for sintering to obtain a carbon matrix (PM);

[0026] 2. Weigh 1g of carbon matrix, 2mL of 50% phytic acid solution, 3mL of 3-aminopropyltriethoxysilane and 20mL of N,N-dimethylformamide;

[0027] Furthermore, the mass ratio of the high molecular organic matter to the low molecular organic matter in step 1 is 1:(2-3).

[0028] 3. Add the phytic acid solution to N,N-dimethylformamide under stirring and stir for 10 minutes, then add 0.2 mL of water and continue stirring for 10 minutes; then add the carbon matrix and stir evenly to obtain a carbon dispersion; finally, add 3-aminopropyltriethoxysilane dropwise, stir for 1 minute after the addition is complete, and then let it stand for 12 hours to obtain a gel;

[0029] Fourth, the gel was placed in a tube furnace and heated to 850 ° C for 2 h under an argon atmosphere to obtain a lithium-ion battery composite material with a honeycomb structure, which was recorded as PM@SiO x / C, where 0<x<2.

[0030] Comparative Example 1: This comparative example prepares a lithium ion battery composite material SiO without adding a carbon matrix (PM) x / C(0<x<2), the specific steps are as follows:

[0031] 1. Weigh 2 mL of 50% phytic acid solution, 3 mL of 3-aminopropyltriethoxysilane, and 20 mL of N,N-dimethylformamide;

[0032] 2. Add the phytic acid solution to N,N-dimethylformamide under stirring for 10 minutes, then add 0.2 mL of water and continue stirring for 10 minutes; then add the silane reagent dropwise, stir for 1 minute after the addition is complete, and then let it stand for 12 hours to obtain a gel;

[0033] 3. The gel was placed in a tube furnace and heated to 850 °C for 2 h under an argon atmosphere to obtain a lithium-ion battery composite material with a honeycomb structure, which was recorded as SiO x / C, where 0<x<2.

[0034] Lithium-ion battery composite material PM@SiO with honeycomb structure prepared in Example 1x The scanning electron microscope photo of / C is as follows Figure 1 and Figure 2 As shown, from Figure 1 and Figure 2 It can be seen that the lithium-ion battery composite material PM@SiO x / C presents a honeycomb pore structure.

[0035] Example 1 Carbon matrix PM prepared in step 1, PM@SiO prepared in step 4 x / C and SiO prepared in Comparative Example 1 x The X-ray diffraction (XRD) spectrum of / C is as follows Figure 3 As shown, from Figure 3 It can be seen that the carbon in the carbon matrix PM is amorphous, SiO x In the PM@SiO2 / C material, Si exists in amorphous form. x The amorphous bulge peak range in / C is wider than that in PM and SiO x / C, indicating the presence of both amorphous carbon and SiO x / C material.

[0036] The PM@SiO prepared in Example 1 x / C and SiO prepared in Comparative Example 1 x / C was subjected to thermogravimetric analysis test, and the obtained thermogravimetric curve was as shown in the figure below. Figure 4 As shown, from Figure 4 It can be seen that SiO x The carbon content of the / C material is 16.9%, and the PM@SiO prepared by introducing PM carbon matrix x The carbon content of / C material is increased to 20.0%.

[0037] The carbon matrix PM prepared in step 1 of Example 1 and the PM@SiO prepared in step 4 were x / C and SiO prepared in Comparative Example 1 x / C was tested for pore size, and the pore size distribution diagram obtained was as follows Figure 5 As shown, from Figure 5 It can be seen that PM@SiO x / C has a larger pore size distribution range, which will provide better buffer space for the volume expansion of silicon.

[0038] The PM@SiO prepared in Example 1 x / C and SiO prepared in Comparative Example 1 x / C cycle performance test, the negative electrode material: conductive carbon black: binder in the ratio of 8:1:1, the negative electrode slurry was prepared, and then coated on the copper foil, dried at 60 degrees Celsius for 6 hours, and then cut into 12mm negative electrode sheets, assembled half-cells, and at a current density of 2Ag -1The voltage range is 0.01V~3V, and the current is 0.04mA. After two cycles of activation, the cycle performance test is carried out. The results show that the -1 The cycling performance diagram under current density is shown in Figure 2. Figure 6 As shown, from Figure 6 It can be seen that PM@SiO x The initial capacity of / C is 422.47 mAh g -1 , in 2Ag -1 At the current density, the discharge capacity after 500 cycles is 403.02 mAh g -1 The capacity retention rate is 95.4%. x Due to its poor conductivity, the polarization is large in the early cycle. After 500 cycles, the capacity is 297.36 mAh g -1 .

[0039] Example 2: PU@SiO2, a lithium-ion battery composite material with a honeycomb structure according to this embodiment x The preparation method of / C is carried out according to the following steps:

[0040] 1. Preparation of carbon matrix: 8 g of polyvinyl pyrrolidone and 4 g of urea were mixed and then ground for 5 minutes to obtain a mixed powder. The mixed powder was then placed in a muffle furnace and heated to 800°C for 2 hours for sintering to obtain a carbon matrix.

[0041] 2. Weigh 1 g of carbon matrix, 2 mL of 50% phytic acid solution, 3 mL of 3-aminopropyltriethoxysilane, and 20 mL of N,N-dimethylformamide;

[0042] 3. Add the phytic acid solution to N,N-dimethylformamide under stirring and stir for 10 minutes, then add 0.2 mL of water and continue stirring for 10 minutes; then add the carbon matrix and stir evenly to obtain a carbon dispersion; finally, add 3-aminopropyltriethoxysilane dropwise, stir for 1 minute after the addition is complete, and then let it stand for 12 hours to obtain a gel;

[0043] Fourth, the gel was placed in a tube furnace and heated to 850 ° C for 2 h under an argon atmosphere to obtain a lithium-ion battery composite material with a honeycomb structure, which was recorded as PU@SiO x / C, where 0<x<2.

[0044] The PU@SiO prepared in Example 2 x / C and SiO prepared in Comparative Example 1 x / C cycle performance test, the negative electrode slurry was prepared according to the ratio of negative electrode material: conductive carbon black: binder at 8:1:1, and then coated on the copper foil, dried at 60℃ for 6h, and then cut into 12mm negative electrode sheets, assembled half-cells, and tested at a current density of 2A. -1 The voltage range is 0.01V~3V, and the current is 0.04mA. After two cycles of activation, the cycle performance test is carried out. The cycle performance curve is as shown in the figure below. Figure 7 As shown, from Figure 7 It can be seen that PU@SiO x The initial capacity of / C is 339.20 mAh g -1 , in 2Ag -1 At the current density, the discharge capacity after 500 cycles is 389.90 mAh g -1 , the capacity retention rate is 87%.

Claims

1. A method for preparing a lithium-ion battery composite material having a honeycomb structure, characterized in that The method proceeds as follows:

1. Preparation of carbon matrix: After uniformly mixing high molecular organic matter and low molecular organic matter, grinding to obtain mixed powder; then sintering the mixed powder in a high temperature furnace to obtain carbon matrix; wherein the high molecular organic matter is polyvinyl pyrrolidone or polyacrylonitrile; the low molecular organic matter is melamine or urea; 2. Weigh the carbon substrate, phytic acid solution, silane reagent and solvent; the silane reagent is 3-aminopropyltriethoxysilane; the solvent is dimethyl sulfoxide or N,N-dimethylformamide; 3. Under stirring conditions, add the phytic acid solution to the solvent and stir for 10-15 minutes, then add water and continue stirring for 10-20 minutes; the volume of the added water is 1%-2% of the volume of the solvent; then add the carbon matrix and stir evenly to obtain a carbon dispersion; finally, add the silane reagent dropwise, stir for 1-2 minutes after the addition is complete, and then let it stand for 8-12 hours to obtain a gel; Fourth, the gel was placed in a tube furnace and heated to 800-900°C in an argon atmosphere for 2 hours for sintering to obtain a lithium-ion battery composite material with a honeycomb structure. The composite material is denoted as: carbon matrix@SiO x / C, where 0<x<2.

2. The method for preparing a lithium-ion battery composite material having a honeycomb structure according to claim 1, characterized in that: The mass ratio of the high molecular organic matter to the low molecular organic matter described in step 1 is 1:(2~3).

3. The method for preparing a lithium-ion battery composite material having a honeycomb structure according to claim 1 or 2, characterized in that: The sintering in step 1 is carried out at a temperature of 800-900° C. for 1.5-2 hours.

4. The method for preparing a lithium-ion battery composite material having a honeycomb structure according to claim 1 or 2, characterized in that: The ratio of the mass of the carbon matrix described in step 2 to the volume of the phytic acid solution is 1 g: (0.5-2) mL; the ratio of the mass of the carbon matrix to the volume of the silane reagent is 1 g: (1-6) mL; and the ratio of the mass of the carbon matrix to the volume of the solvent is 1 g: (10-40) mL.

5. Application of a lithium ion battery composite material having a honeycomb structure prepared by the method of claim 1, characterized in that The application is to use a lithium-ion battery composite material with a honeycomb structure in a lithium-ion battery.

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