A porous silicon material with a MgSiN2 nanocoating, a preparation method and applications thereof

Abstract

The application provides a porous silicon material with MgSiN2 nano coating and relates to the technical field of lithium ion batteries. The material has an ant nest or coral structure porous silicon framework, and the surface of the porous silicon framework has a layer of MgSiN2 nano coating. The preparation method of the material comprises the following steps: heating magnesium silicide powder to a certain temperature in a nitrogen-containing atmosphere, keeping the temperature for a certain time; increasing the temperature again, introducing N2 gas, and keeping the temperature for a certain time; after the keeping time is over, cooling to room temperature, and then performing acid pickling treatment to remove magnesium nitride, so that the porous silicon material with MgSiN2 nano coating is obtained. The synthesis process of the application is simple, controllable, environmentally friendly, and relatively low in energy consumption. The material obtained by the application has stable structure, and has the advantages of high initial efficiency, long cycle capacity, excellent rate performance, good stability under large current density, and the like in the application in lithium ion batteries, and has the potential for large-scale preparation and good commercial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a porous silicon anode material, specifically a porous silicon material with a MgSiN2 nanocoating, its preparation method and its application. Background Technology

[0002] Silicon-based anode materials are widely used in lithium-ion battery anode materials due to their safety at high rates, high abundance on Earth, environmental friendliness, relatively low lithium intercalation potential, and high theoretical capacity ratio. To address the issues of high volume expansion and low conductivity in silicon anodes, the industry has conducted a series of structural and composite material designs. Among these, porous structures can effectively alleviate volume expansion by releasing stress internally. However, when silicon comes into contact with the electrolyte, it forms a fragile and unstable solid electrolyte interphase (SEI) film with low conductivity. When the volume of the silicon anode changes, the SEI film is repeatedly damaged and regenerated, leading to a decrease in the capacity and coulombic efficiency of the silicon anode, severely affecting the long-term electrochemical cycling performance of the silicon anode material. Building upon existing structural designs, designing a thin and tough artificial interface on the silicon surface is a feasible solution. This artificial interface coating can prevent direct contact between silicon and the electrolyte, reducing side reactions; the high-strength and high-toughness coating can further suppress the volume expansion of silicon; simultaneously, after contact with the electrolyte, the coating forms a chemical composition similar to the electrolyte and with high conductivity, which is beneficial for electron / ion transport. Introducing a carbon shell onto the silicon surface is a feasible approach, as the carbon shell possesses high conductivity and facilitates the formation of a stable SEI film. However, carbon exhibits weak interfacial bonding and low mechanical strength, failing to meet the requirements for long-term cycling. Silicon-based ceramic coatings, such as silicon carbide and silicon nitride, have been extensively studied as promising artificial SEI films. However, coating preparation often involves multiple complex raw materials, such as polymers, and the preparation steps are intricate, requiring various methods and long-term induction growth. Furthermore, the preparation of many coatings often involves temperature conditions exceeding 1000°C, resulting in significant energy consumption. Therefore, there is a need to design a method for preparing silicon-based anode coatings that is simple in procedure, low in energy consumption, and produces high-strength and reliable coatings.

[0003] Existing technologies, such as the Chinese patent "A Silicon-Based Material with Composite Coating, Its Preparation Method and Application (Publication No.: CN115747760A)," disclose a method for preparing a silicon-based anode material with composite coating. This method requires the deposition of SiO2 on the surface of the electrode material using radio frequency plasma-enhanced chemical vapor deposition. x A SiC protective layer is then deposited, followed by the deposition of a graphitic carbon functional layer using unbalanced magnetron sputtering. This method, employing magnetron sputtering, requires sophisticated equipment, while chemical deposition removes SiO₂. xLow-pressure conditions are required during coating deposition, and the preparation of SiC protective layers also requires the control of gas ratio to regulate coating growth. This preparation method involves a variety of experimental conditions to regulate coating growth.

[0004] Patent "A Polymer-Coated Silicon-Based Anode Material, Preparation Method, and Application (Publication No.: CN115954457A)" discloses a polymer-coated silicon-based anode material, its preparation method, and its application in lithium-ion batteries. The anode material in this invention exhibits a core-coating structure, comprising a silicon-based anode material core and a polymer coating coupled to the core surface. The polymer in this invention is an amorphous polymer coating formed by click polymerization of octamercaptopropyl oligomeric silsesquioxane and lithium bis(allyl)borate. In the preparation steps of this material, raw materials such as silane coupling agents and allyl malic acid are polymerized under certain conditions in an inert gas environment for a long time to form an amorphous polymer. Then, the silicon-based anode material and the polymer are dispersed in a solution, and ultraviolet irradiation is used to ultimately induce the formation of a polymer coating on the silicon anode material. The process of preparing the coating-coated silicon-based anode material by this patent is quite complicated. It requires two steps to prepare the polymer and also requires various raw materials such as silane coupling agents. In addition, the reaction time required for steps S1 and S2 of this patent is 2h to 48h, and the overall reaction time is relatively long.

[0005] Patent "A Three-Dimensional Porous Silicon-Carbon Composite Lithium-ion Battery Anode, Its Preparation Method, and a Lithium-ion Secondary Battery (Publication No.: CN116031371A)" discloses a three-dimensional porous silicon-carbon composite lithium-ion battery anode, its preparation method, and a lithium-ion secondary battery. The preparation method includes the following steps: S1, dissolving polymer I and polymer II in a solvent to obtain a polymer solution; S2, dispersing elemental silicon powder in the polymer solution to obtain a mixed dispersion; S3, forming a coating on the surface of the negative electrode current collector using the mixed dispersion, drying the coating, and then performing oxygen-free sintering to carbonize polymer I and coat the silicon while polymer II vaporizes to form pores, thereby forming a three-dimensional porous silicon-carbon composite layer on the surface of the negative electrode current collector, resulting in a lithium-ion battery anode. This preparation method also requires the preparation of multiple polymer raw materials, two separate steps to form the porous structure and prepare the coating, and finally, an oxygen-free sintering treatment at 400℃~900℃ on the current collector. It cannot achieve a one-step method to prepare a coated negative electrode material.

[0006] The literature "Silicon carbide as a protective layer to stabilize Si-based nanodes by inhibiting chemical reactions" reports the preparation of SiC and Si3N4 nanolayers as toughening coatings on the surface of Si nanoparticles at high temperatures above 1200℃, reducing the direct contact reaction between Si and the electrolyte. However, the preparation of silicon carbide and silicon nitride in this literature often involves harsh conditions such as high temperature and high pressure, making it difficult to achieve the advantage of large-scale preparation.

[0007] In summary, existing methods for preparing artificial coatings for silicon-based anode materials often require pretreatment of multiple raw materials or long reaction times, with harsh reaction conditions, which are not conducive to large-scale industrial production. Summary of the Invention

[0008] This invention addresses the problems existing in the prior art by providing a porous silicon material with a MgSiN2 nano-coating. The nano-coating of this material can both avoid direct contact between the silicon anode and the electrolyte, stabilizing the cycle performance of the porous silicon, and not affect the porous structure of the porous silicon, enabling it to alleviate silicon volume expansion, ultimately leveraging the dual advantages of "structure-coating". The preparation method of this material is simple and does not involve high-pressure or low-pressure preparation environments; it can be prepared under normal pressure conditions below 900°C.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] The present invention provides a porous silicon material with a MgSiN2 nano-coating, wherein the material has a porous silicon framework with an ant nest or coral structure, and the surface of the porous silicon framework has a layer of MgSiN2 nano-coating.

[0011] This invention also provides a method for preparing porous silicon materials with MgSiN2 nanocoatings, comprising the following steps:

[0012] (1) Heat magnesium silicide powder to a certain temperature in a nitrogen-containing atmosphere and keep it at that temperature for a certain time;

[0013] (2) Stop the flow of nitrogen-containing gas, raise the temperature again, raise the temperature to the next temperature, and then introduce N2 and keep it at the temperature for a certain period of time.

[0014] (3) After the heat preservation time ends and the powder is cooled to room temperature, it is taken out and acid washed to remove magnesium nitride, thus obtaining the porous silicon material with MgSiN2 nano-coating.

[0015] The present invention also provides the application of the above-mentioned porous silicon material with MgSiN2 nanocoating in the preparation of lithium-ion battery anode material, as well as lithium-ion battery anode material and lithium-ion battery containing the above-mentioned porous silicon material with MgSiN2 nanocoating.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The method provided by this invention is based on the preparation of porous silicon by the nitridation reaction of magnesium silicide, and further adds a MgSiN2 nano-coating to the surface of the porous silicon. This invention utilizes the phase separation reaction of a magnesium-silicon alloy with a nitrogen-containing atmosphere at a certain temperature to form Mg3N2 / Si. At this point, the formed Si has an anthill-like or coral-like structure and is tightly encapsulated by Mg3N2. While Mg3N2 and Si are in close contact, N2 is used as the nitrogen source, and the MgSiN2 nano-coating is controllably prepared using the reaction 3Si + 2Mg3N2 + N2 → 3MgSiN2 + Mg3N2. The "one-step" reaction procedure design does not involve additional material usage or preparation steps; only the atmospheric conditions need to be changed, making the process simple and reliable.

[0018] 2. The preparation of silicon-based ceramic coatings of carbides and nitrides in existing technologies often involves high pressure and high temperature conditions. The preparation of the MgSiN2 nano-coating designed in this patent only requires raising the temperature of the original nitriding reaction by a certain amount. The reaction temperature is not higher than 900℃ and the reaction atmosphere is at normal pressure. The time required to prepare the MgSiN2 nano-coating at a certain temperature is extremely short. After changing the atmosphere conditions, it can be prepared by holding the temperature for only a few minutes. The process is simple and easy to control, and has excellent potential for large-scale synthesis.

[0019] 3. The MgSiN2 nano-coating grows tightly along the surface of the porous silicon framework as a protective layer. The nano-coating avoids direct contact between silicon and electrolyte, and instead forms an artificial SEI film. It can form a tough alloy to provide protection, and also form a good ion / electron conductor to improve the conductivity of silicon anode materials. At the same time, the coating growth of MgSiN2 nano-coating does not significantly change the morphology and structure of porous silicon, and retains the advantages of silicon volume expansion in the porous structure environment, ultimately giving full play to the dual advantages of "structure-coating". Attached Figure Description

[0020] Figure 1 This is a schematic diagram of material preparation in Example 1 of the present invention;

[0021] Figure 2 a is a scanning electron microscope image of the nano-coated porous silicon in Example 1 of the present invention; Figure 2 b is a TEM electron transmission image of the nano-coating on porous silicon in Example 1 of the present invention;

[0022] Figure 3 a is a schematic diagram of BET of porous silicon used as a control group in Example 1 of the present invention; Figure 3 b is a schematic diagram of the BET of porous silicon with MgSiN2 nanocoating in Example 1 of the present invention;

[0023] Figure 4 a is the XRD diffraction analysis diagram of porous Si with MgSiN2 nanocoating in Example 1 of the present invention; Figure 4 b is the Raman spectrum of porous Si with MgSiN2 nanocoating in Example 1 of the present invention;

[0024] Figure 5 a is a long-cycle test diagram of porous Si with MgSiN2 nanocoating in Example 1 of the present invention; Figure 5 b is a rate performance test diagram of porous Si with MgSiN2 nanocoating in Example 1 of the present invention;

[0025] Figure 6 a is a scanning electron microscope image of the cross-section of the electrode film of the porous silicon control group in Example 1 of the present invention before battery test cycles; Figure 6 b is a scanning electron microscope image of the cross-section of the electrode film of the porous silicon control group in Example 1 of the present invention after 100 cycles of battery testing; Figure 6 c is a scanning electron microscope image of the cross-section of the electrode film of porous Si with MgSiN2 nanocoating in Example 1 of the present invention before battery test cycling; Figure 6 Image d is a scanning electron microscope image of the cross-section of the electrode film of porous Si with MgSiN2 nanocoating in Example 1 of the present invention after 100 battery test cycles. Detailed Implementation

[0026] The technical solution of the present invention will be described in detail below.

[0027] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0028] There are no particular restrictions on the purity of any raw materials used in this invention. However, it is preferred to use analytical grade or conventional purity used in the field of lithium-ion anode preparation.

[0029] The present invention provides a porous silicon material with a MgSiN2 nano-coating, the material comprising a porous silicon framework with an ant nest or coral structure, the surface of the porous silicon framework having a layer of MgSiN2 nano-coating.

[0030] The MgSiN2 nanocoating is uniformly grown on the surface of the porous silicon framework, covering the pore structure along its pores. Suitable porous spaces are retained within the silicon. These spaces arise from the nitriding reaction of Mg2Si particles, which forms Si and Mg3N2. In the final process, acid washing removes the Mg3N2, leaving behind Si and the pore spaces.

[0031] In some embodiments of the present invention, the particle size of the porous silicon material with MgSiN2 nanocoating is 1-7 μm; the thickness of the MgSiN2 nanocoating uniformly grown on the surface of the porous silicon framework is 3-50 nm.

[0032] This invention also provides a method for preparing porous silicon materials with MgSiN2 nanocoatings, comprising the following steps:

[0033] (1) Heat magnesium silicide powder to a certain temperature in a nitrogen-containing atmosphere and keep it at that temperature for a certain time;

[0034] (2) Stop the flow of nitrogen-containing gas, raise the temperature again, raise the temperature to the next temperature, and then introduce N2 and keep it at the temperature for a certain period of time.

[0035] (3) After the heat preservation time ends and the powder is cooled to room temperature, it is taken out and acid washed to remove magnesium nitride, thus obtaining the porous silicon material with MgSiN2 nano-coating.

[0036] Step (1) is the nitriding reaction of magnesium silicide. In some embodiments of the present invention, the particle size of magnesium silicide is 1-7 μm. The porous silicon material prepared using magnesium silicide with this particle size can obtain a porous silicon material with a particle size distribution of 1-7 μm and a nano-coating in the final step. If the material particle size is too small, the tap density will be low. If the particle size is too large, it will affect the material properties and the reaction kinetics in the dealloying process.

[0037] In some embodiments of the present invention, the heating rate of step (1) is 2-10℃ / min, heating to 700-800℃, and holding at that temperature for 3-6 hours. The nitrogen-containing atmosphere includes one or both of NH3 and N2.

[0038] Step (2) is the growth process of MgSiN2 nanocoating. In some embodiments of the present invention, the heating rate of step (2) is 2-10℃ / min, and the temperature is raised to 800-900℃; the holding time is 1-30 minutes, and more preferably 5-15 minutes.

[0039] After magnesium silicide undergoes a nitriding reaction, it encapsulates silicon. At subsequent high temperatures, silicon reacts with magnesium nitride in a nitrogen-containing atmosphere: 3Si + 2Mg → 3N₂ + N₂ → 3MgSiN₂ + Mg₃N₂, producing MgSiN₂. A holding time of 1-30 minutes is required for the MgSiN₂ nanocoating to begin growing. The thickness of this nanocoating can be controlled between 3-50 nm. Too short a holding time results in a thinner nanocoating that fails to provide adequate protection, while too long a holding time leads to an excessively thick nanocoating that blocks lithium-ion transport and negatively impacts the thickness and performance of the porous silicon framework. Furthermore, the purpose of heating before introducing N₂ during MgSiN₂ nanocoating growth is to more precisely control the thickness of the magnesium silicide protective layer and avoid unnecessary reactions caused by introducing N₂ during the heating process.

[0040] In some embodiments of the present invention, the acid in step (4) is hydrochloric acid; the pickling time is 1-3 hours.

[0041] This patent describes a porous silicon material with a MgSiN2 nanocoating, where the MgSiN2 nanocoating grows in situ along the porous silicon framework. The MgSiN2 nanocoating grown on the surface of the porous silicon possesses the characteristics of an "artificial SEI film." The SEI film formed after the MgSiN2 nanocoating contacts the electrolyte is a LiSi... x N y The components can maintain the stability of the interface; LiSi x N y MgSiN2 is an excellent electronic and ionic conductor, which can effectively improve the conductivity of the SEI film. The Mg in MgSiN2 can form an elastic Li-Mg alloy with Li, which can improve the plasticity of the SEI film. In-situ growth of a dense MgSiN2 nanocoating on the surface of a porous silicon framework helps achieve long-term cycling of Si anode materials. The nanocoating prepared by this method not only improves the material's conductivity, initial coulombic efficiency, and structural stability, but the porous silicon structure remaining after acid leaching further enhances its advantages, resulting in better electrochemical performance. Meanwhile, the method for preparing porous silicon materials with MgSiN2 nano-coatings designed in this patent adopts a "one-step" process. It utilizes multiple nitrogen sources to achieve a full reaction of silicon-magnesium alloy at a certain temperature to form Mg3N2 / Si. Then, at a slightly higher temperature, nitrogen gas is used as the nitrogen source to controllably prepare the MgSiN2 nano-coating using the reaction 3Si + 2Mg3N2 + N2 → 3MgSiN2 + Mg3N2. This process does not involve additional material usage or preparation steps. In the processing steps, only the temperature and atmosphere conditions and the holding time need to be adjusted to obtain the material, which has the potential for large-scale preparation.

[0042] The present invention also provides the application of the above-mentioned porous silicon material with MgSiN2 nanocoating in the preparation of lithium-ion battery anode material, as well as lithium-ion battery anode material and lithium-ion battery containing the above-mentioned porous silicon material with MgSiN2 nanocoating.

[0043] The present invention will now be clearly and completely described in conjunction with the technical solutions in specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Furthermore, it is worth noting that, unless otherwise specified, the raw materials involved in the present invention are all commercially available products.

[0044] Example 1

[0045] Magnesium silicide powder with a particle size of 3 μm was selected. The Mg2Si powder was placed in a tube furnace, and an Ar / NH3 mixed atmosphere was introduced. The furnace was heated at 5 °C for 1 minute. -1 The temperature was increased to 750℃ at a rising rate and held for 6 hours to induce the nitriding reaction. After the holding time for the nitriding reaction was completed, the NH3 atmosphere was shut off, and the temperature of the tube furnace was reduced at a rate of 5℃ / min. -1 The temperature was increased to 880℃ at a controlled heating rate, N2 was introduced, and the mixture was held at this temperature for 10 minutes to allow the MgSiN2 nanocoating to grow. After the holding time, the mixture was cooled to room temperature, and the resulting powder was passed through a 1 mL filter. -1 Mg3N2 was removed by acid washing with HCl solution for 3 hours, followed by filtration to neutrality and vacuum drying to obtain porous silicon with a nano-coating. The thickness of the nano-coating was 3-50 nm, and the overall particle size was mainly concentrated in the range of 2-3 μm.

[0046] Figure 1 The reaction process of this embodiment is shown: First, Mg2Si particles undergo a nitriding reaction under certain conditions in an Ar / NH3 atmosphere. Then, the atmosphere is changed from NH3 atmosphere to N2 atmosphere, and MgSiN2 is grown in situ on the porous silicon surface. Finally, Mg3N2 is removed by acid washing to obtain a porous silicon material (p-Si@MgSiN2) with a MgSiN2 nano-coating on the surface.

[0047] The morphology of the synthesized material was observed using scanning electron microscopy. Figure 2 The SEM image of a clearly shows that the average particle size of the material synthesized in this invention is around 3 μm; the material exhibits a porous structure resembling an ant nest or sea coral. Figure 2 The TEM image of b clearly shows that the thickness of the final nano-coating obtained by this invention is about 10 nm.

[0048] Depend on Figure 3 As can be seen from the BET plot of a, the specific surface area of ​​porous silicon (p-Si) without the MgSiN2 nanocoating, which serves as the control group, is 7.528 m². 2 g -1 ;Depend on Figure 3 As shown in the BET plot (b), the specific surface area of ​​the porous silicon (p-Si@MgSiN2) with the MgSiN2 nanocoating grown on the surface is 7.032 m². 2 g -1 This indicates that the growth of the MgSiN2 nanocoating has no significant impact on the structure of porous silicon and will not destroy the porous structure of the material.

[0049] Depend on Figure 4 The XRD diffraction pattern of a shows that the XRD diffraction patterns of porous silicon (p-Si@MgSiN2) with MgSiN2 nanocoating are basically the same as those of porous silicon (p-Si) without MgSiN2 nanocoating; however, in Figure 4 As can be seen in the Raman spectrum of b, the porous silicon with MgSiN2 nanocoating has peaks for Mg and N, indicating that MgSiN2 was successfully prepared, but the mass ratio is less than 5%, making it difficult to detect by XRD.

[0050] Figure 5 a is a long-cycle test image of porous silicon (p-Si@MgSiN2) with MgSiN2 nano-coating in Example 1 of the present invention. The porous silicon (p-Si@MgSiN2) with MgSiN2 nano-coating is subjected to long-cycle testing at 0.1 A g. -1 It has a current density of 3200mAh g -1 With a high capacity of around 86%, the material maintains an initial coulombic efficiency of 86% and a capacity retention of 91.55% after 100 cycles, demonstrating excellent long-cycle performance. Figure 5 b is a rate performance test graph of porous silicon (p-Si@MgSiN2) with MgSiN2 nano-coating in Example 1 of the present invention. The porous silicon with MgSiN2 nano-coating is tested at rates of 0.1, 0.2, 0.5, 1.0, 2.0 and 5.0 Å g. -1 The capacities at current densities were 2843, 2811, 2529, 2098, 1586, and 888 mAh g, respectively. -1 This indicates that the material has excellent rate performance.

[0051] Figure 6 Image a is a scanning electron microscope (SEM) image of the cross-section of the porous silicon electrode film without the MgSiN2 nanocoating before battery testing cycles. It shows a thickness of 15 μm. Figure 6As can be seen from b, the electrode film cross-sectional thickness of porous silicon without MgSiN2 nano-coating increased to 40μm after 100 battery test cycles, with an expansion rate of 267%. Figure 6 c is a scanning electron microscope (SEM) image of the cross-section of the porous silicon electrode film with MgSiN2 nanocoating in Example 1 of this invention before battery testing cycles; the thickness is also 15 μm. Figure 6 As can be seen, the electrode film cross-sectional thickness of porous silicon with MgSiN2 nano-coating increased to 26 μm after 100 battery test cycles, indicating that the presence of MgSiN2 nano-coating can further significantly improve the volume expansion of silicon.

[0052] Example 2

[0053] Magnesium silicide powder with a particle size of 3 μm was selected. The Mg2Si powder was placed in a tube furnace, and an Ar / NH3 mixed atmosphere was introduced. The furnace was heated at 5 °C for 1 minute. -1 The temperature was increased to 800℃ at a rising rate and held for 3 hours to induce the nitriding reaction. After the holding time for the nitriding reaction was completed, the NH3 atmosphere was shut off, and the temperature of the tube furnace was reduced at a rate of 5℃ / min. -1 The temperature was increased to 900℃ at a controlled heating rate, N2 was introduced, and the temperature was maintained for 5 minutes to allow the MgSiN2 nanocoating to grow. After the holding time, the temperature was cooled to room temperature, and the resulting powder was passed through a 1 mL filter. -1 Mg3N2 was removed by acid washing with HCl solution for 3 hours, followed by filtration to neutrality and vacuum drying to obtain porous silicon with a nano-coating. The thickness of the nano-coating was 3-50 nm, and the overall particle size was mainly concentrated in the range of 2-3 μm.

[0054] Example 3

[0055] Magnesium silicide powder with a particle size of 3 μm was selected. The Mg2Si powder was placed in a tube furnace, and an Ar / NH3 mixed atmosphere was introduced. The furnace was heated at 5 °C for 1 minute. -1 The temperature was increased to 650℃ at a rising rate and held for 6 hours to induce the nitriding reaction. After the holding time for the nitriding reaction was completed, the NH3 atmosphere was shut off, and the temperature of the tube furnace was reduced at a rate of 5℃ / min. -1 The temperature was increased to 880℃ at a controlled heating rate, N2 was introduced, and the mixture was held at this temperature for 10 minutes to allow the MgSiN2 nanocoating to grow. After the holding time, the mixture was cooled to room temperature, and the resulting powder was passed through a 1 mL filter. -1 The solution was acid-washed with HCl solution for 3 hours to remove Mg3N2, and then filtered until neutral and dried under vacuum.

[0056] Because the nitriding reaction temperature is too low, magnesium silicide cannot form magnesium nitride well or does not react, which affects the formation of porous silicon framework. As a result, the subsequent MgSiN2 nanocoating cannot grow effectively and uniformly. The unreacted magnesium silicide is removed by acid washing, which reduces the yield and affects the preparation and performance of the material.

[0057] Example 4

[0058] Magnesium silicide powder with a particle size of 3 μm was selected. The Mg2Si powder was placed in a tube furnace, and an Ar / NH3 mixed atmosphere was introduced. The furnace was heated at 5 °C for 1 minute. -1 The temperature was increased to 750℃ at a rising rate and held for 2 hours to induce the nitriding reaction. After the holding time for the nitriding reaction was completed, the NH3 atmosphere was shut off, and the temperature of the tube furnace was reduced at a rate of 5℃ / min. -1 The temperature was increased to 880℃ at a controlled heating rate, N2 was introduced, and the mixture was held at this temperature for 10 minutes to allow the MgSiN2 nanocoating to grow. After the holding time, the mixture was cooled to room temperature, and the resulting powder was passed through a 1 mL filter. -1 The solution was acid-washed with HCl solution for 3 hours to remove Mg3N2, and then filtered until neutral and dried under vacuum.

[0059] Because the nitriding reaction time is too short, magnesium silicide cannot form magnesium nitride well or does not react at all, affecting the formation of the porous silicon framework. This results in the subsequent MgSiN2 nanocoating not growing effectively and uniformly. The unreacted magnesium silicide is instead removed by acid washing, affecting the preparation and performance of the material.

[0060] Example 5

[0061] Magnesium silicide powder with a particle size of 3 μm was selected. The Mg2Si powder was placed in a tube furnace, and an Ar / NH3 mixed atmosphere was introduced. The furnace was heated at 5 °C for 1 minute. -1 The temperature was increased to 750℃ at a rising rate and held for 6 hours to induce the nitriding reaction. After the holding time for the nitriding reaction was completed, the NH3 atmosphere was shut off, and the temperature of the tube furnace was reduced at a rate of 5℃ / min. -1 The temperature was increased to 880℃ at a controlled heating rate, N2 was introduced, and the temperature was maintained for 30 seconds to allow the MgSiN2 nanocoating to grow. After the holding time, the temperature was cooled to room temperature, and the resulting powder was passed through a 1 mL filter. -1 The solution was acid-washed with HCl solution for 3 hours to remove Mg3N2, and then filtered until neutral and dried under vacuum.

[0062] Because the growth time of the MgSiN2 nanocoating in the reaction is too short and the nanocoating is too thin, it cannot form a significant protective effect. At the same time, the toughness is also insufficient, resulting in a negligible effect in alleviating volume expansion and affecting the long-cycle performance of the material.

[0063] Example 6

[0064] Magnesium silicide powder with a particle size of 3 μm was selected. The Mg2Si powder was placed in a tube furnace, and an Ar / NH3 mixed atmosphere was introduced. The furnace was heated at 5 °C for 1 minute. -1 The temperature was increased to 750℃ at a rising rate and held for 6 hours to induce the nitriding reaction. After the holding time for the nitriding reaction was completed, the NH3 atmosphere was shut off, and the temperature of the tube furnace was reduced at a rate of 5℃ / min. -1 The temperature was increased to 1000℃ at a rising rate, N2 was introduced, and the temperature was maintained for 10 minutes to allow the MgSiN2 nanocoating to grow. After the holding time, the temperature was cooled to room temperature, and the resulting powder was passed through a 1 mL filter. -1 The solution was acid-washed with HCl solution for 3 hours to remove Mg3N2, and then filtered until neutral and dried under vacuum.

[0065] The excessively high growth temperature of the MgSiN2 nanocoating during the reaction caused partial collapse and deformation of the material structure. Furthermore, the excessively high temperature also caused partial decomposition of magnesium nitride, hindering the growth reaction of magnesium silicon nitride and resulting in uneven growth of magnesium silicon nitride.

[0066] Example 7

[0067] Magnesium silicide powder with a particle size of 3 μm was selected. The Mg2Si powder was placed in a tube furnace, and an Ar / NH3 mixed atmosphere was introduced. The furnace was heated at 5 °C for 1 minute. -1 The temperature was rapidly increased to 750℃ and held for 6 hours to induce a nitriding reaction. After the holding time for the nitriding reaction was completed, the NH3 atmosphere was shut off, and the temperature of the tube furnace was simultaneously reduced by 5℃ / min. -1 The temperature was increased to 880℃ at a controlled heating rate, N2 was introduced, and the temperature was maintained for 40 minutes to allow the MgSiN2 nanocoating to grow. After the holding time, the temperature was cooled to room temperature, and the resulting powder was passed through a 1 mL filter. -1 The solution was acid-washed with HCl solution for 3 hours to remove Mg3N2, and then filtered until neutral and dried under vacuum.

[0068] The excessively long growth time of the MgSiN2 nanocoating during the reaction leads to the consumption of excessive Si to form a magnesium silicon nitride coating, ultimately resulting in a decrease in the material's capacity. The excessively thick protective layer also increases the resistance to ion and electron transport, reducing the material's conductivity.

[0069] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a porous silicon material with a MgSiN2 nanocoating, comprising the following steps: (1) Heat magnesium silicide powder to 700-800℃ in a nitrogen-containing atmosphere and keep it at that temperature for 3-6 hours; (2) Stop the flow of nitrogen-containing gas, raise the temperature again, raise the temperature to the next temperature, and then introduce N2 and keep it at the temperature for a certain period of time. (3) After the heat preservation time ends and the powder is cooled to room temperature, it is taken out and acid washed to remove magnesium nitride, and the porous silicon material with MgSiN2 nano-coating is obtained. The particle size of magnesium silicide is 1-7 μm; in step (1), the nitrogen-containing atmosphere includes one or both of NH3 and N2; in step (2), the temperature is raised to 800-900℃ and held for 1-30 minutes; in step (3), the acid is hydrochloric acid and the pickling time is 1-3 hours. The porous silicon material with MgSiN2 nano-coating has a porous silicon framework with an ant nest or coral structure, and the surface of the porous silicon framework has a layer of MgSiN2 nano-coating; the particle size of the material is 1-7μm; the thickness of the MgSiN2 nano-coating is 3-50nm.

2. A lithium-ion battery anode material, characterized in that, This includes the porous silicon material with an MgSiN2 nanocoating as described in claim 1.

3. A lithium-ion battery, characterized in that, Including the lithium-ion battery anode material as described in claim 2.

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