Phosphonic acid modified high-entropy MXene composite separator and preparation method thereof

Abstract

The application provides a phosphonic acid modified high-entropy MXene composite diaphragm and a preparation method thereof, and belongs to the technical field of lithium battery diaphragms. The method comprises the following steps: mixing powders of multiple transition metal elements and carbon powder, performing high-energy ball milling and high-temperature solid-phase sintering treatment to obtain a high-entropy MAX precursor, removing an aluminum layer in a directional manner through wet etching, and separating to obtain two-dimensional multi-layer high-entropy MXene powder; mixing the two-dimensional multi-layer high-entropy MXene powder with a phosphonic acid ligand intercalation agent, performing solvothermal reaction to control the layer spacing, and separating to obtain phosphonic acid modified few-layer high-entropy MXene powder; mixing the phosphonic acid modified few-layer high-entropy MXene powder with a conductive agent and a binder in an organic solvent to obtain high-entropy MXene mixed slurry, coating the high-entropy MXene mixed slurry on the surface of a PE diaphragm, and drying to obtain a composite diaphragm. The phosphonic acid modified few-layer high-entropy MXene coating of the composite diaphragm can promote the rapid migration of lithium ions and improve the flame retardant performance of the diaphragm, and provides an integrated solution for lithium dendrite inhibition, ion transmission optimization and thermal runaway protection in a lithium metal battery.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium battery separators, in particular to a phosphonic acid modified high-entropy MXene composite separator and a preparation method thereof. BACKGROUND

[0002] The global energy structure needs to be transformed into renewable energy, and an energy storage system with ultra-high energy density, fast kinetic response and intrinsic safety characteristics is urgently needed. The traditional lithium ion battery with graphite as the negative electrode has been difficult to meet the development demand due to the limited theoretical capacity (372 mAh / g), and the lithium metal negative electrode with ultra-high specific capacity (3860 mAh / g, 10 times that of the graphite negative electrode) and the lowest redox potential (-3.04 V vs. SHE) is regarded as the ultimate solution for the next generation of high-energy batteries, but its industrialization still faces the following technical bottlenecks: irreversible lithium loss caused by electrolyte side reactions; interface transmission dynamics delay caused by insufficient lithium ion transference number, which induces non-uniform growth of lithium dendrites; early thermal runaway induced by the lack of SEI film thermal stability. The coupling of multiple factors eventually leads to short circuit, electrolyte drying and burning, and other catastrophic failure modes, far beyond the solution ability of traditional local material optimization, and it is urgent to develop a multi-level protection mechanism through systematic engineering means.

[0003] At present, the industry research on lithium metal negative electrode is focused on electrolyte additive optimization and artificial interface construction, but the functionalization of the separator, which is a key link with lithium ion flux regulation and safety protection, is ignored. The commercial separator, as the core component inside the battery, although it bears the functions of physical isolation of the positive and negative electrodes and basic lithium ion conduction, the semi-crystalline polyolefin material (PE / PP) which accounts for more than 80% of the market share has a fundamental defect: the chemical inertness of the pore structure leads to the lack of selective screening of transition metal ions, which aggravates the ion elution cross-talk effect under high-nickel ternary system; the wide pore size distribution causes the dispersion of lithium ion diffusion energy barrier, which drives random lithium deposition at the electrode interface; the insufficient mechanical strength and flame retardancy hides the risk of puncture and fire; ultimately leading to non-selective ion deposition on the surface of the lithium negative electrode, accelerating the dendrite penetration and causing capacity drop and other failure behaviors.

[0004] The prior art usually regulates the pore structure and functional modification of the separator by constructing nano transmission channels (such as anodic aluminum oxide AAO and hollow mesoporous silica HMS) or composite coatings (metal organic framework MOFs, transition metal carbide MXene and the like). However, it is difficult to achieve efficient selective transmission of lithium ions and intrinsic safety characteristics in a synergistic manner due to the limitation of single performance optimization. For example, although the two-dimensional MXene material with a high aspect ratio structure has excellent electrical conductivity and a low lithium ion diffusion barrier, the traditional single metal matrix cannot simultaneously achieve mechanical reinforcement and multi-ion synergistic effect. The high-entropy MXene can realize an atomically toughened structure through the lattice distortion effect of multi-element transition metals, so that the lithium ion diffusion barrier is further reduced. However, the regulation of the interlayer channel is still limited by the steric hindrance effect of the chain intercalation agent, resulting in a too wide distribution of the interlayer spacing and a sub-angstrom ion separation precision that cannot be achieved.

[0005] Therefore, a phosphonic acid modified high-entropy MXene dynamic self-adaptive interlayer engineering strategy is developed to realize the coordination of ordered channel distribution and thermodynamic stability of high-entropy structure, so as to break through the theoretical bottleneck of selective transmission, and then prepare a composite separator with fast ion conduction and flame retardant performance. SUMMARY

[0006] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a phosphonic acid modified high-entropy MXene composite separator and a preparation method thereof. The phosphonic acid modified few-layer high-entropy MXene coating of the composite separator can promote the rapid migration of lithium ions and improve the flame retardant performance of the separator, thereby providing an integrated solution for lithium dendrite inhibition, ion transmission optimization and thermal runaway protection in lithium metal batteries.

[0007] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0008] A preparation method of a phosphonic acid modified high-entropy MXene composite separator, comprising the following steps:

[0009] S1, mixing powders of a plurality of transition metal elements and carbon powder, and performing high-energy ball milling and high-temperature solid-phase sintering treatment to obtain a high-entropy MAX precursor;

[0010] S2, based on the obtained high-entropy MAX precursor, removing the aluminum layer by wet etching to separate a two-dimensional multi-layer high-entropy MXene powder;

[0011] S3, mixing the two-dimensional multi-layer high-entropy MXene powder and a phosphonic acid ligand intercalation agent, and performing a solvent thermal reaction to regulate the interlayer spacing, and separating a phosphonic acid modified few-layer high-entropy MXene powder;

[0012] S4, mixing the phosphonic acid modified few-layer high-entropy MXene powder, a conductive agent and a binder in an organic solvent to obtain a high-entropy MXene mixed slurry;

[0013] S5, coating the high-entropy MXene mixed slurry on the surface of the PE separator, and drying to obtain a phosphonic acid-modified high-entropy MXene composite PE separator.

[0014] Preferably, in S1, the transition metal elements include Ti, V, Nb, Mo, Al, and the molar ratio of the powders of each element to carbon powder is Ti:V:Nb:Mo:Al:C = 1:1:1:1:1.1:2.7.

[0015] Preferably, in S1, the high-energy ball milling is to seal the mixture in agate and mill at a speed of 600 rpm for 20 h; the high-temperature solid-phase sintering is to heat to 1500℃ at a heating rate of 5℃ / min under an Ar atmosphere in a tube furnace, and the flow rate of the Ar atmosphere is 0.5 mL / min; and after sintering, the powder is ground and sieved through a 200-mesh sieve.

[0016] Preferably, in S2, the wet etching is to add the high-entropy MAX precursor into a hydrothermal kettle containing an HCl solution and LiF, and magnetically stir at 55℃ for 96 h to directionally remove the aluminum layer;

[0017] The separation is to centrifuge the suspension after etching at 12000 rpm for 5 min, and repeatedly wash with deionized water and anhydrous ethanol until neutral; and after washing, vacuum dry at 60℃ for 12 h to obtain the two-dimensional multilayer high-entropy MXene powder TiVNbMoC3.

[0018] Preferably, in S3, the phosphonic acid ligand intercalation agent is tetra(4-phosphonophenyl)methane TppmH8, the two-dimensional multilayer high-entropy MXene powder is mixed with TppmH8 at a molar ratio of 1:0.5 to obtain a mixture, and the mixture is sealed in agate and ball milled at a speed of 600 rpm for 12 h.

[0019] Preferably, in S3, the solvothermal reaction is to disperse the mixture after ball milling into a mixed solvent of DMF and water at a volume ratio of 1:2, heat at 110℃ for 12 h at a heating rate of 5℃ / min; and the separation is to repeatedly wash the reaction product at 10000 rpm for 5 min each time, and the washing solvent is deionized water and anhydrous ethanol; and after washing, vacuum dry at 60℃ for 12 h to obtain the phosphonic acid-modified few-layer high-entropy MXene powder TiVNbMoC3 / Tppm.

[0020] Preferably, in S4, the mass ratio of the phosphonic acid-modified few-layer high-entropy MXene powder, conductive carbon black, and polymethyl methacrylate is 8:1:1; and the organic solvent is N,N-dimethylacetamide.

[0021] Preferably, in S5, the coating adopts a wire bar coating method, the wire bar type is OSP-1.5, and the coating mode is single-sided coating.

[0022] Preferably, in S5, the drying treatment is performed at room temperature for 3h, and then in a vacuum oven at 60℃ for 12h.

[0023] The application also provides a phosphonic acid modified high-entropy MXene composite diaphragm prepared by the preparation method of the phosphonic acid modified high-entropy MXene composite diaphragm.

[0024] According to the specific embodiments of the application, the following technical effects are disclosed.

[0025] (1) The phosphonic acid modified high-entropy MXene composite PE diaphragm is prepared by wet chemical etching and intercalation reaction, two-dimensional phosphonic acid regulated high-entropy MXene material is dispersed in the PE diaphragm to form a continuous coating layer, the phosphonic acid modified high-entropy MXene coating layer accurately regulates the interlayer spacing of MXene by the chelation anchoring effect of phosphonic acid molecules, so that the puncture strength and mechanical strength of the PE diaphragm are greatly improved, the good mechanical strength endows the PE diaphragm with excellent ability to inhibit lithium dendrite growth, and in the battery cycle process, the lithium dendrite can be effectively blocked from penetrating the diaphragm, thereby improving the battery cycle performance of the diaphragm.

[0026] (2) In the phosphonic acid modified high-entropy MXene composite PE diaphragm provided by the application, the high-entropy components of the material form lattice distortion, which reduces the lithium ion diffusion energy barrier, and forms a rapid lithium ion transmission nanochannel on the surface of the high-entropy MXene, at the same time, the regulated interlayer spacing nanolimitation effect realizes efficient screening of lithium ions, and the two work together to effectively improve the migration rate of lithium ions, which provides favorable conditions for the rapid transmission of lithium ions in the battery.

[0027] (3) The phosphonic acid molecules in the phosphonic acid modified high-entropy MXene composite PE diaphragm provided by the application can efficiently quench the free radicals of the chain reaction in the electrolyte through pyrolysis reaction, in the process of battery operation, when free radicals are generated in the electrolyte due to chain reaction, the substances generated by pyrolysis of phosphonic acid molecules can quickly capture these free radicals, preventing the further development of chain reaction, thereby realizing the excellent performance of high safety and flame retardance, and significantly improving the safety of the battery.

[0028] (4) This invention prepares a multi-element high-entropy MAX precursor by high-temperature sintering, and prepares a few-layer high-entropy MXene material with precise control of interlayer spacing by wet etching and tetraphosphonic acid ligand intercalation modification process. The phosphonic acid functionalized composite coating membrane is constructed by coating molding technology. The modified composite membrane maintains the lightweight characteristics while significantly improving mechanical properties and ion selective transport capabilities, and simultaneously achieves the inhibition of lithium dendrite growth and the blocking of combustion chain reaction, providing key technical support for the practical application of high-safety and high-energy-density lithium metal batteries. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a flowchart of a method for preparing a phosphonic acid-modified high-entropy MXene composite membrane according to the present invention;

[0031] Figure 2 The structural diagram of the PE@TiVNbMoC3 composite membrane provided by this invention;

[0032] Figure 3 This is a TEM image of HE-MXene / Tppm provided in Embodiment 1 of the present invention;

[0033] Figure 4 The image shown is a SEM image of HE-MXene / Tppm provided in Embodiment 1 of the present invention.

[0034] Figure 5 The EDS diagram of HE-MXene / Tppm provided in Embodiment 1 of the present invention;

[0035] Figure 6 This is a cross-sectional SEM image of the phosphonic acid-modified high-entropy MXene composite membrane provided in Example 1 of the present invention;

[0036] Figure 7 The AFM diagram of HE-MXene / Tppm provided in Embodiment 1 of the present invention;

[0037] Figure 8 These are XRD comparison images of Embodiment 1 and Comparative Examples 1-3 of the present invention;

[0038] Figure 9 This is a comparison diagram of the stress-strain curves of Embodiment 1 and Comparative Examples 1-3 of the present invention;

[0039] Figure 10This is a comparison chart of combustion tests of Example 1 and Comparative Examples 1-3 of the present invention;

[0040] Figure 11 This is a graph showing the change in lithium-ion transference number of the composite PE membrane provided in Embodiment 1 of the present invention;

[0041] Figure 12 A graph showing the change in lithium-ion transference number of the composite PE membrane provided for Comparative Example 1;

[0042] Figure 13 A graph showing the change in lithium-ion transference number of the composite PE membrane provided for Comparative Example 2;

[0043] Figure 14 A graph showing the change in lithium-ion transference number of the composite PE membrane provided for Comparative Example 3;

[0044] Figure 15 The graph shows a comparison of the cycle stability of lithium symmetric batteries assembled with composite PE separators of Example 1 and Comparative Examples 1-3 of the present invention.

[0045] Figure 16 This is a comparison chart of the cycling curves of lithium metal button batteries assembled with composite PE separators of Example 1 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] like Figure 1 As shown, this invention provides a method for preparing a phosphonic acid-modified high-entropy MXene composite membrane, comprising the following steps:

[0049] S1. Mix powders of various transition metal elements with carbon powder, and then process them through high-energy ball milling and high-temperature solid-state sintering to obtain a high-entropy MAX precursor.

[0050] S2. Based on the obtained high-entropy MAX precursor, the aluminum layer is directionally removed by wet etching to separate two-dimensional multilayer high-entropy MXene powder.

[0051] S3. The two-dimensional multilayer high-entropy MXene powder is mixed with a phosphonic acid ligand intercalating agent, and the interlayer spacing is controlled by a solvothermal reaction to obtain phosphonic acid modified few-layer high-entropy MXene powder.

[0052] S4. The phosphonic acid-modified few-layer high-entropy MXene powder is mixed with a conductive agent and a binder in an organic solvent to obtain a high-entropy MXene mixed slurry.

[0053] S5. The high-entropy MXene mixed slurry is coated on the surface of the PE membrane and dried to obtain a phosphonic acid modified high-entropy MXene composite PE membrane.

[0054] Based on the preparation method provided above, the following detailed description will further elaborate on the above content in conjunction with specific embodiments.

[0055] Example 1

[0056] In this embodiment, the preparation method of the phosphonic acid modified high-entropy MXene composite PE membrane includes the following steps:

[0057] Step 1: Powders of Ti, V, Nb, Mo, Al, and C were mixed in a molar ratio of 1:1:1:1:1.1:2.7. The mixture was then sealed in agate and ball-milled at 600 rpm for 20 hours to obtain a powder mixture. The resulting powder mixture was then transferred to a small alumina crucible with an alumina lid, placed in a tube furnace, and heated to 1500℃ in an Ar atmosphere for 600 minutes. The heating rate was 5℃ / min, and the Ar flow rate was 0.5 mL / min. After cooling the obtained powder to room temperature, the sample was ground and sieved through a 200-mesh sieve to obtain uniform high-entropy MAX powder particles for etching.

[0058] Step 2: The obtained high-entropy MXene powder particles were gradually added to a hydrothermal reactor containing HCl solution (12M) and LiF, and magnetically stirred at 55°C for 96 h. The aluminum layer was etched in a hydrogen fluoride atmosphere, and then the etched high-entropy MXene suspension was transferred to a centrifuge tube and centrifuged at 12000 rpm for 5 min. The solution was then washed several times with deionized water and anhydrous ethanol until it was close to neutral (pH≈7). The centrifuged product high-entropy MXene was vacuum dried at 60°C for 12 h to finally obtain two-dimensional multilayer TiVNbMoC3 powder.

[0059] Step 3: The obtained two-dimensional multilayer TiVNbMoC3 powder was added to the phosphonic acid ligand intercalating agent tetra(4-phosphonic acid phenyl)methane (TppmH8) at a molar ratio of 1:0.5. The mixture was then sealed in an agate container and ball-milled at 600 rpm for 12 h. The ball-milled mixture was transferred to a hydrothermal reactor, and a solvent mixture of DMF and water (where the volume ratio of DMF to water was 1:2) was added. The mixture was heated at 110 °C for 12 h at a heating rate of 5 °C / min. The interlayer spacing of the high-entropy MXene was controlled by the solvothermal reaction. The solvothermal reaction product was repeatedly washed five times in a centrifuge at 10,000 rpm with deionized water and anhydrous ethanol for 5 minutes each time. Finally, the centrifuged product was vacuum dried at 60 °C for 12 h to obtain phosphonic acid modified few-layer high-entropy MXene powder.

[0060] Step 4: Mix the obtained phosphonic acid modified few-layer high-entropy MXene powder with conductive carbon black and polymethyl methacrylate in dimethylacetamide solvent and stir mechanically at 500 r / min for 10 hours to obtain phosphonic acid modified high-entropy MXene mixed slurry.

[0061] Step 5: Apply the high-entropy MXene mixed slurry to the surface of the PE membrane using a bar coating method. The bar coating tool used is OSP-1.5, and the coating method is single-sided coating. For drying, first place it at room temperature for 3 hours, then place it in a vacuum oven and dry at 60℃ for 12 hours. After drying, the desired result is as follows: Figure 2 The phosphonic acid-modified high-entropy MXene composite PE membrane shown is PE@TiVNbMoC3 / Tppm.

[0062] The few-layer TiVNbMoC3 / Tppm prepared in Example 1 of this invention was characterized by transmission electron microscopy (TEM), and the results are as follows: Figure 3 As shown, this demonstrates the synthesis of few-layer nanosheets of phosphonic acid-modified high-entropy MXene. Furthermore, this embodiment also underwent scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) characterization, with results as follows: Figure 4 and Figure 5 It was found that the prepared phosphonic acid-modified high-entropy MXene nanosheets had only a few layers. Elemental analysis revealed the presence of various components of the high-entropy material and the phosphorus element in the phosphonic acid intercalating agent. Figure 6 It can be seen that the coating thickness of the phosphonic acid modified high-entropy MXene composite PE membrane PE@TiVNbMoC3 / Tppm prepared in Example 1 is 3.4 μm. Meanwhile, the reference... Figure 7 The atomic force electron microscopy (AFM) characterization results show that the thickness of the few-layer TiVNbMoC3 / Tppm nanosheets prepared in Example 1 is 4.5 nm.

[0063] Comparative Example 1

[0064] This comparative example provides a method for preparing a composite PE membrane (PE@Ti3C2), including the following steps:

[0065] Step 1: Mix Ti, Al, and C powders in a molar ratio of 3:1.1:2, seal the mixture in an agate container, and ball mill at 600 rpm for 20 hours. Then, transfer the resulting powder mixture to a small alumina crucible with an alumina lid, place it in a tube furnace, and heat it to 1500°C in an Ar atmosphere for 600 minutes, with a heating rate of 5°C / min and an Ar flow rate of 0.5 mL / min. Finally, after cooling the resulting powder to room temperature, pulverize the sample and sieve it through a 200-mesh sieve to obtain uniform MAX powder particles for etching.

[0066] Step 2: The obtained MAX was gradually added to a hydrothermal reactor containing HCl solution (9M) and LiF, and magnetically stirred at 55°C for 96 hours to create a hydrogen fluoride atmosphere for directional etching of the aluminum layer. The etched MXene suspension was then transferred to centrifuge tubes and centrifuged at 12000 rpm for 5 minutes. The solution was then washed several times with deionized water and anhydrous ethanol until it was nearly neutral (pH≈7). Finally, the centrifuged MXene product was vacuum dried at 60°C for 12 hours. Multilayer Ti3C2 powder was obtained.

[0067] Step 3: Mix MXene powder with conductive carbon black and polymethyl methacrylate in dimethylacetamide solvent and stir mechanically at 500 r / min for 10 hours to obtain MXene mixed slurry;

[0068] Step 4: Apply the MXene mixed slurry to the surface of the PE membrane using a bar coating method. The bar used for bar coating is OSP-1.5, and the coating method is single-sided coating. When drying, first place it at room temperature for 3 hours, and then place it in a vacuum oven and dry it at 60°C for 12 hours. After drying, the composite PE membrane PE@Ti3C2 is obtained.

[0069] Comparative Example 2

[0070] This comparative example provides a method for preparing a composite PE membrane (PE@Ti3C2 / Tppm), comprising the following steps:

[0071] Step 1: Mix Ti, Al, and C powders in a molar ratio of 3:1.1:2, seal the mixture in an agate container, and ball mill at 600 rpm for 20 hours. Then, transfer the resulting powder mixture to a small alumina crucible with an alumina lid, place it in a tube furnace, and heat it to 1500°C in an Ar atmosphere for 600 minutes, with a heating rate of 5°C / min and an Ar flow rate of 0.5 mL / min. Finally, after cooling the resulting powder to room temperature, pulverize the sample and sieve it through a 200-mesh sieve to obtain uniform MAX powder particles for etching.

[0072] Step 2: The obtained MAX was gradually added to a hydrothermal reactor containing HCl solution (9M) and LiF, and magnetically stirred at 55°C for 96 h to create a hydrogen fluoride atmosphere for directional etching of the aluminum layer. The etched high-entropy MXene suspension was then transferred to a centrifuge tube and centrifuged at 12000 rpm for 5 min. The solution was then washed several times with deionized water and anhydrous ethanol until it was nearly neutral (pH≈7). Finally, the centrifuged product high-entropy MXene was vacuum dried at 60°C for 12 h to obtain multilayer Ti3C2 powder.

[0073] Step 3: Add the two-dimensional multilayer MXene powder to the phosphonic acid ligand intercalating agent tetra(4-phosphonophenyl)methane (TppmH8) at a molar ratio of 1:0.5. Seal the mixture in an agate container and ball mill it at 600 rpm for 12 h. Then, transfer the ball-milled mixture to a hydrothermal reactor and add a solvent mixture of DMF and water (where the volume ratio of DMF to water is 1:2). Heat at 110 °C for 12 h at a heating rate of 5 °C / min to control the interlayer spacing of MXene through solvothermal reaction. Then, wash the solvothermal reaction product repeatedly with deionized water and anhydrous ethanol five times in a centrifuge at 10,000 rpm for 5 minutes each time. Finally, vacuum dry the centrifuged product at 60 °C for 12 h to obtain phosphonic acid modified few-layer MXene powder.

[0074] Step 4: Mix the phosphonic acid modified few-layer MXene powder with conductive carbon black and polymethyl methacrylate in dimethylacetamide solvent and stir mechanically at 500 r / min for 10 hours to obtain phosphonic acid modified MXene slurry.

[0075] Step 5: Apply the MXene mixed slurry to the surface of the PE membrane using a bar coating method. The bar coating tool used is OSP-1.5, and the coating method is single-sided coating. For drying, first place it at room temperature for 3 hours, then place it in a vacuum oven and dry at 60℃ for 12 hours. After drying, the composite PE membrane PE@Ti3C2 / Tppm is obtained.

[0076] Comparative Example 3

[0077] This comparative example provides a method for preparing a composite PE membrane (PE@TiVNbMoC3), including the following steps:

[0078] Step 1: Mix Ti, V, Nb, Mo, Al, and C powders in a molar ratio of 1:1:1:1:1.1:2.7. Seal the mixture in an agate container and ball mill it at 600 rpm for 20 hours. Then, transfer the resulting powder mixture to a small alumina crucible with an alumina lid, place it in a tube furnace, and heat it to 1500℃ in an Ar atmosphere for 600 minutes, with a heating rate of 5℃ / min and an Ar flow rate of 0.5 mL / min. Finally, after cooling the powder to room temperature, pulverize the obtained sample and sieve it through a 200-mesh sieve to obtain uniform high-entropy MAX powder particles for etching.

[0079] Step 2: The obtained high-entropy MXene was gradually added to a hydrothermal reactor containing HCl solution (12M) and LiF, and magnetically stirred at 55°C for 96 hours to create a hydrogen fluoride atmosphere for directional etching of the aluminum layer. The etched high-entropy MXene suspension was then transferred to a centrifuge tube and centrifuged at 12,000 rpm for 5 minutes. The solution was then washed several times with deionized water and anhydrous ethanol until it was nearly neutral (pH≈7). Finally, the centrifuged product high-entropy MXene was vacuum dried at 60°C for 12 hours to obtain multilayer TiVNbMoC3 powder.

[0080] Step 3: Mix high-entropy MXene powder with conductive carbon black and polymethyl methacrylate in dimethylacetamide solvent and stir mechanically at 500 r / min for 10 hours to obtain high-entropy MXene mixed slurry;

[0081] Step 4: Apply the high-entropy MXene mixed slurry to the surface of the PE membrane using a bar coating method. The bar used for bar coating is OSP-1.5, and the coating method is single-sided coating. When drying, first place it at room temperature for 3 hours, and then place it in a vacuum oven and dry it at 60°C for 12 hours. After drying, the composite PE membrane PE@TiVNbMoC3 is obtained.

[0082] To further compare the composite PE membranes prepared in Example 1 of this invention with those prepared in Comparative Examples 1-3, X-ray diffraction (XRD) was used to characterize them, and the results are as follows: Figure 8 As shown; from Figure 8As can be seen, the prepared MXene does not have a prominent characteristic peak corresponding to Al atoms, and the position of the (002) peak, which represents the interplanar spacing, is different. Therefore, it can be concluded that the interplanar spacing of MXene modified with phosphonic acid is significantly increased. Based on this, the mechanical properties of the composite PE membranes prepared in Example 1 and Comparative Examples 1-3 were tested, and the results are as follows: Figure 9 As shown, the tensile strength was significantly improved after loading rigid MXene; however, the modulation of the few-layer structure of MXene by phosphonic acid ligands has been shown to lead to a decrease in mechanical strength; the enhanced mechanical strength of the composite PE membranes compared to Comparative Examples 1 and 3 is attributed to the high entropy effect suppressing dislocation movement caused by lattice distortion. Therefore, the higher tensile strength of the composite PE membrane in Example 1 is further demonstrated.

[0083] Subsequently, the composite PE membranes prepared in Example 1 and Comparative Examples 1-3 were subjected to membrane combustion tests, and the results are as follows. Figure 10 As shown. From Figure 10 As can be seen from the combustion test, the TiVNbMoC3 / Tppm of the composite PE membrane in Example 1 enhances the fire resistance; while Comparative Example 1, Comparative Example 3, and the commercially available PE membrane burn at a faster rate. Therefore, the flame retardancy of MXene is significantly improved when an organophosphonic acid ligand (TppmH8) is introduced onto the MXene surface to precisely adjust the interlayer spacing.

[0084] The composite PE membranes prepared according to Example 1 and Comparative Examples 1-3 were subjected to lithium-ion transference number (it) tests, and the corresponding results are as follows: Figure 11 , Figure 12 , Figure 13 and Figure 14 As shown, comparison Figures 11-14 The results show that the lithium-ion transference number of the composite PE membrane in Example 1 is 0.77, which is greater than that of the composite PE membrane in Comparative Example 1 (0.40), Comparative Example 2 (0.67), and Comparative Example 3 (0.54), respectively. This fully demonstrates that a rapid lithium-ion transport nanochannel was formed on the surface of the high-entropy MXene during the preparation process of Example 1. At the same time, the controlled interlayer spacing nano-confinement effect achieved efficient lithium-ion sieving. The combined effect of these two factors effectively improved the lithium-ion mobility, providing favorable conditions for the rapid transport of lithium-ions in the battery.

[0085] Finally, the composite PE membranes prepared in Example 1 and Comparative Examples 1-3 were used to prepare lithium symmetric batteries and lithium coin batteries, respectively, and their electrochemical performance was tested. In the performance test of the lithium symmetric batteries, Figure 15The differences in their cycle stability were visually presented, with the test conditions set at 1 mA cm⁻¹. -2 The current density and 80% Li utilization rate simulated the moderate-intensity lithium deposition and stripping process in a real lithium battery. It was found that the lithium symmetric battery prepared with the composite PE separator in Example 1 exhibited excellent stability, with a stable cycling time exceeding 1500 hours. During this period, the voltage polarization curve remained consistently flat, indicating that the lithium metal deposition / stripping process on both sides of the separator was uniform and controllable, without significant lithium dendrite piercing of the separator or a sudden increase in interface impedance. Conversely, the lithium symmetric batteries prepared with the composite PE separators in Comparative Examples 1 and 2 both showed a rapid increase in polarization voltage in the early stages of cycling. This result directly verifies the key role of the composite PE separator prepared in Example 1 in suppressing lithium dendrites and stabilizing interface reactions.

[0086] In the full-cell cycle test, lithium metal button batteries were prepared using the composite PE separators prepared in Example 1 and Comparative Examples 1-3, respectively, and the results are as follows: Figure 16 As shown. From Figure 16 As can be seen from the data, the composite PE separator of Example 1 significantly improves the lithium-ion migration efficiency by utilizing the fast lithium-ion transport channels constructed by the high-entropy MXene coating and the nano-confinement effect. At the same time, the phosphonic acid modified layer effectively suppresses the side reactions between the electrolyte and lithium metal, so that the capacity retention rate of the full cell is still close to 90% after 200 cycles, the cycle curve is smooth and the decay rate is slow. In contrast, the full cells of Comparative Example 1 and Comparative Example 2 show a significantly faster capacity decay rate.

[0087] Therefore, based on Figure 15 and Figure 16 The results show that the interfacial stability and mechanical advantages exhibited by the composite PE separator in Example 1 in lithium symmetric batteries are directly translated into excellent cycle stability and capacity retention in the full battery system, verifying the application potential of this separator in practical high-energy-density batteries.

[0088] Based on the comparative analysis above, the few-layer TiVNbMoC3 / Tppm nanosheet modified composite PE membrane prepared by this invention exhibits significant comprehensive performance advantages, specifically:

[0089] In terms of membrane performance, the high-entropy MXene interlayer spacing regulated by phosphonic acid ligand intercalation enables the composite PE membrane to have both thinness and excellent mechanical strength, improving tensile properties and effectively inhibiting lithium dendrite penetration.

[0090] In terms of ion transport dynamics, the lattice distortion caused by high-entropy components and the precisely controlled interlayer spacing form nanoscale lithium-ion transport channels, increasing the ion transference number to 0.77, ensuring efficient sieving and rapid migration of lithium ions.

[0091] In terms of flame retardancy and safety performance, the free radical quenching groups generated by the pyrolysis of phosphonic acid molecules can quickly capture harmful free radicals generated by the chain reaction in the electrolyte, reducing the battery's exothermic peak and blocking the chain reaction before thermal runaway. Battery performance tests have further verified its superiority.

[0092] Therefore, the phosphonic acid modified high-entropy MXene composite membrane prepared in this invention achieves a simultaneous breakthrough in the safety and cycle performance of lithium metal batteries through the synergistic effect of mechanical strengthening, ion transport optimization and interfacial side reaction suppression, thereby providing an integrated solution for lithium dendrite suppression, ion transport optimization and thermal runaway protection in lithium metal batteries.

[0093] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0094] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing a phosphonic acid-modified high-entropy MXene composite membrane, characterized in that, Includes the following steps: S1. Mix powders of various transition metal elements with carbon powder, and then process them through high-energy ball milling and high-temperature solid-state sintering to obtain a high-entropy MAX precursor. In S1, the transition metal elements include Ti, V, Nb, Mo, and Al, and the molar ratio of each element powder to carbon powder is Ti:V:Nb:Mo:Al:C = 1:1:1:1:1.1:2.7; The high-energy ball milling involves sealing the mixture in agate and ball milling it at 600 rpm for 20 hours; the high-temperature solid-state sintering involves heating the mixture to 1500°C at a heating rate of 5°C / min and holding it at that temperature for 600 minutes in a tube furnace under an Ar atmosphere, with the Ar atmosphere flowing at a rate of 0.5 mL / min; after sintering, the powder is ground and sieved through a 200-mesh sieve. S2. Based on the obtained high-entropy MAX precursor, the aluminum layer is directionally removed by wet etching to separate two-dimensional high-entropy MXene powder. S3. The two-dimensional high-entropy MXene powder is mixed with a phosphonic acid ligand intercalating agent, and the interlayer spacing is controlled by a solvothermal reaction to obtain phosphonic acid modified high-entropy MXene powder. In S3, the phosphonic acid ligand intercalating agent is tetra(4-phosphonophenyl)methane TppmH8. The two-dimensional high-entropy MXene powder is mixed with TppmH8 at a molar ratio of 1:0.5 to obtain a mixture. The mixture is then sealed in agate and ball-milled at 600 rpm for 12 hours. S4. The phosphonic acid-modified high-entropy MXene powder is mixed with a conductive agent and a binder in an organic solvent to obtain a high-entropy MXene mixed slurry; In S4, the mass ratio of the phosphonic acid-modified high-entropy MXene powder, conductive carbon black, and polymethyl methacrylate is 8:1:1; the organic solvent is N,N-dimethylacetamide. S5. The high-entropy MXene mixed slurry is coated on the surface of the PE membrane and dried to obtain a phosphonic acid modified high-entropy MXene composite PE membrane.

2. The method for preparing a phosphonic acid-modified high-entropy MXene composite membrane according to claim 1, characterized in that, In S2, the wet etching process involves adding the high-entropy MAX precursor into a hydrothermal reactor containing HCl solution and LiF, and magnetically stirring at 55°C for 96 hours to directionally remove the aluminum layer. The separation process involved centrifuging the etched suspension at 12,000 rpm for 5 min and repeatedly washing it with deionized water and anhydrous ethanol until neutral. After washing, the suspension was vacuum dried at 60 °C for 12 h to obtain the two-dimensional high-entropy MXene powder TiVNbMoC3.

3. The method for preparing a phosphonic acid-modified high-entropy MXene composite membrane according to claim 1, characterized in that, In S3, the solvothermal reaction involves dispersing the ball-milled mixture in a mixed solvent of DMF and water at a volume ratio of 1:2, heating at 110°C for 12 hours at a heating rate of 5°C / min; the separation involves washing the reaction product repeatedly at 10,000 rpm for 5 minutes each time, using deionized water and anhydrous ethanol as the washing solvent; after washing, the product is vacuum dried at 60°C for 12 hours to obtain the phosphonic acid-modified high-entropy MXene powder TiVNbMoC3 / Tppm.

4. The method for preparing a phosphonic acid-modified high-entropy MXene composite membrane according to claim 1, characterized in that, In S5, the coating is performed using a wire bar coating method, with the wire bar model being OSP-1.5, and the coating method being single-sided coating.

5. The method for preparing a phosphonic acid-modified high-entropy MXene composite membrane according to claim 1, characterized in that, In S5, the drying process involves first placing the product at room temperature for 3 hours, and then drying it in a vacuum oven at 60°C for 12 hours.

6. A phosphonic acid modified high-entropy MXene composite PE membrane prepared by the method of preparing the phosphonic acid modified high-entropy MXene composite membrane according to any one of claims 1 to 5.

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