Carbon-coated silica graphite composite material and preparation method thereof

Abstract

The invention belongs to the technical field of lithium ion battery negative electrode materials, and particularly relates to a carbon-coated silicon-oxygen-graphite composite material and a preparation method and application thereof, and the microstructure of the carbon-coated silicon-oxygen-graphite composite material is SiOx (0lt; xlt; the method comprises the steps of raw material screening and configuration, acid leaching, high-energy ball milling, composite carbonization and the like, the raw materials are specifically selected, and the specific method steps are arranged, so that cheap cast iron is used as a silicon source and a carbon source at the same time, and the silicon source and the carbon source are combined to form the core-shell structure. The silicon-oxygen graphite composite material coated with silicon-oxygen, graphite and amorphous carbon is successfully prepared through the preparation method, and when the composite material serves as a lithium ion battery negative electrode material, the composite material shows excellent electrochemical performance, the problem of the pain point of a silicon-based negative electrode material is solved, and the composite material has great commercial application potential.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery negative electrode materials, and particularly relates to a carbon-coated silicon-oxygen-graphite composite material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have been widely used in portable electronic devices, electric vehicles and large-scale energy storage systems due to their high energy density, long cycle life and no memory effect. At present, the commercial lithium ion battery negative electrode material is mainly graphite, and its theoretical specific capacity is only 372 mAh g -1 , which has approached its theoretical limit and is difficult to meet the demand of the next generation of high energy density batteries. Therefore, the development of new high-capacity negative electrode materials has become a research hotspot. The theoretical specific capacity of pure Si material is 4200 mAh g⁻¹, which is 10 times that of graphite, has a low delithiation potential (~0.4V vs. Li / Li + ) and is environmentally friendly, and is considered to be one of the most potential next-generation negative electrode materials. However, silicon will undergo more than 300% volume expansion and contraction during charging and discharging, and this repeated volume change will cause the pulverization and shedding of active material particles and lose electrical contact with the current collector, thereby causing a sharp capacity decay. Compared with pure Si negative electrode material, silicon oxide (SiO x , 0<x<2) has a lower volume expansion rate (100~200%) than pure silicon material and a theoretical specific capacity (>2000 mAh·g⁻¹). Therefore, SiO x material is considered to be one of the most potential next-generation lithium ion battery negative electrode materials to replace graphite. At present, the synthesis process of carbon-coated silicon-oxygen-graphite composite material mainly uses high-purity nano-silicon powder, SiO x powder or organic silicon as the silicon source, and realizes the composite by mechanical ball milling or chemical vapor deposition (CVD) with carbon sources such as graphite. However, the existing method has the following disadvantages: 1) high cost of raw materials; 2) expensive equipment and high energy consumption; 3) difficulty in realizing uniform composite of silicon oxide and graphite and uniform coating of carbon layer.

[0003] Chinese patent application CN111403740A discloses a preparation method of a silicon-graphite composite material in the field of battery technology. The silicon powder and the silicon dioxide powder are pressed, then high-temperature sintering is carried out in a vacuum state, and then gas sublimation is realized by cooling with graphite, and then secondary sintering is carried out in a high-temperature state, and then the silicon / graphite composite material is obtained after crushing and grading. The technical scheme has high requirements for processes such as vacuum and high temperature.

[0004] Therefore, it is urgent to develop a preparation method with low-cost raw materials, simple process and uniform in-situ composite of silicon oxide and graphite and uniform carbon coating. SUMMARY

[0005] For the above reasons, the purpose of the present application is to solve the above problems by first proposing a carbon-coated silicon-oxygen-graphite composite material, as well as its preparation method and application. The present application proposes a completely new technical solution: using cheap cast iron as both the silicon source and the carbon source, through a three-step synergistic process of "acid leaching + high-energy ball milling + carbonization", a silicon-oxygen-graphite composite material coated with silicon-oxygen / amorphous carbon is successfully prepared.

[0006] Specifically, to solve the problems as described above, the present application provides the following technical solutions: A carbon-coated silicon-oxygen-graphite composite material, the microstructure of the composite material is SiO x and graphite to form a layered or sheet-shaped inner core coated with an amorphous carbon layer; wherein 0 < x < 2, and SiO x and graphite to form a layered or sheet-shaped inner core coated with an amorphous carbon layer; wherein 0 < x < 2, and SiO The chemical element composition of the composite material is, in terms of mass percentage: Si: 4.6-20.88 wt.%, O: 16.16-47.36 wt.%, C: 26.76-76.2 wt.%.

[0007] A preparation method of a carbon-coated silicon-oxygen-graphite composite material, comprising the following steps: S1. Selecting cast iron with a C content of 3.0-4.45 wt.% and a Si content of 1.8-3.2 wt.%, crushing and sieving the cast iron to obtain cast iron powder with a particle size of 100-1000 μm (or cast iron powder formed by thin sheets with a thickness of 100-1000 μm).

[0008] S2. Immersing the cast iron powder obtained in step S1 into an excess of an acid solution, stirring and reacting at a temperature of 30-95°C for 3-25 h to remove iron from the cast iron powder, then filtering the reaction mixture, washing the filter cake multiple times and drying to obtain a silicon-oxygen composite material precursor.

[0009] S3. Pre-mixing the obtained silicon-oxygen composite material precursor and carbon source in a mass ratio of (0.8-1.2):(0.1-0.3), then high-energy ball milling under the protection of an inert gas to obtain a carbon-silicon-oxygen composite powder.

[0010] S4. The obtained carbon-silicon-oxygen composite powder is placed into a heating furnace, heated to 580-1200°C at a rate of 1-18°C / min under the protection of inert gas, then kept for 1-6 h, and after natural cooling, a carbon-coated silicon-oxygen graphite composite material is obtained.

[0011] As preferred, the cast iron in step S1 is one or a mixture of gray cast iron, compacted graphite cast iron, ductile cast iron or malleable cast iron with C content of 3.2-4.5 wt.%, and Si content of 2.0-3.0 wt.%.

[0012] As preferred, the acid solution in step S2 is one or a mixture of hydrochloric acid, sulfuric acid, phosphoric acid or nitric acid with concentration of 1-13 mol / L.

[0013] As preferred, the reaction temperature in step S2 is 30-80°C, and the reaction time is 4-24 h.

[0014] As preferred, the heating in step S2 is performed by water bath heating.

[0015] As preferred, the filtration in step S2 is performed by suction filtration or centrifugal filtration separation, and the washing is performed by repeated washing with deionized water and alcohol (first with deionized water, then with alcohol, then with deionized water again, then with alcohol again, and so on); the washing endpoint is that the filtrate is neutral (pH≈7); and the drying treatment is that the black powder after filtration and washing is placed in a vacuum oven at 90-110°C (further preferably 100°C) for drying for 10-18 h (further preferably 12 h).

[0016] As preferred, the carbon source in step S3 is one or a mixture of glucose, sucrose, pitch, citric acid, starch, phenolic resin or polyacrylonitrile.

[0017] As preferred, the silicon-oxygen composite material precursor and the carbon source are premixed at a mass ratio of 1:(0.1-0.3).

[0018] As preferred, the parameters of the high-energy ball milling in step S3 are as follows: ball-to-material mass ratio (10-60):1, ball milling speed of 300-800 rpm, and ball milling time of 6-72 h.

[0019] As preferred, step S4 is specifically that the obtained carbon-silicon-oxygen composite powder is placed into an atmosphere heating furnace, heated to 600-1100°C at a rate of 1-10°C / min under the protection of argon or nitrogen, then kept for 1-5 h for carbonization treatment, and after natural cooling, a carbon-coated silicon-oxygen graphite composite material is obtained.

[0020] The lithium ion battery negative plate is characterized in that the lithium ion battery negative plate is prepared by taking the carbon-coated silicon-oxygen graphite composite material or the carbon-coated silicon-oxygen graphite composite material prepared by the preparation method as raw material.

[0021] Preferably, the lithium ion battery negative plate is prepared by the following steps: (1) The carbon-coated silicon-oxygen graphite composite material or the carbon-coated silicon-oxygen graphite composite material prepared by the preparation method is mixed with a conductive agent and a binder at a mass ratio of (6-10):(0.8-1.3):(0.9-1.1), and is uniformly stirred to obtain a mixed slurry.

[0022] (2) The mixed slurry obtained in step (1) is uniformly applied on a copper foil current collector to obtain a copper foil composite.

[0023] (3) The obtained copper foil composite is dried, rolled and punched to obtain the lithium ion battery negative plate.

[0024] Preferably, the conductive agent is acetylene black, and the binder is sodium carboxymethyl cellulose (CMC).

[0025] Preferably, the carbon-coated silicon-oxygen graphite composite material is mixed with the conductive agent and the binder at a mass ratio of 8:1:1.

[0026] A lithium ion battery, which is a lithium ion battery taking the lithium ion battery negative plate as a negative plate and taking a lithium sheet as a counter electrode.

[0027] Preferably, the lithium ion battery takes 1.0M LiPF6 in EC:DMC:DEC=1:1:1 vol% as an electrolyte (1.0M molar concentration of lithium hexafluorophosphate as an electrolyte lithium salt is mixed with an organic solvent formed by mixing ethylene carbonate, dimethyl carbonate and diethyl carbonate at a volume ratio of 1:1:1).

[0028] The technical effect of the present application is that: 1. The present application finds, through the research on the specific C and Si content of cast iron, that the cast iron contains a flocculent mixture of SiO x (0 x The graphite in the flocculent mixture is in situ symbiotic with SiO xThe application is a kind of carbon-coated silicon-oxygen-graphite composite material with core-shell structure, which is prepared by a three-step method using cast iron powder as raw material.

[0029] 2. In the preparation method, the specific cast iron raw material is sieved to a specific particle size, then the Fe is removed by acid leaching while generating silicon-oxygen-graphite composite material in situ, and then high-energy ball milling is performed after mixing with carbon source. Due to the specific structure of the raw material, the purposes of simultaneous silicon-oxygen nanocrystallization, graphite exfoliation, and uniform composite with carbon source are achieved, which lays the foundation for forming an efficient conductive network. Then, through the high-temperature pyrolysis and carbonization treatment step matched with the raw material of the application, an integrated and uniformly coated amorphous carbon coating layer is formed outside the silicon-oxygen-graphite core. When this "silicon-oxygen-graphite in-situ composite-amorphous carbon shell" structure is used as the negative electrode of lithium ion battery, it has high specific capacity (>600 mAhg -1 ), excellent cycle stability and good rate performance, successfully solving the core problems of fast capacity decay and short service life of silicon-based materials. The application obtains carbon-coated silicon-oxygen-graphite composite material with specific structure and composition through the specific raw material setting and the specific method steps and parameter matching. The application method reduces the production cost and the preparation difficulty, and improves the material performance, providing a new technical path for the large-scale production of high-performance silicon-based negative electrodes. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The figure is a flowchart of the process method of the application.

[0031] Figure 2 The figure is an SEM image of the carbon-coated silicon-oxygen-graphite composite material of one embodiment of the application.

[0032] Figure 3 The figure is an XRD pattern of the carbon-coated silicon-oxygen-graphite composite material of one embodiment of the application.

[0033] Figure 4 The figure is a TEM image of the carbon-coated silicon-oxygen-graphite composite material of one embodiment of the application.

[0034] Figure 5The carbon-coated silicon-oxygen graphite composite material of one embodiment of the present application has a specific capacity of 0.05 A g -1 The first charge-discharge curves at a current density of 0.05 A g

[0035] Figure 6 The electrochemical performance comparison chart of the examples and the comparative examples of the present application. DETAILED DESCRIPTION

[0036] The technical solutions of the present application will be further illustrated below by combining with the examples and the drawings. Unless specifically described, each feature is only an example in a series of equivalent or similar features. Only to help understand the present application, those skilled in the art should understand that the examples are only to help understand the present application, and should not be regarded as a specific limitation on the present application.

[0037] Example 1 This example includes the following steps: S1. Take 100 g of cast iron waste with a silicon content of 3.5 wt%, mechanically crush it to obtain cast iron powder with an average diameter of 500 µm (where the maximum diameter is not more than 600 µm).

[0038] S2. Put the cast iron powder prepared in step S1 into a 10 mol / L hydrochloric acid solution, stir under the condition of 35 ℃ water bath heating for 12 h, and remove Fe. After the reaction is completed, perform suction filtration, repeatedly wash the solid obtained by suction filtration with deionized water and alcohol until the filtrate is neutral (pH ≈ 7), and then place the black powder after filtration and washing in a 100 ℃ vacuum oven for drying for 12 h to obtain a silicon-oxygen composite material precursor.

[0039] S3. Then take 4.25 g of the silicon-oxygen composite material precursor obtained in step S2 and 0.75 g of pitch (i.e. pitch addition ratio 15 wt%) together into the ball milling tank of the planetary ball mill. Fill argon gas as protective atmosphere in the tank, select zirconia grinding balls, set the ball-to-material ratio to 50:1, and high-speed ball mill at a speed of 500 rpm for 24 h to obtain carbon-silicon-oxygen composite powder without carbonization.

[0040] S4. Then transfer the black powder after ball milling in step S3 to a tube furnace, heat to 800 ℃ at a heating rate of 5 ℃ / min under Ar atmosphere protection, and keep for 2 h to make the pitch fully carbonized to form an amorphous carbon coating layer. After the reaction is completed, naturally cool to room temperature, and finally obtain a carbon-coated silicon-oxygen graphite composite material.

[0041] The final product of this example is characterized for phase and morphology, and the results are as follows Figure 2 、 Figure 3 and Figure 4 . Through Figure 3The structural characteristics of the silicon-oxygen composite material can be seen, the graphite characteristic peak is obvious at 26°, and the non-crystalline silicon-oxygen (SiO x ) bun peak is found at about 23°, thereby proving that the silicon-oxygen graphite composite material of the present application exists in the form of graphite and non-crystalline silicon-oxygen (SiO x ); by Figure 2 It can be seen that the final composite material presents a smooth layered morphology under the microstructure, and such morphology is more conducive to the formation of a conductive network, and by Figure 2 It can be seen that in the microstructure, each particle is a layered particle coated with amorphous carbon on the outside, and the maximum size in the field of view is about 6µm, and there are less than about 10 such large-size particles, and the size of about 3µm is the main body, and the size of less than about 2µm is uniformly distributed around the large particles, and the average size is in the range of about 1~6µm. As shown in Figure 4 , wherein Figure 4 (a) is a TEM image with a calibrated length of 50nm, Figure 4 (b) is a field of view with a calibrated length of 2nm (i.e. further magnifying the field of view of Figure 4 (a) by 25 times), by Figure 4 (a), it can be clearly seen that the silicon-oxygen graphite uniformly forms a core and is completely coated with a uniform amorphous carbon layer, and the thickness of the coating layer is basically uniform, Figure 4 (b) can be seen that the graphite combined with the amorphous carbon layer is graphite, and the graphite is closely and seamlessly combined with the inside of the amorphous carbon, thereby proving that the coating composite structure obtained by the present application is stably present.

[0042] As a further study, the above carbon-coated silicon-oxygen graphite composite material obtained in Example 1 is used as an active material, and then mixed with a conductive agent (acetylene black) and a binder (CMC) at a mass ratio of 8:1:1 to prepare a slurry, and then uniformly coated on a copper foil current collector, and then dried, rolled and punched to prepare a negative electrode sheet. Then, lithium sheet is used as a counter electrode to assemble a CR2032 type button cell in an argon-filled glove box, and 1.0M LiPF6 in EC:DMC:DEC=1:1:1 vol% is used as an electrolyte. The assembled battery is subjected to electrochemical performance test, and the results are shown in Figure 5 and Figure 6 It can be seen from Figure 5 that at a current density of 0.05A g -1 , the initial discharge specific capacity can reach 1320mAh g -1 , the initial charge specific capacity can reach 965mAh g -1 , and the initial coulombic efficiency is 73%. It can be seen from Figure 6 (a) that at a current density of 0.5A g -1at a current density of 0.2 A g -1 , the specific capacity remained at 622 mAh g Figure 6 -1 after 100 cycles, and the capacity retention was as high as 97%. Meanwhile, by Figure 6 (b) can also exhibit good rate performance. When the current density increased from 0.05 A g -1 to 3.0 A g -1 , the reversible specific capacity of the material can still maintain at 740 mAh g -1 .

[0043] Example 2 This example includes the following steps: S1. Take 100 g of cast iron waste with a silicon content of 3.5 wt%, mechanically crush it to obtain cast iron powder with a diameter of 500 pm.

[0044] S2. Put the obtained cast iron powder into a 10 mol / L hydrochloric acid solution, stir under the condition of a 55°C water bath heating for 12 h to remove Fe. After the reaction is completed, perform suction filtration, and repeatedly wash with deionized water and alcohol until the filtrate is neutral (pH ≈ 7). Then, dry the filtered black powder in a vacuum oven at 100°C for 12 h to obtain a silicon-oxygen composite material precursor.

[0045] S3. Then, take 3 g of the silicon-oxygen composite material precursor obtained in step S2 and 0.75 g of pitch (pitch addition ratio 20 wt%) together into the ball milling tank of a planetary ball mill. Fill argon gas as a protective atmosphere in the tank, select zirconia grinding balls, set the ball-to-material ratio to 50:1, and high-speed ball mill at a speed of 500 rpm for 24 h.

[0046] S4. Then, transfer the milled black powder to a tube furnace, heat to 800°C at a heating rate of 5°C / min under Ar atmosphere protection, and keep for 2 h to make the pitch fully carbonized to form an amorphous carbon coating layer. After the reaction is completed, naturally cool to room temperature, and finally obtain a carbon-coated silicon-oxygen graphite composite material.

[0047] As a further study, mix the above-mentioned composite material of Example 2 as an active material, a conductive agent (acetylene black), and a binder (CMC) in a mass ratio of 8:1:1 to prepare a slurry, uniformly coat it on a copper foil current collector, and after drying, rolling, and punching, prepare a negative electrode sheet. Use lithium sheet as a counter electrode, assemble into a CR2032 type button cell in an argon-filled glove box, and use 1.0 M LiPF6 in EC:DMC:DEC=1:1:1 vol% as the electrolyte.

[0048] The assembled battery was subjected to electrochemical performance test to obtain the following results: Figure 6The results show that: at a current density of 0.05 A g -1 , the first specific discharge capacity reaches 1172 mAh g -1 , the first specific charge capacity reaches 838 mAh g -1 , and the first coulombic efficiency is 72%. At a current density of 0.5 A g -1 , after 100 cycles, the specific capacity remains 579 mAh g -1 , and the capacity retention rate is as high as 95%. At the same time, the material also shows good rate performance. When the current density increases from 0.05 A g -1 to 3.0 A g -1 and then returns to 0.05 A g -1 , the reversible specific capacity can still maintain at 736 mAh g -1 .

[0049] Example 3 This example includes the following steps: S1. Take 100 g of cast iron waste with a silicon content of 3.5 wt%, mechanically crush it to obtain cast iron powder with a diameter of 500 μm.

[0050] S2. Put the obtained cast iron powder into a 10 mol / L hydrochloric acid solution, stir under the condition of 38°C water bath heating for 12 h, remove Fe (mainly Fe). After the reaction is completed, perform suction filtration, and repeatedly wash with deionized water and alcohol until the filtrate is neutral (pH ≈ 7), then dry the filtered black powder in a vacuum oven at 100°C for 12 h to obtain a silicon-oxygen composite material precursor.

[0051] S3. Then put 6.75 g of the silicon-oxygen composite material precursor obtained in step S2 and 0.75 g of pitch (pitch addition ratio 10 wt%) into the ball milling tank of the planetary ball mill. Fill argon gas as protective atmosphere in the tank, select zirconia grinding balls, set the ball-to-material ratio to 50:1, and high-speed ball mill at 500 rpm for 24 h.

[0052] S4. Transfer the black powder after ball milling in step S3 to a tube furnace, heat to 800°C at a rate of 5°C / min under Ar atmosphere protection, and keep for 2 h to make the pitch fully carbonized to form an amorphous carbon coating layer. After the reaction is completed, naturally cool to room temperature, and finally obtain a carbon-coated silicon-oxygen graphite composite material.

[0053] As a further study, the composite material of Example 3 above was mixed with conductive agent (acetylene black), binder (CMC) at a mass ratio of 8:1:1 to prepare slurry, which was uniformly coated on a copper foil current collector, and then dried, rolled, punched to form a negative electrode sheet. Lithium sheet was used as the counter electrode to assemble a CR2032 type button cell in an argon-filled glove box, and 1.0 M LiPF6 in EC:DMC:DEC=1:1:1 vol% was used as the electrolyte.

[0054] The assembled battery was subjected to electrochemical performance test to obtain results as shown in Figure 6 The results showed that the first discharge specific capacity reached 1292 mAh g -1 at a current density of 0.05 A g -1 , the first charge specific capacity reached 914 mAh g -1 , and the first coulombic efficiency was 71%. After 100 cycles at a current density of 0.5 A g -1 , the specific capacity remained at 507 mAh g -1 , and the capacity retention rate was as high as 75%. At the same time, the rate performance results of the material showed that when the current density increased from 0.05 A g -1 to 3.0 A g -1 and then returned to 0.05 A g -1 , the reversible specific capacity could still maintain at 701 mAh g -1 .

[0055] Comparative Example 1 The present comparative example is used to show a comparative test for preparing a composite material without setting an additional carbon source, comprising the following steps: S1. 100 g of cast iron waste with a silicon content of 3.5 wt% was mechanically crushed to obtain cast iron powder with a diameter of 500 µm.

[0056] S2. The obtained cast iron powder was placed in a 10 mol / L hydrochloric acid solution and stirred at 35°C water bath heating condition for 12 h to remove Fe. After the reaction, suction filtration was performed, and deionized water and alcohol were repeatedly washed until the filtrate was neutral (pH≈7). Subsequently, the filtered black powder was placed in a 100 ℃ vacuum oven for drying for 12 h to obtain a silicon-oxygen composite material precursor.

[0057] S3. Subsequently, the above silicon-oxygen composite material precursor was placed in a ball milling tank of a planetary ball mill. Argon was filled in the tank as a protective atmosphere, zirconia grinding balls were selected, the ball-to-material ratio was set to 50:1, and high-speed ball milling was performed at a speed of 500 rpm for 24 h.

[0058] S4. The ball-milled black powder was then transferred to a tube furnace and heated to 800 °C at a rate of 5 °C / min under Ar atmosphere and kept for 2 h. After the ball-milling was completed, the sample was naturally cooled to room temperature, and the final composite was obtained.

[0059] The above composite was mixed with conductive agent (acetylene black) and binder (CMC) as active material at a mass ratio of 8:1:1 to make slurry, which was uniformly coated on a copper foil current collector, and then dried, rolled, and punched to form a negative electrode sheet. Lithium sheet was used as the counter electrode to assemble a CR2032 button cell in an argon-filled glove box, with 1.0 M LiPF6 in EC:DMC:DEC = 1:1:1 vol% as the electrolyte. The assembled battery was tested for electrochemical performance: at a current density of 0.05 A g -1 , the initial specific discharge capacity reached 1131 mAh g -1 , the initial specific charge capacity reached 447 mAh g -1 , and the initial coulombic efficiency was 40 %. At a current density of 0.5 A g -1 , the specific capacity remained at 499 mAh g -1 after 100 cycles, with a capacity retention rate of 75 %. At the same time, the rate performance of the material was as follows: when the current density increased from 0.05 A g -1 to 3.0 A g -1 and then returned to 0.05 A g -1 , the reversible specific capacity remained at 545 mAh g -1 .

[0060] The electrochemical performance of Example 1, Example 2, Example 3, and Comparative Example is shown in Figure 6 , wherein Figure 6 (a) is the reversible specific capacity after 100 cycles at 0.5 A / g, Figure 6 (b) is the performance test result at a rate of 0.05-3 A / g. The abscissa is the cycle number, and the ordinate is the reversible specific capacity. From Figure 6 (a), it can be seen that the reversible specific capacity of Example 1 is about 600 mAh / g from the initial to 100 cycles, while Comparative Example 1 is significantly insufficient, less than 400 mAh / g from the initial count, and less than 500 mAh / g at the end, although it has certain electrochemical performance, but the index is significantly less than the setting of the additional carbon source; and from Figure 6 (b), it can be seen that the reversible specific capacity of Example 2 is about 600 mAh / g from the initial to 100 cycles, while Comparative Example 2 is significantly insufficient, less than 400 mAh / g from the initial count, and less than 500 mAh / g at the end, although it has certain electrochemical performance, but the index is significantly less than the setting of the additional carbon source; and from Figure 6(b) It can also be seen that at the beginning of the cycle stage of 0.05 A / g rate, Example 1, Example 2 and Example 3 are all around 800~1000mAh / g, while Comparative Example 1 is around 400mAh / g, and then each cycle number of Comparative Example 1 is significantly lower than the reversible specific capacity values of Examples 1~3. Thus, it is shown that the composite material with certain electrochemical performance is preferred to be extracted and processed, and then on the basis of the composite material, the carbonization treatment of the specific additional carbon source can realize the further substantial improvement of the electrochemical performance of the composite material.

[0061] The technical principles of the present application are described above in combination with specific embodiments. These descriptions are only for explaining the principles of the present application, and cannot be interpreted as limiting the protection scope of the present application in any way. Based on the explanations herein, other specific embodiments of the present application can be conceived by those skilled in the art without creative labor, and these embodiments will all fall within the protection scope of the present application.

Claims

1. A carbon-coated silicene graphite composite material, characterized by, The microstructure of the composite material is SiO x The composite structure is that the amorphous carbon layer is coated outside the layered or sheet-shaped core composed of graphite; wherein 0 < x < 2, and SiO x The core is composed of graphite in a crinkled lamella structure, the average thickness of the amorphous carbon layer coated outside the core is 25 nm to 80 nm, and the average size of the core is 1 to 6 µm. The composite material has a chemical element composition of, by mass percentage: Si: 4.6-20.88 wt.%, O: 16.16-47.36 wt.%, C: 26.76-76.2 wt.%.

2. A method for producing a carbon-coated silicene graphite composite material, characterized by, The method comprises the following steps: S1. Selecting cast iron with a C content of 3.0-4.45 wt.% and a Si content of 1.8-3.2 wt.%, crushing and sieving the cast iron to obtain cast iron powder with a particle size of 100-1000 μm; S2. Immersing the cast iron powder obtained in step S1 in an excess acid solution, stirring and reacting at a temperature of 30-95℃ for 3-25 h to remove iron from the cast iron powder, then filtering the reaction mixture, washing the filter cake multiple times and drying to obtain a silicon-oxygen composite material precursor; S3. Pre-mixing the obtained silicon-oxygen composite material precursor and carbon source at a mass ratio of (0.8-1.2):(0.1-0.3), then high-energy ball milling under the protection of an inert gas to obtain a carbon-silicon-oxygen composite powder; S4. Placing the obtained carbon-silicon-oxygen composite powder into a heating furnace, heating at a rate of 1-18℃ / min to 580-1200℃ under the protection of an inert gas, then holding for 1-6 h, and naturally cooling to obtain a carbon-coated silicon-oxygen graphite composite material.

3. The preparation method according to claim 2, characterized in that, The cast iron in step S1 is one or a mixture of more than one of gray cast iron, compacted graphite cast iron, ductile cast iron or malleable cast iron with a C content of 3.2-4.5 wt.% and a Si content of 2.0-3.0 wt.%.

4. The production method according to claim 2, characterized by, The acid solution in step S2 is one or more of hydrochloric acid, sulfuric acid, phosphoric acid or nitric acid with a concentration of 1-13 mol / L; The reaction temperature in step S2 is 30-80℃, and the reaction time is 4-24 h.

5. The preparation method according to claim 2, characterized in that, The carbon source in step S3 is one or more of glucose, sucrose, pitch, citric acid, starch, phenolic resin or polyacrylonitrile; The silicon-oxygen composite material precursor and the carbon source are pre-mixed at a mass ratio of 1:(0.1-0.3).

6. The preparation method according to claim 2, characterized in that, The parameters of the high-energy ball milling in step S3 are: a ball-to-material mass ratio of (10-60):1, a ball milling speed of 300-800 rpm, and a ball milling time of 6-72 h.

7. The preparation method according to claim 2, characterized in that, Step S4 specifically comprises placing the obtained carbon-silicon-oxygen composite powder into an atmosphere heating furnace, heating at a rate of 1-10℃ / min to 600-1100℃ under the protection of argon or nitrogen, then holding for 1-5 h for carbonization treatment, naturally cooling in the furnace, and then obtaining a carbon-coated silicon-oxygen graphite composite material.

8. A lithium-ion battery negative electrode sheet, characterized by, The lithium ion battery negative electrode sheet is prepared using the carbon-coated silicon-oxygen graphite composite material as a raw material.

9. The lithium-ion battery anode sheet of claim 8, wherein, The lithium ion battery negative electrode sheet is prepared using the following steps: (1) The carbon-coated siloxene graphite composite material of claim 1 or the carbon-coated siloxene graphite composite material prepared by the preparation method of any one of claims 2-7 is mixed with a conductive agent and a binder at a mass ratio of (6-10):(0.8-1.3):(0.9-1.1), and stirred uniformly to obtain a mixed slurry; (2) The mixed slurry obtained in step (1) is uniformly applied on a copper foil current collector to obtain a copper foil composite; (3) The copper foil composite obtained is dried, rolled and punched to obtain a lithium ion battery negative plate.

10. A lithium-ion battery, characterized by, The lithium ion battery is a lithium ion battery using the lithium ion battery negative plate of claim 8 or 9 as a negative plate and a lithium sheet as a counter electrode.

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