A silicon-carbon composite material, its preparation method and application

Abstract

The present invention discloses a silicon-carbon composite material, a preparation method and an application thereof. The silicon-carbon composite material at least comprises silicon-based particles as a core and a coating layer as a shell; wherein, the coating layer comprises a fast ion conductive layer coated on the outer surface of the silicon-based particles and an electron conductive layer coated on the outer surface of the fast ion conductive layer, and the mass ratio among the silicon-based particles, the fast ion conductive layer and the electron conductive layer is 100:1-8:1-8. The present invention significantly improves the coating integrity of the silicon-based material, and simultaneously significantly improves the power and cycle performance of the applied battery.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion battery preparation, and particularly relates to a silicon-carbon composite material. The present invention also relates to a preparation method and application of the silicon-carbon composite material. Background Art

[0002] Silicon-carbon materials have become the preferred anode materials for high-energy-density lithium-ion batteries due to their high energy density and wide material sources. However, defects such as large self-expansion and poor electronic conductivity of the materials result in poor full-charge expansion and cycling performance of the materials, restricting their wide application. One of the measures to reduce the material expansion and improve the electronic conductivity of the materials is surface coating and doping of the materials. Currently, the doping substances are mainly metal elements such as magnesium and aluminum and amorphous carbon materials coated thereon to improve the above defects. However, there are defects such as poor coating integrity and insignificant improvement in electronic conductivity when using a single coating.

[0003] Based on the above situation, based on the applicant's inventors' many years of focused research experience in silicon-based materials and the field of lithium-ion batteries, it is decided to seek technical solutions to solve the above technical problems. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a silicon-carbon composite material, a preparation method and application thereof, which significantly improve the coating integrity of the silicon-based material, and at the same time significantly improve the power and cycling performance of the applied battery.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A silicon-carbon composite material, at least including silicon-based particles as the core and a coating layer as the shell; wherein, the coating layer includes a fast ion conductive layer coated on the outer surface of the silicon-based particles and an electronic conductive layer coated on the outer surface of the fast ion conductive layer, and the mass ratio of the silicon-based particles, the fast ion conductive layer and the electronic conductive layer is 100:1-8:1-8.

[0007] Preferably, the fast ion conductive layer is coated on the outer surface of the silicon-based particles by atomic vapor deposition; and / or, the material of the electronic conductive layer is amorphous carbon containing boron and / or carbon fiber.

[0008] Preferably, the silicon-based particles include a Si / SiOx composite matrix, wherein, 0 < X < 2, and the Si in the Si / SiOx composite matrix and SiO XThe mass ratio therebetween is 10:1 - 10; and / or, the material of the fast ion conductive layer includes LiTi2(PO4)3 and / or Li3V2(PO4)3 and / or Li3Zr2(PO4)3 and / or Li3Sr2(PO4)3 and / or Li3Fe2(PO4)3 and / or Li3Ti2(PO4)3.

[0009] Preferably, the mass proportion of boron in the electron conductive layer is 1 - 10%, the mass proportion of carbon fiber in the electron conductive layer is 1 - 10%, and the rest is amorphous carbon.

[0010] Preferably, a preparation method of the silicon-carbon composite material as described above includes the following operation steps:

[0011] S10): Using nano-Si and SiO2 particles as raw materials, after mixing them evenly, at least part of the raw materials undergo a disproportionation reaction under a heating environment, and after condensation and crushing, a Si / SiOx composite matrix is obtained, and the Si / SiOx composite matrix is used as the silicon-based particles;

[0012] S20): Depositing and coating a fast ion conductor used as a target on the silicon-based particles by atomic vapor deposition to obtain silicon-based particles coated with a fast ion conductive layer;

[0013] S30): Dispersing and mixing the silicon-based particles coated with a fast ion conductive layer in a pre-coating solution, drying and then carbonizing by vapor deposition to form and coat an electron conductive layer on the outer surface of the fast ion conductive layer;

[0014] S40): Obtaining the silicon-carbon composite material.

[0015] Preferably, the pre-coating solution in the step S30) includes carbon fiber, borane compound, and a water-soluble phenolic resin organic solvent solution, wherein the mass ratio among carbon fiber, borane compound, water-soluble phenolic resin, and silicon-based particles is 1 - 8:1 - 8:8 - 15:100; in the carbonization by vapor deposition after drying, the temperature range is set at 700 - 1100 °C for carbonization for at least 1 hour.

[0016] Preferably, the borane compound includes diborane and / or tetraborane and / or pentaborane and / or hexaborane; the organic solvent includes ethylene glycol and / or ethanol and / or butanediol and / or benzyl alcohol and / or phenylpentanol and / or allyl alcohol.

[0017] Preferably, in the step S10), the mass ratio of the nano-Si and SiO2 particles is 1-2:1; in the heating environment, the temperature range is set at 1500-2000 °C, and the temperature is maintained for at least 1 hour under this temperature condition, while the vacuum range is set at 100-1000 Pa.

[0018] Preferably, in the atomic vapor deposition method of the step S20), the temperature range is set at 800-1200 °C, and the pressure range is set at 0.1-0.5 Torr, so that the fast ion conductor is vaporized and deposited on the silicon-based particles after being vaporized.

[0019] Preferably, for the application of the silicon-carbon composite material as described above, the silicon-carbon composite material is used as the active material raw material for preparing the battery electrode sheet.

[0020] It should be noted that the nano-Si involved in this application refers to crystalline silicon particles with a diameter less than 20 nanometers, which can be directly purchased from the market.

[0021] The present invention proposes a core-shell coated silicon-carbon composite material composed of silicon-based particles, a fast ion conductive layer, and an electron conductive layer with a mass ratio of 100:1-8:1-8, which significantly improves the coating integrity of the silicon-based material, and at the same time significantly improves the power and cycle performance of the applied battery.

[0022] The present invention further preferably proposes to deposit and coat a fast ion conductor on the inner core Si / SiOx composite matrix by atomic vapor deposition to form a fast ion conductive layer, avoiding the conventional solid-phase coating method. The present invention has the advantages of high density, low impedance, and good uniformity. When applied, it can effectively improve the first efficiency of the battery, reduce the full-charge swelling, and at the same time effectively utilize the ionic conductivity characteristics of the fast ion conductor material to improve its diffusion ability during the charge and discharge process of the material.

[0023] The present invention further preferably proposes an electron conductive layer solution containing boron and carbon fibers. In actual application, not only does the fiber structure of the carbon fiber restrain the expansion of silicon during the charge and discharge process of the battery, but boron has the characteristic of high electron conductivity, which can significantly reduce the impedance, so that it forms a network structure with high electron conductivity as the coating outer layer of the silicon-carbon composite material to reduce its expansion and improve its power performance.

[0024] The present invention further preferably proposes to carry out carbonization deposition of amorphous carbon containing boron and carbon fibers by vapor deposition method, avoiding the conventional liquid-phase coating method. The present invention has good uniformity, high density, and process controllability, avoids direct contact between the inner core and the electrolyte to improve the first efficiency, and improves the cycle and power performance. Description of the Drawings

[0025] Figure 1 This is the SEM image of the silicon-carbon composite material in Embodiment 1 of the present invention. Detailed implementation manners

[0026] This embodiment discloses a silicon-carbon composite material, which at least includes silicon-based particles as the core and a coating layer as the shell; wherein, the coating layer includes a fast ion conductive layer coated on the outer surface of the silicon-based particles and an electron conductive layer coated on the outer surface of the fast ion conductive layer. The mass ratio among the silicon-based particles, the fast ion conductive layer and the electron conductive layer is 100:1-8:1-8. More preferably, the mass ratio among the silicon-based particles, the fast ion conductive layer and the electron conductive layer is 100:1-6:1-6. Further preferably, the mass ratio among the silicon-based particles, the fast ion conductive layer and the electron conductive layer is 100:1-5:1-5.

[0027] Preferably, in this implementation manner, the fast ion conductive layer is coated on the outer surface of the silicon-based particles by atomic vapor deposition method; and / or, the material of the electron conductive layer is amorphous carbon containing boron and / or carbon fiber; Further preferably, in this implementation manner, the silicon-based particles include a Si / SiOx composite matrix, wherein 0 < X < 2, and the mass ratio of Si to SiO in the Si / SiOx composite matrix is 10:1-10; and / or, in this implementation manner, the material of the fast ion conductive layer includes LiTi2(PO4)3 and / or Li3V2(PO4)3 and / or Li3Zr2(PO4)3 and / or Li3Sr2(PO4)3 and / or Li3Fe2(PO4)3 and / or Li3Ti2(PO4)3. Of course, when implementing this application, it is recommended to consider using these preferred materials for the fast ion conductive layer. This material can facilitate the atomic vapor deposition method, but these preferred solutions are not the only options of this application. Those skilled in the art can select other suitable materials as the fast ion conductive layer in combination with common general knowledge. X Preferably, in this implementation manner, the mass proportion of boron in the electron conductive layer is 1-10%, and the mass proportion of carbon fiber in the electron conductive layer is 1-10%, and the rest is amorphous carbon; wherein, boron has the characteristic of high electron conductivity, which can significantly reduce the impedance, so that it forms a network structure with high electron conductivity on the outer coating of the silicon-carbon composite material to reduce its expansion and improve its power performance. At the same time, the fiber structure of the carbon fiber restricts the expansion of silicon during the charge and discharge process of the battery.

[0028] In order to efficiently, reliably and stably obtain the silicon-carbon composite material described above in this embodiment, this embodiment also proposes a preparation method for the silicon-carbon composite material, including the following operation steps:

[0029]

[0030] ​S10), Using nano - Si and SiO2 particles as raw materials, after mixing them evenly, at least part of the raw materials undergo disproportionation reaction under a heating environment. After condensation and crushing, a Si / SiOx composite matrix is obtained, and the Si / SiOx composite matrix is used as the silicon - based particles; Preferably, in this step S10), the mass ratio of nano - Si and SiO2 particles is 1 - 2:1; In the heating environment, the temperature range is set at 1500 - 2000 °C, and the temperature is maintained for at least 1 hour under this temperature condition, more preferably for 1 - 10 hours, and further preferably for 1 - 6 hours. At the same time, the vacuum range is set at 100 - 1000 pa;

[0031] S20), Deposit and coat the fast - ion conductor as a target on the silicon - based particles by atomic vapor deposition to obtain silicon - based particles coated with a fast - ion conductive layer; Preferably, in the atomic vapor deposition method in this step S20), the temperature range is set at 800 - 1200 °C, and the pressure range is set at 0.1 - 0.5 Torr, so that the fast - ion conductor is vaporized and then deposited and coated on the silicon - based particles; To further facilitate the deposition efficiency and deposition quality, in this step S20) when implementing the atomic vapor deposition method, the gas flow range is set at 0.01 - 0.1 sccm, and the time is 10 - 120 seconds;

[0032] S30), Disperse and mix the silicon - based particles coated with a fast - ion conductive layer in a pre - coating solution, and after drying, perform carbonization by vapor deposition to form an electron - conductive layer on the outer surface of the fast - ion conductive layer; Preferably, in this step S30), the pre - coating solution includes carbon fiber, borane compound, and a water - soluble phenolic resin organic solvent solution. Among them, the mass ratio of carbon fiber, borane compound, water - soluble phenolic resin, and silicon - based particles is 1 - 8:1 - 8:8 - 15:100, more preferably 1 - 6:1 - 6:9 - 12:100; Further preferably 1 - 5:1 - 5:10:100; When specifically preparing the pre - coating solution, prepare carbon fiber, borane compound, and a water - soluble phenolic resin organic solvent solution according to the preset mass ratio, mix them evenly, and then disperse a preset amount of silicon - based particles coated with a fast - ion conductive layer in the pre - coating solution by ultrasonic method. After spray drying, transfer it to a carbonization furnace (specifically, a tube furnace can be used), dry it under an inert atmosphere, and then perform carbonization by vapor deposition; Preferably, in this step S30), in the carbonization by vapor deposition after drying, the temperature range is set at 700 - 1100 °C for carbonization for at least 1 hour, more preferably for 1 - 10 hours, and further preferably for 1 - 6 hours; Specifically preferably, the borane compound includes diborane and / or tetraborane and / or pentaborane and / or hexaborane; The organic solvent includes ethylene glycol and / or ethanol and / or butanediol and / or benzyl alcohol and / or phenylpentanol and / or allyl alcohol.

[0033] S40) Obtain the silicon-carbon composite material described above in this embodiment.

[0034] It should be specifically noted that through a large number of experiments, this application lists various preferred range parameters through the above embodiments. Those skilled in the art can select within these preferred parameter ranges (including endpoint values and intermediate values) according to the actual situation. To save space in the specification, this embodiment will not be elaborated one by one.

[0035] Preferably, this embodiment also proposes an application of the silicon-carbon composite material as described above, using the silicon-carbon composite material as the active material raw material for preparing battery electrode sheets; specifically, it can be used as the negative electrode sheet of the battery and can be selected according to actual requirements; in specific implementation, the process for preparing the negative electrode sheet of the battery can adopt any well-known process, which does not belong to the innovative content of this application and this application does not impose any restrictions on it; it should also be noted that when this application is implemented, the battery can be a button battery, a soft-pack battery or other well-known batteries, and those skilled in the art can apply it according to actual needs, and this application does not make any special restrictions on this.

[0036] In order to enable those skilled in the art to better understand the technical solutions in this invention, the following will clearly and completely describe the technical solutions in the embodiments of this invention with reference to the accompanying drawings in the embodiments of this invention. Obviously, the described embodiments are only a part of the embodiments of this invention, rather than all of the embodiments. Based on the embodiments of this invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the scope of protection of this invention.

[0037] Example 1: Operate according to the following steps:

[0038] Step 1: Weigh 42 g (about 1.5 mol) of nano-Si and 60 g (about 1 mol) of SiO2 particle powder respectively, and mix them evenly to obtain the core raw material;

[0039] Step 2: Place the above core raw material in a heating device, heat it to 1800 °C and keep it warm for 3 hours under a vacuum of 500 Pa, so that the core raw material sublimes and undergoes disproportionation reaction. After condensation and crushing, a Si / SiOx composite matrix is obtained, and this Si / SiOx composite matrix serves as the silicon-based particles;

[0040] Step 3: Place the Si / SiOx composite matrix in an atomic vapor deposition device. Using LiTi2(PO4)3 as the target, while setting the temperature to 1000 °C and the pressure to 0.3 Torr, vaporize LiTi2(PO4)3 and deposit it on the Si / SiOx composite matrix. Among them, in atomic vapor deposition, the gas flow rate is 0.05 sccm and the time is 60 seconds for each, to obtain the Si / SiOx composite matrix coated with LiTi2(PO4)3;

[0041] Step 4: Add 3 g of carbon fiber and 3 g of diborane to 1000 ml of a water-soluble phenolic resin ethylene glycol solution with a mass concentration of 1%. After dispersing evenly, add 100 g of the Si / SiOx composite matrix coated with LiTi2(PO4)3. After ultrasonic dispersion evenly, perform spray drying;

[0042] Step 5: Transfer the material obtained in Step 4 to a tubular carbonization furnace, and carbonize it for 3 hours under the conditions of an argon inert atmosphere and a temperature of 900 °C to obtain an amorphous carbon / LiTi2(PO4)3 double-coated Si / SiOx composite matrix containing boron and carbon fiber, which is the silicon-carbon composite material prepared in Example 1.

[0043] This application conducts SEM (scanning electron microscope) tests on the silicon-carbon composite material obtained in Example 1, and the test results are as Figure 1 shown. We can see through Figure 1 that the particle size distribution of the silicon-carbon composite material obtained in Example 1 is uniform and reasonable, and there is slight adhesion. The particle size of the particles is between 5 - 10 μm.

[0044] Example 2: Operate according to the following steps:

[0045] Step 1: Weigh 28 g (about 1 mol) of nano-Si and 60 g (about 1 mol) of SiO2 particle powder respectively, and mix them evenly to obtain the core raw material;

[0046] Step 2: Place the above core raw material in a heating device, heat it to 1500 °C under a vacuum of 100 Pa and keep it warm for 6 hours, so that the core raw material sublimates and undergoes a disproportionation reaction. After condensation and crushing, obtain the Si / SiOx composite matrix, and this Si / SiOx composite matrix serves as the silicon-based particles;

[0047] Step 3: Place the Si / SiOx composite matrix in an atomic vapor deposition device, use Li3V2(PO4)3 as the target, while set the temperature to 800 °C and the pressure to 0.1 Torr, so that Li3V2(PO4)3 is vaporized and deposited on the Si / SiOx composite matrix. Among them, in atomic vapor deposition, the gas flow rate is 0.01 sccm and the time is 120 seconds for each, to obtain the Si / SiOx composite matrix coated with Li3V2(PO4)3;

[0048] Step 4: Add 1 g of carbon fiber and 1 g of diborane to 1000 ml of a water-soluble phenolic resin butanediol solution with a mass concentration of 1%. After dispersing evenly, add 100 g of the Si / SiOx composite matrix coated with Li3V2(PO4)3. After ultrasonic dispersion evenly, perform spray drying;

[0049] Step 5: Transfer the material obtained in Step 4 to a tube-type carbonization furnace, and carbonize it for 6 hours under the condition of an argon inert atmosphere and a temperature of 700 °C to obtain an amorphous carbon / Li3V2(PO4)3 double-coated Si / SiOx composite matrix containing boron and carbon fiber, which is the silicon-carbon composite material prepared in Example 2.

[0050] Example 3: Operate according to the following steps:

[0051] Step 1: Weigh 56 g (about 2 mol) of nano-Si and 60 g (about 1 mol) of SiO2 particle powder respectively, and mix them evenly to obtain the core raw material;

[0052] Step 2: Place the above core raw material in a heating device, heat it to 2000 °C and keep it warm for 1 hour under a vacuum of 1000 Pa, so that the core raw material sublimates and undergoes a disproportionation reaction. After condensation and crushing, a Si / SiOx composite matrix is obtained, and this Si / SiOx composite matrix is used as the silicon-based particles;

[0053] Step 3: Place the Si / SiOx composite matrix in an atomic vapor deposition device, use Li3Zr2(PO4)3 as the target, while set the temperature to 1200 °C and the pressure to 0.5 Torr, so that Li3Zr2(PO4)3 is vaporized and deposited on the Si / SiOx composite matrix. Among them, in atomic vapor deposition, the gas flow rate is 0.1 sccm and the time is 10 seconds for each, to obtain the Si / SiOx composite matrix coated with Li3Zr2(PO4)3;

[0054] Step 4: Add 5 g of carbon fiber and 5 g of pentaborane to 1000 ml of a water-soluble phenolic resin butanediol solution with a mass concentration of 1%. After dispersing evenly, add 100 g of the Si / SiOx composite matrix coated with Li3Zr2(PO4)3. After ultrasonic dispersion, spray drying is carried out.

[0055] Step 5: Transfer the material obtained in Step 4 to a tubular carbonization furnace and carbonize it for 1 hour under the conditions of an argon inert atmosphere and a temperature of 1100 °C to obtain an amorphous carbon / Li3Zr2(PO4)3 double-coated Si / SiOx composite matrix containing boron and carbon fiber, which is the silicon-carbon composite material prepared in Example 3 of the present application.

[0056] To verify the technical effects achieved in the embodiments of the present application, the present application also specifically sets the following comparative examples:

[0057] Comparative Example 1: The technical solution of this Comparative Example 1 is the same as that of Example 1, except that in the preparation of the silicon-carbon composite material in this comparative example, Step 3 is cancelled, and the Si / SiOx composite matrix obtained in Step 2 is used to replace the Si / SiOx composite matrix coated with LiTi2(PO4)3 in Step 4, and Steps 4 and 5 are directly implemented to obtain the silicon-carbon composite material of this Comparative Example 1.

[0058] Comparative Example 2: The technical solution of this Comparative Example 2 is the same as that of Example 1, except that Steps 4 and 5 are cancelled, and the Si / SiOx composite matrix coated with LiTi2(PO4)3 obtained in Step 3 is used as the silicon-carbon composite material in this Comparative Example 2.

[0059] Comparative Example 3: Take 100 g of the Si / SiOx composite matrix obtained in Step 2 of Example 1 and 10 g of LiTi2(PO4)3 respectively and put them into a ball mill for ball milling. The ball milling speed is 400 r / min and the ball milling time is 2 hours to obtain a precursor powder;

[0060] Then add 90 g of the precursor powder, 5 g of phenolic resin and 5 g of carbon fiber to a mixer and stir at room temperature. Stir and mix at a speed of 500 r / min for 60 min to obtain a mixture;

[0061] Then transfer the mixture to a sintering furnace and carry out heat sintering in an argon atmosphere. The heating rate is 5 °C / min, and it is heated to 850 °C and held for 3 hours to obtain the silicon-carbon composite material of this Comparative Example 3.

[0062] Comparative Example 4: In this Comparative Example 4, 100 g of the Si / SiOx composite matrix coated with LiTi2(PO4)3 obtained in Step 3 of Example 1 was taken and added to 500 ml of a water-soluble phenolic resin ethylene glycol solution with a mass concentration of 1%. After ultrasonic dispersion to uniformity, it was spray-dried; then it was transferred to a tubular carbonization furnace and carbonized for 1 hour under an argon inert atmosphere at a temperature of 1100 °C to obtain a Si / SiOx composite matrix coated with amorphous carbon / LiTi2(PO4)3 bilayer, and the silicon-carbon composite material of this Comparative Example 4 was obtained.

[0063] In order to conduct effect comparison and verification for the above examples and comparative examples, the present application used the silicon-carbon composite materials obtained in the above Examples 1-3 and Comparative Examples 1-4 as the active substance raw materials for the negative electrode material of a lithium-ion battery, and assembled 7 button cells from them respectively through the following method:

[0064] A binder, a conductive agent and a solvent were added to the corresponding silicon-carbon composite material, stirred to make a slurry, coated on a copper foil, and dried and rolled to obtain a negative electrode sheet. Among them, the binder used was LA132, the conductive agent was conductive carbon black (SP), the solvent was N-methylpyrrolidone (NMP), and the dosage ratio of the silicon-carbon composite material, SP, LA132, and NMP was 95 g: 1 g: 4 g: 220 mL; a metal lithium sheet was used as the counter electrode, the separator was a polypropylene (PP) film, the electrolyte used LiPF6 as the electrolyte, and a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1 was used as the solvent; the button cells were assembled in a glove box filled with argon.

[0065] The present application conducted electrochemical performance tests on the button cells respectively prepared corresponding to the above Examples 1-3 and Comparative Examples 1-4. Among them, the electrochemical performance tests were specifically carried out on a Wuhan Blue Electric CT2001A battery tester. Among them, the charge-discharge conditions adopted during the test were: the charge-discharge voltage range was 0.005 V - 2.0 V, and the charge-discharge rate was 0.1 C.

[0066] Please refer to Table 1 below for the test results:

[0067] Table 1 Comparative results of electrochemical performance tests of button cells prepared in each example and comparative example

[0068]

[0069] It can be seen from the data performance in Table 1 that when the silicon-carbon composite materials prepared in Examples 1-3 of the present invention are used as the active material raw material for the battery negative electrode sheet, the battery can obtain significantly higher specific capacity and its first efficiency performance (compared with Comparative Examples 1-4). During actual operation, the fast ion conductor discharges and releases lithium ions, reducing its irreversible capacity and thus effectively improving the first efficiency. At the same time, the electron coating layer reduces the polarization of the material, improves the specific capacity per gram of the material, and thus improves the specific capacity of the material. At the same time, the double coating layer provided in Examples 1-3 can restrain the expansion of silicon during charge and discharge, thereby reducing the full charge expansion of the battery.

[0070] In order to compare and verify the effects of the above examples and comparative examples, the present application also used the silicon-carbon composite materials obtained in the above Examples 1-3 and Comparative Examples 1-4 as the active material raw materials for the negative electrode materials of lithium-ion batteries, and assembled them into 7 soft-pack batteries with a specification of 5 Ah through the following methods respectively. According to the order of Example 1, Example 2, Example 3 and Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, the corresponding soft-pack batteries prepared were respectively marked as C1, C2, C3 and D1, D2, D3, D4:

[0071] Dope 90 wt% (by weight percentage of the negative electrode sheet) of artificial graphite in the corresponding silicon-carbon composite material to prepare a negative electrode sheet. Use ternary material (Li(Ni 0.6 Co 0.2 Mn 0.2 )O2) as the positive electrode material, use Celgard 2400 membrane as the separator, use LiPF6 as the electrolyte for the electrolyte, and use a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1 as the solvent, and the concentration of LiPF6 is 1.3 mol / L; prepare a 5 Ah soft-pack battery.

[0072] First, the present application conducted the following performance tests on the negative electrode sheets corresponding to the above Examples 1-3 and Comparative Examples 1-4 respectively. For the test results, please refer to Table 2 and Table 3 below:

[0073] A. Liquid absorption capacity test: Use a 1 mL burette, suck V mL of electrolyte, drop a drop on the surface of the negative electrode sheet, and start timing until the electrolyte is completely absorbed. Record the required time t, and calculate the liquid absorption speed of the electrode sheet as V / t.

[0074] B. Liquid retention rate test: Calculate the theoretical liquid absorption amount m1 of the negative electrode sheet according to the negative electrode sheet parameters, and weigh the weight m2 of the electrode sheet. Then soak the negative electrode sheet in the electrolyte for 24 h, weigh the weight of the negative electrode sheet as m3, calculate the liquid absorption amount of the negative electrode sheet = m3 - m2, and calculate the liquid retention rate according to the following formula:

[0075] Liquid retention rate = (m3 - m2) * 100% / m1.

[0076] Table 2 Comparison results of liquid absorption and retention capacity tests of negative electrode sheets prepared in each example and comparative example

[0077]

[0078] As can be seen from Table 2 above, when the silicon-carbon composite materials prepared in Examples 1-3 of the present invention are used as the active material raw materials of the battery negative electrode sheet, the liquid absorption and retention capacities of the negative electrode sheets are significantly higher than those of Comparative Examples 1-4. The experimental results show that the negative electrode sheets prepared with the silicon-carbon composite materials provided by the present invention have higher liquid absorption and retention capacities.

[0079] C. Testing of the resistivity of the electrode sheet: Use a resistivity tester to test the resistivity of the electrode sheet.

[0080] D. Testing of the rebound rate of the electrode sheet: First, use a thickness gauge to measure the average thickness of the negative electrode sheet as D1. Then, place the negative electrode sheet in a vacuum drying oven at 80 °C for 48 hours, measure the thickness of the negative electrode sheet as D2, and calculate the rebound rate according to the following formula:

[0081] Rebound rate = (D2 - D1) * 100% / D1.

[0082] Table 3 Comparison results of rebound rate tests of negative electrode sheets prepared in each example and comparative example

[0083]

[0084]

[0085] As can be seen from Table 3 above, when the silicon-carbon composite materials prepared in Examples 1-3 of the present invention are used as the active material raw materials of the battery negative electrode sheet, the rebound rate of the negative electrode sheet is significantly lower than that of Comparative Examples 1-4, confirming that the negative electrode sheet prepared with the silicon-carbon composite materials provided by the present invention has a lower rebound rate.

[0086] Then, the present application carried out the following cycle performance tests on the soft-pack batteries corresponding to Examples 1-3 and Comparative Examples 1-4 above:

[0087] The charge and discharge conditions used for the cycle performance test are: at a charge and discharge rate of 1C / 1C and a voltage range of 2.5V - 4.2V, test the cycle performance of the battery at a temperature of 25 ± 3 °C. The test results are shown in Table 4 below:

[0088] Table 4 Comparison results of cycle performance tests of soft-pack batteries prepared in each example and comparative example

[0089]

[0090] As can be seen from Table 4, when the silicon-carbon composite materials prepared in Examples 1-3 of the present invention are used as the active material raw material for the battery negative electrode sheet, the battery can obtain significantly better cycle performance (compared with Comparative Examples 1-4); during actual operation, the negative electrode sheet made of the silicon-carbon composite material provided by the present invention has a lower expansion rate, ensuring that the structure of the electrode sheet is more stable during the charge and discharge process of the battery, and improving the cycle performance of the battery.

[0091] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be construed as limiting the claimed claim.

[0092] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A silicon-carbon composite material, characterized in that, It at least includes silicon-based particles as the core and a coating layer as the shell; wherein, the coating layer includes a fast ion conductive layer coated on the outer surface of the silicon-based particles and an electron conductive layer coated on the outer surface of the fast ion conductive layer, and the mass ratio among the silicon-based particles, the fast ion conductive layer and the electron conductive layer is 100:1-8:1-8; The fast ion conductive layer is coated on the outer surface of the silicon-based particles by atomic vapor deposition; the silicon-based particles include a Si / SiOx composite matrix, where 0 < X < 2, and the mass ratio of Si to SiO in the Si / SiOx composite matrix is 10:1 - 10; the material of the fast ion conductive layer includes LiTi2(PO4)3 and / or Li3V2(PO4)3 and / or Li3Zr2(PO4)3 and / or Li3Sr2(PO4)3 and / or Li3Fe2(PO4)3 and / or Li3Ti2(PO4)3; the material of the electron conductive layer is amorphous carbon containing boron and carbon fiber. Specifically, the silicon-based particles coated with the fast ion conductive layer are dispersed and mixed in a pre-coating solution, dried and then carbonized by vapor deposition to form the electron conductive layer on the outer surface of the fast ion conductive layer; the pre-coating solution includes carbon fiber, borane compound and a water-soluble phenolic resin organic solvent solution, where the mass ratio of carbon fiber, borane compound, water-soluble phenolic resin to silicon-based particles is 1 - 8:1 - 8:8 - 15:100; in the carbonization by vapor deposition after drying, the temperature range is set at 700 - 1100 °C for at least 1 hour of carbonization; the mass proportion of boron in the electron conductive layer is 1 - 10%, and the mass proportion of carbon fiber in the electron conductive layer is 1 - 10%, and the rest is amorphous carbon. X The fast ion conductive layer is coated on the outer surface of the silicon-based particles by atomic vapor deposition; the silicon-based particles include a Si / SiOx composite matrix, where 0 < X < 2, and the mass ratio of Si to SiO in the Si / SiOx composite matrix is 10:1 - 10; the material of the fast ion conductive layer includes LiTi2(PO4)3 and / or Li3V2(PO4)3 and / or Li3Zr2(PO4)3 and / or Li3Sr2(PO4)3 and / or Li3Fe2(PO4)3 and / or Li3Ti2(PO4)3; the material of the electron conductive layer is amorphous carbon containing boron and carbon fiber. Specifically, the silicon-based particles coated with the fast ion conductive layer are dispersed and mixed in a pre-coating solution, dried and then carbonized by vapor deposition to form the electron conductive layer on the outer surface of the fast ion conductive layer; the pre-coating solution includes carbon fiber, borane compound and a water-soluble phenolic resin organic solvent solution, where the mass ratio of carbon fiber, borane compound, water-soluble phenolic resin to silicon-based particles is 1 - 8:1 - 8:8 - 15:100; in the carbonization by vapor deposition after drying, the temperature range is set at 700 - 1100 °C for at least 1 hour of carbonization; the mass proportion of boron in the electron conductive layer is 1 - 10%, and the mass proportion of carbon fiber in the electron conductive layer is 1 - 10%, and the rest is amorphous carbon.

2. The preparation method of the silicon-carbon composite material according to claim 1, characterized in that, It includes the following operation steps: S10): Using nano-Si and SiO2 particles as raw materials, after mixing the two evenly, at least part of the raw materials undergo disproportionation reaction under a heating environment, and after condensation and crushing, a Si / SiOx composite matrix is obtained, and the Si / SiOx composite matrix is used as the silicon-based particles; S20): Depositing and coating a fast ion conductor used as a target on the silicon-based particles by atomic vapor deposition to obtain silicon-based particles coated with a fast ion conductive layer; S30): Dispersing and mixing the silicon-based particles coated with a fast ion conductive layer in a pre-coating solution, drying and then carbonizing by vapor deposition to form and coat an electron conductive layer on the outer surface of the fast ion conductive layer; The pre-coating solution therein includes carbon fiber, borane compound and a water-soluble phenolic resin organic solvent solution, wherein the mass ratio among the carbon fiber, the borane compound, the water-soluble phenolic resin and the silicon-based particles is 1-8:1-8:8-15:100; in the carbonization by vapor deposition after drying, the temperature range is set at 700-1100 °C for carbonization for at least 1 hour; S40): Obtaining the silicon-carbon composite material.

3. The preparation method according to claim 2, characterized in that, The borane compound includes diborane and / or tetraborane and / or pentaborane and / or hexaborane; the organic solvent includes ethylene glycol and / or ethanol and / or butanediol and / or benzyl alcohol and / or phenylpentanol and / or allyl alcohol.

4. The preparation method according to claim 2, wherein, In step S10), the mass ratio of the nano-Si and SiO2 particles is 1-2:1; in the heating environment, the temperature range is set at 1500-2000 °C, and at this temperature condition, it is kept warm for at least 1 hour, and at the same time, the vacuum degree range is set at 100-1000 Pa.

5. The preparation method according to claim 2, characterized in that, In the atomic vapor deposition method of step S20), the temperature range is set at 800-1200 °C, and the pressure range is set at 0.1-0.5 Torr, so that the fast ion conductor is vaporized and then deposited and coated on the silicon-based particles.

6. The application of the silicon-carbon composite material according to claim 1, characterized in that, Using the silicon-carbon composite material as the active substance raw material for preparing a battery electrode sheet.

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