A silicon-based negative electrode material and its preparation method and application

Abstract

A silicon-based anode material, its preparation method, and its application relate to the field of battery anode material preparation. The preparation method comprises solvent-free mixing of the silicon-based material, a first component, a second component, and a third component under inert gas protection, followed by heat treatment at 50-800°C to obtain the silicon-based anode material. This preparation method has simple technical steps and requires no solvents throughout the process. It enables low-cost, large-scale preparation of silicon-based anode materials with high specific capacity, high rate capability, 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 demands ever-higher energy density for lithium-ion batteries. Currently, graphite is the mainstream anode material for commercial lithium-ion batteries. However, in practical applications, graphite has already approached its theoretical capacity, leaving limited room for further energy density improvements, making it difficult to meet growing market demand. Therefore, developing anode materials with high specific capacity to replace graphite has become an urgent task for the industry.

[0003] Among the many candidate anode materials, silicon stands out due to its extremely high theoretical specific capacity (3579 mAh / g), nearly 10 times that of graphite. Furthermore, silicon is the second most abundant element in the Earth's crust, with abundant reserves and the potential for low-cost production, making it a highly promising anode material option.

[0004] However, large-scale silicon anodes face two key challenges. First, silicon undergoes significant volume changes during charge and discharge, exceeding 300%. This repeated expansion and contraction can cause silicon particles to pulverize and even peel off the electrode coating. It also leads to an unstable solid-liquid interface (SEI) film, which repeatedly forms and thickens, reducing ionic conductivity and increasing impedance, ultimately resulting in poor battery rate performance and shortened cycle life. Second, as a semiconductor material, silicon's conductivity is far lower than that of carbon materials like graphite, severely limiting its rate performance.

[0005] To address these issues, researchers have adopted a variety of strategies. On the one hand, nanoscaling silicon materials can mitigate volume changes during charge and discharge to a certain extent. On the other hand, surface coating can improve conductivity and further suppress volume expansion, with carbon coating being the most studied approach. While these strategies have improved the electrochemical performance of silicon anodes, achieving an ideal balance between specific capacity, rate capability, and cycle performance remains elusive.

[0006] Looking back at the development of silicon anode material preparation methods, early wet grinding was used (CN111755677B), followed by spray drying and high-temperature sintering to obtain the silicon-carbon anode. However, the products prepared by this method have the problems of high energy consumption and long process steps. In addition, wet grinding requires the use of large amounts of solvents, and the procurement, storage, and disposal of solvents all incur corresponding costs. The large-scale use of solvents will increase the cost of raw materials. In addition, to ensure safety and environmental protection, additional funds are required for the construction of solvent storage facilities, the purchase of safety protection equipment, and wastewater treatment, which increases the overall cost of preparing silicon-carbon anode materials.

[0007] While the emergence of silicon-oxygen anodes has improved cycle life to some extent, their low initial efficiency limits their widespread use in combination with graphite. In recent years, vapor deposition (CN114976026B) has garnered significant attention. This method, which deposits nanosilicon into the pores of porous carbon via the cracking of silane, produces silicon-carbon anodes with excellent cycle life. However, the silane used in this method is flammable and explosive, making continuous production difficult. Currently, scaling up production capacity is difficult, and the deposition process parameters are extremely difficult to control, resulting in poor batch stability. 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] 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 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; and the third component is one or more of fluorinated graphite, fluorinated carbon nanotubes and fluorinated graphene.

[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 ball milling to obtain mixture I;

[0012] S2: The second component and the third component are ball-milled for the second time to obtain 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 0.5-500 nm.

[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; and 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 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, flammable and explosive raw materials such as silane, or high temperatures, making it easy to industrialize and a low-cost, easy-to-operate method. Silicon-based negative electrode materials are directly prepared through ball milling and heat treatment, facilitating continuous and automated production. No solvent is added during the preparation process, reducing overall production costs, eliminating the solvent treatment step, shortening the production cycle, and improving production efficiency. It avoids atmospheric pollution from solvent volatilization and the impact of solvent emissions on soil and water, contributing to green production and reducing negative environmental impacts.

[0025] By adopting the method of the present invention, the first component decomposes to form pores under heat treatment conditions, thereby providing space for the volume expansion of the silicon-based material during subsequent charge and discharge processes.

[0026] During sintering, the second and third components undergo an in-situ cross-linking reaction, whereby the second component reduces the third component. This reduction process involves the second component removing a fluorine atom from the surface of the third component (fluorinated graphite and fluorinated graphene have poor conductivity), restoring its conjugated aromatic structure and the graphite's high conductivity. It also involves the second component simultaneously removing two fluorine atoms from two adjacent third components, causing coupling and enhancing the mechanical strength of the coating. The resulting carbon material and fluoride are then in-situ coated on the surface of the silicon-based material, achieving a single, in-situ coating of the silicon-based material with the two different coating materials. The carbon material is a good electronic conductor, while the fluoride is a good ionic conductor. The in-situ generation of the carbon material and fluoride not only enhances the electronic and ionic conductivity of the resulting material, but also mitigates the volume change of the silicon-based material during charge and discharge, facilitating the formation of a stable SEI film. The second component also prevents silicon oxidation, reducing silicon oxides to a certain extent and improving 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 time. 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 This is 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 batteries assembled with silicon-based negative electrode materials prepared in Example 1, Comparative Examples 1, 2, and 3 are shown;

[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. Parts not described and disclosed in detail in the following embodiments of the present invention should be understood as existing technologies known or should be known to those skilled in the art.

[0034] The present 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 ball milling to obtain 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 pulverized silicon-based material is 0.5-500 nm, preferably 0.5-150 nm. The first component is added to the pulverized silicon-based material and subjected to a primary ball milling process for 5-48 hours to uniformly mix the first component and the silicon-based material.

[0038] S2: The second component and the third component are subjected to 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 secondary ball milling time is 1-15 hours, and the secondary ball milling temperature is lower than 35°C, preferably -10-20°C.

[0039] S3: ball-milling the mixture I and the mixture II three times to obtain a mixture III; the time for 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 present invention has simple technical steps, mild process conditions, does not require the use of organic solvents or high temperatures throughout the 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 to a ball mill, 20 g of ammonium carbonate was added, and ball milled under nitrogen for 24 hours to obtain mixture I, which was a nano-silicon / ammonium carbonate mixture;

[0044] S2. 10 g of metallic sodium and 30 g of graphite fluoride were ball-milled under nitrogen protection at 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 ball milling and mixing for 10 hours under nitrogen protection and controlling the temperature at 15° C. to obtain mixture III;

[0046] S4. Transfer 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 μm to obtain a silicon-based negative electrode material.

[0047] Example 2

[0048] S1. 100 g of silicon oxide 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 the mixture was treated under nitrogen for 15 hours to obtain mixture I, which was a nano-silicon oxide / ammonium bicarbonate mixture;

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

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

[0051] S4. Transfer mixture III into a sintering furnace and heat-treat it at 280° C. for 8 hours under nitrogen protection. Grind the heat-treated material into a particle size of 1-10 μm 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 to a ball mill, 15 g of lithium carbonate was added, and the mixture was treated under nitrogen 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 ball-milled 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 ball milling for 8 hours under nitrogen protection and controlling the temperature at 10° C. to obtain mixture III;

[0056] S4. Transfer 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 μm and classify it to obtain a silicon-based negative electrode material.

[0057] Example 4

[0058] S1. 100 g of silica 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 the mixture was treated under nitrogen for 15 hours to obtain a mixture I, which was a nano-silicon dioxide / ammonium carbonate mixture;

[0059] S2. 20 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 10 hours to obtain a mixture II, which is a metallic lithium / fluorinated graphene mixture;

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

[0061] S4. Transfer mixture III into a sintering furnace and heat-treat it at 280° C. for 8 hours under nitrogen protection. Grind the heat-treated material into a particle size of 1-10 μm 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 for 15 hours to obtain mixture I, which was a nano-silicon-germanium alloy / ammonium carbonate mixture;

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

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

[0066] S4. Transfer mixture III into a sintering furnace and heat-treat it at 300°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.

[0067] Example 6

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

[0069] S2, mixing 20 g of metallic magnesium and 40 g of fluorinated carbon nanotubes by ball milling under argon protection and controlling the temperature at 10° C. for 10 hours to obtain a mixture II, which is a metallic magnesium / fluorinated carbon nanotube mixture;

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

[0071] S4. Transfer the mixture III into a sintering furnace and heat-treat it at 50° C. for 15 hours under argon protection. Grind the heat-treated material into a particle size of 1-25 μm 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 to a ball mill, 5 g of calcium carbonate was added, and the mixture was 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 controlling the temperature at 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 mixture III into a sintering furnace and heat-treat it at 50° C. for 15 hours under hydrogen protection. Grind the heat-treated material into a particle size of 1-25 μm 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 to a ball mill, 25 g of zinc carbonate was added, and the mixture was 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 controlling the temperature at -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 metallic zinc / graphene fluoride into a ball mill, and continuing ball milling for 15 hours under hydrogen protection and controlling the temperature at -10°C to obtain mixture III;

[0081] S4. Transfer mixture III into a sintering furnace and heat-treat it at 500°C for 7 hours under hydrogen protection. Grind the heat-treated material into 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 metallic sodium is not 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 metallic lithium is not 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 fluorinated graphene is not added in this comparative example.

[0094] The electrical performance of the silicon-based negative electrode materials obtained in the above examples and comparative examples was 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 anode material or comparative material (i.e., the silicon-based anode material prepared in Comparative Examples 1-6) and conductive agent Super-P, grind and mix them uniformly, then dropwise add CMC aqueous solution and continue grinding and mixing to obtain a slurry; wherein the weight ratio of silicon-based anode material or comparative material to conductive agent Super-P and CMC is 80:10:10;

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

[0099] 4) A button cell battery was assembled using a lithium sheet as the counter electrode, a polyethylene / polypropylene composite separator, and a 1.0 mol / L LiPF6 electrolyte in ethylene carbonate / dimethyl carbonate / diethyl carbonate (volume ratio 1:1:1) with 10% fluoroethylene carbonate. The charge and discharge voltage was limited to 0.005–1.5 V.

[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 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 more than 90%. This is because the pores of the obtained material provide space for the expansion of silicon, and the in-situ generated carbon coating and fluoride provide good 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 and Comparative Examples 1, 2, and 3 are shown in Table 1:

[0105] Table 1

[0106] Specific capacity (mAh / g) Electrical conductivity (S / cm) First efficiency (%) 100-cycle 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

[0107] from Figure 3 As 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 and escapes to form pores, providing space for the volume expansion of the silicon-based material; 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 the silicon-based material 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.

[0108] 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:

[0109] Table 2

[0110] Specific capacity (mAh / g) Electrical conductivity (S / cm) First efficiency (%) 100-cycle 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

[0111] As a negative electrode material for lithium-ion batteries, silicon dioxide has better cyclability than nano-silicon, but its initial efficiency is low (<80%). Therefore, improving its initial efficiency and further increasing its cyclability are the only way for silicon dioxide to be commercialized. As can be seen from Table 2, Example 2, which adopts the solution of the present invention, has higher specific capacity and initial efficiency, and more stable cycling. This is because the metallic lithium improves the conductivity of the fluorinated graphene after reduction ball milling and forms a good coating. In addition, due to the presence of metallic lithium, the silicon dioxide undergoes pre-lithiation, resulting in a higher initial efficiency and specific capacity.

[0112] 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:

[0113] Table 3

[0114] Specific capacity (mAh / g) Electrical conductivity (S / cm) First efficiency (%) 100-cycle 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

[0115] As can be seen from Table 3, the disclosed solution, whether nano-silicon, silicon oxide, or silicon alloy, all exhibit high initial efficiency and cycle stability. This is particularly true for the silicon dioxide described in Example 4. Similar to silicon monoxide, silicon dioxide has extremely poor conductivity and, as a negative electrode material, exhibits an initial efficiency below 70%. The present invention significantly improves initial efficiency through pre-lithiation of metallic lithium and the generation of fluorinated graphene.

[0116] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily 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 is not limited to the embodiments shown herein but is intended to conform 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 inert gas protection, a silicon-based material, a first component, a second component, and a 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; The heat treatment time is 1-15 hours; The silicon-based material is one or more of silicon element, silicon oxide and silicon alloy; 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).

2. The method for preparing a silicon-based negative electrode material according to claim 1, wherein: 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 ball milling to obtain mixture I; S2: The second component and the third component are ball-milled for the second time to obtain 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, wherein: 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, wherein: 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.

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

6. The silicon-based negative electrode material obtained by the preparation method according to any one of claims 1 to 5.

7. Use of the silicon-based negative electrode material as claimed in claim 6 in lithium-ion batteries.

Images