Preparation method of gradient sulfur-doped silicon-based negative electrode material, negative electrode material and application

Abstract

The application discloses a preparation method of a gradient sulfur-doped silicon-based negative electrode material, the negative electrode material and application. The preparation method of the gradient sulfur-doped silicon-based negative electrode material comprises the following steps: metal reduction pretreatment of a silicon-based material by using a metal material to obtain a pretreated product; acid washing of the pretreated product, then water washing and drying to obtain an acid-washed product; treatment of the acid-washed product by using ammonia water, then water washing and drying to obtain a hydroxylated product; the hydroxylated product is placed in a furnace, heated under an inert atmosphere, gradient heating to at least two different temperatures and heat preservation, sulfur doping treatment of the hydroxylated product in the heat preservation stage, then further heating, carbon deposition, sieving and magnetic removal to obtain the gradient sulfur-doped silicon-based negative electrode material. The application can effectively improve the intrinsic conductivity and performance stability of the silicon-based negative electrode material, is beneficial to improving the specific capacity and initial efficiency of the material, and makes the material have higher rate and cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of battery anode material technology, and particularly relates to a method for preparing a silicon-based anode material, the anode material itself, and its applications. Background Technology

[0002] Silicon-based anode materials are considered key anode materials for next-generation high-energy-density lithium-ion batteries due to their advantages such as high capacity, abundant sources, and environmental friendliness. However, silicon-based materials such as silicon suboxide have problems as anode materials for lithium-ion batteries, including low initial coulombic efficiency, large cycle expansion, and poor intrinsic electronic conductivity. These problems greatly limit the commercial application of silicon-based anode materials.

[0003] The intrinsic electronic conductivity of silicon-based materials affects the specific capacity and first-efficiency electrochemical performance of the anode material. Doping with heteroatoms such as sulfur and nitrogen is an effective method to improve the conductivity of silicon-based materials, but existing sulfur doping treatments struggle to achieve an ideal gradient distribution. If sulfur accumulates only on the surface, it easily forms elemental sulfur, which readily reacts with lithium salts in the electrolyte to form soluble products such as lithium sulfide. These products migrate with the electrolyte, consuming active lithium and causing deterioration in cycle performance.

[0004] In addition, to improve the problems of low initial coulombic efficiency and large cycle expansion of silicon-based anode materials, metal pretreatment (such as magnesium, lithium, etc.) can be used to treat the silicon-based anode materials. However, this process is an exothermic reaction, which easily causes heat accumulation, leading to excessively rapid silicon crystal growth and further deterioration of the material's cycle performance. Taking magnesium pretreatment of silicon suboxide as an example, the common practice is to mix magnesium powder and silicon suboxide material and then perform high-temperature treatment. The use of magnesium powder increases the risk of storage and transportation. Patent CN114014325A proposes a method and apparatus for preparing porous silica materials by magnesium thermal reduction in a tube furnace. In this apparatus, silicon suboxide powder and magnesium powder are placed in an upper and lower position. During the reaction, the exothermic magnesium thermal reaction easily leads to a temperature rise in the apparatus, causing silicon grain growth, which will affect the electrochemical performance of the material, such as cycle stability. Therefore, it has the problem of not being able to gradually and precisely control the generation rate of magnesium vapor to control the magnesium thermal reaction rate, thus failing to control the growth of silicon grain size in silicon-based materials. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a method for preparing gradient sulfur-doped silicon-based anode materials, anode materials and applications, which can effectively improve the intrinsic conductivity and performance stability of silicon-based anode materials, which is conducive to improving the specific capacity and first efficiency of the materials, and giving them higher rate performance and cycle performance.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A method for preparing a gradient sulfur-doped silicon-based anode material includes the following steps: S1. Pretreatment of silicon-based materials by metal reduction with metallic materials to obtain pretreated products; S2. The pretreated product is acid-washed, then washed with water and dried to obtain the acid-washed product; S3. The product after acid washing is treated with ammonia water, and then washed with water and dried to obtain the hydroxylated product; S4. The hydroxylation product is placed in a furnace and heated under an inert atmosphere. The temperature is gradually increased to at least two different temperatures and held. During the holding stage, the hydroxylation product is subjected to sulfur doping treatment. Then, after further heating, carbon deposition, sieving, and demagnetization, a gradient sulfur-doped silicon-based anode material is obtained.

[0008] The preparation method of this invention first pre-treats silicon-based materials, such as silicon suboxide, with metal reduction, and then generates porous silicon-based materials, such as porous silica-oxygen materials, through subsequent acid washing. Next, hydroxylation treatment is performed. Based on this porous silicon-based material, such as porous silica-oxygen, gradient controllable sulfur doping technology is used to improve sulfur deposition efficiency. Sulfur doping further improves the intrinsic conductivity of the silicon-based material, such as porous silica-oxygen. The lithium storage activity of the Si-S bonds generated after doping increases the number of lithium insertion sites, improving the specific capacity and first-time efficiency of the material. Furthermore, the Si-S bond structure (with a longer bond length than Si-Si) can further buffer the volume expansion of silicon during lithium insertion, thereby improving the performance stability of the material.

[0009] In the preferred embodiment of the above preparation method, in step S1, the silicon-based material is a silicon-oxygen anode powder with a median particle size of 5-10 μm, the carbon content of the silicon-based material is 1-5 wt%, and the metal material is magnesium blocks or magnesium granules, with the ratio of the metal material to the total amount of silicon-based material and metal material being 1-20 wt%. Typically, pretreatment of silicon-oxygen anode powder with metallic magnesium requires consideration of reaction rate and uniformity, necessitating the use of magnesium powder with a smaller particle size. However, the storage and transportation risks of magnesium powder are relatively high. This method, on the other hand, can use magnesium blocks or magnesium granules, which have no safe storage issues and are low in cost, offering advantages such as convenient operation, reliable operation, compact device structure, and low material cost.

[0010] In the preferred embodiment of the above preparation method, in step S1, the metal material and the silicon-based material are placed in a gas-phase generator and a reactor, respectively, and the gas-phase generator and the reactor are connected sequentially. Then, an inert gas is introduced to raise the temperature in the gas-phase generator to 800-950°C and the temperature in the reactor to 800-1000°C, ensuring that the temperature in the reactor is not lower than the temperature in the gas-phase generator. The introduced inert gas carries the metal vapor evaporated from the metal material to the reactor to react with the silicon-based material, obtaining a pretreated product. This invention proposes a gas-phase controllable pre-metal (pre-magnesium) technology capable of kilogram-scale preparation. This involves placing a low-melting-point metal in a gas-phase generator and heating it under an inert atmosphere until it evaporates. The vapor is then carried by the inert gas to the reaction zone of the reactor to undergo a gas-solid reaction with the solid material (silicon-based material). The reaction rate can be adjusted by controlling the amount of metal vapor, such as temperature, rotation rate, and inert gas carrier gas flow rate, thereby reducing the thermal aggregation effect of the exothermic reaction and achieving the goal of controlling the growth of silicon grain size in silicon-based materials. The silicon-oxygen materials prepared by this method have higher rate capability and cycle performance.

[0011] In the above preparation method, preferably, in step S2, the pretreated product is placed in a pickling agent and stirred for 1 to 24 hours, more preferably 4 hours, wherein the pickling agent is acetic acid or formic acid, and the mass ratio of the pretreated product to the pickling agent is 1:5 to 1:20, more preferably 1:5 to 1:10.

[0012] In the preferred embodiment of the above preparation method, in step S3, the acid-washed product is placed in a 0.5-3 mol / L ammonia solution and heated and stirred at 30-60°C for 2-6 hours. The acid-washed product is a porous material, such as porous silica. Treatment with ammonia forms hydroxylated Si (Si-OH), which facilitates the subsequent reaction to generate mercaptosilicon and further Si-S bonds. The weakly alkaline environment of ammonia promotes the dissociation of water molecules on the material surface, generating hydroxyl radicals (…). OH- can be uniformly adsorbed on the Si active sites of silicon-oxygen materials. The resulting Si-OH not only distributes on the outer surface of the material but also penetrates into the inner surface of the pores, achieving uniform hydroxylation across the entire surface. Compared to strong bases containing alkali metals (such as NaOH and KOH), silicon-oxygen materials hydroxylated with ammonia have higher purity and can avoid interference from impurity ions on subsequent sulfur doping reactions (such as the formation of sulfide impurities by Na, K, and other metal ions with the sulfur source).

[0013] In the above-described preparation method, preferably, in step S4, the temperature is gradually increased to a first temperature, a second temperature, and a third temperature, and each temperature is held for 0.5 to 6 hours. During the holding stage, H2S gas is introduced into the furnace. The first temperature is 120 to 160°C, the second temperature is 180 to 220°C, and the third temperature is 220 to 260°C. The mass flow rate ratio of the inert atmosphere to the H2S gas is 1:(0.5 to 0.1). More preferably, the first temperature is 150°C, the second temperature is 200°C, and the third temperature is 250°C. By designing a temperature gradient, gradient sulfur-doped silicon-based materials, such as porous silicon-oxygen materials, are achieved. The low-temperature stage pre-activates active sites, the medium-temperature stage accelerates the reaction and accumulates sulfur content, and the high-temperature stage achieves cross-linking and sulfur fixation, ultimately forming a synergistic structure of highly stable doping within the pores and highly conductive doping on the surface. Low doping in the core region can preserve the intrinsic structural stability of silicon-based materials such as silicon-oxygen materials and avoid lattice distortion caused by excessive Si-S bonds; high doping on the surface can improve the interfacial conductivity between the material and the electrolyte through Si-S bonds and reduce charge transfer impedance.

[0014] The above preparation method, preferably, involves further heating to a fourth temperature and holding at that temperature for 0.5-10 hours, more preferably for 1 hour, and finally heating to a fifth temperature. Acetylene is then introduced for carbon deposition treatment for 2-5 hours. The fourth temperature is 280-350°C, more preferably 300°C, and the fifth temperature is 500-800°C. During carbon deposition treatment, the mass flow ratio of inert atmosphere to acetylene gas is 1:(1-0.25). Heating to the fourth temperature is for preliminary sulfur fixation, and heating to the higher fifth temperature is for introducing a hydrocarbon atmosphere for carbon coating treatment. The carbon coating temperature should not be too high, as excessively high temperatures can easily cause Si-S bonds to break and precipitate from the material structure.

[0015] As a general technical concept, this invention also provides a gradient sulfur-doped silicon-based anode material prepared by the above-described preparation method. The sulfur content of the anode material exhibits a gradient distribution, with the sulfur content gradually increasing from the inside to the outside. The low sulfur doping in the core region of the anode material of this invention preserves the intrinsic structural stability of silicon-based materials such as silicon-oxygen materials, avoiding lattice distortion caused by excessive Si-S bonds; while the high sulfur doping in the surface region enhances the interfacial conductivity between the material and the electrolyte through Si-S bonds, reducing charge transfer impedance.

[0016] Preferably, the sulfur content of the aforementioned anode material is 0.1~5 wt%, more preferably 0.5~5 wt%, and the Si(111) crystal grain size is 3.00~30.00 nm, more preferably 3.00~10.00 nm. Specifically, the sulfur content is the mass fraction of sulfur.

[0017] As a general technical concept, the present invention also provides a negative electrode material prepared by the aforementioned preparation method or the application of the aforementioned negative electrode material in the field of battery materials.

[0018] The specific process for preparing gradient sulfur-doped silicon-based anode materials is as follows: (1) Add silicon-oxygen anode powder and metal materials into the reaction chamber of the reactor and the crucible of the gas phase generator, respectively. Connect the equipment, that is, connect the output end of the gas phase generator to the input end of the reactor and introduce inert gas for oxygen removal treatment; wherein the inert gas is preferably argon.

[0019] The gas-phase generator and reactor are heated to the target temperature via program control. The gas-phase generator temperature is 800~950℃, and the reactor temperature is 800~1000℃. It is crucial to ensure that the reactor temperature does not fall below that of the gas-phase generator to prevent metal vapor from condensing during the process. Once the target temperature is reached, the inert gas flow rate is adjusted to the target value, and the equipment rotation is initiated. The gas-phase generator and reactor are rotated together by a rotary motor. Metal vapor, produced by the evaporation of the metal material added under high-temperature conditions, is carried by the inert gas into the reaction chamber of the reactor, where it reacts with the silicon-oxygen anode powder. The resulting material is the pretreated product.

[0020] (2) A certain amount of the pretreated product is added to one of acetic acid, acetic acid, and formic acid, along with ultrapure water. The mass ratio of the pretreated product to the acid is 1:5 to 1:20, preferably 1:5 to 1:10. The pretreated product powder and acid solution are placed in a container and stirred electrically for 4 hours. After pressure filtration, the filter cake is washed three times with ultrapure water and then dried in a vacuum drying oven at 80°C to obtain the acid-washed product.

[0021] (3) The acid-washed product is placed in a 0.5-3 mol / L ammonia solution and heated and stirred at 30-60℃ for 2-6 h. After repeated washing with water and centrifugation, the filtrate is neutralized. The filter cake is then vacuum dried at 80℃ to obtain the hydroxylated product.

[0022] (4) The hydroxylated product is placed in a CVD rotary furnace and treated with a gradient heating method under an argon atmosphere. First, it is held at 150℃, 200℃, and 250℃ for 1 h each, with H2S gas introduced during the holding period. Then, the temperature is raised to 300℃ and held for 1 h. Finally, the temperature is raised to 500~800℃. After the temperature is constant, acetylene is introduced for carbon deposition for 2~5 h. The mass flow ratio of argon gas to hydrogen sulfide gas introduced during the process is 1:(0.5~0.1), and the mass flow ratio of argon gas to acetylene gas is 1:(1~0.25). The coated material is then screened and demagnetized to obtain the gradient sulfur-doped silicon-based anode material.

[0023] The preparation method of this invention first pre-treats silicon-based materials, such as silicon suboxide, with metal reduction, and then generates porous silicon-based materials, such as porous silica, through subsequent acid washing. The porous silicon-based materials are then hydroxylated with ammonia to form hydroxylated Si (Si-OH), and a reaction of Si-OH + H2S → Si-SH + H2O occurs to generate mercaptosilicon. After subsequent heat treatment, sulfur crosslinking occurs, generating Si-S bonds. This effectively incorporates sulfur into the silicon-based materials, such as porous silica, improving sulfur deposition efficiency and enhancing the intrinsic conductivity of the silicon-based materials, such as porous silica. The lithium storage activity of the Si-S bonds generated after doping increases the number of lithium insertion sites, improving the specific capacity and first-time efficiency of the anode material. Furthermore, the Si-S bond structure (with a longer bond length than Si-Si) can further buffer the volume expansion of silicon during the lithium insertion process, thereby improving the performance stability of the material.

[0024] Compared with the prior art, the advantages of the present invention are as follows: (1) The preparation method of the present invention first performs metal reduction pretreatment on silicon-based materials such as silicon suboxide, and then generates porous silicon-based materials such as porous silicon oxide through subsequent acid washing treatment, and then performs hydroxylation treatment. Based on this porous silicon-based material such as porous silicon oxide, gradient controllable sulfur doping technology is used to improve sulfur deposition efficiency, and the intrinsic conductivity of silicon-based materials such as porous silicon oxide is further improved through sulfur doping. The lithium storage activity of the Si-S bond generated after doping is used to increase the lithium insertion sites, improve the specific capacity and first efficiency of the material, and the Si-S bond structure (bond length is longer than Si-Si) can further buffer the volume expansion of silicon during the lithium insertion process, thereby achieving the purpose of improving the performance stability of the material.

[0025] (2) The low sulfur doping in the core region of the anode material of the present invention can retain the intrinsic structural stability of silicon-based materials such as silicon-oxygen materials and avoid lattice distortion caused by excessive Si-S bonds; the high sulfur doping in the surface region can improve the interfacial conductivity between the material and the electrolyte through Si-S bonds and reduce the charge transfer impedance. Therefore, the gradient sulfur-doped silicon-based anode material of the present invention has good performance stability, good specific capacity and first-time efficiency, as well as higher rate and cycle performance.

[0026] (3) The preparation method of the gradient sulfur-doped silicon-based anode material of the present invention and the anode material have good application prospects in the field of battery materials. Attached Figure Description

[0027] Figure 1 The images show XPS tests performed on the product materials prepared in Example 1 and Comparative Example 4 after argon ion etching for 50 s, 100 s, and 150 s, respectively. Detailed Implementation

[0028] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0029] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0030] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0031] This invention employs the following apparatus to prepare negative electrode materials: a gas-phase generator and a reactor are connected sequentially, forming a highly efficient gas-phase rotary reaction system. The gas-phase generator is equipped with a screw-lifting assembly, spring bolts, support pulleys, guide rails, a spiral inlet preheating section, a gas-phase generation section, a gas insulation section, and a connecting section. The reactor includes a reaction section and a rotary motor. The spiral inlet preheating section of the gas-phase generator uses a snap-fit ​​design to ensure convenient installation and good sealing. During operation, the height of the gas-phase generator can be precisely adjusted through the precise cooperation of the screw-lifting assembly and spring bolts, ensuring that its connection point with the reactor is strictly on the same horizontal line. The support pulleys then move smoothly along the guide rails for rapid docking, and finally, the flanges and bolts of the connecting section securely fasten the assembly, forming an integrated structure. The rotary motor of the reactor provides strong rotational power, and through the pulley linkage design, it drives the gas-phase generator to rotate synchronously, ensuring the stability and uniformity of the reaction process.

[0032] The gas phase generator has three heating zones: an inlet preheating section, a gas phase generation section, and a gas insulation section. The inlet preheating section has a spiral inlet pipe through which the incoming atmosphere is fed into the subsequent gas phase generation section. The spiral inlet pipe and heating components in the inlet preheating section ensure that the incoming gas is preheated quickly, preventing the temperature from dropping too low and reducing evaporation efficiency in the gas phase generation section. The gas phase generation section consists of heating components and a cylindrical graphite crucible with openings at both ends at the center, connecting to the tail end of the spiral inlet pipe in the inlet preheating section and the front end of the gas pipe in the gas insulation section, respectively. The crucible is filled with magnesium blocks, magnesium granules, or other metals. When heated to a temperature above the metal's melting point, the metal vaporizes. Simultaneously, an externally introduced inert gas, after preheating, enters the gas phase generation section and carries the evaporated metal vapor to the gas insulation section and the subsequent rotary reactor to react with the reactants.

[0033] The structure of the reactor is similar to that of a conventional batch CVD rotary furnace, consisting of a reactor tube, heating components, and a frame. The material to be pretreated by metal reduction is added into the reactor tube, which is then rotated by a rotary motor. Inside the reactor tube are lifting plates that can lift the reaction powder during rotation, increasing contact with the metal vapor and improving the uniformity of the reaction.

[0034] In terms of the gas flow, an inert gas (such as argon) first enters the spiral inlet preheating section, where it is fully preheated by the combined action of the spiral inlet pipe and the heating device, providing ideal initial conditions for the subsequent reaction. The preheated gas then enters the gas phase generation section, where it contacts a crucible containing a magnesium source and generates magnesium vapor under the action of a high-temperature heating device. Driven by the pressure of the inert gas, the magnesium vapor enters the gas insulation section, ensuring that it maintains a stable temperature during transport and preventing condensation. Finally, the magnesium vapor enters the reaction section of the reactor, where it reacts fully with the silica material inside the reactor tubes under high-temperature conditions, achieving a highly efficient gas-solid reaction process.

[0035] Example 1: A method for preparing a gradient sulfur-doped silicon-based anode material includes the following steps: S1. Place 1.8 kg of silicon suboxide in the furnace tube of the reactor and 0.2 kg of magnesium block in the crucible of the gas phase generator. After connecting the equipment, introduce argon gas for oxygen removal treatment. The median particle size of silicon suboxide is 5 μm and the carbon content is 3 wt%.

[0036] After the oxygen removal is completed, heating is turned on, with the temperature of the gas phase generator and the reactor both set to 910℃. When the temperature reaches the set value, the rotation frequency is adjusted to 20 Hz, the argon flow rate is adjusted to 7 NL / min, and the reaction is carried out for 8 hours. After the equipment cools down, the pretreated product is taken out. S2. Take 100 g of the pretreated product and 10 g of glacial acetic acid and 1000 mL of ultrapure water and stir with an electric mixer for 4 h. After pressure filtration, take the filter cake and wash it with ultrapure water three times. Then place it in an 80℃ vacuum drying oven to dry it and obtain the acid-washed product. S3. The acid-washed product was placed in a 1 mol / L ammonia solution and heated and stirred at 60°C for 3 hours. After repeated washing with water and centrifugation, the filtrate was neutralized. The filter cake was then vacuum dried at 80°C to obtain the hydroxylated product. S4. The hydroxylated product is placed in a CVD rotary furnace and treated with a gradient heating method under an argon atmosphere. First, it is held at 150℃, 200℃, and 250℃ for 1 h each, with H2S gas introduced during the holding period (argon flow rate 1 NL / min, H2S gas flow rate 0.2 NL / min). Then, the temperature is raised to 300℃ and held for 1 h. Finally, the temperature is raised to 550℃ and acetylene is introduced for carbon deposition treatment for 2 h, with argon flow rate 1 NL / min and acetylene flow rate 0.5 NL / min. The coated material is then sieved and demagnetized to obtain gradient sulfur-doped silicon-based anode material.

[0037] Example 2 In this embodiment, the negative electrode material was prepared using a method that is basically the same as that in Example 1, except that the argon gas flow rate in step S1 was adjusted to 5 NL / min.

[0038] Example 3 In this embodiment, the negative electrode material was prepared using a method that is basically the same as that in Example 1. The difference is that the argon gas flow rate in step S1 was adjusted to 5 NL / min, and the reaction processing time was increased to 12 h.

[0039] Example 4 In this embodiment, the negative electrode material was prepared using a method that is basically the same as that in Example 1, except that the flow rate of H2S gas introduced in step S4 was adjusted to 0.5 NL / min.

[0040] Example 5 In this embodiment, the negative electrode material was prepared using a method that is basically the same as that in Example 1. The difference is that in step S4, the material was kept at 120°C and 260°C for 1 h each, and H2S gas was introduced during the heat preservation.

[0041] Example 6 In this embodiment, the negative electrode material was prepared using a method that is basically the same as that in Example 1. The difference is that in step S3, the concentration of ammonia water was adjusted to 3 mol / L, the treatment time was 2 h, and in step S4, the temperature was maintained at 150℃, 200℃, and 250℃ for 2 h each, with H2S gas introduced during the temperature maintenance.

[0042] Comparative Example 1 The negative electrode material in this comparative example was prepared in basically the same way as in Example 1, except that no magnesium block was added in step S1.

[0043] Comparative Example 2 1.9 kg of silicon suboxide and 0.2 kg of magnesium powder (below 200 mesh) were mixed evenly in a high-speed mixer and then placed directly into the reactor tube of the reactor, without filling the gas phase generator with magnesium blocks. The remaining preparation steps were performed in Example 1.

[0044] Comparative Example 3 The negative electrode material in this comparative example was prepared using a method that was essentially the same as that in Example 1, except that H2S gas was not introduced in step S4.

[0045] Comparative Example 4 The negative electrode material in this comparative example was prepared in basically the same way as in Example 1, except that no temperature gradient was set in step S4, and H2S gas was introduced directly while the temperature was kept at 150°C for 6 h.

[0046] Comparative Example 5 The negative electrode material in this comparative example was prepared in basically the same way as in Example 1, except that no temperature gradient was set in step S4, and the material was directly kept at 250°C for 2 h 10 min while H2S gas was introduced.

[0047] Comparative Example 6 The negative electrode material in this comparative example was prepared using a method that was essentially the same as that in Example 1, except that ammonia was not used for hydroxylation in step S3.

[0048] The products prepared in the above examples and comparative examples were subjected to X-ray diffraction tests in the range of 5~80°. The XRD patterns were fitted with peaks between 10° and 40°. The 2θ angle value and half-width at half-maximum (WHM) of the Si (111) peak near 28° were taken, and the grain size of Si under this crystal plane was calculated according to the Scherrer formula. The results are shown in Table 1. The magnesium content (mass fraction of magnesium) and sulfur content (mass fraction of sulfur) of the materials were obtained by inductively coupled plasma spectroscopy (ICP).

[0049] Table 1. Test results of magnesium content, sulfur content, and Si(111) crystal grain size.

[0050] The negative electrode materials prepared in the above examples and comparative examples were mixed with water at a mass ratio of negative electrode material: conductive agent (Super-p): binder (LA133) = 8:1:1 to form a slurry. The dispersed slurry was coated on copper foil and dried, punched into an electrode sheet with a diameter of 16 mm, and then vacuum dried before being assembled into CR2032 coin cells in a glove box. The prepared electrode sheet served as the positive electrode, the lithium metal sheet served as the negative electrode, and the electrolyte was 1 M LiPF6 (solvent: EC, DEC (volume ratio 1:1); solute: LiPF6; additives: 1% FEC, etc.). The prepared coin cells were left to stand at room temperature for 24 h, and then constant current charge-discharge tests were performed on the Blue Electric test system. The cells were activated by charge-discharge at a current density of 0.1 C (designed according to 1C = 1500 mAh / g) for 3 cycles, followed by 3 cycles at a current density of 1 C, and then 50 cycles at a current density of 0.5 C. The charge-discharge cutoff voltage was 0.005~1.5 V. The results are shown in Table 2.

[0051] Table 2 Charge and discharge test results

[0052] A comparison of Examples 1 and 2, and Examples 2 and 3, shows that the amount of magnesium vapor introduced into the reaction can be controlled by adjusting the argon flow rate and extending the reaction time. This is because gaseous magnesium in the argon gas has a certain saturation concentration under high temperature conditions.

[0053] A comparison between Example 1 and Example 3 shows that by adjusting the argon flow rate and the gas flow duration, the same amount of magnesium reaction can be achieved. At the same time, the amount of magnesium vapor carried into the reaction zone by argon per unit time can be reduced to decrease the exothermic reaction. In comparison, this reduces the size of silicon crystal grains and improves the cycling performance of the material.

[0054] By comparing Example 1 and Comparative Example 2, it can be seen that the preparation method of Example 1 can effectively reduce the silicon grain size of the material and improve the cycle performance of the material under the same magnesium content conditions.

[0055] A comparison of Example 1 and Comparative Example 3 shows that sulfur doping can improve the specific capacity and first efficiency of the material, as well as improve the rate performance and cycle stability of the material.

[0056] By comparing Example 1 with Comparative Example 6, it can be seen that the addition of ammonia can achieve hydroxylation treatment of porous silicon oxide materials, thereby achieving effective directional sulfur fixation in subsequent sulfur doping treatment and improving sulfur deposition efficiency.

[0057] The materials from Example 1 and Comparative Example 4 were subjected to XPS tests using argon ion etching for 50 s, 100 s, and 150 s, respectively. The tests focused on the sulfur element. Figure 1As shown, sulfur doping can achieve a gradient design where the sulfur doping amount inside the material particles gradually increases from the inside out.

[0058] As can be seen from Table 2, by performing gradient design treatment on sulfur doping, not only can the intrinsic structural stability of silicon-based materials be preserved, but the interfacial conductivity between the material and the electrolyte can also be improved, and the charge transfer impedance can be reduced, thereby obtaining higher rate capability and cycling performance.

Claims

1. A method for preparing a gradient sulfur-doped silicon-based anode material, characterized in that, Includes the following steps: S1. Pretreatment of silicon-based materials by metal reduction with metallic materials to obtain pretreated products; S2. The pretreated product is acid-washed, then washed with water and dried to obtain the acid-washed product; S3. The product after acid washing is treated with ammonia water, and then washed with water and dried to obtain the hydroxylated product; S4. The hydroxylation product is placed in a furnace and heated under an inert atmosphere. The temperature is gradually increased to at least two different temperatures and held. During the holding stage, the hydroxylation product is subjected to sulfur doping treatment. Then, after further heating, carbon deposition, sieving, and demagnetization, a gradient sulfur-doped silicon-based anode material is obtained.

2. The preparation method according to claim 1, characterized in that, In step S4, the temperature is gradually increased to a first temperature, a second temperature, and a third temperature, and each temperature is maintained for 0.5 to 6 hours. During the maintenance phase, H2S gas is introduced into the furnace. The first temperature is 120 to 160°C, the second temperature is 180 to 220°C, and the third temperature is 220 to 260°C. The mass flow rate ratio of the inert atmosphere to the H2S gas is 1:(0.5 to 0.1).

3. The preparation method according to claim 2, characterized in that: Further heating to the fourth temperature and holding at that temperature for 0.5~10h, then heating to the fifth temperature, followed by acetylene introduction for carbon deposition treatment for 2~5h. The fourth temperature is 280~350℃, and the fifth temperature is 500~800℃. During the carbon deposition treatment, the mass flow ratio of inert atmosphere to acetylene gas is 1:(1~0.25).

4. The preparation method according to claim 1, characterized in that: In step S3, the acid-washed product is placed in a 0.5-3 mol / L ammonia solution and heated and stirred at 30-60°C for 2-6 hours.

5. The preparation method according to claim 1, characterized in that: In S1, the silicon-based material is a silicon-oxygen anode powder with a median particle size of 5-10 μm, the carbon content of the silicon-based material is 1-5 wt%, the metal material is magnesium block or magnesium granules, and the ratio of the metal material to the total amount of silicon-based material and metal material is 1-20 wt%.

6. The preparation method according to claim 5, characterized in that: In step S1, the metal material and the silicon-based material are placed into a gas-phase generator and a reactor, respectively, and the gas-phase generator and the reactor are connected in sequence. Then, an inert gas is introduced to raise the temperature in the gas-phase generator to 800~950℃ and the temperature in the reactor to 800~1000℃, while ensuring that the temperature in the reactor is not lower than the temperature in the gas-phase generator. The introduced inert gas carries the metal vapor evaporated from the metal material to the reactor to react with the silicon-based material to obtain a pretreated product.

7. The preparation method according to claim 1, characterized in that: In step S2, the pretreated product is placed in a pickling agent and stirred for 1 to 24 hours. The pickling agent is acetic acid or formic acid, and the mass ratio of the pretreated product to the pickling agent is 1:5 to 1:

20.

8. A negative electrode material prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The sulfur content of the negative electrode material is distributed in a gradient, and the sulfur content gradually increases from the inside to the outside.

9. The negative electrode material according to claim 8, characterized in that: The sulfur content of the negative electrode material is 0.5~5wt%, and the Si(111) crystal grain size is 3.00~30.00 nm.

10. The application of a negative electrode material prepared by the preparation method according to any one of claims 1 to 7 or the negative electrode material according to any one of claims 8 to 9 in the field of battery materials.

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