Lignin-derived carbon-tiO2 double-coated silicon-carbon material, and preparation method and application thereof

Abstract

This invention discloses a lignin-derived carbon-TiO2 dual-coated silicon-carbon material, its preparation method, and its applications, belonging to the field of lithium-ion battery anode materials. This invention achieves synergistic suppression of the volume expansion of nano-silicon through the construction of a core-heterogeneous shell multi-level structure. The SiO2 transition layer, acting as a gradient modulus buffer medium, effectively dissipates the cyclic strain of the silicon core and ensures interfacial mechanical integrity through Si-O-C covalent bonding, avoiding interfacial failure during long-term cycling. The inner heterogeneous shell layer (amorphous carbon / amorphous TiO2 composite) combines stress release and electron conduction functions, constructing a long-range conductive network while maintaining structural stability. The outermost TiO2 protective shell utilizes its low strain and structural stability characteristics to alleviate stress concentration and inhibit silicon particle pulverization, while reducing interfacial side reactions and maintaining effective lithium-ion transport. This multi-level design, through the synergistic coupling of mechanical buffering and electrochemical kinetics, endows the composite anode with excellent cycling stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode materials, and in particular to a lignin-derived carbon-TiO2 double-coated silicon-carbon material, its preparation method, and its application. Background Technology

[0002] Currently, with the rapid growth of renewable energy sources such as solar and wind power, the demand for more advanced energy storage devices is becoming increasingly urgent. Furthermore, the expanding demand for consumer electronics and the development of the new energy vehicle industry are also driving the battery industry towards improvements in energy density, long cycle life, and environmental friendliness. Among many anode materials, silicon (Si) stands out due to its superior theoretical specific capacity (e.g., Li). 4.4 Si has 4200 mAh g -1 Its specific capacity is approximately ten times that of traditional commercial graphite, it is abundant in the Earth's crust, environmentally friendly, and has a suitable operating potential (0.4 V vs. Li). + Silicon-based anodes have emerged as a promising alternative to graphite, particularly due to their high performance (e.g., Li). However, silicon-based anodes still face numerous challenges in practical applications, including volume expansion during charging and discharging, fragile and pulverized material structures, poor intrinsic conductivity, and instability of the solid electrolyte interphase (SEI) film. These problems severely restrict their commercialization.

[0003] To address these issues, researchers have proposed improvements such as nanostructure design, surface modification, and composite structure design, but further improvements are still possible. 1) Nanoscaled silicon materials: By nanoscaled silicon nanoparticles, nanowires, nanosheets, nanotubes, and porous nanostructures, the small size effect can alleviate volumetric strain. For example, one study prepared a sealed tubular silicon nanostructure using chemical vapor deposition combined with a zinc oxide template, achieving an initial discharge capacity of 3860 mAh g⁻¹. -1 It exhibits a high initial coulombic efficiency (>85%). However, when the silicon size decreases to below 100 nm, the contact area with the electrolyte increases due to the smaller material size, resulting in rapid thickening of the SEI film and a sharp decrease in capacity retention. Simultaneously, nanoscale silicon particles agglomerate due to electrostatic interactions, forming micron-sized silicon, thus losing the advantage of its smaller size. 2) Surface modification: Constructing a protective layer on the silicon surface (using methods such as carbon coating, oxide coating, polymer coating, or pre-lithiation) forms a dense and flexible interface layer, which helps maintain structural integrity and provides an electron conduction pathway, isolates electrolyte contact, and stabilizes the SEI. Researchers have synthesized a cobalt-nitrogen co-doped double-carbon coated silicon / carbon / metal-organic framework multinuclear yolk shell structure mesoporous material using the sol-gel method and metal-organic framework self-templating method, achieving a high initial coulombic efficiency (>85%). -1 After more than 300 cycles, the energy content remained at 852 mAh g.-1 The reversible capacity of the Li₂O₃ coating is high. However, if the coating is too thick (>10 nm), it will increase the Li₂O₃'s capacity. + Transport resistance reduces reversible capacity. 3) Composite structure design: Combining silicon with carbon materials (graphite, graphene, carbon nanotubes), conductive polymers, metals / metal oxides, etc., to construct core-shell, porous, three-dimensional network structures, simultaneously addressing mechanical, conductive, and interface issues; the carbon matrix provides elastic buffering and a continuous conductive network; silicon serves as the main capacity carrier for lithium storage; and the optimized interface structure helps regulate SEI composition and lithium-ion transport kinetics. However, the improved silicon-carbon composite materials still cannot effectively limit the volume expansion of nano-silicon during cycling, and the outer carbon layer is at risk of cracking, requiring further improvement. Summary of the Invention

[0004] The purpose of this invention is to provide a lignin-derived carbon-TiO2 dual-coated silicon-carbon material, its preparation method, and its applications, to solve the aforementioned problems in the background art. This invention uses in-situ coordination-carbonization technology as its core, constructing a core-heterogeneous shell structure with a synergistic effect of "SiO2 transition buffer—inner flexible carbon / TiO2 heterogeneous buffer—outer rigid TiO2 protective constraint." The SiO2 transition layer, acting as an interface adjustment layer between the silicon core and the heterogeneous shell, can alleviate interface modulus mismatch and disperse volumetric strain during cycling. The inner heterogeneous shell (amorphous carbon / amorphous TiO2) combines stress release and electron conduction functions, while the outermost TiO2 protective shell provides mechanical constraint through low strain and high structural stability, alleviating stress concentration and inhibiting silicon particle pulverization, while simultaneously stabilizing the interface and maintaining effective lithium-ion transport. By leveraging the synergistic effect of the SiO2 transition layer and the inner / outer TiO2 layers, a gradient stress regulation system of "interface buffering - flexible pressure relief - rigid constraint" was constructed, realizing the synergistic coupling of stress buffering and electrochemical kinetics, and breaking through the technical bottleneck of the cycle stability of silicon-carbon anodes from the intrinsic structural level of the material.

[0005] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention is to provide a method for preparing a lignin-derived carbon-TiO2 double-coated silicon-carbon material, comprising the following steps: Nano-silicon and hexadecyltrimethylammonium bromide (CTAB) were mixed in water to obtain a modified nano-silicon solution; Lignin is dissolved in water and then added to the modified nano-silicon solution for lignin coating treatment. Subsequently, solid-liquid separation is performed to obtain lignin-coated silicon (when the lignin is preferably sodium lignin sulfonate, it is denoted as Si@LS). Tetrabutyl titanate (TBOT) and the lignin-coated silicon were mixed in isopropanol to obtain a mixture, which was then subjected to a hydrothermal reaction, followed by solid-liquid separation and high-temperature calcination to obtain the lignin-derived carbon-TiO2 double-coated silicon-carbon material (Si@C-TiO2 composite material).

[0006] Preferably, the mass ratio of the nano-silicon to hexadecyltrimethylammonium bromide is 10~1:1; the particle size of the nano-silicon is 10~300 nm; The lignin is sodium lignin sulfonate and / or ammoniated lignin.

[0007] Preferably, the mixing time is 5 to 60 minutes.

[0008] Preferably, the mass ratio of lignin to nano-silicon is 10 to 1:1.

[0009] Preferably, the lignin coating treatment takes 1 to 36 hours and is carried out at a temperature of 15 to 45°C.

[0010] Preferably, the volume ratio of isopropanol to tetrabutyl titanate is 10~150:1~12; The mass concentration of the lignin-coated silica in the mixture is 0.32~2.81 wt%; the mass concentration of the tetrabutyl titanate in the mixture is 3.08~27.65 wt%.

[0011] Preferably, the hydrothermal reaction is carried out at a temperature of 40-200℃ for a time of 1-24 hours.

[0012] Preferably, the high-temperature calcination temperature is 500~650℃ and the time is 1~10 h.

[0013] The second technical solution of the present invention provides a lignin-derived carbon-TiO2 double-coated silicon-carbon material obtained according to the above preparation method.

[0014] The third technical solution of the present invention provides an application of the above-mentioned lignin-derived carbon-TiO2 double-coated silicon-carbon material in the field of battery anode materials.

[0015] Preferably, the battery anode material is a lithium-ion battery anode material.

[0016] The beneficial technical effects of the present invention are as follows: This invention designs a lignin-derived carbon-TiO2 dual-coated silicon-carbon material (Si@C-TiO2 composite material). By constructing a core-heterogeneous shell structure, a SiO2 transition layer is introduced between the nano-silicon and the heterogeneous shell to alleviate interfacial modulus mismatch and buffer volumetric strain during cycling. The lignin-derived carbon layer serves as an elastic buffer matrix and electron conduction pathway, while the inner amorphous TiO2 component acts as a rigid constraint framework and interfacial stabilizing layer. Together, they form a continuous heterogeneous shell, effectively suppressing the volume expansion of nano-silicon and efficiently dissipating cyclic stress. Furthermore, the outermost TiO2 protective layer, with its low strain and high structural stability, further constrains the volume changes of silicon particles during charge and discharge, reducing the risk of silicon particle breakage and pulverization. Simultaneously, it stabilizes the electrode interface and maintains effective lithium-ion transport, thereby improving the material's structural stability and cycle performance. This structural design solves key technical challenges at the intrinsic material level, such as the easy pulverization of silicon-carbon anodes, active material shedding, and rapid capacity decay. The assembled lithium-ion battery exhibits excellent long-cycle stability and has clear prospects for industrial application.

[0017] The preparation method defined in this invention is simple, with mild reaction conditions, low calcination temperature, and controllable energy consumption. The main raw materials used are widely available, green, and inexpensive, and the entire process does not require the use of hazardous chemicals or special equipment. It has the characteristics of low cost and easy scale-up production, providing a promising solution for the commercial development of high-performance silicon-carbon anode materials. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 The image shows the SEM image of the Si@C material prepared in Comparative Example 2.

[0020] Figure 2 The image shows a SEM image of the Si@C-TiO2 composite material prepared in Example 1.

[0021] Figure 3 This is a TEM image of the Si@C-TiO2 composite material prepared in Example 1.

[0022] Figure 4 This is a high-magnification TEM image of the Si@C-TiO2 composite material prepared in Example 1.

[0023] Figure 5The image shows the XRD pattern of the Si@C-TiO2 composite material prepared in Example 1.

[0024] Figure 6 The coin cell assembled from the Si@C-TiO2 composite material of Example 1 operates at a current density of 1 A g. -1 The long-cycle performance graph. Detailed Implementation

[0025] 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. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0026] Furthermore, regarding the 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. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] 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. It should be noted that any aspects of this invention not described in detail are conventional practices in the art and are not the focus of this invention.

[0028] The terms “comprising,” “including,” “having,” “containing,” etc., used in this invention are all open-ended terms, meaning that they include but are not limited to.

[0029] This invention provides a method for preparing a lignin-derived carbon-TiO2 dual-coated silicon-carbon material, comprising the following steps: (1) Add nano-silicon and hexadecyltrimethylammonium bromide (CTAB) to water and mix them evenly by ultrasonication to obtain a modified nano-silicon solution with a positive charge on the surface; After this modification, the agglomeration of nano-silicon can be effectively reduced by utilizing the repulsive effect between charges; (2) Dissolve lignin (preferably sodium lignin sulfonate) in water, and then add it to the modified nano-silicon solution for lignin coating treatment. Use electrostatic adsorption to adsorb lignin onto the surface of the modified nano-silicon. After centrifugation and drying, lignin-coated silicon (Si@LS) is obtained. Sodium lignosulfonate has good water solubility and its aqueous solution is negatively charged. During the electrostatic adsorption process, it can achieve complete coating of nano-silicon and is conducive to anchoring the growth sites of TiO2 on the sodium lignosulfonate framework, thereby enhancing the interaction between sodium lignosulfonate and TiO2. (3) The Si@LS was dispersed in isopropanol solution, tetrabutyl titanate (TBOT) was added dropwise and stirring was continued to obtain a mixture. Then it was transferred to a hydrothermal reactor for hydrothermal reaction. After centrifugation, washing and drying, the obtained solid powder was calcined at high temperature to obtain the lignin-derived carbon-TiO2 double-coated silicon-carbon material (Si@C-TiO2 composite material).

[0030] During stirring, the hydroxyl groups (-OH) and sulfonic acid groups (-SO3H) on sodium lignin sulfonate act as coordination sites, undergoing in-situ coordination reactions with TBOT to form CO-Ti bonds. This induces in-situ uniform nucleation and confined growth of amorphous TiO2 on the lignin framework. After a one-step high-temperature carbonization, a core-heterogeneous shell composite material is constructed in situ. During carbonization, the oxygen-containing components in lignin promote the in-situ formation of a SiO2 transition layer on the silicon core surface to regulate interface matching and buffer cyclic volumetric strain. Simultaneously, the carbon layer formed by lignin carbonization significantly improves the electronic conductivity of the composite material and, synergistically with amorphous TiO2, constitutes a continuous heterogeneous shell layer that combines flexible buffering and rigid support. This effectively alleviates the volume changes and stress accumulation of nano-silicon during charge-discharge cycles. The outermost TiO2 protective shell further constrains the volume changes of silicon particles and stabilizes the electrode interface, thereby enhancing the structural stability and long-cycle performance of the composite anode material.

[0031] This invention modifies nano-silicon with CTAB to impart a positive charge to its surface, effectively mitigating nano-silicon agglomeration through the repulsion between charges. Then, sodium lignin sulfonate, with its excellent water solubility and negatively charged aqueous solution, is used for electrostatic adsorption, achieving complete coating of the nano-silicon and constructing an inner carbon conductive network. This network also helps to disperse stress generated during the volume expansion of the nano-silicon. Through hydrothermal reaction and subsequent carbonization, a SiO2 interface transition layer is formed between the silicon core and the heterogeneous shell, further constructing a continuous heterogeneous shell composed of lignin-derived carbon and amorphous TiO2. The SiO2 transition layer acts as an interface modulator and stress buffer, helping to alleviate interfacial stress between the silicon core and the outer shell. The lignin-derived carbon provides a continuous electron conduction pathway and flexible buffering effect, while the amorphous TiO2, as a structural reinforcing component, provides rigid support. Together, they maintain the structural integrity of the heterogeneous shell. Building upon this, the outermost TiO2 protective layer further constrains the volume changes of silicon particles during charging and discharging, and helps stabilize the electrode interface and reduce side reactions. Thus, it works synergistically with the SiO2 transition layer and the inner carbon / TiO2 heterogeneous shell to alleviate the volume expansion of silicon particles and the accumulation of cyclic stress, enhancing the structural stability and cycling performance of the composite material. The lithium-ion half-cell assembled from the Si@C-TiO2 composite material prepared using the above method exhibits excellent cycling stability.

[0032] Furthermore, the mass ratio of the nano-silicon to hexadecyltrimethylammonium bromide is 10 to 1:1, preferably 6 to 2:1, and more preferably 2:1.

[0033] Furthermore, the ultrasonic mixing time is 5 to 60 minutes, preferably 30 minutes.

[0034] Furthermore, the particle size of the nano-silicon is 10~300 nm, preferably 30~100 nm.

[0035] Furthermore, the lignin is sodium lignin sulfonate and / or ammoniated lignin, preferably one or both of sodium lignin sulfonate and ammoniated lignin.

[0036] Furthermore, the mass ratio of lignin to nano-silicon is 10 to 1:1, preferably 8 to 3:1, and more preferably 6:1.

[0037] Furthermore, the lignin coating treatment time is 1~36 h, preferably 24 h, and the temperature is 15~45℃, preferably 25℃. Furthermore, the volume ratio of isopropanol to tetrabutyl titanate is 10~150:1~12, preferably 20~80:2~8, and more preferably 40:6.

[0038] Furthermore, the mass concentration of Si@LS in the mixed solution is 0.32~2.81 wt%, preferably 0.58~1.81 wt%, and more preferably 1.06 wt%.

[0039] Furthermore, the mass concentration of the tetrabutyl titanate in the mixed solution is 3.08~27.65 wt%, preferably 5.98~20.30 wt%, and more preferably 16.04 wt%.

[0040] Furthermore, the temperature of the heating reaction is 40-200 ℃, preferably 80-180 ℃, more preferably 150 ℃; the time of the heating reaction is 1-24 h, preferably 2-12 h, more preferably 6 h.

[0041] Furthermore, the high-temperature calcination temperature is 500~650℃, preferably 550~650℃, more preferably 600℃; the high-temperature calcination time is 1~10 h, preferably 2~4 h, more preferably 3 h.

[0042] All raw materials used in the following embodiments and comparative examples of the present invention are commercially available products.

[0043] Example 1 A method for preparing a lignin-derived carbon-TiO2 dual-coated silicon-carbon material, comprising the following steps: (1) 0.4 g of nano-silicon (30 nm) and 0.2 g of CTAB were added to 120 mL of ultrapure water and sonicated at 25 °C for 30 min to obtain a modified nano-silicon solution with a positive charge on the surface.

[0044] (2) Dissolve 2.4 g LS in 40 mL of ultrapure water, then add it to the modified nano-silicon solution. Use the modified nano-silicon to electrostatically adsorb sodium lignosulfonate and let it stand at 25 °C for 24 h to adsorb. After centrifugation and drying, sodium lignosulfonate coated silicon (Si@LS) is obtained.

[0045] (3) 0.4 g of Si@LS material was dispersed in 40 mL of isopropanol, 6 mL of TBOT was added dropwise and stirring was continued to obtain a mixture. Then, it was transferred to a hydrothermal reactor and hydrothermally reacted at 150 °C for 6 h. After centrifugation, washing and drying, the obtained solid powder was placed in a tube furnace under N2 atmosphere and calcined at 600 °C for 3 h to obtain lignin-derived carbon-TiO2 double-coated silicon-carbon material (Si@C-TiO2 composite material).

[0046] Example 2 (Effect of Tetrabutyl Titanate Addition Amount) A method for preparing a lignin-derived carbon-TiO2 dual-coated silicon-carbon material, comprising the following steps: (1) 0.4 g of nano-silicon (30 nm) and 0.2 g of CTAB were added to 120 mL of ultrapure water and sonicated at 25 °C for 30 min to obtain a modified nano-silicon solution with a positive charge on the surface.

[0047] (2) Dissolve 2.4 g LS in 40 mL of ultrapure water, then add it to the modified nano-silicon solution. Use the modified nano-silicon to electrostatically adsorb sodium lignosulfonate and let it stand at 25 °C for 24 h to adsorb. After centrifugation and drying, sodium lignosulfonate coated silicon (Si@LS) is obtained.

[0048] (3) 0.4 g of Si@LS material was dispersed in 40 mL of isopropanol, 4 mL of TBOT was added dropwise and stirring was continued to obtain a mixture. Then, it was transferred to a hydrothermal reactor and hydrothermally reacted at 150 °C for 6 h. After centrifugation, washing and drying, the obtained solid powder was placed in a tube furnace under N2 atmosphere and calcined at 600 °C for 3 h to obtain lignin-derived carbon-TiO2 double-coated silicon carbon material (Si@C-TiO2 composite material).

[0049] Example 3 (Effect of Tetrabutyl Titanate Addition Amount) (1) 0.4 g of nano-silicon (30 nm) and 0.2 g of CTAB were added to 120 mL of ultrapure water and sonicated at 25 °C for 30 min to obtain a modified nano-silicon solution with a positive charge on the surface.

[0050] (2) Dissolve 2.4 g LS in 40 mL of ultrapure water, then add it to the modified nano-silicon solution. Use the modified nano-silicon to electrostatically adsorb sodium lignosulfonate and let it stand at 25 °C for 24 h to adsorb. After centrifugation and drying, sodium lignosulfonate coated silicon (Si@LS) is obtained.

[0051] (3) 0.4 g of Si@LS material was dispersed in 40 mL of isopropanol, 8 mL of TBOT was added dropwise and stirring was continued to obtain a mixture. Then, it was transferred to a hydrothermal reactor and hydrothermally reacted at 150 °C for 6 h. After centrifugation, washing and drying, the obtained solid powder was placed in a tube furnace under N2 atmosphere and calcined at 600 °C for 3 h to obtain lignin-derived carbon-TiO2 double-coated silicon-carbon material (Si@C-TiO2 composite material).

[0052] Example 4 (Effect of replacing sodium lignosulfonate with ammonia-oxidized lignin) (1) 0.4 g of nano-silicon (30 nm) and 0.2 g of CTAB were added to 120 mL of ultrapure water and sonicated at 25 °C for 30 min to obtain a modified nano-silicon solution with a positive charge on the surface.

[0053] (2) 2.4 g of ammonia-oxidized lignin (AOL) was dissolved in 40 mL of ultrapure water and then added to the modified nano-silicon solution. The modified nano-silicon was used to electrostatically adsorb the ammonia-oxidized lignin and allowed to stand at 25 °C for 24 h for adsorption. After centrifugation and drying, ammonia-oxidized lignin coated with silicon (Si@AOL) was obtained.

[0054] (3) 0.4 g of Si@AOL material was dispersed in 40 mL of isopropanol, 6 mL of TBOT was added dropwise and stirring was continued to obtain a mixture. Then, it was transferred to a hydrothermal reactor and hydrothermally reacted at 150 °C for 6 h. After centrifugation, washing and drying, the obtained solid powder was placed in a tube furnace under N2 atmosphere and calcined at 600 °C for 3 h to obtain lignin-derived carbon-TiO2 double-coated silicon-carbon material (Si@C-TiO2 composite material).

[0055] Comparative Example 1 (The effect of not coating nano-silicon) 0.4 g of nano-silicon (30 nm) and 0.2 g of CTAB were sequentially added to 120 mL of ultrapure water, and the mixture was sonicated at 25 °C for 30 min to obtain a modified nano-silicon solution with a positively charged surface. This solution was then centrifuged and dried to obtain surface-modified nano-silicon. No further coating was performed, and it was directly used as the negative electrode material for the battery.

[0056] Comparative Example 2 (Effect of not adding tetrabutyl titanate) (1) 0.4 g of nano-silicon (30 nm) and 0.2 g of CTAB were added to 120 mL of ultrapure water and sonicated at 25 °C for 30 min to obtain a modified nano-silicon solution with a positive charge on the surface.

[0057] (2) Dissolve 2.4 g LS in 40 mL of ultrapure water, then add it to the modified nano-silicon solution. Use the modified nano-silicon to electrostatically adsorb sodium lignosulfonate and let it stand at 25 °C for 24 h to adsorb. After centrifugation and drying, sodium lignosulfonate coated silicon (Si@LS) is obtained.

[0058] Then, the Si@LS material was calcined at 600 °C for 3 h in a tube furnace under a N2 atmosphere, and the resulting product was denoted as Si@C.

[0059] Comparative Example 3 (Effect of not adding sodium lignosulfonate) (1) 0.4 g of nano-silicon (30 nm) and 0.2 g of CTAB were added to 120 mL of ultrapure water, sonicated at 25 °C for 30 min, and then centrifuged and dried to obtain modified nano-silicon with positive charge on the surface.

[0060] (2) 0.4 g of modified nano-silicon material was dispersed in 40 mL of isopropanol, 6 mL of TBOT was added dropwise and stirring was continued to obtain a mixture. Then, it was transferred to a hydrothermal reactor and hydrothermally reacted at 150 °C for 6 h. After centrifugation, washing and drying, the obtained solid powder was placed in a tube furnace under N2 atmosphere and calcined at 600 °C for 3 h to obtain Si@TiO2 composite material.

[0061] Comparative Example 4 (Effect of glucose replacing sodium lignosulfonate) (1) 0.4 g of nano-silicon (30 nm) and 0.2 g of CTAB were added to 120 mL of ultrapure water and sonicated at 25 °C for 30 min to obtain a modified nano-silicon solution with a positive charge on the surface.

[0062] (2) Dissolve 2.4 g of glucose in 40 mL of ultrapure water, then add it to the modified nano-silicon solution, let it stand at 25 °C for 24 h for adsorption, and then centrifuge and dry to obtain glucose-coated silicon (Si@Glc).

[0063] (3) 0.4 g Si@Glc material was dispersed in 40 mL isopropanol, 6 mL TBOT was added dropwise and stirring was continued to obtain a mixture. Then the mixture was transferred to a hydrothermal reactor and hydrothermally reacted at 150 °C for 6 h. After centrifugation, washing and drying, the obtained solid powder was placed in a tube furnace under N2 atmosphere and calcined at 600 °C for 3 h to obtain glucose-derived carbon-TiO2 double-coated silicon-carbon material (Si@C-TiO2 composite material).

[0064] Comparative Example 5 (Effect of calcination temperature) (1) 0.4 g of nano-silicon (30 nm) and 0.2 g of CTAB were added to 120 mL of ultrapure water and sonicated at 25 °C for 30 min to obtain a modified nano-silicon solution with a positive charge on the surface.

[0065] (2) Dissolve 2.4 g LS in 40 mL of ultrapure water, then add it to the modified nano-silicon solution. Use the modified nano-silicon to electrostatically adsorb sodium lignosulfonate and let it stand at 25 °C for 24 h to adsorb. After centrifugation and drying, sodium lignosulfonate coated silicon (Si@LS) is obtained.

[0066] (3) 0.4 g of Si@LS material was dispersed in 40 mL of isopropanol, 6 mL of TBOT was added dropwise and stirring was continued to obtain a mixture. Then, it was transferred to a hydrothermal reactor and hydrothermally reacted at 150 °C for 6 h. After centrifugation, washing and drying, the obtained solid powder was placed in a tube furnace under N2 atmosphere and calcined at 700 °C for 3 h to obtain lignin-derived carbon-TiO2 double-coated silicon-carbon material (Si@C-TiO2 composite material).

[0067] Example 1 The materials prepared in Example 1 and Comparative Example 2 were used to test their morphology and size using a scanning electron microscope (SEM, Hitach SU8220). The results are shown in the figure. Figures 1-2 .

[0068] Figure 1 The image shows the SEM image of the Si@C material prepared in Comparative Example 2. As can be seen from the image, a lignin-carbon layer is coated on the surface of nano-silicon. The silicon particles are clearly dispersed and there is no obvious agglomeration. This indicates that lignin-derived carbon was successfully coated on the surface of nano-silicon through surface modification and electrostatic adsorption.

[0069] Figure 2 The image shows a SEM image of the Si@C-TiO2 composite material prepared in Example 1. As can be seen from the image, the Si@C-TiO2 composite material consists of relatively uniformly distributed spherical nanoparticles with a uniform coating layer. The complete core-shell structure effectively suppresses silicon volume expansion.

[0070] The internal structure of the material prepared in Example 1 was tested using a transmission electron microscope (TEM, Talos F200S), and the results are shown in the figure. Figure 3 , 4 As can be seen, a core-heterogeneous shell structure was successfully fabricated using Si@C-TiO2 composite material. The inner layer consists of a SiO2 transition layer and a continuous heterogeneous shell layer of lignin-derived carbon / amorphous TiO2. The SiO2 transition layer, located between the silicon core and the heterogeneous shell, acts as an interface modulus adjustment and stress buffer layer, mitigating interfacial modulus mismatch and dispersing volumetric strain during cycling. The lignin-derived carbon serves as an elastic buffer matrix and constructs a continuous electron transport pathway, while the amorphous TiO2 acts as a rigid reinforcing component, jointly maintaining the structural integrity of the heterogeneous shell. The outermost TiO2 protective shell utilizes its low strain and high structural stability to provide mechanical constraint, alleviating stress concentration and inhibiting silicon particle pulverization, while simultaneously stabilizing the interface and maintaining lithium-ion transport. In this multi-level structure, the inner heterogeneous shell and the outer TiO2 protective shell form a synergistic mechanical constraint system, significantly enhancing the overall structural stability of the composite particles and effectively suppressing the volume expansion of nano-silicon during charging and discharging.

[0071] Figure 5 The XRD pattern of the Si@C-TiO2 composite material prepared in Example 1 shows that the material has five characteristic peaks belonging to silicon, indicating that the silicon crystal phase was not destroyed. The broad peak observed near 20-25° corresponds to the amorphous peaks of lignin carbon and silicon oxide, and the anatase diffraction peak of TiO2 was observed near 25.3°, proving that the Si@C-TiO2 composite material was successfully synthesized.

[0072] Example 2 The materials obtained from Examples 1-4 and Comparative Examples 1-5 were used to assemble lithium-ion half-cells, and their electrochemical performance was tested. The battery model was CR2032; the negative electrode material consisted of 70 wt% of the product from each example or comparative example, 20 wt% carbon black, and 10 wt% PAA (polyacrylic acid); a lithium sheet was used as the counter electrode; the electrolyte was prepared using 1 mol / L LiPF6 as the solute and ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 as the solvent. The entire assembly process of the lithium-ion half-cells was completed in an argon-protected glove box. The Neware battery performance testing system was used to test the performance at 0.1 A g in the voltage range of 0.01-2.0 V. -1 and 1 A g -1 The constant current charge / discharge performance of the battery was tested at different current densities. The results are shown in Table 1 and... Figure 6 As shown.

[0073] Figure 6 The coin cell assembled from the Si@C-TiO2 composite material of Example 1 operates at a current density of 1 A g. -1 The long-cycle performance graph.

[0074] from Figure 6 As can be seen, the discharge specific capacity is still as high as 1099.91 mAh g after 300 cycles. -1 The capacity retention rate is 91.1%, which is significantly better than similar materials.

[0075] Table 1. Comparison of the performance of different lithium-ion battery anodes prepared in each embodiment and comparative example. Table 1 shows that, in Example 1, at 1 A g -1 The initial charge / discharge specific capacity is 1195.11 / 1207.49 mAh g. -1 After 300 cycles, the discharge specific capacity is 1099.91 mAh g. -1 The capacity retention rate was 91.1%. This demonstrates that the material prepared in Example 1 maintains a high specific capacity during the initial cycling process, exhibiting excellent cycling stability, superior to similar materials.

[0076] Examples 2 and 3 were used to investigate the effect of TBOT addition on the TiO2 content and electrochemical performance of Si@C-TiO2 composites. The results showed that reducing the TBOT addition decreased the TiO2 loading in the composite. Although the capacity increased due to the relatively higher proportion of active silicon, the reduced rigid TiO2 content weakened the mechanical constraint of the heterogeneous shell, leading to structural integrity damage and decreased cycling stability during long-term cycling. Conversely, excessive TBOT addition resulted in the formation of a continuous and dense TiO2 coating layer on the material surface, which, while enhancing mechanical constraint, significantly increased Li content. + Interfacial diffusion impedance during transmission limits the rate capability and capacity utilization of the material.

[0077] Example 4 investigated the effect of ammoniated lignin replacing sodium lignin sulfonate on the structure and electrochemical properties of Si@C-TiO2 composite materials. The results showed that ammoniated lignin, due to its origin from the alkaline oxidative ammonolysis modification reaction pathway, exhibited poor molecular structure uniformity, with problems such as uneven functional group distribution and relatively wide molecular weight dispersion. Compared to sodium lignin sulfonate, the uniformity of coating with ammoniated lignin was slightly worse, but it could still form a heterogeneous shell with TiO2, effectively suppressing silicon volume expansion.

[0078] As shown in Comparative Example 1, when CTAB-modified nano-silicon is directly used as an electrode and assembled into a battery, its electrochemical performance is far inferior to that of Example 1. This is mainly attributed to the severe volume expansion and contraction effect of the nano-silicon particles during repeated lithiation / delithiation processes, which causes the active particles to gradually pulverize, crack, and eventually detach from the current collector surface and become inactive. Simultaneously, repeated volume changes continuously damage the conductive network inside the electrode, increasing the contact resistance between the electrode and the current collector, further exacerbating capacity decay.

[0079] As shown in Comparative Example 2, using lignin as the carbon source to coat nano-silicon cannot achieve the same effect as in Example 1. This is mainly because, although a single-layer lignin-derived carbon coating can provide a certain conductive network and achieve a high initial specific capacity, its single core-shell structure lacks sufficient mechanical constraint, making it difficult to effectively suppress the volume expansion of nano-silicon during long-term cycling. As cycling continues, the cumulative stress generated by repeated volume expansion and contraction will cause the outer carbon shell to fracture brittlely, losing its coating protection for the internal silicon core; at the same time, the exposed nano-silicon particles gradually pulverize due to lack of constraint, eventually detaching from the current collector surface and becoming inactive, resulting in a sharp decline in electrode capacity.

[0080] As shown in Comparative Example 3, coating nano-silicon with TiO2 alone cannot achieve the effect of Example 1. This is mainly due to the following two aspects: First, TiO2 (especially amorphous TiO2) is a wide-bandgap semiconductor with extremely low intrinsic electronic conductivity. Although nano-silicon has a high theoretical specific capacity, its electronic conductivity is also poor. The combination of the two fails to construct an effective electron transport pathway, resulting in a significant increase in charge transfer impedance inside the electrode, making it difficult to fully release the capacity. Second, although the rigid framework of TiO2 can physically constrain the volume expansion of nano-silicon to some extent, this single inorganic coating layer lacks a flexible buffer medium and cannot dissipate the accumulated stress generated during cycling. This leads to local stress concentration at the interface, and there is still a risk of coating layer cracking and interface delamination after long-term cycling.

[0081] As shown in Comparative Example 4, replacing sodium lignosulfonate with glucose cannot achieve the same effect as in Example 1. This is because the aqueous solution of glucose is electrically neutral, causing glucose molecules to randomly attach to the silicon surface. Some silicon particles have only a small number of molecules attached, while other areas experience localized excess due to molecular aggregation. Ultimately, this results in neither a continuous coating layer nor proper silicon particle agglomeration, which has almost no effect on improving the material's conductivity or suppressing the volume expansion of nano-silicon.

[0082] As shown in Comparative Example 5, increasing the calcination temperature of the material cannot achieve the same effect as in Example 1. The main reason is that increasing the calcination temperature induces the anatase phase TiO2 to gradually transform into the rutile phase. While increased crystallinity is beneficial for structural stability, the intrinsic conductivity of TiO2 decreases with increasing crystallinity. Furthermore, excessive crystallinity may lead to grain growth and increased particle size, thereby prolonging the lithium-ion diffusion path and increasing interfacial transport resistance. Therefore, the cycle stability and charge-discharge specific capacity of the composite material prepared in Comparative Example 5 are worse than those of the Si@C-TiO2 composite material prepared in Example 1.

[0083] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a lignin-derived carbon-TiO2 dual-coated silicon-carbon material, characterized in that, Includes the following steps: Nano-silicon and hexadecyltrimethylammonium bromide were mixed in water to obtain a modified nano-silicon solution; Lignin was dissolved in water and then added to the modified nano-silicon solution for lignin coating treatment. Subsequently, solid-liquid separation was performed to obtain lignin-coated silicon. Tetrabutyl titanate and the lignin-coated silicon were mixed in isopropanol to obtain a mixture, which was then subjected to a hydrothermal reaction, followed by solid-liquid separation and high-temperature calcination to obtain the lignin-derived carbon-TiO2 double-coated silicon-carbon material.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the nano-silicon to hexadecyltrimethylammonium bromide is 10~1:1; the particle size of the nano-silicon is 10~300 nm; The lignin is sodium lignin sulfonate and / or ammoniated lignin.

3. The preparation method according to claim 1, characterized in that, The mixing time is 5 to 60 minutes.

4. The preparation method according to claim 1, characterized in that, The mass ratio of lignin to nano-silicon is 10~1:

1.

5. The preparation method according to claim 1, characterized in that, The lignin coating treatment lasted for 1 to 36 hours at a temperature of 15 to 45 degrees Celsius.

6. The preparation method according to claim 1, characterized in that, The volume ratio of isopropanol to tetrabutyl titanate is 10~150:1~12; The mass concentration of the lignin-coated silica in the mixture is 0.32~2.81 wt%; the mass concentration of the tetrabutyl titanate in the mixture is 3.08~27.65 wt%.

7. The preparation method according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 40-200 °C for a duration of 1-24 h.

8. The preparation method according to claim 1, characterized in that, The high-temperature calcination is carried out at a temperature of 500~650℃ for 1~10 h.

9. A lignin-derived carbon-TiO2 double-coated silicon-carbon material obtained by the preparation method according to any one of claims 1-8.

10. The application of the lignin-derived carbon-TiO2 double-coated silicon-carbon material as described in claim 9 in the field of battery anode materials.

Images