Multi-metallic mof modified current collector, method of making and use in a negative electrode-free sodium battery

Abstract

The application discloses a kind of multi-metal MOF modified current collector and its preparation method and application in anode-free sodium battery.The method first synthesizes zinc-based MOF crystal material, then zinc-based MOF crystal material is mixed with copper salt solution, doping is carried out after treatment, to obtain multi-metal MOF crystal material, finally multi-metal MOF crystal material is mixed with conductive agent, binder, dispersing agent and solvent to form slurry, coated on the surface of current collector substrate, to obtain multi-metal MOF modified current collector.The application can controllably introduce various sodium-philic metal centers to synthesize multi-metal MOF modified current collector by post-synthesis ion exchange strategy, while retaining the complete topological structure of MOF.The multi-metal MOF modified current collector of the application can be used to construct anode-free sodium metal battery, reduce sodium deposition nucleation overpotential through the porous structure and sodium-philic metal center of MOF, provide abundant sodium ion transmission channels, inhibit sodium dendrite growth, and significantly improve the cycle stability of anode-free sodium metal battery.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a multi-metal MOF-modified current collector, its preparation method, and its application in a negative electrode-free sodium battery. Background Technology

[0002] Sodium-ion batteries are considered an important development direction in the post-lithium-ion battery era due to their advantages such as abundant raw material reserves, low cost, and relatively high safety. Among them, the anode-less sodium metal battery directly utilizes the sodium source in the positive electrode material to form a metallic sodium anode in situ on the negative electrode current collector, eliminating the complex process of pre-placed sodium anodes and significantly improving the theoretical energy density of the battery, demonstrating great application potential.

[0003] However, the commercialization of sodium metal batteries without a negative electrode is severely hampered by key challenges on the negative electrode side. First, sodium metal has extremely high chemical reactivity and poor interfacial affinity with traditional current collectors such as copper and aluminum, resulting in a high overpotential for deposition and nucleation. This leads to heterogeneous nucleation and growth, easily forming dendrites. Sodium dendrites can not only puncture the separator and cause short circuits, but their fracture can also produce "dead sodium," causing irreversible loss of active material and capacity decay. Second, during cycling, the significant volume changes caused by repeated deposition / dissolution of sodium metal continuously damage and reconstruct the solid electrolyte interphase (SEI) membrane, constantly consuming limited electrolyte and active sodium, accelerating battery failure.

[0004] To address these challenges, researchers have proposed modifying the surface of current collectors to guide uniform sodium deposition. Among these modifications, metal-organic frameworks (MOFs) have attracted significant attention due to their highly ordered porous structure, tunable pore size, and chemical environment, particularly for controlling metal ion deposition behavior. A mainstream strategy in existing technologies involves using MOFs as precursors and performing high-temperature carbonization in an inert atmosphere to obtain MOF-derived porous carbon materials for modifying current collectors. While this method yields porous carbon frameworks with good conductivity and retains some metal active sites, the high-temperature process irreversibly destroys the intricate crystal structure, regular channels, and abundant organic functional groups of MOFs, sacrificing their intrinsic structural advantages and well-ordered sodium ion transport channels. Furthermore, the carbonization process places stringent requirements on the thermal stability of the metals in the precursor MOF, limiting the range of metals that can be used to construct sodium-loving sites, and the process is energy-intensive.

[0005] Another approach is to directly modify the current collector using uncarbonized MOF crystals to preserve its complete structure and functional group characteristics. However, simple MOF modification layers often suffer from insufficient conductivity and poor long-term stability in electrolytes. More importantly, the sodium affinity and catalytic effect provided by a single metal center may be limited. In existing technologies, the synthesis of multi-metal MOF materials often relies on a one-step synthesis method that directly mixes different metal salts with organic ligands. Due to the significant differences in the coordination ability and coordination configuration of different metal ions with ligands, this method is prone to severe competitive coordination during the reaction, leading to phase separation, lattice distortion, or the formation of amorphous impurities. It is difficult to achieve atomically uniform doping of the target metal in the MOF framework, resulting in poor controllability of the product structure and thus affecting the electrochemical stability of the modified layer. Especially in anode-less sodium batteries, the irreversible consumption of any active sodium leads to a sharp reduction in battery capacity and cycle life. Therefore, anode-less sodium batteries place much higher demands on the sodium affinity, deposition uniformity, and structural buffering capacity of the current collector interface than conventional sodium metal batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a multi-metal MOF-modified current collector, its preparation method, and its application in a negative electrode-free sodium battery. This method, without disrupting the main MOF topology, allows heterogeneous metal ions to preferentially accumulate on the crystal surface and pore surfaces through diffusion. Utilizing the porous structure, abundant functional groups, and sodium-loving metal centers of the MOF itself, more efficient sodium ion transport and deposition control are achieved.

[0007] The technical solution for achieving the objective of this invention is as follows:

[0008] The preparation method of multi-metal MOF modified current collectors involves first synthesizing zinc-based MOF crystals, followed by a Cu ion doping post-processing via liquid-phase impregnation. This process controllably introduces Cu metal centers while preserving the complete framework structure of the zinc-based MOF. Finally, a multi-metal MOF coating with multiple sodium-loving sites is coated onto the surface of the current collector substrate. The specific steps include:

[0009] (1) At room temperature, zinc salt is ultrasonically dissolved in water or an organic solvent to obtain solution A;

[0010] (2) Dissolve the organic ligand in water or an organic solvent by sonication to obtain solution B;

[0011] (3) Add solution A slowly to solution B at a molar ratio of Zn to organic ligand of 1:4±0.2 and stir ultrasonically until a homogeneous mixed solution C is formed;

[0012] (4) Continue stirring the mixed solution C to react. After the reaction is complete, centrifuge, wash and dry to obtain MOF crystal material;

[0013] (5) Mix the MOF crystal material with water or organic solution of copper salt at a molar ratio of Zn to Cu of 1:1 and heat and stir at 60±10 °C to carry out metal ion doping treatment. After cooling and crystallization, centrifuge, wash and dry to obtain multi-metal doped MOF crystal material.

[0014] (6) Mix the multi-metal doped MOF crystal material, conductive agent, binder and dispersant in proportion, and then mix with solvent to form a slurry;

[0015] (7) The slurry is uniformly coated on the surface of the current collector substrate to form a uniform and dense MOF coating. After drying, a multi-metal MOF modified current collector is obtained.

[0016] Furthermore, in step (1), the zinc salts include, but are not limited to, zinc nitrate, zinc oxide, zinc sulfate, zinc acetate, zinc carbonate, etc.

[0017] Furthermore, in step (2), the organic ligands include, but are not limited to, carboxylic acid ligands such as terephthalic acid (H2BDC) and trimesic acid (H3BTC), nitrogen-containing heterocyclic ligands such as 2-methylimidazole (Hmim), benzimidazole (Hbim), 4-nitroimidazole, and 2-ethylimidazole; and chiral ligands such as L-tartaric acid and chiral imidazole.

[0018] Furthermore, in steps (1), (2), or (5), the organic solvents include, but are not limited to, methanol, ethanol, acetone, acetonitrile, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), diethylformamide (DEF), N-methylpyrrolidone (NMP), thionamide, dimethyl sulfoxide, etc.

[0019] Furthermore, in step (5), the copper salts include, but are not limited to, copper sulfate, copper chloride, copper carbonate, and copper nitrate.

[0020] Further, in step (1), the concentration of Zn salt in solution A is 1 mol / L; in step (2), the concentration of organic ligand in solution B is 4 mol / L; in step (5), the concentration of Cu salt in water or organic solution is 1 mol / L.

[0021] Furthermore, in step (6), based on a total mass of 100%, the mass ratio of multi-metal doped MOF crystal material, conductive agent, binder, and dispersant is 70~85wt%: 5~10wt%: 5~10wt%: 5~10wt%.

[0022] Further, in step (6), the conductive agent includes, but is not limited to, conductive carbon black, acetylene black, carbon nanotubes, superP, and Ketjenhead; the binder includes, but is not limited to, polyvinylidene fluoride (PVDF), polyimide (PI), polyacrylic acid (PAA), and carboxymethyl cellulose (CMC); the dispersant includes, but is not limited to, polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and carboxymethyl cellulose (CMC); and the solvent includes, but is not limited to, water, ethanol, ethylene glycol, acetone, N-methylpyrrolidone, and N,N-dimethylformamide.

[0023] Furthermore, in step (7), the current collector substrate includes, but is not limited to, aluminum foil, copper foil, carbon paper, copper foam, copper mesh, etc.

[0024] The present invention provides a multi-metal MOF modified current collector prepared by the above preparation method.

[0025] The present invention also provides the application of the above-mentioned multi-metal MOF modified current collector in a negative electrode-free sodium battery.

[0026] Furthermore, the present invention provides a negative electrode-free sodium battery, comprising the above-mentioned multi-metal MOF modified current collector, separator, electrolyte and positive electrode.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] (1) The present invention adopts a post-processing doping process, which flexibly introduces heterogeneous sodium-loving Cu metal centers while preserving the complete three-dimensional porous framework structure of the initial zinc-based MOF. Multiple metal centers can generate electronic structure modulation and synergistic effects, providing richer sodium ion adsorption and nucleation sites with a wider energy level distribution. Compared with MOF, it can more effectively reduce the nucleation overpotential of sodium deposition and guide the formation of a uniform and dense sodium deposition layer.

[0029] (2) Compared with the one-step synthesis of multimetal MOFs, the stepwise method (synthesis followed by doping) of the present invention has a wide process window and good reproducibility. The amount and distribution of heterometals can be controlled by precisely controlling the concentration, temperature and time of the doping solution, thus avoiding the phase separation problem caused by metal ion competition coordination in direct synthesis. At the same time, the entire process does not require high-temperature carbonization, the conditions are mild and the energy consumption is low.

[0030] (3) The inherent high specific surface area and porous structure of MOF provide ample space for sodium deposition, effectively buffering the volume expansion during cycling and reducing mechanical stress damage to the SEI film. At the same time, the sodium-loving Cu metal centers introduced by doping further enhance the sodium affinity at the interface and can suppress the longitudinal growth of sodium dendrites. The addition of conductive agents compensates for the insufficient intrinsic conductivity of MOF.

[0031] (4) The multi-metal-doped MOF coating on the surface of the current collector of the present invention can effectively reduce the sodium deposition overpotential, promote uniform nucleation and deposition of sodium ions, inhibit dendrite growth, and alleviate volume expansion. Specifically, compared with the undoped ZIF-8 modified current collector, the Cu-ZIF modified current collector prepared in this invention significantly reduces the sodium deposition nucleation overpotential from about 22.3 mV to 5.8 mV; at 1 mA / cm 2 Current density and 1 mAh / cm 2 After 500 cycles at the areal capacity, the average coulombic efficiency remains above 99.97%, and the cycle life is significantly improved, thereby significantly improving the cycle stability and safety of the anode-free sodium metal battery. Attached Figure Description

[0032] Figure 1 The image shows a scanning electron microscope (SEM) image of the Cu-ZIF material prepared in Example 1.

[0033] Figure 2 The X-ray diffraction (XRD) spectra of the ZIF-8 material and Cu-ZIF material prepared in Example 1 are shown.

[0034] Figure 3 The image shows a scan of the Cu-ZIF material prepared in Example 1 using an energy dispersive spectroscopy (EDS) analyzer.

[0035] Figure 4 The nitrogen adsorption-desorption isotherm (BET) of ZIF-8 and Cu-ZIF materials prepared in Example 1 is shown.

[0036] Figure 5 The image shows the pore size distribution curves of ZIF-8 and Cu-ZIF materials prepared in Example 1.

[0037] Figure 6 Fourier transform infrared (FTIR) spectra of ZIF-8 and Cu-ZIF materials prepared in Example 1;

[0038] Figure 7 The charge-discharge curves of the Cu-ZIF material prepared in Example 1 in a sodium-filled battery without a negative electrode at 0.1 C to 5 C are shown.

[0039] Figure 8 The graph shows a comparison of the cycle performance of the sodium-free battery constructed with the Cu-ZIF modified current collector prepared in Example 1, the sodium-free battery constructed with the ZIF-8 modified current collector prepared in Comparative Example 1, and the sodium-free battery constructed with the Zn / Cu-ZIF modified current collector prepared in Comparative Example 2.

[0040] Figure 9 XRD patterns of Cu-ZIF materials with different Cu doping concentrations;

[0041] Figure 10 Comparison of cycle performance of sodium-based batteries without anodes constructed using Cu-ZIF current collectors with different Cu doping levels. Detailed Implementation

[0042] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0043] Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0044] Example 1

[0045] This embodiment provides a method for preparing a multi-metal MOF (Cu-ZIF) modified current collector for a non-anode sodium battery by introducing Cu metal centers into a zinc-based zeolite imidazole ester framework material (ZIF-8) through post-processing doping. The specific steps are as follows:

[0046] (1) At room temperature, 0.1 mol Zn(NO3)2·6H2O was dissolved in 200 ml of methanol and ultrasonically stirred for 30 minutes to obtain a colorless and transparent solution A.

[0047] (2) Dissolve 0.4 mol of 2-methylimidazole in 200 ml of methanol and stir ultrasonically until completely dissolved to obtain solution B.

[0048] (3) Under vigorous mechanical stirring at 500~800 rpm, quickly pour solution A into solution B.

[0049] (4) The mixture immediately became milky white and turbid. The reaction was continued with stirring at room temperature for 24 hours. The resulting white suspension was centrifuged for 10 minutes, and the solid precipitate was collected. The precipitate was washed three times with fresh methanol to remove unreacted raw materials and byproducts. Finally, the washed white powder was dried in a vacuum drying oven at 80 °C for 12 hours to obtain ZIF-8 powder.

[0050] (5) Disperse ZIF-8 powder in 100 ml of a 0.1 mol / L methanol solution of copper nitrate trihydrate (Cu(NO3)2·3H2O). Transfer the mixture to a round-bottom flask equipped with a stir bar and magnetically stir in an oil bath at 50 °C for 18 hours. During this process, the solution gradually changes from colorless to light blue, and the solid powder changes from pure white to light gray. After the doping reaction is complete, centrifuge the mixture and collect the solid. Wash the solid three times each with methanol and deionized water until the supernatant is colorless to ensure the removal of physically adsorbed copper ions. Dry the final product overnight in a vacuum drying oven at 80 °C to obtain Cu-doped ZIF-8 powder, denoted as Cu-ZIF.

[0051] (6) Weigh the following components according to the following mass ratio: 80 wt% Cu-ZIF powder, 10 wt% conductive agent acetylene black, 5 wt% binder PVDF, and 5 wt% dispersant polyethylene glycol. After initially mixing the above dry powder materials evenly in a mortar, transfer them to a planetary mixing tank. Add an appropriate amount of NMP as a solvent, with a solvent-to-solid mass ratio of 1:1. Under an inert atmosphere, stir at 500 rpm for 1 hour, then at 2000 rpm for 4 hours to finally obtain a uniform slurry with suitable viscosity.

[0052] (7) A smooth copper foil with a thickness of 10 μm was selected as the substrate for the current collector. An automatic doctor blade coater was used to uniformly coat the slurry onto the surface of the copper foil. The wet film thickness was set to 120 μm. The modified electrode was then transferred to a forced-air drying oven at 80 ℃ for preliminary drying for 2 hours, and then placed in a vacuum drying oven at 100 ℃ for 12 hours to completely remove residual solvent. The thickness of the Cu-ZIF composite coating finally formed on the surface of the copper foil was measured to be 8~10 μm, thus obtaining a Cu-doped ZIF-8 modified current collector.

[0053] (8) The dried Cu-ZIF modified current collector was cut into discs with a diameter of 14 mm and used as working electrodes. In a glove box filled with argon (H2O<0.1 ppm, O2<0.1 ppm), sodium iron pyrophosphate was used as the counter electrode and reference electrode, Whatman GF / D glass fiber membrane was used as the separator, and a solution of 1 mol / L sodium hexafluorophosphate (NaPF6) dissolved in diethylene glycol dimethyl ether (G2) with 5% fluoroethylene carbonate (FEC) was used as the electrolyte to assemble a CR2032 type coin cell without a negative electrode for electrochemical performance evaluation.

[0054] like Figure 1 As shown, the 10,000x magnified SEM image of the Cu-ZIF material proves that after copper ion doping treatment, the material still maintains a good three-dimensional porous framework structure without obvious structural collapse or morphological damage.

[0055] like Figure 2 As shown, the XRD patterns of ZIF-8 and Cu-ZIF materials show highly consistent diffraction peak positions, proving that the post-processing doping is isomorphic substitution, that is, copper ions are introduced while retaining the original crystal topology, and no impurity phase is generated.

[0056] like Figure 3 As shown, the EDS scan of Cu-ZIF material shows that the signal distribution of copper element has a high degree of overlap with other elements, proving that copper ions have been successfully and uniformly doped into the ZIF-8 framework, rather than just physically adsorbed on the surface.

[0057] like Figure 4 As shown, the specific surface area and pore structure tests of the material demonstrate that it has a high specific surface area, which provides abundant active sites for the adsorption of sodium ions and helps to reduce the nucleation overpotential.

[0058] like Figure 5 As shown, the pore size distribution curve proves that the material has a regular microporous structure. This structure can act as an "ion sieve" to regulate the transport channels of sodium ions and guide the uniform deposition of sodium metal.

[0059] like Figure 6 As shown, FTIR testing confirms that the organic ligand successfully coordinates with Zn / Cu metal ions, forming a stable chemical bond.

[0060] like Figure 7 As shown, the charge-discharge curves (0.1 C ~ 5 C) of the assembled NFPP‖Cu-ZIF anode-free sodium battery indicate that the battery can still maintain a certain capacity even at a high current density of 5 C, proving that the material has excellent conductivity and fast ion transport capability, and can meet the requirements of high-power charge and discharge.

[0061] Comparative Example 1

[0062] This comparative example provides a method for preparing a ZIF-8 modified current collector, the specific steps of which are as follows:

[0063] (1)~(4) Same as Example 1.

[0064] (5) Weigh the following components according to the following mass ratio: 80wt% ZIF-8, 10wt% conductive agent acetylene black, 5wt% binder PVDF, and 5wt% dispersant polyethylene glycol. After initially mixing the above dry powder materials evenly in a mortar, transfer them to a planetary mixing tank. Add an appropriate amount of NMP as a solvent, with a solvent-to-solid mass ratio of 1:1. Under an inert atmosphere, stir at 500 rpm for 1 hour, then at 2000 rpm for 4 hours to finally obtain a uniform slurry with suitable viscosity.

[0065] (6) A smooth copper foil with a thickness of 10 μm was selected as the substrate for the current collector. An automatic doctor blade coater was used to uniformly coat the slurry onto the surface of the copper foil. The wet film thickness was set to 120 μm. The modified electrode was then transferred to a forced-air drying oven at 80 ℃ for preliminary drying for 2 hours, and then placed in a vacuum drying oven at 100 ℃ for 12 hours to completely remove residual solvent, thus obtaining the ZIF-8 modified current collector.

[0066] (7) The dried ZIF-8 modified current collector was cut into discs with a diameter of 12 mm and used as working electrodes. Under the same electrolyte, separator, counter electrode and assembly conditions as in Example 1, a CR2032 coin cell sodium battery without negative electrode was assembled for electrochemical performance evaluation.

[0067] Comparative Example 2

[0068] This comparative example provides a one-step method for directly synthesizing Zn / Cu bimetallic MOFs (denoted as Zn / Cu-ZIF) and preparing Zn / Cu-ZIF modified current collectors for anode-free sodium batteries. The specific steps are as follows:

[0069] (1) At room temperature, 0.1 mol of Zn(NO3)2·6H2O and 0.1 mol of Cu(NO3)2·3H2O were dissolved together in 200 mL of methanol and ultrasonically stirred for 30 minutes to obtain a mixed metal salt solution A.

[0070] (2) Dissolve 0.8 mol of 2-methylimidazole in 200 mL of methanol and stir ultrasonically until completely dissolved to obtain solution B.

[0071] (3) Under vigorous mechanical stirring at 500~800 rpm, slowly add solution B to solution A.

[0072] (4) The mixture immediately turned blue-green turbidity. The reaction was continued to be stirred at room temperature for 24 hours. The resulting blue-green suspension was centrifuged for 10 minutes and the solid precipitate was collected. The precipitate was washed three times with fresh methanol to remove unreacted raw materials and byproducts. Finally, the washed blue-green powder was placed in a vacuum drying oven at 80 °C and dried for 12 hours to obtain the Zn / Cu-ZIF powder synthesized in one step.

[0073] (5) Weigh the following components according to the following mass ratio: 80wt% Zn / Cu-ZIF powder, 10wt% conductive agent acetylene black, 5wt% binder PVDF, and 5wt% dispersant polyethylene glycol. Mix the above dry powder materials, add an appropriate amount of NMP as a solvent, and prepare a uniform slurry.

[0074] (6) A smooth copper foil with a thickness of 10 μm was selected as the substrate for the current collector. An automatic doctor blade coater was used to uniformly coat the slurry on the surface of the copper foil, and the wet film thickness was set to 120 μm. The electrode was then transferred to an 80 ℃ forced-air drying oven for preliminary drying for 2 hours, and then placed in a 100 ℃ vacuum drying oven for drying for 12 hours to obtain a one-step Zn / Cu-ZIF modified current collector.

[0075] (7) The dried Zn / Cu-ZIF modified current collector was cut into discs with a diameter of 12 mm and used as working electrodes. Under the same electrolyte, separator, counter electrode and assembly conditions as in Example 1, CR2032 coin cells were assembled for electrochemical performance evaluation.

[0076] like Figure 8 As shown, the capacity retention rates of the batteries constructed using Cu-ZIF in Example 1, monometallic ZIF-8 in Comparative Example 1, and Zn / Cu-ZIF synthesized in one step in Comparative Example 2 during cycling demonstrate the superior performance of the "post-treatment doping method." This is because the post-treatment method can better preserve the pore structure of the MOF and achieve uniform doping, thereby more effectively suppressing sodium dendrite growth and dead sodium formation.

[0077] Comparative Example 3

[0078] This comparative study investigated the effect of different copper nitrate concentrations on the structure of Cu-ZIF materials and the performance of the constructed anode-free sodium battery during the doping process. Based on the synthesis method of Example 1, only the Zn in step (5) was changed. 2+ and Cu 2+ The molar ratios were 1:1, 1:2, 1:3, and 2:1. Cu-ZIF materials with different Cu doping amounts were prepared. These materials were then coated onto the surface of the current collector substrate to prepare current collectors modified with Cu-ZIF with different Cu doping amounts. CR2032 coin cells were assembled under the same electrolyte, separator, counter electrode, and assembly conditions as in Example 1 for electrochemical performance evaluation.

[0079] like Figure 9 As shown, the XRD patterns of Cu-ZIF materials with different Cu doping amounts demonstrate the changes in the crystal structure of the materials synthesized under different copper-zinc molar ratios, proving that the crystal structure of the materials can remain stable within a certain ratio range.

[0080] like Figure 10 As shown in the figure, the comparison of the cycling performance of MOF materials with different copper doping concentrations in a sodium-free battery with an anode shows the superior performance of the optimal copper-zinc ion ratio.

Claims

1. A method for preparing a multi-metal MOF-modified current collector, characterized in that, Specifically, the steps include the following: (1) At room temperature, zinc salt is ultrasonically dissolved in water or an organic solvent to obtain solution A; (2) Dissolve the organic ligand in water or an organic solvent by sonication to obtain solution B; (3) Add solution A slowly to solution B according to the molar ratio of Zn to organic ligand of 1:4±0.2, and stir ultrasonically until a homogeneous mixed solution C is formed; (4) Continue stirring the mixed solution C to react. After the reaction is complete, centrifuge, wash and dry to obtain MOF crystal material; (5) Mix the MOF crystal material with water or organic solution of copper salt at a molar ratio of Zn to Cu of 1:1 and heat and stir at 60±10℃ to carry out metal ion doping treatment. After cooling and crystallization, centrifuge, wash and dry to obtain multi-metal doped MOF crystal material. (6) Mix the multi-metal doped MOF crystal material, conductive agent, binder and dispersant in proportion, and then mix with solvent to form a slurry; (7) The slurry is uniformly coated on the surface of the current collector substrate to form a uniform and dense MOF coating. After drying, a multi-metal MOF modified current collector is obtained.

2. The preparation method according to claim 1, characterized in that, In step (1), the zinc salt is selected from zinc nitrate, zinc oxide, zinc sulfate, zinc acetate or zinc carbonate; in step (2), the organic ligand is selected from carboxylic acid ligands, nitrogen-containing heterocyclic ligands or chiral ligands; in step (5), the copper salt is selected from copper sulfate, copper chloride, copper carbonate or copper nitrate.

3. The preparation method according to claim 2, characterized in that, The carboxylic acid ligands are terephthalic acid or trimesoic acid; the nitrogen-containing heterocyclic ligands are 2-methylimidazole, benzimidazole, 4-nitroimidazole or 2-ethylimidazole; and the chiral ligands are L-tartaric acid or chiral imidazole.

4. The preparation method according to claim 1, characterized in that, In steps (1), (2), or (5), the organic solvent is methanol, ethanol, acetone, acetonitrile, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, diethylformamide, N-methylpyrrolidone, thionamide, or dimethyl sulfoxide.

5. The preparation method according to claim 1, characterized in that, In step (1), the concentration of Zn salt in solution A is 1 mol / L; in step (2), the concentration of organic ligand in solution B is 4 mol / L; in step (5), the concentration of Cu salt in water or organic solution is 1 mol / L.

6. The preparation method according to claim 1, characterized in that, In step (6), based on a total mass of 100%, the mass ratio of multi-metal doped MOF crystal material, conductive agent, binder and dispersant is 70~85wt%: 5~10wt%: 5~10wt%: 5~10wt%.

7. The preparation method according to claim 1, characterized in that, The conductive agent is selected from conductive carbon black, acetylene black, carbon nanotubes, super P or Ketjenhead, the binder is selected from polyvinylidene fluoride, polyimide, polyacrylic acid or carboxymethyl cellulose, the dispersant is selected from polyvinylpyrrolidone, polyethylene glycol or carboxymethyl cellulose, and the solvent is selected from water, ethanol, ethylene glycol, acetone, N-methylpyrrolidone or N,N-dimethylformamide; in step (7), the current collector substrate is selected from aluminum foil, copper foil, carbon paper, copper foam or copper mesh.

8. A multi-metal MOF-modified current collector prepared by any one of the preparation methods according to claims 1 to 7.

9. The application of the multi-metal MOF modified current collector according to claim 8 in a negative electrode-free sodium battery.

10. A sodium battery without a negative electrode, characterized in that, It includes the current collector, separator, electrolyte and positive electrode plate modified with multi-metal MOF as described in claim 8.

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