MXene material, preparation method and application

Abstract

The invention relates to the technical field of battery materials, in particular to an MXene material, a preparation method and application, a ternary layered compound material is placed in an etching solution to be etched, an MXene structure is obtained, and the etched MXene structure can form a multi-layer nanosheet layer structure; the MXene structure is placed in a lithium chloride solution for a reaction, an MXene nanosheet is obtained, lithium chloride serves as an intercalation agent, lamellar stripping of the MXene structure can be further achieved, and the nanosheet is formed; finally, the MXene nanosheet is placed in an alkali solution for a reaction, functional groups on the surface of the MXene nanosheet are adjusted, so that the surface of the MXene nanosheet is rich in oxygen atom groups with high electronegativity, and the oxygen-enriched MXene material is obtained. The MXene material can effectively regulate and control the diffusion and deposition process of lithium ions, promote the uniform distribution of lithium metal, contribute to improving the cycling stability and rate capability of a lithium metal battery, and solve the problem that the MXene material in the prior art is poor in regulation and control of lithium ion transmission and deposition uniformity.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and specifically to an MXene material, a preparation method and an application thereof, in particular to an MXene material, a preparation method and an application thereof based on high electronegativity. Background Art

[0002] Lithium metal batteries (LMBs) are considered to be the key to the next-generation high-energy density energy storage system due to their high theoretical capacity (3860 mAh g -1 ), and low electrochemical potential (-3.04 V vs. versus standard hydrogen electrode), and have great potential in the fields of electric vehicles, consumer electronics, etc.

[0003] A lithium metal battery is a rechargeable battery with metallic lithium or a lithium alloy as the negative electrode, and the positive electrode material can be sulfur (Li-S), oxygen (Li-O2) or metal oxide (Li-LMO), etc. The lithium metal negative electrode faces many challenges in practical applications, including problems such as lithium dendrite growth, interface instability and electrolyte decomposition. The root cause of these problems lies in the uneven distribution of lithium ions at the electrode interface and the electric field gradient, resulting in the deposition of lithium metal into whisker-like, moss-like or filamentous structures, which in turn leads to battery short circuit and rapid capacity decay, and poor cycle stability and rate performance.

[0004] In the prior art, three-dimensional (3D) framework structures or interface modification strategies are used to inhibit lithium dendrite growth, but these methods often cannot effectively solve the problem of volume change of lithium metal during charge and discharge. MXene materials are two-dimensional layered materials derived from transition metal carbides / nitrides / carbonitrides (such as Ti3C2), with the chemical formula M n+1 X n T x (M is a transition metal, X is C or N, T is a surface functional group, such as -OH, -F, -O, n = 1-3), and was first discovered in 2011 by Professor Yury Gogotsi and Michel Barsoum at Drexel University in the United States, and is named "MXene" because of its two-dimensional layered structure similar to graphene. MXene materials have high electrical conductivity, tunable surface chemistry and two-dimensional layered structure, and are widely used in lithium metal batteries as electrode materials to improve the cycle stability and rate performance of lithium metal batteries.

[0005] However, the existing MXene materials still have deficiencies in regulating the lithium ion transport and deposition uniformity, and cannot effectively improve the lithium ion transport kinetics. Therefore, there is an urgent need for a new MXene material design strategy to improve the performance of lithium metal batteries and promote the development of lithium metal batteries. Summary of the Invention

[0006] In view of the problem of poor regulation of lithium ion transport and deposition uniformity in MXene materials in the existing technology, the present invention provides an MXene material, a preparation method and an application thereof.

[0007] To achieve the above object, the present invention adopts the following technical solutions: The present invention provides a method for preparing an MXene material, comprising: Etching a ternary layered compound material in an etching solution to obtain an MXene structure; the ternary layered compound material is a MAX phase layered compound material; Reacting the MXene structure in a lithium chloride solution to obtain MXene nanosheets; Reacting the MXene nanosheets in an alkali solution to obtain an MXene material.

[0008] Optionally, the etching solution comprises HCl, HF and water, wherein the volume percentage of HCl is 40% - 70%, and the volume percentage of HF is 10% - 50%.

[0009] Optionally, the mass concentration of the lithium chloride solution is 1 - 6M.

[0010] Optionally, the molar concentration of the alkali solution is 6 - 12mol / L.

[0011] Optionally, the alkali solution is a KOH solution, an NaOH solution or an LiOH solution.

[0012] The present invention also provides an MXene material prepared by using the above method for preparing an MXene material.

[0013] A negative electrode of a lithium metal battery, the negative electrode of the lithium metal battery uses the above MXene material as a framework, and the MXene material is internally provided with metallic lithium.

[0014] The preparation method of the negative electrode of the lithium metal battery as described above comprises: Preparing an MXene material framework by using an MXene material; Placing the MXene material framework on the surface of molten lithium, and enabling the molten lithium to enter the MXene material framework to obtain a negative electrode of a lithium metal battery.

[0015] Optionally, the method for preparing the MXene material framework by using the MXene material is: Dispersing the MXene material in water and performing suction filtration to obtain an MXene material framework.

[0016] A lithium metal battery includes a positive electrode and the above-mentioned lithium metal battery negative electrode. The material of the positive electrode is LiCoO2, LiFePO4, NCM811 or sulfur.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing MXene material. In this method, a ternary layered compound material is etched in an etching solution to obtain an MXene structure, and the etched MXene structure will form a multi-layered nanosheet structure. The MXene structure is reacted in a lithium chloride solution to obtain MXene nanosheets. Lithium chloride, as an intercalating agent, can further realize the exfoliation of the MXene structure into nanosheets. Finally, the MXene nanosheets are reacted in an alkaline solution to adjust the functional groups on the surface of the MXene nanosheets, making the surface of the MXene nanosheets rich in highly electronegative oxygen atom groups, thus obtaining an oxygen-rich MXene material. The highly electronegative atoms on the surface of this MXene material can have a strong interaction with lithium ions, forming a stable interfacial structure. This interface can effectively regulate the diffusion and deposition processes of lithium ions, promote the uniform distribution of lithium metal, not only help reduce the risk of dendrite formation, but also delay the corrosion and over-lithiation of the lithium metal electrode, effectively optimize the interaction between the electrolyte and the lithium metal interface, and improve the efficiency and stability of the battery. In addition, the two-dimensional structure of the MXene material also helps to enhance the mechanical strength of the battery, improve the stability of the electrolyte, and prevent excessive swelling or rupture of the interface. At the same time, the high conductivity of the MXene material can also accelerate the charge and discharge reactions of the battery, improving the power density and energy density of the battery.

[0018] The present invention also provides an MXene material prepared by using the above-mentioned MXene material preparation method. The surface of this MXene material contains highly electronegative atoms, and when used as the negative electrode of a lithium metal battery together with lithium, it can have a strong interaction with lithium ions, forming a stable interfacial structure. This interface can effectively regulate the diffusion and deposition processes of lithium ions, promote the uniform distribution of lithium metal, and help improve the cycle stability and rate performance of the lithium metal battery.

[0019] A lithium metal battery negative electrode uses the above-mentioned MXene material as a framework, and the MXene material contains metallic lithium inside. This MXene material has the characteristics of low curvature and high stability. As a framework, it can enable the electrolyte to quickly penetrate, promote the rapid diffusion of lithium ions, effectively regulate the lithium ion transport. At the same time, it reduces the nucleation overpotential of lithium metal, inhibits the growth of lithium dendrites, improves the stability and safety of the battery, and the lithium metal battery negative electrode can effectively improve the electrochemical performance of the battery, such as cycle performance, rate performance and Coulomb efficiency.

[0020] The present invention provides a method for preparing a negative electrode of a lithium metal battery as described above. This method prepares a MXene material framework by using MXene materials; placing the MXene material framework on the surface of molten lithium. Since the MXene material has abundant lithiumophilic groups, the molten lithium can be rapidly injected into the framework prepared from the MXene material to obtain a negative electrode of the lithium metal battery. This method uses MXene materials with an expanded interlayer spacing to provide a physical confinement effect for the uniform deposition of lithium metal. The abundant interlayer channels can effectively accommodate the volume expansion of lithium metal and relieve the stress concentration during the cycling process, significantly inhibiting the formation of lithium dendrites, thereby improving the safety of the battery and extending the cycle life. The lithiumophilic functional groups on the surface of the MXene material can greatly reduce the interfacial energy between the molten lithium and the framework, promoting the rapid wetting and spontaneous injection of lithium. Compared with traditional copper / carbon-based current collectors, the strong chemical affinity between the MXene material framework and lithium can reduce the nucleation barrier of lithium deposition, realizing the uniform nucleation and dense filling of lithium metal, and avoiding the problem of "dead lithium" caused by local accumulation. This method does not require complex electrochemical prelithiation or high-pressure infiltration processes, and can achieve the rapid filling of lithium metal through simple physical contact, reducing energy consumption and equipment costs. The process is simple, cost controllable and has excellent performance, providing a solution for the industrialization of high-energy-density and high-safety lithium metal batteries.

[0021] The present invention also provides a lithium metal battery, including the negative electrode of the lithium metal battery as described above. This lithium metal battery shows a more stable current density distribution during the cycling process, the surface of the lithium metal electrode remains smoother and more uniform, avoiding the growth of lithium dendrites and the problem of internal short circuit of the battery, having a higher cycle life and safety, and having great application potential. Brief Description of the Drawings

[0022] Figure 1 It is a schematic flow chart of a method for preparing a MXene material of the present invention.

[0023] Figure 2 It is the SEM image and TEM image of the MXene nanosheets prepared in Example 2 of the present invention; among them, a is the SEM image and b is the TEM image.

[0024] Figure 3 It is the SEM image and TEM image of the MXene material prepared in Example 2 of the present invention; among them, a is the SEM image and b is the TEM image.

[0025] Figure 4 It is a flow chart of the method for preparing the negative electrode of the lithium metal battery of the present invention.

[0026] Figure 5Optical photograph and SEM cross-sectional view of the MXene material framework prepared in Example 10 of the present invention; wherein, a is the optical image of the appearance of the MXene material framework, b is the optical image of the bending process of the MXene material framework; c is the SEM cross-sectional image of the MXene material framework.

[0027] Figure 6 Optical image of the negative electrode of the lithium metal battery prepared in Example 10 of the present invention.

[0028] Figure 7 Long cycle deposition and stripping performance diagram of the half-cell prepared using the MXene material framework prepared in Example 10 of the present invention.

[0029] Figure 8 Cycling performance diagram of the full cell (with the positive electrode being LFP) at 1C prepared using the negative electrode of the lithium metal battery prepared in Example 10 of the present invention.

[0030] Figure 9 Cycling performance diagram of the full cell at 1C (with the positive electrode being NCM811) prepared using the negative electrode of the lithium metal battery prepared in Example 10 of the present invention. Detailed implementation manners

[0031] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art regarding the present invention. In case of conflict, the definition in this specification shall prevail.

[0032] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0033] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0034] In this article, unless otherwise specified, terms such as "comprising", "including", "containing", "having", or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A only comprises a".

[0035] In this document, for the sake of brevity of description, not all possible combinations of all the technical features in each implementation or embodiment are described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation or embodiment can be combined arbitrarily, and all possible combinations should be considered as falling within the scope described in this specification.

[0036] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0037] In the following embodiments, conventional instrument devices in the art are used. For the experimental methods without specific conditions noted in the following embodiments, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. In the following embodiments, various raw materials are used. Unless otherwise specified, commercially available products are used, and their specifications are the conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0038] The present invention will be further described in detail below in conjunction with specific embodiments, which are explanations rather than limitations of the present invention.

[0039] Example 1 See Figure 1 , the present invention provides a method for preparing an MXene material, comprising: S11: Place the ternary layered compound material in an etching solution for etching to obtain a MXene structure. Preferably, the ternary layered compound material is a MAX-phase layered compound material, especially a MAX phase containing main group elements such as aluminum, silicon, tin, germanium, etc. By controlling the etching conditions, selective etching of the A layer such as Al, Si, Sn, etc. can be carried out to prepare a MXene structure. Among them, the aluminum-containing MAX phase is Ti3AlC2, Ti2AlC, Cr2AlC, V2AlC, etc., the silicon-containing MAX phase is Ti3SiC2, Ti2SiC, etc., the tin-containing MAX phase is Ti2SnC, Nb2SnC, etc., and the germanium-containing MAX phase is Ti2GeC, Mo2GeC, etc. The etching solution includes HCl, HF, and water. The volume percentage of HCl is 40% - 70%, and the volume percentage of HF is 10% - 50%. Among them, as a strong acid, HF preferentially reacts with the A layer to form soluble fluorides (such as AlF3), precisely removing the Al layer in the MAX phase and retaining the two-dimensional layered structure of MXene. At the same time, HCl further promotes the etching process by dissolving these fluorides. For example, for Ti3AlC2, HF converts it into Ti3C2 and generates AlF3, while HCl reacts with AlF3 to form AlCl3, cooperating with HF to enhance the etching effect. The obtained MXene structure has a moderate interlayer binding force, providing an ideal substrate for subsequent intercalation and exfoliation. The specific operation is as follows: Place the ternary layered compound material in the etching solution and stir at 25°C - 60°C at 355 - 1000 rpm for 2 - 48 h, and then wash with deionized water until neutral to obtain a MXene structure. Among them, the concentration of the ternary layered compound material is 100 g / L.

[0040] S12: React the MXene structure in a lithium chloride solution to obtain MXene nanosheets. The concentration of the lithium chloride solution is 1 - 6 M. By using lithium chloride as an intercalating agent to achieve strong intercalation, MXene nanosheets are formed. Specifically: Place the MXene structure in the lithium chloride solution and react for 1.5 - 4 h, and then wash with deionized water to obtain MXene nanosheets.

[0041] S13: React the MXene nanosheets in an alkali solution to obtain a MXene material. The alkali solution is a KOH solution, NaOH, or LiOH solution, and the molar concentration of the alkali solution is 6 - 12 mol / L. Among them, the alkali solution further expands the interlayer spacing through the cation intercalation effect, accelerates ion transport, and reduces the proportion of etching residue functional groups such as fluorine (-F) or chlorine (-Cl), promoting the surface chemistry dominated by oxygen capping, further enhancing the electronegativity of the MXene material, and effectively regulating the lithium ion transport and deposition uniformity, thereby improving the cycle stability and rate performance of the lithium metal battery. Specifically: The MXene nanosheets are placed in an alkaline solution and shaken for 10 - 30 h under a nitrogen atmosphere at 60 °C - 70 °C, washed, and freeze-dried to obtain the MXene material.

[0042] Example 2 1 g of MAX phase Ti3AlC2 is added to an etching agent solution composed of 6 ml of HCl, 1 ml of HF, and 3 ml of deionized water, and stirred at 41 °C at 400 rpm for 17 h. Subsequently, it is washed with deionized water until the pH value is neutral (4500 rpm, 5 min) to obtain the MXene structure; The MXene material is immersed in a 25 mL deionized water solution containing 1.5 g of LiCl. After the reaction lasts for 2 h, it is repeatedly washed with deionized water (3500 revolutions per minute, 5 min) again to obtain MXene nanosheets; 0.05 g of MXene nanosheets is mixed with 50 mL of 10 mol / L KOH solution, continuously shaken under a N2 atmosphere at 67 °C for 24 h, the obtained product is collected, washed, and dried by freeze-drying technology to obtain the MXene material.

[0043] Example 3 1 g of MAX phase Ti3AlC2 is added to an etching agent solution composed of 6 ml of HCl, 1 ml of HF, and 3 ml of deionized water, and stirred at 41 °C at 400 rpm for 17 h. Subsequently, it is washed with deionized water until the pH value is neutral (4500 rpm, 5 min) to obtain the MXene structure; The MXene material is immersed in a 25 mL deionized water solution containing 1.5 g of LiCl. After the reaction lasts for 2 h, it is repeatedly washed with deionized water (3500 revolutions per minute, 5 min) again to obtain MXene nanosheets; 0.05 g of MXene nanosheets is mixed with 50 mL of 9 mol / L NaOH solution, continuously shaken under a N2 atmosphere at 60 °C for 30 h, the obtained product is collected, washed, and dried by freeze-drying technology to obtain the MXene material.

[0044] Example 4 1 g of MAX phase Ti3AlC2 is added to an etching agent solution composed of 6 ml of HCl, 1 ml of HF, and 3 ml of deionized water, and stirred at 41 °C at 400 rpm for 15 h. Subsequently, it is washed with deionized water until the pH value is neutral (4500 rpm, 5 min) to obtain the MXene structure; The MXene material was immersed in 30 mL of deionized aqueous solution containing 2.0 g of LiCl. After the reaction continued for 2 h, it was repeatedly washed with deionized water (3500 revolutions per minute, 5 min) to obtain MXene nanosheets; 0.05 g of MXene nanosheets was mixed with 50 mL of 11 mol / L LiOH solution and continuously oscillated for 15 h under a N2 atmosphere at 60 °C. The obtained product was collected, washed, and dried by freeze-drying technology to obtain the MXene material.

[0045] Example 5 1 g of MAX phase Cr2AlC was added to an etching agent solution composed of 4 ml of HCl, 5 ml of HF, and 1 ml of deionized water, and stirred at 1000 rpm at 41 °C for 30 h. Subsequently, it was washed with deionized water until the pH value was neutral (4500 rpm, 5 min) to obtain the MXene structure; The MXene material was immersed in 20 mL of deionized aqueous solution containing 1.5 g of LiCl. After the reaction continued for 2 h, it was repeatedly washed with deionized water (3500 revolutions per minute, 5 min) to obtain MXene nanosheets; 0.05 g of MXene nanosheets was mixed with 50 mL of 12 mol / L LiOH solution and continuously oscillated for 18 h under a N2 atmosphere at 65 °C. The obtained product was collected, washed, and dried by freeze-drying technology to obtain the MXene material.

[0046] Example 6 1 g of MAX phase Ti3SiC2 was added to an etching agent solution composed of 6 ml of HCl, 4 ml of HF, and 1 ml of deionized water, and stirred at 500 rpm at 50 °C for 48 h. Subsequently, it was washed with deionized water until the pH value was neutral (4500 rpm, 5 min) to obtain the MXene structure; The MXene material was immersed in 25 mL of deionized aqueous solution containing 1.5 g of LiCl. After the reaction continued for 2 h, it was repeatedly washed with deionized water (3500 revolutions per minute, 5 min) to obtain MXene nanosheets; 0.05 g of MXene nanosheets was mixed with 50 mL of 9 mol / L KOH solution and continuously oscillated for 20 h under a N2 atmosphere at 75 °C. The obtained product was collected, washed, and dried by freeze-drying technology to obtain the MXene material.

[0047] Example 7 1 g of MAX phase Ti2GeC was added to an etching solution composed of 6 ml of HCl, 3 ml of HF and 1 ml of deionized water, and stirred at 500 rpm at 45 °C for 24 h. Subsequently, it was washed with deionized water until the pH value was neutral (4500 rpm, 5 min) to obtain the MXene structure; The MXene material was immersed in 25 mL of deionized aqueous solution containing 1.5 g of LiCl. After the reaction continued for 2 h, it was washed repeatedly with deionized water (3500 rpm, 5 min) to obtain MXene nanosheets; 0.05 g of MXene nanosheets was mixed with 50 mL of 8 mol / L KOH solution, and continuously oscillated in a N2 atmosphere at 65 °C for 25 h. The obtained product was collected, washed, and dried by freeze-drying technology to obtain the MXene material.

[0048] Participate Figure 2 And Figure 3 And, the MXene nanosheets and MXene materials prepared in Example 2 were respectively subjected to SEM tests and TEM tests for comparison. It can be seen that the prepared MXene material did not change the structural characteristics of the MXene nanosheets. And after comparing the oxidation processes of the MXene nanosheets and MXene materials prepared in Example 2 respectively, it was found that the anti-oxidation effect of the MXene material was better than that of the MXene nanosheets. Existing MXene materials are very easy to oxidize. Under air conditions, oxidation easily starts from the edges and surfaces, and dendritic cracks or particles will be generated, and the mechanical strength is low. The anti-oxidation effect of the MXene material prepared in the present invention can effectively improve the mechanical properties of the anode material skeleton in the later stage.

[0049] Example 8 The present invention provides a MXene material, which is prepared by using the MXene material preparation method provided in the above embodiments. The surface of this MXene material contains atoms with high negative electronegativity. When used as the anode of a lithium metal battery together with lithium, it can have a strong interaction with lithium ions to form a stable interfacial structure. This interface can effectively regulate the diffusion and deposition processes of lithium ions, promote the uniform distribution of lithium metal, and contribute to improving the cycle stability and rate performance of lithium metal batteries.

[0050] Example 9 The present invention provides a negative electrode for a lithium metal battery. The negative electrode of the lithium metal battery uses the above-mentioned MXene material as a skeleton, and the MXene material contains metallic lithium. The MXene material has the characteristics of low curvature and high stability. As a skeleton, it can enable the electrolyte to quickly penetrate, promote the rapid diffusion of lithium ions, effectively regulate the lithium ion transport. At the same time, it reduces the nucleation overpotential of metallic lithium, inhibits the growth of lithium dendrites, improves the stability and safety of the battery. The negative electrode of the lithium metal battery can effectively improve the electrochemical performance of the battery, such as cycle performance, rate performance and Coulomb efficiency.

[0051] Example 10 See Figure 4 , the present invention also provides a method for preparing the negative electrode of the lithium metal battery as described above, including: S21: Prepare a MXene material skeleton using the MXene material. Specifically: Disperse the MXene material in an aqueous solution and disperse it with a cell disruptor, and obtain a MXene material skeleton by vacuum filtration.

[0052] S22: Place the MXene material skeleton on the surface of molten lithium, and enable the molten lithium to enter the MXene material skeleton to obtain a negative electrode of the lithium metal battery. Preferably, the molten lithium is generated by heating fresh lithium to 350 °C on a hot plate. Specifically: Place the prepared MXene material skeleton on the surface of molten lithium. Since the MXene material has abundant lithiumophilic groups, the molten lithium can be quickly injected into the MXene material skeleton to obtain a negative electrode of the lithium metal battery, denoted as Li / MXene.

[0053] See Figure 5 , conduct optical testing, flexibility testing and SEM testing on the MXene material skeleton. The results show that the MXene material skeleton prepared by the present invention has excellent mechanical properties, and the skeleton has a rich layered structure, providing a structural basis for improving lithium ion transport kinetics. See Figure 6 , it can be seen from the optical diagram of the negative electrode of the lithium metal battery that the MXene material skeleton has excellent lithium affinity. See Figure 7 , use the MXene material skeleton prepared in this example as the positive electrode, use lithium as the negative electrode, use polypropylene (PP2500) as the separator, and use CR2025 as the battery case. Assemble a button battery in a glove box filled with argon to obtain a half-cell. After standing in a constant temperature oven at 30 °C for 6 h, conduct electrochemical testing. First, activate 5 times at a current density of 0.5 mA cm -2 , and then conduct deposition and stripping testing at 1 mA cm -2 . At a current density of 0.5 mA cm -2 and a areal capacity of 0.5 mAh cm-2 Under the conditions, the MXene material skeleton exhibits an ultra-high Coulombic efficiency (99.41%) after 1600 cycles, indicating excellent electrochemical reversibility and a highly stable lithium deposition / stripping process. A high Coulombic efficiency means high lithium utilization and effective suppression of side reactions such as dead lithium formation and electrolyte decomposition.

[0054] Example 11 The present invention provides a lithium metal battery, including a positive electrode and the above-mentioned lithium metal battery negative electrode. The material of the positive electrode is LiCoO2, LiFePO4, NCM811 or sulfur. This lithium metal battery uses a standard electrolyte, and the electrolyte components include esters, ethers, and solid electrolytes, etc., to meet different battery requirements. This lithium metal battery shows a more stable current density distribution during cycling, the lithium metal electrode surface remains smoother and more uniform, avoiding the growth of lithium dendrites and internal short-circuit problems of the battery, having a higher cycle life and safety, and great application potential.

[0055] Using the lithium metal battery negative electrode prepared in Example 10 as the negative electrode, matching a high-loading lithium iron phosphate (LFP) as the positive electrode, and the battery case is CR2025. Button cells are assembled in a glove box filled with argon. After the obtained full cells are left standing in a 30 °C constant temperature oven for 6 h, electrochemical tests are carried out. First, they are activated by 5 charge-discharge cycles at 0.1C, and then charge-discharge cycle tests are carried out at 1C. The test voltage range is 2.8~3.9V. See Figure 8 and it is found that the full cell matching the high-loading LFP positive electrode with a surface loading of 20.0 mg cm -2 After cycling 300 times at 1C rate, the full cell can still provide a specific capacity of 133.9 (close to 80% of the theoretical capacity of LFP~170 mAhg -1 ), indicating that the lithium metal negative electrode modified with MXene material can effectively support the high-loading positive electrode, reduce polarization and maintain cycle stability.

[0056] Using the lithium metal battery negative electrode prepared in Example 10 as the negative electrode, matching a high-loading nickel cobalt manganese ternary positive electrode material (NCM811) as the positive electrode, and the battery case is CR2025. Button cells are assembled in a glove box filled with argon. After the obtained full cells are left standing in a 30 °C constant temperature oven for 6 h, electrochemical tests are carried out. First, they are activated by 5 charge-discharge cycles at 0.1C, and then charge-discharge cycle tests are carried out at 1C. The test voltage range is 2.8~3.9V. See Figure 9 and it is found that after cycling 750 times at 1C rate, the capacity retention rate reaches 75.5%, indicating that the MXene material prepared by the present invention has universality and is compatible with LFP (low cost and long life) and NCM811 (high energy density).

[0057] It can be seen that the electronegativity-regulated MXene material optimizes the lithium deposition behavior and interface stability by regulating the lithium-ion concentration at the reaction interface, enabling the lithium-metal battery to exhibit excellent cycling performance at high cathode loadings and in different chemical systems (from LFP to NCM811).

[0058] The above are only the preferred embodiments of the present invention and are not intended to limit the technical solutions of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principle of the present invention, the technical solutions can be subject to several simple modifications and substitutions, and these modifications and substitutions also fall within the protection scope covered by the claims.

Claims

1. A method for preparing MXene materials, characterized in that, Comprising: Etching a ternary layered compound material in an etching solution to obtain a MXene structure; The ternary layered compound material is a MAX-phase layered compound material; Reacting the MXene structure in a lithium chloride solution to obtain MXene nanosheets; Reacting the MXene nanosheets in an alkali solution to obtain a MXene material.

2. The method for preparing the MXene material according to claim 1, wherein, The etching solution comprises HCl, HF and water, wherein the volume percentage of HCl is 40% - 70%, and the volume percentage of HF is 10% - 50%.

3. The method for preparing MXene material according to claim 1, wherein The mass concentration of the lithium chloride solution is 1 - 6 M.

4. The method for preparing the MXene material according to claim 1, wherein The molar concentration of the alkali solution is 6 - 12 mol / L.

5. The method for preparing the MXene material according to claim 1, wherein, The alkali solution is a KOH solution, a NaOH solution or a LiOH solution.

6. An MXene material, characterized in that, Prepared by using the method for preparing a MXene material according to any one of claims 1 - 5.

7. A negative electrode of a lithium metal battery, characterized in that, The negative electrode of the lithium metal battery uses the MXene material according to claim 6 as a framework, and the MXene material contains metallic lithium inside.

8. The method for preparing the negative electrode of the lithium metal battery according to claim 7, characterized in that, Comprising: Preparing a MXene material framework by using a MXene material; Placing the MXene material framework on the surface of molten lithium to allow the molten lithium to enter the MXene material framework to obtain a negative electrode of a lithium metal battery.

9. The preparation method of the negative electrode of the lithium metal battery according to claim 8, wherein The method for preparing a MXene material framework by using a MXene material is as follows: Disperse the MXene material in water and perform suction filtration to obtain a MXene material framework.

10. A lithium metal battery, characterized in that, Comprising a positive electrode and the negative electrode of a lithium metal battery according to claim 7, and the material of the positive electrode is LiCoO2, LiFePO4, NCM811 or sulfur.

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