A flexible porous silicon-carbon@MXene-rGO film negative electrode material based on a self-propagating method

Abstract

This disclosure belongs to the field of electrochemistry and new energy technology, specifically relating to the preparation of a flexible porous silicon-carbon@MXene-rGO thin-film anode material based on a self-propagating method and its application in lithium-ion batteries. The method proposes a self-propagating reduction strategy, which involves in-situ polymerization of modified silicon particles with phenolic resin followed by carbonization, and then assembly with the two-dimensional material MXene-rGO. A three-dimensional porous membrane structure is constructed by vacuum filtration combined with a self-propagating reduction reaction. This thin film requires no conductive agent, binder, or current collector and can be directly used as an anode material for lithium-ion batteries. (The last sentence appears to be incomplete and requires further context.) ‑1 After 50 cycles, the capacity is 1334 mAh g. ‑1 2 A g 1 The capacity at current density is 726 mAh g. 1 This invention demonstrates excellent cycle stability and rate performance. The process is simple to operate, requires minimal equipment, is highly efficient and convenient, and operates under mild conditions, providing an effective strategy for constructing high-performance, highly stable silicon-based anode materials.

Description

Technical Field

[0001] This invention belongs to the field of electrochemistry and new energy technology, specifically relating to the preparation of a flexible porous silicon-carbon@MXene-rGO thin film anode material based on the self-propagating method and its application in lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and large-scale energy storage due to their advantages such as high energy density, long cycle life, and environmental friendliness. With the market's continued increase in demand for energy density, developing high-specific-capacity anode materials to overcome the bottlenecks of existing systems has become a current research hotspot.

[0003] Silicon anodes are known for their extremely high theoretical specific capacity (~4200 mAh g). -1 Lower lithium intercalation potential (~0.4 V vs. Li / Li) + Silicon, with its abundant crustal reserves, is considered an ideal anode material for next-generation high-energy-density lithium-ion batteries. However, silicon anodes face three major challenges in practical applications: drastic volume expansion (>300%) during charging and discharging leads to pulverization of active particles and electrical contact failure; the unstable solid electrolyte interface film continues to grow, consuming electrolyte and increasing polarization; and silicon's inherently poor conductivity (10⁻⁶ ppm) further complicates the problem. -5 ~ 10 -3 S cm -1 This limits the rate performance.

[0004] To overcome these problems, the design and fabrication of silicon-based composite materials have attracted widespread attention, with Si / C composites based on carbon materials exhibiting excellent electrochemical and physical properties being one of the main directions. MXene is a transition metal carbon or nitrogen compound with the general chemical formula M. n+1 X n T x Where M is a transition metal such as Ti, V, or Mo, X is C or N, and T is T. x Representing surface functional groups such as -OH, -F, and -O, it possesses metallic-grade conductivity (≈10). 5 S cm -1 High Young's modulus (≈330 GPa), abundant surface functional groups, and good hydrophilicity. Reduced graphene oxide (rGO) is a common two-dimensional carbon material with large specific surface area, high flexibility, excellent conductivity, and strong mechanical properties, and is widely used to construct self-supporting electrodes. Active materials can be assembled with GO or MXene into flexible composite membranes via vacuum filtration, followed by reduction treatment to restore the conductivity of GO. However, traditional thermal or chemical reduction methods usually require high temperatures or long processing times, which can easily damage the membrane structure or introduce impurities.

[0005] Therefore, developing a mild reduction technology that can rapidly and efficiently reduce GO while avoiding high-temperature damage and impurity residue, and enabling the formation of a three-dimensional conductive network by firmly bonding the two-dimensional sheet stacked framework of silicon-based materials with MXene and rGO through interfaces, is of great scientific significance and application value for breaking through the performance bottleneck of traditional silicon-based anodes and constructing self-supporting anode materials with high capacity, long cycle life and excellent rate performance. Summary of the Invention

[0006] The purpose of this invention is to provide a flexible porous silicon-carbon@MXene-rGO thin-film anode material constructed using a self-propagating method, creating an integrated self-supporting structure of "silicon core-carbon layer-MXene / rGO network". This film releases a large amount of gas through a self-propagating reaction, forming abundant micro- and nano-pores between the two-dimensional layers, which facilitates rapid ion transport, electrolyte penetration, and full exposure of active sites. It requires no conductive agents, binders, or current collectors and can be directly used as an anode material for lithium-ion batteries (LIBs).

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The preparation of a flexible porous silicon-carbon@MXene-rGO thin film anode material based on a self-propagating method and its application in lithium-ion batteries includes the following steps: (1) Preparation of GO dispersion: GO dispersion was prepared using the modified Hummer's method.

[0008] (2) Preparation of MXene dispersion: Ti3AlC2MAX phase was etched in situ using a LiF / HCl mixed solution, and then a single-layer or few-layer Ti3AlC2MXene aqueous dispersion was obtained after water washing, ultrasonic exfoliation and centrifugation; (3) Preparation and carbonization of silicon-carbon materials: Silicon nanoparticles and silane coupling agents were surface modified in deionized water, and then phenolic resin precursors were added for in-situ polymerization. The mixture was carbonized in an inert atmosphere to obtain silicon-carbon composite materials. (4) Assembly of three-dimensional porous structure: The silicon-carbon composite particles obtained in step (3), the GO dispersion obtained in step (1) and the MXene dispersion obtained in step (2) are thoroughly stirred in proportion, and a flexible self-supporting porous silicon-carbon@MXene-rGO composite film material is obtained by vacuum filtration and self-propagating reduction.

[0009] Preferably, the MXene in step (2) is selected from Ti3C2T. x The temperature is 30-40 ℃ and the time is 20-28h.

[0010] Preferably, the silane coupling agent in step (3) is KH570; the temperature is room temperature, and the time is 12-36 h. The molar ratio of resorcinol to formaldehyde is 1:(1.8-2.5); the temperature is 45-55℃, and the time is 20-28 h.

[0011] Preferably, the carbonization process is carried out in an argon atmosphere at a temperature of 650-850 °C for 2-5 h.

[0012] Preferably, the ratio of the mass of silicon-carbon composite material, solid GO and solid MXene in step (4) is (7.5-8.5):(1.5-2.5):(0.5-1.5).

[0013] Preferably, the vacuum filtration in step (4) is carried out through a Celgard 3501 membrane; the self-propagating reduction reaction is initiated in a glove box by contacting one end of the membrane with a 300 °C hot plate.

[0014] This invention also provides the application of a flexible porous silicon-carbon@MXene-rGO thin film anode material constructed based on the self-propagating method in lithium-ion batteries, as described in the above technical solution.

[0015] The purpose of this invention is to provide a flexible porous silicon-carbon@MXene-rGO thin-film anode material constructed using a self-propagating method, creating an integrated self-supporting structure of "silicon core-carbon layer-MXene / rGO network". This film releases a large amount of gas through a self-propagating reaction, forming abundant micro- and nano-pores between the two-dimensional layers, which facilitates rapid ion transport, electrolyte penetration, and full exposure of active sites. It requires no conductive agents, binders, or current collectors and can be directly used as an anode material for lithium-ion batteries.

[0016] This work proposes a self-propagating reduction method, which is simpler, more efficient, and more convenient to operate compared to traditional thermal or chemical reduction. The constructed silicon-carbon@MXene-rGO composite film possesses a three-level synergistic protection structure of "silicon core-carbon layer-MXene / rGO network". First, a uniform amorphous carbon shell layer is constructed on the surface of modified silicon particles through in-situ phenolic resin polymerization and carbonization, which acts as an internal buffer layer to effectively constrain the drastic volume expansion of silicon and enhance its conductivity and interfacial stability. Second, MXene and reduced graphene oxide (rGO) sheets are tightly stacked through van der Waals forces, hydrogen bonds, and other interactions to synergistically construct a continuous, flexible, integrated three-dimensional conductive network. Finally, the oxygen-containing functional groups (-OH, -COOH, -O-, etc.) on the GO surface are rapidly decomposed through a self-propagating reaction, releasing a large amount of CO2, H2O, and other gases to form abundant micro- and nano-pores between the rGO sheets, providing rapid channels for ion transport and ensuring sufficient electrolyte wetting. Attached Figure Description

[0017] Figure 1 The images show (a) a cross-section of a monolayer MXene film and (b) a cross-section of modified silicon nanoparticles prepared in Example 1 of this invention. from Figure 1 As can be seen, the monolayer MXene film exhibits a clear layered stacking structure with uniform interlayer spacing, confirming the successful exfoliation of the Al atomic layer and the monolayer characteristics. Its abundant interlayer voids can provide a fast channel for ion transport.

[0018] from Figure 1 As can be seen from b, the modified silicon particles are well dispersed, have a uniform particle size distribution, and show no obvious agglomeration on the surface, providing active sites for subsequent binding with carbon precursors.

[0019] Figure 2 The images shown are (a) scanning electron microscope (SEM) images and (bd) corresponding elemental distribution diagrams of Si, C, and O of the silicon-carbon composite material prepared in Example 1 of this invention. from Figure 2 As can be seen from a, the silicon-carbon composite particles have a regular morphology and a relatively uniform particle size distribution; from Figure 2 As can be seen from bd, the signal distributions of Si, C, and O elements are highly overlapping and uniform, confirming that the modified silicon particles were successfully and uniformly coated by the phenolic resin-derived carbon layer.

[0020] Figure 3 The images shown are (a) a surface view and (b) a cross-sectional view of the silicon-carbon@MXene-rGO composite thin film material prepared in Example 1 of this invention using a scanning electron microscope (SEM). from Figure 3 As can be seen, the surface of the thin-film electrode exhibits a wrinkled, layered stacked structure. From... Figure 3 As can be seen from b, the cross-section of the thin film exhibits a distinct loose porous structure and a three-dimensional interconnected framework.

[0021] Figure 4 The charge-discharge curves are for the half-cell of the silicon-carbon@MXene-rGO composite thin film anode prepared in Example 1 of this invention.

[0022] Figure 5 The figures show (a) cycle performance and (b) rate performance of the half-cell with silicon-carbon@MXene-rGO composite thin film anode prepared in Example 1 of this invention. Detailed Implementation

[0023] The purpose of this invention is to provide a flexible porous silicon-carbon@MXene-rGO thin-film anode material constructed using a self-propagating method, creating an integrated self-supporting structure of "silicon core-carbon layer-MXene / rGO network". This film releases a large amount of gas through a self-propagating reaction, forming abundant micro- and nano-pores between the two-dimensional layers, which facilitates rapid ion transport, electrolyte penetration, and full exposure of active sites. It requires no conductive agents, binders, or current collectors and can be directly used as an anode material for lithium-ion batteries (LIBs).

[0024] Unless otherwise specified, the present invention does not have special requirements for the source of raw materials used. Silicon nanoparticles, MXene dispersion (prepared by MAX phase etching), GO dispersion (prepared using a modified Hummer's method), resorcinol, formaldehyde, etc. are all prepared using commercially available products or conventional methods well known to those skilled in the art.

[0025] In this invention, the etching temperature of the MAX phase is 30-40 °C, and the time is 20-30 h, to ensure complete removal of the Al layer and obtain a monolayer Ti3C2T. x The silicon-carbon composite particles are a composite of modified nano-silicon particles and porous hard carbon, prepared by in-situ carbonization of nano-silicon modified with silane coupling agent KH570 and phenolic resin. Calcination temperature and time: The calcination temperature of the silicon-carbon particles is 600-800 ℃, and the time is 2-4 h; if the temperature is too low (<600 ℃), the phenolic resin carbonization is incomplete, the porous carbon skeleton structure is loose, and it cannot effectively buffer the volume expansion of silicon; if the temperature is too high (>800 ℃), the carbon skeleton is excessively graphitized, the porosity decreases, and lithium-ion diffusion is hindered.

[0026] In this invention, the material ratio is a key parameter: when the proportion of silicon-carbon composite particles is too low (mass ratio < 6), the strong van der Waals forces between rGO and MXene nanosheets will cause the nanosheets to self-stack, reducing the specific surface area and reactive sites of the composite film, and limiting ion diffusion; when the proportion is too high (mass ratio > 10), the loading of silicon-carbon particles is too large, and some particles cannot be fully encapsulated and connected by the two-dimensional material network, which easily leads to direct aggregation and rapid capacity decay during cycling.

[0027] This work proposes a self-propagating reduction method, which is simpler, more efficient and convenient to operate compared with traditional thermal reduction or chemical reduction. The constructed silicon-carbon@MXene-rGO composite film has a three-level synergistic protection structure of "silicon core-carbon layer-MXene / rGO network".

[0028] As one embodiment, the method for preparing the self-supporting electrode includes the following steps: Silicon-carbon composite particles, MXene dispersion, and GO dispersion were stirred evenly in a specific ratio and then vacuum filtered onto a Celgard 3501 membrane to form a flexible composite film. After drying, one end of the film was contacted with a hot plate to initiate a self-propagating reduction reaction, thus obtaining a porous silicon-carbon@MXene-rGO composite film. After drying, the film was cut into electrode sheets, which were directly used as the negative electrode of a lithium-ion battery. This preparation process does not require the addition of any conductive agents, binders, or metal current collectors.

[0029] To achieve the above-mentioned objectives, the present invention provides the following technical solution: a flexible porous silicon-carbon@MXene-rGO thin film anode material constructed based on the self-propagating method, the composition of which includes silicon-carbon composite particles, MXene, and rGO, with a solid mass ratio of 6-9:3-1:3-1, and in a specific embodiment, it is 8:1:1.

[0030] In one embodiment, the present invention does not have a special limitation on the amount of water used, as long as a uniformly dispersed mixture can be obtained; the stirring time is 24 h to ensure that the components are fully mixed; the vacuum filtration is a conventional operation in the art; the drying is vacuum drying; the drying temperature is 50-70 ℃, specifically 60 ℃ in the embodiment, and the time is 10-14 h, specifically 12 h in the embodiment; the self-propagating reduction is initiated by contacting one end of the film with a 250-350 ℃ hot plate, specifically 300 ℃ in the embodiment; the reduction process is completed instantaneously in a glove box filled with argon gas.

[0031] This invention also provides a lithium-ion battery, comprising a negative electrode, an electrode sheet, an electrolyte, and a separator; the electrode sheet is the flexible porous silicon-carbon@MXene-rGO self-supporting electrode sheet described in the above technical solution; the electrolyte comprises a lithium salt, a solvent, and additives; the lithium salt is lithium hexafluorophosphate (LiPF6); the solvent comprises ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC); the volume ratio of ethylene carbonate, diethyl carbonate, and dimethyl carbonate is 1:1:1; the additives are fluoroethylene carbonate (FEC) and vinylene carbonate (VC), with addition amounts of 5% and 1% of the total mass of the electrolyte, respectively; the concentration of the lithium salt in the electrolyte is 1 mol / L. -1 The diaphragm is Celgard 2500.

[0032] As one embodiment, the lithium-ion battery is prepared by encapsulating the electrode, lithium sheet, separator and electrolyte into a lithium-ion battery in a glove box filled with Ar gas; the lithium-ion battery is a CR2025 type lithium-ion battery.

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0034] Example 1 This embodiment describes a flexible porous silicon-carbon@MXene-rGO thin-film anode material constructed using a self-propagating method, prepared through the following steps: Graphite powder was added to a flask using a modified Hummer's method. H₂SO₄ (18 M concentration) was added under constant temperature ice-water bath conditions. After continuous stirring and mixing for 30 min, KMnO₄ was added. The mixture was stirred and mixed continuously, then heated to 35 °C. After 2 h, deionized water was added, maintaining the temperature below 80 °C throughout the process. The temperature was then raised to 98 °C and reacted for 10 min, followed by cooling to 28 °C. 30% H₂O₂ was added. The mixture was centrifuged, washed, and ultrasonically dispersed to obtain a GO solution.

[0035] Weigh 0.99 g LiF and add it to 10 mL HCl (12 mol L). -1 In a solution containing 1 g of Ti3AlC2MAX phase precursor powder, stir for 30 min until LiF is completely dissolved. Then, add 1 g of Ti3AlC2MAX phase precursor powder to the above mixed solution in small amounts several times, and etch in a water bath for 24 h at an etching temperature of 35 °C. After cooling to room temperature, centrifuge and wash until neutral, and obtain monolayer or few-layer MXene dispersions by multiple ultrasonic exfoliations (power 300 W, time 1 h).

[0036] 500 mg of commercial silicon nanoparticles (approximately 30 nm in diameter) were dispersed in 100 mL of deionized water. 1 mL of KH570 was added, and the mixture was magnetically stirred at room temperature for 24 h. After the reaction, the mixture was filtered, thoroughly washed with deionized water, and then vacuum dried at 60 °C for 12 h to obtain modified silicon particles. 200 mg of the modified silicon particles were dispersed in 30 mL of deionized water and sonicated for 1 h. 0.1 mL of ammonia (28 wt%), 560 mg of resorcinol, and 760 μL of formaldehyde (37 wt%) were added sequentially to the above dispersion system, and the mixture was stirred at 50 °C for 24 h to achieve uniform polymerization and coating of phenolic resin on the surface of the modified silicon particles. The product was then subjected to argon atmosphere at 5 °C for 1 min. -1 The temperature was increased to 750 °C at a certain rate, carbonized for 3 h, and then naturally cooled to obtain a silicon-carbon composite material.

[0037] Weigh 50.3 mg of silicon-carbon composite material and 1.13 mL of MXene dispersion (5.58 mg / mL). -1 ) and 1.74 mL GO dispersion (7.237 mg / mL) -1The electrode was dispersed in 100 mL of deionized water, and stirred at room temperature for 24 h after purging with argon gas. After vacuum filtration, a flexible composite membrane was formed on a Celgard 3501 membrane. After drying, the membrane was held in a glove box filled with Ar gas and one end of the electrode was brought into contact with a hot plate to initiate a self-propagating reduction reaction. After drying, the membrane was cut to obtain a porous silicon-carbon@MXene-rGO self-supporting electrode.

[0038] Application Example 1 The porous silicon-carbon@MXene-rGO self-supporting electrode prepared in Example 1 was directly used as the negative electrode of the lithium-ion battery. Celgard 2500 with a diameter of 16 mm was used as the separator. A mixed solution of 1M LiPF6 dissolved in EC:DMC:EMC (volume ratio 1:1:1) with the addition of 5% FEC and 1% VC was used as the electrolyte. The battery was encapsulated in an argon-filled glove box to form a CR2025 type lithium-ion battery.

[0039] Test Example 1 The battery assembled for use case 1 was subjected to charge / discharge performance testing under the following conditions: constant current charge / discharge mode; current density of 0.1 A g. -1 Voltage window 0.01-2.0 V (vs. Li + / Li). The battery assembled in Application Example 1 was in 0.1 A g. -1 The first three charge-discharge curves at current density. (Example) Figure 4 As shown, the first-cycle discharge / charge specific capacity is 2950 mAh g. -1 and 2092 mAh g -1 The initial coulombic efficiency was 70.9%. The charge-discharge curves for the second and third cycles show a significant decrease in capacity decay and a stable, highly overlapping charge-discharge plateau. This indicates that the porous flexible membrane structure constructed by self-propagating reduction rapidly formed a stable electrode / electrolyte interface during the initial cycling process, providing ample buffer space for silicon volume expansion and promoting uniform electrolyte penetration and rapid lithium-ion transport.

[0040] Test Example 2 Cycle performance testing was performed on the batteries assembled for use case 1, such as... Figure 5 As shown in (a), the battery assembled using Example 1 is in 0.5 A g. -1 After 50 cycles at a current density, the specific capacity remained at 1334 mAh g. -1 This demonstrates excellent capacity retention and structural stability. Figure 5 (b) It can be seen that the battery assembled using Example 1 exhibits better rate performance at 0.1 A g. -1 0.3 A g -10.5 A g -1 0.8 Ag -1 1 A g -1 2 A g -1 and 0.1 Ag -1 The specific capacities are 2113 mAh g. -1 1898 mAh g -1 1628 mAh g -1 1289 mAh g -1 1051 mAh g -1 426 mAh g -1 and 1864 mAh g -1 The material has a viscosity of up to 2 A g. -1 Even under high current, it can still provide 726 mAh g -1 High reversible specific capacity; when the current density recovers to 0.1 A g -1 At that time, the specific capacity quickly rebounded to approximately 1864 mAh g. -1 This fully demonstrates the high efficiency of its internally constructed highly efficient electron / ion dual continuous transport channels and its rapid reaction kinetics.

[0041] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing flexible porous silicon-carbon@MXene-rGO thin film anode material based on a self-propagating method, characterized in that, Includes the following steps: (1) Preparation of GO dispersion: GO dispersion was prepared using the modified Hummer's method. (2) Preparation of MXene dispersion: Ti3AlC2 MAX phase was etched in situ using a LiF / HCl mixed solution, and then a single-layer or few-layer Ti3AlC2 MXene aqueous dispersion was obtained after water washing, ultrasonic exfoliation and centrifugation; (3) Preparation and carbonization of silicon-carbon materials: Silicon nanoparticles and silane coupling agents were surface modified in deionized water, and then phenolic resin precursors were added for in-situ polymerization. The mixture was carbonized in an inert atmosphere to obtain silicon-carbon composite materials. (4) Assembly of three-dimensional porous structure: The silicon-carbon composite particles obtained in step (3), the GO dispersion obtained in step (1) and the MXene dispersion obtained in step (2) are thoroughly stirred in proportion, and a flexible self-supporting porous silicon-carbon@MXene-rGO composite film material is obtained by vacuum filtration and self-propagating reduction.

2. The method according to claim 1, characterized in that... The MXene mentioned in step (2) is a two-dimensional transition metal carbide selected from Ti3C2T x The sheet thickness is 0.5-1.5 nm, the lateral dimension is 0.5-5 μm, and the conductivity is 10. 4 -10 5 S cm -1 .

3. The preparation method according to claim 1, characterized in that... The silane coupling agent in step (3) is KH570; the temperature is room temperature, and the time is 12-36 h. The molar ratio of resorcinol to formaldehyde is 1:(1.8-2.5); the temperature is 45-55℃, and the time is 20-28 h.

4. The silicon-carbon composite particles according to claim 1, characterized in that... The carbonization is carried out in an argon atmosphere at a temperature of 650-850 °C for 2-5 h.

5. The preparation method according to claim 1, characterized in that... The ratio of the mass of silicon-carbon composite material, solid GO and solid MXene in step (4) is (7.5-8.5):(1.5-2.5):(0.5-1.5).

6. The preparation method according to claim 1, characterized in that... The vacuum filtration in step (4) is carried out through a Celgard 3501 membrane; the self-propagating reduction reaction is initiated in a glove box by contacting one end of the membrane with a 300 °C hot plate.

7. An application of lithium-ion batteries, characterized in that, The porous silicon-carbon@MXene-rGO composite thin film material described in claim 1 can be directly used as a negative electrode material for lithium-ion batteries.

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