Multilayer-coated mxene / silicon-carbon composite negative electrode material

Abstract

This disclosure belongs to the field of electrochemistry and new energy technology, specifically relating to the preparation of a multilayer coated MXene / silicon-carbon composite anode material and its application in lithium-ion batteries. The method first involves electrostatic self-assembly of silicon nanoparticles modified with a silane coupling agent and carboxylated MXene to construct a conductive buffer framework with strong interfacial bonding. Subsequently, phenolic resin is polymerized in situ on the surface of the composite material to form a uniform and dense carbon coating layer. Finally, high-temperature carbonization transforms the resin into an amorphous carbon layer, thus forming a multilayer synergistic coating structure of "MXene conductive network - phenolic resin-derived carbon protective shell". The obtained material has a compressive strength of 0.5 A g. ‑1 After 200 cycles, the capacity is 745 mAh g. ‑1 2 A g 1 The capacity at current density is 1114 mAh g. 1 This invention demonstrates superior cycle stability and rate performance. The process is simple and cost-effective, providing an innovative solution for high-energy-density, long-life lithium-ion battery 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 multilayer coated MXene / silicon-carbon composite anode material and its application in lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries, as the most competitive electrochemical energy storage devices currently available, have been widely used in portable electronic devices, electric vehicles, and large-scale energy storage. With the market's continued increase in demand for energy density, the development of high-specific-capacity anode materials to overcome the bottlenecks of existing systems has become particularly urgent.

[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 anodes, with their abundant crustal reserves, are considered ideal candidate materials. However, silicon anodes experience volume expansion of up to >300% during charge and discharge, leading to the following fatal defects: an unstable solid electrolyte interphase (SEI) layer; pulverization and breakage of active particles, resulting in loss of electrical contact; collapse of the conductive network, increased polarization, and rapid capacity decay; and inherently low conductivity (10⁻⁶ ppm). -5 ~ 10 -3 S cm -1 ) and low lithium-ion diffusion coefficient (10 -14 ~ 10 -13 cm s -1 This results in poor rate performance.

[0004] MXene (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) possessing metallic-grade electrical conductivity (≈10). 5 S cm -1 Silicon nanoparticles possess high Young's modulus (≈330 GPa), abundant surface functional groups, and good hydrophilicity. These rich surface chemical properties allow silicon nanoparticles to distribute well on MXene nanosheets, which helps suppress silicon nanoparticle aggregation, promotes interfacial charge transfer, and improves the wettability of the electrolyte to the active material, thereby improving lithium storage performance. Furthermore, carbon coating of silicon nanoparticles has become the mainstream technical solution for the commercial production of silicon-carbon composite materials. The outer carbon layer acts as a mechanical buffer, effectively constraining the drastic volume deformation of silicon during lithium insertion / extraction; the excellent conductivity of the carbon layer improves its conductivity and rate performance; and the carbon layer also significantly reduces the direct contact between silicon and the electrolyte, reducing side reactions and enhancing interfacial stability.

[0005] Therefore, achieving efficient and stable structural coupling between silicon and the MXene / carbon composite framework to realize robust interfacial electrical contact and long-term structural integrity remains a core challenge and key research direction for constructing next-generation high-performance lithium-ion battery anode materials. Summary of the Invention

[0006] The purpose of this invention is to provide a multilayer coated MXene / silicon-carbon composite anode material. By uniformly coating silicon nanoparticles with an inner MXene substrate and an outer carbon layer, a conductive porous framework is formed, which solves the problems of conductive network breakage, interface peeling and capacity decay caused by silicon volume expansion, thereby improving the cycle stability and kinetic performance of the anode.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The preparation of a multilayer coated MXene / silicon-carbon composite anode material and its application in lithium-ion batteries includes the following steps: (1) Preparation of carboxylated MXene: MXene powder, succinic anhydride and catalyst are dispersed in an organic solvent and esterified under an inert atmosphere. The carboxylated MXene is obtained by centrifugation and washing. (2) Pretreatment of silicon-based materials: The nano-silicon particles and silane coupling agent are subjected to surface modification treatment in deionized water to obtain positively charged aminated silicon particles. (3) Electrostatic self-assembly composite: The product of step (1) and the product of step (2) are mixed in deionized water and obtained by electrostatic self-assembly reaction to obtain Si / MXene composite material; (4) In-situ polymerization coating and carbonization: Phenolic resin precursor is added to the Si / MXene composite dispersion system for in-situ polymerization reaction, and carbonization is carried out under an inert atmosphere to obtain MXene / silicon-carbon composite material. Preferably, the MXene in step (1) is selected from Ti3C2T. x The organic solvent is anhydrous DMF; the catalyst is DMAP; the temperature is 70-90 °C; and the time is 24-72 h.

[0008] Preferably, the silane coupling agent in step (2) is APTES; the temperature is room temperature and the time is 12-36 h.

[0009] Preferably, the mass ratio of the product in step (2) to the product in step (1) is (1.5-3):1; and the time is 0.5-2 h.

[0010] Preferably, in step (4), the phenolic resin precursor includes resorcinol and formaldehyde, and ammonia is added to adjust the pH value; the temperature is 40-60 ℃ and the time is 20-30 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] The present invention also provides the application of the multilayer coated MXene / silicon-carbon composite anode material described in the above technical solution in lithium-ion batteries.

[0013] The purpose of this invention is to provide a multilayer coated MXene / silicon-carbon composite anode material. By uniformly coating silicon nanoparticles with an inner MXene substrate and an outer carbon layer, a conductive porous framework is formed, which solves the problems of conductive network breakage, interface peeling and capacity decay caused by silicon volume expansion, thereby improving the cycle stability and kinetic performance of the anode.

[0014] This invention employs an innovative process combining electrostatic self-assembly and in-situ polymerization to achieve precise multi-scale coating of silicon nanoparticles. The strong electrostatic interaction between carboxylated MXene and aminated silicon particles ensures stable interfacial contact, while the outer carbon layer provides durable mechanical protection, thus forming a multi-layered synergistic coating structure of "MXene conductive network - phenolic resin-derived carbon protective shell." This structure fully utilizes the high conductivity and mechanical toughness of MXene, as well as the physical confinement and interfacial stabilization effects of the resin carbon layer, achieving dual suppression of silicon particle volume expansion and SEI film growth; forming a conductive porous framework and promoting interfacial electron transfer; significantly improving electrode structure stability and ion / electron transport efficiency; and ultimately achieving long-cycle stable operation and excellent rate performance of high-energy-density lithium-ion batteries. Attached Figure Description

[0015] Figure 1 The images shown are: (a) a digital photograph of a monolayer carboxylated MXene film prepared in Example 1 of the present invention; (b) a scanning electron microscope (SEM) image of the cross section of the monolayer carboxylated MXene film; and (c) a scanning electron microscope (SEM) image of aminated silicon nanoparticles. from Figure 1 As can be seen, the monolayer carboxylated MXene film exhibits a layered structure with a smooth surface and metallic luster, indicating that the MXene sheets are well dispersed and regularly oriented, which is conducive to the construction of a dense conductive network.

[0016] from Figure 1As can be seen from b, the cross-section of the monolayer carboxylated 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.

[0017] from Figure 1 As can be seen from c, the aminated silicon particles are well dispersed, with a uniform particle size distribution and no obvious agglomeration on the surface, providing an ideal surface property basis for subsequent electrostatic self-assembly.

[0018] Figure 2 The images shown are (a) scanning electron microscope (SEM) images and (be) corresponding elemental distribution diagrams of Si, C, O, and Ti of the Si / MXene@C composite material prepared in Example 1 of this invention. from Figure 2 As can be seen, the composite material exhibits a uniform microstructure, with silicon nanoparticles uniformly attached to the surface of the 2DMXene conductive substrate. The surface is tightly wrapped by a carbon layer, with no obvious exposed particles.

[0019] from Figure 2 As can be seen, the signal distributions of Si, C, and Ti elements are highly overlapping and uniform, confirming... Silicon particles were successfully and uniformly coated with MXene and carbon layers; the O element mainly came from the natural oxidation of silicon nanoparticles and the surface carboxyl functional groups of MXene.

[0020] Figure 3 The half-cell charge-discharge curve of the Si / MXene@C composite material prepared in Example 1 of this invention; Figure 4 The figures show (a) cycle performance and (b) rate performance of the half-cell assembled from the Si / MXene@C composite material prepared in Example 1 of this invention. Detailed Implementation

[0021] The purpose of this invention is to provide a multilayer coated MXene / silicon-carbon composite anode material. By uniformly coating silicon nanoparticles with an inner MXene substrate and an outer carbon layer, a conductive porous framework is formed, which solves the problems of conductive network breakage, interface peeling and capacity decay caused by silicon volume expansion, thereby improving the cycle stability and kinetic performance of the anode.

[0022] Unless otherwise specified, the present invention does not have special requirements for the source of raw materials used. Aminated silicon nanoparticles (prepared by APTES modification), carboxylated MXene conductive substrate (prepared by MAX phase etching followed by modification with succinic anhydride), resorcinol, formaldehyde, etc. are all prepared using commercially available products or conventional methods known to those skilled in the art.

[0023] 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 carboxylation reaction of MXene was carried out in anhydrous DMF solvent with DMAP as a catalyst at a temperature of 70-90 °C for 24-72 h to ensure that succinic anhydride was fully grafted onto the surface of the MXene sheets and to obtain stable carboxyl functional groups. The aminated silicon particles were silicon nanoparticles with APTES-modified surfaces. This reaction was carried out in an aqueous phase at room temperature for 12-36 h to ensure the formation of a uniform positively charged surface with suitable charge density. Calcination temperature and time: The calcination temperature of the Si / MXene@C composite material was 650-850 °C for 2-4 h. When the temperature was too low (<600 °C), the phenolic resin carbonization was incomplete, the porous carbon skeleton structure was loose, and it could not effectively buffer the volume expansion of silicon; when the temperature was too high (>800 °C), the carbon skeleton was over-graphitized, the porosity decreased, and lithium-ion diffusion was hindered.

[0024] In this invention, the material ratio is a key parameter: when the proportion of aminated silicon particles is too low (mass ratio <1.5), excessive carboxylated MXene may cause self-stacking between layers, failing to provide sufficient coating and support for silicon particles; when the proportion is too high (mass ratio >3), the silicon particle loading is too large, and some particles cannot be effectively coated by MXene, which is prone to direct agglomeration and capacity decay during cycling.

[0025] As one embodiment, the tap density of the composite material is ≥0.8 g / cm³. -3 Electrode conductivity ≥ 500 Scm -1 .

[0026] This invention achieves precise multi-scale coating of silicon nanoparticles through a synergistic process of electrostatic self-assembly and in-situ polymerization and carbonization. It fully utilizes the high conductivity and mechanical toughness of MXene, as well as the physical confinement and interfacial stabilization effects of the resin carbon layer, thus solving the three major bottleneck problems of silicon-based anodes: volume expansion, interfacial instability, and kinetic sluggishness. When applied to lithium-ion battery anodes, it enables long-term stable operation at high energy density and excellent rate performance.

[0027] As one embodiment, the method for preparing the electrode includes the following steps: The active material, conductive agent, binder and water are mixed, and the resulting slurry is coated on the current collector. After drying, it is cut to obtain the electrode sheet.

[0028] To achieve the above-mentioned objectives, this invention provides the following technical solution: a multilayer coated MXene / silicon-carbon composite anode material, the preparation process parameters and ratios of which are optimized as follows: In one embodiment, the mass ratio of aminated silicon particles to carboxylated MXene in the electrostatic self-assembly process is (1.5-3):1, and in a specific embodiment it is 2:1; the mass ratio of the phenolic resin precursor (based on the mass of resorcinol) to aminated silicon particles is (0.1-0.5):1, and in a specific embodiment it is 0.28:1.

[0029] In one embodiment, the in-situ polymerization reaction uses ammonia as a catalyst, the pH of the reaction system is 8-11, and in a specific embodiment it is 10; the reaction temperature is 40-60 ℃, and in a specific embodiment it is 50 ℃; the reaction time is 20-30 h, and in a specific embodiment it is 24 h.

[0030] In one embodiment, the carbonization treatment is carried out under an argon atmosphere, with a heating rate of 2-7 °C / min. -1 In the specific embodiment, it is 5 ℃ min. -1 Carbonization temperature: 650-850 ℃, 750 ℃ ​​in the specific embodiment; isothermal time: 2-5 h, 3 h in the specific embodiment.

[0031] This invention also provides a lithium-ion battery, comprising a negative electrode, an electrode sheet, an electrolyte, and a separator; the active material used in the electrode sheet is the MXene / silicon-carbon composite negative electrode material with a multilayer coated structure described in the above-mentioned 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), and their addition amounts are 5% and 1% of the total mass of the electrolyte, respectively; the concentration of 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 The MXene / silicon-carbon composite anode material based on a multilayer coated structure in this embodiment is prepared by the following steps: 0.99 g of LiF is weighed and placed in 10 mL of HCl (12 mol L). -1In a solution of Mg2+, the mixture was stirred for 30 min until LiF was completely dissolved. Then, 1 g of Ti3AlC2MAX phase precursor powder was added to the above mixed solution in small amounts several times, and etched in a water bath for 24 h at an etching temperature of 35 °C. After cooling to room temperature, the mixture was centrifuged and washed until neutral, and then subjected to multiple ultrasonic exfoliations (300 W power, 1 h time) to obtain monolayer or few-layer MXene dispersions. The freeze-dried MXene powder was dispersed in 50 mL of DMF, sonicated under an argon atmosphere for 30 min, and then 500 mg of succinic anhydride and 50 mg of DMAP were added. The mixture was stirred at 80 °C for 48 h. The final product was freeze-dried to obtain carboxylated MXene powder.

[0035] 500 mg of commercial silicon nanoparticles (approximately 30 nm in diameter) were dispersed in 100 mL of deionized water. 1 mL of ATPES 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 aminated silicon particles. 200 mg of the aminated silicon particles were dispersed in 30 mL of deionized water and sonicated for 1 h. 100 mg of carboxylated MXene powder was added, and stirring was continued for 30 min to form a Si / MXene primary composite via electrostatic self-assembly. 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 in-situ polymerization and coating of phenolic resin on the surface of the composite. The product was then subjected to argon atmosphere at 55 °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 the final product, Si / MXene@C composite material.

[0036] Application Example 1 The Si / MXene@C composite material prepared in Example 1 was used as the active material. It was mixed with SuperP and CMC at a mass ratio of 8:1:1. Water was added, and the mixture was stirred and homogenized to form a uniform slurry. The slurry was then uniformly coated onto a copper current collector foil and dried in a vacuum oven at 60 °C for 12 h. Finally, it was cut into electrode sheets with a diameter of 8 mm. Celgard 2500 with a diameter of 16 mm was used as the separator. A mixed solution of 1 M 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 mixture was then encapsulated in an argon-filled glove box to form a CR2025 type lithium-ion battery.

[0037] 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 3 As shown, the first-cycle discharge / charge specific capacity is 2274 mAh g. -1 and 1824 mAh g -1 The initial coulombic efficiency was 80.2%. The capacity decay rate decreased and the plateau stability increased in the second and third charge-discharge curves, indicating that the multilayer coating structure composed of carboxylated MXene and phenolic resin-derived carbon layers rapidly formed a stable interface in the initial cycle, effectively suppressing the continuous side reactions between the active material and the electrolyte and improving the reversibility of the electrochemical reaction.

[0038] Test Example 2 Cycle performance testing was performed on the batteries assembled for use case 1, such as... Figure 4 As shown in (a), the battery assembled using Example 1 is in 0.5 A g. -1 After 200 cycles at a current density, the specific capacity remained at 745 mAh g⁻¹. -1 This demonstrates excellent capacity retention and structural stability. From Figure 4 (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 -1 0.5 A g -1 0.8 Ag -1 1 A g -1 2 A g -1 and 0.1 Ag -1 The specific capacity is 1845 mAh g. -1 1709.6 mAh g -1 1596.7 mAh g -1 1467.2 mAh g -1 1389.7 mAh g -1 1114mAh g -1 and 1566.5 mAh g -1 The material has a viscosity of up to 2 A g. -1 Even under high current, it can still provide 1114 mAh g -1 Its high reversible specific capacity fully demonstrates the effectiveness of its internally constructed efficient electron / ion dual continuous transport channels and its fast reaction kinetics.

[0039] 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 a multilayer coated MXene / silicon-carbon composite anode material, characterized in that, Includes the following steps: (1) Preparation of carboxylated MXene: MXene powder, succinic anhydride and catalyst are dispersed in an organic solvent and esterified under an inert atmosphere. The carboxylated MXene is obtained by centrifugation and washing. (2) Pretreatment of silicon-based materials: Silicon nanoparticles and silane coupling agents are surface modified in deionized water to obtain positively charged aminated silicon particles. (3) Electrostatic self-assembly composite: The product of step (1) and the product of step (2) are mixed in deionized water to carry out electrostatic self-assembly reaction to obtain Si / MXene composite material; (4) In-situ polymerization coating and carbonization: Phenolic resin precursor is added to the Si / MXene composite dispersion system for in-situ polymerization reaction and carbonization is carried out under an inert atmosphere to obtain MXene / silicon-carbon composite material.

2. The method according to claim 1, characterized in that... The MXene mentioned in step (1) is selected from Ti3C2T x ， The organic solvent is anhydrous DMF; the catalyst is DMAP; the temperature is 70-90 °C, and the time is 24-72 h.

3. The preparation method according to claim 1, characterized in that... The silane coupling agent in step (2) is APTES; the temperature is room temperature and the time is 12-36 h.

4. The preparation method according to claim 1, characterized in that... The mass ratio of the product in step (2) to the product in step (1) is (1.5-3):1; the time is 0.5-2 h.

5. The preparation method according to claim 1, characterized in that... The phenolic resin precursor in step (4) includes resorcinol and formaldehyde, and ammonia is added to adjust the pH value; the temperature is 40-60 ℃ and the time is 20-30 h.

6. The silicon-carbon composite anode material 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.

7. The MXene / silicon-carbon composite anode material according to claim 1, characterized in that, The material has a multi-layered encapsulation structure with Si as the core, an inner MXene substrate, and an outer carbon layer as the shell.

8. An application of lithium-ion batteries, characterized in that, The MXene / silicon-carbon composite material described in claim 1 is used as a negative electrode material for lithium-ion batteries.

Images