Structure and preparation method of partially double-coated silicon negative electrode material

Abstract

The application relates to a structure and a preparation method of a partially double-coated silicon negative electrode material, in particular to the technical field of composite material preparation, and comprises the following steps: S1, silicon particles and a nitrogen-containing compound are ball-milled and mixed in a preset mass ratio H to obtain a mixture; S2, the mixture is transferred into a vacuum tube furnace for heat preservation to obtain a heat-treated product; S3, the heat-treated product is dissolved in N, N-dimethylformamide, G grams of PAN are added for stirring to obtain slurry with a solid content of M; and S4, the slurry is uniformly coated on a Cu foil, and the coated pole piece is transferred into a vacuum tube furnace for heating, and the pole piece after heating is cooled with the furnace to obtain a partially double-coated silicon negative electrode. The structure and the preparation method of the partially double-coated silicon negative electrode material provided by the application can absorb the stress caused by the volume expansion of silicon, improve the performance of the material, and avoid the capacity loss caused by the use of a binder.

Description

Technical Field

[0001] This invention relates to the field of composite material preparation technology, and in particular to the structure and preparation method of a partially double-coated silicon anode material. Background Technology

[0002] With the further popularization of electric vehicles, the development of key electrode materials is crucial for improving battery performance. Silicon anodes have received widespread attention due to their high specific capacity. However, the large volume change of silicon during lithiation / delithiation and the poor conductivity of silicon also limit the performance of the electrode. Nano-sizing of large silicon particles still cannot meet the actual needs of use. The buffering effect of simply physically mixing silicon particles with materials such as graphite is limited. In addition, in order to make the electrode material and the current collector a whole, a certain proportion of binder needs to be added during the slurry preparation process, which leads to some capacity loss.

[0003] Chinese Patent Publication No. CN114188512A discloses a silicon-carbon composite material, its preparation method, and its application, comprising the following steps: (1) mixing silicon particles with carbon particles to obtain silicon-carbon mixed particles; (2) mixing the silicon-carbon mixed particles obtained in step (1) with graphite-phase C3N4 particles to obtain a C3N4 / silicon-carbon mixture; (3) mixing the C3N4 / silicon-carbon mixture obtained in step (2) with a coating agent to obtain a coating mixture; and subjecting the coating mixture to heat treatment to obtain the silicon-carbon composite material. However, in this patent, the coating layers are only physically bonded, and the bonding force between the coating layers and the silicon is low, resulting in poor structural stability. Furthermore, a binder is still added during the preparation of the electrode sheet, failing to solve the performance and structural problems of the material. Summary of the Invention

[0004] Therefore, the present invention provides a structure and preparation method for a partially double-coated silicon anode material to overcome the problems of poor conductivity, low mechanical strength, poor cycle performance, low electronic conductivity, and capacity loss caused by the use of binders in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for preparing a partially double-coated silicon anode material, comprising:

[0006] Step S1: The silicon particles and nitrogen-containing compound are ball-milled and mixed at a preset mass ratio H to obtain a mixture;

[0007] Step S2: The mixture is transferred to a vacuum tube furnace for heat treatment to obtain a heat-treated product;

[0008] Step S3: Dissolve the heat-treated product in N,N-dimethylformamide, add G grams of PAN and stir to obtain a slurry with a solid content of M;

[0009] Step S4: The slurry is uniformly coated on Cu foil, and the coated electrode is transferred to a vacuum tube furnace for heating. The heated electrode is cooled with the furnace to obtain a partially double-coated silicon anode.

[0010] Further, in step S1, silicon particles with a mass of G1 and nitrogen-containing compound with a mass of G2 are weighed and placed together in a ball mill for ball milling, with G1 / G2 = H, wherein the rotational speed of the ball mill is N, and a mixture is obtained after time T4.

[0011] Further, in step S2, when the mixture is kept at a certain temperature, an inert gas is added to the vacuum tube furnace, and the vacuum tube furnace is heated to a temperature F1 at a heating rate C1 to keep the mixture at a certain temperature. After keeping the mixture at a certain temperature for a time T1, the heat-treated product is obtained.

[0012] Further, in step S3, the heat-treated product and the N,N-dimethylformamide are placed in a heating stirrer with a volume of V. The heating stirrer is used to stir at a temperature of F2. When the stirring time reaches T2, PAN is added, and the stirring continues at a temperature of F2 until a slurry with a solid content of M is formed.

[0013] Furthermore, in step S4, when heating the coated electrode, an inert gas is added to the vacuum tube furnace, the vacuum tube furnace is heated to temperature F3 at a rate C2, and after holding at that temperature for time T3, it is cooled with the furnace to obtain a partially double-coated silicon anode. The inert gas is argon.

[0014] Furthermore, the heat-treated product is a single-layer Si@g-C3N4 coating.

[0015] Furthermore, the partially double-coated silicon anode is a Si@g-C3N4@c-PAN electrode.

[0016] Furthermore, the nitrogen-containing compound is urea, and the silicon particles are a combination of elemental silicon particles and SiOx particles.

[0017] Furthermore, the preset mass ratio H is set to 1 / 3≤H≤1 / 2, the mass ratio of the PAN addition amount to the silicon particles is set to H1, and H1=G / G1, 1 / 4≤H1≤1.

[0018] Furthermore, the present invention also provides a structure for a partially double-coated silicon anode material, comprising,

[0019] Nano-sized silicon;

[0020] The first coating layer is made of a loosely structured g-C3N4 material, and the first coating layer partially coats the nano-silicon;

[0021] The second coating layer is made of elastic, dense c-PAN. The second coating layer is connected to the first coating layer by hydrogen bonds, and the second coating layer is chemically bonded to the nano-silicon not covered by the first coating layer by SiN bonds.

[0022] Specifically, the mass ratio of the first coating layer is set to H2, where 5% ≤ H2 ≤ 20%, and the mass ratio of the first coating layer is defined as the percentage of the mass of the first coating layer to the total mass of the partially double-coated silicon anode material. The mass ratio of the second coating layer is set to H3, where 10% ≤ H3 ≤ 30%, and the mass ratio of the second coating layer is defined as the percentage of the mass of the second coating layer to the total mass of the partially double-coated silicon anode material.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: In step S1, silicon particles and nitrogen-containing compounds are ball-milled and mixed under a preset mass ratio H to generate a stress buffering effect, thereby improving the conductivity of the silicon anode material. After obtaining the mixture, in step S2, the mixture is transferred to a vacuum tube furnace for heat treatment to obtain a heat-treated product, thereby achieving more uniform mixing and obtaining more active sites, further improving the conductivity of the silicon anode material. In step S3, the heat-treated product is dissolved in N,N-dimethylformamide, and G grams of PAN are added and stirred to obtain a solid content of a preset solid content M. The slurry is used to optimize the structural stability of the material, thereby further improving the conductivity of the silicon anode material. In step S4, the slurry is uniformly coated on Cu foil and the coated electrode is transferred to a vacuum tube furnace for heating. After heating, it is cooled with the furnace to obtain a partially double-coated silicon anode. This makes the outer PAN elastic after heat treatment cyclization, effectively alleviating the volume expansion of the material and acting as a binder. No additional additives are needed, thereby improving the conductivity and mechanical strength of the silicon anode material, optimizing the cycle performance and electronic conduction of the silicon anode material, and avoiding the use of binders, thus reducing the capacity loss caused by the use of binders.

[0024] In particular, in step S1, a first preset weight G1 of micron-sized silicon powder and a second preset weight G2 of urea are weighed and ball-milled together at a preset rotation speed N under the condition that the mass ratio of silicon particles to nitrogen-containing compounds is a preset mass ratio H, in order to generate a buffer stress effect and thereby improve the conductivity of the silicon anode material.

[0025] In particular, step S2 involves transferring the mixture to a vacuum tube furnace, heating it to a first preset temperature F1 at a first preset heating rate C1 under an argon atmosphere, and holding it thereafter. After a first preset time T1, a heat-treated product is obtained, thereby achieving a more uniform mixing of the mixture and obtaining more active sites, further improving the conductivity of the silicon anode material.

[0026] In particular, in step S3, the heat-treated product is dissolved in N,N-dimethylformamide and placed in a heating stirrer with a preset amount of PAN (G) added. The mixture is then heated and stirred until it becomes a slurry with a preset solid content (M). This gives the silicon anode material its own viscosity, eliminating the need for a binder and thus reducing the capacity loss of the electrode.

[0027] In particular, step S4 involves uniformly coating the slurry onto the Cu foil and transferring the coated electrode to a vacuum tube furnace for heat preservation under an inert gas atmosphere. The electrode is then cooled in the furnace to obtain a partially double-coated silicon anode. This allows the outer PAN layer to become elastic after heat treatment and cyclization, effectively mitigating the volume expansion of the material. This improves the conductivity and mechanical strength of the silicon anode material, and optimizes its cycle performance and electronic conductivity. Attached Figure Description

[0028] Figure 1 This is a schematic diagram illustrating the preparation method of part of the double-coated silicon anode material in this embodiment;

[0029] Figure 2 This is a schematic diagram of the structure of a partially double-coated silicon anode material in this embodiment. Detailed Implementation

[0030] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0031] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0032] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0033] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0034] Please see Figure 1 As shown, this is a partial method for preparing double-coated silicon anode materials in this embodiment. The method includes,

[0035] Step S1: The silicon particles and nitrogen-containing compound are ball-milled and mixed at a preset mass ratio H to obtain a mixture;

[0036] Step S2: The mixture is transferred to a vacuum tube furnace for heat treatment to obtain a heat-treated product;

[0037] Step S3: Dissolve the heat-treated product in N,N-dimethylformamide, add G grams of PAN and stir to obtain a slurry with a solid content of M;

[0038] Step S4: The slurry is uniformly coated on the Cu foil, and the coated electrode is transferred to a vacuum tube furnace for heating. The heated electrode is cooled with the furnace to obtain a partially double-coated silicon anode. The electrode refers to the Cu foil after being coated with the slurry.

[0039] Specifically, in step S1, silicon particles and a nitrogen-containing compound are ball-milled and mixed at a preset mass ratio H to generate a stress-buffering effect, thereby improving the conductivity of the silicon anode material. After obtaining the mixture, in step S2, the mixture is transferred to a vacuum tube furnace for heat treatment to obtain a heat-treated product, thereby achieving more uniform mixing and obtaining more active sites, further improving the conductivity of the silicon anode material. In step S3, the heat-treated product is dissolved in N,N-dimethylformamide, and a preset amount of PAN (G) is added and stirred to obtain a slurry with a preset solid content (M). To optimize the structural stability of the material and further improve the conductivity of the silicon anode material, step S4 involves uniformly coating the slurry onto the Cu foil and transferring the coated electrode to a vacuum tube furnace for heating. After heating, the electrode is cooled with the furnace to obtain a partially double-coated silicon anode. This allows the outer PAN layer to become elastic after heat treatment and cyclization, effectively mitigating the volume expansion of the material and acting as a binder without the need for additional additives. This improves the conductivity and mechanical strength of the silicon anode material, optimizes its cycle performance and electronic conductivity, and avoids the use of binders, reducing capacity loss caused by the use of binders.

[0040] Specifically, in step S1, silicon particles with a mass of G1 and a nitrogen-containing compound with a mass of G2 are weighed and placed together in a ball mill for ball milling. The ratio of G1 to G2 is set to H, and the rotational speed of the ball mill is N. After a time of T4, a mixture is obtained. Here, G1 is a first preset weight in grams, G2 is a second preset weight in grams, H is a preset mass ratio, and N is a preset rotational speed. In this embodiment, G1 = 0.2g, G2 = 0.5g, N = 500rpm, and T4 = 4h.

[0041] Specifically, in step S1, a first preset weight G1 of micron-sized silicon powder and a second preset weight G2 of urea are weighed and ball-milled together at a preset rotation speed N under the condition that the mass ratio of silicon particles to nitrogen-containing compounds is a preset mass ratio H, in order to generate a buffer stress effect and thereby improve the conductivity of the silicon anode material.

[0042] Specifically, in step S2, when the mixture is kept at a certain temperature, an inert gas is added to a vacuum tube furnace, and the vacuum tube furnace is heated to a temperature F1 at a heating rate C1 to keep the mixture at a certain temperature. After holding at a certain temperature for a time T1, a heat-treated product is obtained. Here, C1 is a first preset heating rate, F1 is a first preset temperature, and T1 is a first preset time. In this embodiment, C1 = 5℃ / min, F1 = 500℃, and T1 = 6h.

[0043] Specifically, in step S2, the mixture is transferred to a vacuum tube furnace and heated to a first preset temperature F1 at a first preset heating rate C1 under an argon atmosphere. After holding at this temperature for a first preset time T1, a heat-treated product is obtained. This process achieves a more uniform mixing of the mixture and obtains more active sites, thereby further improving the conductivity of the silicon anode material.

[0044] Specifically, in step S3, the heat-treated product and the N,N-dimethylformamide are placed in a heating stirrer with a volume of V. The heating stirrer is used to stir at a temperature of F2. When the stirring time reaches T2, PAN is added, and the stirring continues at a temperature of F2 until a slurry with a solid content of M is formed. Here, V is a preset volume, F2 is a second preset temperature, T2 is a second preset time, and G is a preset weight in grams. In this embodiment, V = 10 mL, F2 = 70 °C, T2 = 5 min, and M = 45%.

[0045] Specifically, in step S3, the heat-treated product is dissolved in N,N-dimethylformamide and placed in a heating stirrer. A preset amount of PAN (G) is added, and the mixture is heated and stirred until it becomes a slurry with a preset solid content (M). This gives the silicon anode material its own viscosity, eliminating the need for a binder and reducing the capacity loss of the electrode. PAN refers to polyacrylonitrile, a nitrogen-containing polymer. When PAN is heated at 300-500°C in an inert atmosphere, a typical cyclization reaction occurs to generate cyclized PAN (c-PAN). c-PAN is elastic and has good mechanical properties. During the cyclization process, chemical bonds are broken, and PAN easily forms chemical bonds with other components, further enhancing the bonding force between the components. PAN has a certain viscosity and can act as a binder, making the electrode material and the current collector tightly bonded.

[0046] Specifically, in step S4, when heating the coated electrode, an inert gas is added to the vacuum tube furnace, and the vacuum tube furnace is heated to temperature F3 at a rate C2. After holding at this temperature for a time T3, it is cooled with the furnace to obtain a partially double-coated silicon anode. The inert gas is argon. C2 is the second preset heating rate, F3 is the third preset temperature, and T3 is the third preset time. In this embodiment, C2 = 5℃ / min, F3 = 400℃, and T3 = 2h.

[0047] Specifically, in step S4, the slurry is uniformly coated onto the Cu foil, and the coated electrode is transferred to a vacuum tube furnace. It is kept at a constant temperature under an inert gas atmosphere and cooled with the furnace to obtain a partially double-coated silicon anode. This makes the outer PAN elastic after heat treatment and cyclization, effectively alleviating the volume expansion of the material, thereby improving the conductivity and mechanical strength of the silicon anode material, and optimizing the cycle performance and electronic conductivity of the silicon anode material.

[0048] Specifically, the heat treatment product is a single-layer Si@g-C3N4 coating.

[0049] Specifically, the partially double-coated silicon anode is a Si@g-C3N4@c-PAN electrode.

[0050] Specifically, the nitrogen-containing compound is urea, and the silicon particles are a combination of elemental silicon particles and SiOx particles.

[0051] Specifically, the mass ratio of the silicon particles to the nitrogen-containing compound is set to a preset mass ratio H, where H = G1 / G2, 1 / 3 ≤ H ≤ 1 / 2, and the preset mass ratio of the PAN addition amount to the silicon particles is set to H1 = G / G1, 1 / 4 ≤ H1 ≤ 1. The inert gas is argon.

[0052] Specifically, this embodiment does not specifically limit the types of nitrogen-containing compounds. Those skilled in the art can freely set them according to actual needs, such as setting the nitrogen-containing compound to one or more of urea, melamine, and thiourea.

[0053] Specifically, this embodiment does not specifically limit the type of silicon particles. Those skilled in the art can freely set them according to actual needs, such as any one or at least a combination of elemental silicon particles or SiOx particles.

[0054] Specifically, this embodiment does not impose a specific limitation on the preset mass ratio H of silicon particles to nitrogen-containing compounds. Those skilled in the art can freely set it according to actual needs, such as setting 1 / 5≤H≤1.

[0055] Specifically, this embodiment does not impose a specific limit on the preset mass ratio of PAN addition to silicon particles. Those skilled in the art can freely set it according to actual needs, such as setting 1 / 10≤H1≤1.

[0056] Specifically, this embodiment does not limit the type of inert gas. Those skilled in the art can freely set it according to actual needs, such as setting the nitrogen-containing compound as nitrogen, helium, argon and neon, etc.

[0057] Please see Figure 2 As shown, this is the structure of a partially double-coated silicon anode material in this embodiment. The structure includes,

[0058] Nanoscale silicon 1, located in the core of the material, involves nanoscaleping of bulk silicon particles to improve electrical conductivity;

[0059] The first coating layer 2, made of loosely structured g-C3N4, is partially coated and connected to the nano-silicon 1 to provide a buffer space and conductive network for silicon expansion.

[0060] The second coating layer 3 is made of elastic, dense c-PAN and is connected to the first coating layer by hydrogen bonds. The part of the first coating layer 2 that is not coated with nano-silicon 1 is chemically bonded to nano-silicon 1 by SiN bonds, which improves the overall mechanical strength and reduces the direct contact between the silicon core and the electrolyte.

[0061] Wherein, the mass ratio of the first coating layer is set to H2, 5% ≤ H2 ≤ 20%, where the mass ratio of the first coating layer refers to the percentage of the mass of the first coating layer to the total mass of the partially double-coated silicon anode material; and the mass ratio of the second coating layer is set to H3, 10% ≤ H3 ≤ 30%, where the mass ratio of the second coating layer refers to the percentage of the mass of the second coating layer to the total mass of the partially double-coated silicon anode material.

[0062] Specifically, the implementation method of some of the double-coated silicon anode materials in this embodiment is as follows:

[0063] Example 1:

[0064] The preparation of partially double-coated silicon anode materials includes the following steps:

[0065] (1) Weigh 0.2g of micron-sized silicon powder and 0.5g of urea and ball mill them together in a ball mill at a speed of 500rpm. After 4 hours, a mixture is obtained.

[0066] (2) The mixture was transferred to a vacuum tube furnace and heated to 500°C at a heating rate of 5°C / min under an argon atmosphere. The temperature was then maintained for 6 hours to obtain the heat-treated product.

[0067] (3) Dissolve the heat-treated product in 10 ml of DMF, heat and stir at 70°C for 5 min, add 0.1 g of PAN, and continue heating and stirring until the mixture becomes a slurry;

[0068] (4) Use a scraper to evenly coat the slurry onto the copper foil, transfer the coated electrode to a vacuum tube furnace, and heat the vacuum tube furnace to 400°C at a heating rate of 5°C / min under an argon atmosphere and hold for 2 hours. After holding, cool with the furnace to obtain a partially double-coated silicon anode material.

[0069] Example 2:

[0070] The preparation of a partially double-coated silicon anode includes the following steps:

[0071] (1) Weigh 0.2g of micron-sized silicon powder and 0.4g of urea and ball mill them together in a ball mill at a speed of 500rpm. After 4 hours, a mixture is obtained.

[0072] (2) Transfer the ball-milled powder to a vacuum tube furnace, heat the vacuum tube furnace to 500°C at a heating rate of 5°C / min under an argon atmosphere, and hold for 6 hours to obtain the heat-treated product.

[0073] (3) Dissolve the heat-treated product in 10 ml of DMF, heat and stir at 70°C for 5 min, add 0.1 g of PAN and continue heating and stirring until the mixture becomes a slurry;

[0074] (4) Use a scraper to evenly coat the slurry onto the copper foil, transfer the coated electrode to a vacuum tube furnace, and heat the vacuum tube furnace to 400°C at a heating rate of 5°C / min under an argon atmosphere for 2 hours; then cool it with the furnace. The resulting electrode is the partially double-coated silicon anode prepared.

[0075] Example 3:

[0076] The preparation of a partially double-coated silicon anode includes the following steps:

[0077] (1) Weigh 0.2g of micron-sized silicon powder and 0.6g of urea and ball mill them together in a ball mill at a speed of 500rpm. After 4 hours, a mixture is obtained.

[0078] (2) Transfer the ball-milled powder to a vacuum tube furnace, heat the vacuum tube furnace to 500°C at a heating rate of 5°C / min under an argon atmosphere, and hold for 6 hours to obtain the heat-treated product.

[0079] (3) Dissolve the heat-treated product in 10 ml of DMF, heat and stir at 70°C for 5 min, add 0.1 g of PAN, and continue heating and stirring until the mixture becomes a slurry;

[0080] (4) Use a scraper to evenly coat the slurry onto the copper foil, transfer the coated electrode to a vacuum tube furnace, and heat the vacuum tube furnace to 400°C at a heating rate of 5°C / min under an argon atmosphere for 2 hours; then cool it with the furnace. The resulting electrode is the partially double-coated silicon anode prepared.

[0081] Example 4:

[0082] The preparation of a partially double-coated silicon anode includes the following steps:

[0083] (1) Weigh 0.2g of micron-sized silicon powder and 0.5g of urea and ball mill them together in a ball mill at a speed of 500rpm. After 4 hours, a mixture is obtained.

[0084] (2) The mixture was transferred to a vacuum tube furnace and heated to 500°C at a heating rate of 5°C / min under an argon atmosphere. The temperature was then maintained for 6 hours to obtain the heat-treated product.

[0085] (3) Dissolve the heat-treated product in 10 ml of DMF, heat and stir at 70°C for 5 min, add 0.05 g of PAN, and continue heating and stirring until the mixture becomes a slurry;

[0086] (4) Use a scraper to evenly coat the slurry onto the copper foil, transfer the coated electrode to a vacuum tube furnace, and heat the vacuum tube furnace to 400°C at a heating rate of 5°C / min under an argon atmosphere for 2 hours; then cool it with the furnace. The resulting electrode is the partially double-coated silicon anode prepared.

[0087] Example 5:

[0088] The preparation of a partially double-coated silicon anode includes the following steps:

[0089] (1) Weigh 0.2g of micron-sized silicon powder and 0.5g of urea and ball mill them together in a ball mill at a speed of 500rpm. After 4 hours, a mixture is obtained.

[0090] (2) The mixture was transferred to a vacuum tube furnace and heated to 500°C at a heating rate of 5°C / min under an argon atmosphere. The temperature was then maintained for 6 hours to obtain the heat-treated product.

[0091] (3) Dissolve the heat-treated product in 10 ml of DMF, heat and stir at 70°C for 5 min, add 0.2 g of PAN, and continue heating and stirring until the mixture becomes a slurry;

[0092] (4) Use a scraper to evenly coat the slurry onto the copper foil, transfer the coated electrode to a vacuum tube furnace, and heat the vacuum tube furnace to 400°C and hold it for 2 hours at a heating rate of 5°C / min under an argon atmosphere; then cool it with the furnace, and the resulting electrode is the partially double-coated silicon anode prepared.

[0093] Specifically, the existing methods for preparing silicon anode materials are as follows:

[0094] Example 6:

[0095] The preparation of pure silicon electrode materials includes the following steps:

[0096] (1) Weigh 0.2g of micron-sized silicon powder and ball mill it in a ball mill at a speed of 500rpm for 4h;

[0097] (2) Transfer the ball-milled powder to a vacuum tube furnace and heat the vacuum tube furnace to 500°C at a heating rate of 5°C / min, and hold for 6 hours.

[0098] (3) The above materials, acetylene black and polyvinylidene fluoride (PVDF) are made into a slurry in a mass ratio of 80:10:10 and coated on copper foil and dried. The resulting electrode is the negative electrode of Example 6.

[0099] Example 7:

[0100] The preparation of Si@g-C3N4 composite electrode material includes the following steps:

[0101] (1) Weigh 0.2g of micron-sized silicon powder and 0.5g of urea and ball mill them together in a ball mill at a speed of 500rpm for 4h;

[0102] (2) Transfer the ball-milled powder to a vacuum tube furnace and heat the vacuum tube furnace to 500°C at a heating rate of 5°C / min, and hold for 6 hours.

[0103] (3) The above materials, acetylene black and polyvinylidene fluoride (PVDF) are made into a slurry in a mass ratio of 80:10:10 and coated on copper foil and dried. The resulting electrode is the negative electrode of Example 7.

[0104] Example 8:

[0105] The preparation of Si@PAN composite electrode material includes the following steps:

[0106] (1) Weigh 0.2g of micron-sized silicon powder and ball mill it in a ball mill at a speed of 500rpm for 4h.

[0107] (2) Transfer the ball-milled powder to a vacuum tube furnace and heat the vacuum tube furnace to 500°C at a heating rate of 5°C / min, and hold for 6 hours.

[0108] The heat-treated powder was transferred to a beaker and dissolved in 10 ml of DMF. The mixture was heated and stirred at 70°C for 5 min, and then 0.1 g of PAN was added. The mixture was heated and stirred until it became a slurry.

[0109] (3) Use a scraper to evenly coat the slurry onto the copper foil, transfer the coated electrode to a vacuum tube furnace, argon atmosphere, set the heating program to a heating rate of 5℃ / min to heat the vacuum tube furnace to 400℃ and hold for 2h; then cool with the furnace, the resulting electrode is the partially double-coated silicon anode prepared.

[0110] Specifically, the experimental data of this embodiment are compared with those of the prior art as follows:

[0111]

[0112]

[0113] Specifically, the experimental data shows that the capacity retention rate after 50 cycles in Examples 1-5 is higher than that in Examples 6-7. The method for preparing partially double-coated silicon anode materials in this example is superior to the method for preparing partially double-coated silicon anode materials in the prior art.

[0114] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a partially double-coated silicon anode material, characterized in that, include, Step S1: The silicon particles and nitrogen-containing compound are ball-milled and mixed at a preset mass ratio H to obtain a mixture; Step S2: The mixture is transferred to a vacuum tube furnace for heat treatment to obtain a heat-treated product; Step S3: Dissolve the heat-treated product in N,N-dimethylformamide, add G grams of PAN and stir to obtain a slurry with a solid content of M; Step S4: The slurry is uniformly coated on the Cu foil, and the coated electrode is transferred to a vacuum tube furnace for heating. The heated electrode is cooled with the furnace to obtain a partially double-coated silicon anode. In step S1, silicon particles with a mass of G1 and nitrogen-containing compound with a mass of G2 are weighed and placed together in a ball mill for ball milling. G1 / G2=H is set, and the rotational speed of the ball mill is N. After time T4, a mixture is obtained. In step S2, when the mixture is kept at a certain temperature, an inert gas is added to the vacuum tube furnace, and the vacuum tube furnace is heated to a temperature F1 at a heating rate C1 to keep the mixture at a certain temperature. After keeping the mixture at a certain temperature for a time T1, the heat-treated product is obtained. In step S4, when heating the coated electrode, an inert gas is added to the vacuum tube furnace, the vacuum tube furnace is heated to temperature F3 at a rate C2, and then cooled with the furnace after holding at temperature T3, to obtain a partially double-coated silicon anode. The inert gas is argon. The preset mass ratio H is set to 1 / 3≤H≤1 / 2, and the mass ratio of the PAN addition amount to the silicon particles is set to H1, where H1=G / G1, and 1 / 4≤H1≤1.

2. The method for preparing partially double-coated silicon anode material according to claim 1, characterized in that, In step S3, the heat-treated product and the N,N-dimethylformamide are placed in a heating stirrer with a volume of V. The heating stirrer is used to stir at a temperature of F2. When the stirring time reaches T2, PAN is added, and the stirring continues at a temperature of F2 until a slurry with a solid content of M is formed.

3. The method for preparing partially double-coated silicon anode material according to claim 1, characterized in that, The heat-treated product is a single-layer Si@g-C3N4 coating.

4. The method for preparing partially double-coated silicon anode material according to claim 1, characterized in that, The partially double-coated silicon anode is a Si@g-C3N4@c-PAN electrode.

5. The method for preparing partially double-coated silicon anode material according to claim 1, characterized in that, The nitrogen-containing compound is urea, and the silicon particles are a combination of elemental silicon particles and SiOx particles.

6. A partially double-coated silicon anode material prepared by the preparation method according to any one of claims 1-5, characterized in that, include, Nano-sized silicon; The first coating layer is made of a loosely structured g-C3N4 material, and the first coating layer partially coats the nano-silicon; The second coating layer is made of elastic, dense c-PAN. The second coating layer is connected to the first coating layer by hydrogen bonds, and the second coating layer is chemically bonded to the nano-sized silicon not coated by the first coating layer by Si-N bonds. Specifically, the mass ratio of the first coating layer is set to H2, where 5% ≤ H2 ≤ 20%, and the mass ratio of the first coating layer is defined as the percentage of the mass of the first coating layer to the total mass of the partially double-coated silicon anode material. The mass ratio of the second coating layer is set to H3, where 10% ≤ H3 ≤ 30%, and the mass ratio of the second coating layer is defined as the percentage of the mass of the second coating layer to the total mass of the partially double-coated silicon anode material.

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