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

Abstract

The present invention discloses a silicon-based negative electrode material, its preparation method, and application. The main material of the negative electrode material is a tin-doped pre-magnesium silicon oxide material, on the surface of which a carbon layer and a molybdenum disulfide-doped polyphenylene sulfide coating layer are sequentially coated. The preparation method is as follows: S1, silicon, silicon dioxide, and tin are crushed, mixed, and tableted; S2, the tableted material obtained in S1 is sintered to obtain a tin-doped silicon oxide material; S3, the product S2 is crushed and classified to control the particle size distribution; S4, the product S3 is placed in a rotary kiln under an inert atmosphere and heated to the sintering temperature, dimethylcyclopentadienyl magnesium is placed in a gas reactor, sintered, and discharged at room temperature to obtain an intermediate product A; S5, product A and molybdenum disulfide are dispersed in acetylacetone, diphenyl disulfide is added, oxygen is introduced for reaction, and the temperature is raised a second time under a nitrogen atmosphere to obtain a silicon-based negative electrode material coated with molybdenum disulfide-doped polyphenylene sulfide.

Description

Technical Field

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

[0002] With the development of electric vehicles and portable appliances, the demand for high-energy-density lithium-ion batteries is increasing. Traditional graphite anode materials have a theoretical specific capacity of only 372 mAh / g, which is difficult to meet market demand. Silicon materials, with their initial gram capacity of 4200 mAh / g, offer advantages such as a higher lithium insertion platform, abundant reserves in the Earth's crust, and environmental friendliness, and are gradually attracting widespread attention from researchers.

[0003] However, silicon's volume expansion can reach as high as 300%. During cycling, this not only causes silicon to separate from the surrounding conductive carbon network, forming "dead silicon," but also causes silicon to peel off from the current collector. Furthermore, this large volume expansion causes the SEI film on the surface to continuously reorganize and destroy, making the SEI film thicker and continuously consuming the positive electrode's Li+, reducing the Coulombic efficiency. Finally, the large volume expansion causes the silicon material to pulverize in the later stages of the cycle. These problems ultimately lead to a sharp deterioration in cycling performance.

[0004] Due to these issues, academia and industry have shifted some of their attention to silicon dioxide. Compared to nano-silicon, silicon dioxide sacrifices some capacity, but its expansion is relatively small (~100%). Furthermore, the byproducts generated during the charge and discharge process, such as lithium oxide, lithium silicate, and lithium metasilicate, can provide a buffering effect, greatly improving the material's cycling performance. However, the material's conductivity is relatively poor, and its initial coulombic efficiency is low. Lee DJ et al. [Lee DJ, Ryou MH, Lee JN, et al. Nitrogen-doped carbon coating for a high-performance SiO anode in lithium-ion batteries[J]. Electrochemistry Communications, 2013, 34:98-101.] prepared nitrogen-doped carbon-coated SiO materials by liquid-phase mixing followed by high-temperature carbonization. This material exhibited relatively good cycling performance, but the initial coulombic efficiency was low. Jee HoYom et al. [Yom JH, Sun WH, Cho SM, et al. Improvement of irreversible behavior of SiO anodes for lithium ion batteries by a solidstate reaction at high temperature[J]. Journal of Power Sources, 2016, 311:159-166.] prepared a high-first-efficiency silicon-based negative electrode material by reacting SiO with lithium metal in a solid-state reaction and then coating it with carbon. This method improved the material's initial coulombic efficiency, but the material's cycling performance was relatively poor. Since lithium metal was used as a reactant, the synthesis conditions were relatively harsh, posing a safety risk, and there was a risk of gas production during the battery slurry process. In addition, due to the generation of byproducts such as lithium silicate in the reaction, the electronic conductivity of the material was further reduced, and the cost was high. Of course, some patents, such as CN201710193442.6, use magnesium vapor (high-temperature treatment of magnesium powder) to pre-magnesiumize silicon dioxide to improve its initial coulombic efficiency. However, magnesium vapor reacts with the heating system (molybdenum wire) to form a molybdenum-magnesium alloy, damaging the heating system, affecting production efficiency and increasing costs. At the same time, the magnesium silicate phase, a byproduct of pre-magnesiumization, hinders the diffusion of lithium ions during charge and discharge (the radius of magnesium ions is larger than that of lithium ions, and lithium ions need to bypass magnesium ions to diffuse), resulting in increased material impedance and affecting cycle and rate performance. CN201911024768.1 uses magnesium powder and magnesium oxide to pre-magnesiumize silicon dioxide in the solid phase. The pre-magnesium uniformity is poor, and the silicon grains are relatively large, affecting circulation and expansion. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a modified gas phase pre-magnesium silicon-based negative electrode material and a preparation method thereof.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A modified gas-phase pre-magnesium silicon-based negative electrode material, wherein the main material is a tin-doped pre-magnesium silicon oxide material, and a carbon layer and a molybdenum disulfide-doped polyphenylene sulfide coating layer are sequentially coated on the surface of the main material;

[0008] The method for preparing the modified gas-phase pre-magnesium silicon-based negative electrode material comprises the following steps:

[0009] S1, crushing silicon, silicon dioxide and tin, mixing them in a certain proportion and pressing them into tablets;

[0010] S2, placing the pressed material obtained in S1 in a heating chamber of a kiln under controlled vacuum for sintering, condensing and collecting in a collecting chamber, and discharging the material at room temperature after the reaction is completed to obtain a tin-doped silicon dioxide material;

[0011] S3, crushing and classifying the tin-doped silicon oxide produced in S2 to control the particle size distribution;

[0012] S4, placing the product of S3 in a rotary kiln under the protection of an inert atmosphere and raising the temperature to a sintering temperature, placing bismethylcyclopentadienyl magnesium in a gas reactor of the rotary kiln, controlling the temperature of the gas reactor to gasify it, controlling the ratio of the mixed gas of the inert gas and bismethylcyclopentadienyl magnesium and the rotation speed of the rotary kiln, sintering, and discharging at room temperature to obtain an intermediate product A, i.e., a carbon-coated tin-doped pre-magnesium silicon oxide material;

[0013] S5. Disperse the intermediate product A obtained in S4 and molybdenum disulfide in acetylacetone, then add diphenyl disulfide, and then introduce oxygen to react. After the reaction is completed, stop introducing oxygen, heat to 160~300℃ under nitrogen atmosphere, keep warm for 0.5h~2h, then filter, wash, and dry to obtain a molybdenum disulfide-doped polyphenylene sulfide-coated silicon-based negative electrode material.

[0014] Silicon dioxide (SiO) has poor conductivity, low initial efficiency, and high expansion, limiting its widespread application in lithium-ion batteries. Pre-magnesium-prepared SiO has high impedance, relatively difficult to control grain size, and relatively poor cycling and rate performance. This invention incorporates tin into the silicon lattice during the synthesis of the SiO precursor, inducing lattice expansion and reducing the lithium ion diffusion barrier. Leveraging the isomorphism of tin and silicon atoms, this improves the intrinsic ionic conductivity of the matrix material, thereby offsetting the negative impact of the subsequent increase in impedance caused by magnesium incorporation. This lowered lithium ion diffusion barrier significantly reduces the proportion of lithium ions trapped in the lattice during delithiation, thereby improving initial efficiency. Secondly, bismethylcyclopentadienylmagnesium, which is less reactive than magnesium powder and magnesium vapor, is used through low-temperature vaporization to form a uniform gas-solid contact with SiO, creating magnesium ion pre-occupancy and further enhancing the material's initial efficiency. This low-intensity reaction and minimal heat generation facilitate control of silicon grain size, thereby improving expansion and cycling performance. At the same time, the bismethylcyclopentadienyl groups present in the gas phase can also be uniformly carbonized to form a uniform and dense carbon coating, which improves the electrical conductivity of the material and thus improves the cycle performance and rate performance. Bismethylcyclopentadienyl magnesium has low activity and is more friendly to equipment relative to magnesium, which can increase the frequency of use of the equipment and thus reduce costs. Finally, polyphenylene sulfide is in situ polymerized on the surface of the material and doped with molybdenum disulfide. By doping polyphenylene sulfide, the mechanical and electrical properties are significantly improved, which can not only effectively buffer the volume expansion of the material but also improve structural stability. In addition, polyphenylene sulfide itself has the characteristics of high temperature resistance and corrosion resistance, which can avoid the corrosion of silicon oxide by HF in the electrolyte, thereby improving the material cycle performance and high temperature performance.

[0015] Furthermore, the tin-doped pre-magnesium silicon oxide material contains 2% to 5% tin doping, with the tin incorporated into the silicon lattice. The pre-magnesium content is 8% to 16%, primarily present as magnesium orthosilicate and magnesium metasilicate. Magnesium incorporation alone reacts with silicon dioxide in the silicon oxide to form magnesium silicate, creating pre-occupied sites and thereby improving the material's initial efficiency, but also increasing the material's impedance. By leveraging the isomorphic effect of tin and silicon atoms (tin atoms have a larger atomic radius, and incorporation into the silicon lattice causes lattice expansion, thereby reducing the diffusion barrier for lithium ions), the intrinsic ionic conductivity of the matrix material can be enhanced, thereby compensating for the negative impact of increased impedance caused by magnesium incorporation. Due to the reduced lithium ion diffusion barrier, the proportion of lithium ions trapped in the lattice and unable to escape during delithiation is significantly reduced, thereby improving the initial efficiency. Therefore, the co-doping of magnesium and tin, through their synergistic effect, effectively improves the initial efficiency while also compensating for the shortcomings of magnesium doping, thereby improving ionic conductivity. The mechanisms of improving the first efficiency of the two are different. Tin is doped into the silicon lattice inside silicon oxide, reducing the proportion of lithium ions that cannot escape from the silicon lattice during the charging and discharging process. Magnesium reacts with silicon dioxide inside silicon oxide to form a magnesium silicate phase, forming a pre-occupied position in the material synthesis, thereby avoiding the lithium ions from the positive electrode consumed by side reactions during the charging process, thereby improving the first efficiency.

[0016] Furthermore, the mass of the carbon layer is 4% to 10% of the mass of the main material; and the mass of the molybdenum disulfide-doped polyphenylene sulfide coating layer is 2% to 6% of the mass of the intermediate product A.

[0017] Furthermore, the mass ratio of molybdenum disulfide to polyphenylene sulfide in the molybdenum disulfide-doped polyphenylene sulfide coating is 1:1 to 1:4. If the molybdenum disulfide ratio is too low, the polymer's conductivity will be poor, affecting rate performance. If the molybdenum disulfide ratio is too high, the polymer's mechanical strength will be poor, and its ability to suppress silicon volume expansion will be impaired. Therefore, the ratio needs to be controlled.

[0018] Furthermore, in step S1, the median particle size D50 of silicon dioxide is 500 nm to 5000 nm, the median particle size D50 of the tin particles is 10 nm to 500 nm, the mass ratio of silicon, silicon dioxide and tin is 14:30:0.9 to 14:30:2.5 respectively; and the mixing method is kneading by adding water.

[0019] To ensure uniform doping, this step S1 requires controlling the particle size of the material. The ratios of the three elements must also be controlled. Too little tin will have little effect on the material's initial efficiency and ionic conductivity. Too much tin, due to its large atomic radius, will cause a "narrow channel" effect, narrowing the diffusion channel. This, in turn, affects lithium ion diffusion and escape, resulting in negative effects such as increased impedance and reduced initial efficiency. Therefore, the tin ratio must be controlled.

[0020] Furthermore, in step S2, the vacuum degree in S2 is 10Pa~100Pa, the temperature of the heating chamber is 1300℃~1800℃, and the temperature of the condensing chamber is 600℃~800℃. This step is mainly to generate tin-doped silicon oxide, and tin is uniformly incorporated into the silicon lattice inside the silicon oxide while the silicon oxide precursor is synthesized by a one-step gas phase reaction. Under vacuum conditions, not only the reaction energy barrier is reduced, but also the silicon oxide vapor and tin vapor generated by silicon and silicon dioxide are in full contact, thereby achieving the purpose of fully and uniform doping. In order to improve the quality of the product, it is necessary to control the temperature of the condensing chamber. If the temperature of the condensing chamber is too low, glassy silicon oxide will appear, affecting the circulation. If the temperature of the condensing chamber is too high, it will cause silicon oxide disproportionation and silicon grains to increase, which will not only lead to increased expansion but also worsen the circulation. Therefore, it is necessary to control the temperature of the condensing chamber.

[0021] Furthermore, in step S3, the graded particle size of tin-doped silicon oxide is Dmin ≥ 1.5 μm, D10 ≥ 3 μm, 5 ≤ D50 ≤ 7 μm, and Dmax ≤ 10 μm, and the value of (D90-D10) / D50 is controlled between 0.6 and 1. The purpose of controlling the SiO particle size distribution is to make the silicon oxide particle size distribution uniform, to prevent the problem of excessive pre-magnesiumization of small particles and insufficient pre-magnesiumization of large particles during subsequent pre-magnesiumization, which in turn leads to deterioration of material properties. Therefore, the values ​​of Dmin and (D90-D10) / D50 are strictly controlled.

[0022] Furthermore, in step S4, the mass ratio of the S3 product to dimethylcyclopentadienyl magnesium is (0.72-1.59):1; the temperature of the dimethylcyclopentadienyl magnesium in the gas reactor is 80°C~150°C; the inert gas is one or more of helium, neon, argon, krypton, and xenon; the volume ratio of the inert gas to dimethylcyclopentadienyl magnesium vapor is 4:1~1:1; the sintering process also requires controlling the rotation speed of the rotary kiln, which is 0.25r / min~2r / min; the sintering is a two-stage sintering, with a sintering temperature of 300°C~500°C and a sintering time of 2h~6h in the first stage, a sintering temperature of 600°C~800°C and a sintering time of 2h~4h in the second stage, and a heating rate of 1°C / min~3°C / min in the sintering process. Dimethylcyclopentadienyl magnesium has a low boiling point and can be converted into steam by slight heating to fully contact the dynamic silicon oxide material in the kiln. The gas-solid contact plus the dynamic rotation of the kiln make the pre-magnesium more uniform. At the same time, the activity of dimethylcyclopentadienyl magnesium is much lower than that of magnesium powder and magnesium vapor, so the silicon grains are easier to control, and the cycle performance is better while improving the first effect. Dimethylcyclopentadienyl magnesium is more equipment-friendly than magnesium and can increase the frequency of equipment use. At the first sintering temperature, dimethylcyclopentadienyl magnesium vapor reacts with silicon oxide to perform uniform gas-phase pre-magnesium to obtain tin-doped pre-magnesium silicon oxide material. At the second sintering temperature, the dimethylcyclopentadienyl in the dimethylcyclopentadienyl is uniformly carbonized to form a uniform and dense carbon coating layer with good electrical conductivity, thereby improving the cycle stability of the material. The two-stage temperature and heating rate need to be strictly controlled, mainly to reduce the grain size of silicon in silicon oxide while ensuring the electrical conductivity of the carbon layer, thereby reducing expansion and improving cycle performance.

[0023] Furthermore, in step S5, the median particle size D50 of molybdenum disulfide is 10 nm~200 nm, the mass ratio of intermediate product A and molybdenum disulfide is 99:1~97:3, the mass ratio of intermediate product A and diphenyl disulfide is 99:1~96:4, the oxygen flow rate is 1 ml / min~5 ml / min, the reaction temperature is 20~60°C, and the reaction time is 0.5h~3h; the secondary heating temperature is 160~300°C, and the insulation time is 0.5h~2h.

[0024] This step S5 is mainly to form a conductive polymer coating layer of molybdenum disulfide-doped polyphenylene sulfide on the surface of the material. At low temperature, acetylacetone is used to catalyze and control the oxygen flow rate to cause in-situ oxidative polymerization of diphenyl disulfide on the surface of the material, while not causing oxidation of the material. Polyphenylene sulfide can be further melted, polycondensed, and further doped with molybdenum disulfide during the secondary temperature treatment to form a composite coating with good electronic and ionic conductivity coated on the surface of the silicon dioxide carbon layer. After being doped with molybdenum disulfide, the mechanical and electrical properties of polyphenylene sulfide are significantly improved, and it has its own high temperature resistance and corrosion resistance. It can not only effectively buffer the volume expansion of the material and improve the structural stability, but also avoid the corrosion of silicon dioxide by HF in the electrolyte, thereby improving the cycle performance of the material.

[0025] Another object of the present invention is to provide a modified gas-phase pre-magnesium silicon-based negative electrode material prepared by the above preparation method.

[0026] Another object of the present invention is to provide the use of the above-mentioned modified gas-phase pre-magnesium silicon-based negative electrode material in the preparation of lithium-ion batteries.

[0027] The present invention also provides a lithium ion battery.

[0028] The lithium-ion battery comprises a positive electrode, a negative electrode, an electrolyte and a separator, and the material of the negative electrode comprises the silicon-based negative electrode material of the present invention.

[0029] The lithium-ion battery may include a button battery, a soft-pack battery, a hard-shell battery, etc.

[0030] Taking button batteries as an example, the preparation method of the button batteries may include: mixing the modified gas-phase pre-magnesium silicon-based negative electrode material, conductive agent, and binder to obtain negative electrode slurry; coating the negative electrode slurry on the surface of the current collector, drying to obtain a negative electrode sheet, and then assembling the positive electrode sheet, negative electrode sheet, separator, electrolyte, and button battery shell in a glove box to obtain the button battery.

[0031] In the above-mentioned button cell manufacturing method, the positive electrode sheet is generally a lithium sheet. The separator may include one or a combination of two or more of Celgard 2400, Celgard 2325, Celgard 2500, etc. The electrolyte may include a lithium hexafluorophosphate solution. The button cell shell may include a CR2016 battery shell, a CR2023 battery shell, or a CR2450 battery shell.

[0032] The silicon-based material of the present invention is used as a negative electrode material to prepare a lithium-ion battery, and the electrochemical performance of the prepared lithium-ion battery is tested. The specific capacity, first efficiency and cycle stability of the prepared lithium-ion battery are all improved.

[0033] Conventional silicon oxide materials have low initial Coulombic efficiency. Partially magnesium-treated silicon oxide generates byproducts such as magnesium silicate, further reducing the material's intrinsic electronic and ionic conductivity. The reaction is also too intense, leading to rapid silicon grain growth and further deteriorating the material's cycling and rate performance. Furthermore, magnesium is not device-friendly, shortening its lifespan and increasing material costs. The present invention aims to address this shortcoming.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1) This invention incorporates tin into the silicon lattice in a single step during the synthesis of a silicon oxide precursor, triggering lattice expansion and lowering the diffusion barrier for lithium ions. By leveraging the isomorphism of tin and silicon atoms, the intrinsic ionic conductivity of the matrix material is enhanced, thereby compensating for the negative impact of increased impedance caused by subsequent magnesium incorporation. Due to the reduced lithium ion diffusion barrier, the proportion of lithium ions trapped in the lattice and unable to escape during delithiation is significantly reduced, thereby improving the initial efficiency.

[0036] 2) The present invention uses dimethylcyclopentadienyl magnesium, which has lower reactivity (relative to magnesium powder and magnesium vapor), to form a uniform gas-solid contact with silicon oxide through low-temperature vaporization, forming magnesium ion pre-occupancy, thereby improving the material's initial efficiency. The low reaction intensity and low heat generation are more conducive to controlling silicon grain size, thereby reducing expansion and improving cycle performance. At the same time, the dimethylcyclopentadienyl groups in the gas phase can also be uniformly carbonized to form a uniform and dense carbon coating, increasing the material's electrical conductivity, thereby improving cycle performance and rate performance.

[0037] 3) Dimethylcyclopentadienyl magnesium has low activity and is more equipment-friendly than magnesium. It can increase the frequency of equipment use and thus reduce costs.

[0038] 4) In-situ polymerization of polyphenylene sulfide (PPS) and doping with molybdenum disulfide (MoS2) on the material surface significantly improves its mechanical and electrical properties. This not only effectively mitigates the material's volume expansion and enhances its structural stability, but the inherent high-temperature and corrosion resistance of PPS prevents HF in the electrolyte from corroding silicon oxide, thereby enhancing the material's cycling and high-temperature performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is the EDS mapping diagram of magnesium in the silicon-based negative electrode material prepared in Example 1;

[0040] Figure 2 This is the EDS mapping diagram of magnesium in the silicon-based negative electrode material prepared in Comparative Example 1;

[0041] Figure 3The XRD patterns of the silicon-based negative electrode materials prepared in Example 1 and Comparative Example 4 and Comparative Example 1;

[0042] Figure 4 The first charge-discharge curves of the silicon-based negative electrode material prepared in Example 1 and Comparative Example 1 at 0.1C;

[0043] Figure 5 The graphs are rate performance diagrams of the materials mixed with graphite in Example 1, Comparative Example 1 and Comparative Example 2 under full battery conditions;

[0044] Figure 6 The DCR curves of the materials mixed with graphite in Example 1, Comparative Example 1 and Comparative Example 2 under full battery conditions are shown;

[0045] Figure 7 The HPPC curves (power density diagram) of the materials mixed with graphite in Example 1 and Comparative Example 1 and Comparative Example 2 under full battery conditions are shown;

[0046] Figure 8 The graphite-doped materials of Example 1, Comparative Example 1, and Comparative Example 2 are shown in the full cell cycle performance curves at a current density of 1C / 1C. DETAILED DESCRIPTION

[0047] The present invention will be further described in detail below in conjunction with specific embodiments. The examples provided are only for illustrating the present invention and are not intended to limit the scope of the present invention. The examples provided below can serve as a guide for further improvements by those skilled in the art and are not intended to limit the present invention in any way.

[0048] Unless otherwise specified, the experimental methods in the following examples are conventional methods and were performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials and reagents used in the following examples, unless otherwise specified, were all commercially available.

[0049] Example 1

[0050] 2.8 kg of silicon, 6.6 kg of silicon dioxide (D50: 5000 nm), and 0.18 kg of tin (D50: 500 nm) were mixed with water, pressed into tablets, and dried.

[0051] The above materials were placed in a heating chamber of a kiln and the vacuum degree was controlled at 10 Pa. The temperature was raised to 1300°C for reaction. The temperature of the collection chamber was controlled at 600°C for condensation and collection. After the reaction was completed, the material was discharged at room temperature to obtain tin-doped silicon dioxide material.

[0052] The above materials were placed in a jet mill for pulverization and classification, and Dmin was controlled to be 1.5 μm, D10 ≥ 3 μm, D50 to be 6 μm, Dmax to be 10 μm, and the value of (D90-D10) / D50 to be controlled to be 1.

[0053] 840 g of the crushed material was placed in a rotary kiln protected by an argon atmosphere, and 1160 g of dimethylcyclopentadienyl magnesium (160 g in terms of magnesium) was placed in the gas reactor (container H) of the rotary kiln. The rotation speed of the rotary kiln was controlled to 2 r / min, and the temperature was increased to 500°C at 3°C / min. At this time, the container H was heated to 80°C to vaporize the dimethylcyclopentadienyl magnesium. The gas ratio of argon and dimethylcyclopentadienyl magnesium vapor was controlled to 4:1 (v / v) and introduced into the rotary kiln. The reaction time was 2 h at 500°C to completely volatilize the dimethylcyclopentadienyl magnesium in the container H. The temperature was then increased to 800°C and maintained for 4 h to completely carbonize the dimethylcyclopentadienyl group. The intermediate product A was discharged at room temperature.

[0054] 97g of intermediate product A and 3g of molybdenum disulfide (D50: 200nm) were dispersed in acetylacetone, and then 2g of diphenyl disulfide was added. Oxygen was introduced at a flow rate of 1ml / min and the reaction was carried out at 60°C for 3h. The introduction of oxygen was stopped, and the temperature was raised to 300°C under a nitrogen atmosphere and kept warm for 0.5h. Then, the mixture was filtered, washed, and dried to obtain a molybdenum disulfide-doped polyphenylene sulfide-coated silicon negative electrode material, that is, a modified gas-phase pre-magnesium silicon-based negative electrode material.

[0055] The mass of the carbon layer of the material accounts for 10% of the mass of the main material (tin-doped pre-magnesium silicon oxide material), and the molybdenum disulfide-doped polyphenylene sulfide coating layer accounts for 5% of the mass of the intermediate product A (carbon-coated tin-doped pre-magnesium silicon oxide material).

[0056] Figure 1 The EDS diagram of the magnesium element in the silicon-based negative electrode material prepared in Example 1 shows that the magnesium element is distributed quite evenly within the material. Figure 2 The EDS diagram of magnesium in Comparative Example 1 shows that the magnesium is unevenly distributed, with some areas showing a gradient distribution. This is because Example 1 uses bismethylcyclopentadienyl magnesium vapor for dynamic pre-treatment, resulting in a more uniform magnesium distribution.

[0057] Figure 3The XRD patterns of Example 1, Comparative Examples 1, and Comparative Examples 4 reveal the presence of magnesium orthosilicate and metasilicic acid phases in all materials, a result of pre-magnesium treatment. However, the material prepared in Example 1 exhibits the largest half-peak width of crystalline silicon diffraction at approximately 28.4°C, followed by Comparative Example 1. The smallest width is in the material prepared in Comparative Example 4, reflecting the smallest silicon grains in the material prepared in Example 1, which helps reduce expansion and improve the material's cyclic performance. This phenomenon occurs because Example 1 utilizes less active bismethylcyclopentadienylmagnesium vapor (relative to magnesium powder) for vapor-phase dynamic pre-magnesium treatment. This results in a more controllable and uniform reaction, minimizes heat generation, and minimizes grain size, resulting in optimal cyclic performance.

[0058] The prepared silicon-based negative electrode material: SP: LA133 = 8:1:1 ratio (mass ratio) was mixed into a slurry and coated on an 8μm copper foil to prepare a negative electrode sheet. A lithium sheet was used as the counter electrode to assemble a CR2016 button battery. The electrolyte used was a 1mol / L LiPF6 EC+DMC (1:1, v / v) solution, and the electrochemical performance was tested.

[0059] The results are as follows Figure 4 As shown in Table 1, at a current density of 0.1C, the material prepared in Example 1 has an initial discharge capacity of 1561.4 mAh / g, a charge capacity of 1380.3 mAh / g, and an initial coulombic efficiency of 88.4%. After 50 cycles, the specific capacity is 1298.9 mAh / g, and the capacity retention rate is 94.1%. Furthermore, the silicon grain size of the material prepared in Example 1 is 5.5 nm, the powder resistance is 0.81 Ω / cm, and the lithium ion diffusion coefficient is 8.2×10 -8 m 2 / s.

[0060]

[0061] Comparative Example 1

[0062] Commercial pre-magnesium silicon oxide materials are used. The synthesis method mainly uses magnesium powder as the magnesium source and uses a CVD process for carbon coating.

[0063] Comparative Example 2

[0064] The difference from Example 1 is that: in Example 1, no tin is added;

[0065] Comparative Example 3

[0066] The difference from Example 1 is that: Example 1 does not add tin, does not use bismethylcyclopentadienyl magnesium, and the carbon coating is CVD coating;

[0067] Comparative Example 4

[0068] The difference from Example 1 is that: in Example 1, bismethylcyclopentadienyl magnesium is not used, and magnesium powder and acetylene are used for CVD carbon coating;

[0069] Comparative Example 5

[0070] The difference from Example 1 is that: in Example 1, polyphenylene sulfide coating is not used;

[0071] Comparative Example 6

[0072] The difference from Example 1 is that molybdenum disulfide is not used in Example 1.

[0073] The materials prepared in Comparative Examples 1 to 6 were mixed and coated in a ratio of SP:LA133=8:1:1 (mass ratio), and CR2016 button batteries were assembled. The electrolyte used was a 1mol / L LiPF6 EC+DMC solution, and the electrochemical performance test was performed. The results are shown in Table 1. At a current density of 0.1C, the material prepared in Comparative Example 1 had an initial discharge capacity of 1531.8mAh / g, a charge capacity of 1299mAh / g, and an initial coulombic efficiency of 84.8%. After 50 cycles, the specific capacity was 1131.4mAh / g, and the capacity retention rate was 87.1%. The silicon grains of the material prepared in Comparative Example 1 were 7.2nm, the powder resistance was 1.13Ω / cm, and the lithium ion diffusion coefficient was 2×10 -10 m 2 / s. Figure 4 It can be found that in the charge and discharge curve diagram of Example 1, the lithium insertion platform on its discharge curve is higher, and the discharge curve is relatively inclined. There is no obvious lithium de-lithiation characteristic platform at 0.4V. This is because the material prepared in Example 1 has smaller grains. By comparing Example 1 with Comparative Example 1, it can be found that the material prepared by the present invention is superior to the commercial material in discharge specific capacity, first efficiency, and cycle capacity retention rate. At the same time, the silicon grains of the prepared material are smaller and have a higher lithium ion diffusion coefficient. This is because Example 1 uses less active dimethylcyclopentadienyl magnesium vapor (relative to magnesium powder) for gas phase dynamic pre-magnesium, so the reaction is more controllable and uniform, and the heat generation is small, so the grains are smallest and the cycle performance is optimal. At the same time, polyphenylene sulfide doped with molybdenum disulfide is used for modification, and its mechanical properties and electrical properties are significantly improved, which can effectively buffer the volume expansion of the material and improve the structural stability. In addition, Example 1 performs tin doping during the precursor synthesis to induce lattice expansion in advance, reduce the diffusion energy barrier of lithium ions, and utilize the equivalent isomorphism effect of tin and silicon atoms of the same family to improve the ionic conductivity of the matrix material, thereby compensating for the negative impact of the impedance increase caused by the subsequent magnesium doping, thereby improving the rate performance.

[0074] The material prepared in Comparative Example 2 had an initial discharge capacity of 1539 mAh / g, a charge capacity of 1311.2 mAh / g, and an initial coulombic efficiency of 85.2%. After 50 cycles, the specific capacity was 1111.2 mAh / g, and the capacity retention rate was 89.3%. Meanwhile, the silicon grain size of the material prepared in Example 1 was 6.1 nm, the powder resistance was 0.96 Ω / cm, and the lithium ion diffusion coefficient was 4×10 - 10 m 2 / s. By comparing Example 1 with Comparative Example 2, it can be found that lattice doping of silicon particles in silicon oxide with tin in the precursor synthesis can reduce the diffusion energy barrier (equivalent isomorphism effect), effectively improve the lithium ion diffusion coefficient, and thus improve the rate performance of the material ( Figure 5 Since the lithium ion diffusion barrier is reduced, the proportion of lithium ions that are trapped in the lattice and cannot be released during delithiation is greatly reduced, thereby improving the first efficiency. Therefore, compared with the use of magnesium reduction alone, tin doping and magnesium reduction can work synergistically to further improve the first coulombic efficiency of the material.

[0075] The material prepared in Comparative Example 3 has an initial discharge capacity of 2060 mAh / g, a charge capacity of 1610.9 mAh / g, and an initial coulombic efficiency of 78.2%. After 50 cycles, the specific capacity is 1490.1 mAh / g, and the capacity retention rate is 89.3%. The silicon grain size of the material prepared in Comparative Example 3 is 2.4 nm, the powder resistance is 0.92 Ω / cm, and the lithium ion diffusion coefficient is 1.2×10 -10 m 2 / s. By comparing Example 1 with Comparative Example 3, it can be found that since Comparative Example 3 does not undergo pre-magnesium treatment, the initial efficiency of Comparative Example 3 is low, the grains are smaller (pre-magnesium treatment is an exothermic reaction, which will cause the grains to grow), and the cycle is relatively poor. This is mainly because the elastic modulus of the magnesium silicate phase formed by pre-magnesium treatment is higher, and the expansion capacity of the buffer material is stronger, so the structure is more stable and the cycle is better.

[0076] The material prepared in Comparative Example 4 has an initial discharge capacity of 1476.8 mAh / g, a charge capacity of 1302.5 mAh / g, and an initial coulombic efficiency of 88.2%. After 50 cycles, the specific capacity is 1061.5 mAh / g, and the capacity retention rate is 81.5%. The silicon grain size of the material prepared in Comparative Example 4 is 7.8 nm, the powder resistance is 1.25 Ω / cm, and the lithium ion diffusion coefficient is 6.5×10 -8 m 2 / s. By comparing Example 1 with Comparative Example 4, it can be found that the silicon grains in Example 1 are smaller and the circulation is better. This is because Comparative Example 4 uses magnesium powder instead of dimethylcyclopentadienyl magnesium and performs CVD coating. Since the reactivity of magnesium powder is higher than that of dimethylcyclopentadienyl magnesium, and the magnesium powder and the material are in solid-solid contact, while the low-temperature vaporization of dimethylcyclopentadienyl magnesium and the material are in gas-solid contact, the latter has better reaction uniformity. In addition, the reaction activity is low and the reaction controllability is stronger. Therefore, Example 1 has smaller grains and better circulation.

[0077] The material prepared in Comparative Example 5 had an initial discharge capacity of 1509.2 mAh / g, a charge capacity of 1332.2 mAh / g, and an initial coulombic efficiency of 88.3%. After 50 cycles, the specific capacity was 1202 mAh / g, and the capacity retention rate was 90.2%. Meanwhile, the silicon grain size of the material prepared in Example 1 was 5.6 nm, the powder resistance was 0.64 Ω / cm, and the lithium ion diffusion coefficient was 7.8×10 - 8 m 2 / s. By comparing Example 1 with Comparative Example 5, it can be found that although the impedance of the material is reduced in Comparative Example 5 using only molybdenum disulfide coating, the cycling performance of the material is reduced. This is because Comparative Example 5 does not use polyphenylene sulfide coating, and the mechanical strength of the coating is insufficient to improve the impact of the huge volume expansion of silicon during the charge and discharge process.

[0078] The material prepared in Comparative Example 6 had an initial discharge capacity of 1491.2 mAh / g, a charge capacity of 1309.3 mAh / g, and an initial coulombic efficiency of 87.8%. After 50 cycles, the specific capacity was 1195.4 mAh / g, and the capacity retention rate was 91.3%. Meanwhile, the silicon grain size of the material prepared in Example 1 was 5.5 nm, the powder resistance was 3.45 Ω / cm, and the lithium ion diffusion coefficient was 5.4×10 -8 m 2 By comparing Example 1 with Comparative Example 6, it can be found that Comparative Example 6 only uses polyphenylene sulfide coating, which has poor electrical conductivity, resulting in a sharp increase in the powder resistivity of the material, and also affecting the ionic conductivity of the material, thereby affecting the cycle performance and rate performance of the material.

[0079] Based on the above, the performance of the material prepared in Example 1 is better through the above steps and the raw materials and proportions used.

[0080] With NCM622 as the positive electrode, the materials prepared in Example 1 and Comparative Example 1 vs. 2 were mixed with artificial graphite to 420 mAh / g and used as the negative electrode. The 10Ah soft pack battery was assembled by slurry mixing, coating, rolling, slitting, die cutting, lamination, welding the tabs, top and side sealing, baking, and liquid injection. After the battery was divided into different capacities, a short-term performance test was carried out. The results are as follows: Figures 5-7 As shown, the current full battery cycle is 1200 weeks, and the capacity retention rate is 86.5%. The material after mixing in Comparative Example 1 has the smallest DCR in the full battery (50% DOD: 21.45mΩ), the largest constant current charging ratio (3C: 63.4%), and the largest power density in the HPPC test (50% DOD: 2196.44W / kg). The rate performance and power performance of the material are better. This is because Example 1 uses tin doping, and utilizes the isovalent and isostructural effect of tin and silicon to reduce the lithium ion diffusion energy barrier and improve the ionic conductivity of the material. Regardless of whether it is the commercial Comparative Example 1 material or Comparative Example 2 that only uses pre-magnesium, the magnesium ion radius in the magnesium silicate phase formed by its pre-occupancy is large, which hinders the diffusion of lithium ions to the inside during the lithium insertion process, resulting in increased impedance, thereby affecting the rate and power performance. Subsequently, a room temperature cycle test at 25°C was carried out at a current density of 1C / 1C, and the results are as follows Figure 8 As shown, after 600 cycles, the capacity retention rate of Example 1 is 93.4%, while the capacity retention rates of Comparative Examples 1 and Comparative Examples 2 after 500 cycles are 90.5% and 86.4%, respectively. The cycle performance of Example 1 is significantly improved. This is because Example 1 not only uses tin doping, but also utilizes the isovalent and isostructural effect of tin and silicon to improve the lithium ion conductivity of the material. It also uses bismethylcyclopentadienyl magnesium vapor (relative to magnesium powder and magnesium vapor) with lower reactivity, low reaction intensity and low heat generation, which is more conducive to controlling the silicon grain size, thereby reducing expansion and improving cycle performance. At the same time, the bismethylcyclopentadienyl groups present in the gas phase can also be uniformly carbonized to form a uniform and dense carbon coating layer, thereby improving the conductivity of the material and improving the cycle performance and rate performance. Finally, polyphenylene sulfide is in situ polymerized on the surface of the material and doped with molybdenum disulfide. The mechanical and electrical properties of the doped polyphenylene sulfide are significantly improved, which can not only effectively buffer the volume expansion of the material but also improve the structural stability. In addition, polyphenylene sulfide itself has the characteristics of high temperature resistance and corrosion resistance, which can prevent HF in the electrolyte from corroding silicon oxide, thereby improving the material's cycle performance and high temperature performance.

[0081] Example 2

[0082] 2.8 kg of silicon, 6.6 kg of silicon dioxide (D50: 500 nm), and 0.46 kg of tin (D50: 10 nm) were mixed with water, pressed into tablets, and dried.

[0083] The above materials were placed in a heating chamber of a kiln and the vacuum degree was controlled to be 100 Pa. The temperature was raised to 1800°C for reaction. The temperature of the collection chamber was controlled to be 600°C for condensation and collection. After the reaction was completed, the material was discharged at room temperature to obtain tin-doped silicon dioxide material.

[0084] The above materials were placed in a jet mill for pulverization and classification, and Dmin, D10, D50, Dmax, and (D90-D10) / D50 were controlled to be 2 μm, 3.5 μm, 6 μm, and 9 μm, respectively. The value of (D90-D10) / D50 was also controlled to be 0.8.

[0085] 920 g of the crushed material was placed in a rotary kiln protected by an argon atmosphere, and 580 g of dimethylcyclopentadienyl magnesium (80 g in terms of magnesium) was placed in the gas reactor (container H) of the rotary kiln. The rotation speed of the rotary kiln was controlled to 0.25 r / min, and the temperature was increased to 300° C. at 1° C. / min. At this time, the container H was heated to 150° C. to vaporize the dimethylcyclopentadienyl magnesium. The gas ratio of argon and dimethylcyclopentadienyl magnesium vapor was controlled to be 1:1 and introduced into the rotary kiln. The reaction time was 6 h at 300° C. to completely volatilize the dimethylcyclopentadienyl magnesium in container A. The temperature was then increased to 800° C. and maintained for 4 h to completely carbonize the dimethylcyclopentadienyl group. The intermediate product A was discharged at room temperature.

[0086] 99g of intermediate product A and 1g of molybdenum disulfide (D50: 10nm) were dispersed in acetylacetone, and then 1g of diphenyl disulfide was added. Oxygen was introduced at a flow rate of 5ml / min and the reaction was carried out at 20°C for 3h. The introduction of oxygen was stopped, and the temperature was raised to 160°C under a nitrogen atmosphere and kept warm for 2h. Then, the mixture was filtered, washed, and dried to obtain a molybdenum disulfide-doped polyphenylene sulfide-coated silicon negative electrode material, that is, a modified gas-phase pre-magnesium silicon-based negative electrode material.

[0087] The mass of the carbon layer of this material accounts for 4% of the mass of the main material, and the molybdenum disulfide-doped polyphenylene sulfide coating layer accounts for 2% of the mass of the intermediate product A.

[0088] The prepared silicon-based negative electrode material: SP: LA133 = 8:1:1 ratio was mixed and coated, and CR2016 button batteries were assembled. The electrolyte used was 1 mol / L LiPF6 EC+DMC solution, and the electrochemical performance test was performed. The electrochemical test was also carried out according to the above steps. The test results are shown in Table 2. The material prepared in Example 2 had an initial discharge capacity of 1823.2 mAh / g, a charge capacity of 1462.2 mAh / g, and an initial coulombic efficiency of 80.2%. After 50 cycles, the specific capacity was 1430 mAh / g, and the capacity retention rate was 97.8%. At the same time, the silicon grains of the material prepared in Example 2 were 3.1 nm, the powder resistance was 0.64 Ω / cm, and the lithium ion diffusion coefficient was 8.6×10 -8 m 2 / s.

[0089] Example 3

[0090] 2.8 kg of silicon, 6.6 kg of silicon dioxide (D50: 2000 nm), and 0.27 kg of tin (D50: 100 nm) were mixed with water, pressed into tablets, and dried.

[0091] The above materials were placed in a heating chamber of a kiln and the vacuum degree was controlled to be 10Pa. The temperature was raised to 1500°C for reaction. The temperature of the collection chamber was controlled to be 700°C for condensation and collection. After the reaction was completed, the material was discharged at room temperature to obtain tin-doped silicon dioxide material.

[0092] The above materials were placed in a jet mill for pulverization and classification, and Dmin, D10, D50, Dmax, and (D90-D10) / D50 were controlled to be 2 μm, 3.2 μm, 5 μm, and 9 μm, respectively.

[0093] 900 g of the crushed material was placed in a rotary kiln protected by an argon atmosphere, and 725 g of dimethylcyclopentadienyl magnesium (100 g in terms of magnesium) was placed in the gas reactor (container H) of the rotary kiln. The rotation speed of the rotary kiln was controlled to 1 r / min, and the temperature was increased at 2°C / min to 400°C. At this time, the container H was heated to 100°C to vaporize the dimethylcyclopentadienyl magnesium. The gas ratio of argon and dimethylcyclopentadienyl magnesium vapor was controlled to 2:1 and introduced into the rotary kiln. The reaction was carried out at 400°C for 3 hours to completely volatilize the dimethylcyclopentadienyl magnesium in the container H. The temperature was then increased to 700°C and maintained for 3 hours to completely carbonize the dimethylcyclopentadienyl group. The intermediate product A was discharged at room temperature.

[0094] 98g of intermediate product A and 2g of molybdenum disulfide (D50: 50nm) were dispersed in acetylacetone, and then 2g of diphenyl disulfide was added. Oxygen was introduced at a flow rate of 2ml / min and the reaction was carried out at 40°C for 1h. The introduction of oxygen was stopped, and the temperature was raised to 200°C under a nitrogen atmosphere and kept warm for 1h. Then, the mixture was filtered, washed, and dried to obtain a molybdenum disulfide-doped polyphenylene sulfide-coated silicon negative electrode material, that is, a modified gas-phase pre-magnesium silicon-based negative electrode material.

[0095] The mass of the carbon layer of this material accounts for 6% of the mass of the main material, and the molybdenum disulfide-doped polyphenylene sulfide coating layer accounts for 4% of the mass of the intermediate product A.

[0096] The prepared silicon-based negative electrode material: SP: LA133 = 8:1:1 ratio was mixed and coated, and CR2016 button batteries were assembled. The electrolyte used was 1 mol / L LiPF6 EC+DMC solution, and the electrochemical performance test was performed. The electrochemical test was also carried out according to the above steps. The test results are shown in Table 2. The material prepared in Example 3 had an initial discharge capacity of 1749.3 mAh / g, a charge capacity of 1432.7 mAh / g, and an initial coulombic efficiency of 81.9%. After 50 cycles, the specific capacity was 1384 mAh / g, and the capacity retention rate was 96.6%. At the same time, the silicon grains of the material prepared in Example 3 were 3.8 nm, the powder resistance was 0.93 Ω / cm, and the lithium ion diffusion coefficient was 9.5×10 -8 m 2 / s.

[0097] Example 4

[0098] 2.8 kg of silicon, 6.6 kg of silicon dioxide (D50: 1000 nm), and 0.367 kg of tin (D50: 200 nm) were mixed with water, pressed into tablets, and dried.

[0099] The above materials were placed in a heating chamber of a kiln and the vacuum degree was controlled to be 50 Pa. The temperature was raised to 1600°C for reaction. The temperature of the collection chamber was controlled to be 650°C for condensation and collection. After the reaction was completed, the material was discharged at room temperature to obtain tin-doped silicon dioxide material.

[0100] The above materials were placed in a jet mill for pulverization and classification, with Dmin controlled to be 3 μm, D10≥ to be 4.2 μm, D50 to be 7 μm, Dmax to be 9.5 μm, and the value of (D90-D10) / D50 to be controlled to be 0.7.

[0101] 880 g of the crushed material was placed in a rotary kiln protected by an argon atmosphere, and 870 g of dimethylcyclopentadienyl magnesium (120 g in terms of magnesium) was placed in the gas reactor (container H) of the rotary kiln. The rotation speed of the rotary kiln was controlled to 0.5 r / min, and the temperature was increased to 450°C at 3°C / min. At this time, the container H was heated to 120°C to vaporize the dimethylcyclopentadienyl magnesium. The gas ratio of argon and dimethylcyclopentadienyl magnesium vapor was controlled to 3:1 and introduced into the rotary kiln. The reaction was carried out at 450°C for 4 hours to completely volatilize the dimethylcyclopentadienyl magnesium in the container H. The temperature was then increased to 800°C and maintained for 2 hours to completely carbonize the dimethylcyclopentadienyl group. The intermediate product A was discharged at room temperature.

[0102] 96g of intermediate product A and 1g of molybdenum disulfide (D50: 30nm) were dispersed in acetylacetone, and then 3g of diphenyl disulfide was added. Oxygen was introduced at a flow rate of 2ml / min and the reaction was carried out at 60°C for 0.5h. The introduction of oxygen was stopped, and the temperature was raised to 250°C under a nitrogen atmosphere and kept warm for 1h. The mixture was then filtered, washed, and dried to obtain a molybdenum disulfide-doped polyphenylene sulfide-coated silicon negative electrode material, that is, a modified gas-phase pre-magnesium silicon-based negative electrode material.

[0103] The mass of the carbon layer of this material accounts for 7% of the mass of the main material, and the molybdenum disulfide-doped polyphenylene sulfide coating layer accounts for 4% of the mass of the intermediate product A.

[0104] The prepared silicon-based negative electrode material: SP: LA133 = 8:1:1 ratio was mixed and coated, and CR2016 button batteries were assembled. The electrolyte used was 1 mol / L LiPF6 EC+DMC solution, and the electrochemical performance test was performed. The electrochemical test was also carried out according to the above steps. The test results are shown in Table 2. The material prepared in Example 4 had an initial discharge capacity of 1655.3 mAh / g, a charge capacity of 1392.1 mAh / g, and an initial coulombic efficiency of 84.1%. After 50 cycles, the specific capacity was 1335 mAh / g, and the capacity retention rate was 95.9%. At the same time, the silicon grains of the material prepared in Example 4 were 4.6 nm, the powder resistance was 0.72 Ω / cm, and the lithium ion diffusion coefficient was 1.6×10 -7 m 2 / s.

[0105] Example 5

[0106] 2.8 kg of silicon, 6.6 kg of silicon dioxide (D50: 800 nm), and 0.4 kg of tin (D50: 120 nm) were mixed with water, pressed into tablets, and dried.

[0107] The above materials were placed in a heating chamber of a kiln and the vacuum degree was controlled to be 10 Pa. The temperature was raised to 1400°C for reaction. The temperature of the collection chamber was controlled to be 650°C for condensation and collection. After the reaction was completed, the material was discharged at room temperature to obtain tin-doped silicon dioxide material.

[0108] The above materials were placed in a jet mill for pulverization and classification, and Dmin, D10, D50, Dmax, and (D90-D10) / D50 were controlled to be 2.6 μm, 4.3 μm, 7 μm, and 9.3 μm, respectively. The value of (D90-D10) / D50 was also controlled to be 0.6.

[0109] 860 g of the crushed material was placed in a rotary kiln protected by an argon atmosphere, and 1015 g of dimethylcyclopentadienyl magnesium (140 g in terms of magnesium) was placed in the gas reactor (container H) of the rotary kiln. The rotation speed of the rotary kiln was controlled to 2 r / min, and the temperature was increased to 350°C at 3°C / min. At this time, the container H was heated to 90°C to vaporize the dimethylcyclopentadienyl magnesium. The gas ratio of argon and dimethylcyclopentadienyl magnesium vapor was controlled to 3:1 and introduced into the rotary kiln. The reaction time was 6 h at 350°C to completely volatilize the dimethylcyclopentadienyl magnesium in the container H. The temperature was then increased to 800°C and maintained for 4 h to completely carbonize the dimethylcyclopentadienyl group. The intermediate product A was discharged at room temperature.

[0110] 97g of intermediate product A and 3g of molybdenum disulfide (D50: 150nm) were dispersed in acetylacetone, and then 3g of diphenyl disulfide was added. Oxygen was introduced at a flow rate of 3ml / min and the reaction was carried out at 60°C for 1h. The introduction of oxygen was stopped, and the temperature was raised to 300°C under a nitrogen atmosphere and kept warm for 6h. Then, the mixture was filtered, washed, and dried to obtain a molybdenum disulfide-doped polyphenylene sulfide-coated silicon negative electrode material, that is, a modified gas-phase pre-magnesium silicon-based negative electrode material.

[0111] The mass of the carbon layer of this material accounts for 8% of the mass of the main material, and the molybdenum disulfide-doped polyphenylene sulfide coating layer accounts for 6% of the mass of the intermediate product A.

[0112] The prepared silicon-based negative electrode material: SP: LA133 = 8:1:1 ratio was mixed and coated, and CR2016 button batteries were assembled. The electrolyte used was 1 mol / L LiPF6 EC+DMC solution, and the electrochemical performance test was performed. The electrochemical test was also carried out according to the above steps. The test results are shown in Table 2. The material prepared in Example 5 had an initial discharge capacity of 1608.5 mAh / g, a charge capacity of 1378.5 mAh / g, and an initial coulombic efficiency of 85.7%. After 50 cycles, the specific capacity was 1312.3 mAh / g, and the capacity retention rate was 95.2%. At the same time, the silicon grains of the material prepared in Example 5 were 5.1 nm, the powder resistance was 0.75 Ω / cm, and the lithium ion diffusion coefficient was 1.2×10 -7 m 2 / s.

[0113] By comparing Examples 1 to 5, it can be found that with the increase of the amount of pre-magnesium, the first effect of the material is improved, but the grain size gradually increases, and the cycle performance is declining. This is because the magnesium content increases during the pre-magnesium process, and the heat release increases sharply, resulting in excessive grain growth, which in turn affects the cycle performance. At the same time, as the amount of tin doping in the precursor increases, the lithium ion diffusion coefficient tends to increase first and then decrease. This is because excessive tin doping, due to its large atomic radius, will cause a "narrow channel" effect, resulting in the narrowing of the diffusion channel, thereby affecting the diffusion and escape of lithium ions, and instead increasing the negative effects of increased impedance and reduced first effect. In summary, it is necessary to strictly control the proportion of tin doping and the amount of pre-magnesium in the process of material preparation.

[0114]

[0115] The present invention has been described in detail above. It will be apparent to those skilled in the art that the present invention may be practiced over a wide range of parameters, concentrations, and conditions without departing from the spirit and scope of the present invention and without unnecessary experimentation. Although specific embodiments have been given herein, it should be understood that further modifications may be made to the present invention. In summary, this application is intended to encompass any variations, uses, or improvements to the present invention, including those made by conventional techniques known in the art that depart from the scope of the present invention. Applications of the essential features may be made within the scope of the following claims.

Claims

1. A method for preparing a silicon-based negative electrode material, characterized in that: The main material of the silicon-based negative electrode material is a tin-doped pre-magnesium silicon oxide material, and a carbon layer and a molybdenum disulfide-doped polyphenylene sulfide coating layer are sequentially coated on the surface of the main material; wherein the mass ratio of molybdenum disulfide to polyphenylene sulfide in the molybdenum disulfide-doped polyphenylene sulfide coating layer is 1:1 to 1:4; The method for preparing the silicon-based negative electrode material comprises the following steps: S1, crushing silicon, silicon dioxide and tin, mixing them in a certain proportion and pressing them into tablets; S2, placing the pressed material obtained in S1 in a heating chamber of a kiln under controlled vacuum for sintering, condensing and collecting in a collecting chamber, and discharging the material at room temperature after the reaction is completed to obtain a tin-doped silicon dioxide material; S3, crushing and classifying the tin-doped silicon oxide material to control the particle size distribution; S4, placing the product of S3 in a rotary kiln under the protection of an inert atmosphere and heating the temperature to a sintering temperature, placing bismethylcyclopentadienyl magnesium in a gas reactor of the rotary kiln to gasify it, controlling the ratio of the mixed gas of the inert gas and bismethylcyclopentadienyl magnesium, sintering, and discharging at room temperature to obtain an intermediate product A, i.e., a carbon-coated tin-doped pre-magnesium silicon oxide material; S5. Disperse the intermediate product A obtained in S4 and molybdenum disulfide in acetylacetone, then add diphenyl disulfide, and then introduce oxygen to react. After the reaction is completed, stop introducing oxygen, and heat the reaction a second time under a nitrogen atmosphere. After the reaction is completed, filter, wash, and dry to obtain a molybdenum disulfide-doped polyphenylene sulfide-coated silicon-based negative electrode material.

2. The preparation method according to claim 1, wherein: The tin doping amount in the tin-doped pre-magnesium silicon oxide material is 2% to 5%, and the tin is doped into the silicon lattice; the pre-magnesium amount is 8% to 16%; And / or, the mass of the carbon layer is 4% to 10% of the mass of the tin-doped pre-magnesium silicon oxide material; the mass of the molybdenum disulfide-doped polyphenylene sulfide coating layer is 2% to 6% of the mass of the intermediate product A.

3. The preparation method according to claim 1 or 2, characterized in that: In step S1, the median particle size D50 of the silicon dioxide is 500 nm to 5000 nm, and the median particle size D50 of the tin particles is 10 nm to 500 nm; And / or, the mass ratio of silicon, silicon dioxide and tin is 14:30:0.9 to 14:30:2.5; And / or, the mixing method is kneading by adding water.

4. The preparation method according to claim 1 or 2, characterized in that: In step S2, the vacuum degree is 10Pa~100Pa, the temperature of the heating chamber is 1300℃~1800℃, and the temperature of the collecting chamber is 600℃~800℃.

5. The preparation method according to claim 1 or 2, characterized in that: In step S3, the graded particle size of the tin-doped silicon oxide is Dmin≥1.5 μm, D10≥3 μm, 5≤D50≤7 μm, and Dmax≤10 μm, and the value of (D90-D10) / D50 is controlled to be 0.6-1.

6. The preparation method according to claim 1 or 2, characterized in that: In the step S4, the mass ratio of the S3 product to bismethylcyclopentadienyl magnesium is (0.72-1.59):1; and / or, the temperature of bismethylcyclopentadienylmagnesium in the gas reactor is 80° C. to 150° C.; And / or, the inert gas is one or more of helium, neon, argon, krypton, and xenon; And / or, the volume ratio of the inert gas to the bis(methylcyclopentadienylmagnesium) vapor is 4:1 to 1:1; And / or, the sintering process also requires controlling the rotation speed of the rotary kiln, and the rotation speed of the rotary kiln is 0.25 r / min to 2 r / min; And / or, the sintering is a two-stage sintering, the first stage sintering temperature is 300℃~500℃, the sintering time is 2h~6h, the second stage sintering temperature is 600℃~800℃, the sintering time is 2h~4h, and the heating rate of the sintering process is 1℃ / min~3℃ / min.

7. The preparation method according to claim 1 or 2, characterized in that: In step S5, the median particle size D50 of molybdenum disulfide is 10 nm to 200 nm; and / or, the mass ratio of the intermediate product A to molybdenum disulfide is 99:1 to 97:3; and / or, the mass ratio of the intermediate product A to diphenyl disulfide is 99:1 to 96:4; And / or, the oxygen flow rate is 1 ml / min to 5 ml / min; and / or, the reaction temperature is 20-60° C., and the reaction time is 0.5-3 h; And / or, the secondary heating temperature is 160-300° C. and the heat preservation time is 0.5 h-2 h.

8. The silicon-based negative electrode material prepared by the method according to any one of claims 1 to 7.

9. Use of the silicon-based negative electrode material according to claim 8 in the preparation of lithium-ion batteries.

10. A lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that: The material of the negative electrode includes the silicon-based negative electrode material according to claim 8.

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