Preparation method of heteroatom functionalized MXene modified silicon-carbon negative electrode material, negative electrode composite material and application

Abstract

This invention belongs to the field of lithium-ion battery manufacturing technology, and discloses a method for preparing heteroatom-functionalized MXene-modified silicon-carbon anode materials, anode composite materials, and their applications. This method significantly improves the conductivity, interfacial stability, and lithium-ion diffusion capacity of MXene by introducing heteroatom doping functionalization modification onto the MXene surface. The functionalized MXene is then composited with silicon nanoparticles and porous graphite and other carbon materials to construct a micron-nano hierarchical porous structure and a three-dimensional conductive intercalation network, thereby buffering the volume expansion of silicon and maintaining conductive continuity. The heteroatom-functionalized MXene / silicon / carbon composite anode material can be used in lithium-ion capacitors, electric vehicle power batteries, and large-scale energy storage systems. This anode material significantly improves the conductive network and interfacial stability of silicon-based anodes, giving them both high energy density and high power long-lifetime performance, making them suitable for next-generation wide-temperature high-power energy storage devices.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery preparation technology, specifically relating to a method for preparing heteroatom functionalized MXene-modified silicon-carbon anode material, anode composite materials, and their applications. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics, electric vehicles, and grid energy storage due to their high energy density and long cycle life. However, the theoretical specific capacity of traditional graphite anodes is only about 372 mAh / g, which is gradually approaching its performance limit. Silicon, with its ultra-high theoretical specific capacity of about 4200 mAh / g, is considered one of the most promising next-generation anode materials. However, silicon undergoes volume expansion and contraction of up to about 300% during charge and discharge, leading to material pulverization, increased electrode structural stress, and repeated rupture / regeneration of the solid electrolyte interphase (SEI) film, resulting in large initial irreversible capacity loss, low coulombic efficiency, and a sharp decline in cycle life. To alleviate these problems, researchers have proposed various silicon anode modification strategies, such as fabricating silicon into nanoparticles or introducing it into organic / inorganic buffer matrices, coating the silicon surface with carbon layers or elastic coatings, and forming silicon / carbon composite anodes by combining silicon with conductive carbon materials. These methods have improved the cycle stability and conductivity of silicon anodes to some extent, but they still cannot simultaneously meet the requirements of long cycle life and high rate performance under high silicon content conditions.

[0003] In recent years, novel two-dimensional materials MXene (such as Ti3C2T) have emerged. x MXene (e.g., silicon nanosheets) has attracted widespread attention due to its metallic conductivity, tunable surface chemistry, and layered structure. Using MXene as an additive or functional coating in battery anodes can provide excellent conductive networks and improve interfacial contact. Studies have shown that the high conductivity and mechanical flexibility of two-dimensional MXene nanosheets can alleviate the volume expansion of silicon anodes, improve structural stability and ion transport, thereby significantly improving the cycle performance and capacity retention of silicon anodes. When MXene is combined with silicon materials, the volume change of silicon is suppressed, the conductive connections in the electrode are strengthened, and a high capacity can still be maintained after hundreds of cycles, demonstrating the enhancing effect of MXene on silicon anodes. However, pure MXene materials also have certain problems in the electrochemical environment: their layers are prone to stacking, certain functional groups on the surface (such as –F, –OH) may induce unfavorable side reactions, and their structural stability is insufficient under long cycles. Furthermore, the mainstream preparation methods of MXene involve fluorinated etchants, and the introduced –F terminal groups can reduce its conductivity and reduce electrochemical active sites. Therefore, it is necessary to further functionalize MXene to fully realize its enhancement effect in silicon anodes.

[0004] Heteroatom doping is an effective method for material modification. Introducing heteroatoms (such as nitrogen, phosphorus, and boron) into carbon-based materials like graphene and carbon nanotubes has been shown to significantly improve their electrical conductivity, chemical stability, and ion storage performance. Although heteroatom functionalization has achieved positive results in theoretical research and in certain material systems, research on heteroatom doping of MXene is still in its early stages, and there are no mature solutions for using functionalized MXene to modify silicon-carbon anodes to simultaneously improve high-rate and long-lifetime performance.

[0005] Specific methods for introducing heteroatoms mainly include high-temperature heat treatment and plasma treatment. High-temperature heat treatment typically involves mixing MXene with a dopant source and heating them together at temperatures above 600°C, thereby embedding heteroatoms into the interlayer of MXene or replacing surface groups. However, excessively high temperatures can easily lead to oxidation or phase transformation (such as conversion to metal oxides) of MXene sheets, destroying their original conductive framework. Moreover, the doping concentration is difficult to control precisely under high-temperature conditions. Plasma treatment utilizes plasma to excite a gas containing heteroatoms, which can bombard and implant heteroatoms into the MXene surface at lower temperatures. However, this method requires sophisticated equipment, has a limited processing area, and is difficult to apply uniformly to large batches of materials, thus limiting its large-scale application.

[0006] In summary, existing silicon-carbon anode technologies still face challenges such as insufficient conductive network, interface instability, and difficulty in suppressing volume expansion. While the introduction of MXene has improved the performance of silicon anodes to some extent, there is still room for further optimization, especially in simultaneously achieving high power density and long cycle life. Summary of the Invention

[0007] To address the aforementioned technical problems of poor conductivity, unstable interfaces, and severe volume expansion in silicon-carbon anodes, the primary objective of this invention is to provide a method for preparing heteroatom-functionalized MXene-modified silicon-carbon anode materials. By doping with heteroatoms, the electronic conductivity, interlayer spacing, and interfacial bonding ability of MXene are comprehensively improved. Furthermore, the modified MXene is composited with silicon nanoparticles and porous carbon materials to construct a multi-level channel and a three-dimensional interconnected conductive network, thereby preparing a silicon-carbon anode material with high capacity, high rate capability, wide temperature range, low expansion, and ultra-long cycle life. This material has broad application prospects in lithium-ion capacitors, electric vehicle power batteries, and large-scale energy storage systems, representing a novel solution that surpasses existing mainstream technologies.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing heteroatom-functionalized MXene-modified silicon-carbon anode material includes the following steps: S1. Preparation of heteroatom-functionalized MXene: Layered MXenes are dispersed in an organic solvent, and a precursor compound containing heteroatom elements is added to carry out a solvothermal reaction, thereby introducing heteroatom doping into the interlayer or surface terminal groups of the MXenes to obtain heteroatom-functionalized MXenes; the doping content of the heteroatom elements in the MXenes is 1~15 at% S2, Preparation of silicon-carbon composite materials: Heteroatom-functionalized MXene, silicon nanoparticles, and porous carbon materials are mixed and dispersed in a medium in a certain proportion, and ultrasonically stirred to form a suspension. After processing, a three-dimensional cross-linked gel-like precursor or a porous powder-like precursor is obtained. The precursor is dried under an inert atmosphere and lightly pressed to obtain a silicon-carbon composite material powder modified with heteroatom-functionalized MXene, which is the modified silicon-carbon anode material.

[0009] Preferably, in S1, MXene is a two-dimensional layered material of transition metal carbides or nitrides, with the general formula M n+1 X n T x , where M is a transition metal element, X is carbon or nitrogen, and T is a terminal group on the surface of MXene; The heteroatomic element includes any one or more of nitrogen, phosphorus, and boron. The precursor compounds containing heteroatoms include nitrogen source precursors, phosphorus source precursors, and boron source precursors; The nitrogen source precursor includes any one of urea, melamine, and ammonia water; The phosphorus source precursor includes any one of phosphoric acid, phosphate, and organic phosphorus-containing compounds; The boron source precursor includes any one of boric acid and organoborides; The organic solvent is a water-organic mixed solvent or a polar organic solvent; The solvothermal reaction temperature is no higher than 200℃.

[0010] Preferably, the MXene is Ti3C2T. x ; The solvothermal reaction temperature is 120~200℃, and the duration is 4~24h.

[0011] This solvothermal method, conducted at relatively low temperatures (120–200°C) and in a closed solvent system, effectively preserves the structural integrity of MXene. By selecting suitable organic or inorganic precursors, the solvothermal reaction can introduce heteroatom-containing functional groups onto the MXene surface or achieve mild heteroatom doping of the MXene lattice. The solvothermal method offers mild reaction conditions, simple operation, and easy control of the doping degree, and is therefore preferred in this invention for heteroatom functionalization of MXene.

[0012] Preferably, in S2, the mass fraction ratio of heteroatom-functionalized MXene, silicon nanoparticles, and porous carbon material is (5~40wt%):(15~50wt%):(10~45wt%). The average particle size of the silicon nanoparticles is 50~1000 nm; The porous carbon material is selected from any one of porous graphite, graphene, hard carbon, and soft carbon; The dispersion medium is water or ethanol; The process to obtain the three-dimensional cross-linked precursor includes vacuum filtration or freeze-drying.

[0013] A heteroatom-functionalized MXene-modified silicon-carbon anode composite material is obtained by the preparation method described above.

[0014] Preferably, the modified silicon-carbon anode composite material comprises a mixture of heteroatom-functionalized MXene-modified silicon-carbon composite material powder, a conductive agent, and a binder, which are mixed to form a slurry, uniformly coated on a copper foil current collector, dried, and rolled to form the composite material. The mass ratio of the heteroatom-functionalized MXene-modified silicon-carbon composite powder, conductive agent, and binder is 8:1:1. The conductive agent is acetylene black; The adhesive is a water-based adhesive; The water-based adhesive includes one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber latex (SBR), polyacrylic acid (PAA), and sodium alginate.

[0015] In the aforementioned modified silicon-carbon anode composite material, MXene two-dimensional sheets overlap and connect to form a conductive network framework, which coats or embeds the silicon nanoparticles and porous carbon, thereby constructing a multi-level porous structure from micrometer to nanometer scale. This structure allows the electrolyte to fully penetrate into the electrode interior, and lithium ions can diffuse rapidly between MXene sheets and in the pores of silicon particles and carbon materials; it also provides spatial buffering for volume changes in silicon during charge-discharge cycles. More importantly, the heteroatom-doped MXene surface has abundant active functional groups, forming a strong interfacial bond with the silicon particle surface: on the one hand, it effectively suppresses silicon shedding and pulverization during cycling; on the other hand, nitrogen-containing functional groups on the MXene surface can form chemical bonds with silicon surface oxides or binder molecules, which helps to build a uniform and stable SEI film during the first cycle, reducing electrolyte decomposition and side reactions on the silicon surface. Therefore, the composite anode material as a whole exhibits a continuous three-dimensional electronic conduction path and ion transport channel, enabling the electrode to maintain low polarization and good capacity output even at high rates.

[0016] A lithium-ion battery anode sheet comprising the aforementioned heteroatom-functionalized MXene-modified silicon-carbon anode composite material.

[0017] Application of a heteroatom-functionalized MXene-modified silicon-carbon anode composite material in the preparation of lithium-ion batteries, lithium-ion capacitors, electric vehicle power batteries, and battery cells for large-scale energy storage systems.

[0018] Preferably, the lithium-ion battery is composed of a positive electrode, a separator, an electrolyte, and the heteroatom-functionalized MXene-modified silicon-carbon anode composite material as the negative electrode.

[0019] Preferably, the electrolyte is an organic solvent electrolyte containing lithium salt; The lithium-ion battery is suitable for an operating temperature range of -30℃ to 60℃.

[0020] Compared with the prior art, the present invention has at least the following technical effects: (I) This invention provides a method for preparing heteroatom-functionalized MXene-modified silicon-carbon anode materials. This method, through synergistic innovative design of material composition and structure, successfully solves the three major problems of poor conductivity, interface instability, and volume expansion in high-silicon anodes, achieving a unified high specific capacity, high rate capability, and long lifespan for silicon anodes: initial coulombic efficiency is increased to over 90%, cycle life reaches 1500 cycles with capacity retention still above 80%, and performance close to theoretical capacity can still be output at a high rate of 10C. The technical solution of this invention provides a new approach and effective method for the development of high-performance lithium-ion battery anode materials.

[0021] This method specifically improves the conductivity, interfacial stability, and lithium-ion diffusion capacity of MXene by introducing heteroatom doping (preferably nitrogen, but also phosphorus, boron, etc., with a doping content of 1-15 at%) onto the MXene surface. The functionalized MXene is then composited with silicon nanoparticles and porous graphite and other carbon materials to construct a micron-nano hierarchical porous structure and a three-dimensional conductive intercalation network, thereby buffering the volume expansion of silicon and maintaining conductive continuity. In this scheme, a low-temperature solvothermal method is preferably used (reaction temperature 120-200°C, time 4-24 h, with precursors of the heteroatom elements such as urea, melamine, phosphoric acid, boric acid, etc.) to introduce heteroatoms into the MXene interlayer, achieving uniform doping without damaging the MXene structure. The prepared heteroatom-functionalized MXene / silicon / carbon composite anode material can be used in lithium-ion capacitors (LIC), electric vehicle batteries (EV), and large-scale energy storage systems (BESS).

[0022] In the above applications, the anode material exhibits excellent rate performance (supporting high-speed charge and discharge above 10C), long cycle life (>1500 cycles), and initial coulombic efficiency above 90%.

[0023] (ii) The materials and preparation methods provided by this invention significantly improve the conductivity network and interface stability of the modified silicon-carbon anode material, giving it both high energy density and high power and long life performance, making it suitable for a new generation of wide-temperature high-power energy storage devices.

[0024] Furthermore, the anode material obtained by the preparation method of this application maintains excellent electrochemical performance even under harsh low-temperature environments. This overall performance far surpasses that of traditional silicon / carbon anodes and unfunctionalized comparative materials. The technical solution of this invention provides new ideas and effective approaches for the development of high-performance lithium-ion battery anode materials.

[0025] (III) The heteroatom-functionalized MXene-modified silicon-carbon anode material prepared by the above method has the following technical characteristics and advantages: 3.1 Improved Conductivity: Due to the reduction of surface inert groups and the adjustment of electronic structure, heteroatom-doped MXene exhibits significantly improved conductivity, providing a more efficient conductive framework for silicon anodes. Compared to unmodified MXene, doped MXene in composite electrodes can reduce interfacial resistance and charge transfer impedance, contributing to improved charge-discharge performance at high rates.

[0026] 3.2 Interface Stability: The doped MXene surface is rich in functional groups (e.g., –NH, –CO, etc.), which can form chemical bonds or strong interactions with the silicon particle surface, significantly enhancing the bonding strength of the silicon / MXene interface. Simultaneously, these functional groups facilitate the induction of a uniform and stable SEI film during the initial cycle, reducing electrolyte decomposition and side reactions on the silicon surface. Therefore, the initial coulombic efficiency of the anode of this invention is significantly improved (from less than 80% in the undoped state to approximately 92%), and the cycle life is greatly extended.

[0027] 3.3 Ion Diffusion Channels: Heteroatom incorporation widens the interlayer spacing of MXene, facilitating smoother lithium-ion diffusion between MXene layers. Simultaneously, the multi-level porous structure formed by the prepared heteroatom-functionalized MXene-modified silicon-carbon anode composite material (including nanochannels between MXene layers, mesopores between silicon particles / layers, and micropores in the carbon material itself) constitutes a rapid lithium-ion transport network throughout the entire electrode. When the charge / discharge rate is increased to above 10C, the ion concentration gradient and ohmic polarization within the electrode are significantly reduced, ensuring that most of the capacity can still be released at high rates.

[0028] 3.4 Volume Expansion Buffer: The three-dimensional conductive network and porous structure provide ample buffer space for the volume changes of silicon particles. Heteroatom-functionalized MXene sheets form a flexible framework when coating and supporting silicon particles, absorbing the stress generated by silicon expansion; the pores of porous carbon materials such as graphite can accommodate some of the volume changes. Tests show that, in the fully lithium-intercalated state, the thickness of the modified silicon-carbon anode composite material of this invention increases by only about 20% compared to the initial thickness, far lower than the expansion of over 40% without MXene. This excellent volume stability ensures that the electrode structure does not pulverize during long-term cycling and that the active material does not adhere to the current collector.

[0029] 3.5 Low-Temperature Performance: Heteroatom functionalization also endows the composite anode with excellent low-temperature electrochemical performance. Due to the improved conductivity of MXene and the effect of interface stabilization, the modified silicon-carbon anode composite material of this invention can still maintain good kinetic characteristics and capacity output even at low temperatures of -20°C and even -40°C. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the surface structure and interlayer spacing expansion of MXene after heteroatom doping functionalization; Figure 2 A schematic diagram comparing the XRD patterns of pristine MXene and nitrogen-doped MXene; Figure 3 A schematic diagram of a three-dimensional conductive network and lithium-ion diffusion channels formed by heteroatom-functionalized MXene, silicon nanoparticles, and porous carbon materials. Detailed Implementation

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the present invention will be briefly introduced below in conjunction with the accompanying drawings and descriptions of the embodiments or the prior art. Obviously, the following description of the structure of the accompanying drawings is 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. It should be noted that the description of these embodiments is for the purpose of helping to understand the present invention, but does not constitute a limitation of the present invention.

[0032] One specific embodiment of the present invention is as follows: A method for preparing heteroatom-functionalized MXene-modified silicon-carbon anode material includes the following steps: (1) Preparation of heteroatom-functionalized MXene: Layered MXene is dispersed in an organic solvent, a precursor compound containing heteroatom elements is added, and the mixture is sealed and placed in a reaction vessel for solvothermal reaction, so that heteroatom doping is introduced into the interlayer or surface terminal groups of MXene to obtain heteroatom-functionalized MXene.

[0033] In a preferred embodiment, the reaction temperature is 160°C and the reaction time is 6 hours, with urea (providing a nitrogen source) as the precursor compound containing heteroatoms. After the reaction, the product is centrifuged and washed repeatedly with deionized water and ethanol, and then vacuum dried to obtain nitrogen-doped functionalized MXene powder.

[0034] like Figure 1 The diagram shows the surface structure and interlayer spacing expansion of MXene after heteroatom doping functionalization. The diagram illustrates how heteroatoms (such as nitrogen, yellow atoms) are introduced into the interlayer or surface of MXene, replacing some inert terminal groups and significantly increasing the interlayer spacing.

[0035] Combination Figure 1 The results show that the introduction of heteroatoms (taking nitrogen doping as an example, the yellow atoms in the figure) replaces some of the inert terminal groups on the MXene surface and enters the interlayer gap, significantly increasing the interlayer gap, thereby providing a wider channel for lithium ion insertion / extraction and improving the conductivity and interfacial reactivity of MXene.

[0036] like Figure 2 The image shows a schematic diagram comparing the XRD patterns of pristine MXene and nitrogen-doped MXene.

[0037] The results are as follows Figure 2 As can be seen from the XRD results, after N doping, the (002) peak of MXene shifted to the left from 7.36 to 6.64. According to the Bragg formula, the interlayer spacing increased from 1.185 nm to 1.331 nm, an increase of 0.146 nm, which is about 12.3%. This quantitatively proves that N doping successfully expanded the interlayer spacing of MXene.

[0038] Increasing the interlayer spacing facilitates lithium ion insertion / extraction, improves ion diffusion rate, and thus enhances rate performance and low-temperature performance.

[0039] Verification: X-ray diffraction (XRD) detection in this doped MXene confirmed the successful introduction of heteroatoms. For example, when nitrogen-doped, the amount of N element introduced was approximately 8 at% (atomic percentage) and mainly in the form of –NH4+. x The presence of functional groups and Ti-N bonds increases the interlayer spacing of MXene from approximately 1.2 nm in the undoped form to approximately 1.4 nm.

[0040] Besides nitrogen doping, this invention can also employ similar solvothermal methods to introduce heteroatoms such as phosphorus and boron. For example, using phosphoric acid as the phosphorus source and boric acid as the boron source, the reaction is carried out at 150-180°C to obtain the corresponding phosphorus (P) or boron (B) element-functionalized MXenes. If necessary, co-doping or stepwise functionalization of the two heteroatoms can also be used to obtain synergistic effects. The resulting heteroatom-functionalized MXenes retain a two-dimensional layered structure in morphology, but the interlayer spacing is increased and the surface functional groups are more abundant, making them more suitable as conductive frameworks and interface modulation components in composite materials.

[0041] (2) Construction of silicon-carbon / MXene composite anode material: The heteroatom-functionalized MXene obtained in step (1) above is mixed with silicon nanoparticles and porous carbon materials in a certain proportion to form a composite material precursor.

[0042] The silicon nanoparticles have an average particle size of approximately 100 nm and account for 30% of the total mass of the silicon-carbon / MXene composite anode material. Porous graphite, as a porous carbon material, accounts for 50% of the total mass of the silicon-carbon / MXene composite anode material. Heteroatom-doped MXene accounts for 20% of the total mass of the silicon-carbon / MXene composite anode material. The three materials are mixed in a dispersion medium (e.g., water or ethanol) and a homogeneous suspension is prepared by ultrasonic stirring. This suspension is then vacuum-filtered or freeze-dried to obtain a three-dimensionally cross-linked gel-like or porous powder precursor. Subsequently, the obtained precursor is dried under an inert atmosphere and lightly pressed into shape to obtain the heteroatom-functionalized MXene / silicon / carbon composite powder.

[0043] like Figure 3 The diagram shows a three-dimensional conductive network and lithium-ion diffusion channels formed by heteroatom-functionalized MXene, silicon nanoparticles, and porous carbon materials. In the diagram, MXene sheets (blue) overlap and encapsulate silicon particles (yellow spheres), the porous carbon framework (gray) provides additional conductive pathways and structural support, and lithium ions (red spheres) diffuse along the interlayer and pores.

[0044] Results combined Figure 3 It is evident that in the composite structure composed of heteroatom-functionalized MXene (blue sheets), silicon particles (yellow spheres), and a porous graphitic carbon framework (gray), the MXene sheets overlap and encapsulate the silicon particles, forming a tight interfacial connection; the porous graphite intersperses within, providing additional conductive pathways and structural support. Lithium ions (red spheres) can efficiently diffuse along the nanopores extending between the MXene layers and the mesopores / micropores of the carbon material, while electrons are rapidly conducted through the MXene and carbon network, thus endowing the composite anode with the ability to rapidly charge and discharge at high rates and a stable structure.

[0045] (3) Preparation of negative electrode sheet: The heteroatom functionalized MXene / silicon / carbon composite material powder can be mixed with conductive agent (such as acetylene black) and binder (such as water-based binder such as PVDF or CMC-sodium alginate), and mixed with solvent to form a slurry. The slurry is then uniformly coated on copper foil current collector, dried, and rolled to form a negative electrode sheet.

[0046] Example 1: Application of nitrogen-doped MXene / silicon / carbon composite anode in 5Ah pouch cell 1.1 Material preparation: Nitrogen-doped MXene and composite anode materials were prepared according to the methods described in the specific embodiments above.

[0047] The specific steps are as follows: First, take Ti3C2T x MXene precursor powder (obtained by etching Ti3AlC2, with –F and –OH terminal groups on the surface of the lamellars) was dispersed in dimethylformamide (DMF) solvent, and urea (providing a nitrogen source) at 5% by mass of MXene was added. The mixture was transferred to a sealed stainless steel reactor and subjected to a solvothermal reaction at 160°C for 8 hours. After the reaction, the product was centrifuged, repeatedly washed with water and ethanol, and vacuum dried to obtain nitrogen-doped MXene (denoted as N-MXene) powder.

[0048] 1.2 Subsequently, the obtained N-MXene was mixed with silicon nanoparticles (average particle size 100 nm) and porous graphite at a mass ratio of 2:3:5, and ultrasonically dispersed in deionized water for 1 hour to obtain a homogeneous slurry. The slurry was then rapidly frozen and freeze-dried under vacuum to obtain N-MXene / Si / C composite powder with a three-dimensional porous network structure.

[0049] Take 80 parts (by weight) of the above composite powder, add 10 parts of conductive carbon black and 10 parts of binder (carboxymethyl cellulose CMC: sodium alginate = 1:1 mixed binder), and use deionized water as solvent to prepare a slurry. Coat the slurry evenly on a copper foil current collector, vacuum dry and then calender to prepare a negative electrode sheet with a thickness of about 50 µm.

[0050] The active material (N-MXene / Si / C composite powder) coating in this negative electrode is approximately 2.0 mg / cm². 2 (Of which silicon accounts for approximately 0.8 mg / cm³) 2 This corresponds to approximately 40% of the total mass fraction of silicon in the active material.

[0051] 1.3 Battery Assembly: The above-mentioned negative electrode sheet is used as the negative electrode of the battery, and combined with commercially available layered Ni 0.8 Co 0.1 Mn 0.1O2 (NCM811) positive electrode sheets are paired and assembled into a stacked soft-pack lithium-ion battery with a capacity of about 5Ah (the negative electrode capacity is slightly extra in the design to ensure that lithium is not excessively consumed in the whole battery).

[0052] The electrolyte consisted of 1 M LiPF6 dissolved in a mixed solvent of ethylene carbonate / dimethyl carbonate (EC / DMC, volume ratio 1:1), with 10 wt% fluoroethylene carbonate (FEC) added as an additive. A 20 µm thick three-layer composite microporous membrane was used as the separator. To improve the initial coulombic efficiency and reduce irreversible lithium loss from the silicon anode during initial cycling, the anode sheet underwent pre-lithiation treatment after vacuum packaging and before formal formation. Specifically, the assembled pouch cell was left to stand for 12 hours to fully wet the electrolyte, followed by low-current pre-lithiation formation at a constant temperature of 25°C. First, the battery was charged at a constant current of 0.02C until the anode potential approached the lithium intercalation plateau region (corresponding to a full cell voltage of approximately 2.5~3.0V). Then, the charge was switched to constant voltage mode and maintained for 2~6 hours, with the cutoff current set at 0.005C, allowing a suitable amount of lithium ions to slowly intercalate into the silicon-carbon anode. After pre-lithiation, a shallow charge-discharge activation at 0.05C is performed to promote the formation of a uniform and stable SEI film on the negative electrode surface. The amount of lithium inserted during the entire pre-lithiation process is controlled to be 60-90% of the initial irreversible capacity of the negative electrode to avoid lithium plating or local stress concentration on the electrode due to excessive lithium insertion.

[0053] Performance testing: The manufactured 5Ah pouch cells underwent electrochemical performance testing at room temperature and low temperature.

[0054] First, the battery was subjected to one complete charge-discharge cycle at 0.1C (approximately 0.5A) at room temperature to determine the initial capacity and initial coulombic efficiency. Rate performance was then evaluated by cycling 10 times each at 1C, 5C, and 10C. Finally, a long-cycle life test was conducted at 5C. Simultaneously, the battery was placed at -20°C to test its low-temperature discharge performance.

[0055] Initial capacity and initial efficiency: The battery achieves an initial charge capacity of 5.2 Ah and an initial discharge capacity of 4.8 Ah at 0.1C, corresponding to an initial coulombic efficiency of 92.3%, which meets the target requirement of >90% proposed in this invention.

[0056] In contrast, the control cell using undoped MXene (Comparative Example 1) had an initial efficiency of only about 84%, showing that the introduction of N-MXene effectively reduced irreversible losses in the first cycle.

[0057] Rate performance: At 1C discharge, the battery of this invention discharges a capacity of about 5.0 Ah, which is equivalent to 96% of the capacity at 0.1C; at a high rate of 5C, the discharge capacity is about 4.6 Ah (accounting for 88% of the initial capacity); even when the discharge rate is increased to 10C for ultra-high rate and high current discharge, the battery can still output about 4.3 Ah (accounting for 83% of the initial capacity).

[0058]

[0059] Furthermore, the battery also exhibits excellent performance under low-temperature conditions: for example, when discharged at a 1C rate at -20°C, it can still release approximately 4.5 Ah of capacity, reaching more than 90% of the room temperature capacity, demonstrating the excellent capacity retention capability of the material of this invention at low temperatures.

[0060] Cycle life: Long-term cycle testing was conducted at room temperature using a 1C rate. Results showed that after 1500 cycles, the battery retained approximately 85% of its capacity; after 800 cycles at a 5C high rate, the capacity retention was approximately 78%. The coulombic efficiency remained stable above 99.5% during cycling. Disassembly analysis revealed that the N-MXene-constructed conductive network effectively mitigated silicon particle volume expansion, no significant pulverization of the negative electrode was observed, and the electrode thickness increased by approximately 20%. In contrast, the comparative battery exhibited significantly poorer cycle stability under the same conditions.

[0061] Comparative Example 1: Comparison of unmodified MXene / silicon / carbon composite anode pouch cells To highlight the effect of heteroatom functionalization on MXene modification, this embodiment prepared a silicon-carbon anode material without MXene doping and tested its performance in a 5Ah pouch cell of the same specification. The results were compared with those of Example 1.

[0062] Material preparation: The preparation process is basically the same as in Example 1, but without MXene heteroatom doping. That is, the original Ti3C2T is directly prepared. x MXene (unfunctionalized, still containing –F and –OH terminal groups on its surface) was mixed with silicon nanoparticles and porous graphite at a mass ratio of 2:3:5, and then ultrasonically dispersed and dried to obtain MXene / Si / C composite powder. Subsequently, it was coated and fabricated using the same method as in Example 1, and assembled into a 5Ah stacked soft-pack battery. Except for the different negative electrode active material, the positive electrode, separator, electrolyte, and other components and assembly processes of the battery were identical to those in Example 1.

[0063] Performance testing: The rate performance and cycle life of the comparative battery were evaluated under the same test conditions as in Example 1.

[0064] Initial efficiency: The initial charge-discharge test at 0.1C showed that the initial coulombic efficiency of the comparative battery was approximately 84.5%, significantly lower than the 92.3% of Example 1. This is because the inert groups such as -F on the surface of the undoped MXene sheets resulted in poor contact with the silicon interface, leading to the formation of a thicker and more unstable SEI film during the first cycle, which consumed more reversible lithium source.

[0065] Rate performance: The comparison battery has a capacity of about 4.8 Ah at 1C discharge, which is equivalent to 95% of the initial capacity, not much different from Example 1; however, the capacity drops to about 4.2 Ah at 5C (accounting for 83% of the initial capacity), and only outputs about 3.5 Ah at 10C high current discharge (about 67% of the initial capacity).

[0066] In contrast, Example 1 retained 83% of its capacity at 10C discharge. This indicates that the unmodified MXene composite anode exhibits a more significant increase in internal impedance and polarization at high rates, limiting the release of usable capacity. This is because the undoped MXene layers are more tightly stacked, restricting lithium-ion diffusion channels, and the MXene-silicon interface has a higher contact resistance, leading to performance degradation at high rates.

[0067] Cycle life: In long-cycle testing at 1C rate, the capacity retention of the comparison battery decreased to about 72% after about 1000 cycles; after continuing to cycle to 1500 cycles, the capacity retention further decreased to about 60%. Under 5C high-rate cycling conditions, the capacity retention of the comparison battery was already below 70% after about 500 cycles, and the degradation subsequently accelerated significantly.

[0068] During the cycle, its coulombic efficiency fluctuated significantly in the initial stage (approximately 98.5%~99.2%), and gradually stabilized at around 99.3% in the later stage, but the overall stability was still significantly lower than that of Example 1.

[0069] Disassembly analysis revealed that the undoped MXene anode exhibited a certain degree of localized pulverization and active material detachment after cycling, with some silicon particles peeling off from the MXene layers. The anode thickness expanded by approximately 30% after cycling, significantly higher than the approximately 20% in Example 1, indicating that the MXene without heteroatom functionalization treatment has relatively limited buffering capacity and interface stabilizing effect on silicon volume expansion.

[0070] The above results show that although unmodified MXene can improve the conductive network and cycling stability of silicon anodes to some extent, its overall performance is still significantly inferior to the heteroatom-functionalized MXene system proposed in this invention.

[0071] Comparative Example 2: Comparison of conventional silicon / carbon anode pouch cells without MXene This embodiment prepares a battery using a conventional silicon / carbon composite anode material without MXene addition to evaluate the performance benchmark without the MXene system.

[0072] Material Preparation: Silicon nanoparticles and porous graphite from the same batch as in the previous examples were selected as raw materials. They were directly mixed at a mass ratio of 3:7 as the negative electrode active material (the silicon ratio was appropriately reduced compared to Examples 1 and 2 to ensure slurry processability, but the silicon content remained approximately 30 wt%). 10% by mass of binder (CMC / SBR mixed binder) and a small amount of conductive agent were added to prepare a slurry, which was then coated onto copper foil, dried, and compacted to prepare an MXene-free silicon / carbon composite negative electrode sheet. A soft-pack battery with a capacity of approximately 5 Ah was assembled: the negative electrode used the aforementioned silicon / carbon negative electrode sheet, while the positive electrode and electrolyte were the same as in Examples 1 and 2. Due to the lack of an MXene framework, the negative electrode sheet underwent pre-lithiation treatment before battery formation to minimize silicon powdering, but the effect was limited.

[0073] Performance testing: The battery was tested using a method similar to that described in the previous embodiments, and the results are as follows: Initial efficiency: The initial coulombic efficiency of this battery, measured at 0.1C, was only about 72%. The initial charge capacity was approximately 5.0 Ah, while the initial discharge capacity was only about 3.6 Ah, indicating significant reversible capacity loss. This is mainly attributed to the formation of a large amount of lithium-ion-consuming SEI and by-reaction products under high silicon content. Due to the absence of effective interfacial stabilizing components such as MXene, silicon particles are exposed to the electrolyte during the first cycle and undergo severe side reactions, resulting in an initial efficiency far lower than that of Example 1 and Comparative Example 1, which contain MXene.

[0074] Rate performance: At 1C discharge, the battery's discharge capacity is approximately 4.0 Ah (only 80% of the rated capacity); at 2C, it drops to approximately 3.0 Ah (60%); at 5C, it is less than 2.0 Ah (<40%); and at a high rate of 10C, the battery can barely function (discharge capacity is less than 20% of the initial capacity, and the discharge voltage plateau drops significantly). It is evident that the silicon / carbon electrode without MXene participation exhibits poor rate performance due to the lack of an effective conductive network and severe polarization. This result contrasts sharply with Example 1—which still maintained over 80% capacity output at 10C, while this example struggles to maintain normal capacity above 5C.

[0075] Cycle life: Cyclic tests were conducted at 1C rate. The results showed that the capacity retention of this conventional silicon / carbon anode battery decreased to about 80% after about 300 cycles; the capacity retention decreased to about 55% after 600 cycles; and after about 800 cycles, the battery showed significant capacity decay and increased polarization, making it difficult to continue to operate stably.

[0076] During cycling, the battery's coulombic efficiency fluctuated significantly, and the interfacial impedance continued to increase. Disassembly revealed that the negative electrode exhibited significant pulverization, active material detachment, and severe thickness expansion, with the overall thickness of the negative electrode increasing by more than 45%. Simultaneously, a large number of uneven SEI byproduct layers formed on the surface of the silicon particles, indicating that without the MXene conductive framework and interfacial stabilization, the silicon negative electrode is unable to withstand the volumetric stress generated during long-term cycling.

[0077] The above results indicate that the traditional silicon / carbon anode system has poor cycle stability under high silicon content conditions, making it difficult to achieve both high rate capability and long lifespan performance.

[0078] The technical solution proposed in this invention successfully combines the high capacity of silicon with the high power and long cycle characteristics close to those of supercapacitors, which is a significant improvement over traditional technology.

[0079] In conclusion, the comparative results of the above embodiments fully demonstrate the effectiveness of the present invention. By functionalizing silicon-carbon anode materials with heteroatoms MXene, the key performance indicators of the battery were significantly improved.

[0080] The nitrogen-doped MXene / silicon / carbon anode 5Ah pouch cell shown in Example 1 achieved excellent performance, including an initial efficiency >90%, 10C rate capacity retention >80%, and a cycle life exceeding 1500 cycles with capacity retention still above 80%. In contrast, Comparative Example 1 (without MXene heteroatom doping) and Comparative Example 2 (completely without MXene) showed significant performance deficiencies, particularly in cycle life and high-rate output. These data clearly demonstrate the enhancing effect of heteroatom functionalization on MXene modification and the crucial importance of MXene in improving the performance of silicon anodes.

[0081] In summary, the preparation method of heteroatom-functionalized MXene-modified silicon-carbon anode material provided by this invention is practical and effective. Through innovative design of material composition and structure, it successfully solves the three major problems of insufficient conductivity, interface instability, and severe volume expansion in high-silicon anodes, enabling silicon-based anodes to possess both high energy density and high power, as well as long lifespan. This novel composite material shows great application potential in lithium-ion capacitors, electric vehicle power batteries, and large-scale energy storage systems, and is expected to promote further development in related fields. The specific embodiments and data mentioned in the above specification are intended to better illustrate the principles of this invention. Those skilled in the art should understand that various equivalent substitutions or modifications can be made to the details without departing from the spirit of this invention, and all such modifications or variations fall within the scope of protection claimed by this invention.

[0082] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a heteroatom-functionalized MXene-modified silicon-carbon anode material, characterized in that, Includes the following steps: S1. Preparation of heteroatom-functionalized MXene: Layered MXenes are dispersed in an organic solvent, and a precursor compound containing heteroatom elements is added to carry out a solvothermal reaction, thereby introducing heteroatom doping into the interlayer or surface terminal groups of the MXenes to obtain heteroatom-functionalized MXenes; the doping content of the heteroatom elements in the MXenes is 1~15 at% S2, Preparation of silicon-carbon composite materials: Heteroatom-functionalized MXene, silicon nanoparticles, and porous carbon materials are mixed and dispersed in a medium in a certain proportion, and ultrasonically stirred to form a suspension. After processing, a three-dimensional cross-linked gel-like precursor or a porous powder-like precursor is obtained. The precursor is dried under an inert atmosphere and lightly pressed to obtain a silicon-carbon composite material powder modified with heteroatom-functionalized MXene, which is the modified silicon-carbon anode material.

2. The method according to claim 1, characterized in that, In S1, MXene is a two-dimensional layered material of transition metal carbides or nitrides, with the general formula M n+1 X n T x , where M is a transition metal element, X is carbon or nitrogen, and T is a terminal group on the surface of MXene; The heteroatomic element includes any one or more of nitrogen, phosphorus, and boron. The precursor compounds containing heteroatoms include nitrogen source precursors, phosphorus source precursors, and boron source precursors; The nitrogen source precursor includes any one of urea, melamine, and ammonia water; The phosphorus source precursor includes any one of phosphoric acid, phosphate, and organic phosphorus-containing compounds; The boron source precursor includes any one of boric acid and organoborides; The organic solvent is a water-organic mixed solvent or a polar organic solvent; The solvothermal reaction temperature is no higher than 200℃.

3. The method according to claim 2, characterized in that, The MXene is Ti3C2T x ; The solvothermal reaction temperature is 120~200℃, and the duration is 4~24h.

4. The method according to claim 1, characterized in that, In S2, the mass fraction ratio of heteroatom-functionalized MXene, silicon nanoparticles, and porous carbon materials is (5~40wt%):(15~50wt%):(10~45wt%). The average particle size of the silicon nanoparticles is 50~1000 nm; The porous carbon material is selected from any one of porous graphite, graphene, hard carbon, and soft carbon; The dispersion medium is water or ethanol; The process to obtain the three-dimensional cross-linked precursor includes vacuum filtration or freeze-drying.

5. A heteroatom-functionalized MXene-modified silicon-carbon anode composite material, characterized in that, Obtained by the preparation method according to any one of claims 1 to 4.

6. The heteroatom-functionalized MXene-modified silicon-carbon anode composite material according to claim 5, characterized in that, The modified silicon-carbon anode composite material comprises heteroatom-functionalized MXene-modified silicon-carbon composite material powder, conductive agent and binder mixed and blended into a slurry, uniformly coated on copper foil current collector, dried and rolled into shape; The mass ratio of the heteroatom-functionalized MXene-modified silicon-carbon composite powder, conductive agent, and binder is 8:1:

1. The conductive agent is acetylene black; The adhesive is a water-based adhesive; The water-based adhesive includes one or more of sodium carboxymethyl cellulose, styrene-butadiene rubber latex, polyacrylic acid, and sodium alginate.

7. A lithium-ion battery negative electrode sheet, characterized in that, It includes the heteroatom-functionalized MXene-modified silicon-carbon anode composite material as described in claim 5.

8. The application of the heteroatom-functionalized MXene-modified silicon-carbon anode composite material as described in claim 5 in the preparation of lithium-ion batteries, lithium-ion capacitors, electric vehicle power batteries, and battery cells for large-scale energy storage systems.

9. The application according to claim 8, characterized in that, The lithium-ion battery is composed of a positive electrode, a separator, an electrolyte, and the heteroatom-functionalized MXene-modified silicon-carbon anode composite material as the negative electrode.

10. The application according to claim 9, characterized in that, The electrolyte is an organic solvent electrolyte containing lithium salt; The lithium-ion battery is suitable for an operating temperature range of -30 to 60°C.

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