Silicon-carbon composite material and preparation and application thereof

Abstract

The invention provides a silicon-carbon composite material as well as preparation and application thereof. Raw materials for preparing the silicon-carbon composite material comprise a silicon material and a compound A, wherein the chemical structure of the silicon material is shown as a formula (I); the chemical structure of the compound A is shown as a formula (II); r1, R2 and R3 are independently selected from a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group and a substituted or unsubstituted enamine group; and at least one of R1, R2, and R3 contains an alkenyl group. In the application, after the silicon material with a plurality of reaction sites and the compound A containing the vinyl and the thiazole ring are subjected to in-situ polymerization, a cage-shaped nano structure can be introduced into the silicon-carbon composite material, so that active sites embedded by lithium ions are increased, and the electrochemical performance of the silicon-carbon composite material is improved. In addition, a thiazole ring in the compound A can provide an N element and an S element for the silicon-carbon composite material, so that the cycling stability of the silicon-carbon composite material is enhanced; the introduction of the S element can enhance the conductivity of the silicon-carbon composite material, and the introduction of the S-C bond can enhance the mechanical strength of the carbon matrix and improve the structural stability of the silicon-carbon negative electrode. Therefore, the silicon-carbon composite material provided by the invention has good electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the field of secondary batteries, and particularly relates to a silicon-carbon composite material, its preparation and application. Background Art

[0002] In the lithium-ion battery preparation technology, graphite is often used as the anode material due to its stable electrochemical performance and low working voltage. However, the theoretical specific capacity of the graphite anode is only 372 mAh / g, and the current technology has approached its limit, making it difficult to meet the demand for higher energy density. Silicon, on the other hand, has a theoretical specific capacity as high as 4200 mAh / g and a moderate working voltage, so it is regarded as the most likely material to replace the graphite anode. With the continuous improvement of the requirements for battery energy density and fast charging performance in fields such as new energy vehicles and smart phones, the silicon-carbon anode has broad application prospects due to its high energy density and fast charging performance advantages. In the field of new energy vehicles, the silicon-carbon anode material has been preliminarily applied, and with the maturity of new silicon-carbon technologies, it is expected to accelerate penetration into other fields.

[0003] However, the silicon-carbon anode faces many problems in the development process. For example, the silicon material has a large specific surface area, resulting in the formation of a large-area SEI film during the first lithium intercalation process of the electrode, which consumes lithium ions in the battery and makes the first Coulomb efficiency relatively low. There is a significant volume effect during the charge and discharge process of the silicon anode, resulting in the fragmentation of its particles, loss of electrical contact with the current collector, and serious interfacial side reactions. In addition, nano-silicon has a high surface energy and is extremely easy to agglomerate into micron-sized particles, which makes the core difficulty in the production of silicon-carbon anodes lie in the preparation of nano-silicon powder. Moreover, the preparation process of silicon-based anode materials is complex, and each process is different, and the products have not yet reached standardization, resulting in their high prices.

[0004] Currently, many domestic enterprises have laid out the silicon-carbon anode industry, attracting a large amount of capital investment, and the industry's production capacity has accelerated expansion. In order to further improve the market competitiveness of silicon-carbon anodes, it is necessary to improve the above problems, such as suppressing the volume expansion of silicon-carbon anodes and reducing the cost of silicon-carbon anodes, so that they can be comparable to graphite anode materials.

[0005] The new silicon-carbon anode uses the CVD chemical vapor deposition method to load nano-silicon in porous carbon. The cavities of the porous carbon retain enough space for the expansion of the silicon anode and a larger specific surface area. However, this further exacerbates the interfacial side reactions and affects the long-term cycle performance of the silicon-carbon anode material. And the CVD chemical vapor deposition method requires the use of special equipment and processes, with high equipment costs, complex processes, and high technical requirements for operators; in addition, the deposition rate of the CVD chemical vapor deposition method is relatively low, and a long time is required during the preparation process, affecting production efficiency. Summary of the Invention

[0006] In order to improve the electrochemical performance of the silicon-carbon composite material, the present application provides a silicon-carbon composite material and its preparation and application.

[0007] According to one aspect of the present application, there is provided a silicon-carbon composite material. The raw materials for preparing the silicon-carbon composite material include a silicon material and a compound A. Among them, the chemical structure of the silicon material is shown in formula (I); the chemical structure of the compound A is shown in formula (II); R1, R2, and R3 are independently selected from a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, and a substituted or unsubstituted enamine group; and at least one of R1, R2, and R3 contains an alkenyl group.

[0008]

[0009] In the present application, after in-situ polymerization of the silicon material with multiple reaction sites and the compound A containing both a vinyl group and a thiazole ring, a cage-shaped nanostructure can be introduced into the silicon-carbon composite material, thereby increasing the active sites for lithium ion insertion and improving the electrochemical performance of the silicon-carbon composite material. In addition, the thiazole ring in the compound A can provide N and S elements for the silicon-carbon composite material. Among them, the introduction of the N element can improve the surface polarization of the silicon-carbon composite material, the introduction of the S element can enhance the conductivity of the silicon-carbon composite material, and the introduction of the S-C bond can enhance the mechanical strength of the carbon matrix. Therefore, by introducing the thiazole ring simultaneously, the first Coulomb efficiency and long-term cycling performance of the silicon-carbon composite material can be improved. Thus, the silicon-carbon composite material provided by the present application has good electrochemical performance.

[0010] Preferably, the compound A includes at least one of

[0011] Preferably, the method for preparing the silicon-carbon composite material includes the following steps: S1. Sequentially mix the silicon material, the compound A, and a photoinitiator, and carry out an in-situ polymerization reaction under ultraviolet light to obtain a first reactant; S2. Calcinate the first reactant in an inert atmosphere to obtain a second reactant; S3. Mix the second reactant with magnesium powder and carry out a magnesiothermic reduction reaction in an inert atmosphere to obtain a third reactant; S4. Mix the third reactant with molten lithium metal and carry out a prelithiation reaction to obtain the silicon-carbon composite material.

[0012] In this application, first, the silicon material is connected to compound A through ultraviolet polymerization, and the special three-dimensional framework of the silicon material can be completely maintained. The silicon material and compound A still maintain structural integrity after in-situ polymerization, which is the key to ensuring that the silicon-carbon composite material still has a unique polyhedral structure after steps such as carbonization, reduction, and prelithiation. The magnesium thermal reduction method can further reduce the impurities in the silicon-carbon composite material and improve the purity and structural integrity of the silicon-carbon composite material. Finally, through the prelithiation reaction, lithium can be stored to continuously supplement lithium loss and compensate for the formation of CEI and SEI on the positive and negative electrodes and irreversible lithium loss during the first cycle. In addition, the prelithiation reaction can also obtain a silicon-carbon negative electrode material with a solid electrolyte interface film containing lithium oxide. Thus, through the preparation method provided in this application, it is possible to alleviate the volume effect while reducing interfacial side reactions, thereby improving the first Coulombic efficiency.

[0013] Preferably, in S1, calculated by mass ratio, silicon material: compound A = 1:(5 - 10).

[0014] Preferably, the mass of the photoinitiator is 1 - 5% of that of compound A.

[0015] Preferably, the photoinitiator is benzophenone, and in S1, the wavelength of the ultraviolet light is one of 250 nm, 370 nm, and 620 nm.

[0016] Preferably, in S1, the reaction temperature of the in-situ polymerization reaction is 80 - 150 °C, and the reaction time is 20 - 30 minutes.

[0017] Preferably, the first reactant is sequentially subjected to washing treatment, drying treatment, grinding treatment and then calcination treatment.

[0018] Preferably, in S2, the calcination temperature of the calcination treatment is 400 - 800 °C, and the calcination time is 5 - 6 hours.

[0019] Preferably, in S3, calculated by mass ratio, magnesium powder: second reactant = 1:(0.5 - 1).

[0020] Preferably, in S3, the reaction temperature of the magnesium thermal reduction reaction is 500 - 800 °C, and the reaction time is 8 - 20 hours.

[0021] Preferably, in S4, calculated by mass ratio, the lithium metal: the third reactant = 1:(5 - 10).

[0022] Preferably, in S4, the reaction temperature of the prelithiation reaction is 300 - 350 °C, and the reaction time is 1 - 3 hours.

[0023] In the second aspect of the present application, a negative electrode is provided, which includes the silicon-carbon composite material as described above.

[0024] In the second aspect of the present application, a lithium-ion battery is provided, which includes the negative electrode as described above. Detailed implementation manners

[0025] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0026] Embodiment 1

[0027] 1. Raw materials for preparing the silicon-carbon composite material

[0028] In this embodiment, the raw materials required for preparing the silicon-carbon composite material are weighed according to Table 1, wherein the chemical structure of the silicon material is shown in Formula (I). That is, calculated by mass ratio, silicon material: Compound A = 1:5, and the mass of the photoinitiator is 1% of Compound A.

[0029] Table 1. Raw materials required for this embodiment

[0030]

[0031] 2. Method for preparing the silicon-carbon composite material

[0032] In this embodiment, the silicon-carbon composite material is prepared according to the following steps:

[0033] S1. Add the silicon material to Compound A, and under the action of magnetic stirring, mix evenly. Then add the photoinitiator and stir evenly, and then put the reaction system into an ultraviolet analyzer. Under the action of ultraviolet light with a wavelength of 370 nm, carry out an in-situ polymerization reaction for 20 minutes to obtain a first reactant;

[0034] S2. Filter and wash the first reactant with absolute ethanol, then vacuum dry it at 85 °C for 12 h, and then grind it to obtain a powder of the first reactant. Subsequently, place the above powder in a nitrogen atmosphere and calcine it under the condition of high-temperature calcination at 700 °C for 5 hours to obtain a second reactant;

[0035] S3. Mix 0.8 parts of the second reactant with 1 part of magnesium powder. Place the mixture in an argon atmosphere and calcine it at 700 °C for 10 hours to carry out the magnesiothermic reduction reaction. After the reaction is completed, add hydrochloric acid with a concentration of 1 mol / L to the obtained powdered solid, soak it to remove the excess magnesium powder and magnesium oxide, then wash it with deionized water. Subsequently, dry it at 100 °C for 8 hours to obtain the third reactant;

[0036] S4. Add the third reactant to molten lithium metal at 300 °C and carry out the prelithiation reaction under N2 protection to obtain the silicon-carbon composite material.

[0037] 3. Preparation of the negative electrode and lithium-ion battery

[0038] (1) Preparation of the positive electrode sheet: Mix lithium iron phosphate (LiFePO4), SP, CNT, and VDF in a mass ratio of 96:1.8:1.5:0.7 and stir. Use NMP as the solvent to obtain the positive electrode slurry. Subsequently, coat the positive electrode slurry on a 12-μm carbon-coated aluminum foil and dry it at 90 °C to obtain a dried positive electrode sheet.

[0039] (2) Preparation of the negative electrode sheet: Mix the above-prepared silicon-carbon composite material, SP, CMC, and SBR in a mass ratio of 95.5:2:0.5:2 and stir. Use deionized water as the solvent to obtain the negative electrode slurry. Then coat the negative electrode slurry on an 8-μm copper foil and vacuum-dry it at 100 °C to obtain a dried negative electrode sheet.

[0040] (3) Preparation of the lithium-ion battery electrolyte: Prepare the electrolyte in a glove box filled with argon, where the water content in the glove box is less than 10 ppm and the oxygen content is less than 1 ppm. The preparation of the electrolyte includes the following steps: Configure an electrolyte of 1.2 mol / L lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LFSI) with a volume ratio of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) = 30:40:30. Among them, calculate the mass ratio of LiPF6:LFSI = 1.1:0.1, then add 0.5 wt.% of the additive vinylene carbonate (VC), 1.5 wt.% of fluoroethylene carbonate (FEC), 0.5% of divinyl sulfone (DTD), and 0.5% of lithium difluorophosphate (LiPO2F2), and mix evenly for later use.

[0041] (4) Assembly of the lithium-ion battery: Carry out punching treatment on the vacuum-dried positive and negative electrode sheets and the separator, and then assemble them into a CR2032 button battery in a glove box filled with argon.

[0042] Example 2

[0043] This example prepares a silicon-carbon composite material, as well as a negative electrode and a lithium-ion battery using the same, with reference to the formulation and method provided in Example 1. The difference from Example 1 is that when preparing the silicon-carbon composite material in this example, the mass fraction of compound A used is 3.5 parts, and the mass fraction of the photoinitiator is 0.035 parts (that is, calculated by mass ratio, silicon material: compound A = 1:7; the mass of the photoinitiator is 1% of compound A). Except for the above differences, the operating steps for preparing the silicon-carbon composite material, as well as the negative electrode and lithium-ion battery using the same, in this example are strictly the same as those in Example 1.

[0044] Example 3

[0045] This example prepares a silicon-carbon composite material, as well as a negative electrode and a lithium-ion battery using the same, with reference to the formulation and method provided in Example 1. The difference from Example 1 is that when preparing the silicon-carbon composite material in this example, the mass fraction of compound A used is 5 parts, and the mass fraction of the photoinitiator is 0.05 parts (that is, calculated by mass ratio, silicon material: compound A = 1:10; the mass of the photoinitiator is 1% of compound A). Except for the above differences, the operating steps for preparing the silicon-carbon composite material, as well as the negative electrode and lithium-ion battery using the same, in this example are strictly the same as those in Example 1.

[0046] Example 4

[0047] This example prepares a silicon-carbon composite material, as well as a negative electrode and a lithium-ion battery using the same, with reference to the formulation and method provided in Example 1. The difference from Example 1 is that when preparing the silicon-carbon composite material in this example, the mass fraction of compound A used is 6 parts, and the mass fraction of the photoinitiator is 0.06 parts (that is, calculated by mass ratio, silicon material: compound A = 1:12; the mass of the photoinitiator is 1% of compound A). Except for the above differences, the operating steps for preparing the silicon-carbon composite material, as well as the negative electrode and lithium-ion battery using the same, in this example are strictly the same as those in Example 1.

[0048] Example 5

[0049] This example prepares a silicon-carbon composite material, as well as a negative electrode and a lithium-ion battery using the same, with reference to the formulation and method provided in Example 1. The difference from Example 1 is that when preparing the silicon-carbon composite material in this example, the mass fraction of compound A used is 1 part, and the mass fraction of the photoinitiator is 0.01 parts (that is, calculated by mass ratio, silicon material: compound A = 1:2; the mass of the photoinitiator is 1% of compound A). Except for the above differences, the operating steps for preparing the silicon-carbon composite material, as well as the negative electrode and lithium-ion battery using the same, in this example are strictly the same as those in Example 1.

[0050] Example 6

[0051] This example prepares a silicon-carbon composite material, as well as a negative electrode and a lithium-ion battery using the same, with reference to the formula and method provided in Example 2. The difference from Example 2 is that when preparing the silicon-carbon composite material in this example, the mass fraction of the photoinitiator used is 0.105 parts (that is, the mass of the photoinitiator is 3% of that of Compound A). Except for the above difference, the operating steps for preparing the silicon-carbon composite material, as well as the negative electrode and the lithium-ion battery using the same, in this example are strictly the same as those in Example 2.

[0052] Example 7

[0053] This example prepares a silicon-carbon composite material, as well as a negative electrode and a lithium-ion battery using the same, with reference to the formula and method provided in Example 2. The difference from Example 2 is that when preparing the silicon-carbon composite material in this example, the mass fraction of the photoinitiator used is 0.175 parts (that is, the mass of the photoinitiator is 5% of that of Compound A). Except for the above difference, the operating steps for preparing the silicon-carbon composite material, as well as the negative electrode and the lithium-ion battery using the same, in this example are strictly the same as those in Example 2.

[0054] Example 8

[0055] This example prepares a silicon-carbon composite material, as well as a negative electrode and a lithium-ion battery using the same, with reference to the formula and method provided in Example 6. The difference from Example 6 is that when preparing the silicon-carbon composite material in this example, the structural formula of Compound A used is: Except for the above difference, the operating steps for preparing the silicon-carbon composite material, as well as the negative electrode and the lithium-ion battery using the same, in this example are strictly the same as those in Example 6.

[0056] Example 9

[0057] This example prepares a silicon-carbon composite material, as well as a negative electrode and a lithium-ion battery using the same, with reference to the formula and method provided in Example 6. The difference from Example 6 is that when preparing the silicon-carbon composite material in this example, the structural formula of Compound A used is: Except for the above difference, the operating steps for preparing the silicon-carbon composite material, as well as the negative electrode and the lithium-ion battery using the same, in this example are strictly the same as those in Example 6.

[0058] Example 10

[0059] This example prepares a silicon-carbon composite material, as well as a negative electrode and a lithium-ion battery using the same, with reference to the formula and method provided in Example 6. The difference from Example 6 is that when preparing the silicon-carbon composite material in this example, the structural formula of Compound A used is: Except for the above difference, the operating steps for preparing the silicon-carbon composite material, as well as the negative electrode and the lithium-ion battery using the same, in this example are strictly the same as those in Example 6.

[0060] Example 11

[0061] This example prepares a silicon-carbon composite material, as well as a negative electrode and a lithium-ion battery using the same, with reference to the formulation and method provided in Example 6. The difference from Example 6 is that when preparing the silicon-carbon composite material in this example, the structural formula of compound A used is: Except for the above differences, the operating steps for preparing the silicon-carbon composite material, as well as the negative electrode and the lithium-ion battery using the same, in this example are strictly the same as those in Example 6.

[0062] Example 12

[0063] This example prepares a silicon-carbon composite material, as well as a negative electrode and a lithium-ion battery using the same, with reference to the formulation and method provided in Example 6. The difference from Example 6 is that when preparing the silicon-carbon composite material in this example, the calcination temperature in S2 is 800 °C. Except for the above differences, the operating steps for preparing the silicon-carbon composite material, as well as the negative electrode and the lithium-ion battery using the same, in this example are strictly the same as those in Example 6.

[0064] Example 13

[0065] This example prepares a silicon-carbon composite material, as well as a negative electrode and a lithium-ion battery using the same, with reference to the formulation and method provided in Example 6. The difference from Example 6 is that when preparing the silicon-carbon composite material in this example, the calcination temperature in S2 is 1000 °C. Except for the above differences, the operating steps for preparing the silicon-carbon composite material, as well as the negative electrode and the lithium-ion battery using the same, in this example are strictly the same as those in Example 6.

[0066] Example 14

[0067] This example prepares a silicon-carbon composite material, as well as a negative electrode and a lithium-ion battery using the same, with reference to the formulation and method provided in Example 12. The difference from Example 12 is that when preparing the silicon-carbon composite material in this example, the temperature of the magnesiothermic reduction reaction in S3 is 800 °C. Except for the above differences, the operating steps for preparing the silicon-carbon composite material, as well as the negative electrode and the lithium-ion battery using the same, in this example are strictly the same as those in Example 12.

[0068] Example 15

[0069] This example prepares a silicon-carbon composite material, as well as a negative electrode and a lithium-ion battery using the same, with reference to the formulation and method provided in Example 12. The difference from Example 12 is that when preparing the silicon-carbon composite material in this example, the temperature of the magnesiothermic reduction reaction in S3 is 1000 °C. Except for the above differences, the operating steps for preparing the silicon-carbon composite material, as well as the negative electrode and the lithium-ion battery using the same, in this example are strictly the same as those in Example 12.

[0070] Example 16

[0071] In this embodiment, a silicon-carbon composite material, a negative electrode using the same, and a lithium-ion battery are prepared with reference to the formulation and method provided in Example 14. The difference from Example 14 is that during the preparation of the silicon-carbon composite material in this embodiment, prelithiation treatment is not performed (i.e., step S4 is omitted, and the third reactant is used as the silicon-carbon composite material). Except for the above difference, the operating steps for preparing the silicon-carbon composite material, the negative electrode using the same, and the lithium-ion battery in this embodiment are strictly the same as those in Example 14.

[0072] Comparative Example 1

[0073] In this comparative example, a negative electrode and a lithium-ion battery are prepared with reference to the formulation and method provided in Example 1. The difference from Example 1 is that during the preparation of the negative electrode in this comparative example, the active material used is commercially available Si@C (by mass ratio Si:C = 6:4). Except for the above difference, the operating steps for preparing the negative electrode and the lithium-ion battery in this comparative example are strictly the same as those in Example 1.

[0074] Comparative Example 2

[0075] In this comparative example, a silicon-carbon composite material, a negative electrode using the same, and a lithium-ion battery are prepared with reference to the formulation and method provided in Example 14. The difference from Example 14 is that during the preparation of the silicon-carbon composite material in this comparative example, the structural formula of compound A used is: Except for the above difference, the operating steps for preparing the silicon-carbon composite material, the negative electrode using the same, and the lithium-ion battery in this comparative example are strictly the same as those in Example 14.

[0076] Comparative Example 3

[0077] In this comparative example, a silicon-carbon composite material, a negative electrode using the same, and a lithium-ion battery are prepared with reference to the formulation and method provided in Example 14. The difference from Example 14 is that during the preparation of the silicon-carbon composite material in this comparative example, the structural formula of compound A used is: Except for the above difference, the operating steps for preparing the silicon-carbon composite material, the negative electrode using the same, and the lithium-ion battery in this comparative example are strictly the same as those in Example 14.

[0078] Comparative Example 4

[0079] In this comparative example, a silicon-carbon composite material, a negative electrode using the same, and a lithium-ion battery are prepared with reference to the formulation and method provided in Example 14. The difference from Example 14 is that during the preparation of the silicon-carbon composite material in this comparative example, the structural formula of compound A used is: Except for the above difference, the operating steps for preparing the silicon-carbon composite material, the negative electrode using the same, and the lithium-ion battery in this comparative example are strictly the same as those in Example 14.

[0080] Test Example

[0081] 1. Test objects

[0082] The lithium-ion batteries prepared in Examples 1-16 and Comparative Examples 1-4.

[0083] 2. Test methods

[0084] (1) 25°C 1C charge-discharge cycle test: Charge and discharge at 1C for 2000 cycles at 25°C, with the voltage range of 2.5 - 3.65V. Calculate the capacity retention rate according to the following formula: Capacity retention rate = Discharge capacity after 2000 cycles / Initial capacity * 100%.

[0085] (2) Initial efficiency test: At room temperature, perform electrochemical tests on the battery using relevant battery test equipment. The charge-discharge regime in the first week is 0.1C / 0.1C, the voltage range is 2.5 - 3.65, 1C = 1600 mA / g. Calculate the initial efficiency according to the following formula: Initial efficiency = First discharge capacity / First charge capacity * 100%.

[0086] 3. Test results and analysis

[0087] The test data of this test example are shown in Table 1. Among them, by comparing the data of Examples 1-16 and Comparative Examples 1-4, it can be seen that in this application, by using a silicon material with a specific structure and a compound A having both vinyl and thiazole rings for in-situ polymerization, high-temperature carbonization, magnesiothermic reduction, and prelithiation treatment in sequence, a silicon-carbon composite material with good electrochemical performance can be obtained. Moreover, the silicon-carbon composite material obtained by the preparation method provided in this application has a high degree of consistency, a simple process, and good industrial application prospects. This is because the silicon material and compound A provided in this application still maintain structural integrity after in-situ polymerization, so that they still have a unique polyhedral structure even after high-temperature carbonization, magnesiothermic reduction, and prelithiation treatment.

[0088] It can be found in Examples 1-5 that during the in-situ polymerization reaction, the ratio between the silicon material and compound A will affect the bonding of Si-C bonds in the silicon-carbon composite material, and the S-C bonds in compound A will affect the structural stability of the silicon-carbon composite material. Thus, when the mass ratio between the silicon material and compound A satisfies 1:(5 - 10), the Si-C bonds and S-C bonds synergistically enhance the structural stability of the silicon-carbon composite material, thereby improving the long-term cycle performance of the battery. Moreover, the introduction of the thiazole ring helps to improve the surface polarization of the silicon-carbon composite material, inhibit the side reaction between the electrolyte and the electrode material, and achieve an enhanced initial Coulomb efficiency of the silicon-carbon composite material. And it can be confirmed in Examples 2, 6-7 that the content of the initiator will also affect the electrochemical performance of the silicon-carbon composite material.

[0089] Furthermore, it can be seen from Examples 6 and 8 to 11 that the selection of the material of different Compound A will also affect the initial Coulombic efficiency and long-term cycling performance of the silicon-carbon composite material. Considering the data of Comparative Examples 2 to 3, it is possible that the vinyl polymerization reaction between the silicon material and Compound A affects the stability of the polyhedral structure of the silicon-carbon composite material.

[0090] It can be found in Examples 6 and 12 to 13 that the calcination temperature of the calcination treatment will affect the carbonization effect; similarly, based on the data of Examples 12 and 14 to 15, it can be known that the reaction temperature of the magnesiothermic reduction reaction will affect the purity and structural integrity of the silicon-carbon composite material; and by comparing Example 14 with Example 16, it can be confirmed that by performing a prelithiation reaction on the silicon-carbon material, its electrochemical performance can be significantly improved.

[0091] Table 1. Test Results

[0092]

[0093]

[0094] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A silicon-carbon composite material, characterized in that, The raw materials for preparing the silicon-carbon composite material include a silicon material and Compound A; Among them, the chemical structure of the silicon material is shown in Formula (I); The chemical structure of Compound A is shown in Formula (II); R1, R2, and R3 are independently selected from a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, and a substituted or unsubstituted enamine group; And at least one of R1, R2, and R3 contains an alkenyl group.

2. The silicon-carbon composite material according to claim 1, wherein The compound A includes at least one of them.

3. The silicon-carbon composite material according to claim 1, characterized in that, The method for preparing the silicon-carbon composite material includes the following steps: S1. Sequentially mix the silicon material, Compound A, and a photoinitiator, and carry out an in-situ polymerization reaction under ultraviolet light to obtain a first reactant; S2. Calcinate the first reactant in an inert atmosphere to obtain a second reactant; S3. Mix the second reactant with magnesium powder and carry out a magnesiothermic reduction reaction in an inert atmosphere to obtain a third reactant; S4. Mix the third reactant with molten lithium metal and carry out a prelithiation reaction to obtain the silicon-carbon composite material.

4. The silicon-carbon composite material according to claim 3, wherein In S1, calculated by mass ratio, the silicon material: Compound A = 1:(5-10).

5. The silicon-carbon composite material according to claim 3 or 4, characterized in that, The mass of the photoinitiator is 1-5% of Compound A.

6. The silicon-carbon composite material according to claim 3, wherein, The photoinitiator is benzophenone, and in S1, the wavelength of the ultraviolet light is one of 250 nm, 370 nm, and 620 nm.

7. The silicon-carbon composite material according to claim 3, wherein In S2, the calcination temperature of the calcination treatment is 400-800 °C, and the calcination time is 5-6 hours. In S3, the temperature of the magnesiothermic reduction reaction is 500-800 °C, and the calcination time is 8-20 hours.

8. The silicon-carbon composite material according to claim 3, wherein In S4, calculated by mass ratio, the lithium metal: the third reactant = 1:(5-10).

9. A negative electrode, characterized in that, The negative electrode includes the silicon-carbon composite material according to any one of claims 1-8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode according to claim 9.

Images