Preparation method of low-expansion silicon-carbon negative electrode material, silicon-carbon negative electrode material and application thereof

Abstract

The application discloses a preparation method of low-expansion silicon-carbon negative electrode material, silicon-carbon negative electrode material and application thereof, and comprises the following operation steps: step S1a), modified porous carbon is prepared; carbon source is uniformly mixed with a nonmetallic activator, and then dried to obtain a dried product; under an inert atmosphere, the temperature is raised to a temperature condition of not less than 200 DEG C and kept for at least 1 hour, then the temperature is raised to a temperature condition of not less than 700 DEG C and kept for at least 1 hour for carbonization, and the modified porous carbon is obtained; step S1b), polysilane solution is obtained; step S2), the modified porous carbon is added into a reaction kettle, and under vacuum heating, the polysilane solution is sprayed on the modified porous carbon in a liquid spray mode, so that the polysilane solution is subjected to liquid cracking; the low-expansion silicon-carbon negative electrode material obtained by the application has the advantages of low cracking temperature, small silicon grain growth, low expansion, low requirement on manufacturing environment, low cost and the like, and has good structural stability and excellent performance after being applied to a battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium ion battery material preparation, and particularly relates to a preparation method of a low-expansion silicon-carbon negative electrode material. BACKGROUND

[0002] The silicon-carbon material prepared by the sand milling method has defects such as high full-cell expansion and poor cycle performance, which limits its application in the field of electric vehicles and the like, and can only be applied in the field of small-power electrical appliances such as electric tools and digital devices. The silicon-carbon material prepared by the conventional silane cracking method has advantages such as small silicon crystal grains, small expansion and excellent cycle performance, but because it is a porous structure, the impedance is large, the safety hidden danger is large, and it is difficult to realize batch industrialization. The silicon-carbon material prepared by the liquid silane cracking method has advantages such as not harsh manufacturing environment, low reaction temperature and small safety hidden danger, but because the cracking temperature is low, the structure stability of nano-silicon and amorphous carbon is poor, the storage and the first efficiency are low, and therefore the silicon-carbon material prepared by the liquid silane cracking method is also difficult to be truly applied in the high specific energy density lithium ion battery.

[0003] The patent application with the publication number CN114556621A discloses a preparation method of a negative electrode material, and specifically proposes: dissolving a silicon source in an organic solvent to obtain a first mixture; mixing and stirring the porous carbon material with the first mixture, then heating to remove the solvent, and drying the obtained product to obtain a dried product; high-temperature cracking the dried product to obtain a Si-M-C@ porous carbon material; forming a conductive carbon layer on the surface of the Si-M-C@ porous carbon material to obtain the negative electrode material; although the method mentions preparing liquid silane, when it is implemented, the liquid silane is dried, and then the dried product also needs to be cracked by high-temperature cracking, so that the advantages of the liquid silane cracking method for preparing the silicon-carbon material are also lost.

[0004] Therefore, based on the concentrated research experience of the applicant in the field, a new technical solution is sought to solve the above technical problems. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a preparation method of a low-expansion silicon-carbon negative electrode material, the silicon-carbon negative electrode material and the application thereof, which has the advantages of low cracking temperature, small silicon crystal grain growth, low expansion, low manufacturing environment requirement, low cost and the like; at the same time, the silicon-carbon negative electrode material prepared by the present application has good structure stability, excellent performance after being applied in a battery, and effectively promotes the development process of batch application of the silicon-carbon material prepared by the liquid silane method in the high specific energy density lithium ion battery.

[0006] The technical scheme adopted by the present application is as follows:

[0007] A preparation method of a low-expansion silicon-carbon negative electrode material, at least comprising the following operation steps:

[0008] Step S1a), preparing modified porous carbon: uniformly mixing a carbon source and a non-metallic activator, drying to obtain a dried product, heating to a temperature condition of not less than 200 DEG C under an inert atmosphere and keeping for at least 1 hour, then heating to a temperature condition of not less than 700 DEG C and keeping for at least 1 hour for carbonization, to obtain modified porous carbon;

[0009] Step S1b), adding polydimethylsilane into a cracking reaction kettle, introducing inert gas under vacuum environment, cracking at a temperature condition of not higher than 350 DEG C, to obtain polysilane; then uniformly dispersing the polysilane in an organic solvent to obtain a polysilane solution;

[0010] Wherein, the step S1a) and the step S1b) can be carried out simultaneously or sequentially;

[0011] Step S2), using a silane cracking method, adding the modified porous carbon obtained in the step S1a) into a reaction kettle, under vacuum heating, spraying the polysilane solution obtained in the step S1b) to the modified porous carbon by liquid spraying, so that the polysilane solution is liquid cracked;

[0012] Step S3), obtaining the low-expansion silicon-carbon negative electrode material.

[0013] Preferably, in the step S1a), the weight ratio of the carbon source to the activated carbon is in the range of 100:1-20, preferably 100:1-10; the heating rate is 1-10 DEG C / min.

[0014] Preferably, in the step S1a), under an inert atmosphere, heating to a temperature condition of 200-300 DEG C and keeping for 1-6 hours, then heating to a temperature condition of 700-900 DEG C and keeping for 1-6 hours.

[0015] Preferably, in the step S1a), the carbon source is selected from any one or mixture of several of triethylamine, hydroxytriethylamine, diethylamine; the non-metallic activator is selected from any one or mixture of several of H3PO4, HNO3, boric acid.

[0016] Preferably, in the step S1b), polydimethylsilane is added to a cracking reaction kettle, vacuumed to ≤100 pa, then inert gas is introduced to 0.5-1 Mpa, then heated to a temperature condition of 200-300 DEG C for cracking, to obtain the polysilane.

[0017] Preferably, in the step S1b), the weight ratio of the polysilane to the organic solvent ranges from 1-20:500, preferably from 1-10:500.

[0018] Preferably, in the step S1b), the organic solvent is selected from any one or mixture of several of xylene, toluene, 1,4-dimethylbenzene, m-xylene, bromomethylbenzene, chlorotoluene, mesitylene.

[0019] Preferably, in the step S2), the modified porous carbon obtained in the step S1a) is added into a reaction kettle, the reaction kettle is vacuumed to not higher than 1 Mpa, and heated to 300-500℃, the polysilane solution obtained in the step S1b) is sprayed to the modified porous carbon by liquid spray method, so that the polysilane solution is subjected to liquid cracking, and the liquid cracking time is 1-6 hours.

[0020] Preferably, a low-expansion silicon-carbon negative electrode material is obtained by the preparation method of the low-expansion silicon-carbon negative electrode material as described above.

[0021] Preferably, the low-expansion silicon-carbon negative electrode material as described above is used as an active material raw material for preparing a battery electrode sheet, preferably as an active material raw material for a lithium ion battery negative electrode sheet.

[0022] The present application uses polydimethylsilane as a silicon source raw material to prepare a silicon-carbon material by liquid silane cracking method, which has the advantages of low cracking temperature, small silicon grain growth, low expansion, low requirement for manufacturing environment, low cost, etc. Meanwhile, the present application particularly uses a non-metallic activator to activate and dope the porous carbon, to obtain a non-metallic doped porous carbon material (i.e. modified porous carbon), which not only has the advantages of mild reaction conditions and no introduction of impurities, but also expands the interlayer spacing of the silicon-carbon material through the activator and introduces elements (such as nitrogen, boron, phosphorus, etc.) with high electronic conductivity to reduce the electronic impedance of the silicon-carbon material. Ultimately, the silicon-carbon negative electrode material prepared by the present application has good structural stability and excellent performance when applied to a battery, which effectively promotes the development process of applying the liquid silane method to prepare silicon-carbon materials in large quantities to high specific energy density lithium ion batteries. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a preparation step block diagram of the silicon-carbon negative electrode material in the specific embodiment of the present application;

[0024] Figure 2 is an SEM image of the silicon-carbon negative electrode material prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0025] Please refer to Figure 1As shown, the embodiment provides a preparation method of a low-expansion silicon-carbon negative electrode material, at least comprising the following operation steps:

[0026] Step S1a), preparing modified porous carbon: uniformly mixing a carbon source and a non-metallic activator, drying to obtain a dried material, under an inert atmosphere, heating to a temperature condition of not less than 200 DEG C (preferably 200-300 DEG C) and keeping for at least 1 hour (preferably 1-6 hours), and then heating to a temperature condition of not less than 700 DEG C (preferably 700-900 DEG C) and keeping for at least 1 hour (preferably 1-6 hours) for carbonization to obtain modified porous carbon; preferably, in this step S1a), the weight ratio of the carbon source to the activated carbon is in the range of 100:1-20, preferably 100:1-10; the heating rate is 1-10 DEG C / min; the carbon source is selected from any one or mixture of several of triethylamine, hydroxytriethylamine, and diethylamine; the non-metallic activator is selected from any one or mixture of several of H3PO4, HNO3, and boric acid;

[0027] Step S1b), adding polydimethylsilane into a cracking reactor, introducing inert gas (which can be argon, preferably, the pressure of the reactor is kept at 0.5-1 Mpa after the inert gas is introduced) under vacuum environment (preferably, the reactor is vacuumed to ≤100 pa), and cracking at a temperature condition of not higher than 350 DEG C (preferably 200-300 DEG C) to obtain polysilane; then dispersing the polysilane in an organic solvent to obtain a polysilane solution; preferably, in this step S1b), the weight ratio of the polysilane to the organic solvent is in the range of 1-20:500, preferably 1-10:500; the organic solvent is selected from any one or mixture of several of dimethylbenzene, toluene, 1,4-dimethylbenzene, m-xylene, bromomethylbenzene, chlorotoluene, and mesitylene;

[0028] In the implementation of the present application, steps S1a) and S1b) can be performed simultaneously or sequentially. It should be noted that steps S1a) and S1b) can be performed sequentially, which includes performing step S1a) first and then performing step S1b), or performing step S1b) first and then performing step S1a);

[0029] Step S2), the modified porous carbon obtained in step S1a) is added into a reaction kettle, and a polysilane solution obtained in step S1b) is sprayed onto the modified porous carbon by liquid spraying under vacuum heating, so that the polysilane solution is subjected to liquid cracking; more preferably, in the present step S2), the modified porous carbon obtained in step S1a) is added into a reaction kettle, the reaction kettle is vacuumed to not higher than 1 MPa, and heated to 300-500°C, a polysilane solution obtained in step S1b) is sprayed onto the modified porous carbon by liquid spraying, so that the polysilane solution is subjected to liquid cracking, and the liquid cracking time is 1-6 hours.

[0030] Step S3), obtaining a low-expansion silicon-carbon negative electrode material.

[0031] Preferably, the present embodiment proposes a low-expansion silicon-carbon negative electrode material, which is prepared by the preparation method of the low-expansion silicon-carbon negative electrode material as described above.

[0032] Preferably, the present embodiment proposes an application of the low-expansion silicon-carbon negative electrode material as described above, and the low-expansion silicon-carbon negative electrode material provided by the present embodiment is used as an active material raw material for preparing a battery negative electrode sheet, and preferably as an active material raw material for a lithium ion battery negative electrode sheet.

[0033] The person skilled in the art can make specific applications according to actual needs during implementation, and the specific application method should belong to the routine technical means of the person skilled in the art, therefore the present embodiment does not particularly limit the application mode.

[0034] In order to enable the person skilled in the art to better understand the technical solutions in the present application, the technical solutions in the present embodiment will be described clearly and completely below in combination with the drawings in the present embodiment, obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without making creative efforts should belong to the protection scope of the present application.

[0035] On the basis of the above-described embodiments, the present application further proposes the following specific embodiments:

[0036] Embodiment 1: the silicon-carbon negative electrode material is prepared according to the following operation steps in the present embodiment 1:

[0037] Step S1a), preparing a modified porous carbon: 100 g of triethylamine is uniformly mixed with 5 g of H3PO4, dried, heated to 250°C at a heating rate of 5°C / min under an argon inert atmosphere, and then heated to a temperature of 800°C, and kept for 3 hours, to obtain a non-metal doped porous carbon material (i.e. a modified porous carbon).

[0038] Step S1b), polydimethylsilane was added to the cracking reactor, vacuumed to 50 pa, then argon was introduced to 0.8 Mpa, and then the temperature was raised to 250°C for 1 hour of cracking, and the temperature was lowered to room temperature to obtain polysilane; then 5 g of polysilane was added to 500 g of dimethylbenzene and uniformly dispersed by ultrasonic dispersion to obtain a polysilane solution;

[0039] Step S2), the non-metallic doped porous carbon material obtained in step S1a) was added to the reactor, the reactor was vacuumed to a vacuum degree of 0.8 Mpa, and heated to 400°C at the same time, and the polysilane solution obtained in step S1b) was sprayed onto the non-metallic doped porous carbon material by liquid spray method, so that the polysilane solution was liquid cracked, and the cracking time was 3 hours;

[0040] Step S3), the temperature was lowered to room temperature to obtain the low-expansion silicon-carbon negative electrode material of Example 1.

[0041] The silicon-carbon negative electrode material obtained in Example 1 was subjected to SEM (scanning electron microscope) morphology test, and the test results are shown in Figure 2 It can be seen that the material has a granular structure, uniform and reasonable size distribution, and the surface of the particles is coated with amorphous carbon, and the particle size D50 is between 2-8 μm. Figure 2

[0042] Example 2: The silicon-carbon negative electrode material was prepared according to the following operation steps in Example 2:

[0043] Step S1a), preparation of modified porous carbon: 100 g of hydroxytriethylamine was mixed with 1 g of HNO3, dried, and then heated to 200°C at a heating rate of 1°C / min under an argon inert atmosphere, and kept for 3 hours, then continued to heat to a temperature of 700°C, and kept for 6 hours to obtain a non-metallic doped porous carbon material (modified porous carbon);

[0044] Step S1b), polydimethylsilane was added to the cracking reactor, vacuumed to 50 pa, then argon was introduced to 0.5 Mpa, and then the temperature was raised to 200°C for 1 hour of cracking, and the temperature was lowered to room temperature to obtain polysilane; then 1 g of polysilane was added to 500 g of toluene organic solvent and uniformly dispersed by ultrasonic dispersion to obtain a polysilane solution;

[0045] ​Step S2), the non-metallic doped porous carbon material obtained in step S1a) is added into a reaction kettle, the reaction kettle is vacuumized to a vacuum degree of 0.5 Mpa, and meanwhile, heated to 300 DEG C, the polysilane solution obtained in step S1b) is sprayed to the non-metallic doped porous carbon material by liquid spraying, so that the polysilane solution is subjected to liquid cracking, and the cracking time is 6 hours;

[0046] Step S3), cooling to room temperature to obtain the low-expansion silicon-carbon negative electrode material of Example 2.

[0047] Example 3: The silicon-carbon negative electrode material is prepared according to the following operation steps in Example 3:

[0048] Step S1a), preparation of modified porous carbon: 100 g of diethylamine is uniformly mixed with 10 g of boric acid, dried, and then heated to 300 DEG C at a heating rate of 10 DEG C / min under an argon inert atmosphere, and then heated to a temperature of 900 DEG C for 1 hour to obtain a non-metallic doped porous carbon material (i.e., modified porous carbon);

[0049] Step S1b), 10 g of polydimethylsilane is added into a cracking reaction kettle, vacuumized to 50 pa, and then argon is introduced to 1 Mpa, and then heated to 300 DEG C for cracking for 1 hour, and then cooled to room temperature to obtain polysilane; then 10 g of polysilane is added into 500 g of m-xylene organic solvent and uniformly dispersed by ultrasonic dispersion to obtain a polysilane solution;

[0050] Step S2), the non-metallic doped porous carbon material obtained in step S1a) is added into a reaction kettle, the reaction kettle is vacuumized to a vacuum degree of 1 Mpa, and meanwhile, heated to 500 DEG C, the polysilane solution obtained in step S1b) is sprayed to the non-metallic doped porous carbon material by liquid spraying, so that the polysilane solution is subjected to liquid cracking, and the cracking time is 1 hour;

[0051] Step S3), cooling to room temperature to obtain the low-expansion silicon-carbon negative electrode material of Example 3.

[0052] Comparative Example 1: The non-metallic doped porous carbon material obtained in step S1a) in Example 1 is transferred into a reaction kettle, the reaction kettle is vacuumized to 50 pa, and then silane gas is introduced and heated to a temperature condition of 500 DEG C for cracking for 1 hour, and then cooled to room temperature to obtain the silicon-carbon negative electrode material of Comparative Example 1.

[0053] Comparative Example 2: A conventional porous carbon material was added to a reaction kettle, the reaction kettle was vacuumized to a vacuum degree of 1 Mpa, and heated to 500 DEG C at the same time, and the polysilane solution obtained in step S1b) of Example 1 was sprayed to the porous carbon material by liquid spraying, so that the polysilane solution was subjected to liquid cracking, the cracking time was 1 hour, and the temperature was lowered to room temperature to obtain the silicon-carbon negative electrode material of Comparative Example 2.

[0054] Comparative Example 3: The drying product was obtained by using the step scheme in CN114556621A: "dissolving the organic silicon source in a xylene solvent, adding the porous graphite into the xylene solvent in a certain proportion after complete dissolution, stirring for 4 h, so that the organic silicon source solution is completely impregnated between the pore layers of the porous graphite, then removing the solvent by stirring and heating at 80 DEG C, and then placing the product in a 80 DEG C oven for drying for 24 h"; then the drying product was added to a reaction kettle, the reaction kettle was heated to 400 DEG C for cracking, the cracking time was 3 hours, and the silicon-carbon negative electrode material of Comparative Example 3 was obtained.

[0055] Comparative Example 4: The remaining technical solutions of Comparative Example 4 are the same as those of Example 1, except that in step S2) of Comparative Example 4, the non-metallic doped porous carbon material obtained in step S1a) of Example 1 was mixed with the polysilane solution obtained in step S1b) by impregnation, and then the solvent was removed by stirring under heating at 80 DEG C, and then the product was placed in an 80 DEG C oven for drying for 24 hours to obtain a drying product; then the drying product was added to a reaction kettle, the reaction kettle was heated to 400 DEG C for cracking, the cracking time was 3 hours, and the silicon-carbon negative electrode material of Comparative Example 4 was obtained.

[0056] Comparative Example 5: The negative electrode material proposed in Example 1 of CN114556621A was used as the silicon-carbon negative electrode material of Comparative Example 5.

[0057] In order to compare and verify the effects of the above examples and comparative examples, the silicon-carbon negative electrode materials obtained in Examples 1-3 and Comparative Examples 1-5 were subjected to the following physical and chemical performance tests and button cell tests:

[0058] 1). The specific surface area and tap density of each silicon-carbon negative electrode material obtained in Examples 1-3 and Comparative Examples 1-5 were tested according to the method in the national standard GB / T 38823-2020 "Silicon Carbon", the electrical conductivity of each silicon-carbon negative electrode material was tested by a four-probe tester, and the silicon grain size of each silicon-carbon negative electrode material was tested by XRD; the test results are shown in Table 1 below.

[0059] 2). Button cell test:

[0060] Each silicon-carbon negative electrode material obtained from Examples 1-3 and Comparative Examples 1-5 was used as an active material of a battery negative electrode sheet to prepare eight button cells, respectively. The specific preparation process of each button cell was as follows:

[0061] Preparation of battery negative electrode sheet: a binder, a conductive agent and a solvent were added to each silicon-carbon negative electrode material (as an active material of a battery negative electrode sheet) corresponding to Examples 1-3 and Comparative Examples 1-5, respectively, to prepare a slurry by stirring, which was coated on a copper foil, and then dried and rolled to obtain each battery negative electrode sheet; wherein the binder was LA132 binder, the conductive agent was SP (conductive carbon black), and the solvent was NMP, and the ratio was: silicon-carbon negative electrode material: SP: LA132: NMP = 95 g: 1 g: 4 g: 220 mL.

[0062] Preparation of button cell: the electrolyte was a LiPF6 solution, wherein the concentration of LiPF6 was 1 mol / L, and the solvent was a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DMC) in a weight ratio of 1:1; a metal lithium sheet was used as the counter electrode, and a polypropylene (PP) membrane was used as the separator; the simulation battery was assembled in an argon-filled glove box, and the electrochemical performance was tested on a Wuhan Lan Electric CT2001A battery tester, and the test conditions were as follows: the charge and discharge voltage range was 0.005 V to 2.0 V, and the charge and discharge rate was 0.1 C; at the same time, the full charge expansion test of each button cell was carried out, and the test method was as follows:

[0063] Firstly, the thickness D1 of the negative electrode sheet of the button cell sheet after rolling was tested, then the negative electrode sheet of the button cell was disassembled after full charging to 100% SOC, and the full charge thickness D2 of the negative electrode sheet was tested, and then the full charge expansion rate was calculated, which was (D2-D1) / D1*100%; the test results are shown in Table 1.

[0064] Table 1

[0065]

[0066] As can be seen from Table 1, the silicon-carbon negative electrode material provided by Example 1-3 has a high specific surface area, and the button cell prepared therefrom has excellent performance; the reason may be mainly that the silicon-carbon negative electrode material provided by Example 1-3 expands the interlayer spacing of the silicon-carbon material by using a non-metallic activator, and reduces the electronic impedance of the silicon-carbon material by introducing elements such as nitrogen, boron and phosphorus with high electronic conductivity through the carbon source, thereby significantly improving the specific capacity of the material, and the non-metallic doped porous carbon material further suppresses the expansion.

[0067] 3). Soft package battery test:

[0068] The silicon-carbon negative electrode material obtained in each of Examples 1-3 and Comparative Examples 1-5 was doped with 90% artificial graphite as a negative electrode material (i.e., a negative electrode sheet), and a ternary material LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 as a positive electrode material, an electrolyte, and a separator to assemble a 5 Ah soft package battery; wherein the separator of the soft package battery was Celegard 2400, the electrolyte was a LiPF6 solution, wherein the solvent of the LiPF6 solution was a mixed solution of EC and DEC at a volume ratio of 1:1, and the concentration of LiPF6 was 1.3 mol / L; the soft package batteries prepared from each of the silicon-carbon negative electrode materials of Examples 1-3 and Comparative Examples 1-5 were respectively marked as A-2, B-2, C-2, D-2, E-2, F-2, G-2, H-2, and each of the battery negative electrode sheets corresponding thereto were subjected to the following performance tests:

[0069] a. Liquid absorption capacity test: a 1 mL burette was used to absorb V mL of electrolyte, and the electrolyte was added dropwise on the surface of the negative electrode sheet, timing was performed until the electrolyte was completely absorbed, the time t was recorded, and the liquid absorption speed V / t of the negative electrode sheet was calculated; the test results are shown in Table 2.

[0070] b. Liquid retention rate test: the theoretical liquid absorption amount m1 of the negative electrode sheet was calculated according to the negative electrode sheet parameters, and the weight m2 of the negative electrode sheet was weighed, then the negative electrode sheet was placed in the electrolyte for 24 hours, the weight of the negative electrode sheet was weighed as m3, the liquid absorption amount m3-m2 of the negative electrode sheet was calculated, and the liquid retention rate was calculated according to the following formula: liquid retention rate = (m3-m2)*100% / m1; the test results are shown in Table 2.

[0071] Table 2

[0072] Silicon-carbon negative electrode material employed Sorption speed (V / t) Liquid retention rate Example 1 56 90.1％ Example 2 59 89.2％ Example 3 63 88.4％ Comparative Example 1 73 83.9％ Comparative Example 2 82 82.7％ Comparative Example 3 80 83.2％ Comparative Example 4 89 80.7％ Comparative Example 5 95 79.3％

[0073] As can be seen from Table 2, the liquid absorption and retention capacity of the negative electrode sheet made of the silicon-carbon negative electrode material provided in Examples 1-3 is significantly higher than that of Comparative Examples 1-5; the reason may be that the specific surface area of the silicon-carbon negative electrode material provided in Examples 1-3 is larger, which can improve the liquid absorption and retention capacity of the silicon-carbon negative electrode material.

[0074] c. Rate and its cycle performance: the cycle performance test and rate test were carried out on the soft package batteries A-2, B-2, C-2, D-2, E-2, F-2, G-2 and H-2; wherein the cycle test conditions were as follows: the charge and discharge voltage range was 2.5-4.2 V, the temperature was 25±3.0℃, the charge and discharge rate was 0.5C / 1.0C, and the cycle number was 500 times; the rate test conditions were as follows: the constant current ratio of the material under 2C condition was tested, then each soft package battery was dissected and analyzed after being charged to 100% SOC, and the full charge rebound rate of the negative electrode sheet was tested (the specific test method was the same as the full charge expansion rate test of the button cell in the text of the present application); and the test results were shown in Table 3.

[0075] Table 3

[0076]

[0077] From the above Table 3, it can be seen that the cycle performance of the soft package lithium ion batteries prepared by using the silicon-carbon negative electrode material provided in the embodiments 1-3 was obviously better than that of the comparative examples 1-5, and the reason might be that the silicon grains of the silicon-carbon negative electrode material provided in the embodiments 1-3 were small, the powder conductivity was low, and the expansion was low, which could significantly improve the cycle performance and rate performance of the lithium ion battery applied thereto.

[0078] It is apparent to those skilled in the art that the present application is not limited to the details of the foregoing exemplary embodiments, and that the present application can be implemented in other particular forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, and the scope of the present application should be defined by the appended claims rather than the above description, and it is intended to include all changes falling within the meaning and range of equivalents of the claims. Any reference signs in the claims should not be construed as limiting the claims to which the reference signs belong.

[0079] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be combined appropriately to form other embodiments that those skilled in the art can understand.

Claims

1. A method for preparing a low-expansion silicon-carbon negative electrode material, characterized by, At least comprising the following operation steps: Step S1a), preparing modified porous carbon: uniformly mixing a carbon source with a non-metallic activator, drying to obtain a dried product, under inert atmosphere, heating to a temperature condition not lower than 200 DEG C and keeping for at least 1 hour, then heating to a temperature condition not lower than 700 DEG C and keeping for at least 1 hour for carbonization, to obtain modified porous carbon; In the step S1a), the carbon source is selected from any one or mixture of several of triethylamine, hydroxytriethylamine, diethylamine; the non-metallic activator is selected from any one or mixture of several of H3PO4, HNO3, boric acid; Step S1b), adding polydimethylsilane into a cracking reaction kettle, under vacuum environment, inert gas is introduced, cracking is carried out under a temperature condition not higher than 350 DEG C, to obtain polysilane; then the polysilane is added into an organic solvent to disperse uniformly, to obtain polysilane solution; Wherein, the step S1a) and step S1b) can be carried out simultaneously or sequentially; Step S2), using silane cracking method, adding the modified porous carbon obtained in the step S1a) into a reaction kettle, under vacuum heating state, the polysilane solution obtained in the step S1b) is sprayed to the modified porous carbon by liquid spraying method, so that the polysilane solution is subjected to liquid cracking; Step S3), obtaining the low-expansion silicon-carbon negative electrode material.

2. The method of claim 1, wherein the low-expansion silicon-carbon negative electrode material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture at a temperature of 800-1,200°C for 1-10 hours in an inert gas atmosphere. In the step S1a), under inert atmosphere, heating to a temperature condition of 200-300 DEG C and keeping for 1-6 hours, then heating to a temperature condition of 700-900 DEG C and keeping for 1-6 hours.

3. The method for preparing the low-expansion silicon-carbon anode material according to claim 1, characterized in that, In the step S1b), polydimethylsilane is added into a cracking reaction kettle, vacuum is extracted to ≤100 pa, then inert gas is introduced to 0.5-1 Mpa, then heating to a temperature condition of 200-300 DEG C for cracking, to obtain the polysilane.

4. The method for preparing the low-expansion silicon-carbon anode material according to claim 1, characterized in that, In the step S1b), the weight ratio of the polysilane to the organic solvent ranges from 1-20:

500.

5. The method of claim 4, wherein the low-expansion silicon-carbon negative electrode material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture to form the low-expansion silicon-carbon negative electrode material. In the step S1b), the weight ratio of the polysilane to the organic solvent ranges from 1-10:

500.

6. The method for preparing the low-expansion silicon-carbon anode material according to claim 1, 4, or 5, characterized in that, In the step S1b), the organic solvent is selected from any one or mixture of several of xylene, toluene, bromomethylbenzene, chlorotoluene, mesitylene.

7. The method of claim 1, wherein the low-expansion silicon-carbon negative electrode material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture at a temperature of 800-1,200°C for 1-10 hours in an inert gas atmosphere. In the step S2), the modified porous carbon obtained in the step S1a) is added into a reaction kettle, the reaction kettle is vacuum extracted to not higher than 1 Mpa, and heated to 300-500 DEG C, the polysilane solution obtained in the step S1b) is sprayed to the modified porous carbon by liquid spraying method, so that the polysilane solution is subjected to liquid cracking, and the liquid cracking time is 1-6 hours.

8. A low-expansion silicon-carbon negative electrode material, characterized by, The low-expansion silicon-carbon negative electrode material is prepared by the method as claimed in any one of claims 1-7.

9. Use of the low-expansion silicon-carbon negative electrode material according to claim 8, characterized in that, The low-expansion silicon-carbon negative electrode material is used as active material raw material for preparing battery electrode sheet.

10. Use of the low-expansion silicon-carbon negative electrode material according to claim 8, characterized in that, The low-expansion silicon-carbon negative electrode material is used as active material raw material for lithium ion battery negative electrode sheet.

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