Preparation method of double-layer carbon-coated porous silicon lithium ion battery negative electrode material

Abstract

The invention relates to a preparation method of a double-layer carbon-coated porous silicon lithium ion battery negative electrode material, which comprises the following steps: etching an aluminum-silicon alloy by hydrochloric acid to obtain porous silicon, carrying out surface modification on the porous silicon, and compounding with a carbon nanotube by an electrostatic self-assembly method to obtain a porous silicon / carbon nanotube composite microsphere; carrying out in-situ polymerization on phenolic resin on the surfaces of the porous silicon / carbon nanotube composite microspheres by using a sol-gel method, and then carbonizing in a tubular furnace to obtain the double-layer carbon-coated porous silicon lithium ion battery negative electrode material. According to the preparation method, the porous silicon is obtained through acid etching, the buffer space of volume expansion is increased, the porous silicon is evenly coated with the carbon nanotubes, the porous silicon is anchored in a three-dimensional conductive network, the structural stability and conductivity are improved, the conductivity of the material is further improved by combining the carbon nanotubes with the derivative carbon layer of the phenolic resin, and the service life of the material is prolonged. Therefore, the cycling stability of the lithium ion battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a method for preparing a double-layer carbon-coated porous silicon lithium ion battery negative electrode material. Background Art

[0002] After the silicon anode material is fully lithiated at room temperature, its capacity can reach , over 10 times that of traditional graphite materials, and boasting a lower charge-discharge plateau. Furthermore, silicon is widely available, abundant, inherently non-toxic, and environmentally friendly. Therefore, silicon anodes are widely recognized as the preferred anode material for next-generation high-energy-density lithium-ion batteries. However, silicon anode materials currently face challenges such as volume expansion of up to 300%, poor conductivity, slow lithium-ion diffusion, and complex and costly preparation processes. To address these issues, the synthesis of silicon and carbon materials has become a research hotspot, but several challenges remain. First, the weak bond between silicon and carbon makes them easily broken, leading to structural collapse. Second, the preparation of silicon-carbon composites involves the manipulation of multiple components, resulting in a complex process and the expensive silicon source. Furthermore, traditional single carbon coating strategies offer only limited buffering effects and are unable to effectively address the structural fragmentation and persistent growth of the solid electrolyte interface (SEI) during repeated lithium ion insertion and deinsertion, severely limiting the industrial application of silicon-based anode materials.

[0003] Carbon nanotubes have excellent mechanical properties and electrical conductivity, acting as a buffer space while increasing the transfer rate of lithium ions during cycling. The three-dimensional conductive network they create ensures good electrical contact between the materials. However, due to their extremely high tensile strength, effective composite bonding with silicon is difficult without surface treatment.

[0004] The carbon layer produced by pyrolysis of phenolic resin exhibits high porosity, low resistivity, a controllable pore structure, a high specific surface area, excellent electrical conductivity, and superior thermal and mechanical properties, making it a promising carbon material for core-shell structures. However, due to the negative surface charge of phenolic resin, its weak binding to silicon requires surface modification.

[0005] Therefore, it is a technical challenge to synthesize a method for preparing a lithium-ion battery negative electrode material with simple process, low cost, and excellent cycle performance and rate performance. Summary of the Invention

[0006] In view of the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing a lithium-ion battery negative electrode material with double-layer carbon-coated porous silicon. The 3D conductive network composed of CNTs interwoven on the surface of the obtained porous silicon wraps the porous silicon in a conductive frame, and the carbon layer after carbonization of the phenolic resin tightly wraps the porous silicon particles and CNTs, ensuring a close connection between the porous silicon and CNTs, ensuring excellent electrical contact, and the double-layer carbon-coated structure ensures the structural stability of the composite material during the cycle. At the same time, the amorphous carbon layer produced by pyrolysis has excellent electrical conductivity and pore structure, which avoids direct contact with the porous silicon and the electrolyte, and helps to reduce consumption, effectively improving the first coulombic efficiency of the material.

[0007] The present invention provides a method for preparing a double-layer carbon-coated porous silicon negative electrode material for lithium-ion batteries. The method comprises synthesizing porous silicon and a carbon layer, wherein the porous silicon is modified porous silicon with a positive surface charge, the inner layer of the carbon layer is carbon nanotubes, and the outer layer is amorphous carbon. The method comprises the following steps: Step 1: Add 5 g of aluminum-silicon alloy to 800 mL of HCl solution, stir for 24 h, wash the precipitate with deionized water by centrifugation until the solution is neutral, and collect the black precipitate p-Si.

[0008] Step 2: Take 1 g of p-Si and 100 mL of ethanol, then add 10 mL of 3-aminopropyltriethoxysilane. After magnetic stirring for 6 hours, wash with ethanol and deionized water, and dry in a vacuum oven for 12 hours to obtain modified p-Si.

[0009] Step 3: The modified p-Si and CNTs were dispersed in deionized water and ethanol, magnetically stirred for 6 hours and dried for 12 hours to obtain p-Si / CNTs.

[0010] Step 4: Weigh 0.5 g of p-Si / CNTs and 0.5 g of CTAB and disperse them by ultrasonication. Then, add 25 mL of ethanol and 1 mL of ammonia water. After thorough mixing, add 0.5 g of resorcinol and stir magnetically for 20 minutes. Then, add 0.7 mL of formaldehyde solution dropwise and stir magnetically for 12 hours to obtain p-Si / CNTs / RF.

[0011] Step 5: Place the p-Si / CNTs / RF in a tube furnace under argon atmosphere at 800 °C for 3 hours with a heating rate of 5 °C / min. Then, the annealed powder sample is washed with deionized water and ethanol and dried in a vacuum oven for 12 hours.

[0012] Furthermore, the precursor of the porous silicon is an aluminum-silicon alloy Al90Si10 with a silicon mass percentage of 10 wt% and a particle size of 1 μm to 10 μm.

[0013] Furthermore, the molar concentration of the HCl solution is 1 mol / L.

[0014] Furthermore, p-Si and ethanol were mixed and ultrasonicated for 1 h, and the mass ratio of p-Si to CNTs was 5:1.

[0015] Furthermore, 3-aminopropyltriethoxysilane was added to the p-Si solution and then magnetically stirred in a water bath at 30° C. for 6 hours.

[0016] Furthermore, the modified p-Si was ultrasonicated in 100 mL of deionized water for 1 h, and the CNTs were ultrasonicated in 30 mL of ethanol for 1 h, with the mass ratio of p-Si to CNTs being 5:1.

[0017] Furthermore, p-Si / CNTs and CTAB were ultrasonicated in 50 mL of deionized water for 30 min.

[0018] Further, after the formaldehyde solution was added dropwise, the mixture was magnetically stirred in a water bath at 35° C. for 12 hours and aged for 12 hours.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects: The present invention uses aluminum-silicon alloy instead of commercial nano-silicon as the silicon source, effectively reducing the preparation cost. The synthesized porous silicon has abundant holes and pores, providing a fast transmission channel for lithium ions.

[0020] The present invention modifies the surface of porous silicon so that porous silicon and carbon nanotubes are combined through electrostatic self-assembly. The 3D conductive network composed of CNTs ensures good electrical contact of the material and improves the overall conductivity and structural stability of the material. The present invention wraps porous silicon particles and CNTs through the self-polymerization of resorcinol and formaldehyde. The carbon layer produced by pyrolysis has excellent electrical conductivity and pore structure, which avoids direct contact between porous silicon and electrolyte, and helps to reduce consumption, effectively improving the first coulombic efficiency of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 are SEM images of the p-Si / CNTs / RF5 powder sample in Example 1 at scales of 3 μm and 8 μm; Figure 2 is the XRD pattern of the p-Si / CNTs / RF5 powder sample in Example 1; Figure 3 The p-Si / CNTs / RF5 powder sample and the original p-Si sample in Example 1 are Cycling performance diagram under current density; Figure 4is the rate performance diagram of the p-Si / CNTs / RF5 powder sample and the original p-Si sample in Example 1; Figure 5 The p-Si / CNTs / RF5 powder sample and the original p-Si sample in Example 1 are Cycling performance diagram under current density; Figure 6 These are SEM images of the p-Si / CNTs / RF10 powder sample in Example 2 at scales of 2 μm and 3 μm. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] Unless the context requires otherwise, throughout the specification and claims, the term "including" is to be interpreted as meaning open inclusion, that is, "including, but not limited to". In the description of the specification, the terms "one embodiment", "some embodiments", "exemplary embodiments", "example", "specific example" or "some examples" and the like are intended to indicate that the specific features, structures, materials or characteristics associated with the embodiment or example are included in at least one embodiment or example of the present disclosure. The schematic representation of the above terms does not necessarily refer to the same embodiment or example. In addition, the specific features, structures, materials or characteristics may be included in any one or more embodiments or examples in any appropriate manner, that is, although they may be carried in the embodiments or examples of the above terms due to reasons such as the order and position of appearance, it is not limited to that they can be carried in combination by one embodiment or example.

[0024] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present disclosure, unless otherwise specified, "multiple" means two or more. In addition, for example, the description may also use the method of adding "A" and "B" at the end to describe the same type of nouns as two independent individuals. In this case, the corresponding features defined as "A" and "B" are only used to distinguish the description purposes of the same type of individuals, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated.

[0025] In the description of the present invention, the expression "A and / or B" (where A and B are used to formally represent specific characteristic contents) is involved, and the corresponding expressions include the following three combinations: only A, only B, and a combination of A and B.

[0026] As used herein, "about," "substantially," or "approximately" includes the stated value and an average value that is within an acceptable range of deviation from the particular value as determined by one of ordinary skill in the art taking into account the measurements in question and errors associated with measurement of the particular quantity (i.e., limitations of the measurement system).

[0027] In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] Example 1: This embodiment provides a double-layer carbon-coated porous silicon lithium-ion battery negative electrode material and a preparation method thereof, comprising the following steps: Preparation of p-Si: Add 1 g of Al90Si10 to 200 mL of 1 M HCl solution and stir for 2 h. After etching, wash the precipitate with deionized water by centrifugation until the solution becomes neutral, and collect the black precipitate (p-Si).

[0029] Preparation of p-Si / CNTs / RF5 composite material. Take 1 g of p-Si and 100 mL of ethanol and ultrasonicate for 1 hour. After adding 10 mL of APTES in a 30 °C water bath and magnetically stirring for 6 hours, wash with ethanol and deionized water, and dry in a vacuum oven for 12 hours to obtain modified p-Si. Take 0.15 g of modified p-Si and 50 mL of deionized water, disperse them in a 100 mL beaker and ultrasonicate for 30 minutes. Then take 0.03 g of CNTs and disperse them in 30 mL of ethanol and ultrasonicate for 30 minutes. The above p-Si and CNTs dispersions are thoroughly mixed, ultrasonicated for 1 hour, magnetically stirred for 6 hours, and dried for 12 hours to obtain p-Si / CNTs.

[0030] 500 mg of p-Si / CNTs and 500 mg of CTAB were ultrasonically dispersed in 50 mL of deionized water for 1 hour. 25 mL of ethanol and 1 mL of ammonia were then added and thoroughly mixed. Resorcinol was then added and ultrasonicated for 1 hour. The mixture was then magnetically stirred at 30 °C for 20 minutes. Formaldehyde solution was then added dropwise, and the mixture was magnetically stirred in a 35 °C water bath for 12 hours to obtain p-Si / CNTs / RF5. The p-Si / CNTs / RF5 was then washed with ethanol and deionized water to remove excess CTAB and dried for 12 hours. The collected p-Si / CNTs / RF5 was calcined in a tube furnace under argon atmosphere at 800 °C for 3 hours at a heating rate of 5 °C / min. The annealed powder sample was then washed with deionized water and ethanol and dried in a vacuum oven for 12 hours.

[0031] Figure 1 The SEM images of the p-Si / CNTs / RF5 powder sample obtained in Example 1 of the present invention at scales of 3 μm and 8 μm are shown. It can be seen that the powder synthesized by this method is porous silicon spheres fixed in a three-dimensional carbon nanotube conductive framework.

[0032] Figure 2 The XRD pattern of the p-Si / CNTs / RF5 powder sample obtained in Example 1 of the present invention is shown. It can be seen that p-Si / CNTs / RF5 exhibits typical diffraction peaks of silicon (JCPDS No. 99-0092) at 28.4°, 47.3°, 56.1°, 69.1°, 76.3°, and 88.0°, which are typical diffraction peaks of the (111), (220), (311), (400), (331), and (422) crystal planes (JCPDS No. 27-1402). Since a large amount of Al remains in the porous silicon sample after 2 hours of etching, the sample exhibits obvious Al diffraction peaks.

[0033] Figure 3 The p-Si / CNTs / RF5 powder sample and the original p-Si sample in Example 1 are Cycling performance diagram under current density. The first discharge specific capacity of p-Si / CNTs / RF5 powder sample is , after 100 cycles, the capacity is , the capacity retention rate is 52%, after 200 cycles, the capacity remains at . Before the composite p-Si The initial capacity is After 100 cycles, the capacity is , the capacity retention rate is 30%, and the cycle stability of the material is poor.

[0034] Figure 4Figure 1 is the rate performance diagram of the p-Si / CNTs / RF5 powder sample and the original p-Si sample in Example 1. The corresponding discharge specific capacities are 、 , when the ratio current returns to When the specific capacity increases to , indicating that the material has good reversibility. Figure 5 The p-Si / CNTs / RF5 powder sample and the original p-Si sample in Example 1 are Cycling performance diagram of p-Si / CNTs / RF5 powder sample at current density The first discharge specific capacity at high current is , after 100 cycles, the capacity is The capacity retention rate is 47%, indicating that the material has excellent cycle stability under large current.

[0035] Example 2: This embodiment provides a double-layer carbon-coated porous silicon lithium-ion battery negative electrode material and a preparation method thereof, comprising the following steps: Preparation of p-Si: 1 g of Al90Si10 was added to 200 mL of 1 M HCl solution and stirred for 24 h. After etching, the precipitate was washed with deionized water by centrifugation until the solution became neutral, and the black precipitate (p-Si) was collected.

[0036] Preparation of p-Si / CNTs / RF20 composites. 1 g of p-Si and 100 mL of ethanol were ultrasonicated for 1 hour. 10 mL of APTES was added to a 30°C water bath and magnetically stirred for 6 hours. The mixture was then washed with ethanol and deionized water and dried in a vacuum oven for 12 hours to obtain modified p-Si. 0.2 g of the modified p-Si and 50 mL of deionized water were dispersed in a 100 mL beaker and ultrasonicated for 30 minutes. 0.02 g of CNTs were then dispersed in 30 mL of ethanol and ultrasonicated for 30 minutes. The p-Si and CNTs dispersions were thoroughly mixed, ultrasonicated for 1 hour, magnetically stirred for 6 hours, and dried for 12 hours to obtain p-Si / CNTs.

[0037] 500 mg of p-Si / CNTs and 500 mg of CTAB were ultrasonically dispersed in 50 mL of deionized water for 1 hour. 25 mL of ethanol and 1 mL of ammonia were then added and thoroughly mixed. Resorcinol was then added and ultrasonicated for 1 hour. The mixture was then magnetically stirred at 30 °C for 20 minutes. Formaldehyde solution was then added dropwise, and the mixture was magnetically stirred in a 35 °C water bath for 12 hours to obtain p-Si / CNTs / RF. The p-Si / CNTs / RF was then washed with ethanol and deionized water to remove excess CTAB and dried for 12 hours. The collected p-Si / CNTs / RF was calcined in a tube furnace under argon atmosphere at 800 °C for 3 hours at a heating rate of 5 °C / min. The annealed powder sample was then washed with deionized water and ethanol and dried in a vacuum oven for 12 hours.

[0038] Figure 6 The following are SEM images of the p-Si / CNTs / RF10 powder sample at scales of 3 μm and 8 μm in Example 2. It can be seen that p-Si / CNTs / RF10 has a similar morphology to p-Si / CNTs / RF5.

[0039] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a double-layer carbon-coated porous silicon lithium-ion battery negative electrode material, characterized in that: The invention comprises synthetic porous silicon and a carbon layer, wherein the synthetic porous silicon is modified porous silicon with a positive charge on the surface, the inner layer of the carbon layer is carbon nanotubes, and the outer layer is amorphous carbon. The preparation method comprises the following steps: Step 1: Add 5 g of aluminum-silicon alloy to 800 mL of HCl solution, stir for 2 h, wash the precipitate with deionized water by centrifugation until the solution is neutral, and collect the black precipitate p-Si; Step 2: Take 1 g of p-Si and 100 mL of ethanol, then add 10 mL of 3-aminopropyltriethoxysilane, stir magnetically for 6 hours, wash with ethanol and deionized water, and dry in a vacuum oven for 12 hours to obtain modified p-Si; Step 3: 0.15 g of modified p-Si and 0.03 g of CNTs were dispersed in deionized water and ethanol, magnetically stirred for 6 h, and dried for 12 h to obtain p-Si / CNTs. Step 4: Weigh 0.5 g of p-Si / CNTs and 0.5 g of CTAB and disperse them by ultrasonication. Then, add 25 mL of ethanol and 1 mL of ammonia water. After thorough mixing, add 0.5 g of resorcinol and magnetically stir for 20 minutes. Then, add 0.7 mL of formaldehyde solution dropwise and magnetically stir for 12 hours to obtain p-Si / CNTs / RF. Step 5: Place the p-Si / CNTs / RF in a tube furnace under argon atmosphere at 800 °C for 3 hours with a heating rate of 5 °C / min. Then, the annealed powder sample is washed with deionized water and ethanol and dried in a vacuum oven for 12 hours.

2. The method for preparing a double-layer carbon-coated porous silicon lithium-ion battery negative electrode material according to claim 1, characterized in that: The precursor of the porous silicon is an aluminum-silicon alloy Al90Si10 with a silicon mass percentage of 10 wt % and a particle size of 1 μm to 10 μm.

3. The method for preparing a double-layer carbon-coated porous silicon lithium-ion battery negative electrode material according to claim 1, characterized in that: The molar concentration of the HCl solution is 1 mol / L.

4. The method for preparing a double-layer carbon-coated porous silicon lithium-ion battery negative electrode material according to claim 1, characterized in that: The p-Si and ethanol were mixed and ultrasonicated for 1 hour, and the mass ratio of p-Si to CNTs was 5:

1.

5. The method for preparing a double-layer carbon-coated porous silicon lithium-ion battery negative electrode material according to claim 1, characterized in that: The 3-aminopropyltriethoxysilane was added to the p-Si solution and then magnetically stirred in a 30° C. water bath for 6 hours.

6. The method for preparing a double-layer carbon-coated porous silicon lithium-ion battery negative electrode material according to claim 1, characterized in that: The modified p-Si was ultrasonicated in 100 mL of deionized water for 1 hour, and the CNTs were ultrasonicated in 30 mL of ethanol for 1 hour.

7. The method for preparing a double-layer carbon-coated porous silicon lithium-ion battery negative electrode material according to claim 1, characterized in that: p-Si / CNTs and CTAB were ultrasonicated in 50 mL of deionized water for 30 min.

8. The method for preparing a double-layer carbon-coated porous silicon lithium-ion battery negative electrode material according to claim 1, characterized in that: After the formaldehyde solution was added dropwise, the mixture was magnetically stirred in a 35°C water bath for 12 hours and aged for 12 hours.

Images