A nitrogen and phosphorus co-doped silicon-oxygen-carbon-tin composite negative electrode material, a preparation method and application thereof

Abstract

This invention relates to the field of lithium-ion battery anode material technology, and particularly to a nitrogen-phosphorus co-doped silicon-oxygen-carbon-tin oxide composite anode material, its preparation method, and its application. The invention involves mixing diatomaceous earth with an acidic solution for purification. The purified diatomaceous earth is then mixed with a silicon source and a solvent, and the pH is adjusted to alkaline to react and obtain a SiOC precursor gel. This gel is calcined under an inert atmosphere to obtain SiOC. SiOC, a morphology modifier, and a tin source are mixed, and a carbon source is added for a hydrothermal reaction. The resulting anode material precursor is then calcined under an inert atmosphere to obtain a SiOC-SnO2-C precursor. Finally, the SiOC-SnO2-C precursor and a phosphorus source are calcined under an ammonia and inert atmosphere to obtain the nitrogen-phosphorus co-doped silicon-oxygen-carbon-tin oxide composite anode material. This anode material exhibits excellent initial discharge specific capacity, initial coulombic efficiency, and capacity retention, achieving a balance between high capacity and long cycle life.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, and in particular to a nitrogen-phosphorus co-doped silicon-oxygen-carbon-tin oxide composite anode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have been widely used in consumer electronics, new energy vehicles, and large-scale energy storage due to their advantages such as high energy density, long cycle life, and no memory effect. As application scenarios continue to increase the requirements for range and power, traditional graphite anodes (theoretical capacity of only 372 mAh / g) can no longer meet the development needs of high capacity and long range. Developing new anode materials with high specific capacity has become a key direction for the industry.

[0003] Silicon-based anode materials are considered the most promising next-generation anode system due to their ultra-high theoretical specific capacity (Si≈4200 mAh / g). However, pure silicon materials have a volume deformation rate of over 300% during lithium insertion / extraction, which can easily lead to problems such as electrode pulverization, repeated rupture of the solid electrolyte interphase (SEI) film, and rapid decay of cycle life, which seriously limits their commercial application.

[0004] Silicon-oxygen-carbon (SiOC) ceramic materials, as amorphous silicon-carbon based composite materials, have the characteristics of high structural stability, good mechanical strength, mild volume effect, moderate lithium storage platform, and low cost. They can effectively alleviate the volume expansion problem of traditional silicon-based anodes, and at the same time have certain reversible capacity and good interfacial compatibility, making them an important research direction for high-stability silicon-based anodes. However, pure SiOC materials have obvious shortcomings: (1) low intrinsic electronic conductivity and significant polarization during charge and discharge processes; (2) limited active sites, making it difficult for reversible specific capacity to meet the requirements of high energy density; and (3) long ion transport paths and poor rate performance.

[0005] To overcome the performance bottleneck of SiOC, the introduction of high-capacity metal oxides for composite modification has become the mainstream technical route. Tin oxide (SnO2) has advantages such as a high theoretical lithium storage capacity (≈782 mAh / g), moderate lithium intercalation potential, readily available raw materials, and ease of nano-sizing and uniform dispersion. It can form a synergistic lithium storage effect with the SiOC matrix, significantly improving the overall capacity of the composite material. However, SnO2 has defects similar to those of silicon-based anodes: large volume change during charge and discharge, easy structural collapse, insufficient conductivity, and poor cycle stability. How to achieve efficient composite of SiOC and SnO2, while improving capacity, has become the core technical challenge in this field.

[0006] In terms of raw materials, existing SiOC materials mostly use organosilicones such as vinyltriethoxysilane (VTES) and tetraethyl orthosilicate (TEOS) as silicon sources and are prepared by the sol-gel method. These organosilicon sources have high purity and mature processes, but they are expensive, rely on chemical synthesis, and lack natural pore structures, making it difficult to meet the industrial demand for low cost, large scale, and high performance.

[0007] Natural diatomite is a biogenic silica mineral formed from the sedimentary remains of ancient diatoms. Its main component is amorphous SiO2, and it possesses unique advantages such as abundant reserves, low price, natural hierarchical porous structure, large specific surface area, and good biocompatibility, making it an ideal low-cost green silicon source. Its porous structure can be retained in situ within a SiOC matrix, providing natural advantages for lithium-ion transport, electrolyte wetting, and volume expansion buffering. Currently, research on the direct preparation of SiOC-based composite materials using natural diatomite as a silicon source is limited, and the technology of in-situ composite of diatomite-based SiOC with SnO2 to construct heterogeneous anodes has not been reported, indicating a significant technological gap.

[0008] In summary, the existing technology still has the following key problems: (1) The cost of silicon source is high, making it difficult to achieve low-cost large-scale preparation; (2) In the process of SiOC and SnO2 composite, problems such as SnO2 agglomeration, uneven distribution and weak interface bonding are easy to occur; (3) There is a lack of integrated process to simultaneously realize "SiOC in-situ generation, uniform loading of SnO2 nanocrystals and construction of conductive carbon network"; (4) The material structure is not stable enough, and the capacity decays quickly during cycling.

[0009] Therefore, developing a composite anode material that uses natural diatomaceous earth as a cheap silicon source, synthesizes SiOC-SnO2-C heterostructure in situ, has a simple and controllable process, and is suitable for industrialization, is of great theoretical and engineering significance for promoting the low-cost commercialization of high-capacity silicon-carbon anodes. Summary of the Invention

[0010] The purpose of this invention is to provide a nitrogen-phosphorus co-doped silicon-oxygen-carbon-tin oxide composite anode material, its preparation method, and its application, so as to overcome the technical defects of existing silicon-oxygen-carbon anode materials, such as high silicon source cost, insufficient conductivity, low capacity, poor cycle stability, and serious volume expansion, easy pulverization, and difficulty in industrialization of SnO2-based materials.

[0011] To achieve the above-mentioned objectives, the present invention provides the following technical solution: One of the technical solutions of this invention provides a method for preparing a nitrogen-phosphorus co-doped silicon-oxygen-carbon-tin oxide composite anode material, comprising the following steps: (1) The diatomaceous earth was mixed with an acidic solution and purified to obtain purified diatomaceous earth; (2) After mixing purified diatomaceous earth, silicon source and solvent, the pH was adjusted to alkaline and the reaction was carried out to obtain SiOC precursor gel; (3) The SiOC precursor gel was calcined under an inert atmosphere to obtain SiOC; (4) After mixing SiOC, morphology modifier and tin source, carbon source is added to carry out hydrothermal reaction to obtain a negative electrode material precursor; (5) The negative electrode material precursor was calcined in an inert atmosphere to obtain SiOC-SnO2-C negative electrode material precursor; (6) The SiOC-SnO2-C anode material precursor and phosphorus source were calcined in an atmosphere of ammonia and inert atmosphere to obtain a nitrogen-phosphorus co-doped silicon-oxygen-carbon-tin oxide composite anode material.

[0012] The second technical solution of the present invention provides a nitrogen-phosphorus co-doped silicon-oxygen-carbon-tin oxide composite anode material prepared by the above-mentioned preparation method.

[0013] The third technical solution of the present invention provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator and an electrolyte; the negative electrode includes the above-mentioned nitrogen-phosphorus co-doped silicon-oxygen-carbon-tin oxide composite negative electrode material.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention directly uses natural diatomaceous earth as the silicon source, replacing expensive organosilicon sources such as tetraethyl orthosilicate and silicone resin used in the preparation of traditional silicon-oxygen-carbon materials. The raw material cost is reduced by more than 50%, and natural diatomaceous earth resources are abundant and widely available, making it suitable for large-scale industrial production.

[0015] 2. Utilizing the natural microporous structure of diatomaceous earth as a template, uniform distribution and firm anchoring of tin oxide nanoparticles (5-50 nm in diameter) in a silicon-oxygen-carbon porous matrix were achieved through sol-gel in-situ composite and heat treatment. This structure effectively buffers the volume expansion of tin oxide during charge and discharge (reducing the volume expansion rate by approximately 60%), avoiding electrode pulverization and rapid capacity decay.

[0016] 3. The diatomaceous earth-based silicon-oxygen-carbon-tin oxide composite anode material prepared by this invention exhibits an initial discharge specific capacity of 950-1100 mAh / g and an initial coulombic efficiency of 65-70%. After 100 cycles at a current density of 0.5 A / g, the capacity retention rate is ≥85%, and the rate performance (capacity retention rate ≥60% at 2 A / g) is significantly superior to that of SiOC / SnO2 composite materials prepared by traditional mechanical mixing methods. The excellent lithium-ion conductivity and mechanical strength of the silicon-oxygen-carbon matrix, combined with the high specific capacity of tin oxide, create a synergistic effect, achieving a balance between high capacity and long cycling time.

[0017] 4. This invention adopts a "one-step sol-gel + one-step heat treatment" process route. Compared with the complex process of multiple impregnation and heat treatment in the prior art, the process steps are reduced, the operating window is wide, the batch stability is high, and it is easy to achieve large-scale production. At the same time, the tin oxide content can be precisely controlled by adjusting the amount of tin source added (10~40 wt%) to meet the capacity and cycle life requirements of different application scenarios.

[0018] 5. This invention uses natural minerals as raw materials, and no toxic or harmful solvents are required in the preparation process. The pickling waste liquid can be recycled after neutralization treatment, which meets the requirements of green chemical industry and sustainable development. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the preparation method of the present invention.

[0020] Figure 2 The image shows a TEM image of the SiOC-SnO2-CP composite anode material prepared in Example 1 of this invention. (a) shows the original SiOC matrix microspheres, (b) shows the SiOC-SnO2-C microspheres loaded with SnO2, and (c) shows the morphology of the SnO2 layer.

[0021] Figure 3 This is a mapping diagram of the SiOC-SnO2-CP composite anode material prepared in Example 1 of the present invention.

[0022] Figure 4 The image shows the XRD pattern of the SiOC-SnO2-CP composite anode material prepared in Example 1 of this invention.

[0023] Figure 5 The image shows the electrochemical performance of the SiOC-SnO2-CP composite anode material prepared in Example 1 of this invention. Detailed Implementation

[0024] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0025] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0026] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0027] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0028] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0029] All raw materials used in this invention can be obtained commercially or prepared using existing technologies.

[0030] This invention achieves a triple functional synergy through an integrated process of diatomite purification and activation, sol-gel composite, hydrothermal regulation, and calcination crystallization. This process enables the in-situ conversion of natural SiO2 to SiOC, uniform loading of SnO2 nanocrystals, and simultaneous construction of a conductive carbon network. It achieves innovative breakthroughs in raw materials, structure, and performance, ultimately obtaining a high-capacity, highly stable, and low-cost lithium-ion battery anode material.

[0031] Specifically, this invention provides a method for preparing a silicon-oxygen-carbon-tin oxide composite anode material, comprising the following steps: (1) The diatomaceous earth was mixed with an acidic solution and purified to obtain purified diatomaceous earth; (2) After mixing purified diatomaceous earth, silicon source and solvent, the pH was adjusted to alkaline and the reaction was carried out to obtain SiOC precursor gel; (3) The SiOC precursor gel was calcined under an inert atmosphere to obtain SiOC; (4) After mixing SiOC, morphology modifier and tin source, carbon source is added to carry out hydrothermal reaction to obtain a negative electrode material precursor; (5) The negative electrode material precursor was calcined in an inert atmosphere to obtain SiOC-SnO2-C negative electrode material precursor; (6) The SiOC-SnO2-C anode material precursor and phosphorus source were calcined in an atmosphere of ammonia and inert atmosphere to obtain a nitrogen-phosphorus co-doped silicon-oxygen-carbon-tin oxide composite anode material.

[0032] Step (1) of this invention involves adding diatomaceous earth to an acidic solution, stirring and purifying it in a water bath for 6 hours, filtering, washing with deionized water until the filtrate is neutral, and drying to obtain purified diatomaceous earth.

[0033] Step (1) of this invention uses natural diatomaceous earth as raw material, which is acid-washed to remove metal oxide impurities while retaining its unique microporous structure (pore size distribution of 50~500 nm, specific surface area of ​​10~100 m²). 2 / g). This microporous structure serves as a natural template in subsequent reactions, guiding the selective loading of organosilicon, carbon, and tin sources to achieve in-situ polymerization of precursors inside and outside the diatomite channels.

[0034] In this invention, the drying temperature in step (1) is 100°C and the drying time is 12h.

[0035] In this invention, the diatomaceous earth has a particle size of 15-20 μm, a pore size of 50-500 nm, and a specific surface area of ​​10-100 m². 2 / g.

[0036] In a preferred embodiment of the present invention, the diatomite is natural diatomite, for example, it can be natural diatomite produced in Changbai Mountain, Jilin Province.

[0037] In this invention, the acidic solution is a hydrochloric acid solution or a sulfuric acid solution; the concentration of the acidic solution is 1~1.5 mol / L, for example, it can be 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L or 1.5 mol / L, etc.; the material-to-liquid ratio of the diatomaceous earth and the acidic solution is 1:10~12 (g:mL), for example, it can be 1:10 (g:mL), 1:11 (g:mL) or 1:12 (g:mL), etc.

[0038] In this invention, the purification temperature is 80~90℃, for example, 80℃, 85℃ or 90℃, and the time is 4~6h, for example, 4h, 5h or 6h.

[0039] This invention involves heating and stirring natural diatomaceous earth in a strong acid solution to remove metallic impurities such as Fe, Al, Ca, and Mg. After washing and drying, high-purity amorphous SiO2 porous powder is obtained, preserving the natural multi-level pore structure of diatomaceous earth and providing a structural basis for subsequent SiOC conversion and ion transport.

[0040] Step (2) of this invention involves dispersing purified diatomaceous earth and silicon source in a solvent, adjusting the pH to alkaline, and heating and stirring the mixture in a water bath to obtain SiOC precursor gel.

[0041] Step (2) of this invention involves reacting purified diatomaceous earth with an organosilicon source in an alkaline environment using a sol-gel reaction. By controlling the pH, temperature, and reaction time, the silicon source undergoes hydrolysis and condensation on the surface and within the pores of the diatomaceous earth, forming a three-dimensional network structure.

[0042] In this invention, the silicon source includes vinyltriethoxysilane; the solvent is composed of ethanol and water; the volume ratio of ethanol to water is 4:1; the mass ratio of purified diatomaceous earth to silicon source is 1:1 to 2, for example, it can be 1:1, 1:1.5 or 1:2, etc.

[0043] In this invention, the solvent for adjusting the pH in step (2) is ammonia; the pH is 9~10, for example, it can be 9, 9.5 or 10; the reaction temperature is 40~80℃, for example, it can be 40℃, 50℃, 60℃, 70℃ or 80℃, and the time is 6~12h, for example, it can be 6h, 8h, 10h or 12h.

[0044] Step (3) of this invention involves calcining the SiOC precursor gel under an inert atmosphere, followed by natural cooling to obtain SiOC.

[0045] In a preferred embodiment of the present invention, the precursor gel needs to be dried and ground before calcination, and the drying temperature is 80°C and the time is 12 hours.

[0046] In this invention, the heating rate of calcination in step (3) is 3~5℃ / min, for example, it can be 3℃ / min, 4℃ / min or 5℃ / min, the calcination temperature is 500~900℃, for example, it can be 500℃, 600℃, 700℃, 800℃, 850℃ or 900℃, and the calcination time is 2~6h, for example, it can be 2h, 3h, 4h, 5h or 6h.

[0047] In this invention, the inert atmosphere is preferably nitrogen or argon; the nitrogen flow rate is 300 mL / min.

[0048] In some embodiments of the present invention, calcination is carried out in a tubular furnace.

[0049] Step (4) of this invention involves mixing SiOC, morphology modifier and tin source to obtain a precursor, adding carbon source to the precursor for hydrothermal reaction, and drying to obtain a negative electrode material precursor.

[0050] In this invention, the morphology modifier is tetrapropylammonium hydroxide; the tin source includes tin tetroxide, stannous oxalate, or stannous chloride (preferably SnCl2·2H2O); and the carbon source includes phenolic resin, glucose, or sucrose (analytical grade). The mass ratio of SiOC, morphology modifier, and tin source is 1:0.2~1:0.25~2, for example, it can be 1:0.2:0.25, 1:0.2:2, 1:1:0.25, or 1:1:2; the mass ratio of tin source and carbon source is 0.5~1:1~1.5, for example, it can be 0.5:1, 0.5:1.5, 1:1, or 1:1.5, etc. The hydrothermal reaction temperature is 150~200℃, for example, 150℃, 160℃, 170℃, 180℃, 190℃ or 200℃, etc., and the time is 8~14h, for example, 8h, 10h, 12h or 14h.

[0051] In a preferred embodiment of the present invention, the SiOC, morphology modifier and tin source are mixed at a temperature of 80°C for 6 hours.

[0052] In a preferred embodiment of the present invention, the drying temperature is 100°C and the drying time is 12 hours.

[0053] In a preferred embodiment of the present invention, the hydrothermal reaction is carried out in a hydrothermal reactor.

[0054] In this invention, tetrapropylammonium hydroxide (TPAOH) is added to the composite gel as a structure directing agent and morphology modifier, and a hydrothermal reaction is carried out in a closed system to further promote component homogenization, construct mesoporous channels, and improve the specific surface area and ion transport capacity of the material.

[0055] Step (5) of this invention involves grinding the anode material precursor and then calcining it under an inert atmosphere. After naturally cooling to room temperature, a SiOC-SnO2-C anode material precursor is obtained.

[0056] In this invention, the heating rate of calcination in step (5) is 2~10℃ / min, for example, it can be 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 8℃ / min or 10℃ / min, etc., the calcination temperature is 500~600℃, for example, it can be 500℃, 550℃ or 600℃, etc., and the calcination time is 1~4h, for example, it can be 1h, 2h, 3h or 4h, etc.

[0057] In a preferred embodiment of the present invention, the inert atmosphere in step (5) is preferably argon.

[0058] In a preferred embodiment of the present invention, the calcination in step (5) is preferably carried out in a tubular furnace.

[0059] Step (6) of this invention involves calcining the SiOC-SnO2-C anode material precursor and phosphorus source under ammonia and inert atmosphere, and then naturally cooling them to obtain a nitrogen-phosphorus co-doped silicon-oxygen-carbon-tin oxide composite anode material.

[0060] In a preferred embodiment of the present invention, the calcination in step (6) is preferably carried out in a tubular furnace.

[0061] In a preferred embodiment of the present invention, during the calcination step (6), a phosphorus source is placed in front of the SiOC-SnO2-C anode material precursor.

[0062] In this invention, the heating rate of calcination in step (6) is 5℃ / min, the calcination temperature is 800~1000℃, for example, it can be 800℃, 850℃, 900℃, 950℃ or 1000℃, etc., and the time is 1~4h, for example, it can be 1h, 2h, 3h or 4h, etc. The phosphorus source is sodium dihydrogen phosphate; the volume ratio of ammonia to inert atmosphere is 1:0.5~1.5, for example, it can be 1:0.5, 1:1 or 1:1.5, etc.; the mass ratio of SiOC-SnO2-C anode material precursor to phosphorus source is 1:0.5~1.5, for example, it can be 1:0.5, 1:1 or 1:1.5, etc.

[0063] In this invention, a multi-stage calcination crystallization process is employed: under the protection of a high-purity argon inert atmosphere, a segmented heating calcination process is used. Low temperature stage: organic residues are removed and the precursor is initially cross-linked; medium temperature stage: diatomaceous earth SiO2 undergoes a carbothermic reduction reaction with the carbon source to generate SiOC ceramic matrix in situ; high temperature stage: the tin source is completely transformed into highly crystalline SnO2 nanocrystals, while forming a continuous conductive carbon network, and finally obtaining SiOC-SnO2-C heterostructure composite material.

[0064] The present invention also provides a silicon-oxygen-carbon-tin oxide composite anode material prepared by the above preparation method.

[0065] The present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the negative electrode comprises the aforementioned silicon-oxygen-carbon-tin oxide composite negative electrode material.

[0066] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0067] This invention discloses a natural diatomaceous earth SiOC-SnO2-C anode material, its preparation method, and lithium-ion battery technology. Figure 1 As shown, its core feature is that it uses natural diatomaceous earth as raw material and combines sol-gel and heat treatment processes to successfully prepare silicon-oxygen-carbon-tin oxide composite anode materials.

[0068] Example 1 (S1) Take 50 g of natural diatomaceous earth (particle size D50≈15 μm, specific surface area≈45 m²) 2 Add g) to 500 mL of 1 mol / L hydrochloric acid solution, stir in an 80℃ water bath for 6 h, filter, wash with deionized water until the filtrate is neutral, and dry at 100℃ for 12 h to obtain purified diatomaceous earth.

[0069] (S2) Take 10 g of purified diatomaceous earth, add 20 g of vinyltriethoxysilane, disperse it in a mixed solvent of 200 mL ethanol and 50 mL water, add ammonia to adjust the pH to 10, stir the reaction in a 60℃ water bath for 8 h to obtain SiOC precursor gel.

[0070] (S3) The SiOC precursor gel was dried at 80℃ for 12 h, ground and placed in a tube furnace. Under an argon atmosphere, the temperature was increased to 800℃ at 5℃ / min, held for 3 h, and then naturally cooled to obtain the diatomite-based silicon-oxygen-carbon anode material, denoted as SiOC.

[0071] (S4) 20g SiOC, 4g TPAOH and 5g SnO4 were stirred in an oil bath at 80℃ for 6 h to obtain a precursor. 15g phenolic resin was added and placed in a hydrothermal reactor and reacted at 180℃ for 12 h. After drying at 100℃ for 12 h, the mixture was ground and placed in a tube furnace. The temperature was increased to 550℃ at 5℃ / min under an argon atmosphere and held for 2 h. After natural cooling, the SiOC-SnO2-C anode material precursor was obtained.

[0072] (S5) The SiOC-SnO2-C anode material precursor was placed in a tube furnace with an equal amount of NaH2PO4-H2O placed in front. The temperature was increased to 900℃ at 5℃ / min under an atmosphere of 50% NH3 and argon, held for 2 h, and then naturally cooled to obtain nitrogen-phosphorus co-doped SiOC-SnO2-C anode material (SiOC-SnO2-CP).

[0073] Example 2 The rest is the same as in Example 1, except that: in step (S4), glucose is used instead of phenolic resin, stannous oxalate is used as the tin source, and in step (S5), the heat treatment temperature is 700°C and the heat treatment time is 6 hours.

[0074] Example 3 The rest is the same as in Example 1, except that: in step (S4), the mass ratio of silicon oxide carbon, TPAOH and SnO4 is 1:0.2:0.5, and the mass ratio of SnO4 and phenolic resin is 0.5:2; in step (S5), the heat treatment temperature is 800℃ and the holding time is 4 h.

[0075] Example 4 The rest is the same as in Example 1, except that: in step (S1), 50 g of natural diatomaceous earth from Changbai Mountain in Jilin Province (particle size D50≈20 μm, specific surface area≈38 m²) is taken. 2 (g), added to 600 mL of a 1.5 mol / L sulfuric acid solution.

[0076] Example 5 The rest is the same as in Example 1, except that: in step (S3), the precursor gel is dried at 80°C for 12 h, ground and placed in a tube furnace, high-purity nitrogen gas (flow rate 300 mL / min) is introduced, the temperature is increased to 850°C at 3°C / min, held for 3 h, and then cooled naturally.

[0077] Example 6 The rest is the same as in Example 1, except that in step (S4), sucrose (analytical grade) is used to replace phenolic resin to obtain the precursor gel.

[0078] Comparative Example 1 Compared with Example 1, the difference is that natural diatomaceous earth is not used, and tetraethyl orthosilicate is used directly as the silicon source to replace purified diatomaceous earth, while the remaining steps and process parameters are the same.

[0079] Comparative Example 2 Compared with Example 1, the difference is that step (S5) does not use sodium dihydrogen phosphate monohydrate and 50% ammonia, while the remaining steps and process parameters are the same, and SiOC-SnO2-C is obtained.

[0080] Comparative Example 3 Compared to Example 1, the difference is that natural diatomaceous earth is not used; instead, fumed silica (AEROSIL® 200, specific surface area ≈ 200 m²) is used. 2 (g) can replace purified diatomaceous earth, and the remaining steps and process parameters are the same.

[0081] Comparative Example 4 Compared with Example 1, the difference is that step (S4) does not use TPAOH and directly obtains the comparison sample DE-SiOC / SnO2-reverse.

[0082] Comparative Example 5 Compared with Example 1, the difference is that phenolic resin is not added in step (S4). The remaining steps and process parameters are the same, and SiOC-SnO2-P composite material is obtained.

[0083] Comparative Example 6 Compared with Example 1, the difference is that tin tetroxide is not added in step (S4). The remaining steps and process parameters are the same, and the SiOC-P composite material is obtained.

[0084] Experimental data analysis Microstructure was observed using a Zeiss Sigma 500 field emission scanning electron microscope (SEM); crystal structure was measured using a MiniFlex 600 benchtop X-ray diffractometer (XRD); ionic conductivity was measured using a CHI660 electrochemical workstation. Nyquist plots obtained from these tests were fitted using Zview software to determine grain size, grain boundaries, and total resistance. Finally, ionic conductivity was calculated using a formula.

[0085] The electrochemical performance test results of the examples and comparative examples are shown in Table 1.

[0086] Table 1. Electrochemical performance test results of the examples and comparative examples.

[0087] The electrochemical performance and structural stability test results of the examples and comparative examples clearly demonstrate that the present invention successfully constructed a heterostructure in which SnO2 nanocrystals are uniformly loaded onto a porous SiOC matrix and coated with a conductive carbon network using a natural diatomaceous earth template and an integrated process. Figure 2 , Figure 4 The invention effectively buffers the volume expansion of SnO2, improving structural stability. Examples 1-6 all exhibit excellent performance with an initial specific capacity ≥912 mAh / g and a retention rate ≥84.5% after 100 cycles. Among them, Example 1 has the best overall performance (initial specific capacity 1052 mAh / g, retention rate 86.2%), demonstrating the significant progress and industrialization potential of the technical solution of this invention in the development of low-cost, high-performance silicon-carbon anode materials. Comparative Example 1 (tetraethyl orthosilicate replacing diatomaceous earth) has a high specific surface area, but its cycling performance is significantly reduced due to the lack of the natural porous structure of diatomaceous earth for buffering. Comparative Example 2 (without nitrogen and phosphorus doping) has a significantly lower specific capacity, demonstrating the key contribution of nitrogen and phosphorus doping to capacity. Comparative Example 3 (vapor phase SiO2 replacement) has the worst cycling performance, indicating that the natural porous structure of diatomaceous earth is crucial for volume buffering. Comparative Example 4 (without topography modifier) ​​has reduced specific surface area and pore volume, resulting in uneven silicon deposition and SnO2 distribution, leading to poor capacity and cycling performance. Comparative Example 5 (carbon-free matrix) exhibited the lowest capacity and the fastest cycle decay, confirming the crucial role of the SiOC matrix in structural stability. Comparative Example 6 (without SnO2) showed a significantly lower specific capacity, confirming the key contribution of SnO2 to capacity. While the comparative examples used artificial silicon sources such as tetraethyl orthosilicate and fumed silica, or methods involving reversed process sequences, this invention, relying on the inexpensive porous structure of natural diatomaceous earth and an in-situ composite strategy, significantly improved the specific capacity, cycle retention, and rate performance of the materials (Table 1). Figure 5 This verifies the synergistic advantages of raw material selection and process route.

[0088] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen-phosphorus co-doped silicon-oxygen-carbon-tin oxide composite anode material, characterized in that, Includes the following steps: (1) The diatomaceous earth was mixed with an acidic solution and purified to obtain purified diatomaceous earth; (2) After mixing purified diatomaceous earth, silicon source and solvent, the pH was adjusted to alkaline and the reaction was carried out to obtain SiOC precursor gel; (3) The SiOC precursor gel was calcined under an inert atmosphere to obtain SiOC; (4) After mixing SiOC, morphology modifier and tin source, add carbon source to carry out hydrothermal reaction to obtain a negative electrode material precursor; (5) The negative electrode material precursor was calcined in an inert atmosphere to obtain SiOC-SnO2-C negative electrode material precursor; (6) The SiOC-SnO2-C anode material precursor and phosphorus source were calcined in an atmosphere of ammonia and inert atmosphere to obtain a nitrogen-phosphorus co-doped silicon-oxygen-carbon-tin oxide composite anode material.

2. The preparation method according to claim 1, characterized in that, The diatomaceous earth has a particle size of 15-20 μm, a pore size of 50-500 nm, and a specific surface area of ​​10-100 m². 2 / g; The acidic solution is a hydrochloric acid solution or a sulfuric acid solution; the concentration of the acidic solution is 1~1.5 mol / L; the ratio of diatomaceous earth to acidic solution is 1:10~12 (g:mL). The purification process is carried out at a temperature of 80-90°C for 4-6 hours.

3. The preparation method according to claim 1, characterized in that, The silicon source includes vinyltriethoxysilane; The solvent is composed of ethanol and water; the volume ratio of ethanol to water is 4:

1. The mass ratio of purified diatomaceous earth to silicon source is 1:1~2.

4. The preparation method according to claim 1, characterized in that, The solvent used to adjust the pH in step (2) is ammonia; the pH is 9-10; the reaction temperature is 40-80℃ and the reaction time is 6-12h.

5. The preparation method according to claim 1, characterized in that, In step (3), the heating rate of calcination is 3~5℃ / min, the calcination temperature is 500~900℃, and the calcination time is 2~6h.

6. The preparation method according to claim 1, characterized in that, The morphology modifier is tetrapropylammonium hydroxide; the tin source includes tin tetroxide, stannous oxalate, or stannous chloride; the carbon source includes phenolic resin, glucose, or sucrose. The mass ratio of SiOC, morphology modifier, and tin source is 1:0.2~1:0.25~2; the mass ratio of tin source and carbon source is 0.5~1:1~1.

5. The hydrothermal reaction is carried out at a temperature of 150-200℃ for 8-14 hours.

7. The preparation method according to claim 1, characterized in that, In step (5), the heating rate of calcination is 2~10℃ / min, the calcination temperature is 500~600℃, and the calcination time is 1~4h.

8. The preparation method according to claim 1, characterized in that, In step (6), the heating rate of calcination is 5℃ / min, the calcination temperature is 800~1000℃, and the time is 1~4h; The phosphorus source is sodium dihydrogen phosphate; the volume ratio of ammonia to inert atmosphere is 1:0.5~1.5; the mass ratio of SiOC-SnO2-C anode material precursor to phosphorus source is 1:0.5~1.

5.

9. The nitrogen-phosphorus co-doped silicon-oxygen-carbon-tin oxide composite anode material prepared by the preparation method according to any one of claims 1 to 8.

10. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode includes the nitrogen-phosphorus co-doped silicon-oxygen-carbon-tin oxide composite negative electrode material as described in claim 9.

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