A silicon-carbon negative electrode, its preparation method and application

Abstract

The present invention provides a silicon-carbon negative electrode, a preparation method thereof and an application. The preparation method comprises the following steps: mixing an organosilicon source, a polymer and a solvent to obtain a spinning solution, subjecting the spinning solution to electrospinning to obtain electrospun fibers; mixing a coating solution and the electrospun fibers and carbonizing them to obtain the silicon-carbon negative electrode. The preparation method can avoid the problem that the agglomeration of silicon materials during the preparation process causes the coating layer to break, thereby being unable to inhibit the expansion of silicon materials, and can obtain a silicon-carbon negative electrode with a stably coated carbon layer, effectively inhibiting the expansion of silicon materials, improving the cycle performance of the battery. At the same time, the prepared silicon-carbon negative electrode can be directly used as a self-supporting negative electrode, improving the volume energy density of the battery.

Description

Technical Field

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

[0002] Currently, the commercially available negative electrode materials are mainly graphite materials. However, their specific capacity is relatively low, making it difficult to meet the market demand. Silicon materials have the advantages of large specific capacity, wide material sources and simple preparation processes, and have received extensive attention. However, during the charge and discharge process, the volume of silicon materials will expand violently (up to 300%), and even the silicon-carbon composite materials obtained by compounding with carbon still have the problem of high expansion rate, resulting in rapid capacity decay and limited application. Therefore, it is necessary to suppress the volume expansion of silicon materials, improve the structural stability and conductivity of the materials to accelerate the application of silicon-carbon negative electrodes. At the same time, in the prior art, silicon-carbon materials need to be made into a slurry and coated on a current collector for application, and the volume energy density of the obtained silicon-carbon negative electrode sheet needs to be improved.

[0003] For example, CN 103367727A discloses a silicon-carbon negative electrode for a lithium-ion battery, which includes nano-silicon, a graphite polymer and organic pyrolysis carbon. The graphite polymer is composed of granular graphite, the nano-silicon is intercalated between the voids of the granular graphite or attached to the surface of the granular graphite, and the organic pyrolysis carbon coats the nano-silicon / graphite polymer; the preparation method of the material includes: mixing nano-silicon, a dispersant, a binder and granular graphite in an organic solvent, and drying to obtain a composite nano-silicon / graphite polymer: adding the obtained composite nano-silicon / graphite polymer to a dispersion of a carbon source precursor, mixing, and then drying: subjecting the obtained material to heat treatment to obtain a silicon-carbon negative electrode for a lithium-ion battery; although the method of intercalating nano-silicon between the voids of granular graphite and coating the nano-silicon / graphite polymer with organic pyrolysis carbon can provide space for silicon expansion, there is agglomeration of nano-silicon during its preparation process, and there are still problems of particle and organic pyrolysis carbon fragmentation during long-term cycling.

[0004] Based on the above research, it is necessary to provide a preparation method for a silicon-carbon negative electrode. The preparation method can avoid the agglomeration of silicon materials during the preparation process, thereby reducing the volume expansion of silicon materials, making the obtained silicon-carbon materials stable during long-term cycling, and improving the cycling performance and volume energy density of the battery. Summary of the Invention

[0005] The purpose of the present invention is to provide a silicon-carbon negative electrode, a preparation method thereof and an application thereof. The preparation method can avoid the problem that the coating layer breaks due to the agglomeration of silicon materials during the preparation process and cannot inhibit the expansion of silicon materials, obtain a silicon-carbon fiber material with a stably coated carbon layer, effectively inhibit the expansion of silicon materials, improve the cycling performance of the battery, and at the same time, the prepared silicon-carbon negative electrode can be directly used as a self-supporting negative electrode, improving the volume energy density of the battery.

[0006] To achieve the object of this invention, the following technical solutions are adopted in this invention:

[0007] In a first aspect, this invention provides a method for preparing a silicon-carbon negative electrode, and the preparation method includes the following steps:

[0008] (1) Mix an organosilicon source, a polymer, and a solvent to obtain a spinning solution, and perform electrospinning on the spinning solution to obtain electrospun fibers;

[0009] (2) Mix the coating solution and the electrospun fibers in step (1) and perform carbonization to obtain the silicon-carbon negative electrode.

[0010] This invention uses an organosilicon source and a polymer to prepare a spinning solution together. Since the organosilicon source can be dissolved and dispersed in the spinning solution, after electrospinning, the organosilicon source can be evenly distributed inside and on the surface of the electrospun fibers. The organosilicon source can generate silicon materials that are evenly dispersed in the fibers after subsequent carbonization. Compared with the method of directly using silicon or silicon dioxide to prepare the spinning solution, the in-situ generated silicon and silicon dioxide in this invention have better dispersion, avoiding the problem of agglomeration of silicon or silicon dioxide during the preparation process; moreover, after the electrospun fibers of this invention are mixed and carbonized with the coating solution, a carbon layer can be coated on the fiber surface. Through the synergistic effect of the carbon fiber and the carbon coating layer, the expansion of the silicon material is inhibited, the cycle performance is improved, and at the same time, the silicon-carbon negative electrode obtained by electrospinning can be directly used as the negative electrode without using a current collector, improving the volume energy density.

[0011] Preferably, the mass ratio of the organosilicon source to the polymer in step (1) is (0.5 - 4):1, for example, it can be 0.5:1, 1.5:1, 2.5:1, 3.5:1, or 4:1, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0012] Preferably, the mass ratio of the polymer to the solvent in step (1) is (0.05 - 0.25):1, for example, it can be 0.05:1, 0.1:1, 0.2:1, or 0.25:1, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0013] Preferably, the organosilicon source in step (1) includes tetraethyl orthosilicate and / or tetramethyl orthosilicate.

[0014] Preferably, the polymer in step (1) includes PAN (polyacrylonitrile).

[0015] Preferably, the electrospun fibers in step (1) are not thermally cured and / or calcined, and are directly mixed and carbonized with the coating source, or are first thermally cured and / or calcined and then mixed and carbonized with the coating source. Preferably, they are not thermally cured and / or calcined.

[0016] Since the fibers after electrospinning usually need to be heated for curing and calcination before subsequent processing, and the curing and calcination steps are omitted in the present invention. This is because an organosilicon source is used in electrospinning. To avoid premature thermal decomposition of the organosilicon source on the fiber surface and its inability to hydrolyze during the mixing with the coating source, after electrospinning in the present invention, heating for curing is not carried out, and high-temperature calcination treatment is not carried out either. Instead, it is directly mixed with the coating source. If thermal curing is carried out first and then step (2) is performed, the stability of the silicon material formed on the fiber surface will decrease.

[0017] Preferably, the temperature of the thermal curing is 200 - 300 °C, for example, it can be 200 °C, 250 °C or 300 °C, and the time is 1 - 3 h, for example, it can be 1 h, 2 h or 3 h. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0018] Preferably, the heating rate of the thermal curing is 0.5 - 1.5 °C / min, for example, it can be 0.5 °C / min, 1 °C / min or 1.5 °C / min, and the atmosphere is an air atmosphere.

[0019] The calcination conditions in the present invention are the same as the carbonization conditions described in step (2).

[0020] Preferably, the mixing in step (1) includes first stirring the polymer and the solvent, and then adding the organosilicon source for ultrasonic dispersion.

[0021] Preferably, the temperature of the stirring is 50 - 90 °C, for example, it can be 50 °C, 70 °C or 90 °C, and the time is 3 - 10 min, for example, it can be 3 min, 5 min or 10 min. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0022] Preferably, the number of times of ultrasonic dispersion is 2 - 5 times, for example, it can be 2 times, 3 times, 4 times or 5 times.

[0023] Preferably, the time for each ultrasonic dispersion is 10 - 30 min, for example, it can be 10 min, 20 min or 30 min. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0024] Preferably, the voltage of the electrospinning in step (1) is 10 - 20 KV, for example, it can be 10 KV, 15 KV or 20 KV, and the temperature is 25 - 35 °C, for example, it can be 25 °C, 30 °C or 35 °C. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0025] Preferably, the humidity of the electrospinning in step (1) is 10-40%, for example, it can be 10%, 25% or 40%, and the time is 10-14h, for example, it can be 10h, 12h or 14h. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0026] Preferably, the distance from the tip of the needle to the receiving plate of the electrospinning in step (1) is 15-20 cm, for example, it can be 15 cm, 17.5 cm or 20 cm. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0027] Preferably, the injection speed of the electrospinning in step (1) is 0.2-0.6 mL / h, for example, it can be 0.2 mL / h, 0.4 mL / h or 0.6 mL / h. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0028] Preferably, the coating solution in step (2) includes dopamine.

[0029] The carbon after carbonization in the present invention is respectively PAN-based carbon and polydopamine-based carbon. Both of these two carbons have a large specific surface area and belong to hierarchical porous carbon. Therefore, it can provide a buffer space for the volume expansion of Si, and at the same time can store more electrolyte and increase the wettability of the electrolyte to the negative electrode.

[0030] Preferably, the mixing in step (2) includes a hydrothermal reaction of the electrospun fibers in the coating solution.

[0031] The present invention uses dopamine as the carbon source for the carbon coating layer and combines a hydrothermal reaction. Dopamine in the coating solution can first in-situ polymerize on the surface of the electrospun fibers to form polydopamine; at the same time, the organosilicon source on the surface of the electrospun fibers can undergo hydrolysis and condensation reactions during the hydrothermal process to generate n(Si-O-Si)(-Si-O-Si-), thereby generating a network structure of -Si-O-Si- on the fiber surface. Then, after subsequent carbonization, the dopamine-based carbon can coat the -Si-O-Si- structure on the surface and cooperate with the network structure of Si to improve the stability of the material.

[0032] Preferably, the temperature of the hydrothermal reaction is 100-150 °C, for example, it can be 100 °C, 125 °C or 150 °C, and the time is 10-20h, for example, it can be 10h, 15h or 20h. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0033] Preferably, the coating solution in step (2) further includes hydroxymethylaminomethane and deionized water.

[0034] Preferably, the coating solution in step (2) further includes urea.

[0035] During the hydrothermal reaction process of the present invention, urea is also added. On the one hand, the addition of urea can enhance the synergistic effect of the in-situ polymerization coating of dopamine with the -Si-O-Si- network structure, improving the stability of the silicon material on the fiber surface. On the other hand, the addition of urea will increase the nitrogen element content of the carbon fiber. Nitrogen doping can improve the chemical reactivity, conductivity, and lithium ion adsorption rate of the carbon material. The nitrogen-containing functional groups play a role in promoting electron conduction during high-current charge and discharge, provide a large number of chemically reactive sites, and can also quickly intercalate lithium ions, avoiding the precipitation of lithium ions on the negative electrode surface and improving the battery cycle performance.

[0036] Preferably, in the coating solution, the mass ratio of urea to deionized water is (1 - 2):50, for example, it can be 1:50 or 2:50. The mass ratio of dopamine to deionized water is (0.5 - 1.5):50, for example, it can be 0.5:50, 1:50, or 1.5:50, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0037] Preferably, the pH of the coating solution in step (2) is 8.5 - 9.0, for example, it can be 8.5, 8.7, or 9.0, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0038] Preferably, the temperature of the carbonization in step (2) is 600 - 800 °C, for example, it can be 600 °C, 700 °C, or 800 °C, and the time is 1 - 3 h, for example, it can be 1 h, 2 h, or 3 h, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0039] Preferably, the heating rate of the carbonization in step (2) is 1 - 5 °C / min, for example, it can be 1 °C / min, 2.5 °C / min, or 5 °C / min, and the atmosphere is a nitrogen atmosphere.

[0040] The electrospun fibers of the present invention are taken out after the hydrothermal reaction in the coating solution and then carbonized.

[0041] As a preferred technical solution of the preparation method, the preparation method includes the following steps:

[0042] (1) Stir the polymer and the solvent at 50 - 90 °C for 3 - 10 min, then add the organosilicon source and perform ultrasonic dispersion 2 - 5 times. The time for each ultrasonic dispersion is 10 - 30 min to obtain a spinning solution. Electrospin the spinning solution for 10 - 14 h under the conditions of a voltage of 10 - 20 KV, a temperature of 25 - 35 °C, a humidity of 10 - 40%, and a distance from the needle tip to the receiving plate of 15 - 20 cm to obtain electrospun fibers;

[0043] Among them, the mass ratio of the silicone source to the polymer is (0.5 - 4):1, and the mass ratio of the polymer to the solvent is (0.05 - 0.25):1; the silicone source includes tetraethyl orthosilicate and / or tetramethyl orthosilicate, and the polymer includes PAN.

[0044] (2) The electrospun fibers in step (1) are not subjected to thermal curing and / or calcination, and are directly hydrothermally reacted with the coating solution at 100 - 150 °C for 10 - 20 h, and then the electrospun fibers are taken out and carbonized at a heating rate of 1 - 5 °C / min and a temperature of 600 - 800 °C for 2 - 10 h to obtain the silicon-carbon negative electrode.

[0045] The coating solution includes dopamine, tris(hydroxymethyl)aminomethane, urea and deionized water, and the pH of the coating solution is 8.5 - 9.0.

[0046] In a second aspect, the present invention provides a silicon-carbon negative electrode obtained by using the preparation method as described in the first aspect.

[0047] The silicon-carbon negative electrode of the present invention has a core-shell structure, wherein the inner core includes a Si-SiO2-carbon fiber material, and the outer shell includes a nitrogen-containing carbon layer.

[0048] In a third aspect, the present invention provides a battery including the silicon-carbon negative electrode as described in the second aspect.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1) In the present invention, a spinning solution is prepared by using a silicone source. After electrospinning the spinning solution, the silicone source will be uniformly dispersed inside and / or on the surface of the spun nanofibers. Then, through mixing with the coating solution, the surface silicone source is preliminarily treated, and at the same time, the coating source is coated on the fiber surface. Subsequently, through carbonization, the fiber and the coating layer are converted into carbon, and the silicone source is reduced to Si and SiO2 at high temperature.

[0051] (2) The silicon-carbon negative electrode obtained by the present invention has a core-shell nanofiber three-dimensional conductive network structure, has high mechanical strength and electrical conductivity, can completely coat the silicon material inside the carbon layer, and includes two kinds of carbon. The two kinds of carbon inhibit the volume expansion of silicon through synergistic action and can promote the electron transfer between silicon materials; at the same time, the carbon nanofiber membrane in the silicon-carbon negative electrode obtained by the present invention has high mechanical strength, can be cut into any shape, and has good electrical conductivity. Therefore, the silicon-carbon negative electrode of the present invention does not require a current collector, a binder, a conductive agent, etc., and can be directly used as a self-supporting lithium battery negative electrode, increasing the energy density of the entire battery. Detailed embodiments

[0052] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0053] Example 1

[0054] This example provides a preparation method of a silicon-carbon negative electrode. The preparation method includes the following steps:

[0055] (1) Stir PAN and DMF at 70 °C for 5 min, then add an organosilicon source and perform ultrasonic dispersion 3 times. The time for each ultrasonic dispersion is 20 min to obtain a spinning solution. Load the spinning solution into a 20 mL medical syringe, and then perform electrospinning for 12 h under the conditions of an injection speed of 0.4 mL / h, a voltage of 15 KV, a temperature of 30 °C, a humidity of 35%, and a distance from the needle tip to the receiving plate of 18 cm to obtain electrospun fibers;

[0056] Among them, the organosilicon source is tetraethyl orthosilicate, and the mass ratio of the organosilicon source to PAN is 2:1, and the mass ratio of PAN to DMF is 0.1:1;

[0057] (2) Without thermal curing and calcination, directly hydrothermally react the electrospun fibers obtained in step (1) with dopamine, hydroxymethylaminomethane, urea, and deionized water at 120 °C for 18 h, and then take out the electrospun fibers and perform carbonization at a heating rate of 3 °C / min and a temperature of 700 °C for 5 h to obtain the silicon-carbon negative electrode;

[0058] The pH of the coating solution is 8.7, the mass ratio of urea to deionized water is 1:50, and the mass ratio of dopamine to deionized water is 1:50.

[0059] Example 2

[0060] This example provides a preparation method of a silicon-carbon negative electrode. The preparation method includes the following steps:

[0061] (1) Stir PAN and DMF at 50 °C for 10 min, then add an organosilicon source and perform ultrasonic dispersion 5 times. The time for each ultrasonic dispersion is 10 min to obtain a spinning solution. Load the spinning solution into a 20 mL medical syringe, and then perform electrospinning for 10 h under the conditions of an injection speed of 0.6 mL / h, a voltage of 10 KV, a temperature of 35 °C, a humidity of 40%, and a distance from the needle tip to the receiving plate of 20 cm to obtain electrospun fibers;

[0062] Among them, the organosilicon source is tetraethyl orthosilicate, and the mass ratio of the organosilicon source to PAN is 0.5:1, and the mass ratio of PAN to DMF is 0.25:1;

[0063] (2) The electrospun fibers described in step (1) are not subjected to thermal curing and roasting, but directly undergo hydrothermal reaction with dopamine, hydroxymethylaminomethane, urea and deionized water at 100 °C for 20 h. Then, the electrospun fibers are taken out and carbonized at a heating rate of 1 °C / min and a temperature of 600 °C for 10 h to obtain the silicon-carbon negative electrode;

[0064] The pH of the coating solution is 9.0, the mass ratio of urea to deionized water is 1:50, and the mass ratio of dopamine to deionized water is 0.5:50.

[0065] Example 3

[0066] This example provides a method for preparing a silicon-carbon negative electrode. The preparation method includes the following steps:

[0067] (1) PAN and DMF are stirred at 90 °C for 3 min, then an organosilicon source is added and ultrasonic dispersion is carried out 2 times, with the time for each ultrasonic dispersion being 30 min to obtain a spinning solution. The spinning solution is filled into a 20 mL medical syringe, and then electrospinning is carried out for 14 h under the conditions of an injection speed of 0.2 mL / h, a voltage of 20 KV, a temperature of 25 °C, a humidity of 10%, and a distance from the needle tip to the receiving plate of 15 cm to obtain electrospun fibers;

[0068] Among them, the organosilicon source is methyl orthosilicate, the mass ratio of the organosilicon source to PAN is 4:1, and the mass ratio of PAN to DMF is 0.05:1;

[0069] (2) The electrospun fibers described in step (1) are not subjected to thermal curing and roasting, but directly undergo hydrothermal reaction with dopamine, hydroxymethylaminomethane, urea and deionized water at 150 °C for 10 h. Then, the electrospun fibers are taken out and carbonized at a heating rate of 5 °C / min and a temperature of 800 °C for 2 h to obtain the silicon-carbon negative electrode;

[0070] The pH of the coating solution is 8.5, the mass ratio of urea to deionized water is 2:50, and the mass ratio of dopamine to deionized water is 1.5:50.

[0071] Example 4

[0072] This example provides a method for preparing a silicon-carbon negative electrode. Except that the electrospun fibers described in step (1) are first subjected to thermal curing and then undergo hydrothermal reaction with a coating source, the rest are the same as in Example 1;

[0073] Among them, the thermal curing is carried out in an air atmosphere. The temperature is raised from room temperature to 280 °C at a heating rate of 1 °C / min, and curing is carried out for 2 h. After natural cooling, the cured electrospun fibers are obtained.

[0074] Example 5

[0075] This example provides a method for preparing a silicon-carbon negative electrode. Except that the electrospun fibers in step (1) are first calcined and then subjected to a hydrothermal reaction with a coating source, the rest are the same as in Example 1;

[0076] Among them, the calcination is carried out in an argon atmosphere, the temperature is raised from room temperature to 700 °C at a heating rate of 3 °C / min, the calcination is completed after holding for 2 h, and the calcined electrospun fibers are obtained after natural cooling.

[0077] Example 6

[0078] This example provides a method for preparing a silicon-carbon negative electrode. Except that the electrospun fibers in step (1) are first thermally cured and calcined and then subjected to a hydrothermal reaction with a coating source, the rest are the same as in Example 1;

[0079] Among them, the thermal curing is carried out in an air atmosphere, the temperature is raised from room temperature to 280 °C at a heating rate of 1 °C / min, and curing is carried out for 2 h. The calcination is carried out in an argon atmosphere, the temperature is raised from room temperature to 700 °C at a heating rate of 3 °C / min, and the calcination is completed after holding for 2 h.

[0080] Example 7

[0081] This example provides a method for preparing a silicon-carbon negative electrode. Except that the coating solution in step (2) does not include urea, the rest are the same as in Example 1.

[0082] Example 8

[0083] This example provides a method for preparing a silicon-carbon negative electrode. Except that dopamine in step (2) is replaced with polydopamine in equal mass, the rest are the same as in Example 1.

[0084] Example 9

[0085] This example provides a method for preparing a silicon-carbon negative electrode. Except that the electrospun fibers in step (2) are directly mixed with polydopamine and then carbonized, the rest are the same as in Example 1.

[0086] Example 10

[0087] This example provides a method for preparing a silicon-carbon negative electrode. Except that in step (2), no hydrothermal reaction is carried out, but instead, stirring and mixing are directly carried out at room temperature for 15 h, the rest are the same as in Example 1.

[0088] Comparative Example 1

[0089] This comparative example provides a method for preparing a silicon-carbon negative electrode. Except that the organosilicon source described in step (1) is replaced with nano-silicon in equal mass, the rest are the same as in Example 1.

[0090] Comparative Example 2

[0091] This comparative example provides a method for preparing a silicon-carbon negative electrode. Except that the organosilicon source described in step (1) is replaced with silicon dioxide in equal mass, the rest are the same as in Example 1.

[0092] The silicon-carbon negative electrodes obtained from the above examples and comparative examples are made into lithium-ion batteries together with a lithium cobalt oxide positive electrode, an electrolyte (including 85% ethylene carbonate, 12% lithium hexafluorophosphate, and 3% vinylene carbonate), and a polyethylene separator. The lithium-ion battery is tested under the conditions of constant current and constant voltage charging at 0.5C to 4.2V, a cut-off current of 0.02C, constant current discharge: 1C discharge, and a cut-off voltage of 3.0V. The initial efficiency, capacity retention rates after 100 cycles and 500 cycles are tested.

[0093] The test results are shown in the following table:

[0094] Table 1

[0095]

[0096] It can be seen from the above table that:

[0097] (1) The silicon-carbon negative electrode obtained by the present invention can be directly used as a negative electrode and has excellent electrochemical performance at the same time; it can be seen from Example 1 and Examples 4-6 that the present invention omits the steps of fiber thermal curing and fiber roasting and carbonization, but directly performs hydrothermal reaction on the obtained polymer fiber, which can perform surface treatment on the surface organosilicon source, further improve the stability of the surface material silicon material, and improve the long-cycle performance of the battery; it can be seen from Example 1 and Example 7 that the addition of urea in the present invention can further improve the stability of the surface silicon material and further improve the battery performance; it can be seen from Example 1 and Example 8 that the in-situ generation of polydopamine on the fiber surface in the present invention can improve the uniformity and denseness of the surface-coated carbon layer, thereby further improving the cycle performance.

[0098] (2) As can be seen from Example 1 and Example 9, when directly coated with polydopamine, the organosilicon source on the fiber surface cannot be hydrolyzed and condensed, resulting in a decrease in the stability of the surface silicon material and a decline in the long-cycle performance of the battery; as can be seen from Example 1 and Example 10, the hydrothermal reaction can promote hydrolysis and the in-situ formation of polydopamine on the fiber surface. If directly stirred at room temperature, it is not conducive to the formation of polydopamine on the fiber surface; as can be seen from Example 1 and Comparative Examples 1-2, the present invention uses an organosilicon source for electrospinning and then generates Si and SiO2 through subsequent carbonization. Compared with directly electrospinning with silicon and silicon dioxide, the agglomeration of particles during the preparation process is avoided, and the dispersibility of silicon and silicon dioxide particles in the carbon fiber is higher, resulting in better performance of the silicon-carbon negative electrode.

[0099] In summary, the present invention provides a silicon-carbon negative electrode, a preparation method thereof, and an application thereof. The preparation method can avoid the problem that the agglomeration of silicon materials during the preparation process causes the coating layer to break and cannot inhibit the expansion of silicon materials, obtain a silicon-carbon fiber material with a stable carbon coating layer, effectively inhibit the expansion of silicon materials, improve the cycle performance of the battery, and at the same time, the prepared silicon-carbon negative electrode can be directly used as a self-supporting negative electrode, improving the volume energy density of the battery.

[0100] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing a silicon-carbon negative electrode, characterized in that, The preparation method includes the following steps: (1) Mix an organosilicon source, a polymer, and a solvent to obtain a spinning solution, and electrospin the spinning solution to obtain electrospun fibers; (2) Mix the coating solution and the electrospun fibers obtained in step (1) and carbonize them to obtain the silicon-carbon negative electrode; The coating solution in step (2) includes dopamine and urea; the mixing in step (2) includes subjecting the electrospun fibers to a hydrothermal reaction in the coating solution.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the organosilicon source to the polymer in step (1) is (0.5 - 4):

1.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the polymer to the solvent in step (1) is (0.05 - 0.25):

1.

4. The preparation method according to claim 1, wherein The organosilicon source in step (1) includes tetraethyl orthosilicate and / or tetramethyl orthosilicate.

5. The preparation method according to claim 1, wherein The polymer in step (1) includes PAN.

6. The preparation method according to claim 1 or 2, characterized in that, The electrospun fibers in step (1) are either directly mixed and carbonized with the coating source without thermal curing and / or roasting, or first subjected to thermal curing and / or roasting and then mixed and carbonized with the coating source.

7. The preparation method according to claim 6, characterized in that, The temperature of the thermal curing is 200 - 300 °C, and the time is 1 - 3 h.

8. The preparation method according to claim 6, characterized in that, The heating rate of the thermal curing is 0.5 - 1.5 °C / min, and the atmosphere is an air atmosphere.

9. The preparation method according to any one of claims 1 to 3, characterized in that, The mixing in step (1) includes first stirring the polymer and the solvent, and then adding the organosilicon source for ultrasonic dispersion.

10. The preparation method according to claim 9, characterized in that, The temperature of the stirring is 50 - 90 °C, and the time is 3 - 10 min.

11. The preparation method according to claim 9, characterized in that, The number of times of ultrasonic dispersion is 2 - 5 times.

12. The preparation method according to claim 9, characterized in that, The time for each ultrasonic dispersion is 10 - 30 min.

13. The preparation method according to any one of claims 1-4, characterized in that, The voltage of the electrospinning in step (1) is 10 - 20 KV, and the temperature is 25 - 35 °C.

14. The preparation method according to claim 1, wherein, The humidity of the electrospinning in step (1) is 10 - 40%, and the time is 10 - 14 h.

15. The preparation method according to claim 1, characterized in that, The distance from the tip of the electrospinning needle to the receiving plate in step (1) is 15 - 20 cm.

16. The preparation method according to any one of claims 1-5, characterized in that, The temperature of the hydrothermal reaction is 100 - 150 °C, and the time is 10 - 20 h.

17. The preparation method according to claim 1, wherein The coating solution in step (2) further includes tris(hydroxymethyl)aminomethane and deionized water.

18. The preparation method according to claim 1, characterized in that, The pH of the coating solution in step (2) is 8.5 - 9.

0.

19. The preparation method according to claim 1, characterized in that, The temperature of the carbonization in step (2) is 600 - 800 °C, and the time is 1 - 3 h.

20. The preparation method according to claim 1, characterized in that, The heating rate of the carbonization in step (2) is 1 - 5 °C / min, and the atmosphere is a nitrogen atmosphere.

21. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Stir the polymer and the solvent at 50 - 90 °C for 3 - 10 min, then add the organosilicon source for ultrasonic dispersion 2 - 5 times, with the time for each ultrasonic dispersion being 10 - 30 min, to obtain a spinning solution. Electrospin the spinning solution for 10 - 14 h under the conditions of a voltage of 10 - 20 KV, a temperature of 25 - 35 °C, a humidity of 10 - 40%, and a distance from the tip of the needle to the receiving plate of 15 - 20 cm to obtain electrospun fibers; wherein, the mass ratio of the organosilicon source to the polymer is (0.5 - 4):1, and the mass ratio of the polymer to the solvent is (0.05 - 0.25):1; the organosilicon source includes tetraethyl orthosilicate and / or tetramethyl orthosilicate, and the polymer includes PAN; (2) The electrospun fibers described in step (1) are directly subjected to hydrothermal reaction with the coating solution at 100 - 150 °C for 10 - 20 h without thermal curing and / or calcination, and then the electrospun fibers are taken out and carbonized at a heating rate of 1 - 5 °C / min and a temperature of 600 - 800 °C for 2 - 10 h to obtain the silicon-carbon negative electrode; The coating solution includes dopamine, tris(hydroxymethyl)aminomethane, urea, and deionized water, and the pH of the coating solution is 8.5 - 9.

0.

22. A silicon-carbon negative electrode, characterized in that, The silicon-carbon negative electrode is obtained by the preparation method described in any one of claims 1 - 21.

23. A battery, characterized in that, The battery includes the silicon-carbon negative electrode described in claim 22.

Images