SAs-MXene / MOF-graphite aerogel composite material, negative electrode plate and preparation method

Abstract

The invention provides an SAs-MXene / MOF-graphite aerogel composite material, a negative electrode plate and a preparation method, and relates to the technical field of lithium ion battery negative electrode materials, the aerogel composite material comprises graphite, single atoms and MXene / MOF aerogel; the MXene / MOF aerogel is aerogel which is formed by transition metal carbide or nitride and a metal organic framework and is of a three-dimensional structure. The graphite is dispersed in pores and / or the surface of the three-dimensional structure of the MXene / MOF aerogel; and the single atoms are anchored on the surface of the transition metal carbide or nitride in the MXene / MOF aerogel. According to the SAs-MXene / MOF-graphite composite aerogel structure design, the interlayer spacing of MXene is increased, intercalation and deintercalation of lithium ions in the cycle process are facilitated, the problem of volume expansion in the negative electrode cycle process is effectively relieved, the cycle life of the battery is prolonged, and the safety of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, and in particular to an SAs-MXene / MOF-graphite aerogel composite material, an anode sheet, and a preparation method thereof. Background Technology

[0002] With the development of technology, lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and environmentally friendly characteristics. Currently, commercially available lithium-ion batteries mainly use graphite as the anode material. During charging and discharging, graphite undergoes volume expansion, although much less than silicon-based materials. However, long-term accumulation or extreme conditions can still cause significant damage to battery performance and safety, such as capacity decay, shortened cycle life, and thermal runaway.

[0003] Several patented inventions have been developed to address the expansion problem of lithium-ion battery anode materials during cycling. One approach involves coating graphite with amorphous carbon, carbon nanotubes, or graphene. This utilizes the carbon layer to buffer volume changes, suppress particle pulverization, and improve conductivity. However, excessively thick coatings can hinder lithium-ion diffusion, reducing rate performance; carbon materials themselves still exhibit volume expansion (e.g., soft carbon), resulting in insufficient long-term cycle stability; and the preparation process is complex (e.g., CVD), leading to high costs. Another approach involves depositing metals (Ag, Cu) or oxides (SiO2, Al2O3) on the graphite surface. This utilizes a rigid coating to limit expansion while simultaneously improving conductivity. However, metal coatings are expensive, and oxide coatings increase interfacial impedance; however, the coating-graphite interface is prone to peeling, leading to long-term cycle failure; and the processes are complex (e.g., magnetron sputtering), hindering large-scale application.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide an SAs-MXene / MOF-graphite aerogel composite material, a negative electrode sheet, and a preparation method. By combining SAs-MXene with a metal-organic framework (MOF) and graphite to form an SAs-MXene / MOF-graphite composite aerogel structure, the recombination of MXene nanosheets is effectively prevented. This solves the problem of strong interlayer van der Waals forces and hydrogen bonds between MXene layers in the prior art, which lead to nanosheet aggregation, and significantly improves the performance of MXene as an electrode material.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides an SAs-MXene / MOF-graphite aerogel composite material, comprising graphite, single atoms, and MXene / MOF aerogel;

[0008] The MXene / MOF aerogel is a three-dimensional aerogel formed from transition metal carbides or nitrides and a metal-organic framework.

[0009] The graphite is dispersed in the pores and / or surface of the MXene / MOF aerogel three-dimensional structure;

[0010] The single atom is anchored to the surface of the transition metal carbide or nitride in the MXene / MOF aerogel.

[0011] Furthermore, based on the above technical solution, the graphite and the single atom are connected by coordinate bonds;

[0012] And / or, the transition metal carbides or nitrides and the metal-organic framework are chemically cross-linked to form a three-dimensional conductive network;

[0013] And / or, the graphite surface is covered by layers of the transition metal carbides or nitrides and crystals of the metal-organic framework;

[0014] And / or, the edge oxygen-containing groups of the graphite form a hydrogen bond network with the MXene / MOF aerogel;

[0015] And / or, the transition metal carbides or nitrides include Ti3C2Tx, Ti3C2, Ti4C3, V2C, Ta4C3T x or Nb2CT x At least one of them, where x is 1 to 2;

[0016] And / or, the single atom includes at least one of Ru, Ni, Cu, Co, and Mn;

[0017] And / or, the metal-organic framework includes at least one of ZIF-67, ZIF-8, MIL-101, MIL-125, UIO-66, and UIO-67;

[0018] And / or, the graphite loading in the SAs-MXene / MOF-graphite aerogel composite material is 35-55 wt%.

[0019] The present invention also provides a method for preparing the SAs-MXene / MOF-graphite aerogel composite material as described above, comprising the following steps:

[0020] S1: Add MAX ceramic phase powder to HF solution, stir, and then dry and deposit to obtain MXene powder;

[0021] S2: Disperse MXene powder in water, add a first metal salt, and process it to obtain metal ion modified MXene. Then anneal the metal ion modified MXene to obtain metal single-atom modified MXene material, namely SAs-MXene material.

[0022] S3: The second metal salt and the organic ligand are placed in solvents to obtain solution A and solution B respectively; the SAs-MXene material is then dispersed in solution A, and solution B is slowly added to solution A while stirring to obtain the SAs-MXene@MOF complex;

[0023] S4: The SAs-MXene@MOF composite is mixed with a chitosan solution, ultrasonically dispersed, pre-frozen, and freeze-dried to obtain SAs-MXene@MOF aerogel; the SAs-MXene@MOF aerogel is impregnated in a graphite ethanol dispersion and dried to obtain an SAs-MXene / MOF-graphite aerogel composite material.

[0024] Furthermore, based on the above technical solution, in step S1, the mass ratio of MAX ceramic phase powder to HF solution is 1:5 to 1:8;

[0025] And / or, the MAX ceramic phase powder includes one or more of Ti3AlC2, Ti4AlC3, V2AlC, Ta4AlC3, and Nb2AlC;

[0026] And / or, in step S1, the stirring includes: stirring at a temperature of 45-65°C for 12-24 hours until the pH value is 6-8 and stirring is stopped.

[0027] And / or, in step S1, the drying deposition includes: drying deposition for 8-10 hours in a vacuum oven at 50-70°C and a vacuum degree of 0.1-1 kPa.

[0028] Furthermore, based on the above technical solution, in step S2, the mass-to-volume ratio of MXene powder to water is 1-5 mg: 1 mL;

[0029] And / or, in step S2, the first metal salt includes one of RuCl3 and its crystalline hydrate, NiCl2 and its crystalline hydrate, CuCl2 and its crystalline hydrate, CoCl2 and its crystalline hydrate, and MnCl2 and its crystalline hydrate;

[0030] And / or, in step S2, the mass ratio of the first metal salt to the MXene powder is 1:50 to 1:200;

[0031] And / or, in step S2, the treatment includes: adjusting pH, magnetic stirring under a protective atmosphere, centrifuging and then collecting the precipitate and freeze-drying;

[0032] Adjusting pH refers to using dilute hydrochloric acid to adjust the pH to 3-4.

[0033] The magnetic stirring time is 8-12 hours, and the speed is 300-500 rpm;

[0034] And / or, the annealing includes: annealing at 300-400°C for 1-2 hours in a mixed gas atmosphere;

[0035] The mixed gas atmosphere refers to a mixture of hydrogen and argon.

[0036] Hydrogen accounts for 3-10% of the total volume of the mixed gas;

[0037] And / or, the loading of metal single atoms in the SAs-MXene material is 0.5-2 wt%.

[0038] Furthermore, based on the above technical solution, the second metal salt includes one of Zn(NO3)2 and its crystalline hydrate, Co(NO3)2 and its crystalline hydrate, Cr(NO3)3 and its crystalline hydrate, TiCl4, Ti(OBu)4, ZrCl2, ZrOCl2 and its crystalline hydrate;

[0039] And / or, in step S3, the mass-to-volume ratio of the SAs-MXene material to the liquid A is 1-2.5 mg: 1 mL;

[0040] And / or, in step S3, the organic ligand includes one of 2-methylimidazolium, terephthalic acid, and 4,4'-biphenyldicarboxylic acid;

[0041] And / or, in step S3, the solvent includes one or more of methanol, ethanol, isopropanol, N,N-dimethylformamide, and dimethyl sulfoxide;

[0042] And / or, in step S3, the molar ratio of the second metal salt to the organic ligand is 1:4 to 1:8;

[0043] And / or, in step S3, the stirring refers to stirring at room temperature for 6-12 hours to allow the MOF to grow on the surface of the SAs-MXene material.

[0044] Furthermore, based on the above technical solution, the mass-volume ratio of the SAs-MXene@MOF complex to the chitosan solution is 1g:7mL to 1g:10mL;

[0045] And / or, in step S4, the mass percentage concentration of the chitosan solution is 0.2% to 0.5%;

[0046] And / or, in step S4, the pre-freezing temperature is -50 to -80°C, and the time is 12 to 24 hours;

[0047] And / or, in step S4, the freeze-drying temperature is -60 to -80°C, and the time is 24 to 48 hours;

[0048] And / or, in step S4, the graphite ethanol dispersion is prepared by dispersing 1-2g of graphite in 50-100mL of ethanol solution.

[0049] And / or, in step S4, the drying temperature is 50-70°C and the time is 6-12 hours;

[0050] And / or, in step S4, the impregnation includes: impregnating for 30 to 60 minutes under a vacuum of -0.08 to -0.1 MPa, and repeating the impregnation 4 to 7 times.

[0051] The present invention also provides a negative electrode sheet, the negative electrode sheet comprising the SAs-MXene / MOF-graphite aerogel composite material as described above or the SAs-MXene / MOF-graphite aerogel composite material prepared by the method described above.

[0052] The present invention also provides a method for preparing the negative electrode sheet as described above, comprising the following steps:

[0053] The SAs-MXene / MOF-graphite aerogel composite material prepared by the above-described method or the SAs-MXene / MOF-graphite aerogel composite material prepared by the above-described method, the conductive agent, the first binder and the second binder are mixed and homogenized, coated on the current collector, dried, rolled and sliced ​​to obtain the negative electrode sheet.

[0054] Furthermore, based on the above technical solution, the conductive agent includes one or more of conductive carbon black, carbon nanotubes, and graphene.

[0055] And / or, the first binder is sodium carboxymethyl cellulose (CMC);

[0056] And / or, the second adhesive is styrene-butadiene rubber latex (SBR);

[0057] And / or, the mass ratio of the SAs-MXene / MOF-graphite aerogel composite material, the conductive agent, the first binder, and the second binder is (96-96.5):(0.3-0.8):(1-1.5):(1.8-2.3);

[0058] And / or, the current collector is copper foil;

[0059] And / or, the drying temperature is 75-85℃.

[0060] The present invention provides an SAs-MXene / MOF-graphite aerogel composite material, a negative electrode sheet, and a preparation method, with the following beneficial effects:

[0061] 1. By anchoring single atoms on the MXene surface as an electrochemical catalyst, the formation of stable components such as LiF and Li2CO3 in the SEI film is promoted, the electrolyte decomposition and repeated SEI film rupture are inhibited, the interfacial impedance is reduced, the cycle life is extended, and the catalytic regulation of lithium-ion migration is enhanced. Single atoms can also promote uniform lithium-ion deposition and reduce local volume abrupt changes through strong metal-support (MXene) interaction (SMSI).

[0062] 2. By combining SAs-MXene with metal-organic frameworks (MOF) to form SAs-MXene / MOF-graphite composite aerogel structure, the recombination of MXene nanosheets is effectively prevented, solving the problem of strong interlayer van der Waals forces and hydrogen bonds between MXene layers in the prior art that lead to nanosheet aggregation, and significantly improving the performance of MXene as an electrode material.

[0063] 3. The SAs-MXene / MOF-graphite composite aerogel structure design provided by this invention increases the interlayer spacing of MXene, which is beneficial for the insertion and extraction of lithium ions during cycling, effectively alleviates the volume expansion problem during negative electrode cycling, and improves the cycle life and safety of the battery.

[0064] 4. This invention utilizes the advantages of metal-organic framework (MOF) materials, such as high specific surface area, uniform pores, and stable structure, to adsorb electrolyte through the multi-level porous structure (micropore-mesopore) of MOF, thereby alleviating stress concentration during the lithium insertion / deintercalation process of graphite; the addition of SAs-MXene material can not only improve the conductivity of the composite material, but also serve as the framework of the aerogel structure, further enhancing the mechanical strength and stability of the composite material.

[0065] 5. The SAs-MXene@MOF-graphite composite material adopts an aerogel structure design, which has good porosity and flexibility, and can effectively buffer the expansion of the negative electrode during cycling, thereby improving the overall performance and safety of the battery.

[0066] 6. MOF and MXene are chemically cross-linked (e.g., carboxyl / amino bonding) to construct a three-dimensional porous network, forming an aerogel framework with high mechanical strength and adjustable porosity. The "double buffer" mechanism of the three-dimensional aerogel inhibits the directional regulation of graphite anode expansion. Moreover, the three-dimensional aerogel has high thermal stability (MXene and MOF have high temperature resistance), which can reduce the risk of thermal runaway and enhance safety performance.

[0067] 7. The composite material preparation method of the present invention is simple and controllable, with a mild process, and is suitable for large-scale production. Attached Figure Description

[0068] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0069] Figure 1 This is a schematic diagram illustrating the preparation of the SAs-MXene@MOF aerogel provided by the present invention. Detailed Implementation

[0070] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0071] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0072] According to a first aspect of the present invention, an SAs-MXene / MOF-graphite aerogel composite material is provided, comprising graphite, single atoms (SAs), and MXene / MOF aerogel;

[0073] The MXene / MOF aerogel is an aerogel with a three-dimensional structure formed by transition metal carbides or nitrides (MXene) and metal-organic frameworks (MOF).

[0074] The graphite is dispersed in the pores and / or surface of the MXene / MOF aerogel three-dimensional structure;

[0075] The single atom is anchored to the surface of the transition metal carbide or nitride in the MXene / MOF aerogel.

[0076] Specifically, transition metal carbides or nitrides (MXenes), as novel two-dimensional materials, have shown great potential in electrode materials for secondary batteries and supercapacitors due to their high conductivity, hydrophilicity, abundant surface functional groups, and flexible tunable composition. The high conductivity of graphite can synergize with the conductivity of MXenes to form an efficient electron transport network, reducing the internal resistance of the electrode material. Moreover, the inventors discovered that MXenes are excellent supports for single-atom catalysts (SCAs), with single atoms (SAs) dispersed in an isolated form on the support, achieving nearly 100% atomic utilization. However, the strong interlayer van der Waals forces and hydrogen bonds between MXene sheets easily lead to nanosheet aggregation, severely limiting their practical application. Furthermore, the inventors found that metal-organic frameworks (MOFs), due to their high specific surface area, uniform pores, and structural stability, can serve as ideal MXene modification materials, effectively preventing MXene nanosheet stacking and improving their performance as electrode materials. Therefore, by combining single-atom modified MXene (SAs-MXene) with metal-organic frameworks (MOFs) to form a three-dimensional MXene / MOF aerogel, the single atoms, anchored on the MXene surface, act as electrochemical catalysts, promoting the formation of stable components such as LiF and Li2CO3 in the SEI film, inhibiting electrolyte decomposition and repeated SEI film rupture, and also reducing interfacial impedance and extending cycle life. MXene can improve the conductivity of MOF materials, while MOFs can improve the stacking problem of MXene nanosheets, increase the interlayer spacing of MXene, which is beneficial for lithium ion insertion and extraction during cycling, and also helps to further buffer the expansion of the negative electrode during cycling.

[0077] This invention utilizes a single-atom catalyst to stabilize the SEI film, suppress lithium dendrite formation, and reduce interfacial impedance; MXene constructs a conductive network to accelerate ion transport and enhance mechanical stability; and MOFs optimize ion transport by buffering volume expansion through multi-level pores. The combination of these three elements achieves a comprehensive performance optimization encompassing interfacial stability, enhanced conductivity, and expansion suppression.

[0078] In an optional embodiment of the present invention, the graphite and the single atom are connected by coordinate bonds.

[0079] Specifically, single atoms, such as Ru, possess d-orbital vacancies, which can form Ru-C coordination bonds with graphite defect sites. The Ru single atom is firmly fixed to the defect sites on the graphite substrate through these Ru-C coordination bonds. This strong interaction effectively inhibits the migration and aggregation of single atoms during charging and discharging, thereby improving its thermal and chemical stability. Furthermore, the Ru-C coordination structure possesses the characteristics of a metal-like active center, which can induce specific reduction reactions at the interface. It can selectively catalyze the decomposition of carbonate solvents (such as EC and DEC) or LiPF6 in the electrolyte, promoting the preferential formation of stable SEI components such as LiF and Li₂CO₃. These components have high mechanical strength and ionic conductivity, contributing to the construction of a uniform, dense, and stable SEI film, reducing side reactions and lithium dendrite growth.

[0080] As an optional embodiment of the present invention, the transition metal carbide or nitride (MXene) and the metal-organic framework (MOF) are chemically cross-linked to form a three-dimensional conductive network.

[0081] As an optional embodiment of the present invention, the graphite surface is covered by the sheets of the transition metal carbide or nitride and the crystals of the metal-organic framework;

[0082] The edge oxygen-containing groups of the graphite form a hydrogen bond network with the MXene / MOF aerogel.

[0083] Specifically, MXene itself has metal-like conductivity, and when combined with graphite, it can form a highly efficient electron transport channel. The hydrogen bond network may further optimize electron migration efficiency and reduce interface resistance by regulating charge distribution. Meanwhile, the coating of transition metal carbide / nitride sheets and MOF crystals can effectively enhance the mechanical strength of graphite and prevent it from cracking or collapsing under stress.

[0084] Furthermore, the graphite loaded on the pores and / or surface of the MXene / MOF aerogel has a layered structure and is chemically inert, which can further synergize with MOF to buffer the stress of MXene nanosheets during lithium ion insertion / extraction, reduce interlayer slippage or fracture, extend material life, and also serve as a physical support to prevent graphite from collapsing due to volume expansion or contraction during cycling.

[0085] As an optional embodiment of the present invention, the transition metal carbide or nitride (MXene) includes Ti3C2T. x , Ti3C2, Ti4C3, V2C, Ta4C3T x or Nb2CT x At least one of them, where x is 1 to 2;

[0086] Specifically, the present invention applies MXene (such as Ti3C2T) in composite materials. x It has high electrical conductivity similar to metals (~6000 S / cm), and its unique two-dimensional sheets form a continuous conductive network in the aerogel, which makes up for the insufficient conductivity of graphite itself (graphite conductivity ~100 S / cm) and ensures rapid ion transport. Moreover, MXene has excellent mechanical strength (elastic modulus ~330 GPa), which can enhance the toughness of the aerogel skeleton and prevent structural collapse caused by graphite expansion during cycling.

[0087] The single atoms (SAs) include at least one of Ru, Ni, Cu, Co, and Mn, preferably Ru;

[0088] Specifically, MXene (such as Ti3C2T) x The surface of MXene often contains functional groups (Tx) such as hydroxyl (-OH), fluorine (-F), and oxygen (-O). These functional groups have lone pairs of electrons, which are natural anchoring sites for single atoms and can be combined with single atoms (such as metal atoms) through coordination bonds. In this invention, single atoms, by anchoring to the MXene surface, can act as electrochemical catalysts to promote the generation of stable components such as LiF and Li2CO3 in the SEI film, inhibit electrolyte decomposition and repeated SEI film rupture. In addition, single atoms can also reduce interfacial impedance, such as the d orbital electrons of Ru forming weak interactions with Li+ in the electrolyte, accelerating the transport of lithium ions at the electrode-electrolyte interface, reducing charge transfer impedance. A stable SEI film can reduce the continuous consumption of active lithium and electrolyte, thereby extending cycle life. Furthermore, single atoms can also improve low-temperature performance, making its catalytic effect still effective at low temperatures (-20°C).

[0089] The metal-organic framework (MOF) includes at least one of ZIF-67, ZIF-8, MIL-101, MIL-125, UIO-66, and UIO-67, with ZIF-8 being preferred.

[0090] Specifically, MOFs have high porosity (>70%) and adjustable pore sizes (micropores ~1.2nm, mesopores ~3nm). Their three-dimensional channels provide a physical buffer space for the volume expansion of graphite during charging and discharging, disperse local stress, and reduce particle breakage and active material shedding. Moreover, the regular channels of MOFs can also serve as channels for rapid lithium-ion diffusion, reducing the diffusion resistance of lithium-ion insertion / extraction from the graphite layer and improving rate performance. MOF materials can effectively suppress expansion and stabilize the SEI film to reduce the risk of thermal runaway.

[0091] As an optional embodiment of the present invention, the graphite loading in the SAs-MXene / MOF-graphite aerogel composite material is 35-55 wt% (e.g., 40 wt%, 45 wt%, 50 wt%, etc.).

[0092] According to a second aspect of the invention, such as Figure 1 As shown, a method for preparing the SAs-MXene / MOF-graphite aerogel composite material as described above is provided, comprising the following steps:

[0093] S1: Add MAX ceramic phase powder to HF solution, stir, and then dry and deposit to obtain MXene powder;

[0094] S2: Disperse MXene powder in water, add a first metal salt, and process it to obtain metal ion modified MXene. Then anneal the metal ion modified MXene to obtain metal single-atom modified MXene material, namely SAs-MXene material.

[0095] S3: The second metal salt and the organic ligand are placed in solvents to obtain solution A and solution B respectively; the SAs-MXene material is then dispersed in solution A, and solution B is slowly added to solution A while stirring to obtain the SAs-MXene@MOF complex;

[0096] S4: The SAs-MXene@MOF composite is mixed with a chitosan solution, ultrasonically dispersed, pre-frozen, and freeze-dried to obtain SAs-MXene@MOF aerogel; the SAs-MXene@MOF aerogel is impregnated in a graphite ethanol dispersion and dried to obtain an SAs-MXene / MOF-graphite aerogel composite material.

[0097] As an optional embodiment of the present invention, in step S1, the mass ratio of MAX ceramic phase powder to HF solution is 1:5 to 1:8, such as 1:6, 1:7, etc.

[0098] The HF solution has a mass-volume percentage concentration of 20-30% (e.g., 23%, 25%, 27%, etc.), and its function is to obtain MXene by chemically etching the atom layer in the MAX material. Typically, and not specifically, the HF solution chemically etches the Al atomic layer in Ti3AlC2 to form Ti3C2T. x x is 1 to 2;

[0099] The stirring includes: stirring at a temperature of 45-65℃ (e.g., 47℃, 50℃, 55℃, 60℃, etc.), stirring for 12-24h (e.g., 14h, 18h, 20h, 22h, etc.), until the pH value is 6-8 and stirring is stopped.

[0100] The drying deposition includes: drying and depositing for 8-10 hours (e.g., 8.5 hours, 9 hours, 9.5 hours, etc.) in a vacuum oven at 50-70℃ (e.g., 55℃, 57℃, 60℃, 65℃, 68℃, etc.) and a vacuum degree of 0.1-1kPa (e.g., 0.3kPa, 0.5kPa, 0.7kPa, etc.);

[0101] The MAX ceramic phase powder includes one or more of Ti3AlC2, Ti4AlC3, V2AlC, Ta4AlC3, and Nb2AlC.

[0102] As an optional embodiment of the present invention, in step S2, MXene powder is dispersed in water and ultrasonicated under a protective atmosphere, typically and non-limitingly, under a nitrogen atmosphere for 30 to 60 minutes, so that MXene powder is fully dispersed in water.

[0103] As an optional embodiment of the present invention, in step S21, in order to balance dispersibility, reaction efficiency and operational feasibility, the mass-volume ratio of MXene powder to water is 1 to 5 mg: 1 mL (e.g., 2 mg: 1 mL, 3 mg: 1 mL, 4 mg: 1 mL, etc.).

[0104] The first metal salt includes one of RuCl3 and its crystalline hydrate (e.g., RuCl3·3H2O), NiCl2 and its crystalline hydrate (e.g., NiCl2·6H2O), CuCl2 and its crystalline hydrate (e.g., CuCl2·2H2O), CoCl2 and its crystalline hydrate (e.g., CoCl2·6H2O), and MnCl2 and its crystalline hydrate (e.g., MnCl2·4H2O);

[0105] Specifically, in this invention, single atoms anchored on the MXene surface act as electrochemical catalysts, promoting the generation of stable components such as LiF and Li2CO3 in the SEI film, inhibiting electrolyte decomposition and repeated SEI film rupture, reducing interfacial impedance, extending cycle life, and enhancing catalytic regulation of lithium-ion migration; in addition, single atoms can also promote uniform lithium-ion deposition through strong metal-support interactions, reducing the effect of local volume abrupt changes.

[0106] The mass ratio of the first metal salt to the MXene powder is 1:50 to 1:200 (e.g., 1:70, 1:90, 1:100, 1:130, 1:150, 1:180, etc.);

[0107] As an optional embodiment of the present invention, in step S2, the process includes: adjusting pH, performing magnetic stirring under a protective atmosphere, centrifuging and then taking the precipitate and freeze-drying.

[0108] Adjusting pH refers to using dilute hydrochloric acid (concentration of 1 mol / L) to adjust the pH to 3-4 in order to promote the adsorption of metal ions;

[0109] The magnetic stirring time is 8-12 hours (e.g., 9 hours, 10 hours, 11 hours, etc.), and the speed is 300-500 rpm (e.g., 350 rpm, 400 rpm, 450 rpm, etc.).

[0110] As an optional embodiment of the present invention, the annealing includes: annealing at 300-400℃ (e.g., 320℃, 340℃, 360℃, 370℃, 380℃, etc.) for 1-2 hours (e.g., 1.3 hours, 1.5 hours, 1.7 hours, etc.) in a mixed gas atmosphere;

[0111] Specifically, annealing reduces metal ions to a single-atom state; the single metal atom can form strong covalent bonds with the functional groups on the MXene surface, such as Ru-O-Ti; annealing can also enhance the strength of chemical bonds; if the annealing temperature is >400℃, it will lead to the decomposition of MXene, and if the annealing temperature is <300℃, it will lead to insufficient reduction of metal ions.

[0112] The mixed gas atmosphere refers to a mixture of hydrogen and argon.

[0113] Hydrogen accounts for 3-10% of the total volume of the mixed gas (e.g., 4%, 5%, 6%, 7%, 8%, 9%, etc.), preferably 5-6%;

[0114] Specifically, the present invention limits the volume percentage of hydrogen in the mixed gas atmosphere because 3-10% hydrogen can provide appropriate reducing power. If the hydrogen percentage is less than 3%, it will lead to incomplete reduction of single atoms. If the hydrogen percentage is greater than 10%, it will lead to excessive reduction and destruction of the MXene carbon layer, causing the aggregation of single atoms. Argon is an inert gas to prevent MXene oxidation.

[0115] The loading of metal single atoms in the SAs-MXene material is 0.5-2wt%, such as 0.7wt%, 1wt%, 1.3wt%, 1.5wt%, 1.7wt%, etc.

[0116] Specifically, this invention limits the loading of metal single atoms in the SAs-MXene material to ensure the electrochemical catalytic effect of the metal single atoms anchored on the MXene surface. If the loading of metal single atoms is too high, it will lead to the aggregation of metal single atoms to form metal nanoparticles. Metal nanoparticles have a high proportion of low-activity atoms, which are suitable for inactive matrices that are not sensitive to the support structure, such as carbon black. However, the MXene surface contains a variety of active functional groups. When metal nanoparticles are loaded on the MXene surface, it is difficult for them to connect with the functional groups on the MXene surface through chemical bonds, and it will also destroy the layered structure advantage of the MXene surface. This not only affects the performance of the MXene material, but also significantly reduces its catalytic activity and stability. Conversely, if the loading of metal single atoms is too low, its catalytic effect will be poor.

[0117] As an optional embodiment of the present invention, the second metal salt includes one of Zn(NO3)2 and its hydrates (e.g., Zn(NO3)2·6H2O), Co(NO3)2 and its hydrates (e.g., Co(NO3)2·6H2O), Cr(NO3)3 and its hydrates (e.g., Cr(NO3)3·9H2O), TiCl4, Ti(OBu)4, ZrCl4, ZrOCl2 and its hydrates (e.g., ZrOCl2·8H2O);

[0118] In step S3, the mass-to-volume ratio of the SAs-MXene material to the liquid A is 1 to 2.5 mg: 1 mL, such as 1.2 mg: 1 mL, 1.5 mg: 1 mL, 1.8 mg: 1 mL, 2 mg: 1 mL, 2.3 mg: 1 mL, etc.

[0119] The organic ligand includes one of 2-methylimidazolium, terephthalic acid, and 4,4'-biphenyldicarboxylic acid;

[0120] The solvent includes one or more of methanol, ethanol, isopropanol, N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO); typically, without limitation, the amount of solvent added is sufficient to allow the second metal salt and the organic ligand to dissolve uniformly.

[0121] The molar ratio of the second metal salt to the organic ligand is 1:4 to 1:8, such as 1:5, 1:6, 1:7, etc.

[0122] As an optional embodiment of the present invention, in step S3, the solution B is slowly added to solution A, and the pH needs to be adjusted to 10-11 using triethylamine;

[0123] In step S3, stirring refers to stirring at room temperature for 6-12 hours (e.g., 7 hours, 8 hours, 9 hours, 11 hours, etc.) to allow MOF to grow on the surface of SAs-MXene material; typically, but not specifically, the obtained SAs-MXene@MOF composite is centrifuged, the precipitate is washed with methanol to remove unreacted MOF particles, and then dried at 60°C for later use.

[0124] As an optional embodiment of the present invention, the mass-volume ratio of the SAs-MXene@MOF complex to the chitosan solution is 1g:7mL to 1g:10mL, such as 1g:8mL, 1g:9mL, etc.

[0125] Specifically, if the content of SAs-MXene@MOF composite is too low and the content of chitosan solution is too high, it may lead to problems such as insufficient strength of aerogel structure or excessive pores. If the content of chitosan is relatively high, it will not only dilute the active material, but also reduce the conductivity of the composite material because it is an insulator. At the same time, it may cause pore blockage and affect mass transfer and electrochemical performance.

[0126] Conversely, if the content of SAs-MXene@MOF complex is too high and the content of chitosan solution is too low, it will lead to insufficient mechanical strength, failure to effectively crosslink the composite particles, uneven dispersion of SAs-MXene@MOF complex, and easy cracking defects during freeze-drying, thereby affecting the overall structure and performance stability of the aerogel.

[0127] In step S4, the mass percentage concentration of the chitosan solution is 0.2% to 0.5%, such as 0.3% or 0.4%.

[0128] Specifically, if the concentration of chitosan as a binder is too high, it will block the porous structure; if the concentration is too low, it will cause the aerogel to be brittle due to insufficient mechanical strength.

[0129] In step S4, the pre-freezing temperature is -50 to -80℃ (e.g., -60℃, -70℃, etc.), and the time is 12 to 24 hours (e.g., 14 hours, 18 hours, 20 hours, 22 hours, etc.).

[0130] In step S4, the freeze-drying temperature is -60 to -80℃ (e.g., -65℃, -70℃, -75℃, etc.), and the time is 24 to 48 hours (e.g., 28 hours, 30 hours, 35 hours, 40 hours, etc.).

[0131] In step S4, the graphite ethanol dispersion is prepared by dispersing 1-2g (e.g., 1.3g, 1.5g, 1.8g, etc.) of graphite in 50-100mL (e.g., 60mL, 70mL, 80mL, 90mL, etc.) of ethanol solution.

[0132] In step S4, the drying temperature is 50-70℃ (e.g., 55℃, 60℃, 65℃, etc.), and the time is 6-12h (e.g., 8h, 10h, 11h, etc.).

[0133] In step S4, the impregnation includes: impregnating for 30 to 60 minutes under a vacuum of -0.08 to -0.1 MPa, and repeating the impregnation 4 to 7 times.

[0134] According to a third aspect of the present invention, a negative electrode is provided, the negative electrode comprising the SAs-MXene / MOF-graphite aerogel composite material as described above.

[0135] According to a fourth aspect of the present invention, a method for preparing the negative electrode sheet as described above is provided, comprising the following steps:

[0136] The SAs-MXene / MOF-graphite aerogel composite material, conductive agent, first binder and second binder are mixed and homogenized into a slurry, coated onto the current collector, dried, rolled and sliced ​​to obtain the negative electrode sheet.

[0137] As an optional embodiment of the present invention, the conductive agent includes one or more of conductive carbon black, carbon nanotubes, and graphene;

[0138] The first binder is sodium carboxymethyl cellulose (CMC).

[0139] The second adhesive is styrene-butadiene rubber latex (SBR).

[0140] The mass ratio of the SAs-MXene / MOF-graphite aerogel composite material, conductive agent, first binder, and second binder as described above is (96-96.5):(0.3-0.8):(1-1.5):(1.8-2.3); preferably 96.2:0.5:1.3:2.

[0141] The current collector is a copper foil;

[0142] The drying temperature is 75-85℃, preferably 80℃.

[0143] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0144] Example 1

[0145] This embodiment provides a RuSAs-MXene / MOF-graphite aerogel composite material, comprising graphite, single-atom Ru, and MXene / MOF aerogel;

[0146] The MXene / MOF aerogel is an aerogel with a three-dimensional structure formed by transition metal carbides or nitrides (MXene) and metal-organic frameworks (MOFs).

[0147] The graphite is dispersed in the pores and / or surface of the three-dimensional structure;

[0148] The single-atom Ru is anchored to the surface of the transition metal carbide or nitride.

[0149] This embodiment also provides a method for preparing RuSAs-MXene / MOF-graphite aerogel composite material, including:

[0150] S1. Preparation of MXene materials:

[0151] Ti3AlC2 powder was slowly added to an HF solution (concentration 30%) at a mass ratio of 1:5. The mixture was then stirred at 60°C for 24 hours until the pH reached 6. The mixture was then dried in a vacuum oven at 50°C for 8 hours to obtain MXene powder.

[0152] S2, Single-atom loading:

[0153] 100 mg of MXene was dispersed in 100 mL of deionized water and sonicated for 30 minutes under a nitrogen atmosphere. Then, 5 mg of RuCl3·3H2O was added, and the pH was adjusted to 4 with dilute hydrochloric acid to promote Ru... 3+ Adsorption was performed under N2 atmosphere with magnetic stirring for 12 hours. After centrifugation, the precipitate was washed three times with ultrapure water and freeze-dried to obtain Ru-modified MXene. After centrifugation, washing, and vacuum drying, the MXene was annealed in a tube furnace at 300°C for 2 hours under an H2 / Ar (5% H2) mixed gas atmosphere to reduce Ru3- metal ions. + As a single-atom state, RuSAs-MXene was obtained. The Ru loading was determined to be 1.8 wt% by ICP-OES.

[0154] S3. Synthesis of RuSAs-MXene@MOF composite materials:

[0155] Zn(NO3)2·6H2O (1 mM) and 2-methylimidazole (4 mM) were dissolved in 20 mL of methanol and named solutions A and B, respectively. 50 mg of RuSAs-MXene was dispersed in solution A, and solution B was slowly added to solution A. Triethylamine was added to adjust the pH of the solution to 10, and the mixture was stirred at room temperature for 8 hours. ZIF-8 grew on the MXene surface, forming a RuSAs-MXene@MOF composite. The mixture was centrifuged and washed three times with methanol to remove unreacted MOF particles, and then dried at 60 °C to obtain the RuSAs-MXene@MOF composite material.

[0156] S4. Constructing a three-dimensional aerogel and loading it with graphite:

[0157] 10 g of RuSAs-MXene@MOF composite material was mixed with 100 mL of 0.3% chitosan solution and ultrasonically dispersed. Then, it was pre-frozen at -80°C for 12 hours and freeze-dried for 24 hours to obtain RuSAs-MXene@MOF aerogel. The RuSAs-MXene@MOF aerogel was immersed in a graphite ethanol dispersion (2 g / 50 mL), vacuumed (-0.1 MPa) for 30 minutes, and this immersion process was repeated 6 times. The mixture was then dried at 60°C to obtain the RuSAs-MXene@MOF-graphite aerogel composite material.

[0158] The graphite loading in the RuSAs-MXene / MOF-graphite aerogel composite material is 50 wt%.

[0159] This embodiment also provides a negative electrode sheet, which comprises the RuSAs-MXene / MOF-graphite aerogel composite material as described above.

[0160] This embodiment also provides a method for preparing the negative electrode sheet as described above, including the following steps:

[0161] The negative electrode formulation mass ratio is: RuSAs-MXene@MOF-graphite aerogel composite material: SuperP:CMC:SBR = 96.2:0.5:1.3:2. The mixture is homogenized, coated on copper foil, and vacuum dried at 80℃.

[0162] Example 2

[0163] In this embodiment, RuCl3·3H2O in step S2 of Example 1 is replaced with CuCl2·2H2O, and the rest is kept the same as in Example 1, finally obtaining CuSAs-MXene@MOF-graphite aerogel.

[0164] Example 3

[0165] In this embodiment, the type of MAX in step S1 of embodiment 1 is replaced with V2AlC, and the rest is consistent with embodiment 1.

[0166] Comparative Example 1: MOF@MXene-graphite composite aerogel material

[0167] The difference between this comparative example and Example 1 is that the MXene powder obtained in step S1 is directly added to step S3, that is, step S2 is omitted and no single-atom loading is performed. The remaining steps and technical parameters are the same as those in Example 1.

[0168] Comparative Example 2: RuSAs-MXene-graphite composite aerogel material

[0169] The difference between this comparative example and Example 1 is that the RuSAs-MXene obtained in step S2 is directly added to step S4 and mixed with the chitosan solution, i.e., step S3 is omitted. The remaining steps and technical parameters are the same as in Example 1.

[0170] Comparative Example 3: MXene-graphite aerogel materials

[0171] The difference between this comparative example and Example 1 is that the MXene powder obtained in step S1 is directly added to step S4 and mixed with the chitosan solution, that is, steps S2 and S3 are omitted. The remaining steps and technical parameters are the same as those in Example 1.

[0172] Comparative Example 4: MOF-graphite aerogel materials

[0173] The difference between this comparative example and Example 1 is that ZIF-8 was prepared and directly mixed with the chitosan solution, i.e., steps S1-S3 were omitted. The remaining steps and technical parameters are the same as in Example 1.

[0174] Comparative Example 5: Pure graphite without any composite material modification

[0175] The difference between this comparative example and Example 1 is that step S5 includes:

[0176] The negative electrode formulation mass ratio is: graphite:SuperP:CMC:SBR = 96.2:0.5:1.3:2. The mixture is homogenized, coated onto copper foil, and vacuum dried at 80℃.

[0177] Comparative Example 6

[0178] The main difference between this comparative example and Example 1 is that the loading of metal single atoms in the RuSAs-MXene material is 5wt%, which is equivalent to adding 14mg of RuCl3·3H2O in step S2. The remaining steps and technical parameters are the same as those in Example 1.

[0179] Comparative Example 7

[0180] The main difference between this comparative example and Example 1 is that in step S2, the annealing temperature is 250°C, while the other steps and technical parameters are the same as in Example 1.

[0181] Comparative Example 8

[0182] The main difference between this comparative example and Example 1 is that in step S4, the mass-to-volume ratio of the RuSAs-MXene@MOF complex to the chitosan solution is 1 g: 4 mL. The remaining steps and technical parameters are the same as in Example 1.

[0183] Performance testing

[0184] Preparation of positive electrode:

[0185] The positive electrode sheet is obtained by homogenizing the material according to the mass ratio of LFP:SP:PVDF = 97:1:2, coating it onto aluminum foil, vacuum drying at 80℃, and then rolling and slicing it.

[0186] Lithium-ion batteries were prepared by injecting electrolyte, forming, and aging the positive electrode sheet and the negative electrode sheet provided in the examples or comparative examples. The performance was tested. The electrolyte was lithium salt (LiPF6 with a concentration of 1M) and solvent (ethylene carbonate and dimethyl carbonate, with a volume ratio of ethylene carbonate and dimethyl carbonate of 1:1). The separator was a 12μmpp separator.

[0187] The test method for capacity retention after 500 cycles: The aforementioned lithium iron phosphate battery was subjected to a cyclic test at 25°C with a 0.33C charge rate followed by a 0.33C discharge rate, using Xinwei testing equipment. The capacity retention data after 500 cycles was recorded. A higher capacity retention rate is better, as it means the battery can maintain a high capacity storage capacity for a longer period during use.

[0188] Test method for electrode expansion rate after 500 cycles: Disassemble the battery after 500 cycles with the power discharged, take out the negative electrode and measure its thickness. Expansion rate = (thickness after cycle - thickness before cycle) / thickness before cycle × 100%.

[0189] Test method for rate performance (capacity retention @ 2C): The aforementioned lithium iron phosphate battery was tested using Xinwei testing equipment at 25°C with a 0.33C charging rate followed by a 2C discharging rate. The cycle was repeated 10 times, and the capacity retention rate data for each cycle of the aforementioned lithium iron phosphate battery was recorded and the average value was calculated.

[0190] Interface impedance (Ω·cm) 2 The testing method for the negative electrode is as follows: The surface resistivity of the negative electrode is tested. Specific steps are: 1. Place the electrode sample on the test platform of the instrument (Yuaneng Technology BER1030). 2. Set the pressure to 0.5-1 MPa and hold for approximately 15 seconds. 3. Record the values ​​obtained from each measurement. Repeat the test multiple times and take the average value to reduce error. A lower surface resistivity indicates better conductivity of the electrode.

[0191] Test method for capacity retention rate at -20℃ during 0.33C high and low temperature discharge: The aforementioned lithium iron phosphate battery was subjected to a test using Xinwei testing equipment. The temperature was adjusted to 25℃ and left to stand for 5 hours. It was then charged at a 0.33C rate until fully charged, left to stand for 5 minutes, and then the temperature was adjusted to -20℃ and left to stand for 8 hours. It was then discharged at a constant current of 0.33C until the battery was completely discharged. The discharge capacity retention rate data of the aforementioned lithium iron phosphate battery was recorded for each cycle after 10 cycles and the average value was calculated.

[0192] Test method for thermal runaway temperature (°C): Before cell testing, take photos of the voltage, internal resistance, and weight. Install two clamps with a preload of 300 kgf. Temperature measurement locations include the positive terminal, negative terminal, explosion-proof valve, center of the large surface area, and ambient environment. Charge the cell at a constant current and voltage of 0.33C to 3.65V, then continue charging at 1C for 12 minutes. Immediately start the heating device and continuously heat the cell at maximum power. When thermal runaway occurs or the heating point temperature reaches 300°C, stop the triggering and turn off the heating device. Observe the cell in the test environment for 1 hour. After cell testing, take photos of the voltage, internal resistance, and weight, and determine the thermal runaway temperature.

[0193] Results data

[0194] The performance of the lithium-ion batteries prepared in the examples and comparative examples was tested, as shown in Table 1:

[0195] Table 1

[0196]

[0197]

[0198] As shown in Table 1, Comparative Examples 1 and 3-5 do not contain single atoms, so their low-temperature capacity retention is low and their interface impedance is high. Comparative Examples 4-5 do not contain MXene conductive networks, so their capacity retention after 500 cycles, electrode expansion rate after 500 cycles, and rate performance are poor.

[0199] As shown in Table 1, the only difference between Example 1 and Example 2 is the type of single atom. According to Table 1, all performance indicators in Example 1 are better than those in Example 2. This is because the bonding ability and catalytic ability of single atom Ru to the support are stronger than those of Cu.

[0200] As shown in Table 1, the types of MXene in Example 3 are different from those in Example 1. The conductivity of MXene in Example 3 is weaker than that in Example 1, so it is slightly inferior to Example 1 in terms of retention rate performance and interface impedance.

[0201] As shown in Table 1, since Comparative Example 1 does not contain single atoms, the lithium-ion battery prepared in it has a lower low-temperature capacity retention rate and a higher interface impedance compared to Example 1.

[0202] As shown in Table 1, Comparative Example 2, lacking MOF, cannot provide an effective physical buffer space for the MXene material, which increases the diffusion resistance of lithium ions intercalating / extracting from the graphite layer, thus affecting the various performance characteristics of the prepared lithium-ion battery.

[0203] As shown in Table 1, Comparative Example 3 contains neither single atoms nor MOF, and the MXene material has a serious stacking problem. The insertion and extraction of lithium ions during cycling are difficult, which easily leads to expansion of the negative electrode during cycling, thus affecting the various performance characteristics of the prepared lithium-ion battery.

[0204] As shown in Table 1, Comparative Example 4 does not contain single atoms or MXene materials, and therefore cannot form an effective MXene conductive network. As a result, the capacity retention rate after 500 cycles, the electrode expansion rate after 500 cycles, and the rate performance are all poor.

[0205] As shown in Table 1, Comparative Example 5 is pure graphite without any composite material modification, and its performance is poor in all aspects.

[0206] As shown in Table 1, in Comparative Example 6, due to the excessive loading of metal single atoms in the RuSA-MXene material, the single atoms easily aggregate together to form nanoparticles, which greatly reduces the catalytic performance and causes local side reactions, lowering the thermal runaway temperature. Therefore, the performance is worse than that of Example 1.

[0207] As shown in Table 1, in Comparative Example 7, the annealing temperature was lower and the single-atom reduction was insufficient, resulting in a reduced catalytic effect. Therefore, its performance was worse than that of Example 1, but slightly better than that of Comparative Examples 1 and 6.

[0208] As shown in Table 1, Comparative Example 8 has a lower chitosan content and an unstable aerogel structure, resulting in severe expansion after cycling. Therefore, its performance is inferior to that of Example 1.

[0209] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A SAs-MXene / MOF-graphite aerogel composite material, characterized in that, Including graphite, single-atom and MXene / MOF aerogels; The MXene / MOF aerogel is a three-dimensional aerogel formed from transition metal carbides or nitrides and a metal-organic framework. The graphite is dispersed in the pores and / or surface of the MXene / MOF aerogel three-dimensional structure; The single atom is anchored to the surface of the transition metal carbide or nitride in the MXene / MOF aerogel.

2. The SAs-MXene / MOF-graphite aerogel composite material according to claim 1, characterized in that, The graphite and the single atom are connected by coordinate bonds; And / or, the transition metal carbides or nitrides and the metal-organic framework are chemically cross-linked to form a three-dimensional conductive network; And / or, the graphite surface is covered by layers of the transition metal carbides or nitrides and crystals of the metal-organic framework; And / or, the edge oxygen-containing groups of the graphite form a hydrogen bond network with the MXene / MOF aerogel; And / or, the transition metal carbide or nitride includes Ti3C2T x , Ti3C2, Ti4C3, V2C, Ta4C3T x or Nb2CT x At least one of them, where x is 1 to 2; And / or, the single atom includes at least one of Ru, Ni, Cu, Co, and Mn; And / or, the metal-organic framework includes at least one of ZIF-67, ZIF-8, MIL-101, MIL-125, UIO-66, and UIO-67; And / or, the graphite loading in the SAs-MXene / MOF-graphite aerogel composite material is 35-55 wt%.

3. A method for preparing the SAs-MXene / MOF-graphite aerogel composite material as described in any one of claims 1-2, characterized in that, Includes the following steps: S1: Add MAX ceramic phase powder to HF solution, stir, and then dry and deposit to obtain MXene powder; S2: Disperse MXene powder in water, add a first metal salt, and process it to obtain metal ion modified MXene. Then anneal the metal ion modified MXene to obtain metal single-atom modified MXene material, namely SAs-MXene material. S3: The second metal salt and the organic ligand are placed in solvents to obtain solution A and solution B respectively; the SAs-MXene material is then dispersed in solution A, and solution B is slowly added to solution A while stirring to obtain the SAs-MXene@MOF complex; S4: The SAs-MXene@MOF composite is mixed with a chitosan solution, ultrasonically dispersed, pre-frozen, and freeze-dried to obtain SAs-MXene@MOF aerogel; the SAs-MXene@MOF aerogel is impregnated in a graphite ethanol dispersion and dried to obtain an SAs-MXene / MOF-graphite aerogel composite material.

4. The preparation method of the SAs-MXene / MOF-graphite aerogel composite material according to claim 3, characterized in that, In step S1, the mass ratio of MAX ceramic phase powder to HF solution is 1:5 to 1:8; And / or, the MAX ceramic phase powder includes one or more of Ti3AlC2, Ti4AlC3, V2AlC, Ta4AlC3, and Nb2AlC; And / or, in step S1, the stirring includes: stirring at a temperature of 45-65°C for 12-24 hours until the pH value is 6-8 and stirring is stopped. And / or, in step S1, the drying deposition includes: drying deposition for 8-10 hours in a vacuum oven at 50-70°C and a vacuum degree of 0.1-1 kPa.

5. The method for preparing the SAs-MXene / MOF-graphite aerogel composite material according to claim 3, characterized in that, In step S2, the mass-to-volume ratio of MXene powder to water is 1–5 mg: 1 mL; And / or, in step S2, the first metal salt includes one of RuCl3 and its crystalline hydrate, NiCl2 and its crystalline hydrate, CuCl2 and its crystalline hydrate, CoCl2 and its crystalline hydrate, and MnCl2 and its crystalline hydrate; And / or, in step S2, the mass ratio of the first metal salt to the MXene powder is 1:50 to 1:200; And / or, in step S2, the treatment includes: adjusting pH, magnetic stirring under a protective atmosphere, centrifuging and then collecting the precipitate and freeze-drying; Adjusting pH refers to using dilute hydrochloric acid to adjust the pH to 3-4. The magnetic stirring time is 8-12 hours, and the speed is 300-500 rpm; And / or, the annealing includes: annealing at 300-400°C for 1-2 hours in a mixed gas atmosphere; The mixed gas atmosphere refers to a mixture of hydrogen and argon. Hydrogen accounts for 3-10% of the total volume of the mixed gas; And / or, the loading of metal single atoms in the SAs-MXene material is 0.5-2 wt%.

6. The method for preparing the SAs-MXene / MOF-graphite aerogel composite material according to claim 3, characterized in that, The second metal salt includes one of Zn(NO3)2 and its crystalline hydrate, Co(NO3)2 and its crystalline hydrate, Cr(NO3)3 and its crystalline hydrate, TiCl4, Ti(OBu)4, ZrCl4, ZrOCl2 and its crystalline hydrate; And / or, in step S3, the mass-to-volume ratio of the SAs-MXene material to the liquid A is 1-2.5 mg: 1 mL; And / or, in step S3, the organic ligand includes one of 2-methylimidazolium, terephthalic acid, and 4,4'-biphenyldicarboxylic acid; And / or, in step S3, the solvent includes one or more of methanol, ethanol, isopropanol, N,N-dimethylformamide, and dimethyl sulfoxide; And / or, in step S3, the molar ratio of the second metal salt to the organic ligand is 1:4 to 1:8; And / or, in step S3, the stirring refers to stirring at room temperature for 6-12 hours to allow the MOF to grow on the surface of the SAs-MXene material.

7. The method for preparing the SAs-MXene / MOF-graphite aerogel composite material according to claim 3, characterized in that, The mass-to-volume ratio of the SAs-MXene@MOF complex to the chitosan solution is 1g:7mL to 1g:10mL. And / or, in step S4, the mass percentage concentration of the chitosan solution is 0.2% to 0.5%; And / or, in step S4, the pre-freezing temperature is -50 to -80°C, and the time is 12 to 24 hours; And / or, in step S4, the freeze-drying temperature is -60 to -80°C, and the time is 24 to 48 hours; And / or, in step S4, the graphite ethanol dispersion is prepared by dispersing 1-2g of graphite in 50-100mL of ethanol solution. And / or, in step S4, the drying temperature is 50-70°C and the time is 6-12 hours; And / or, in step S4, the impregnation includes: impregnating for 30 to 60 minutes under a vacuum of -0.08 to -0.1 MPa, and repeating the impregnation 4 to 7 times.

8. A negative electrode sheet, characterized in that, The negative electrode includes the SAs-MXene / MOF-graphite aerogel composite material as described in any one of claims 1-2 or the SAs-MXene / MOF-graphite aerogel composite material as described in any one of claims 3-7.

9. A method for preparing a negative electrode sheet as described in claim 8, characterized in that, Includes the following steps: The SAs-MXene / MOF-graphite aerogel composite material prepared by the preparation method of the SAs-MXene / MOF-graphite aerogel composite material as described in any one of claims 1-2 or as described in any one of claims 3-7, a conductive agent, a first binder and a second binder are mixed and homogenized, coated on a current collector, dried, rolled and sliced ​​to obtain a negative electrode sheet.

10. The method for preparing the negative electrode sheet according to claim 9, characterized in that, The conductive agent includes one or more of conductive carbon black, carbon nanotubes, and graphene. And / or, the first binder is sodium carboxymethyl cellulose (CMC); And / or, the second adhesive is styrene-butadiene rubber latex (SBR); And / or, the mass ratio of the SAs-MXene / MOF-graphite aerogel composite material, the conductive agent, the first binder, and the second binder is (96-96.5):(0.3-0.8):(1-1.5):(1.8-2.3); And / or, the current collector is copper foil; And / or, the drying temperature is 75-85℃.

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