Silicon-carbon negative electrode material with multi-layer core-shell structure and preparation method and application thereof

Abstract

The application belongs to the technical field of lithium ion battery negative electrode materials, and specifically discloses a silicon-carbon negative electrode material with a multi-layer core-shell structure, a preparation method and application thereof, and the preparation method comprises the following steps: dispersing silicon particles in a Tris buffer solution, adding dopamine hydrochloride, and reacting at room temperature; filtering and drying to obtain an intermediate; dispersing the intermediate in a solvent B to obtain a suspension; adding a complexing agent and a doping agent in a solvent C in sequence, mixing uniformly, adding a titanium source dropwise, and reacting to obtain a precursor solution; adding the precursor solution into the suspension, performing water bath reaction, and then performing centrifugation, washing and drying to obtain a composite material; mixing the composite material with a carbon source solution, mixing uniformly, performing spray drying to obtain a carbon-coated particle precursor, and then performing carbonization treatment to obtain the silicon-carbon negative electrode material with the multi-layer core-shell structure. The material has the advantages of multi-stage buffering function, double lithium storage capacity and continuous conductive network, and can significantly improve the silicon volume effect and cycle life.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, specifically relating to a multi-layer core-shell silicon-carbon anode material, its preparation method, and its application. Background Technology

[0002] Silicon is considered the most promising next-generation lithium-ion battery anode material due to its ultra-high theoretical specific capacity (approximately 4200 mAh / g). However, silicon undergoes severe volume expansion (>300%) during charge and discharge, leading to structural pulverization, interface instability, and decreased conductivity, which severely restricts its practical application.

[0003] To alleviate the aforementioned problems, researchers have widely adopted strategies such as carbon coating, nano-design, and composite material construction to improve electrochemical stability. However, existing materials generally suffer from issues such as simple structure, poor interfacial continuity, and unsynergistic buffer layer functions. Therefore, designing a novel core-shell composite anode material with multi-level buffering functions, dual lithium storage capacity, and a continuous conductive network is a key approach to solving the silicon volume effect and improving cycle life. Summary of the Invention

[0004] In view of the above-mentioned shortcomings, this invention provides a multi-layer core-shell silicon-carbon anode material, its preparation method, and its applications. This invention achieves multiple synergistic effects of volume expansion control, interface stabilization, and charge transport optimization. Furthermore, through transition metal / rare earth doping, the introduction of oxygen vacancies, and interface construction, it effectively reduces the lithium storage potential of TiO2, increases the material's conductivity, and achieves synergistic work with silicon-based materials, thereby improving the capacity output and energy density of the composite anode system.

[0005] To address the above problems, this invention provides a method for preparing a multilayer core-shell structured silicon-carbon anode material, comprising the following steps:

[0006] S1. After calcining, acid leaching to remove impurities, and vacuum drying, crude silicon powder is added to solvent A and subjected to ultrasonic dispersion treatment, followed by ball milling, filtration, and drying to obtain nano-sized active silicon particles.

[0007] S2. The nanoscale active silicon particles are dispersed in Tris buffer solution, dopamine hydrochloride is added, and the reaction is carried out at room temperature to form a coating layer. After filtration and drying, Si@PDA intermediate is obtained.

[0008] It should be noted that using polydopamine (PDA) as a carbon source allows for in-situ coating of silicon particles through its self-polymerization capability, forming a continuous and dense PDA layer. Unlike traditional blended carbon sources, this PDA layer grows directly on the silicon surface, exhibiting excellent interfacial adhesion and high uniformity. The subsequent carbonization of this PDA layer prevents carbon layer peeling, interfacial debonding, and detachment from the current collector during charge and discharge, thus avoiding "dead silicon" and the resulting rapid capacity decay during cycling.

[0009] S3. The Si@PDA intermediate is uniformly dispersed in solvent B to obtain a uniform suspension; a complexing agent and a dopant are added sequentially to solvent C and mixed well, then a titanium source is added dropwise and reacted to obtain a uniform precursor solution; under stirring, the uniform precursor solution is slowly added dropwise to the uniform suspension, and the mixture is heated and stirred in a water bath, then centrifuged, washed, and dried to obtain the Si@PDA@TiO2 composite material;

[0010] S4. The Si@PDA@TiO2 composite material is mixed and homogenized with a carbon source solution, and then spray-dried to obtain a particle precursor uniformly coated with carbon source. The precursor is then carbonized in a vacuum or inert atmosphere to obtain a silicon-carbon anode material with a Si@C@TiO2@C multilayer core-shell structure.

[0011] Preferably, in step S1, the calcination temperature is 600-800℃ and the time is 1-2h; the acid includes at least one of hydrochloric acid, nitric acid, and hydrofluoric acid, with a concentration of 0.1-1mol / L; the solvent A includes at least one of ethanol and isopropanol, and the mass ratio of the crude silica powder to solvent A is 1:5-15.

[0012] Preferably, in step S1, a dispersant is added during the ball milling process, and the mass ratio of the dispersant to the coarse silica powder is 0.1-5:100.

[0013] Preferably, in step S2, after the nanoscale active silicon particles are dispersed in Tris buffer, the dispersion concentration of the nanoscale active silicon particles is 1-5 mg / mL; the mass ratio of the nanoscale active silicon particles to dopamine hydrochloride is 1:1-2.

[0014] Preferably, in step S3, solvent B comprises anhydrous ethanol and deionized water, and solvent C is anhydrous ethanol; the complexing agent comprises at least one of citric acid, acetylacetone, ethylenediaminetetraacetic acid, and tartaric acid; the dopant is a salt corresponding to a dopant element, and the dopant element comprises at least one of Nb, Fe, Ni, V, Co, Y, and La; the titanium source comprises at least one of tetrabutyl titanate, isopropyl titanate, and ethyl titanate; the mass ratio of the complexing agent to the dopant is 8-12:0.1-0.2; the mass ratio of the complexing agent to the Si@PDA intermediate is 8-12:5; and the mass ratio of the Si@PDA intermediate to the volume of the titanium source is 0.125-0.5 g / mL.

[0015] It should be noted that the purpose of adding a complexing agent (such as citric acid) in this invention is: (1) to complex doped metal ions; (2) to induce the slow-release deposition of titanium oxide in the titanium source, so as to achieve dense coating and heterogeneous interface stability, and avoid uneven titanium oxide deposition and self-aggregation behavior.

[0016] Preferably, in step S3, the temperature of the water bath heating and stirring reaction is 25-50℃, and the time is 6-12h.

[0017] Preferably, in step S4, the carbon source includes at least one of glucose and sucrose; the concentration of the carbon source in the carbon source solution is 5-15 wt%; and the mass ratio of the carbon source to the Si@PDA@TiO2 composite material is 1-3:1.

[0018] Preferably, in step S4, the spray feed temperature of the spray drying is 220-240℃, and the outlet temperature is 100-110℃; the inert atmosphere includes at least one of argon and nitrogen; the carbonization treatment temperature is 600-800℃, and the time is 1-2 hours; the TiO2 in the Si@C@TiO2@C multilayer core-shell silicon-carbon anode material is at least one of anatase, rutile, or amorphous structure.

[0019] It should be noted that when the carbonization temperature is 600℃, the TiO2 in the Si@C@TiO2@C multilayer core-shell silicon-carbon anode material is anatase; when 600℃ < carbonization temperature < 700℃, the TiO2 in the Si@C@TiO2@C multilayer core-shell silicon-carbon anode material is a mixed phase of anatase and rutile; when the carbonization temperature is above 700℃, the TiO2 in the Si@C@TiO2@C multilayer core-shell silicon-carbon anode material is rutile.

[0020] Based on the same inventive concept, the present invention also provides a multilayer core-shell silicon-carbon anode material prepared by any of the above-described preparation methods, wherein the particle size of Si in the Si@C@TiO2@C multilayer core-shell silicon-carbon anode material is 100-500 nm, the thickness of the inner C layer is 3-10 nm, the thickness of TiO2 is 3-5 nm, and the thickness of the outer C layer is 5-10 nm.

[0021] Based on the same inventive concept, this invention also provides the application of the above-mentioned multilayer core-shell structured silicon-carbon anode material in lithium-ion batteries.

[0022] The mechanism of the multilayer core-shell structure of this invention:

[0023] This invention involves sequentially coating a silicon (Si) surface with polydopamine (PDA), titanium oxide (TiO2), and a carbon layer (C), representing a multilayer core-shell structure design strategy aimed at synergistically improving the cycle stability, conductivity, and structural integrity of silicon-based anode materials.

[0024] First, PDA, as the first coating material, can self-polymerize in alkaline aqueous solutions to form a highly adhesive coating that can uniformly coat the silicon surface, achieving effective coating even if the silicon surface has some hydrophobicity. PDA is rich in functional groups such as hydroxyl (-OH) and amino (-NH2), which not only significantly improve the hydrophilicity of the silicon surface but also serve as reaction binding sites for subsequent inorganic coatings. Furthermore, PDA possesses a degree of flexibility, absorbing the stress generated by the volume expansion of silicon particles during lithium-ion charging and discharging, thereby mitigating structural damage.

[0025] The second layer of TiO2 coating possesses excellent thermal stability and mechanical strength, providing skeletal support for the active silicon during charge and discharge processes and suppressing its volume expansion. Simultaneously, it not only acts as a rigid mechanical protective layer but also exhibits certain ionic conductivity, enabling lithium storage. Particularly after amorphous or doped modification, it can participate in constructing a stable solid electrolyte interface (SEI), effectively reducing repeated SEI breakage and side reactions, and improving electrode lifespan. The TiO2 layer, located between the flexible inner PDA layer and the outer conductive carbon layer, forms a stress buffer and interface transition region, further stabilizing the structure.

[0026] Introducing transition metals or rare earth metals into the TiO2 coating process can further optimize the multiple properties of the layer. On the one hand, doping elements can regulate the electronic structure and bandgap of TiO2, improving its electronic conductivity and lithium-ion diffusion rate. On the other hand, some doped ions possess oxygen vacancy-induced capabilities, which, while enhancing ion permeability and interfacial reactivity, also regulate the electronic structure, reducing the lithium storage potential of the material. This facilitates a more stable and reversible lithium intercalation process, thereby improving its lithium storage capacity and reactivity. Furthermore, the high charge-to-radius ratio of certain rare earth elements can further strengthen the rigidity of the Ti-O framework, improve structural stability, and enhance the overall capabilities of the TiO2 coating layer in buffering stress, promoting ion migration, and interfacial regulation.

[0027] The third carbon coating layer primarily enhances overall electronic conductivity, constructs a continuous electron transport network, and compensates for the poor conductivity of silicon itself. It also strengthens structural integrity, provides additional mechanical protection for the entire negative electrode, and further isolates the electrolyte from direct contact with the internal TiO2 or silicon, reducing the occurrence of side reactions.

[0028] In addition, the TiO2 coating layer underwent partial reduction under inert atmosphere and co-calcination with a carbon source, generating Ti 3+ And oxygen vacancy structural defects. These defect structures not only improve the electronic conductivity and lithium-ion diffusion rate of the material, but also provide more active sites for subsequent electrochemical reactions, while enhancing the buffering capacity of the interface structure, which helps to improve the cycle stability and rate performance of the composite material.

[0029] Overall, the PDA layer serves as a functional graft and flexible buffer layer, the TiO2 layer serves as a rigid armor and SEI stabilizing layer, and the doping elements endow the TiO2 composite layer with additional electron / ion transport channels and structural enhancement functions. The carbon layer serves as a conductive network and external barrier. Together, they form a multifunctional synergistic interface-responsive gradient composite structure, which effectively solves the three key problems faced by silicon-based anodes in lithium battery applications: poor conductivity, large volume expansion, and interface instability.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) This invention proposes a multi-layered coaxial core-shell structure material design of “Si@C@TiO2@C”, which adopts a three-in-one synergistic construction method of “inner flexibility / intermediate rigidity / outer conductivity”, which is significantly different from the existing “yolk-shell” or single-layer coating structure. It forms a continuous conductive network and an effective buffer space, realizing the synergistic optimization of mechanical buffering, electronic guidance and interface reaction, and avoiding the problem of unstable electrical contact caused by cavities. The synergistic strategy of “interface induction + complexation control + hydrolysis mitigation” established by this invention has high adaptability and versatility, and can be extended to the construction of various core-shell structures, forming a modularly designed functional composite coating platform.

[0032] (2) In this invention, dopamine hydrochloride can undergo a self-polymerization reaction in an alkaline buffer solution (pH≈8.5, Tris-HCl) to form a dopamine polymer. The hydroxyl groups on the surface of PDA react with Ti 4+ Coordination can occur, controlling Ti 4+ Hydrolysis sites prevent random self-aggregation to form TiO2 agglomerates, improve the selectivity, uniformity and density of TiO2 coating, and avoid carbon layer peeling, interface debonding and falling off from the current collector to become "dead silicon" during charging and discharging, which would cause a sharp capacity decay during cycling.

[0033] (3) This invention introduces Fe 3+ Y 3+ Ni 2+ By doping TiO2 with transition metals or rare earth metals, the electronic structure and bandgap of TiO2 can be effectively controlled, inducing the generation of oxygen vacancies and endowing TiO2 with a layered lithium storage capacity. This not only constructs the traditional Si main lithium storage structure, but also utilizes the doped TiO2 itself to participate in lithium storage behavior (non-inert shell layer). Furthermore, by inducing oxygen vacancies and regulating the electronic structure through doping, TiO2 is no longer just a physical buffer layer, but becomes a lithium storage unit with active functions. It also has the dual functions of ion channel and electronic compensation layer, which improves the interfacial reaction activity and expands the total capacity and reaction stability of the anode.

[0034] (4) The present invention adopts an environmentally friendly citric acid complexation + slow hydrolysis method, combined with a self-polymerized PDA strategy, without the need for toxic template agents or high temperature conditions, avoiding the problem of TiO2 self-polymerization, improving the density and uniformity of the coating, and possessing process repeatability and potential for scale-up.

[0035] (5) The multifunctional shell synergy of the present invention (PDA functional layer + doped TiO2 rigid layer + carbon conductive layer) effectively suppresses volume expansion, improves electron / ion transport rate, stabilizes SEI film formation, and realizes the transformation of silicon-based anode materials from "structural stability" to "reaction stability + high capacity + high efficiency".

[0036] (6) The titanium dioxide of the present invention realizes the secondary lithium storage function. The inner and outer double carbon coating can prevent the electrolyte from directly contacting silicon / oxide, reducing side reactions; it helps to form a dense, uniform, and reversible SEI film; and significantly improves the first-cycle coulombic efficiency and cycle life. The multi-layer coating materials work together to construct a stable lithium-ion diffusion path, and the outer carbon layer improves electron conductivity, which helps to improve rate performance.

[0037] (7) The present invention introduces Ni into the Si@C@TiO2 core-shell anode structure. 2+ Fe 3+ 、Nb 5+ Y 3+By doping with at least one of the following metal elements, the electronic conductivity of the TiO2 shell is improved, the electronic structure of TiO2 is controlled, oxygen vacancies are induced, conductivity and interface stability are enhanced, the lithium intercalation potential is reduced, and the interface structure between Si@C and TiO2 is optimized. This systematically improves the lithium storage capacity, electrochemical kinetics and cycle life of the TiO2 coating layer, and constructs a high-performance composite anode. Attached Figure Description

[0038] Figure 1 The image shows the XRD pattern of the composite material prepared in Example 1 of this invention.

[0039] Figure 2 This is a SEM image of the composite material prepared in Example 1 of the present invention;

[0040] Figure 3 This is a TEM image of the composite material prepared in Example 1 of the present invention;

[0041] Figure 4 The image shows the EDS elemental distribution of the composite material prepared in Example 1 of this invention; wherein, red, yellow and blue in the image correspond to silicon (Si), titanium (Ti) and carbon (C) respectively.

[0042] Figure 5 This is a charge-discharge performance curve of a lithium battery made from the composite material prepared in Example 1 of the present invention;

[0043] Figure 6 This is a charge-discharge performance curve of a lithium battery made from the composite material prepared in Example 2 of the present invention;

[0044] Figure 7 This is a charge-discharge performance curve of a lithium battery made from the composite material prepared in Example 3 of the present invention;

[0045] Figure 8 The graph shows the charge-discharge performance of the composite material prepared in Comparative Example 1 of this invention as a lithium battery.

[0046] Figure 9 The graph shows the charge-discharge performance of the composite material prepared in Comparative Example 2 of this invention as a lithium battery.

[0047] Figure 10 This is a graph showing the charge-discharge performance of a lithium battery made from the composite material prepared in Comparative Example 3 of this invention. Detailed Implementation

[0048] To make the present invention easier to understand, specific embodiments are described below to further illustrate the invention. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. 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. Unless otherwise defined, the technical terms used below have the same meaning as understood by those skilled in the art; unless otherwise specified, the raw materials and reagents involved herein can be purchased commercially or obtained by known methods.

[0049] To address the common problems of existing materials, such as simple structure, poor interface continuity, and uncoordinated buffer layer functions, this invention provides a multi-layer core-shell silicon-carbon anode material, its preparation method, and its applications.

[0050] The following examples and comparative models further illustrate this point.

[0051] Example 1

[0052] A method for preparing a multilayer core-shell structured silicon-carbon anode material includes the following steps:

[0053] (1) Take coarse silicon powder (D50=2μm, D90=3μm) for photovoltaic industry and calcine it at 800℃ for 2 hours in an argon atmosphere; then add the calcined silicon particles to a 1mol / L hydrochloric acid solution for acid leaching to remove impurities; then wash it repeatedly with deionized water and ethanol, and dry it under vacuum at 60℃ for 12 hours; add the above silicon particles to ethanol (the mass ratio of silicon to ethanol is 1:20 / 3), treat it with an ultrasonic disperser for 30 minutes, and then ball mill it (the dispersant is PVP, and the amount added is 2% of the mass of coarse silicon powder) at a speed of 400 rpm for 2 hours to obtain nano-sized active silicon particles (particle size is 100-500nm).

[0054] (2) Disperse 0.5g of nano-sized active silicon particles in 100mL of Tris-HCl buffer (pH≈8.5), add 0.5g of dopamine hydrochloride, and stir at room temperature for 24 hours to obtain Si@PDA intermediate;

[0055] (3) Add 0.5g of Si@PDA intermediate powder to a beaker containing 30mL of anhydrous ethanol and 0.2mL of deionized water, and sonicate for 15 minutes to obtain a uniform suspension, which is denoted as solution A; add 30mL of anhydrous ethanol and 1.0g of citric acid to another beaker, stir for 5 minutes, then add 20mg of Ni(NO3)2·6H2O, continue stirring for 15 minutes, and then add 2.5mL of ethyl titanate (TEOT) dropwise to form Ti 4+-Citrate complex, continue stirring for 30 minutes to form a homogeneous precursor solution, denoted as solution B; slowly add solution B dropwise to solution A at a rate of 1 mL / min while stirring, and continue stirring in a 45°C water bath for 12 hours after the addition is complete, so that Ti 4+ Slow hydrolysis and directional deposition of a doped TiO2 coating layer on the Si@PDA surface were achieved. After the reaction was complete, the sample was centrifuged at 8000 rpm and washed twice each with anhydrous ethanol and deionized water. The precipitated sample was then placed in a vacuum oven and dried and aged at 60°C for 12 hours to obtain the Si@PDA@TiO2 composite material.

[0056] (4) The Si@PDA@TiO2 composite material was mixed with a carbon source solution (10wt% glucose solution) and mixed evenly (the mass ratio of glucose to Si@C@TiO2 was 1:1). After spray drying (the spray feed temperature was 240℃ and the outlet temperature was controlled at 105℃), a carbon source uniformly coated particle precursor was obtained. Then, it was heat-treated at 800℃ for 2 hours under an argon atmosphere at a rate of 5℃ / min to finally obtain the Si@C@TiO2@C composite material.

[0057] Example 2

[0058] A method for preparing a multilayer core-shell structured silicon-carbon anode material includes the following steps:

[0059] (1) Take coarse silicon powder (D50=2μm, D90=3μm) for photovoltaic industry and calcine it at 700℃ for 2 hours in an argon atmosphere; then add the calcined silicon particles to 0.5mol / L hydrochloric acid solution for acid leaching to remove impurities; then wash it repeatedly with deionized water and ethanol, and dry it under vacuum at 60℃ for 12 hours; add the above silicon particles to ethanol (the mass ratio of silicon to ethanol is 1:20 / 3), treat it with an ultrasonic disperser for 30 minutes, and then ball mill it (the dispersant is PVP, and the amount added is 2% of the mass of coarse silicon powder) at a speed of 400rpm for 2 hours to obtain nano-sized active silicon particles (particle size is 100-500nm).

[0060] (2) Take 0.5g of nano-sized active silicon particles and disperse them in 100mL of Tris-HCl buffer (pH≈8.5), add 1g of dopamine hydrochloride, stir at room temperature for 24 hours to obtain Si@PDA intermediate;

[0061] (3) Add 0.5g of Si@PDA intermediate powder to a beaker containing 30mL of anhydrous ethanol and 0.3mL of deionized water, and sonicate for 15 minutes to obtain a uniform suspension, which is denoted as solution A; add 30mL of anhydrous ethanol and 0.8g of citric acid to another beaker, stir for 5 minutes, then add 20mg of Ni(NO3)2·6H2O, continue stirring for 15 minutes, and then add 2.5mL of ethyl titanate (TEOT) dropwise to form Ti 4+ -Citrate complex, continue stirring for 30 minutes to form a homogeneous precursor solution, denoted as solution B; slowly add solution B dropwise to solution A at a rate of 1 mL / min while stirring, and continue stirring in a 45°C water bath for 12 hours after the addition is complete, so that Ti 4+ Slow hydrolysis and directional deposition of a doped TiO2 coating layer on the Si@PDA surface were achieved. After the reaction was complete, the sample was centrifuged at 8000 rpm and washed twice each with anhydrous ethanol and deionized water. The precipitated sample was then placed in a vacuum oven and dried and aged at 60°C for 12 hours to obtain the Si@PDA@TiO2 composite material.

[0062] (4) The Si@PDA@TiO2 composite material was mixed with a carbon source solution (10wt% sucrose solution) and mixed evenly (the mass ratio of sucrose to Si@C@TiO2 was 2:1). After spray drying (the spray feed temperature was 230℃ and the outlet temperature was controlled at 100℃), a carbon source uniformly coated particle precursor was obtained. Then, it was heat-treated at 800℃ for 2 hours under an argon atmosphere at a rate of 2℃ / min to finally obtain the Si@C@TiO2@C composite material.

[0063] Example 3

[0064] A method for preparing a multilayer core-shell structured silicon-carbon anode material includes the following steps:

[0065] (1) Take coarse silicon powder (D50=2μm, D90=3μm) for photovoltaic industry and calcine it at 800℃ for 2 hours in an argon atmosphere; then add the calcined silicon particles to a 1mol / L hydrochloric acid solution for acid leaching to remove impurities; then wash it repeatedly with deionized water and ethanol, and dry it under vacuum at 60℃ for 12 hours; add the above silicon particles to ethanol (the mass ratio of silicon to ethanol is 1:20 / 3), treat it with an ultrasonic disperser for 30 minutes, and then ball mill it (the dispersant is PVP, and the amount added is 2% of the mass of coarse silicon powder) at a speed of 400 rpm for 2 hours to obtain nano-sized active silicon particles;

[0066] (2) Take 0.5g of the above-mentioned nano-sized active silicon particles passing through 200 mesh and disperse them in 100mL Tris-HCl buffer (pH≈8.5), add 0.5g of dopamine hydrochloride, stir at room temperature for 24 hours to obtain Si@PDA intermediate;

[0067] (3) Add 0.5g of Si@PDA intermediate powder to a beaker containing 30mL of anhydrous ethanol and 0.2mL of deionized water, and sonicate for 15 minutes to obtain a uniform suspension, which is denoted as solution A; add 30mL of anhydrous ethanol and 1.0g of citric acid to another beaker, stir for 5 minutes, then add 20mg of Ni(NO3)2·6H2O, continue stirring for 15 minutes, and then add 3mL of ethyl titanate (TEOT) dropwise to form Ti 4+ -Citrate complex, continue stirring for 30 minutes to form a homogeneous precursor solution, denoted as solution B; slowly add solution B dropwise to solution A at a rate of 1 mL / min while stirring, and continue stirring in a 45°C water bath for 12 hours after the addition is complete, so that Ti 4+ Slow hydrolysis and directional deposition of a doped TiO2 coating layer on the Si@PDA surface were achieved. After the reaction was complete, the sample was centrifuged at 8000 rpm and washed twice each with anhydrous ethanol and deionized water. The precipitated sample was then placed in a vacuum oven and dried and aged at 60°C for 12 hours to obtain the Si@PDA@TiO2 composite material.

[0068] (4) The Si@PDA@TiO2 composite material was mixed and homogenized with a carbon source solution (15wt% sucrose solution) (the mass ratio of sucrose to Si@C@TiO2 was 3:1). After spray drying (the spray feed temperature was 240℃ and the outlet temperature was controlled at 105℃), a carbon source uniformly coated particle precursor was obtained. Then, it was heat-treated at 800℃ for 2 hours under an argon atmosphere at a rate of 2℃ / min to finally obtain the Si@C@TiO2@C composite material.

[0069] Comparative Example 1

[0070] The difference between this comparative example and Example 1 is that the nano-silicon is not coated or doped, thus remaining as nano-silicon. Its preparation steps are only step (1) of Example 1, specifically:

[0071] (1) Take coarse silicon powder (D50=2μm, D90=3μm) from the photovoltaic industry and calcine it at 800℃ for 2 hours in an argon atmosphere; then add the calcined silicon particles to a 1mol / L hydrochloric acid solution for acid leaching to remove impurities; then wash it repeatedly with deionized water and ethanol, and dry it under vacuum at 60℃ for 12 hours; add the above silicon particles to ethanol (the mass ratio of silicon to ethanol is 1:20 / 3), treat it with an ultrasonic disperser for 30 minutes, and then ball mill it (the dispersant is PVP, and the amount added is 2% of the mass of the coarse silicon powder) at a speed of 400 rpm for 2 hours to obtain nano-sized active silicon particles (particle size is 100-500nm).

[0072] Comparative Example 2

[0073] The difference between this comparative example and Example 1 is that the nano-silicon only coats the inner carbon layer, and its preparation method is as follows:

[0074] A method for preparing a multilayer core-shell structured silicon-carbon anode material includes the following steps:

[0075] (1) Take coarse silicon powder (D50=2μm, D90=3μm) for photovoltaic industry and calcine it at 800℃ for 2 hours in an argon atmosphere; then add the calcined silicon particles to a 1mol / L hydrochloric acid solution for acid leaching to remove impurities; then wash it repeatedly with deionized water and ethanol, and dry it under vacuum at 60℃ for 12 hours; add the above silicon particles to ethanol (the mass ratio of silicon to ethanol is 1:20 / 3), treat it with an ultrasonic disperser for 30 minutes, and then ball mill it (the dispersant is PVP, and the amount added is 2% of the mass of coarse silicon powder) at a speed of 400 rpm for 2 hours to obtain nano-sized active silicon particles (particle size is 100-500nm).

[0076] (2) Disperse 0.5g of nano-sized active silicon particles in 100mL of Tris-HCl buffer (pH≈8.5), add 0.5g of dopamine hydrochloride, and stir at room temperature for 24 hours to obtain Si@PDA intermediate;

[0077] (3) 0.5g Si@PDA was heat-treated at 800℃ for 2 hours under an argon atmosphere at a rate of 5℃ / min to obtain Si@C composite material.

[0078] Comparative Example 3

[0079] The difference between this comparative example and Example 1 is that it does not have an outer carbon coating, and its preparation method is as follows:

[0080] (1) Take coarse silicon powder (D50=2μm, D90=3μm) for photovoltaic industry and calcine it at 800℃ for 2 hours in an argon atmosphere; then add the calcined silicon particles to a 1mol / L hydrochloric acid solution for acid leaching to remove impurities; then wash it repeatedly with deionized water and ethanol, and dry it under vacuum at 60℃ for 12 hours; add the above silicon particles to ethanol (the mass ratio of silicon to ethanol is 1:20 / 3), treat it with an ultrasonic disperser for 30 minutes, and then ball mill it (the dispersant is PVP, and the amount added is 2% of the mass of coarse silicon powder) at a speed of 400 rpm for 2 hours to obtain nano-sized active silicon particles (particle size is 100-500nm).

[0081] (2) Disperse 0.5g of nano-sized active silicon particles in 100mL of Tris-HCl buffer (pH≈8.5), add 0.5g of dopamine hydrochloride, and stir at room temperature for 24 hours to obtain Si@PDA intermediate;

[0082] (3) Add 0.5g of Si@PDA intermediate powder to a beaker containing 30mL of anhydrous ethanol and 0.2mL of deionized water, and sonicate for 15 minutes to obtain a uniform suspension, which is denoted as solution A; add 30mL of anhydrous ethanol and 1.0g of citric acid to another beaker, stir for 5 minutes, then add 20mg of Ni(NO3)2·6H2O, continue stirring for 15 minutes, and then add 2.5mL of ethyl titanate (TEOT) dropwise to form Ti 4+ -Citrate complex, continue stirring for 30 minutes to form a homogeneous precursor solution, denoted as solution B; slowly add solution B dropwise to solution A at a rate of 1 mL / min while stirring, and continue stirring in a 45°C water bath for 12 hours after the addition is complete, so that Ti 4+ Slow hydrolysis and directional deposition of a doped TiO2 coating layer on the Si@PDA surface were achieved. After the reaction was complete, the sample was centrifuged at 8000 rpm and washed twice each with anhydrous ethanol and deionized water. The precipitated sample was then placed in a vacuum oven and dried and aged at 60°C for 12 hours to obtain the Si@PDA@TiO2 composite material.

[0083] (4) The Si@PDA@TiO2 composite material was heat-treated at 800℃ for 2 hours under an argon atmosphere at a rate of 5℃ / min to obtain the Si@C@TiO2@C composite material.

[0084] Comparative Example 4

[0085] The difference between this comparative example and Example 1 is that no dopant (Ni(NO3)2·6H2O) is added in step (3), while the other steps and parameters are the same as in Example 1.

[0086] Comparative Example 5

[0087] The difference between this comparative example and Example 1 is that no complexing agent (citric acid) is added in step (3), while the other steps and parameters are the same as in Example 1.

[0088] Comparative Example 6

[0089] The difference between this comparative example and Example 1 is as follows: Step (2) involves mixing and homogenizing nano-sized active silicon particles with a carbon source solution (10wt% glucose solution) (the mass ratio of glucose to Si@C@TiO2 is 1:1), followed by spray drying (spray feed temperature is 240℃, and outlet temperature is controlled at 105℃) to obtain carbon source-coated silicon particles, i.e., the intermediate. Other steps and parameters are the same as in Example 1.

[0090] Performance testing and results analysis:

[0091] To verify the structural composition and phase distribution of the Si@C@TiO2@C multilayer core-shell composite material in this invention, the composite material prepared in Example 1 was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results are as follows: Figures 1-3 As shown. By Figure 1 It can be seen that the main diffraction peaks of the composite material prepared in Example 1 can be attributed to silicon (Si), rutile titanium dioxide (TiO2), and nickel (Ni). The sample exhibits strong diffraction peaks at 2θ positions (28.4°, 47.3°, 56.1°, and 69.1°), indicating that the silicon core maintains a good crystal structure and is the main electrochemically active material. Multiple clear diffraction peaks appear at positions (27.4°, 36.1°, 41.2°, and 54.3°), proving that the TiO2 coating layer has completed crystallization and exists in the more thermally stable rutile form. Furthermore, weak diffraction peaks can be observed at 44.5°, 51.8°, and 76.4°, attributed to metallic Ni, indicating that some Ni is doped into the TiO2 lattice, while some nickel exists in elemental form. This structure is beneficial for improving the interfacial integrity and cycle stability of the coating layer. Figure 2 It can be seen that the composite material prepared in Example 1 exhibits a near-spherical aggregated structure with a relatively uniform particle size distribution and a rough surface, demonstrating typical characteristics of secondary particle polymerization. This indicates that each coating layer has a complete structure and is uniformly distributed. Figure 3 It can be seen that the composite particles corresponding to the composite material prepared in Example 1 are composed of a core-shell structure; the center is a crystalline silicon core with clearly distinguishable lattice fringes; the outer periphery is continuously coated with two amorphous layers of different gray levels; the inner amorphous layer is nitrogen-doped carbon (C) formed by dopamine self-polymerization, the middle is a continuous and uniform TiO2 coating layer, and the outermost layer is an outer carbon shell after spray carbonization. The whole structure presents a multi-layered coating structure of Si core / C / TiO2 / C, and the interfaces between each layer are clear and the structure is distinct. This indicates that the coating reaction process is well controlled and the material layers are stable, providing a structural basis for constructing a stable conductive framework and buffering silicon volume expansion.

[0092] The Si@C@TiO2@C composite material prepared in Example 1 was analyzed by energy-dispersive X-ray spectroscopy (EDS), and the results are as follows: Figure 4 As shown. By Figure 4 The EDS elemental distribution results further confirm the core-shell structure of the material: Si is concentrated in the core region of the particle, Ti is uniformly coated in the outer intermediate layer, and carbon exhibits a clear "double-layer distribution" trend, consistent with the double-carbon layer structure observed in the TEM image. This result indicates that both the PDA carbon layer and the outer carbon source achieve effective layered coating, with TiO2 positioned between the two carbon layers, forming a complete buffer and conductive composite structure.

[0093] The materials prepared in Examples 1-3 and Comparative Examples 1-6 were used as negative electrodes, lithium sheets as positive electrodes, SA as binders, and SuperP as conductive agents. A coin cell was fabricated with a ratio of active component (silicon) of the negative electrode to binder to conductive agent of 6:2:2 (mass ratio). The charge-discharge performance of the prepared cells was tested, and the results are shown in Table 1 below. Some charge-discharge performance parameters are shown in Table 1. Figures 5-10 As shown.

[0094] Table 1. Charge-discharge performance of lithium-ion batteries prepared in Examples 1-3 and Comparative Examples 1-6

[0095]

[0096] From Table 1, Figure 5 and Figure 8 The comparison shows that the first-cycle discharge specific capacity and first-cycle coulombic efficiency of Example 1 are lower than those of Comparative Example 1, while the discharge specific capacity and capacity retention rate after 100 cycles are higher than those of Comparative Example 1. This indicates that the multilayer core-shell structure of the silicon-carbon anode converts the high reversible capacity of the first cycle into sustainable output. Because the multilayer core-shell structure effectively controls the lithium insertion depth and volume expansion of silicon, the first-cycle capacity and first-cycle coulombic efficiency (ICE) of Example 1 are slightly lower than those of the bare silicon system of Comparative Example 1. However, it forms a dense and stable SEI and a solid conductive framework, which significantly suppresses pulverization and side reactions. Although Comparative Example 1 has a high first-cycle capacity, it suffers from interface instability and rapid cycle decay, ultimately resulting in long-term cycle performance that is far inferior to that of Example 1.

[0097] From Table 1, Figure 5 and Figure 9 The comparison shows that Example 1 has higher initial discharge specific capacity, initial coulombic efficiency, discharge specific capacity after 100 cycles, and capacity retention after 100 cycles compared to Comparative Example 2. This indicates that adding Ni-TiO2 doping and an outer carbon layer to the PDA carbon layer improves interface stability, conductivity, and mechanical buffering, thereby significantly improving long-cycle capacity and capacity retention while maintaining a high initial capacity.

[0098] From Table 1, Figure 5 and Figure 10 The comparison shows that Example 1 exhibits significantly higher initial discharge capacity, initial coulombic efficiency, discharge capacity after 100 cycles, and capacity retention after 100 cycles compared to Comparative Example 3. This indicates that the outer carbon coating is crucial for enhancing material conductivity, improving ICE (electrical efficiency), suppressing side reactions, stabilizing the structure, and extending cycle life. The lack of an outer carbon coating significantly weakens long-cycle performance, while the multi-layer core-shell structure can achieve high initial capacity and excellent capacity retention.

[0099] As shown in Table 1, Example 1 and Comparative Example 4 exhibit higher first-cycle discharge specific capacity, first-cycle coulombic efficiency, discharge specific capacity after 100 cycles, and capacity retention after 100 cycles compared to Comparative Example 4. This indicates that while Ni doping has little impact on first-cycle performance, it significantly improves long-cycle capacity and retention. Ni doping enhances the conductivity and buffering capacity of TiO2 by introducing oxygen vacancies and regulating electronic structure, thereby strengthening interface stability and suppressing long-term degradation.

[0100] As shown in Table 1, Example 1 and Comparative Example 5 exhibit significantly higher first-cycle discharge specific capacity, first-cycle coulombic efficiency, discharge specific capacity after 100 cycles, and capacity retention rate after 100 cycles compared to Comparative Example 5. This indicates that citric acid complexation is crucial for the uniform deposition and interface stability of the TiO2 shell. The absence of a complexing agent leads to shell discontinuity, severe interface exposure, coating failure, and intensified interface reactions, thereby significantly reducing cycle life and capacity retention rate.

[0101] As shown in Table 1, Example 1 and Comparative Example 6 have similar initial cycle capacity and coulombic efficiency, but significantly higher long-cycle capacity and capacity retention. This indicates that the inner carbon layer of the PDA not only improves the quality of the TiO2 shell but also significantly enhances interfacial stability and long-cycle performance; although the outer carbon shell formed by glucose can provide conductivity and protection, it cannot replace the key role of the PDA in interfacial regulation when used alone.

[0102] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles 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 multilayer core-shell structured silicon-carbon anode material, characterized in that, Includes the following steps: S1. After calcining, acid leaching to remove impurities, and vacuum drying, crude silicon powder is added to solvent A and subjected to ultrasonic dispersion treatment, followed by ball milling, filtration, and drying to obtain nano-sized active silicon particles. S2. The nanoscale active silicon particles are dispersed in Tris buffer solution, dopamine hydrochloride is added, and the reaction is carried out at room temperature to form a coating layer. After filtration and drying, Si@PDA intermediate is obtained. S3. The Si@PDA intermediate is uniformly dispersed in solvent B to obtain a uniform suspension; a complexing agent and a dopant are added sequentially to solvent C and mixed well, then a titanium source is added dropwise and reacted to obtain a uniform precursor solution; under stirring, the uniform precursor solution is slowly added dropwise to the uniform suspension, and the mixture is heated and stirred in a water bath, then centrifuged, washed, and dried to obtain the Si@PDA@TiO2 composite material; S4. The Si@PDA@TiO2 composite material is mixed and homogenized with a carbon source solution, and then spray-dried to obtain a particle precursor uniformly coated with carbon source. The precursor is then carbonized in a vacuum or inert atmosphere to obtain a silicon-carbon anode material with a Si@C@TiO2@C multilayer core-shell structure.

2. The method for preparing the multilayer core-shell structured silicon-carbon anode material according to claim 1, characterized in that, In step S1, the calcination temperature is 600-800℃ and the time is 1-2h; the acid includes at least one of hydrochloric acid, nitric acid, and hydrofluoric acid, with a concentration of 0.1-1mol / L; the solvent A includes at least one of ethanol and isopropanol, and the mass ratio of the crude silica powder to solvent A is 1:5-15.

3. The method for preparing the multilayer core-shell structured silicon-carbon anode material according to claim 1, characterized in that, In step S1, a dispersant is added during the ball milling process, and the mass ratio of the dispersant to the coarse silica powder is 0.1-5:

100.

4. The method for preparing the multilayer core-shell structured silicon-carbon anode material according to claim 1, characterized in that, In step S2, after the nanoscale active silicon particles are dispersed in Tris buffer, the dispersion concentration of the nanoscale active silicon particles is 1-5 mg / mL; the mass ratio of the nanoscale active silicon particles to dopamine hydrochloride is 1:1-2.

5. The method for preparing the multilayer core-shell structured silicon-carbon anode material according to claim 1, characterized in that, In step S3, solvent B includes anhydrous ethanol and deionized water, and solvent C is anhydrous ethanol; the complexing agent includes at least one of citric acid, acetylacetone, ethylenediaminetetraacetic acid, and tartaric acid; the dopant is a salt corresponding to a dopant element, and the dopant element includes at least one of Nb, Fe, Ni, V, Co, Y, and La; the titanium source includes at least one of tetrabutyl titanate, isopropyl titanate, and ethyl titanate; the mass ratio of the complexing agent to the dopant is 8-12:0.1-0.2; the mass ratio of the complexing agent to the Si@PDA intermediate is 8-12:5; and the mass ratio of the Si@PDA intermediate to the volume of the titanium source is 0.125-0.5 g / mL.

6. The method for preparing the multilayer core-shell structured silicon-carbon anode material according to claim 1, characterized in that, In step S3, the temperature of the water bath heating and stirring reaction is 25-50℃, and the time is 6-12h.

7. The method for preparing the multilayer core-shell structured silicon-carbon anode material according to claim 1, characterized in that, In step S4, the carbon source includes at least one of glucose and sucrose; the concentration of the carbon source in the carbon source solution is 5-15 wt%; and the mass ratio of the carbon source to the Si@PDA@TiO2 composite material is 1-3:

1.

8. The method for preparing the multilayer core-shell structured silicon-carbon anode material according to claim 1, characterized in that, In step S4, the spray feed temperature of the spray drying is 220-240℃, and the outlet temperature is 100-110℃; the inert atmosphere includes at least one of argon and nitrogen; the carbonization treatment temperature is 600-800℃, and the time is 1-2h; the TiO2 in the Si@C@TiO2@C multilayer core-shell silicon-carbon anode material is at least one of anatase, rutile, or amorphous structure.

9. A silicon-carbon anode material with a multilayer core-shell structure, characterized in that, The multi-layer core-shell silicon-carbon anode material is prepared by the preparation method of the multi-layer core-shell silicon-carbon anode material according to any one of claims 1-8.

10. The application of the multilayer core-shell structured silicon-carbon anode material according to claim 9 in lithium-ion batteries.

Images