Silicon-carbon negative electrode material, preparation method thereof and application

Abstract

The present invention relates to a silicon-carbon negative electrode material, a preparation method thereof, and an application thereof. The preparation method includes: a. Mixing a first carbon source with a surface modifier and a solvent to obtain a spinning solution; b. Using an electrospinning process to form the spinning solution into a fiber membrane; c. Sealing the pore structure in the fiber membrane with a second carbon source, and then performing carbonization to obtain a carbon layer, wherein the purity of the first carbon source is less than that of the second carbon source; d. Taking steps b and c as one cycle, using the carbon layer as a collection device for electrospinning to perform multiple cycles to obtain an intermediate with at least two carbon layer structures; e. Under the condition of a gaseous carbon source, performing heat treatment on the intermediate to obtain a layered porous carbon material; f. Performing silicon deposition on the layered porous carbon material to obtain a silicon-carbon negative electrode material. The preparation method of the present invention can not only directionally regulate the distribution and size of the pore structure, improve the stability of the pore structure, but also significantly reduce the resistivity of the layered porous carbon material.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a silicon-carbon negative electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] In the field of energy storage, lithium-ion batteries have broad application prospects and demands. In traditional lithium-ion battery systems, graphite is usually used as the main negative electrode material. However, the theoretical specific capacity of graphite is relatively low, making it difficult to meet the performance requirements of the market for lithium-ion batteries with high energy density. Although silicon-based materials have a high theoretical specific capacity, silicon-based materials have performance defects such as poor conductivity. By compounding silicon-based materials with porous carbon materials, their electrical properties can be effectively improved.

[0003] Traditional porous carbon materials can be prepared by the template method or electrospinning method. Among them, the preparation process of the template method is complex, costly, and has a small output, while the electrospinning method has simple equipment, convenient operation, and low cost. The fiber diameter and length can be efficiently controlled by adjusting the electrospinning parameters, and then through carbonization treatment, porous carbon materials can be obtained. However, the pore structure of the porous carbon materials prepared by the electrospinning method is unevenly distributed, with relatively large pore structures. The utilization rate of the pore structure is low during the chemical vapor deposition process, and uneven deposition of nano-silicon is likely to occur, thereby affecting the composite effect of the silicon-based material and the porous carbon material, resulting in insufficient electrochemical properties such as specific capacity and cycle stability. Summary of the Invention

[0004] Based on this, it is necessary to provide a silicon-carbon negative electrode material, a preparation method thereof, and an application thereof in view of the above problems. The preparation method prepares a porous carbon substrate material with a uniform pore structure, directionally regulates the distribution and size of the pore structure, improves the stability of the pore structure, enables the porous carbon material and the silicon material to achieve a good combination, reduces the resistivity of the layered porous carbon material, and thus obtains a lithium-ion battery negative electrode material with both high initial efficiency, high capacity, and excellent cycle stability.

[0005] A preparation method of a silicon-carbon negative electrode material includes the following steps:

[0006] a. Mix a first carbon source with a surface modifier and a solvent to obtain a spinning solution;

[0007] b. Use the electrospinning process to make the spinning solution into a fiber membrane;

[0008] c. Block the pore structure in the fiber membrane with a second carbon source, and then perform carbonization to obtain a carbon layer, where the purity of the first carbon source is less than the purity of the second carbon source;

[0009] d. Take steps b and c as a cycle, and use the carbon layer as the collection device for electrospinning for multiple cycles to obtain an intermediate with at least two carbon layer structures;

[0010] e. Under the condition of a gaseous carbon source, heat-treat the intermediate to obtain a layered porous carbon material;

[0011] f. Perform silicon deposition on the layered porous carbon material to obtain a silicon-carbon negative electrode material.

[0012] In one embodiment, the first carbon source is selected from natural polymer materials, and the second carbon source is selected from synthetic organic materials.

[0013] In one embodiment, step a satisfies at least one of the following conditions:

[0014] (1) The mass fraction of the first carbon source in the spinning solution is 3% - 15%;

[0015] (2) The first carbon source is selected from at least one of chitosan, natural cellulose, hyaluronic acid, gelatin, sodium alginate, collagen, and chitin;

[0016] (3) The mass fraction of the surface modifier in the spinning solution is 0.1% - 2%;

[0017] (4) The surface modifier contains at least one element of P, S, and metal elements.

[0018] In one embodiment, the surface modifier is selected from at least one of sodium stearate, zinc stearate, calcium stearate, sodium alkylbenzene sulfonate, sodium lauryl polyether sulfate, calcium lauryl polyether sulfate, trialkyl phosphite, and sodium didodecyl phosphate.

[0019] In one embodiment, the electrospinning process satisfies at least one of the following conditions:

[0020] (1) The viscosity of the spinning solution is 1 Pa·s - 3 Pa·s;

[0021] (2) The flow rate of the spinning solution is 0.5 mL / min - 10 mL / min;

[0022] (3) The electrospinning voltage is 15 kV - 35 kV.

[0023] In one embodiment, the fiber membrane satisfies at least one of the following conditions:

[0024] (1) The pore diameter of the pore structure in the fiber membrane is greater than or equal to 100 nm;

[0025] (2) The thickness of the fiber membrane is less than or equal to 0.5 μm.

[0026] In one embodiment, step c satisfies at least one of the following conditions:

[0027] (1) The mass of the second carbon source is 0.1%-5% of the mass of the fiber membrane;

[0028] (2) The second carbon source is selected from at least one of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, benzene, toluene, and xylene;

[0029] (3) The carbonization temperature is 500°C - 1000°C, and the time is 2h - 8h.

[0030] In one embodiment, step e satisfies at least one of the following conditions:

[0031] (1) The gaseous carbon source is selected from at least one of methane, acetylene, ethylene, and propane;

[0032] (2) The heat treatment temperature is 700°C - 950°C, and the time is 2h - 15h.

[0033] In one embodiment, the layered porous carbon material satisfies at least one of the following conditions:

[0034] (1) The specific surface area is 1200 m 2 / g - 2400 m 2 / g;

[0035] (2) The pore volume is 0.5 cm 3 / g - 1.8 cm 3 / g;

[0036] (3) The resistivity is less than or equal to 0.05 Ω·m.

[0037] In one embodiment, after the silicon deposition, a coating treatment is further included.

[0038] In the preparation method of the present invention, first, an electrospinning method is used to make a fibrous membrane in a wire mesh shape from a first carbon source with a relatively low purity, and then a second carbon source with a relatively high purity is used to block and carbonize the macropores in the fibrous membrane. On the one hand, a large amount of impurity components in the first carbon source volatilize, which is beneficial to the formation of defective active sites and improves the electrical performance. On the other hand, the second carbon source is in-situ pyrolyzed into a carbon material, so that the pore structure can be directionally regulated by controlling the content of the second carbon source. Not only can the macropores be changed into micro-mesopores, which is beneficial to precisely regulating the proportion of micro-mesopores, but also the pore structure is uniformly distributed, the pore size is relatively uniform, the pore structure is stable and not easy to collapse, and the specific surface area is large. At the same time, the gaseous carbon source is pyrolyzed into carbon and deposited on the intermediate body, which can further improve the conductivity of the surface of the layered porous carbon material, is beneficial to reducing the internal resistance, and improving the ionic conductivity.

[0039] Therefore, the preparation method of the present invention uses three different carbon sources, which can not only realize the directional regulation of the distribution and size of the pore structure, improve the stability of the pore structure, but also significantly reduce the resistivity of the layered porous carbon material. Using the prepared silicon-carbon negative electrode material in a battery is beneficial to improving the electrical performance.

[0040] A silicon-carbon negative electrode material prepared by the preparation method of the silicon-carbon negative electrode material as described above, including the layered porous carbon material and silicon loaded in the layered porous carbon material.

[0041] In one embodiment, the mass fraction of silicon in the silicon-carbon negative electrode material is 45%-55%.

[0042] In one embodiment, the silicon-carbon negative electrode material further includes a carbon coating layer.

[0043] In one embodiment, the mass fraction of the carbon coating layer in the silicon-carbon negative electrode material is 4%-5%.

[0044] In one embodiment, the silicon-carbon negative electrode material satisfies at least one of the following conditions:

[0045] (1) The reversible specific capacity cycle is greater than 1800 mAh / g;

[0046] (2) The first Coulomb efficiency is higher than 90%;

[0047] (3) The 500-cycle stability is higher than 85%;

[0048] (4) The resistivity is lower than 4.1 Ω·m.

[0049] A negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer contains the silicon-carbon negative electrode material as described above.

[0050] A battery includes the negative electrode sheet as described above.

[0051] In the silicon-carbon negative electrode material prepared by the preparation method of the present invention, the layered porous carbon material not only has abundant active sites and good ion and electron transport capabilities, making the resistivity less than or equal to 0.05 Ω·m, but also has an excellent pore structure, with a specific surface area of 1200 m 2 / g - 2400 m 2 / g, and a pore volume of 0.5 cm 3 / g - 1.8 cm 3 / g. When preparing the silicon-carbon negative electrode material, it can adsorb the silicon source gas more uniformly, so that the prepared silicon-carbon negative electrode material has excellent electrochemical performance when used in a battery, with a reversible specific capacity greater than 1800 mAh / g, a first Coulomb efficiency higher than 90%, and up to about 93% at most; it has excellent cycle stability, with a 500-cycle stability higher than 85%, and up to 90% at most; it has a low resistivity below 4.1 Ω·m. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a process schematic diagram of the preparation method of the silicon-carbon negative electrode material of the present invention;

[0053] Figure 2 It is a scanning electron microscope image of the fiber membrane prepared in Example 1;

[0054] Figure 3 It is a scanning electron microscope image of the carbon layer prepared in Example 1;

[0055] Figure 4 It is a pore size distribution diagram, where A is the pore size distribution diagram of the carbon layer prepared in Example 1, B is the pore size distribution diagram of the carbon layer prepared in Example 2, and C is the pore size distribution diagram of the carbon layer prepared in Example 3. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0056] For the convenience of understanding the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure content of the present invention more thorough and comprehensive.

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments or examples and are not intended to limit the present invention.

[0058] The present invention provides a preparation method of a silicon-carbon negative electrode material. First, a layered porous carbon material is prepared, and then the layered porous carbon material is subjected to silicon deposition to obtain the silicon-carbon negative electrode material. Specifically, in combination withFigure 1 As shown, it includes the following steps:

[0059] a. Mix the first carbon source with a surface modifier and a solvent to obtain a spinning solution;

[0060] b. Use the electrospinning process to make the spinning solution into a fiber membrane;

[0061] c. Block the pore structure in the fiber membrane with a second carbon source, and then perform carbonization to obtain a carbon layer, wherein the purity of the first carbon source is less than the purity of the second carbon source;

[0062] d. Take steps b and c as one cycle, and use the carbon layer as the collection device for electrospinning for multiple cycles to obtain an intermediate with at least two carbon layer structures;

[0063] e. Under the condition of a gaseous carbon source, perform heat treatment on the intermediate to obtain a layered porous carbon material;

[0064] f. Perform silicon deposition on the layered porous carbon material to obtain a silicon-carbon negative electrode material.

[0065] The carbon source includes natural polymer materials, synthetic organic materials, fossil fuels, etc. Among them, natural polymer materials have a wide source, relatively complex monomers, low purity, and many impurities, and the cost as a carbon source is relatively low; synthetic organic materials have high purity and few impurities, and high stability as a carbon source. It should be noted that this carbon source belongs to a non-gaseous carbon source.

[0066] In step a, it is preferable to use a natural polymer material as the first carbon source to prepare the fiber membrane. In the subsequent carbonization process, due to the low purity, the volatilization of a large number of impurity components will form defective active sites, which is beneficial to improving the electrochemical performance of the layered porous carbon material.

[0067] Preferably, the mass fraction of the first carbon source in the spinning solution is 3% - 15%, and more preferably 5% - 10%.

[0068] Optionally, the first carbon source is selected from at least one of chitosan, natural cellulose, hyaluronic acid, gelatin, sodium alginate, collagen, and chitin.

[0069] Using a surface modifier can change the surface energy of the electrospun fibers, increase the hydrophobicity, reduce fiber agglomeration, and thus improve the dispersion performance of the fibers, which is beneficial to preparing a fibrous network membrane with a macroporous structure.

[0070] Preferably, the mass fraction of the surface modifier in the spinning solution is preferably 0.1% - 2%, and more preferably 0.5% - 1.5%.

[0071] Preferably, the surface modifier contains at least one element among P, S, and metal elements. The metal element is preferably at least one of Na, Ca, and Zn. Among them, the presence of P and S elements in the surface modifier can endow the layered porous carbon material with more active sites, and the presence of metal elements such as Na, Ca, and Zn in the surface modifier is conducive to providing ion exchange transport channels and improving ion transport ability.

[0072] Optionally, the surface modifier is selected from at least one of sodium stearate, zinc stearate, calcium stearate, sodium alkylbenzene sulfonate, sodium lauryl polyether sulfate, calcium lauryl polyether sulfate, trialkyl phosphite, and sodium didodecyl phosphate.

[0073] The solvent is preferably a solvent with low volatility and high flash point that can dissolve the polymer material. Specifically, the solvent includes but is not limited to at least one of hexafluoroisopropanol, chloroform, formic acid, methanesulfonic acid, and trifluoroacetic acid, and is preferably hexafluoroisopropanol.

[0074] In step b, the electrospinning process satisfies at least one of the following conditions:

[0075] (1) The viscosity of the spinning solution is 1 Pa·s - 3 Pa·s;

[0076] (2) The flow rate of the spinning solution is 0.5 mL / min - 10 mL / min;

[0077] (3) The spinning voltage is 15 kV - 35 kV.

[0078] By controlling the spinning parameters such as the viscosity, flow rate, and spinning voltage of the spinning solution in the electrospinning process, it is more conducive to regulating the formation of a larger pore structure with a pore size of more than 100 nm in the fiber membrane.

[0079] In one embodiment, the fiber membrane satisfies at least one of the following conditions:

[0080] (1) The pore diameter of the pore structure in the fiber membrane is greater than or equal to 100 nm;

[0081] (2) The thickness of the fiber membrane is less than or equal to 0.5 μm.

[0082] Preferably, the fiber membrane simultaneously satisfies that the pore diameter is greater than or equal to 100 nm and the thickness is less than or equal to 0.5 μm, which is more conducive to the subsequent second carbon source fully entering the pore structure and achieving an ideal plugging effect.

[0083] In step c, the macropores in the fiber membrane are filled with the second carbon source, and the second carbon source is in-situ pyrolyzed into a carbon material through carbonization, so as to directionally regulate the pore structure by controlling the content of the second carbon source. This not only turns the macropores into micro-mesopores, which is beneficial to precisely regulating the proportion of micro-mesopores, but also makes the pore structure evenly distributed, the pore size relatively uniform, the pore structure stable and not easy to collapse, and the specific surface area is relatively large.

[0084] Preferably, the second carbon source is selected from synthetic organic materials, and the synthetic organic materials have a high purity and basically no other impurities.

[0085] Optionally, the second carbon source is selected from at least one of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, benzene, toluene, and xylene.

[0086] Preferably, the mass of the second carbon source is 0.1%-5% of the mass of the fiber membrane, and more preferably 0.5%-3.5%.

[0087] Preferably, the temperature of the carbonization is 500°C - 1000°C, and more preferably 700°C - 900°C; the time is 2h - 8h, and more preferably 4h - 6h.

[0088] By controlling the dosage of the second carbon source as well as the carbonization temperature and time, it is more conducive to adjusting the carbon filling amount in the pore structure. This is not only beneficial to adjusting the distribution and size of the pore structure, so as to precisely regulate the proportion of micro-mesopores, but also beneficial to enhancing the binding effect between the second carbon source and the fiber membrane, and avoiding the carbonization and shedding of the second carbon source.

[0089] In step d, by using the carbon layer obtained by carbonization as the collecting device for electrospinning, the fiber membrane can be laminated on the surface of the carbon layer. Then, the pore structure in the fiber membrane laminated on the surface of the carbon layer is blocked and carbonized with the second carbon source, and a two-layer carbon layer structure can be obtained. Then, the two-layer carbon layer structure is used as the collecting device for electrospinning, and this process is cycled multiple times to stack and composite multiple carbon layers to form a layered structure, thereby obtaining an intermediate with at least two carbon layer structures. And by controlling the number of carbon layers, the thickness of the layered porous carbon material can be regulated, and thus the requirements of different products can be met.

[0090] It should be noted that the thickness of any two carbon layers in the intermediate can be the same or different, and the second carbon source used can be the same or different. The present invention does not limit this.

[0091] In step e, during the heat treatment process, the gaseous carbon source is pyrolyzed to form carbon and deposited on the intermediate to achieve the composite with the intermediate. This not only has little influence on the pore size of the layered porous carbon material, but also is beneficial to further improving the surface conductivity of the layered porous carbon material, reducing the internal resistance, and enhancing the ionic conductivity.

[0092] Preferably, the gaseous carbon source is selected from at least one of alkane gases, alkene gases or alkyne gases.

[0093] Optionally, the gaseous carbon source includes but is not limited to at least one of methane, acetylene, ethylene, propane.

[0094] Preferably, the temperature of the heat treatment is 700°C - 950°C, more preferably 850°C - 900°C; the time is 2h - 15h, more preferably 5h - 10h.

[0095] Preferably, the layered porous carbon material satisfies at least one of the following conditions:

[0096] (1) The specific surface area is 1200 m 2 / g - 2400 m 2 / g;

[0097] (2) The pore volume is 0.5 cm 3 / g - 1.8 cm 3 / g;

[0098] (3) The resistivity is less than or equal to 0.05 Ω·m.

[0099] The layered porous carbon material prepared by the preparation method of the present invention not only has rich active sites, has good ion and electron transport capabilities, making the resistivity less than or equal to 0.05 Ω·m, but also has an excellent pore structure, with a specific surface area of 1200 m 2 / g - 2400 m 2 / g, and a pore volume of 0.5 cm 3 / g - 1.8 cm 3 / g, and can adsorb the silicon source gas more uniformly when preparing the silicon-carbon negative electrode material.

[0100] In one embodiment, after the silicon deposition, a coating treatment is further included.

[0101] It should be noted that the present invention does not limit the methods of silicon deposition and coating treatment. Those skilled in the art can adopt conventional preparation processes such as silicon deposition, carbon coating, polymer coating, etc., and the present invention will not elaborate on this.

[0102] The present invention also provides a silicon-carbon negative electrode material prepared by the above-mentioned preparation method, including the layered porous carbon material and silicon loaded on the layered porous carbon material.

[0103] The silicon-carbon negative electrode material described in the present invention has excellent electrochemical performance when used in a battery, with a reversible specific capacity greater than 1800 mAh / g, an initial Coulombic efficiency higher than 90%, and up to about 93% at most. The 500-cycle stability is higher than 85%, and the resistivity is lower than 4.1 Ω·m.

[0104] Preferably, the mass fraction of silicon in the silicon-carbon negative electrode material is 45%-55%.

[0105] In one embodiment, the silicon-carbon negative electrode material further includes a carbon coating layer.

[0106] Preferably, the mass fraction of the carbon coating layer in the silicon-carbon negative electrode material is 4%-5%.

[0107] The present invention also provides a negative electrode plate. The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer contains the silicon-carbon negative electrode material as described above. It can be understood that the negative electrode active material layer may further include materials such as a binder, and the present invention does not limit this.

[0108] The present invention also provides a battery. The battery includes the negative electrode plate as described above. It can be understood that the battery further includes a positive electrode plate, a separator, and an electrolyte, and the present invention does not limit the positive electrode plate, the separator, and the electrolyte.

[0109] Hereinafter, the silicon-carbon negative electrode material, its preparation method, and application will be further described through the following specific examples.

[0110] Example 1

[0111] a. Dissolve 8 g of chitosan and 1 g of sodium alkylbenzenesulfonate in 80 g of hexafluoroisopropanol. After stirring evenly, a spinning solution is obtained.

[0112] b. At a flow rate of 5 mL / min, spray 20 mL of the spinning solution through a nozzle and deposit it on the surface of the collector under a voltage of 25 kV to form a fiber membrane with a thickness of about 0.5 μm. According to Figure 2 It can be known that the pore diameter of the pore structure in the fiber membrane is greater than or equal to 100 nm and is evenly distributed.

[0113] c. Mix the fiber membrane with carboxymethyl cellulose so that the pore structure in the fiber membrane is blocked by the carboxymethyl cellulose. Among them, the mass of the carboxymethyl cellulose is 3% of the mass of the fiber membrane. Then, under an inert atmosphere, carbonize at 850 °C for 6 h and then cool naturally to obtain a carbon layer containing micro-mesopores. According to Figure 3 It can be known that under a magnification of 5000 times, there are basically no obvious macropores.

[0114] d. Repeat steps b and c with the carbon layer as the spinning substrate to obtain a carbon layer with a two-layer structure.

[0115] e. Place the carbon layer with a two-layer structure in a CVD furnace, use acetylene as the carbon source, heat-treat it at 900 °C for 6 h and then cool it to obtain a layered porous carbon material. According to Figure 4 the pore size distribution diagram, the pore size of this layered porous carbon material is basically below 30 nm.

[0116] f. Place the layered porous carbon material in a CVD furnace. Under a nitrogen atmosphere, introduce silane gas into the deposition furnace at a flow rate of 3 L / min, keep the temperature of the deposition furnace at 500 °C, and continuously introduce gas until silicon deposition layers are continuously nucleated inside and on the surface of the layered porous carbon material. Keep the gas introduction time for 10 h to obtain a silicon-carbon material. After the silicon deposition is completed, introduce acetylene gas with a flow rate of 1 L / min under a nitrogen atmosphere, deposit at 900 °C for 2 h for carbon coating, and the carbon coating amount is 5 wt% (based on the product). After being dispersed, screened, and demagnetized, a silicon-carbon negative electrode material is obtained, wherein the mass fraction of silicon in the silicon-carbon negative electrode material is 51%.

[0117] Example 2

[0118] The difference between Example 2 and Example 1 is that toluene is used instead of carboxymethyl cellulose.

[0119] Example 3

[0120] The difference between Example 3 and Example 1 is that the mass of carboxymethyl cellulose is 5% of the mass of the fiber membrane.

[0121] Example 4

[0122] The difference between Example 4 and Example 1 is that the mass of carboxymethyl cellulose is 1% of the mass of the fiber membrane.

[0123] Example 5

[0124] The difference between Example 5 and Example 1 is that chitosan is replaced by gelatin.

[0125] Example 6

[0126] The difference between Example 6 and Example 1 is that sodium alkylbenzene sulfonate is replaced by trialkyl phosphite.

[0127] Example 7

[0128] a. Dissolve 4 g of natural cellulose and 1 g of sodium stearate in 50 g of hexafluoroisopropanol, stir evenly to obtain a spinning solution.

[0129] b. Spray 20 mL of the spinning solution through a nozzle at a flow rate of 6 mL / min, and deposit it on the surface of the collector under a voltage of 20 kV to form a fiber membrane with a thickness of about 0.4 μm.

[0130] c. Mix the fiber membrane with polyvinylidene fluoride so that the pore structure in the fiber membrane is blocked by carboxymethyl cellulose. Here, the mass of carboxymethyl cellulose is 3% of the mass of the fiber membrane. Then, under an inert atmosphere, carbonize at 700 °C for 8 h and then cool naturally to obtain a carbon layer containing micro-mesopores.

[0131] d. Use the carbon layer as the spinning substrate and repeat steps b and c to obtain a carbon layer with a three-layer structure.

[0132] e. Place the carbon layer with a three-layer structure in a CVD furnace, use ethylene as the carbon source, heat-treat at 800 °C for 10 h and then cool to obtain a layered porous carbon material.

[0133] The subsequent silicon deposition and carbon coating treatments are the same as those in Example 1.

[0134] Example 8

[0135] a. Dissolve 13 g of hyaluronic acid and 2 g of sodium lauryl polyether sulfate in 85 g of hexafluoroisopropanol, stir evenly to obtain a spinning solution.

[0136] b. Spray 20 mL of the spinning solution through a nozzle at a flow rate of 4 mL / min, and deposit it on the surface of the collector at a voltage of 15 kV to form a fiber membrane with a thickness of about 0.2 μm.

[0137] c. Mix the fiber membrane with polyvinyl alcohol so that the pore structure in the fiber membrane is blocked by carboxymethyl cellulose. Here, the mass of carboxymethyl cellulose is 3% of the mass of the fiber membrane. Then, under an inert atmosphere, carbonize at 950 °C for 4 h and then cool naturally to obtain a carbon layer containing micro-mesopores.

[0138] d. Use the carbon layer as the spinning substrate and repeat steps b and c to obtain a carbon layer with a five-layer structure.

[0139] e. Place the carbon layer with a five-layer structure in a CVD furnace, use propane as the carbon source, heat-treat at 950 °C for 4 h and then cool to obtain a layered porous carbon material.

[0140] The subsequent silicon deposition and carbon coating treatments are the same as those in Example 1.

[0141] Comparative Example 1

[0142] a. Dissolve 8 g of chitosan and 1 g of alkylbenzene sulfonate in 80 g of hexafluoroisopropanol, stir evenly to obtain a spinning solution.

[0143] b. Spray 20 mL of the spinning solution through a nozzle at a flow rate of 5 mL / min, and deposit it on the surface of the collector at a voltage of 25 kV to form a fiber membrane with a thickness of about 0.5 μm.

[0144] c. Under an inert atmosphere, the fiber membrane is carbonized at 850 °C for 6 h and then naturally cooled to obtain a carbon layer with macropores.

[0145] d. Using the carbon layer as the spinning substrate, repeat steps b and c to obtain a carbon layer with a two-layer structure.

[0146] e. Place the carbon layer with a two-layer structure in a CVD furnace, use acetylene as the carbon source, heat-treat it at 900 °C for 6 h and then cool it to obtain a layered porous carbon material.

[0147] The subsequent silicon deposition and carbon coating treatments are the same as those in Example 1.

[0148] Comparative Example 2

[0149] The difference between Comparative Example 2 and Example 1 is that the mass of carboxymethyl cellulose is 10% of the mass of the fiber membrane.

[0150] Comparative Example 3

[0151] The difference between Comparative Example 3 and Example 1 is that the heat treatment in step e is not carried out.

[0152] The layered porous carbon materials prepared in Examples 1-8 and Comparative Examples 1-3 are tested, and the results are shown in Table 1.

[0153] Table 1

[0154]

[0155]

[0156] Application Example

[0157] Assemble the silicon-carbon negative electrode materials prepared in Examples 1-8 and Comparative Examples 1-3 into batteries respectively, and the specific operations are as follows:

[0158] (1) Preparation of the positive electrode sheet: Mix the positive electrode active material lithium nickel cobalt manganese oxide (NCM811), the conductive agent SuperP, carbon nanotubes, and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1:0.5:1.5 with N-methylpyrrolidone (NMP) to make a positive electrode slurry (solid content: 70%), coat it on both the front and back sides of the current collector aluminum foil, dry it at 100 °C, and then cold-press it at 4 MPa at room temperature. Then, perform trimming, slicing, striping, and welding of the tab to make the positive electrode sheet;

[0159] (2) Preparation of the negative electrode sheet: Under a nitrogen protection atmosphere, the solvent N-methylpyrrolidone (NMP) and the binder PVDF are stirred and mixed evenly, then the conductive agent SuperP is added and stirred evenly, and then the negative electrode active material is added and stirred fully to make a negative electrode slurry (solid content is 50%). Among them, the negative electrode active material is obtained by fully mixing the silicon-carbon negative electrode material and graphite (the gram capacity of the prepared negative electrode material is 450 mAh / g). The negative electrode slurry is coated on both the front and back sides of the current collector copper foil, dried at 100 °C, cold-pressed at 4 MPa at room temperature, and then trimmed, sliced, and slit, and the tab is welded to make the negative electrode sheet;

[0160] (3) Assembly of the lithium-ion battery

[0161] Using a PE porous polymer film as the separator, the prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets, and wound to obtain a bare battery cell; The bare battery cell is placed in an aluminum-plastic shell package and dried at 100 °C under a relative vacuum pressure of -0.95×10 5 Pa until the moisture content is below 100 ppm. The electrolyte is injected into the dried bare battery cell. The electrolyte is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) (EC:EMC:DEC volume ratio = 1:1:1) and LiPF6 (1.0 M), and then it is encapsulated, left standing, formed (constant current charging at 0.02C for 2 h, constant current charging at 0.1C for 2 h), shaped, and capacity tested (grading) to make a soft-packaged liquid lithium-ion battery.

[0162] When assembling the battery, five batteries are prepared for each group of tests, and a total of five groups of data are tested. The final performance is the average value of the five groups of data.

[0163] The battery performance is tested on a Neware device. The specific test conditions are as follows:

[0164] At 25 °C, first discharge at 0.1C to 0.005V, then discharge at 0.08C to 0.001V, discharge at 0.05C to 0.001V, discharge at 0.02C to 0.001V, and leave it standing for 10 min; then charge at 0.1C to 1.5V, leave it standing for 10 min, record the charge and discharge capacity after the first cycle, and calculate the first Coulomb efficiency; cycle 100 times in the above manner, record the charge and discharge capacity after 100 cycles, and calculate the capacity retention rate after 100 cycles. The test and calculation process for the capacity retention rate after 500 cycles adopts the same method; the resistivity is measured by a semiconductor powder resistivity tester (30 MPa four-probe V1.4). The test results are shown in Table 2 below.

[0165] Table 2

[0166]

[0167] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0168] The above-described embodiments only express several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A preparation method of a silicon-carbon anode material, characterized in that, It includes the following steps: a. Mix the first carbon source with a surface modifier and a solvent to obtain a spinning solution; b. Use the electrospinning process to make the spinning solution into a fiber membrane; c. Block the pore structure in the fiber membrane with a second carbon source, and then perform carbonization to obtain a carbon layer. Among them, the purity of the first carbon source is less than that of the second carbon source, and the mass of the second carbon source is 0.1%-5% of the mass of the fiber membrane; d. Take steps b and c as one cycle, and use the carbon layer as the collection device for electrospinning to perform multiple cycles to obtain an intermediate with at least two carbon layer structures; e. Under the condition of a gaseous carbon source, perform heat treatment on the intermediate to obtain a layered porous carbon material; f. Perform silicon deposition on the layered porous carbon material to obtain a silicon-carbon negative electrode material.

2. The preparation method of the silicon-carbon anode material according to claim 1, wherein The first carbon source is selected from natural polymer materials, and the second carbon source is selected from synthetic organic materials.

3. The preparation method of the silicon-carbon anode material according to claim 1 or claim 2, characterized in that, Step a satisfies at least one of the following conditions: (1) The mass fraction of the first carbon source in the spinning solution is 3%-15%; (2) The first carbon source is selected from at least one of chitosan, natural cellulose, hyaluronic acid, gelatin, sodium alginate, collagen, and chitin; (3) The mass fraction of the surface modifier in the spinning solution is 0.1%-2%; (4) The surface modifier contains at least one element of P, S, and metal elements.

4. The preparation method of the silicon-carbon anode material according to claim 3, wherein, The surface modifier is selected from at least one of sodium stearate, zinc stearate, calcium stearate, sodium alkylbenzene sulfonate, sodium lauryl polyether sulfate, calcium lauryl polyether sulfate, trialkyl phosphite, and sodium didodecyl phosphate.

5. The preparation method of the silicon-carbon anode material according to claim 1 or claim 2, characterized in that, The electrospinning process satisfies at least one of the following conditions: (1) The viscosity of the spinning solution is 1 Pa·s - 3 Pa·s; (2) The flow rate of the spinning solution is 0.5 mL / min - 10 mL / min; (3) The electrospinning voltage is 15 kV - 35 kV.

6. The preparation method of the silicon-carbon anode material according to claim 1 or claim 2, characterized in that, The fiber membrane satisfies at least one of the following conditions: (1) The pore diameter of the pore structure in the fiber membrane is greater than or equal to 100 nm; (2) The thickness of the fiber membrane is less than or equal to 0.5 μm.

7. The preparation method of the silicon-carbon anode material according to claim 1 or claim 2, characterized in that Step c satisfies at least one of the following conditions: (1) The second carbon source is selected from at least one of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, benzene, toluene, and xylene; (2) The temperature of the carbonization is 500°C - 1000°C, and the time is 2 h - 8 h.

8. The preparation method of the silicon-carbon negative electrode material according to claim 1 or claim 2, characterized in that, Step e satisfies at least one of the following conditions: (1) The gaseous carbon source is selected from at least one of methane, acetylene, ethylene, and propane; (2) The temperature of the heat treatment is 700°C - 950°C, and the time is 2 h - 15 h.

9. The preparation method of the silicon-carbon anode material according to claim 1 or claim 2, characterized in that, The layered porous carbon material satisfies at least one of the following conditions: (1) Specific surface area is 1200 m 2 / g - 2400 m 2 / g; (2) The pore volume is 0.5 cm 3 / g - 1.8 cm 3 / g; (3) The resistivity is less than or equal to 0.05 Ω·m.

10. The preparation method of the silicon-carbon anode material according to claim 1 or claim 2, characterized in that, After the silicon deposition, a coating treatment is also included.

11. A silicon-carbon negative electrode material prepared by the preparation method of the silicon-carbon negative electrode material according to any one of claims 1 to 10, characterized in that, The silicon-carbon negative electrode material includes the layered porous carbon material and silicon loaded on the layered porous carbon material.

12. The silicon-carbon negative electrode material according to claim 11, wherein, The mass fraction of silicon in the silicon-carbon negative electrode material is 45%-55%.

13. The silicon-carbon negative electrode material according to claim 11, wherein The silicon-carbon negative electrode material also includes a carbon coating layer.

14. The silicon-carbon negative electrode material according to claim 13, wherein The mass fraction of the carbon coating layer in the silicon-carbon negative electrode material is 4% - 5%.

15. The silicon-carbon negative electrode material according to any one of claims 11 to 14, characterized in that, The silicon-carbon negative electrode material satisfies at least one of the following conditions: (1) The reversible specific capacity is greater than 1800 mAh / g; (2) The first Coulombic efficiency is higher than 90%; (3) The 500-cycle stability is higher than 85%; (4) The resistivity is lower than 4.1 Ω·m.

16. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer contains the silicon-carbon negative electrode material according to any one of claims 11 to 15.

17. A battery, characterized in that, It includes the negative electrode sheet according to claim 16.

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