Silicon-based negative electrode material and preparation method and application thereof

Abstract

The invention discloses a silicon-based negative electrode material and a preparation method and application thereof, and relates to the field of preparation of battery negative electrode materials, and the preparation method comprises the following steps: under the protection of inert gas, mixing a silicon-based material, a first component, a second component and a third component in a solvent-free manner, and then carrying out heat treatment at 50-800 DEG C to obtain the silicon-based negative electrode material. The preparation method has simple technical steps, does not need to use a solvent in the whole process, and can realize low-cost and large-scale preparation of the silicon-based negative electrode material with high specific capacity, high magnification and long cycle life.

Description

Technical Field

[0001] The present invention relates to the field of preparation of battery negative electrode materials, in particular to a silicon-based negative electrode material and a preparation method and application thereof. Background Art

[0002] With the development of new energy vehicles, smart electronics and large-scale energy storage, the market has higher and higher requirements for the energy density of lithium-ion batteries. At present, the mainstream negative electrode material of commercial lithium-ion batteries is graphite. However, graphite has been close to its theoretical capacity in practical applications, and there is very limited room for further improving energy density, which is difficult to meet the growing market demand. Therefore, it has become an urgent task for the industry to develop negative electrode materials with high specific capacity to replace graphite.

[0003] Among many candidate negative electrode materials, silicon stands out with its extremely high theoretical specific capacity (3579 mAh / g), which is nearly 10 times that of graphite. In addition, silicon ranks second in abundance in the earth's crust, has abundant reserves, and has the potential for low cost, making it a very promising negative electrode material choice.

[0004] However, silicon negative electrodes face two key challenges in large-scale applications. First, the volume of silicon changes greatly during the charging and discharging process, exceeding 300%. This repeated volume expansion and contraction will cause the silicon particles to pulverize and even peel off the electrode coating. At the same time, it will cause the solid-liquid interface film (SEI) to be unstable, repeatedly generated and thickened, thereby reducing ionic conductivity and increasing impedance, ultimately resulting in poor battery rate performance and shortened cycle life. Second, as a semiconductor material, silicon has a much lower conductivity than carbon materials such as graphite, which seriously restricts silicon's rate performance.

[0005] To solve the above problems, researchers have adopted a variety of strategies. On the one hand, nano-sizing silicon materials can alleviate the volume change during charging and discharging to a certain extent; on the other hand, surface coating can improve conductivity and further inhibit volume expansion, among which surface carbon coating is the most studied method. Although these strategies have improved the electrochemical performance of silicon negative electrodes, it is still difficult to achieve an ideal balance between specific capacity, rate and cycle performance.

[0006] Looking back at the development history of the preparation method of silicon negative electrode materials, wet grinding was used in the early stage (CN111755677B), followed by spray drying and high-temperature sintering to obtain silicon-carbon negative electrodes. However, the products prepared by this method have the problems of high energy consumption and long process. In addition, wet grinding requires the use of a large amount of solvents, and the purchase, storage and treatment of solvents all require corresponding costs. The large-scale use of solvents will increase the cost of raw materials. In addition, in order to ensure safety and environmental protection, additional funds need to be invested in the construction of solvent storage facilities, the purchase of safety protection equipment, and wastewater treatment, which increases the total cost of preparing silicon-carbon negative electrode materials.

[0007] Although the emergence of silicon-oxygen negative electrodes has improved the cycle life to a certain extent, the low initial efficiency limits its large-scale mixing with graphite. In recent years, the vapor deposition method (CN114976026B) has received widespread attention. It deposits nano-silicon into the pores of porous carbon by silane cracking, and the prepared silicon-carbon negative electrode has an excellent cycle life. However, the silane used in the vapor deposition method is flammable and explosive, and is not easy to produce continuously. At present, the production capacity is difficult to expand, and the deposition process parameters are extremely difficult to control, and the batch stability is poor. Summary of the invention

[0008] The present invention provides a silicon-based negative electrode material and a preparation method and application thereof, so as to realize low-cost, large-scale preparation of silicon-carbon negative electrode materials with high specific capacity, high rate and long cycle life.

[0009] In order to achieve the above-mentioned purpose, the specific scheme adopted by the present invention is: a method for preparing a silicon-based negative electrode material, under the protection of an inert gas, a silicon-based material, a first component, a second component and a third component are mixed without a solvent, and then heat-treated at 50-800°C to obtain the silicon-based negative electrode material; wherein the first component is one or more of lithium carbonate, sodium carbonate, potassium carbonate, ammonium carbonate, ammonium bicarbonate, magnesium carbonate, calcium carbonate and zinc carbonate; the second component is one or more of lithium, sodium, potassium, magnesium, calcium, aluminum and zinc; the third component is one or more of graphite fluoride, fluorinated carbon nanotubes and graphene fluoride.

[0010] As a further optimization of the above technical solution, the solvent-free mixing method includes ball milling mixing, which specifically includes the following steps:

[0011] S1: crushing the silicon-based material, adding the first component and performing a ball milling to obtain a mixture I;

[0012] S2: The second component and the third component are ball-milled for a second time to obtain a mixture II;

[0013] S3: ball-milling mixture I and mixture II three times to obtain mixture III;

[0014] S4: heat-treating the mixture III and crushing it to obtain the silicon-based negative electrode material; wherein the heat treatment temperature is 50-800°C.

[0015] As a further optimization of the above technical solution, in step S1, the particle size of the silicon-based material after crushing is 0.5-500nm.

[0016] As a further optimization of the above technical solution, the time for the first ball milling is 5-48 hours; the time for the second ball milling is 1-15 hours; the time for the third ball milling is 1-15 hours; the temperature for the second ball milling is lower than 35°C; the temperature for the third ball milling is lower than 35°C.

[0017] As a further optimization of the above technical solution, the heat treatment time is 1-15 hours.

[0018] As a further optimization of the above technical solution, the silicon-based material is one or more of silicon element, silicon oxide and silicon alloy.

[0019] As a further optimization of the above technical solution, the mass ratio of the silicon-based material, the first component, the second component and the third component is 100: (1~30): (1~20): (1~40).

[0020] As a further optimization of the above technical solution, the inert gas is one or more of nitrogen, argon and hydrogen.

[0021] The silicon-based negative electrode material is prepared by the above-mentioned preparation method.

[0022] The application of the silicon-based negative electrode material prepared by the above preparation method in the preparation of lithium-ion batteries.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The preparation method provided by the present invention has simple technical steps and mild process conditions. It does not require the use of organic solvents, inflammable and explosive raw materials such as silane, or high temperature, and is easy to industrialize. It is a low-cost and easy-to-operate method. Silicon-based negative electrode materials are directly prepared by ball milling and heat treatment, which is convenient for continuous and automated production; no solvent is added during the preparation process, which reduces the overall production cost, eliminates the solvent treatment step, shortens the production cycle, improves production efficiency, avoids the pollution of the atmosphere by solvent volatilization and the impact of solvent emissions on soil and water, and contributes to green production and reduces negative environmental impacts.

[0025] By adopting the method of the present invention, the first component is decomposed to form pores under heat treatment conditions, thereby providing space for the volume expansion of the silicon-based material in the subsequent charging and discharging process.

[0026] The second component and the third component undergo an in-situ cross-linking reaction during sintering, that is, the second component reduces the third component. The reduction process includes the second component knocking off a fluorine atom on the surface of the third component material (fluorinated graphite and fluorinated graphene have poor conductivity) to restore its conjugated aromatic structure and the high conductivity of the graphite structure. It also includes the second component knocking off two fluorine atoms of two adjacent third components at the same time and coupling them to improve the mechanical strength of the coating; the reduced carbon material and fluoride are in-situ coated on the surface of the silicon-based material. The two different coating materials realize the one-time, in-situ coating of the silicon-based material, in which the carbon material is a good electronic conductor and the fluoride is a good ionic conductor. The in-situ generated carbon material and fluoride not only improve the electronic and ionic conductivity of the obtained material, but also the excellent mechanical properties of the two also alleviate the volume change of the silicon-based material during the charging and discharging process, which is conducive to the formation of a stable SEI film. The second component also plays a role in preventing silicon oxidation, and can reduce silicon oxides to a certain extent, thereby improving the initial efficiency.

[0027] The silicon-based negative electrode material prepared by the present invention has the advantages of high specific capacity, high rate and long cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a scanning electron microscope image of the silicon-based negative electrode material prepared in Example 1;

[0029] Figure 2 The first charge and discharge curve of a button cell assembled using the silicon-based negative electrode material prepared in Example 1;

[0030] Figure 3 The cycle performance curves of button-type batteries assembled with silicon-based negative electrode materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3;

[0031] Figure 4 This is the X-ray spectrum of the silicon-based negative electrode material obtained in Example 1;

[0032] Figure 5 This is the X-ray spectrum of the silicon-based negative electrode material obtained in Example 2. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further elaborated in detail below in conjunction with specific embodiments. The parts of the present invention that are not described and disclosed in detail in the following embodiments should be understood as the prior art known or should be known to those skilled in the art.

[0034] The invention discloses a method for preparing a silicon-based negative electrode material. Under the protection of an inert gas, a silicon-based material, a first component, a second component and a third component are mixed without solvent in a mass ratio of 100: (1-30): (1-20): (1-40), and then heat-treated at 50-800° C. to obtain the silicon-based negative electrode material.

[0035] Specifically, the solvent-free mixing method is ball milling mixing, and the preparation method includes the following steps:

[0036] S1: The silicon-based material is crushed, and then the first component is added to perform a ball milling and mixing to obtain a mixture I; the silicon-based material is one or more of silicon, silicon oxide and silicon alloy, and the silicon oxide is SiO x , 2≥x>0; the first component is one or more of lithium carbonate, sodium carbonate, potassium carbonate, ammonium carbonate, ammonium bicarbonate, magnesium carbonate, calcium carbonate and zinc carbonate.

[0037] The silicon-based material is pulverized by a combination of one or more methods including ball milling, roller milling, and air flow crushing. The particle size of the silicon-based material after pulverization is 0.5-500 nm, preferably 0.5-150 nm. The first component is added to the pulverized silicon-based material for a ball milling, and the ball milling time is 5-48 hours to mix the first component and the silicon-based material uniformly.

[0038] S2: The second component and the third component are mixed by secondary ball milling to obtain mixture II; the second component is one or more of lithium, sodium, potassium, magnesium, calcium, aluminum and zinc; the third component is one or more of fluorinated graphite, fluorinated carbon nanotubes and fluorinated graphene, the time of the secondary ball milling is 1-15 hours, and the temperature of the secondary ball milling is lower than 35°C, preferably -10-20°C.

[0039] S3: Mixture I and mixture II are ball-milled three times to obtain mixture III; the time of the three ball-millings is 1-15 hours, and the temperature is lower than 35°C, preferably -10-20°C.

[0040] S4: heat-treating the mixture III and crushing it to obtain the silicon-based negative electrode material; wherein the heat treatment temperature is 50-800° C., preferably 100-500° C., and the heat treatment time is 1-15 hours.

[0041] The preparation method provided by the invention has simple technical steps, mild process conditions, no need to use organic solvents or high temperatures in the whole process, is easy to industrialize, and is a low-cost, easy-to-operate method.

[0042] Example 1

[0043] S1. 100 g of metallic silicon powder was first crushed to 50-150 nm by air flow, then transferred into a ball mill, 20 g of ammonium carbonate was added, and ball milled for 24 hours under nitrogen protection to obtain a mixture I, which was a nano-silicon / ammonium carbonate mixture;

[0044] S2, 10 g of metallic sodium and 30 g of graphite fluoride were mixed by ball milling under nitrogen protection and at a temperature of 15° C. for 5 hours to obtain a mixture II, which was a metallic sodium / graphite fluoride mixture;

[0045] S3, transferring the nano-silicon / ammonium carbonate mixture and the metallic sodium / graphite fluoride mixture into a ball mill, and continuing the ball milling and mixing for 10 hours under nitrogen protection and controlling the temperature at 15° C. to obtain a mixture III;

[0046] S4. Transfer the mixture III into a sintering furnace and heat treat it at 250°C for 5 hours under nitrogen protection. Grind the heat-treated material into a particle size of 1-10 microns to obtain a silicon-based negative electrode material.

[0047] Example 2

[0048] S1, 100 g of silicon dioxide powder was first crushed to 50-150 nm by air flow, then transferred to a ball mill, 25 g of ammonium bicarbonate was added, and treated under nitrogen protection for 15 hours to obtain a mixture I, which was a nano silicon dioxide / ammonium bicarbonate mixture;

[0049] S2, 10 g of metallic lithium and 30 g of fluorinated graphene were mixed by ball milling under nitrogen protection and at a temperature of 15° C. for 6 hours to obtain a mixture II, which was a metallic lithium / fluorinated graphene mixture;

[0050] S3, transferring the nano-silicon oxide / ammonium bicarbonate mixture and the metal lithium / graphene fluoride mixture into a ball mill, and continuing to ball mill for 10 hours under nitrogen protection and controlling the temperature at 20° C. to obtain a mixture III;

[0051] S4. Transfer the mixture III into a sintering furnace, heat treat it at 280°C for 8 hours under nitrogen protection, and crush the heat-treated material into a particle size of 1-10 microns to obtain a silicon-based negative electrode material.

[0052] Example 3

[0053] S1, 100 g of metallic silicon powder was first crushed to 50-150 nm by air flow, then transferred into a ball mill, 15 g of lithium carbonate was added, and treated under nitrogen protection for 20 hours to obtain a mixture I, which was a nano-silicon / lithium carbonate mixture;

[0054] S2, 8 g of metallic lithium and 30 g of graphite fluoride were mixed by ball milling under nitrogen protection and at a temperature of 15° C. for 6 hours to obtain a mixture II, which was a metallic lithium / graphite fluoride mixture;

[0055] S3, transferring the nano-silicon / lithium carbonate mixture and the metallic lithium / graphite fluoride mixture into a ball mill, and continuing to ball mill for 8 hours under nitrogen protection and controlling the temperature at 10° C. to obtain a mixture III;

[0056] S4. Transfer the mixture III into a sintering furnace and heat treat it at 300°C for 3 hours under nitrogen protection. Grind the heat-treated material into a particle size of 1-10 microns and classify it to obtain a silicon-based negative electrode material.

[0057] Example 4

[0058] S1, 100 g of silicon dioxide powder was first crushed to 50-150 nm by air flow, then transferred to a ball mill, 25 g of ammonium carbonate was added, and treated under nitrogen protection for 15 hours to obtain a mixture I, which was a nano-silicon dioxide / ammonium carbonate mixture;

[0059] S2, mixing 20 g of metallic lithium and 30 g of fluorinated graphene by ball milling under nitrogen protection and at a temperature of 15° C. for 10 hours to obtain a mixture II, which is a metallic lithium / fluorinated graphene mixture;

[0060] S3, transferring the nano-silicon dioxide / ammonium carbonate mixture and the metallic lithium / graphene fluoride mixture into a ball mill, and continuing to ball mill for 15 hours under nitrogen protection and controlling the temperature at 20° C. to obtain a mixture III;

[0061] S4. Transfer the mixture III into a sintering furnace, heat treat it at 280°C for 8 hours under nitrogen protection, and crush the heat-treated material into a particle size of 1-10 microns to obtain a silicon-based negative electrode material.

[0062] Example 5

[0063] S1, 100 g of silicon-germanium alloy was first crushed to 50-150 nm by air flow, then transferred to a ball mill, 25 g of ammonium carbonate was added, and the mixture was treated under nitrogen protection for 15 hours to obtain a mixture I, which was a nano silicon-germanium alloy / ammonium carbonate mixture;

[0064] S2, mixing 10 g of metallic lithium and 20 g of graphite fluoride by ball milling under nitrogen protection and at a temperature of 10° C. for 10 hours to obtain a mixture II, which is a metallic lithium / graphite fluoride mixture;

[0065] S3, transferring the nano-SiGe alloy / ammonium carbonate mixture and the metal lithium / graphite fluoride mixture into a ball mill, and continuing to ball mill for 15 hours under nitrogen protection and controlling the temperature at 10° C. to obtain a mixture III;

[0066] S4. Transfer the mixture III into a sintering furnace, heat treat it at 300°C for 5 hours under nitrogen protection, and crush the heat-treated material to a particle size of 1-10 microns to obtain a silicon-based negative electrode material.

[0067] Example 6

[0068] S1, 100 g of silicon-germanium alloy was first crushed into 0.5-100 nm by air flow, then transferred into a ball mill, 30 g of magnesium carbonate was added, and treated under argon protection for 15 hours to obtain mixture I, which was a nano silicon-germanium alloy / magnesium carbonate mixture;

[0069] S2, 20 g of magnesium and 40 g of carbon nanotubes were ball-milled for 10 hours under argon protection and at a temperature of 10° C. to obtain a mixture II, which was a magnesium / carbon nanotube mixture;

[0070] S3, transferring the nano-SiGe alloy / magnesium carbonate mixture and the metal magnesium / fluorinated carbon nanotube mixture into a ball mill, and continuing to ball mill for 7 hours under argon protection and controlling the temperature at 30° C. to obtain a mixture III;

[0071] S4. Transfer the mixture III into a sintering furnace, heat treat it at 50°C for 15 hours under argon protection, and crush the heat-treated material into a particle size of 1-25 microns to obtain a silicon-based negative electrode material.

[0072] Example 7

[0073] S1, 100 g of silicon-germanium alloy was first crushed to 400-500 nm by air flow, then transferred into a ball mill, 5 g of calcium carbonate was added, and treated under hydrogen protection for 15 hours to obtain mixture I, which was a nano silicon-germanium alloy / calcium carbonate mixture;

[0074] S2, mixing 10 g of metallic calcium and 20 g of fluorinated graphene by ball milling under hydrogen protection and at a temperature of 10° C. for 10 hours to obtain a mixture II, which is a metallic calcium / fluorinated graphene mixture;

[0075] S3, transferring the nano-SiGe alloy / calcium carbonate mixture and metallic calcium / fluorinated graphene into a ball mill, and continuing ball milling for 1 hour under hydrogen protection and controlling the temperature at 10° C. to obtain mixture III;

[0076] S4. Transfer the mixture III into a sintering furnace, heat treat it at 50°C for 15 hours under hydrogen protection, and crush the heat-treated material into a particle size of 1-25 microns to obtain a silicon-based negative electrode material.

[0077] Example 8

[0078] S1, 100 g of metallic silicon powder was first crushed to 400-500 nm by air flow, then transferred into a ball mill, 25 g of zinc carbonate was added, and treated under hydrogen protection for 15 hours to obtain a mixture I, which was a nano-silicon / zinc carbonate mixture;

[0079] S2, mixing 10 g of metallic zinc and 20 g of fluorinated graphene by ball milling under hydrogen protection and at a temperature of -10°C for 10 hours to obtain a mixture II, which is a metallic zinc / fluorinated graphene mixture;

[0080] S3, transferring the nano-silicon / zinc carbonate mixture and the metallic zinc / graphene fluoride into a ball mill, and continuing to ball mill for 15 hours under hydrogen protection and controlling the temperature at -10°C to obtain a mixture III;

[0081] S4. Transfer the mixture III into a sintering furnace, heat treat it at 500°C for 7 hours under hydrogen protection, and crush the heat-treated material to a particle size of 1-25 microns to obtain a silicon-based negative electrode material.

[0082] Comparative Example 1

[0083] Compared with Example 1, the overall steps of this comparative example are the same, except that ammonium carbonate is not added in this comparative example.

[0084] Comparative Example 2

[0085] Compared with Example 1, the overall steps of this comparative example are the same, except that no metallic sodium is added in this comparative example.

[0086] Comparative Example 3

[0087] Compared with Example 1, the overall steps of this comparative example are the same, except that no fluorinated graphite is added in this comparative example.

[0088] Comparative Example 4

[0089] Compared with Example 2, the overall steps of this comparative example are the same, except that ammonium bicarbonate is not added in this comparative example.

[0090] Comparative Example 5

[0091] Compared with Example 2, the overall steps of this comparative example are the same, except that no metallic lithium is added in this comparative example.

[0092] Comparative Example 6

[0093] Compared with Example 2, the overall steps of this comparative example are the same, except that no fluorinated graphene is added in this comparative example.

[0094] The electrical properties of the silicon-based negative electrode materials obtained in the above embodiments and comparative examples were tested.

[0095] Here are the steps:

[0096] 1) Prepare a 1.5% solid content carboxymethyl cellulose (CMC) aqueous solution;

[0097] 2) Weigh a certain amount of silicon-based negative electrode material or comparative material (i.e., the silicon-based negative electrode material prepared in Comparative Examples 1-6) and conductive agent Super-P, grind and mix them, then drop CMC aqueous solution and continue grinding and mixing to obtain slurry; wherein the weight ratio of silicon-based negative electrode material or comparative material to conductive agent Super-P and CMC is 80:10:10;

[0098] 3) The slurry is coated on the copper foil, and vacuum dried, rolled and cut into pieces to prepare the electrode;

[0099] 4) A lithium sheet is used as the counter electrode, a polyethylene / polypropylene composite separator is used as the separator, and 1.0 mol / L LiPF6 of ethylene carbonate / dimethyl carbonate / diethyl carbonate (volume ratio 1:1:1) and 10% fluoroethylene carbonate is added as the electrolyte to assemble a button cell. The charge and discharge voltage is limited to 0.005~1.5V.

[0100] Result analysis:

[0101] Depend on Figure 1 It can be seen that the silicon-based negative electrode material prepared in Example 1 has a rich pore structure inside, which is the space left after the decomposition of the carbonate, leaving a buffer space for the volume expansion of the silicon-based negative electrode during the charge and discharge process; and there is a carbon layer on the surface, which is a highly conductive coating layer obtained after the third component is reduced, so the obtained material has a high rate and long cycle life.

[0102] from Figure 4 and Figure 5 It can be seen that the diffraction peaks of nano silicon and sodium fluoride in the silicon-based negative electrode material prepared in Example 1 and nano silicon and lithium fluoride in the silicon-based negative electrode material prepared in Example 2 are very clearly presented, and correspond well to the standard card.

[0103] Figure 2 The first charge and discharge curve of the button cell assembled with the silicon-based negative electrode material prepared in Example 1 is shown in FIG. Figure 2 It can be seen that the material obtained in Example 1 is a typical silicon-carbon negative electrode with a reversible specific capacity of up to 2345.5 mAh / g and an initial efficiency of over 90%, because the pores of the obtained material provide space for the expansion of silicon, and the in-situ generated carbon coating and fluoride provide better electronic and ionic conductivity.

[0104] The electrochemical test results of button-type batteries prepared using the silicon-based negative electrode materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 are shown in Table 1:

[0105] Table 1 Specific capacity (mAh / g) Electrical conductivity (S / cm) First efficiency (%) 100 cycles capacity retention rate (%) Example 1 2345.5 13.4 90.5% 91.2 Comparative Example 1 1984.7 13.0 85.6% 72.9 Comparative Example 2 1683.6 0.068 81.5% 75.5 Comparative Example 3 1786.5 1.46 84.5% 69.9

[0106] from Figure 3As can be seen from Table 1, the silicon-based negative electrode material prepared in Example 1 of the present invention presents the highest specific capacity and first efficiency and excellent cycle stability. After 100 cycles, the capacity retention rate is as high as more than 91%, which is much better than the comparative example. This is because ammonium carbonate decomposes into gas under heating to escape and form pores, providing space for the volume expansion of silicon-based materials; fluorinated graphite is converted into thin-layer graphite and cross-linked after ball milling and metallic sodium reduction, and the generated fluoride is a good ion conductor. Therefore, the carbon material and fluoride generated in situ not only improve the electronic and ionic conductivity of the resulting material, but also the excellent mechanical properties of the two also alleviate the volume change of silicon-based materials during the charge and discharge process; in addition, metallic sodium also plays a role in preventing nano-silicon from being oxidized, thereby improving the first efficiency. Therefore, Example 1 has a higher specific capacity, a higher first efficiency, and better cycle stability.

[0107] The electrochemical test results of button-type batteries prepared using the silicon-based negative electrode materials prepared in Example 2 and Comparative Examples 4, 5 and 6 are shown in Table 2:

[0108] Table 2 Specific capacity (mAh / g) Electrical conductivity (S / cm) First efficiency (%) 100 cycles capacity retention rate (%) Example 2 1850.5 15.6 90.5 94.5 Comparative Example 4 1764.7 14.7 85.4 80.4 Comparative Example 5 1678.5 0.064 75.8 85.7 Comparative Example 6 1740.8 1.89 84.3 82.6

[0109] As a negative electrode material for lithium-ion batteries, silicon dioxide has better cyclability than nano-silicon, but its first efficiency is low (<80%), so improving its first efficiency and further improving its cyclability are the only way for the current commercialization of silicon dioxide. As can be seen from Table 2, Example 2 using the scheme of the present invention has higher specific capacity and first efficiency, and more stable circulation, because metallic lithium improves the conductivity by reducing the fluorinated graphene after ball milling and forms a good coating layer; and due to the presence of metallic lithium, silicon dioxide undergoes pre-lithiation, thus obtaining a higher first efficiency and specific capacity.

[0110] The electrochemical test results of button-type batteries prepared using the silicon-based negative electrode materials prepared in Example 3, Example 4, and Example 5 are shown in Table 3:

[0111] Table 3 Specific capacity (mAh / g) Electrical conductivity (S / cm) First efficiency (%) 100 cycles capacity retention rate (%) Example 3 2260.8 15.8 89.5 91.6 Example 4 1485.4 10.4 84.6 93.4 Example 5 1578.9 15.2 90.7 92.5

[0112] It can be seen from Table 3 that the scheme disclosed in the present invention shows high first efficiency and cycle stability, whether it is nano-silicon or silicon oxide or silicon alloy. Especially for the silicon dioxide described in Example 4, silicon dioxide is similar to silicon monoxide, has very poor conductivity, and as a negative electrode material, the first efficiency is less than 70%. The present invention greatly improves the first efficiency through the pre-lithiation of metallic lithium and the generation of fluorinated graphene.

[0113] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a silicon-based negative electrode material, characterized in that: Under the protection of inert gas, the silicon-based material, the first component, the second component and the third component are mixed without solvent, and then heat-treated at 50-800° C. to obtain the silicon-based negative electrode material; wherein the first component is one or more of lithium carbonate, sodium carbonate, potassium carbonate, ammonium carbonate, ammonium bicarbonate, magnesium carbonate, calcium carbonate and zinc carbonate; The second component is one or more of lithium, sodium, potassium, magnesium, calcium, aluminum and zinc; The third component is one or more of fluorinated graphite, fluorinated carbon nanotubes and fluorinated graphene.

2. The method for preparing a silicon-based negative electrode material according to claim 1, characterized in that: The solvent-free mixing method includes ball milling mixing, which specifically includes the following steps: S1: crushing the silicon-based material, adding the first component and performing a ball milling to obtain a mixture I; S2: The second component and the third component are ball-milled for a second time to obtain a mixture II; S3: ball-milling mixture I and mixture II three times to obtain mixture III; S4: heat-treating the mixture III and crushing it to obtain the silicon-based negative electrode material; wherein the heat treatment temperature is 50-800°C.

3. The method for preparing a silicon-based negative electrode material according to claim 2, characterized in that: In step S1, the particle size of the silicon-based material after crushing is 0.5-500 nm.

4. The method for preparing a silicon-based negative electrode material according to claim 2, characterized in that: The time of the first ball milling is 5-48 hours; the time of the second ball milling is 1-15 hours; the time of the third ball milling is 1-15 hours; the temperature of the second ball milling is lower than 35°C; the temperature of the third ball milling is lower than 35°C.

5. The method for preparing a silicon-based negative electrode material according to claim 1, characterized in that: The heat treatment time is 1-15 hours.

6. The method for preparing a silicon-based negative electrode material according to claim 1, characterized in that: The silicon-based material is one or more of silicon alone, silicon oxide and silicon alloy.

7. The method for preparing a silicon-based negative electrode material according to claim 1, characterized in that: The mass ratio of the silicon-based material, the first component, the second component and the third component is 100: (1-30): (1-20): (1-40).

8. The method for preparing a silicon-based negative electrode material according to claim 1, characterized in that: The inert gas is one or more of nitrogen, argon and hydrogen.

9. The silicon-based negative electrode material obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the silicon-based negative electrode material as claimed in claim 9 in a lithium-ion battery.

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