Application of zinc-based metal organic framework material in water-based zinc ion battery negative electrode protection

Abstract

The invention relates to application of a zinc-based metal organic framework material in water-based zinc ion battery negative electrode protection. The invention relates to an application of a zinc-based metal organic framework material in water-based zinc ion battery negative electrode protection, in particular to a method for coating the zinc-based metal organic framework material Zn (btec) on the surface of a zinc electrode to construct a protective coating and form a Zn (btec) (at) Zn negative electrode. The coating can remarkably inhibit dendritic crystal growth, corrosion, hydrogen evolution and other side reactions of the zinc electrode in the charging and discharging process, and the safety performance and cycling stability of the battery are effectively improved. An electrochemical test shows that the symmetrical battery based on the Zn (becc) (at) Zn negative electrode stably operates for 2100 hours under the conditions of 0.5 mAcm <-2 > and 0.5 mAhcm <-2 >; under the conditions of 4mAcm <-2 > and 1mAhcm <-2 >, the half cell realizes 3000 cycles, and the coulombic efficiency is close to 100%; and after the whole battery circulates for 700 weeks at 1Ag <-1 >, the specific capacity is still kept at 91.4 mAhg <-1 >. Besides, after 86 cycles under 1Ag <-1 >, the capacity retention ratio of a soft package battery assembled by adopting the negative electrode is close to 100%, the specific discharge capacity is 150mAhg <-1 >, a load with the rated voltage of 6V can be successfully driven, and a good practical application prospect is shown. The negative electrode protection method provided by the invention is simple in process, relatively low in cost and suitable for large-scale production, and an effective way is provided for development of high-performance and long-life aqueous zinc ion batteries.

Description

Technical Field

[0001] This invention relates to the fields of electrochemical energy storage and metal-organic framework materials, specifically to the application of a zinc-based metal-organic framework material in the protection of the negative electrode of an aqueous zinc-ion battery. Background Technology

[0002] With the large-scale deployment of energy storage power stations and electric vehicles, the market has placed higher demands on the energy density and overall performance of batteries, and traditional lithium-ion batteries are facing bottlenecks in terms of resources, cost, and safety. Against this backdrop, aqueous zinc-ion batteries (AZIBs) have become a promising and important supplementary technology in the field of large-scale energy storage due to their inherent safety, low cost, and abundant zinc resources.

[0003] The commercialization of aqueous zinc-ion batteries is primarily hampered by interfacial failures at the zinc anode, such as uncontrolled dendrite growth, hydrogen evolution corrosion, and surface passivation, which severely impact cycle life and safety. Current research strategies mainly include electrolyte engineering, electrode structure design, and interface modification, aiming to optimize ion transport, suppress side reactions, and improve electrode stability. Among these, constructing an efficient anode protective layer is considered crucial, as it can directly regulate zinc deposition / dissolution behavior and isolate aqueous phase corrosion, thus providing the most promising solution for achieving long-cycle stability and highly reversible zinc anodes.

[0004] Metal-organic frameworks (MOFs) are a class of porous crystalline materials formed by the self-assembly of metal ions and organic ligands through coordination interactions. They possess characteristics such as designable structure, high specific surface area, and regular, ordered pores. As anode protective coatings, MOFs exhibit significant advantages: their uniform nanopores act as "ion sieves," guiding the uniform transport of metal ions and thus inhibiting dendrite growth; simultaneously, the chemical environment of the pores (such as hydrophilicity / hydrophobicity) can be precisely controlled through ligand design to effectively block water molecules and suppress side reactions. Compared to traditional inorganic coatings or polymer protective layers, MOFs, with their unique advantages of precisely designable structure, customizable pore properties, and strong interfacial stability, provide a more promising interface engineering solution for achieving high-performance aqueous zinc-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to provide an application of a zinc-based metal-organic framework material in the protection of the negative electrode of an aqueous zinc-ion battery. By using the material as a protective coating to modify the zinc electrode, the stability of the electrode / electrolyte interface can be effectively improved, and side reactions such as dendrite growth, corrosion, hydrogen evolution, and surface passivation of the zinc negative electrode during cycling can be significantly suppressed, thereby improving the cycle life and safety performance of the battery.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A zinc-based metal-organic framework material, denoted as Zn(btec), is a crystalline material with a three-dimensional porous structure formed by coordination self-assembly of Zn²⁺ and pyromellitic acid ligands. Its preparation method involves mixing an alkaline solution of pyromellitic acid with an aqueous solution of zinc acetate, reacting the mixture hydrothermally at 175°C for 24 hours, and then washing and drying the resulting product.

[0007] A method for preparing a Zn(btec)-modified zinc electrode (Zn(btec)@Zn) includes the following steps: 1) Mix the dry Zn(btec) powder with polyvinylidene fluoride (PVDF) at a mass ratio of 9:1, and add an appropriate amount of N-methylpyrrolidone (NMP) solvent; 2) Grind thoroughly to obtain a uniform slurry, and use a wet film preparation device to coat it onto the surface of a 50 μm thick zinc foil with a thickness of 150 μm; 3) Dry the coated zinc foil at 70°C for 8 hours, and after cooling, cut it into round pieces with a diameter of 12 mm or rectangular electrode pieces of 5 × 6 cm.

[0008] The CR2032 button cell battery is assembled as follows: 1) Symmetrical cell: Two Zn(btec)@Zn electrodes are used as the positive and negative electrodes, respectively; 2) Copper-zinc half-cell: Zn(btec)@Zn is used as the negative electrode and a 50 μm thick copper sheet is used as the positive electrode; 3) Full cell: Zn(btec)@Zn is used as the negative electrode and manganese dioxide (MnO2) is used as the positive electrode.

[0009] All cells used GF / D glass fiber membranes and were injected with 100 μL of electrolyte: 2 M ZnSO4 solution was used for symmetric cells and half cells, and a 2 M ZnSO4 mixed solution containing 0.2 M MnSO4 was used for full cells.

[0010] The assembly steps for a pouch battery are as follows: A battery cell is constructed by stacking three layers of Zn(btec)@Zn negative electrode, glass fiber separator, manganese dioxide positive electrode and electrolyte in sequence; multiple cells are connected in series and tabs are welded together, the stack is fixed with polyimide tape, and then vacuum-sealed with aluminum-plastic film to obtain a soft-pack battery with a rated voltage of 4.2 V.

[0011] The methods for electrochemical performance testing and material characterization are as follows: The cycle life and capacity of the batteries were evaluated using a blue electric test system and an electrochemical workstation. The morphology, structure, and composition of the electrode materials were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), optical microscopy (OM), and Fourier transform infrared spectroscopy (FTIR). All tests were performed at room temperature, with the symmetric cell test condition being 0.5 mA cm⁻¹. -2 Current density and 0.5 mAh cm⁻¹ -2 The surface capacity of a half-cell is 4 mA cm⁻¹ -2 With 1 mAh cm -2 The full cell capacity is 1 A g. -1 Current density.

[0012] Electrochemical test results show that the Zn(btec) coating significantly improves the cycle stability and reaction reversibility of the zinc electrode: In symmetric cell testing, the unmodified cell short-circuited after 500 cycles, while the Zn(btec)@Zn cell operated stably for 2100 hours. In half-cell testing, the unmodified electrode short-circuited after 100 cycles and exhibited large fluctuations in coulombic efficiency, while the Zn(btec)@Zn electrode achieved stable cycling for 3000 cycles with a coulombic efficiency approaching 100%. In full-cell testing, the specific capacity of the unmodified cell decayed to 53.6 mAh g⁻¹ after 700 cycles. -1 The Zn(btec)@Zn battery still maintains a capacity of 91.4 mAh g. -1 The pouch cell based on the Zn(btec)@Zn anode maintained a discharge specific capacity of 150 mAh g after 86 cycles. -1 The capacity retention rate is close to 100%.

[0013] The above results demonstrate that the Zn(btec) coating can effectively guide the uniform deposition of zinc, inhibit dendrite growth, and slow down side reactions such as corrosion and hydrogen evolution, thereby comprehensively improving the electrochemical performance and practical application potential of aqueous zinc-ion batteries. Attached Figure Description

[0014] Figure 1 SEM image of bare zinc electrode Figure 2 SEM image of Zn(btec)@Zn electrode Figure 3 X-ray diffraction pattern of Zn(btec)@Zn Figure 4 Symmetrical cell cycle curves of Zn(btec)@Zn electrode compared to bare zinc electrode Figure 5 Half-cell cycling curves of Zn(btec)@Zn electrode compared to bare zinc electrode Figure 6Full-cell cycling curves of Zn(btec)@Zn electrode compared to bare zinc electrode Figure 7 SEM images of dendrite growth on the surface of bare zinc electrodes Figure 8 SEM images of dendrite growth on the Zn(btec)@Zn electrode surface Figure 9 SEM images of zinc deposition on the Zn(btec)@Zn electrode surface Figure 10 OM image of dendrite growth on bare zinc electrode Figure 11 OM image of dendrite growth in Zn(btec)@Zn electrode Figure 12 Zn(btec)@Zn electrode pouch cell cycling curve Figure 13 Zn(btec)@Zn electrode for pouch cells Detailed Implementation

[0015] To facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0016] This invention uses 50 μm thick raw zinc foil as the negative electrode substrate. The loading thickness of the zinc-based metal-organic framework (Zn(btec)) protective coating on the zinc foil surface is controlled within the range of 10-30 μm. This thickness design ensures good corrosion resistance while maintaining and improving the conductivity of the electrode, thereby achieving effective protection for the zinc negative electrode. If the coating is too thin, the corrosion resistance will be insufficient; if it is too thick, it will increase the ion / electron transport impedance, which is detrimental to the electrochemical performance. The separator used is a GF / D6227 glass fiber separator with a pore size of approximately 2.76 μm, a thickness of 0.62 mm, a basis weight of 128 g / m², and a tensile strength of 0.5 kN / m. The fabricated pouch cell has a size of 5 × 6 cm.

[0017] The Zn(btec)@Zn anode preparation method provided by this invention specifically includes the following steps: 1) Synthesis of Zn(btec) material: 0.382 g (1.5 mmol) of pyromellitic acid was dissolved in 11 mL of 0.55 mol / L NaOH solution to prepare a ligand solution; 1.5 mmol of zinc acetate dihydrate was dissolved in 5 mL of deionized water to prepare a zinc salt solution. The ligand solution was transferred to a 30 mL polytetrafluoroethylene liner, and the zinc salt solution was slowly added. After sealing, the mixture was reacted at 175 °C for 24 h. After naturally cooling to room temperature, the product was collected by filtration, washed with 10 mL of deionized water, and dried overnight at room temperature to obtain Zn(btec) powder.

[0018] 2) Weighing: Weigh dry Zn (btec) powder and polyvinylidene fluoride (PVDF) at a mass ratio of 9:1, and add about 2 mL of N-methylpyrrolidone (NMP) as a solvent.

[0019] 3) Mixing and coating: Grind the mixture for 10 mins until the slurry is uniform, and use a wet film preparation device (scraper thickness 150 μm) to uniformly coat it onto the surface of a 50 μm thick zinc foil.

[0020] 4) Drying and shaping: The coated zinc foil is placed in a vacuum oven at 70 ℃ and dried for 8 h. After cooling to room temperature, it is cut into round pieces with a diameter of 12 mm. The resulting coating thickness is about 16 μm.

[0021] The method for preparing manganese dioxide cathode provided by this invention is as follows: 1) Synthesis of manganese dioxide: A hydrothermal method was used. 380.3 mg MnSO4·H2O was dissolved in 15 mL of deionized water to obtain solution A; 237 mg KMnO4 was dissolved in 15 mL of deionized water to obtain solution B. Solution B was slowly added to solution A, and the mixture was stirred continuously to form mixture C. The mixture was then transferred to a polytetrafluoroethylene-lined reactor and reacted at 160 °C for 12 h. After cooling, the precipitate was collected by centrifugation, washed three times with deionized water, and vacuum dried overnight to obtain MnO2 powder.

[0022] 2) Weigh the above MnO2 powder, conductive carbon black (Ketjen black) and polyvinylidene fluoride (PVDF) in a mass ratio of 7:2:1, add an appropriate amount of NMP and grind and mix them into a uniform slurry.

[0023] 3) Coat the slurry onto the stainless steel foil current collector and dry it in an 80 ℃ vacuum oven for 12 h.

[0024] 4) Cut into 12 mm diameter discs, with each disc having an active substance loading of approximately 1.2 mg.

[0025] The button battery assembly method provided by this invention is as follows: 1) Symmetrical cell: Two Zn(btec)@Zn electrodes are used as positive and negative electrodes respectively. A GF / D glass fiber separator is used, and 100 μL of 2 M ZnSO4 electrolyte is injected to assemble a button cell with a voltage of about 0 V.

[0026] 2) Copper-zinc half-cell: Using a Zn(btec)@Zn electrode as the negative electrode and a 50 μm thick copper sheet as the positive electrode, a GF / D separator is used, and 100 μL of 2 M ZnSO4 electrolyte is injected to assemble a button cell with a voltage of about 1 V.

[0027] 3) Full cell: Using Zn(btec)@Zn electrode as negative electrode and the above-mentioned MnO2 electrode as positive electrode, a GF / D membrane is used, and 100 μL of mixed electrolyte containing 2 M ZnSO4 and 0.2 M MnSO4 is injected to assemble a button cell with a voltage of about 1.4 V.

[0028] The soft-pack battery assembly method provided by this invention is as follows: 1) Stack Zn(btec)@Zn negative electrode, glass fiber membrane, electrolyte and manganese dioxide positive electrode in sequence, repeat three times to form a three-layer stacked structure.

[0029] 2) Connect the positive and negative electrodes of multiple cells in series and weld the corresponding positive and negative electrode tabs.

[0030] 3) Polyimide insulating tape is used to fix the battery stack to ensure good interface contact. Then, aluminum-plastic film is used for vacuum sealing in a sealing machine to produce a soft pack battery with a rated voltage of 4.2 V.

[0031] Commercial zinc foil, due to the relatively soft nature of zinc and limitations in processing conditions, is prone to issues such as… Figure 1 The surface shows defects such as scratches, impurity adhesion, and oxide layers. These defects become preferential active sites for zinc dendrite growth and side reactions during battery cycling, severely reducing the overall performance of the battery. To address this problem, this invention employs the aforementioned negative electrode protective coating preparation method to construct a uniform and dense Zn(btec) coating (e.g., ...) on the surface of commercial zinc foil. Figure 2 (As shown). This coating completely covers the surface of the zinc electrode, effectively preventing direct contact between the electrolyte and the zinc foil, thereby significantly suppressing side reactions caused by surface defects. It plays an important protective role for the negative electrode of aqueous zinc-ion batteries, thus improving their electrochemical performance.

[0032] After the Zn(btec)@Zn anode was prepared, the Zn(btec) powder, Zn(btec)@Zn composite electrode, and bare zinc foil were characterized by XRD. The results are as follows: Figure 3 As shown, the measured diffraction peaks of Zn(btec) material perfectly match its simulated spectrum; the diffraction peaks of Zn(btec)@Zn contain characteristic peaks of both bare zinc and Zn(btec), confirming that the target coating has been successfully loaded onto the zinc substrate surface.

[0033] In symmetrical cell testing ( Figure 4 ), at 0.5 mA cm -2 Current density and 0.5 mAh cm⁻¹ -2 Under the condition of areal capacity, the bare zinc symmetric cell short-circuited after only 500 h of cycling, while the Zn(btec)@Zn symmetric cell operated stably for up to 2100 h.

[0034] Half-cell test results ( Figure 5 This indicates that at 4 mA cm -2 Current density and 1 mAh cm -2 Under the condition of areal capacity, the bare zinc half-cell short-circuited after 100 cycles and the coulombic efficiency fluctuated significantly; the Zn(btec)@Zn half-cell achieved stable cycling for 3000 cycles and the coulombic efficiency remained close to 100%.

[0035] Full battery performance such as Figure 6 As shown: in 1 A g -1 After 700 cycles at the current density, the discharge specific capacity of the bare zinc-based full cell decayed to 53.6 mAh g⁻¹. -1 Meanwhile, the Zn(btec)@Zn-based full battery still maintains a capacity of 91.4 mAh g. -1 Specific capacity.

[0036] The above button cell tests show that the Zn(btec)@Zn electrode is significantly superior to the bare zinc electrode in terms of cycle life, coulombic efficiency, and capacity retention. Disassembly and observation of the battery after 100 hours of cycling revealed (…). Figure 7 The zinc deposition on the bare zinc electrode surface is uneven, and a large number of by-reaction products are visible. In contrast, the Zn(btec)@Zn electrode surface ( Figure 8 The morphology remained essentially unchanged compared to before cycling, indicating that the coating effectively suppressed side reactions and dendrite formation. Furthermore, Figure 9 The images show that after local removal of the Zn(btec) coating, zinc preferentially and uniformly deposits beneath the coating. The SEM images indicate that the Zn(btec) coating guides zinc ions to deposit uniformly beneath the coating, reducing direct contact between the zinc electrode and water in the electrolyte, thereby suppressing the formation of byproducts. Simultaneously, the coating acts as a physical barrier, separating the deposited zinc from the membrane and reducing the risk of dendrites piercing the membrane.

[0037] To visually verify the inhibitory effect of the Zn(btec) coating on dendrite growth, at 10 mA cm⁻¹... -2 Current density and 1 mAhcm -2 Under the areal capacity condition, in-situ observations of the two electrodes were performed within 1 hour using an optical microscope. Figure 10 The results show that as the deposition time increases, a large number of dendrites gradually form on the surface of the bare zinc electrode; and Figure 11 The uniform zinc deposition on the Zn(btec)@Zn electrode surface directly confirms that the coating effectively inhibits dendrite growth.

[0038] A three-layer pouch cell was assembled by combining a Zn(btec)@Zn negative electrode with a manganese dioxide positive electrode. Figure 12 ), in 1 A g -1After 86 cycles at the current density, the discharge specific capacity remains at 150 mAh g. -1 The capacity retention rate is close to 100%.

[0039] In addition, such as Figure 13 As shown, a single-layer pouch cell consisting of a Zn(btec)@Zn negative electrode and a manganese dioxide positive electrode can be connected in series to successfully light a bulb with a rated voltage of 6 V, demonstrating the potential of this electrode system in practical applications.

Claims

1. The application of a zinc-based metal-organic framework material in the preparation of a protective coating for the negative electrode of an aqueous zinc-ion battery, characterized in that, The zinc-based metal-organic framework material is coated on the surface of the zinc electrode to form a composite negative electrode; the zinc-based metal-organic framework material is a crystal material with a three-dimensional porous structure formed by coordination of Zn²⁺ with pyromellitic ligand.

2. The application according to claim 1, characterized in that, The zinc-based metal-organic framework material is Zn(btec), and its chemical formula is Zn3(C). 10 H2O8)·xH2O.

3. The application according to claim 1, characterized in that, The protective coating has a thickness of 10-30 μm on the zinc electrode surface.

4. A method for preparing a composite zinc anode for an aqueous zinc-ion battery according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Synthesis of zinc-based metal-organic framework materials: An alkaline solution of pyromellitic acid is mixed with an aqueous solution of zinc salt, and after hydrothermal reaction, cooling, washing and drying, zinc-based metal-organic framework material powder is obtained; S2. Preparation of coating slurry: Mix the powder obtained in step S1 with the binder at a mass ratio of 9:1, add solvent, and grind to form a uniform slurry; S3. Coating and drying: The slurry is coated onto the surface of zinc foil and dried to obtain a composite zinc anode with a protective coating on the surface.

5. The preparation method according to claim 4, characterized in that, In step S1, the hydrothermal reaction conditions are: reaction temperature 160-180℃, reaction time 12-24 hours; the zinc salt is zinc acetate.

6. The preparation method according to claim 4, characterized in that, In step S2, the adhesive is polyvinylidene fluoride and the solvent is N-methylpyrrolidone.

7. An aqueous zinc-ion battery, comprising a negative electrode, a positive electrode, a separator, and an electrolyte, characterized in that, The negative electrode is a composite zinc negative electrode prepared by the preparation method according to any one of claims 4-6.

8. The aqueous zinc-ion battery according to claim 7, characterized in that, The battery is a button cell, and its configuration is selected from any of the following: (a) Symmetrical cell: using two composite zinc anodes as the positive and negative electrodes, respectively; (b) Half cell: using the composite zinc negative electrode as the negative electrode and a copper sheet as the counter electrode; (c) Full cell: using the composite zinc anode as the anode and manganese oxide as the cathode.

9. The aqueous zinc-ion battery according to claim 8, characterized in that, The electrolyte is an aqueous solution of ZnSO4, or a mixed aqueous solution containing ZnSO4 and MnSO4.

10. The aqueous zinc-ion battery according to claim 7, characterized in that, The battery is a pouch battery, which is formed by stacking, connecting in series and encapsulating multiple units containing the composite zinc negative electrode, positive electrode and separator.

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