Graphene porous silicon-carbon nanocomposite and preparation method thereof

Abstract

The application relates to a graphene porous silicon-carbon nanocomposite material and a preparation method thereof, and the preparation method comprises the following steps: (1) wet ball milling is conducted on commercial magnesium silicide particles to obtain magnesium silicide nanoparticles; (2) the magnesium silicide nanoparticles are subjected to a heating reaction in an atmosphere of a carbon source gas and an inert gas, and then porous silicon-carbon nanocomposite material is obtained after acid pickling; (3) the porous silicon-carbon nanocomposite material, graphene oxide and a high molecular compound are dispersed in water, and then a hydrothermal reaction is conducted to obtain a precursor, and then the precursor is subjected to heat treatment in an inert gas atmosphere to obtain the graphene porous silicon-carbon nanocomposite material. The battery prepared from the graphene porous silicon-carbon nanocomposite material has high initial coulomb efficiency and cycle stability, the raw materials used in the preparation method are relatively low in cost, the process is controllable, and the reproducibility is good.

Description

Technical Field

[0001] This invention relates to the technical field of nanocomposite materials, and in particular to a graphene porous silicon-carbon nanocomposite material and its preparation method. Background Technology

[0002] Lithium-ion batteries possess characteristics such as high energy density, zero memory effect, long cycle life, and low self-discharge, making them widely used in portable electronic products, new energy vehicles, aerospace, and other fields. As industry demands for longer battery life and higher energy density, there is an urgent need to develop lithium-ion batteries with even higher energy density, greater safety and reliability, and superior cycle performance. The negative electrode materials for lithium-ion batteries mainly include carbon-based materials such as graphite and mesophase carbon spheres, alloy materials such as tin-based and silicon-based materials, and metallic lithium. The battery's chemical energy is stored in the negative electrode as lithium intercalation compounds. During charging and discharging, lithium ions are intercalated and deintercalated between the positive and negative electrodes. The theoretical specific capacity of traditional graphite negative electrodes is only 372 mAh / g. Further increasing the battery's specific capacity requires the development of new negative electrode materials, and silicon is the most promising candidate to replace graphite as the negative electrode material for lithium-ion batteries because it has an extremely high theoretical specific capacity of 4200 mAh / g, a relatively low charge / discharge plateau, and is widely available and environmentally friendly. Meanwhile, silicon also suffers from problems such as volume expansion (approximately 360%) and repeated cracking and regeneration of the solid electrolyte interface (SEI). This makes silicon prone to pulverization during the insertion / extraction process, and the repeated growth of the SEI causes the electrolyte to be continuously consumed, hindering the transport and conduction of lithium ions and electrons.

[0003] To address the aforementioned issues with silicon, the R&D strategies for silicon-based anodes mainly fall into three categories: First, constructing specially structured nano-silicon, including silicon nanoparticles, silicon nanowires, and silicon nanofilms. Nanoscale silicon can effectively cope with the mechanical strain during the lithium insertion / extraction process, while increasing the contact area between active particles and the electrolyte, thereby reducing internal resistance. Second, combining silicon with carbon, metals, and ceramics, such as silicon with graphene, inert metal alloys like Fe, Co, and Cu, and TiO2 ceramics, to act as a buffer framework for silicon and alleviate its volume expansion. Third, employing novel conductive agents and binders. By using appropriate conductive agents and binders, conductivity and stability can be enhanced, reducing electrolyte loss during cycling.

[0004] Currently, research on silicon anode materials focuses on constructing special structures such as nano-silicon, silicon-carbon composites, and silicon-metal composites. However, problems still exist, including high cost, difficulty in process control, low initial coulombic efficiency, and poorer cycle stability compared to graphite. The reasons for these problems include:

[0005] 1. Nano-silicon particles have a large specific surface area, which easily leads to repeated growth of SEI film and consumption of a large amount of electrolyte. In addition, silicon nanospheres are small and prone to agglomeration, resulting in poor cycle stability and relatively high cost.

[0006] 2. Carbon, as a conductive structure and buffer layer in silicon-carbon anodes, can solve the problems of silicon volume expansion and low electronic conductivity to a certain extent. However, the mechanical strength of ordinary amorphous carbon is insufficient to suppress the volume expansion of silicon. Summary of the Invention

[0007] To address at least one of the problems in the prior art, the present invention provides a graphene porous silicon-carbon nanocomposite material and its preparation method. The battery prepared from the graphene porous silicon-carbon nanocomposite material has high initial coulombic efficiency and cycle stability. The preparation method uses relatively inexpensive raw materials, has controllable processes, and good reproducibility.

[0008] The technical solution adopted in this invention is as follows:

[0009] A method for preparing a graphene-porous silicon-carbon nanocomposite material includes the following steps:

[0010] (1) Commercial magnesium silicide particles were wet ball-milled to obtain magnesium silicide nanoparticles;

[0011] (2) In an atmosphere of carbon source gas and inert gas, the magnesium silicide nanoparticles are heated and reacted, and then acid washed to obtain a porous silicon-carbon nanocomposite material.

[0012] (3) The porous silicon-carbon nanocomposite material, graphene oxide and polymer compound are dispersed in water and then subjected to hydrothermal reaction to obtain a precursor. The precursor is then heat-treated in an inert gas atmosphere to obtain a graphene porous silicon-carbon nanocomposite material.

[0013] The preparation method of this invention uses commercial magnesium silicide as raw material, and obtains porous silicon-carbon nanomaterials with porous silicon and amorphous carbon encapsulated in each other through high-energy ball milling, chemical synthesis, acid washing and other steps. Then, graphene is combined with porous silicon-carbon nanomaterials by means of physical blending, graft crosslinking, high-temperature calcination and other methods to finally obtain graphene porous silicon-carbon nanocomposite material.

[0014] The preparation method involves relatively inexpensive raw materials, controllable processes, and good reproducibility. The resulting graphene porous silicon-carbon nanocomposite material has a special structure that can more effectively cope with the expansion strain of silicon and the problem of SEI film rupture and regeneration. It has high initial coulombic efficiency and initial discharge specific capacity, and good cycle stability.

[0015] More preferably, the conditions for wet ball milling in step (1) are as follows: using a planetary ball mill, adding a ball milling solvent, a ball-to-material mass ratio of 10 to 30:1, a ball milling speed of 200 to 300 rpm, and a ball milling time of 6 to 12 hours.

[0016] More preferably, step (1) further includes: ultrasonically treating the ball-milled material for 0.5–1 hour, using an ultrasonic power of 100–500 W / cm². 2 The magnesium silicide nanoparticles are then subjected to filtration, washing, and drying to obtain the magnesium silicide nanoparticles.

[0017] More preferably, in step (2), the carbon source gas is carbon dioxide, the inert gas is argon, and the heating reaction is carried out under the following conditions: the magnesium silicide nanoparticles are laid flat in a heating furnace, carbon dioxide and argon are introduced at a flow ratio of 1:1 to 5, the temperature is raised to 600 to 800°C at a rate of 10 to 15°C / min, the reaction is held at the temperature for 5 to 8 hours, and then cooled to room temperature in an argon atmosphere.

[0018] More preferably, the acid washing in step (2) includes: adding the product obtained from the reaction into dilute hydrochloric acid with a concentration of 1 to 2 mol / L, stirring for 6 to 12 hours, and then performing filtration, water washing, and drying to obtain the porous silicon-carbon nanocomposite material.

[0019] More preferably, in step (3), the polymeric compound is one or more of polyvinylpyrrolidone, carboxymethyl cellulose, and polyvinyl alcohol.

[0020] The polymer compound is used as a crosslinking medium to bridge graphene oxide and porous silicon-carbon nanocomposite materials through a hydrothermal reaction, and after high-temperature calcination, forms a three-dimensional silicon-carbon coated crosslinked support structure with graphene coating porous silicon nanoparticles.

[0021] More preferably, in step (3), the mass ratio of the graphene oxide to the polymer compound is 15 to 5:1.

[0022] More preferably, the temperature of the hydrothermal reaction in step (3) is 100-200℃ and the time is 12-18h.

[0023] More preferably, step (3) further includes: filtering, washing and drying the product obtained from the hydrothermal reaction to obtain the precursor; the heat treatment conditions in step (3) are as follows: the precursor is laid flat in a heating furnace, argon gas is introduced, the temperature is raised to 600-800°C at a rate of 10-15°C / min, held for 5-8 hours, and finally cooled to room temperature in an argon atmosphere.

[0024] The present invention also provides a graphene porous silicon-carbon nanocomposite material obtained by the preparation method, which is suitable for electrode materials of lithium-ion batteries.

[0025] This invention encapsulates and fills carbonaceous materials such as graphene and amorphous carbon into nano-silicon materials, which can effectively buffer the volume expansion of silicon during charging and discharging, inhibit the growth of the SEI film, and enhance the overall conductivity of the electrode.

[0026] Specifically, this invention, while maintaining the nanoscale properties of silicon, endows it with a unique structure of porosity, carbon filling, and coating. Amorphous carbon interweaves and coats silicon, and the porous structure provides a larger specific surface area, shortening the transport distance of lithium ions between the electrolyte and silicon. The amorphous carbon reduces agglomeration between silicon nanoparticles and provides an effective electron conduction path. Furthermore, the overlapping graphene sheets act as buffer layers and conductive networks for silicon, effectively preventing direct contact between silicon and the electrolyte. Combined with the connection of amorphous carbon, this provides a highly conductive circuit and a three-dimensional support structure. The resulting porous silicon-carbon structure is highly stable, effectively mitigating expansion strain in silicon nanoparticles, inhibiting SEI film rupture and regeneration, and facilitating the transport and conduction of lithium ions and electrons. Therefore, this graphene-porous silicon-carbon nanocomposite material, due to its unique structure, can more effectively address the expansion strain of silicon and the SEI film rupture and regeneration problems, thus fully leveraging the technological advantages of silicon nanoparticles.

[0027] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0028] Figure 1 The image shows an XRD pattern of the porous silicon-carbon nanocomposite material prepared in Example 1 of this invention.

[0029] Figure 2 Here is a SEM image of the porous silicon-carbon nanocomposite material prepared in Example 1 of this invention;

[0030] Figure 3 This is a SEM image of the graphene porous silicon-carbon nanocomposite material prepared in Example 1 of the present invention. Detailed Implementation

[0031] The graphene-porous silicon-carbon nanocomposite material of the present invention is prepared according to the following steps:

[0032] (1) Preparation of magnesium silicide nanoparticles by wet ball milling:

[0033] Commercial magnesium silicide particles were ground using a planetary ball mill. The ball mill jar and the ball milling media were both made of stainless steel. The ball milling media consisted of steel balls of three different diameters, ranging from 2 to 10 mm. The ball milling solvent was ethanol, acetone, or propanol, etc.

[0034] Magnesium silicide particles and ball milling solvent are added to the tank. The ball-to-material mass ratio is 30-10:1. The ball milling solvent covers the material by 1-1.5 cm. The ball milling speed is 200-300 rpm. The ball milling time is 6-12 h to obtain magnesium silicide ethanol solution.

[0035] The magnesium silicide ethanol solution obtained after ball milling was sonicated for 30 min to 1 h, with an ultrasonic power of 100–500 W / cm. 2Then, the particles are filtered, washed with water, and dried to obtain magnesium silicide nanoparticles.

[0036] (2) Preparation of porous silicon-carbon nanocomposites:

[0037] The magnesium silicide nanoparticles obtained in step (1) were spread in a crucible and placed in a tube furnace. Carbon source gas CO2 and inert gas Ar were introduced, and the flow rate ratio of CO2:Ar = 1:1 to 1:5 was adopted. The temperature was raised to 600 to 800°C at a rate of 10 to 15°C / min, and the reaction was held at the temperature for 5 to 8 hours. Finally, the temperature was cooled to room temperature in an Ar atmosphere.

[0038] The obtained silicon-carbon composite material was placed in dilute hydrochloric acid with a concentration of 1-2 mol / L, stirred for 6-12 hours, and then filtered, washed with water and dried to obtain porous silicon-carbon nanocomposite material.

[0039] (3) Preparation of graphene-porous silicon-carbon nanocomposite materials:

[0040] In step (2), graphene oxide and a polymer compound with a mass ratio of 15 to 5:1 are added to the porous silicon-carbon nanocomposite material. The mixture is dissolved in pure water, ultrasonically dispersed for 30 minutes, and then placed in a hydrothermal reactor. The mixture is then hydrothermally reacted at 100 to 200°C for 12 to 18 hours. After filtration, washing, and drying, the precursor of the graphene porous silicon-carbon nanocomposite material is obtained. The polymer compound includes polyvinylpyrrolidone (PVP), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), etc.

[0041] The obtained precursor was spread in a crucible and placed in a tube furnace. An inert gas Ar was introduced and the temperature was raised to 600-800°C at a rate of 10-15°C / min. The reaction was held at this temperature for 5-8 hours and finally cooled to room temperature in an Ar atmosphere to obtain a graphene porous silicon-carbon nanocomposite material.

[0042] The graphene porous silicon-carbon nanocomposite material of the present invention is applicable to the field of lithium-ion battery technology, and is especially suitable as a negative electrode material.

[0043] Example 1

[0044] (1) Commercial magnesium silicide particles were ground using a planetary ball mill: the milling jar and milling media were made of stainless steel, and three different diameter steel balls (2mm, 4mm, and 8mm) were used; wet ball milling was performed using solvents such as ethanol: magnesium silicide particles were added to the jar at a ball-to-particle mass ratio of 20:1, and the solvent covered the particles by 1.5cm; the milling speed was 300rpm, and the milling time was 8h to obtain a magnesium silicide ethanol solution. The milled magnesium silicide ethanol solution was ultrasonicated for 1h at an ultrasonic power of 300W / cm. 2 Then, the particles are filtered, washed with water, and dried to obtain magnesium silicide nanoparticles.

[0045] (2) Spread the magnesium silicide nanoparticles obtained in step (1) in a crucible, place it in a tube furnace, introduce carbon source gas CO2 and inert gas Ar with a flow rate ratio of CO2:Ar = 1:5, heat to 700℃ at a rate of 10℃ / min, keep the temperature for 7h, and finally cool to room temperature in Ar atmosphere. Place the obtained silicon-carbon composite material in dilute hydrochloric acid with a concentration of 1mol / L and stir for 10h. Then filter, wash with water and dry to obtain porous silicon-carbon nanocomposite material.

[0046] (3) Graphene oxide and PVP, with a mass ratio of 10:1, were added to the porous silicon-carbon nanocomposite material obtained in step (2), dissolved in pure water, ultrasonically dispersed for 30 min, and placed in a hydrothermal reactor. The mixture was then hydrothermally reacted at 180℃ for 12 h, followed by filtration, washing, and drying to obtain the precursor of the graphene porous silicon-carbon nanocomposite material. The obtained precursor was spread evenly in a crucible, placed in a tube furnace, and inert gas Ar was introduced. The temperature was increased to 600℃ at a rate of 10℃ / min, and the reaction was maintained at this temperature for 6 h. Finally, the mixture was cooled to room temperature in an Ar atmosphere to obtain the graphene porous silicon-carbon nanocomposite material.

[0047] Please see Figure 1-3 , Figure 1 The image shows the XRD pattern of the porous silicon-carbon nanocomposite material obtained in step (2). Figure 2 The image shows a SEM image of the porous silicon-carbon nanocomposite material obtained in step (2). Figure 3 The image shows a SEM image of the graphene porous silicon-carbon nanocomposite material obtained in step (3).

[0048] Example 2

[0049] (1) Commercial magnesium silicide particles were ground using a planetary ball mill: the milling jar and milling media were made of stainless steel, and steel balls of three different diameters (2mm, 6mm, and 8mm) were used; wet ball milling was performed using solvents such as ethanol: magnesium silicide particles were added to the jar at a ball-to-particle mass ratio of 10:1, and the solvent covered the particles by 1.5cm; the milling speed was 300rpm, and the milling time was 8h to obtain a magnesium silicide ethanol solution. The milled magnesium silicide ethanol solution was ultrasonicated for 1h at an ultrasonic power of 300W / cm. 2 Then, the particles are filtered, washed with water, and dried to obtain magnesium silicide nanoparticles.

[0050] (2) Spread the magnesium silicide nanoparticles obtained in step (1) in a crucible, place it in a tube furnace, introduce carbon source gas CO2 and inert gas Ar with a flow rate ratio of CO2:Ar = 1:2, heat to 700℃ at a rate of 10℃ / min, keep the temperature for 6h, and finally cool to room temperature in Ar atmosphere. Place the obtained silicon-carbon composite material in dilute hydrochloric acid with a concentration of 1mol / L and stir for 8h. Then filter, wash with water and dry to obtain porous silicon-carbon nanocomposite material.

[0051] (3) Graphene oxide and PVP, with a mass ratio of 6:1, were added to the porous silicon-carbon nanocomposite material obtained in step (2), dissolved in pure water, ultrasonically dispersed for 30 min, and placed in a hydrothermal reactor. The mixture was then hydrothermally reacted at 180℃ for 12 h, followed by filtration, washing, and drying to obtain the precursor of the graphene porous silicon-carbon nanocomposite material. The obtained precursor was spread evenly in a crucible, placed in a tube furnace, and inert gas Ar was introduced. The temperature was increased to 600℃ at a rate of 15℃ / min, and the reaction was maintained at this temperature for 6 h. Finally, the mixture was cooled to room temperature in an Ar atmosphere to obtain the graphene porous silicon-carbon nanocomposite material.

[0052] Example 3

[0053] (1) Commercial magnesium silicide particles were ground using a planetary ball mill: the milling jar and milling media were made of stainless steel, and three different diameter steel balls (2mm, 4mm, and 8mm) were used; wet ball milling was performed using solvents such as ethanol: magnesium silicide particles were added to the jar at a ball-to-particle mass ratio of 20:1, and the solvent covered the particles by 1.5cm; the milling speed was 300rpm, and the milling time was 8h to obtain a magnesium silicide ethanol solution. The milled magnesium silicide ethanol solution was ultrasonicated for 1h at an ultrasonic power of 300W / cm. 2 Then, the particles are filtered, washed with water, and dried to obtain magnesium silicide nanoparticles.

[0054] (2) Spread the magnesium silicide nanoparticles obtained in step (1) in a crucible, place it in a tube furnace, introduce carbon source gas CO2 and inert gas Ar with a flow rate ratio of CO2:Ar = 1:5, heat to 800℃ at a rate of 15℃ / min, keep the temperature for 7h, and finally cool to room temperature in Ar atmosphere. Place the obtained silicon-carbon composite material in dilute hydrochloric acid with a concentration of 1.5mol / L and stir for 10h. Then filter, wash with water and dry to obtain porous silicon-carbon nanocomposite material.

[0055] (3) Graphene oxide and PVP, with a mass ratio of 8:1, were added to the porous silicon-carbon nanocomposite material obtained in step (2), dissolved in pure water, ultrasonically dispersed for 30 min, and placed in a hydrothermal reactor. The mixture was then hydrothermally reacted at 190℃ for 12 h, followed by filtration, washing, and drying to obtain the precursor of the graphene porous silicon-carbon nanocomposite material. The obtained precursor was spread evenly in a crucible, placed in a tube furnace, and inert gas Ar was introduced. The temperature was increased to 600℃ at a rate of 15℃ / min, and the reaction was maintained at this temperature for 6 h. Finally, the mixture was cooled to room temperature in an Ar atmosphere to obtain the graphene porous silicon-carbon nanocomposite material.

[0056] Performance testing

[0057] The electrochemical performance of the graphene porous silicon-carbon nanocomposite material described in this invention was studied using a coin cell.

[0058] Battery fabrication: The graphene-porous silicon-carbon nanocomposite materials obtained in Examples 1-3 were mixed with graphite at a mass ratio of 1:7. The resulting composite material was then mixed with conductive carbon black and polyacrylic acid at a mass ratio of 6:2:2, and deionized water was added to prepare a slurry. The slurry was uniformly coated onto copper foil using a coating machine, and then dried in an oven at 80°C for 10 hours. After drying, the foil was cut and rolled to form the working electrode, with the loading controlled at 1 mg / cm². 2 In the glove box, CR2032 button batteries were assembled with lithium metal sheets as the positive electrode, Cellgard 2500 membrane as the separator, and a 1.0 mol / L mixed solution of LiPF6 EC and DEC (volume ratio 1:1).

[0059] The battery was subjected to charge and discharge performance tests. The charge and discharge rate was 0.1C and the charge and discharge cutoff voltage was 0.01V to 2.0V. The specific charge and discharge data and cycle performance are shown in Table 1 below.

[0060] Table 1

[0061] Example 1 83.09 652.60 97.3 Example 2 80.64 516.90 96.7 Example 3 81.23 546.30 95.1

[0062] As can be seen from Table 1, the batteries prepared from the graphene porous silicon-carbon nanocomposite materials of Examples 1-3 have high initial coulombic efficiency and initial discharge specific capacity, and good cycle stability. Among them, the battery made using the material of Example 1 has the best performance.

[0063] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a graphene-porous silicon-carbon nanocomposite material, characterized in that, Includes the following steps: (1) Commercial magnesium silicide particles were wet-milled to obtain magnesium silicide nanoparticles; (2) The magnesium silicide nanoparticles are heated and reacted in an atmosphere of carbon dioxide and inert gas, and then acid washed to obtain a porous silicon-carbon nanocomposite material. (3) The porous silicon-carbon nanocomposite material, graphene oxide and polymer compound are dispersed in water and then subjected to hydrothermal reaction to obtain a precursor. The precursor is then heat-treated in an inert gas atmosphere to obtain a graphene porous silicon-carbon nanocomposite material, wherein the polymer compound is one or more of polyvinylpyrrolidone, carboxymethyl cellulose and polyvinyl alcohol.

2. The preparation method according to claim 1, characterized in that, The conditions for wet ball milling in step (1) are as follows: a planetary ball mill is used, a ball milling solvent is added, the ball-to-material mass ratio is 10~30:1, the ball milling speed is 200~300 rpm, and the ball milling time is 6~12 h.

3. The preparation method according to claim 2, characterized in that, Step (1) also includes: ultrasonically treating the ball-milled material for 0.5 to 1 h, using an ultrasonic power of 100 to 500 W / cm. 2 The magnesium silicide nanoparticles are then subjected to filtration, washing, and drying to obtain the magnesium silicide nanoparticles.

4. The preparation method according to claim 1, characterized in that, In step (2), the inert gas is argon, and the heating reaction is carried out under the following conditions: the magnesium silicide nanoparticles are laid flat in a heating furnace, carbon dioxide and argon are introduced at a flow ratio of 1:1~5, the temperature is raised to 600~800℃ at a rate of 10~15℃ / min, the reaction is kept at the temperature for 5~8 h, and then cooled to room temperature in an argon atmosphere.

5. The preparation method according to claim 4, characterized in that, The acid washing in step (2) includes: adding the product obtained from the reaction into dilute hydrochloric acid with a concentration of 1~2 mol / L, stirring for 6~12 h, and then performing filtration, water washing and drying to obtain the porous silicon-carbon nanocomposite material.

6. The preparation method according to claim 5, characterized in that, In step (3), the mass ratio of graphene oxide to polymer compound is 15~5:

1.

7. The preparation method according to claim 5 or 6, characterized in that, In step (3), the hydrothermal reaction temperature is 100~200 ℃ and the time is 12~18 h.

8. The preparation method according to claim 7, characterized in that, Step (3) further includes: filtering, washing and drying the product obtained from the hydrothermal reaction to obtain the precursor; the heat treatment conditions in step (3) are as follows: the precursor is laid flat in a heating furnace, argon gas is introduced, the temperature is raised to 600-800 ℃ at a rate of 10-15 ℃ / min, held for 5-8h, and finally cooled to room temperature in an argon atmosphere.

9. The graphene porous silicon-carbon nanocomposite material obtained by the preparation method according to any one of claims 1-8.

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