A silicon-carbon negative electrode material with core-shell structure, a negative electrode sheet, and a preparation method thereof

Abstract

This invention relates to a core-shell structured silicon-carbon anode material, anode sheet, and their preparation. The preparation process of the silicon-carbon anode material is as follows: first, a sheet-like silicon material and a water-soluble polymer precursor are provided; the sheet-like silicon material and the water-soluble polymer precursor are then combined to obtain a silicon / water-soluble polymer precursor composite material; and then, under the protection of an inert gas, it is pyrolyzed to obtain a silicon-carbon composite material, which is the target product. The core-shell structured silicon-carbon composite material obtained by this invention, when placed on a current collector to prepare anode sheets, can effectively improve the ion transport capacity on the electrode, suppress the volume expansion of silicon, and improve the structural collapse problem caused by the volume expansion and contraction of silicon during the charge and discharge process of the silicon-carbon anode. This significantly improves the first-cycle coulombic efficiency of the battery, maintains the high-capacity cycle stability of the battery under high-current charge and discharge conditions, thereby increasing the specific capacity of the battery and further improving the battery energy density.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, and relates to a core-shell structured silicon-carbon anode material, anode sheet, and its preparation and application. Background Technology

[0002] Lithium-ion batteries are rechargeable batteries that rely on the movement of lithium ions between the positive and negative electrodes to operate. They have excellent properties such as high energy density, high output power, low self-discharge, wide operating temperature range, superior cycle performance, fast charging and discharging, long service life, and no toxic or harmful substances. They have developed rapidly in the battery field and are now widely used in portable electronic devices, electric vehicles, and large-scale energy storage.

[0003] Graphite is commonly used as the negative electrode in lithium-ion batteries, but its theoretical specific capacity is relatively low (372 mAh / g), severely limiting the development of lithium-ion batteries. Silicon materials, on the other hand, possess a higher theoretical specific capacity (4200 mAh / g) and a suitable lithium electrode potential (0.4V vs Li). + Silicon (Li) and its abundant reserves make it a promising anode material for lithium-ion batteries. However, silicon materials undergo several times the volume expansion during lithium insertion / extraction, leading to pulverization of the particle structure and affecting the stability of the solid electrolyte interphase (SEI). This results in rapid capacity decay and low coulombic efficiency of the anode material, severely hindering its application in batteries.

[0004] Currently, most commercial silicon-carbon composite materials are prepared using vapor deposition, a process that is costly, complex, and yields less than ideal performance, resulting in a low cost-effectiveness and hindering their widespread application. The overall production cost needs further reduction, and the electrochemical performance, especially the cycling performance, of the materials requires further improvement. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology by providing a core-shell structured silicon-carbon anode material, anode sheet, and their preparation and application, thereby improving the low specific capacity and other problems of existing batteries.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a core-shell structured silicon-carbon anode material. First, a sheet-like silicon material and a water-soluble polymer precursor are provided. The sheet-like silicon material and the water-soluble polymer precursor are then combined to obtain a silicon / water-soluble polymer precursor composite material. The composite material is then pyrolyzed under the protection of an inert gas to obtain a silicon-carbon composite material, which is the target product.

[0008] Furthermore, the sheet-like silicon material includes at least one of monocrystalline silicon and polycrystalline silicon.

[0009] Furthermore, the water-soluble polymeric precursor includes at least one of polyvinyl alcohol, polyacrylic acid, polyethylene oxide, and polyvinylpyrrolidone.

[0010] Furthermore, the average thickness of the sheet-like silicon material is 5nm to 50nm, the average width is 100nm to 1000nm, the aspect ratio is 2 to 200, and the specific surface area is 10m². 2 / g~30m 2 / g.

[0011] Furthermore, the number-average molecular weight of the water-soluble polymer precursor is between 10,000 and 100,000.

[0012] Furthermore, the mass ratio of the sheet-like silicon material to the water-soluble polymer precursor is (0.05–2):1.

[0013] Furthermore, the composite method of the sheet-like silicon material and the water-soluble polymer precursor is ball milling.

[0014] Furthermore, during the ball milling process, the milling time is 0.5 to 20 hours.

[0015] Furthermore, the rotational speed of the ball mill is 100–2000 r / min.

[0016] Furthermore, the grinding aids used in ball milling include one or more of water, ethanol, and N,N-dimethylformamide.

[0017] Furthermore, grinding beads are added during the ball milling process. The total mass ratio of the grinding beads to the sheet silicon material and the water-soluble polymer precursor is (0.1–10):1.

[0018] More specifically, the grinding beads include one or more of agate, corundum, stainless steel, and zirconium oxide. The diameter of the grinding beads is 1 to 10 mm, and for example, it can be 1 mm, 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm.

[0019] Furthermore, the pyrolysis is carried out under an inert atmosphere at a temperature of 600–1200°C for 1–10 hours.

[0020] In a second aspect, the present invention provides a core-shell structured silicon-carbon anode material, which is prepared by the preparation method described above.

[0021] In a third aspect, the present invention provides a negative electrode sheet, which is prepared by the following process:

[0022] A conductive agent, binder, solvent, and silicon-carbon anode material with a core-shell structure as described above are mixed to obtain an anode slurry;

[0023] The negative electrode slurry is coated onto the current collector and dried to obtain the negative electrode sheet.

[0024] Furthermore, the conductive agent includes one or more of conductive carbon black, conductive graphite, acetylene black, carbon nanotubes, carbon nanofibers, and Ketjen black.

[0025] Furthermore, the adhesive includes one or more of polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, polytetrafluoroethylene emulsion, polyacrylonitrile, polyacrylate, polyamide, polyvinyl alcohol, polyethyleneimine, and polyimide.

[0026] Furthermore, the solvent includes one or more of the following: ethanol, methanol, propylene glycol, glycerol, ethylene glycol, butanol, pentanol, hexanol, n-butanol, isopropanol, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, tetramethylurea, trimethyl phosphate, and dimethylacetamide.

[0027] Furthermore, the current collector includes copper foil, etc.

[0028] Furthermore, the mass ratio of the silicon-carbon composite material, conductive agent, and binder is (70-90):(2-10):(2-10).

[0029] Furthermore, in the negative electrode slurry, the mass concentration of the silicon-carbon negative electrode material is 20% to 80%.

[0030] Compared with existing technologies, this invention uses sheet-like silicon materials and water-soluble polymer precursors as raw materials to prepare silicon-carbon composite materials with core-shell structures. The process is simple and easy to operate. Furthermore, it can be further combined with conductive agents, binders and solvents to prepare negative electrode sheets, which can effectively improve the tap density of the negative electrode and improve the structural collapse problem caused by the volume expansion and contraction of silicon during the charging and discharging process of silicon-carbon negative electrodes. This can effectively improve the first-cycle coulombic efficiency and high-capacity cycle stability of the battery, thereby improving the specific capacity, reliability and safety of the battery. Attached Figure Description

[0031] Figure 1 This is a flowchart of a method for preparing a negative electrode sheet provided in an embodiment of this application;

[0032] Figure 2 This is a schematic diagram of the negative electrode sheet provided in the embodiments of this application;

[0033] Figure 3 This is a scanning electron microscope image of the silicon-carbon composite material provided in Example 1 of this application;

[0034] Figure 4This is a high-resolution transmission electron microscope image of the silicon-carbon composite material provided in Example 1 of this application;

[0035] Figure 5 This is the Raman spectrum of Example 1;

[0036] Figure 6 This is a first-cycle charge-discharge curve of the battery provided in Embodiment 1 of this application;

[0037] Figure 7 This is a first-cycle charge-discharge curve of the battery provided in Embodiment 2 of this application;

[0038] Figure 8 This is a first-cycle charge-discharge curve of the battery provided in Embodiment 3 of this application;

[0039] Figure 9 These are cycle performance diagrams of the batteries provided in Embodiments 1 and 2 and Comparative Example 1 of this application;

[0040] Figure label:

[0041] 10 - Sheet-shaped silicon material; 20 - Amorphous carbon obtained from the pyrolysis of water-soluble polymers. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0043] In this application, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its actual use or operating state, specifically the orientation shown in the accompanying drawings; while "inner" and "outer" refer to the outline of the device. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative purposes and do not impose numerical requirements or establish a numerical order.

[0044] In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0045] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be a single item or multiple items.

[0046] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0047] To improve the existing problems such as low specific capacity of batteries, in the first aspect, the present invention provides a method for preparing a silicon-carbon anode material with a shell-like biomimetic structure. First, a sheet-like silicon material and a water-soluble polymer precursor are provided. The sheet-like silicon material and the water-soluble polymer precursor are mixed and then pyrolyzed to obtain a silicon-carbon composite material, which is the target product.

[0048] For details on the structure of silicon-carbon composite materials, please refer to [link / reference]. Figure 2 As shown, it should be noted that the sheet-like silicon material 10 and the water-soluble polymer precursor in S11 are combined by ball milling and then pyrolyzed to obtain amorphous carbon 20 after water-soluble polymer pyrolysis coating the sheet-like silicon material 10. The resulting silicon-carbon composite material has a core-shell structure.

[0049] In some specific embodiments, the sheet silicon material includes at least one of monocrystalline silicon and polycrystalline silicon.

[0050] In some specific embodiments, the water-soluble polymer precursor includes at least one of polyvinyl alcohol, polyacrylic acid, polyethylene oxide, and polyvinylpyrrolidone. Within this range of water-soluble polymers, they can form hydrogen bonds with water molecules and hydroxyl groups generated during the ball milling process, which is beneficial for the uniform coating of the polymer precursor.

[0051] In some specific embodiments, the number-average molecular weight of the water-soluble polymer precursor is 10,000 to 100,000.

[0052] In some specific embodiments, the average thickness of the sheet-like silicon material is 5nm to 50nm, for example, it can be 8nm to 48nm, 10nm to 45nm, 12nm to 42nm, 15nm to 40nm, 20nm to 30nm, etc. Within the thickness range of the sheet-like silicon material 10, it is beneficial for the sheet-like silicon material 10 to be coated by the water-soluble polymer precursor through chemical and physical processes during ball milling, thereby constructing a core-shell structure.

[0053] In some specific embodiments, the aspect ratio of the sheet-like silicon material is 2 to 200, and the specific surface area is 10m². 2 / g~30m 2 / g, for example, can be 12m 2 / g~29m 2 / g, 15m 2 / g~28m 2 / g, 16m 2 / g~26m 2 / g, 18m 2 / g~25m 2 / g, 20m 2 / g~22m 2 / g etc. Within the specific surface area range of the aforementioned sheet-like silicon material, there are more active sites for lithium insertion / extraction, and the lithium-ion transport path is shorter, which is beneficial to the performance of the final electrode. An excessively large specific surface area will increase unnecessary polymer precursor losses and reduce the first-cycle coulombic efficiency of the electrode, while an excessively small specific surface area will affect the cycle stability of the electrode.

[0054] In some specific embodiments, the mass ratio of the sheet-like silicon material to the water-soluble polymer precursor is (0.05–2):1, for example, it can be (0.1–1.8):1, (0.2–1.6):1, (0.5–1.5):1, (0.6–1.2):1, (0.8–1):1, etc. Within the mass ratio range, the pyrolyzed sheet-like silicon can be well coated by the carbon layer, without excess amorphous carbon or exposed silicon.

[0055] In some specific embodiments, the mixing process includes ball milling. Specifically, the ball milling process can be wet ball milling.

[0056] In a more specific embodiment, the ball milling time is 0.5h to 12h, for example, it can be 1h to 11h, 2h to 12h, 2h to 10h, 3h to 9h, 4h to 8h, 5h to 6h, etc., or it can be any point value within the above range, such as 0.5h, 12h or 6h.

[0057] In a more specific embodiment, the rotational speed of the ball mill is 100 r / min to 2000 r / min, for example, it can be 200 r / min to 1800 r / min, 500 r / min to 1600 r / min, 600 r / min to 1500 r / min, 800 r / min to 1200 r / min, 1000 r / min to 1100 r / min, etc., or it can be any point value within the above range, such as 100 r / min, 2000 r / min, or 1000 r / min, etc.

[0058] In a more specific embodiment, the ball milling includes alternating forward and reverse ball milling or intermittent ball milling.

[0059] In a more specific embodiment, a grinding aid is also added during the ball milling process. This grinding aid includes one or more of water and ethanol. Specifically, the mass ratio of the sheet-like silicon material and the sheet-like carbon material to the grinding aid is 1:(1-10).

[0060] In a more specific embodiment, the ball milling further includes adding grinding beads, which include one or more of agate, corundum, stainless steel, and zirconium oxide. The diameter of the grinding beads is 1 to 10 mm, including 1 mm, 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm. The mass ratio of the added grinding beads is (0.1 to 10): 1.

[0061] In some specific embodiments, the pyrolysis process includes calcination.

[0062] In a more specific embodiment, the calcination time is 1 hour to 10 hours.

[0063] In a more specific embodiment, the calcination temperature is 600℃~1200℃.

[0064] In a more specific embodiment, the calcination holding time is 1 hour to 10 hours.

[0065] In a more specific embodiment, the protective atmosphere for calcination is one or more of nitrogen, argon, helium, etc.

[0066] In this invention, ball milling serves to uniformly disperse and coat the water-soluble polymer precursor and the sheet-like silicon material, preventing localized aggregation. Calcination serves to thermally decompose the polymer precursor into carbon, thereby enhancing the conductivity of the system and suppressing volume changes in the silicon material.

[0067] In addition, in some embodiments, the present invention further provides a negative electrode sheet, which is prepared by the following method:

[0068] The conductive agent, binder and solvent are mixed with the silicon-carbon anode material as described above to obtain the anode slurry;

[0069] The negative electrode slurry is coated onto the current collector and dried to obtain the negative electrode sheet.

[0070] In some specific embodiments, the conductive agent includes one or more of conductive carbon black, conductive graphite, acetylene black, carbon nanotubes, carbon nanofibers, and Ketjen black.

[0071] In some specific embodiments, the adhesive includes one or more of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polytetrafluoroethylene emulsion (PTFE), polyacrylonitrile (PAN), polyacrylate (PAA), polyamide (PAI), polyvinyl alcohol (PVA), polyethyleneimine (PEI), and polyimide (PI).

[0072] In some specific embodiments, the solvent includes one or more of ethanol, methanol, propylene glycol, glycerol, ethylene glycol, butanol, pentanol, hexanol, n-butanol, isopropanol, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, tetramethylurea, trimethyl phosphate, and dimethylacetamide.

[0073] In some specific embodiments, the current collector includes copper foil.

[0074] In some specific embodiments, the mass ratio of the silicon-carbon composite material, the conductive agent, and the binder is (70–90):(2–10):(2–10). For example, it can be (75–85):(2–10):(2–10), (70–90):(5–8):(2–10), (70–90):(2–10):(5–8), etc. Within this mass ratio range, it is beneficial to fully utilize the activity of the silicon-carbon composite material.

[0075] In some specific embodiments, the mass concentration of the silicon-carbon composite material in the negative electrode slurry is 20% to 80%. Within this mass concentration range, the silicon-carbon composite material can be fully dissolved and uniformly dispersed in the solvent.

[0076] In some specific embodiments, the drying temperature is preferably 60℃~100℃, for example, 62℃~95℃, 65℃~90℃, 68℃~88℃, 70℃~85℃, 75℃~80℃, etc. Simultaneously, centrifugation can be performed before drying, preferably at a rate of 1000 r / min~8000 r / min. Thus, within the range of centrifugation rate and drying temperature, liquid substances such as grinding aids can be removed more effectively, resulting in a highly active silicon-carbon composite material. Furthermore, more specifically, after drying, conventional processes such as cutting and rolling can be included to obtain the negative electrode sheet.

[0077] Each of the above implementation methods can be implemented individually, or in any combination of two or more.

[0078] The present application will be specifically described below through specific embodiments. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0079] In the following embodiments, the silicon block is commercially available monocrystalline silicon; the multi-walled carbon nanotubes (brand name: A62063) were purchased from Anhui Anaiji; the polyacrylic acid adhesive (model: SONE) was purchased from Shenzhen Kejing; and the polyvinylpyrrolidone was purchased from Shanghai Yuang Technology.

[0080] Example 1

[0081] This embodiment provides a negative electrode sheet, the preparation method of which is as follows:

[0082] A silicon block is provided, and it is ground with a 1000-mesh diamond abrasive to obtain a sheet silicon material. The sheet silicon material has an average thickness of 10 nm, an average width of 500 nm, and an aspect ratio of 50.

[0083] Polyvinylpyrrolidone (PVP, grade K-30) was provided. The above-mentioned sheet-like silicon material and PVP were mixed at a mass ratio of 1:3. Water was used as a grinding aid (the mass ratio of water to PVP was 100:1), and zirconium oxide was used as grinding beads (the mass ratio of grinding beads to all materials was 5:1). The mixture was placed in a ball mill jar for ball milling at a speed of 300 r / min for 15 h. After ball milling, the mixture was centrifuged and dried at 80 °C to obtain a PVP-coated silicon composite material. Subsequently, the PVP-coated silicon composite material was placed in a tube furnace and heated to 800 °C under a nitrogen atmosphere for 3 hours to obtain a carbon-coated silicon composite material.

[0084] The above silicon-carbon composite material, multi-walled carbon nanotubes, and polyacrylic acid binder were mixed in a mass ratio of 80:10:10 and dissolved and dispersed in water to obtain a negative electrode slurry.

[0085] The above-mentioned negative electrode slurry is coated onto copper foil, and after drying and cutting, a negative electrode sheet is obtained.

[0086] This embodiment also provides a button cell battery, including the above-mentioned negative electrode, electrolyte and lithium iron phosphate positive electrode.

[0087] Example 2

[0088] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the wafer silicon material and PVP are mixed in a 1:1 mass ratio.

[0089] Example 3

[0090] This embodiment is basically the same as embodiment 1, except that in this embodiment, the wafer silicon material and PVP are mixed at a mass ratio of 1:5.

[0091] Comparative Example 1

[0092] This comparative example is basically the same as Example 1, except that the active material used in the negative electrode in this example is pure sheet silicon material.

[0093] Comparative Example 2

[0094] This comparative example is basically the same as Example 1, except that the silicon-carbon composite material used in the negative electrode in this example is a commercial silicon-carbon negative electrode material (SiC S500, purchased from Cyber ​​Electrochemical Materials).

[0095] Comparative Example 3

[0096] This comparative example is basically the same as Example 1, except that the silicon-carbon composite material used in the negative electrode in this example is a commercial silicon-carbon negative electrode material (SiC S600, purchased from Cyber ​​Electrochemical Materials).

[0097] Comparative Example 4

[0098] This embodiment is basically the same as Embodiment 1, except that the sheet silicon material is replaced with commercially available nano silicon particles (with a particle size of about 100-200 nm and a purity of 99.9%).

[0099] Comparative Example 5

[0100] This embodiment is basically the same as Embodiment 1, except that PVP is replaced with cross-linked polyvinylpyrrolidone (PVPP, purchased from Hefei Qiansheng Biotechnology).

[0101] The above embodiments and comparative examples were used to assemble button cells for battery performance testing.

[0102] Transmission electron microscopy (TEM) was performed on the silicon-carbon composite material of Example 1, and TEM images of the composite anode material were obtained. The results are shown in [reference needed]. Figure 3The silicon-carbon composite material of Example 1 was subjected to high-resolution transmission electron microscopy (TEM) analysis, and the high-resolution TEM images of the silicon-carbon composite material were obtained. The results are shown in [reference needed]. Figure 4 .

[0103] Depend on Figure 3 and Figure 4 It can be seen that the carbon-coated silicon-carbon composite material still exhibits a sheet-like morphology similar to that of sheet-like silicon materials. Figure 4 The high-resolution TEM image shows that the outer layer of the sheet-like crystalline silicon material is covered with an amorphous carbon layer of about 4-6 nm thickness. The coating is relatively uniform and can suppress the volume expansion of the sheet-like silicon material.

[0104] Raman spectroscopy was performed on the silicon-carbon composite material of Example 1, and the results are shown in [reference needed]. Figure 5 .

[0105] from Figure 5 It can be seen from this that, except at 500cm -1 Besides the characteristic peaks of crystalline silicon appearing on the left and right sides, at 1350 cm⁻¹... -1 Left and right sides and 1580cm -1 Characteristic peaks of carbon, D and G, appeared on the left and right sides, indicating that the pyrolytic carbon from the polymer effectively coated the sheet-like silicon material. Additionally, the calculated I... D / I G The value was found to be around 0.74, therefore it can be predicted that the outer carbon graphitization degree of the silicon-carbon composite material prepared by the method provided in this application is low, and it is mostly amorphous carbon.

[0106] The batteries assembled from Examples 1-3 and Comparative Examples 1-5 were charged and discharged at a current density of 0.1 A / g and a voltage range of 0.005 V-2.5 V. The first charge-discharge curves of the batteries from Examples 1-3 are shown in the figure. Figures 6-8 As shown in Table 1, the first-cycle specific capacity and first-cycle coulombic efficiency of the batteries in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0107] Table 1

[0108] Battery First-round specific capacity (mAh / g) First-lap coulomb efficiency (%) Example 1 2099 87 Example 2 2234 89 Example 3 1748 86 Comparative Example 1 3100 86 Comparative Example 2 558 85 Comparative Example 3 683 86 Comparative Example 4 2045 85 Comparative Example 5 1978 81

[0109] Depend on Figures 6-8 As shown in Table 1, the first-cycle specific capacity of Examples 1-3 is over 1700 mAh / g, far exceeding that of Comparative Examples 2-3; the first-cycle coulombic efficiency is over 86%, demonstrating good performance. Figure 9A comparison reveals that after 100 cycles at a current density of 0.5 A / g, Examples 1 and 2 still possess specific capacities of 1449.2 mAh / g and 1750.4 mAh / g, respectively, with capacity retention rates of 80% and 79%. In contrast, Comparative Example 1 only has a discharge specific capacity of 1250 mAh / g after 100 cycles at a current density of 0.5 A / g, with a capacity retention rate of less than 50%. The similar first-cycle specific capacity of Example 1 and Comparative Examples 4 and 5 is due to their similar silicon-carbon ratios. However, the capacity retention of Comparative Examples 4 and 5 is worse, especially that of Comparative Example 5, which is similar to that of Comparative Example 1. This is because the polymer PVPP in Comparative Example 5 is insoluble in water and cannot effectively coat the surface of Si, thus failing to suppress the volume expansion of silicon. In contrast, the sheet-like silicon in Example 1 has a certain degree of ductility in the planar direction, which can better adapt to volume changes. Compared to the commercially available nano-silicon particles in Comparative Example 4, its stress distribution caused by volume changes is relatively more uniform, making it less prone to particle breakage and pulverization, thereby maintaining the integrity of the electrode structure and resulting in better cycle performance. Furthermore, the negative electrode sheet prepared using the method provided in this application is low-cost and simple to operate.

[0110] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a core-shell structured silicon-carbon anode material, characterized in that, First, a sheet-like silicon material and a water-soluble polymer precursor are provided. The sheet-like silicon material and the water-soluble polymer precursor are then combined to obtain a silicon / water-soluble polymer precursor composite material. The composite material is then pyrolyzed under the protection of an inert gas to obtain a silicon-carbon composite material, which is the target product.

2. The method for preparing a core-shell structured silicon-carbon anode material according to claim 1, characterized in that, The sheet-like silicon material includes at least one of monocrystalline silicon and polycrystalline silicon; And / or, the water-soluble polymeric precursor includes at least one of polyvinyl alcohol, polyacrylic acid, polyethylene oxide, and polyvinylpyrrolidone.

3. The method for preparing a core-shell structured silicon-carbon anode material according to claim 1, characterized in that, The sheet-like silicon material has an average thickness of 5 nm to 50 nm, an average width of 100 nm to 1000 nm, an aspect ratio of 2 to 200, and a specific surface area of ​​10 m². 2 / g~30m 2 / g; And / or, the number average molecular weight of the water-soluble polymer precursor is between 10,000 and 100,000.

4. The method for preparing a core-shell structured silicon-carbon anode material according to claim 1, characterized in that, The mass ratio of the sheet-like silicon material to the water-soluble polymer precursor is (0.05~2):

1.

5. The method for preparing a core-shell structured silicon-carbon anode material according to claim 1, characterized in that, The lamellar silicon material is combined with the water-soluble polymer precursor by ball milling. During the ball milling process, the milling time is 0.5 to 20 hours. The ball mill rotation speed is 100–2000 r / min; The grinding aids used in ball milling include one or more of water, ethanol, and N,N-dimethylformamide; Grinding beads are also added during the ball milling process.

6. The method for preparing a core-shell structured silicon-carbon anode material according to claim 1, characterized in that, The pyrolysis is carried out under an inert atmosphere at a temperature of 600–1200°C for 1–10 hours.

7. A core-shell structured silicon-carbon anode material, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

8. A negative electrode sheet, characterized in that, It is prepared through the following process: A conductive agent, a binder, a solvent, and a silicon-carbon anode material with a core-shell structure as described in claim 7 are mixed to obtain an anode slurry; The negative electrode slurry is coated onto the current collector and dried to obtain the negative electrode sheet.

9. The negative electrode sheet according to claim 8, characterized in that, The conductive agent includes one or more of conductive carbon black, conductive graphite, acetylene black, carbon nanotubes, carbon nanofibers, and Ketjen black. The adhesive includes one or more of polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, polytetrafluoroethylene emulsion, polyacrylonitrile, polyacrylate, polyamide, polyvinyl alcohol, polyethyleneimine, and polyimide; The solvent includes one or more of the following: ethanol, methanol, propylene glycol, glycerol, ethylene glycol, butanol, pentanol, hexanol, n-butanol, isopropanol, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, tetramethylurea, trimethyl phosphate, and dimethylacetamide. The current collector includes copper foil.

10. The negative electrode sheet according to claim 8, characterized in that, The mass ratio of the silicon-carbon composite material, conductive agent, and binder is (70-90):(2-10):(2-10); In the negative electrode slurry, the mass concentration of the silicon-carbon negative electrode material is 20% to 80%.

Images