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

Abstract

The invention discloses a preparation method and application of a lithium ion battery composite material with a honeycomb structure, and relates to preparation and application of a lithium ion battery negative electrode. The invention aims to solve the technical problems of mechanical failure and poor conductivity caused by volume expansion of a silicon material in the existing high-specific-energy lithium battery. The preparation method comprises the following steps: adding a phytic acid solution into a solvent, stirring, adding water, continuously stirring, adding a carbon matrix, and uniformly stirring to obtain a carbon dispersion liquid; dropwise adding a silane reagent into the carbon dispersion liquid, and standing to obtain gel; and finally, sintering the gel to obtain the lithium ion battery composite material with the honeycomb structure. The initial capacity of a half battery assembled by a negative electrode prepared from the material is 339-423mAh g <-1 > under the conditions that the voltage interval is 0.01-3V and the current density is 2Ag <-1 >, the capacity retention ratio after 500 cycles is 87-95.4%, and the material can be used for a lithium battery.

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. Currently, the most commonly used graphite material has an actual specific capacity of 360-365mAh g -1 , which is very close to the theoretical specific capacity (372 mAh g -1 ), further improving the performance of graphite anodes has limited impact 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 anodes 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 higher specific capacity, its volume expansion and contraction changes by 320% during the charging and discharging process, which will produce greater 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 volume expansion of silicon materials in existing high-energy-density lithium batteries, and to provide a preparation method and application of a lithium-ion battery composite material with a honeycomb structure. The present invention combines the bionics principle 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 with a honeycomb structure of the present invention is carried out according to the following steps:

[0005] 1. Preparation of carbon matrix: after the high molecular organic matter and the small molecular organic matter are mixed evenly, they are ground to obtain mixed powder; the mixed powder is then sintered in a high temperature furnace to obtain a carbon matrix; wherein the high molecular organic matter is polyvinyl pyrrolidone or polyacrylonitrile; the small molecular organic matter is melamine or urea;

[0006] 2. Weigh the carbon matrix, 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 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 to 900° C. for 1.5 to 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 with the honeycomb structure is to use the composite material in lithium-ion batteries.

[0013] The present invention utilizes 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 a "buffer skeleton" and a micro-nano structure, 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, is solved.

[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 lithium ion battery SiO2 having a honeycomb shape. x C composite material. The porous structure of this material can provide space for the volume expansion of silicon oxide and relieve stress, effectively inhibiting the silicon-based negative electrode from crushing due to volume expansion during the cycle. At the same time, the large specific surface area and porous structure allow electrolyte to penetrate, shorten the transmission path of lithium ions, and improve the reaction activity of the composite material.

[0015] The present invention has a honeycomb-shaped 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 2A -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 a honeycomb structure prepared in Example 1 x / SEM photo of C;

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

[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 verified by the following examples.

[0024] Example 1: PM@SiO2, a lithium-ion battery composite material with a honeycomb structure in this examplex 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 evenly, and then ground for 5 minutes to obtain a mixed powder; the mixed powder was placed in a muffle furnace, heated to 800° C. and maintained 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 conditions 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 stand for 12 hours to obtain a gel;

[0029] Fourth, the gel was placed in a tubular furnace, heated to 850 °C and maintained for 2 h for sintering under an argon atmosphere to obtain a lithium-ion battery composite material with a honeycomb structure, denoted 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 conditions and stir 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 stand for 12 hours to obtain a gel;

[0033] Third, the gel was placed in a tubular furnace, heated to 850°C and maintained for 2 hours under an argon atmosphere for sintering to obtain a lithium-ion battery composite material with a honeycomb structure, denoted as SiO x / C, where 0<x<2.

[0034] Example 1: Lithium-ion battery composite material PM@SiO with honeycomb structure preparedx The scanning electron microscope photo of / C is shown in Figure 1 and Figure 2 As shown, from Figure 1 and Figure 2 It can be seen that the lithium-ion battery composite 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, and SiO x In PM@SiO2 / C materials, Si exists in amorphous form. x The amorphous bulge peak range in / C is wider than that in PM and SiO x / C, indicating that there is 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 Figure 4 As shown, from Figure 4 It can be seen that SiO x The carbon content of the / C material is 16.9%. The PM@SiO x / C material carbon content 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 a 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, negative electrode material: conductive carbon black: binder in the ratio of 8:1:1, prepare negative electrode slurry, then apply it on copper foil, dry it at 60 degrees Celsius for 6 hours, then cut it into 12mm negative electrode sheets, assemble half cells, and conduct at a current density of 2A. -1The cycle performance test was carried out after two cycles of activation with a voltage range of 0.01 V to 3 V and a current of 0.04 mA. -1 The cycling performance diagram under current density is shown in 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 / C has a relatively poor conductivity and has a large polarization 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 in this example 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 evenly, and then ground for 5 minutes to obtain a mixed powder; the mixed powder was then placed in a muffle furnace, heated to 800°C and maintained for 2 hours for sintering to obtain a carbon matrix;

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

[0042] 3. Add the phytic acid solution to N,N-dimethylformamide under stirring conditions 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 stand for 12 hours to obtain a gel;

[0043] Fourth, the gel was placed in a tubular furnace, heated to 850 °C and maintained for 2 h for sintering 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 the high molecular organic matter and the small molecular organic matter are mixed evenly, they are ground to obtain mixed powder; the mixed powder is then sintered in a high temperature furnace to obtain a carbon matrix; wherein the high molecular organic matter is polyvinyl pyrrolidone or polyacrylonitrile; the small molecular organic matter is melamine or urea; 2. Weigh the carbon matrix, 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; 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 stand for 8 to 12 hours to obtain a gel; 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.

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 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 to 900° C. for 1.5 to 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 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.

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 the lithium-ion battery composite material with a honeycomb structure in lithium-ion batteries.

Images