Porous silicon-carbon composite electrode material for lithium ion battery and preparation method thereof

Abstract

The application discloses a kind of porous silicon carbon composite electrode materials for lithium ion battery, comprising: silicon carbon nanoparticles and graphene, inorganic carbon layer wrapped nanometer silicon is uniformly dispersed in the graphene sheet layer.Meanwhile, the application discloses a kind of porous silicon carbon composite electrode materials for lithium ion battery preparation method, using acid to reduce water-soluble silicic acid ion and the negative electric property of graphene oxide sheet surface simultaneously, weaken each other electrostatic repulsion, form silicic acid and oxidized graphene composite hydrogel, realize the uniform composite of silicic acid and oxidized graphene;Using carbon source gas is introduced in the magnesium hot reduction process of silicon dioxide / oxidized graphene composite, to realize the reduction of inorganic carbon layer wrapped nanometer silicon and oxidized graphene, finally obtain the porous silicon carbon composite electrode material of high silicon and carbon interface compatibility, nanometer silicon particle uniform dispersion;Preparation process is simple, controllability is high, is suitable for industrial popularization.

Description

Technical Field

[0001] This invention belongs to the field of battery anode material preparation technology, and more specifically relates to a porous silicon-carbon composite electrode material for lithium-ion batteries and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in smartphones, laptops, electric vehicles, and large-scale energy storage power stations due to their advantages such as high operating voltage, high energy density, light weight, small size, and long lifespan. Currently, commercially available graphite anode materials for lithium-ion batteries have a relatively low theoretical capacity (372 mAh / g), which cannot meet the high energy density requirements of various electronic devices and new energy vehicles. Compared to commercial graphite anodes, silicon has a higher theoretical capacity (4200 mAh / g), abundant reserves, and lower cost, and is considered one of the most promising candidates to replace graphite in the next generation. However, during lithium-ion insertion and extraction, the huge volume expansion (~400%) of silicon leads to electrode pulverization and repeated formation of the solid electrolyte interphase (SEI) film, severely affecting the battery's cycle performance. Furthermore, silicon, as a semiconductor material, has a very low electronic conductivity (6.7 × 10⁻⁶). - 2 The S / m ratio hinders the commercial application of silicon anodes.

[0003] To address the aforementioned problems with silicon electrodes, introducing carbon materials onto the surface of silicon particles as a buffer, isolation, and conductive layer is considered the most effective method. Carbon materials exhibit minimal volume expansion (<10%) during charging and discharging, a relatively stable structure, high electrical conductivity, good flexibility, and lubricity, effectively mitigating the volume expansion of silicon. Graphene, as a carbon material, possesses high electronic conductivity, a large specific surface area, and excellent structural flexibility, effectively buffering volume changes in silicon particles and maintaining a stable conductive network. Existing silicon-graphene composite technologies mainly include direct physical mixing of graphene and nano-silicon, chemical vapor deposition (CVD) of nano-silicon on a graphene substrate, and carbothermic reduction reactions between silicon sources and graphene. Cho et al. used ultrasound to mix nano-silicon and graphene oxide, then dried the mixture and pyrolyzed the graphene oxide at 700℃ to obtain a silicon / graphene composite. However, the interfacial compatibility between silicon and graphene was poor, and the nano-silicon agglomerated, resulting in poor cycle stability and a capacity retention of only 48.9% (Journal of Electroanalytical Chemistry 2020, 876, 114475). Liu et al. dispersed silica powder and graphene powder in an ethanol solution, stirred and mixed them, and then prepared a silicon / graphene composite by microwave-induced carbothermal reduction. When applied to lithium-ion batteries, the specific capacity was 806 mAh / g at a low current density of 100 mA / g, indicating poor rate performance due to uneven dispersion of silicon and graphene (Carbon 2022, 196, 633-638). Therefore, in the current technology, the obtained silicon / graphene composite materials suffer from poor interfacial compatibility between silicon and graphene and severe agglomeration of silicon particles, leading to poor rate and cycle performance. Summary of the Invention

[0004] In view of this, one objective of the present invention is to provide a porous silicon-carbon composite electrode material for lithium-ion batteries. This silicon-carbon composite electrode material possesses characteristics such as high compatibility between silicon and carbon interfaces and uniform dispersion of nano-silicon particles within carbon materials, thereby achieving high rate performance and high cycle stability. A second objective of the present invention is to provide a method for preparing a porous silicon-carbon composite electrode material for lithium-ion batteries. This method is simple, highly controllable, and capable of large-scale production.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A porous silicon-carbon composite electrode material for lithium-ion batteries comprises: silicon-carbon nanoparticles and graphene, wherein nano-silicon encapsulated by an inorganic carbon layer is uniformly dispersed in the graphene sheets.

[0007] A method for preparing a porous silicon-carbon composite electrode material for lithium-ion batteries as described above specifically includes the following steps:

[0008] (1) The aqueous solution of water-soluble silicate and the aqueous solution of graphene oxide are stirred and mixed evenly, and then acid is added to react to obtain silica / graphene oxide composite hydrogel. After freeze-drying, composite aerogel is obtained. The composite aerogel is washed with detergent to remove impurities and dried to obtain silica / graphene oxide composite.

[0009] (2) The above-mentioned silica / graphene oxide composite, magnesium oxide and magnesium powder are mixed evenly and then placed in a tube furnace. The first stage of heating is carried out under an inert atmosphere. Then, carbon source gas is introduced under an inert gas load for the second stage of heating, and finally product 1 is obtained.

[0010] (3) The porous silicon-carbon composite electrode material can be obtained by acid washing and drying the above product 1.

[0011] Preferably, the water-soluble silicate in step (1) includes one or more of sodium silicate, lithium silicate, potassium silicate, and ammonium silicate.

[0012] Preferably, in step (1), the mass fraction of the silicate aqueous solution is 20-80 wt%, and the concentration of the graphene oxide aqueous solution is 1-30 mg / mL.

[0013] Preferably, in step (1), the volume ratio of silicate solution to graphene oxide aqueous solution is 1:(0.5-20).

[0014] Preferably, in step (1), the stirring rate is 100-800 rpm and the stirring time is ≥1h.

[0015] Preferably, in step (1), the acid includes one or more of sulfuric acid, hydrochloric acid, and nitric acid, the acid solution concentration is 12-19 mol / mL, the acid volume is 1-10 mL, and the reaction time is ≥1 h.

[0016] Preferably, in step (2), the mass ratio of silica / graphene oxide composite, magnesium oxide and magnesium powder is 1:(0.5-10):(0.5-10).

[0017] Preferably, in step (2), the heating rate is 1 to 10 °C / min, the first stage heating temperature is 500 to 1000 °C, and the second stage heating temperature is 500 to 1000 °C.

[0018] Preferably, in step (2), the carbon source gas includes one or more of CO2, CH4, C2H2 and C2H4, and the inert gas is argon; the flow rate of the inert gas is 5 to 200 sccm, and the flow rate of the carbon source gas is 5 to 150 sccm.

[0019] Preferably, in step (3), the concentration of hydrochloric acid aqueous solution is 0.01-2.0 mol / L, the drying temperature is 60-150℃, and the drying time is >1h.

[0020] The present invention also relates to a lithium-ion battery in which the electrode material is the aforementioned porous silicon-carbon composite electrode material.

[0021] As can be seen from the above technical solution, compared with the prior art, the present invention provides a porous silicon-carbon composite electrode material for lithium-ion batteries and its preparation method, which has the following superior effects:

[0022] (1) This invention provides a porous silicon-carbon composite electrode material for lithium-ion batteries. The nano-silicon coated with an inorganic carbon layer is uniformly dispersed in the graphene sheets. The porous hierarchical structure formed is conducive to the full contact between the electrolyte and the electrode material and the complete penetration of the electrolyte. The silicon-carbon particles have high interface compatibility with the graphene. The inorganic carbon coating layer and the graphene sheets work together to slow down the volume expansion of silicon and prevent the agglomeration of nano-silicon particles. At the same time, the conductivity of the electrode material is improved. The advantages of silicon's ultra-high capacity and carbon's cycle stability are fully utilized to ensure the silicon-carbon composite electrode material's large specific capacity, high rate performance and superior cycle performance.

[0023] (2) In the method for preparing porous silicon-carbon composite electrode material of the present invention, acid is used to simultaneously reduce the negative charge of water-soluble silicate ions and the surface of graphene oxide sheets, weakening their electrostatic repulsion, leading to the formation of a silica-graphene oxide composite hydrogel, thereby achieving a uniform composite of silicate and graphene oxide. The composite hydrogel is internally connected by hydrogen bonds formed by the hydroxyl functional groups of silicate and graphene oxide, ensuring the structural stability of the material;

[0024] (3) In the preparation method of porous silicon-carbon composite electrode material of the present invention, carbon source gas is introduced during the magnesium thermal reduction process of silicon dioxide / graphene oxide composite to realize the reduction of inorganic carbon layer-encapsulated nano-silicon and graphene oxide, and to prepare porous silicon-carbon composite electrode material with high silicon-carbon interface compatibility and uniform dispersion of nano-silicon particles; the raw materials of the preparation method are inexpensive materials commonly used in industry, and the preparation process is safe and controllable. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0026] Figure 1The attached figure is an X-ray diffraction pattern of the silicon-carbon composite electrode material obtained in Example 1.

[0027] Figure 2 The attached figure is an X-ray diffraction pattern of the silicon-carbon composite electrode material obtained in Example 2.

[0028] Figure 3 The attached figure is an X-ray diffraction pattern of the silicon-carbon composite electrode material obtained in Example 3.

[0029] Figure 4 The attached figure is an X-ray diffraction pattern of the silicon-carbon composite electrode material obtained in Example 4.

[0030] Figure 5 The attached figure shows the X-ray diffraction pattern of the silicon-carbon composite electrode material obtained in Comparative Example 1.

[0031] Figure 6 The attached figure is a scanning electron microscope image of the silicon-carbon composite electrode material obtained in Example 1.

[0032] Figure 7 The attached figure is a scanning electron microscope image of the silicon-carbon composite electrode material obtained in Example 2.

[0033] Figure 8 The attached figure is a scanning electron microscope image of the silicon-carbon composite electrode material obtained in Example 3.

[0034] Figure 9 The attached figure is a scanning electron microscope image of the silicon-carbon composite electrode material obtained in Example 4.

[0035] Figure 10 The attached figure is a scanning electron microscope image of the silicon-carbon composite electrode material obtained in Comparative Example 1. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] This invention discloses a method for preparing a porous silicon-carbon composite electrode material for lithium-ion batteries, the specific steps of which include:

[0038] (1) A water-soluble silicate aqueous solution with a mass fraction of 20-80 wt% and a graphene oxide aqueous solution with a concentration of 1-30 mg / mL are mixed uniformly at a volume ratio of 1:(0.5-20) at a stirring speed of 100-800 rpm for ≥1 h. Then, an acid solution with a volume of 1-10 mL and a concentration of 12-19 mol / mL is added to react for ≥1 h to obtain a silica / graphene oxide composite hydrogel. After freeze-drying, a composite aerogel is obtained. The composite aerogel is washed with detergent to remove impurities and then dried at 60-150 °C for >1 h to obtain a silica / graphene oxide composite.

[0039] (2) The above-mentioned silica / graphene oxide composite, magnesium oxide and magnesium powder are mixed evenly in a mass ratio of 1:(0.5-10):(0.5-10), and then placed in a tube furnace. The heating rate is 1-10℃ / min. The first stage of heating is carried out under inert gas argon at a temperature of 500-1000℃. Then, carbon source gas is introduced under inert gas load. The flow rate of inert gas is 5-200 sccm and the flow rate of carbon source gas is 5-150 sccm. The second stage of heating is carried out at a temperature of 500-1000℃. Finally, product 1 is obtained.

[0040] (3) The above product 1 is washed with hydrochloric acid aqueous solution with a concentration of 0.01 to 2.0 mol / L, and then dried at 60 to 150°C for a time of >1 h to obtain porous silicon-carbon composite electrode material.

[0041] To further optimize the technical solution, in step (1), the water-soluble silicate includes one or more of sodium silicate, lithium silicate, potassium silicate, and ammonium silicate; the acid includes one or more of sulfuric acid, hydrochloric acid, and nitric acid; and the detergent includes water or ethanol.

[0042] To further optimize the technical solution, the carbon source gas in step (2) includes one or more of CO2, CH4, C2H2 and C2H4;

[0043] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0044] Example 1

[0045] This embodiment includes the following specific steps:

[0046] (1) 20 mL of 42 wt% water-soluble sodium silicate solution and 10 mL of 4 mg / mL graphene oxide aqueous solution were stirred and mixed, and placed in a reaction vessel with a rotation speed of 800 rpm. 5 mL of 18.4 mol / mL sulfuric acid was added and stirred to react, and silica / graphene oxide composite hydrogel was obtained. After freeze-drying, composite aerogel was obtained. The aerogel was washed with deionized water and ethanol to remove impurities. It was dried in an oven at 80℃ for 14 h to obtain a silica / graphene oxide composite with a carbon content of 3 wt%.

[0047] (2) The above-mentioned silica / graphene oxide composite, magnesium oxide and magnesium powder were mixed evenly in a mass ratio of 1:2:1.3, and then placed in a tube furnace. Argon gas was introduced at a flow rate of 40 sccm, and after 0.5 h, the temperature was raised to 750 °C at a heating rate of 5 °C / min. The temperature was kept constant for 4 h, and then CO2 was introduced at a flow rate of 30 sccm. The temperature was kept constant at 750 °C for another 4 h to obtain product 1.

[0048] (3) Product 1 was washed with an excess of 1.0 mol / L HCl aqueous solution for 12 h, then washed with deionized water until neutral, and dried in an oven at 80 °C for 14 h to obtain a porous silicon-carbon composite electrode material with a carbon content of 6 wt%.

[0049] Example 2

[0050] This embodiment includes the following specific steps:

[0051] (1) 20 mL of water-soluble lithium silicate solution with a mass fraction of 42 wt% was stirred and mixed with 20 mL of graphene oxide aqueous solution with a concentration of 4 mg / mL. The mixture was placed in a reaction vessel with a rotation speed of 700 rpm, and 7 mL of nitric acid with a concentration of 15.3 mol / mL was added and stirred to carry out the reaction, thus obtaining silica / graphene oxide composite hydrogel. After freeze-drying, composite aerogel was obtained. The aerogel was washed with deionized water and ethanol to remove impurities. It was then dried in an oven at 100℃ for 12 h to obtain a silica / graphene oxide composite with a carbon content of 4 wt%.

[0052] (2) The above-mentioned silica / graphene oxide composite, magnesium oxide and magnesium powder were mixed evenly in a mass ratio of 1:2:1.3, and then placed in a tube furnace. Argon gas was introduced at a flow rate of 60 sccm, and after 0.5 h, the temperature was raised to 850 °C at a heating rate of 5 °C / min. The temperature was kept constant for 4 h, and then CH4 was introduced at a flow rate of 50 sccm. The temperature was kept constant at 850 °C for another 4 h to obtain product 2.

[0053] (3) The product 2 was washed with an excess of 1.5 mol / L HCl aqueous solution for 12 h, then washed with deionized water until neutral, and dried in an oven at 100 °C for 12 h to obtain a porous silicon-carbon composite electrode material with a carbon content of 8 wt%.

[0054] Example 3

[0055] This embodiment includes the following specific steps:

[0056] (1) 20 mL of 42 wt% water-soluble potassium silicate solution was stirred and mixed with 40 mL of 4 mg / mL graphene oxide aqueous solution. The mixture was placed in a reaction vessel with a rotation speed of 500 rpm and 10 mL of 12 mol / mL hydrochloric acid was added and stirred to carry out the reaction. The silica / graphene oxide composite hydrogel was obtained. After freeze-drying, the composite aerogel was obtained. The aerogel was washed with deionized water and ethanol to remove impurities. It was dried in an oven at 120℃ for 10 h to obtain a silica / graphene oxide composite with a carbon content of 6 wt%.

[0057] (2) The above silica / graphene oxide composite, magnesium oxide and magnesium powder were mixed evenly in a mass ratio of 1:2:1.3, and then placed in a tube furnace. Argon gas was introduced at a flow rate of 80 sccm, and after 0.5 h, the temperature was raised to 950 °C at a heating rate of 5 °C / min and kept at a constant temperature for 4 h. Then C2H2 was introduced at a flow rate of 60 sccm and kept at a constant temperature of 950 °C for another 4 h to obtain product 3.

[0058] (3) The product 3 was washed with an excess of 2 mol / L HCl aqueous solution for 12 h, then washed with deionized water until neutral, and dried in an oven at 120 °C for 10 h to obtain a porous silicon-carbon composite electrode material with a carbon content of 9 wt%.

[0059] Example 4

[0060] This embodiment includes the following specific steps:

[0061] (1) 20 mL of water-soluble ammonium silicate solution with a mass fraction of 42 wt% was stirred and mixed with 80 mL of graphene oxide aqueous solution with a concentration of 4 mg / mL. The mixture was placed in a reaction vessel with a rotation speed of 400 rpm, and 10 mL of sulfuric acid with a concentration of 18.4 mol / mL was added and stirred to carry out the reaction, and silica / graphene oxide composite hydrogel was obtained. After freeze-drying, composite aerogel was obtained. The aerogel was washed with deionized water and ethanol to remove impurities. It was dried in an oven at 140℃ for 8 h to obtain silica / graphene oxide composite with a carbon content of 9 wt%.

[0062] (2) The above silica / graphene oxide composite, magnesium oxide and magnesium powder were mixed evenly in a mass ratio of 1:2:1.3, and then placed in a tube furnace. Argon gas was introduced at a flow rate of 50 sccm, and after half an hour, the temperature was raised to 1000℃ at a heating rate of 5℃ / min and kept at a constant temperature for 4 hours. Then C2H4 was introduced at a flow rate of 50 sccm and kept at a constant temperature of 1000℃ for another 4 hours to obtain product 4.

[0063] (3) The product 4 was washed with an excess of 0.5 mol / L HCl aqueous solution for 12 h, then washed with deionized water until neutral, and dried in an oven at 140 °C for 8 h to obtain a porous silicon-carbon composite electrode material with a carbon content of 11 wt%.

[0064] Comparative Example 1

[0065] This comparative example includes the following specific steps:

[0066] (1) Place 20 mL of 42 wt% water-soluble sodium silicate solution in a reaction vessel with a rotation speed of 800 rpm, add 5 mL of 18.4 mol / mL sulfuric acid and stir to react, and obtain silicic acid hydrogel. After freeze-drying, obtain aerogel. Wash the aerogel with deionized water and ethanol to remove impurities, and dry it in an oven at 120℃ for 10 h to obtain silicon dioxide.

[0067] (2) Weigh out the above silicon dioxide, magnesium oxide and magnesium powder and mix them evenly in a mass ratio of 1:2:1.3. Then place them in a tube furnace, introduce argon gas at a flow rate of 70 sccm, and start heating to 750°C at a heating rate of 5°C / min after half an hour. Maintain the temperature for 4 hours. Then introduce CO2 at a flow rate of 60 sccm and continue to maintain the temperature at 750°C for 4 hours to obtain product 5.

[0068] (3) The product 5 was washed with an excess of 1.0 mol / L HCl aqueous solution for 12 h, then washed with deionized water until neutral, and dried in an oven at 120 °C for 10 h to obtain a porous silicon-carbon composite electrode material with a carbon content of 2 wt%.

[0069] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0070] (1) X-ray diffraction (XRD) test:

[0071] The tests were conducted using a Rigaku-D / max-2550pc X-ray powder diffractometer from Hitachi, Japan, with Cu-Kα as the radiation source and a wavelength of [wavelength missing]. A Ni filter was used, with a tube current of 40 mA, a tube voltage of 40 kV, a scanning range of 10°–90°, a scanning speed of 10° / min, and a step size of 0.08°. The material was placed in a glass slide, flattened, and then embedded in the center of the instrument's experimental slot for testing. Phase identification and crystal structure information were analyzed using JADE 5.0 software. Specific test results are analyzed below:

[0072] Figure 1 The X-ray diffraction pattern of a porous silicon-carbon composite electrode material for lithium-ion batteries prepared in Example 1 is shown. The vertical axis represents the intensity of X-ray diffraction, and the horizontal axis represents the X-ray scanning angle. Significant characteristic peaks of silicon appear at 2θ of 28.36°, 47.22°, 56.04°, 69.04°, 76.30°, and 87.94°, which correspond to silicon crystal planes (111), (220), (311), (400), (331), and (422), respectively. The X-ray diffraction pattern is consistent with the standard card PDF#27-1402.

[0073] Figure 2 The X-ray diffraction pattern of a porous silicon-carbon composite electrode material for lithium-ion batteries prepared in Example 2 is shown. The vertical axis represents the intensity of X-ray diffraction, and the horizontal axis represents the X-ray scanning angle. Significant silicon characteristic peaks appear at 2θ of 28.28°, 47.14°, 55.98°, 68.98°, 76.22°, and 87.88°, which correspond to silicon crystal planes (111), (220), (311), (400), (331), and (422), respectively. The X-ray diffraction pattern is consistent with the standard card PDF#27-1402.

[0074] Figure 3 The X-ray diffraction pattern of a porous silicon-carbon composite electrode material for lithium-ion batteries prepared in Example 3 is shown. The vertical axis represents the intensity of X-ray diffraction, and the horizontal axis represents the X-ray scanning angle. Significant silicon characteristic peaks appear at 2θ of 28.30°, 47.18°, 56.00°, 68.96°, 76.26°, and 87.92°, which correspond to silicon crystal planes (111), (220), (311), (400), (331), and (422), respectively. The X-ray diffraction pattern is consistent with the standard card PDF#27-1402.

[0075] Figure 4The X-ray diffraction pattern of a porous silicon-carbon composite electrode material for lithium-ion batteries prepared in Example 4 is shown. The vertical axis represents the intensity of X-ray diffraction, and the horizontal axis represents the X-ray scanning angle. Significant silicon characteristic peaks appear at 2θ of 28.28°, 47.20°, 56.04°, 69.08°, 76.30°, and 87.98°, which correspond to silicon crystal planes (111), (220), (311), (400), (331), and (422), respectively. The X-ray diffraction pattern is consistent with the standard card PDF#27-1402.

[0076] Figure 5 The X-ray diffraction pattern of a porous silicon-carbon composite electrode material for lithium-ion batteries prepared in Comparative Example 1 is shown. The vertical axis represents the intensity of X-ray diffraction, and the horizontal axis represents the X-ray scanning angle. Significant characteristic peaks of silicon appear at 2θ of 28.28°, 47.14°, 56.04°, 68.98°, 76.22°, and 87.88°, which correspond to silicon crystal planes (111), (220), (311), (400), (331), and (422), respectively. The X-ray diffraction pattern is consistent with the standard card PDF#27-1402.

[0077] (2) Scanning electron microscopy characterization:

[0078] The morphology of the lithium-ion battery electrode materials prepared in Examples 1-4 and Comparative Example 1 was observed using a HITACHI JSM-7600F scanning electron microscope with an accelerating voltage of 3KV. The specific test results are analyzed as follows:

[0079] Figure 6 The image shown is a scanning electron microscope image of a porous silicon-carbon composite electrode material for lithium-ion batteries prepared in Example 1. It can be clearly seen that many layers of graphene are loaded with silicon particles and exhibit a porous structure.

[0080] Figure 7 The image shown is a scanning electron microscope image of a porous silicon-carbon composite electrode material for lithium-ion batteries prepared in Example 2. It can be clearly seen that many layers of graphene are loaded with silicon particles and exhibit a porous structure.

[0081] Figure 8 The image shown is a scanning electron microscope image of a porous silicon-carbon composite electrode material for lithium-ion batteries prepared in Example 3. It can be clearly seen that many silicon particles are loaded on the sheet graphene and exhibit a porous structure.

[0082] Figure 9 The image shown is a scanning electron microscope image of a porous silicon-carbon composite electrode material for lithium-ion batteries prepared in Example 4. It can be clearly seen that many layers of graphene are loaded with silicon particles and exhibit a porous structure.

[0083] Figure 10The image shown is a scanning electron microscope image of a porous silicon-carbon composite electrode material for lithium-ion batteries prepared as Comparative Example 1. The porous structure of the composite material can be clearly seen.

[0084] (3) Using the silicon-carbon anode material prepared in Examples 1-4 and Comparative Example 1 as the positive electrode and the lithium metal sheet as the negative electrode, and using 1.0 mol / L LiPF6 / EC (ethylene carbonate) + DMC (dimethyl carbonate) + FEC (fluoroethylene carbonate) (EC, DMC and FEC volume ratio 4.5:4.5:1) as the electrolyte, CR2032 button batteries were assembled in an argon glove box.

[0085] The button battery was tested using a Blue Battery Tester manufactured by Wuhan Jinno Electronics Co., Ltd. The test conditions and results are as follows:

[0086] The button cells were subjected to constant current charge-discharge tests at current densities of 100, 200, 500, 1000, 2000, 3000, and 100 mA / g, with a voltage range of 0–1.5 V. The coin cells with silicon-carbon composite electrode materials obtained in Examples 1–4 all exhibited initial discharge capacities higher than 1600 mAh / g and initial coulombic efficiencies higher than 75%. In contrast, the coin cell with silicon-carbon composite electrode material obtained in Comparative Example 1 had a lower initial discharge capacity of only 1366.9 mAh / g and an initial coulombic efficiency of 71.2%. Specific values ​​are detailed in Table 1 (Initial discharge capacity and initial coulombic efficiency of coin cells with silicon-carbon composite electrode materials obtained in Examples 1–4 and Comparative Example 1). The coin half-cells of silicon-carbon composite electrode materials obtained in Examples 1-4 exhibit good capacity retention at different current densities, demonstrating excellent rate cycling performance. Furthermore, they can recover to near their initial capacity after high-current charge and discharge, demonstrating good reversible cycling performance. In contrast, the coin half-cells of silicon-carbon composite electrode materials obtained in Comparative Example 1 have poor rate cycling performance and low discharge capacity. For specific values, please refer to Table 2 (Rate cycling capacity of coin half-cells of silicon-carbon composite electrode materials obtained in Examples 1-4 and Comparative Example 1).

[0087] Table 1

[0088]

[0089] Table 2

[0090]

[0091] The scope of this invention is not limited to the above embodiments; a combination of one or more embodiments can also achieve the purpose of this invention.

[0092] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. The methods disclosed in the embodiments are described simply because they correspond to the methods disclosed in the embodiments; relevant parts can be found in the method section.

[0093] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a porous silicon-carbon composite electrode material for lithium-ion batteries, characterized in that, Specifically, the following steps are included: (1) The aqueous solution of water-soluble silicate and the aqueous solution of graphene oxide are stirred and mixed evenly, and then acid is added to react to obtain silica / graphene oxide composite hydrogel. After freeze-drying, composite aerogel is obtained. The composite aerogel is washed with detergent to remove impurities and dried to obtain silica / graphene oxide composite. (2) The above-mentioned silica / graphene oxide composite, magnesium oxide and magnesium powder are mixed evenly and then placed in a tube furnace. The first stage of heating is carried out under an inert atmosphere. Then, carbon source gas is introduced under an inert gas load for the second stage of heating, and finally product 1 is obtained. (3) The porous silicon-carbon composite electrode material can be obtained by acid washing and drying the above product 1. The porous silicon-carbon composite electrode material includes silicon nanoparticles wrapped in inorganic carbon layers and graphene; the silicon nanoparticles wrapped in inorganic carbon layers are uniformly dispersed in the graphene sheets.

2. The method for preparing a porous silicon-carbon composite electrode material for lithium-ion batteries according to claim 1, characterized in that, In step (1), the water-soluble silicate includes one or more of sodium silicate, lithium silicate, potassium silicate, and ammonium silicate; the mass fraction of the silicate aqueous solution is 20-80 wt%, the concentration of the graphene oxide aqueous solution is 1-30 mg / mL, and the volume ratio of the silicate solution to the graphene oxide aqueous solution is 1:(0.5-20).

3. The method for preparing a porous silicon-carbon composite electrode material for lithium-ion batteries according to claim 1, characterized in that, In step (1), the stirring rate is 100-800 rpm and the stirring time is ≥1 h; the acid includes one or more of sulfuric acid, hydrochloric acid, and nitric acid, the acid solution concentration is 12-19 mol / mL, the acid volume is 1-10 mL, and the reaction time is ≥1 h.

4. The method for preparing a porous silicon-carbon composite electrode material for lithium-ion batteries according to claim 1, characterized in that, The detergent in step (1) includes water or ethanol; the drying temperature is 60-150℃ and the drying time is >1h.

5. The method for preparing a porous silicon-carbon composite electrode material for lithium-ion batteries according to claim 1, characterized in that, In step (2), the silica / graphene oxide composite, magnesium oxide and magnesium powder are in a mass ratio of 1:(0.5-10):(0.5-10).

6. The method for preparing a porous silicon-carbon composite electrode material for lithium-ion batteries according to claim 1, characterized in that, In step (2), the heating rate is 1 to 10 °C / min, the heating temperature in the first stage is 500 to 1000 °C, and the heating temperature in the second stage is 500 to 1000 °C.

7. The method for preparing a porous silicon-carbon composite electrode material for lithium-ion batteries according to claim 1, characterized in that, The carbon source gas in step (2) includes one or more of CO2, CH4, C2H2 and C2H4, and the inert gas is argon; the flow rate of the inert gas is 5 to 200 sccm, and the flow rate of the carbon source gas is 5 to 150 sccm.

8. The method for preparing a porous silicon-carbon composite electrode material for lithium-ion batteries according to claim 1, characterized in that, In step (3), the concentration of hydrochloric acid aqueous solution is 0.01-2.0 mol / L, the drying temperature is 60-150℃, and the drying time is >1h.

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