Polymetal hydroxide and iodine composite material as well as preparation method and application thereof

Abstract

The invention relates to a multi-metal hydroxide and iodine composite material as well as a preparation method and application thereof. According to the invention, efficient chemical adsorption of negatively charged iodine species (such as I <-> and I3) in the electrolyte is realized by utilizing the unique layered structure and the characteristic that the surface of the multi-metal hydroxide material is positively charged, so that the iodine-loaded positive electrode material is successfully prepared. The physical confinement and strong electrostatic interaction of the material can effectively anchor an iodine active substance, inhibit the dissolution and shuttle effect of polyiodide ions, and significantly reduce the loss of the active substance in the cycle process. Meanwhile, bromide ions or chloride ions are introduced into the electrolyte to anchor I < + >, so that a four-electron transfer reaction mechanism of iodine is realized, and the specific capacity of the battery is greatly improved. Experimental results show that the capacity retention rate of the zinc-iodine battery adopting the positive electrode material reaches 88% or above after circulation for 30000 times under the current density of 10 Ag <-1 >, and the zinc-iodine battery shows excellent high-capacity performance and long circulation stability. The invention provides a new technical scheme for developing a high-performance aqueous zinc-iodine battery, and has a wide application prospect in the field of energy storage.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage materials, and particularly relates to a composite material of a multi-metal hydroxide and iodine, a preparation method and a use thereof. Background Art

[0002] The continuous rise of global energy consumption has prompted people to seek green and sustainable energy to reduce greenhouse gas emissions and air pollution. Against the background of the global energy structure transformation towards renewable energy, the development of efficient, safe and low-cost electrochemical energy storage systems has become an urgent need. Aqueous zinc-ion batteries have attracted much attention due to their high intrinsic safety, environmental friendliness and rich zinc resources. Among them, zinc-iodine batteries are regarded as a highly potential candidate system due to the high theoretical capacity (~211 mAh / g) and low redox potential (~1.2 V vs. Zn 2+ / Zn) of the iodine cathode. However, traditional zinc-iodine batteries face serious shuttle effects caused by the dissolution of polyiodide ions (I3 - etc.), resulting in bottleneck problems such as irreversible loss of active substances and short cycle life. In addition, the redox reaction of iodine usually only involves two-electron transfer (I - / I 0 ), which limits the capacity performance.

[0003] In order to solve the above problems, this application is proposed. Summary of the Invention

[0004] It is found in the research of this application that: an efficient and low-cost iodine species "host" catalyst is crucial for improving the performance of zinc-iodine batteries. This application uses metal hydroxide as the "host", and its positively charged surface electrostatically attracts negatively charged iodine species (I - , [I2Br] - , [IBr2] - ), and combines with the nano-confinement effect to fix iodine species, inhibit the dissolution and diffusion of polyiodide ions, and improve iodine utilization. By efficiently fixing iodine species, this application realizes a four-electron reaction mechanism, breaks through the capacity limit, improves the theoretical specific capacity, reduces the loss of active substances, realizes a long cycle life, and creates a high-performance aqueous zinc-iodine battery.

[0005] In the first aspect of this application, a composite material of a multi-metal hydroxide and iodine is provided, and the composite material includes: a multi-metal hydroxide supported on a porous conductive substrate, and iodide ions adsorbed on the surface of the multi-metal hydroxide.

[0006] Preferably, the mass ratio of iodine to the multi-metal hydroxide is (1.2~5.5):1.

[0007] Preferably, the multi-metal hydroxide is selected from one of NiFe-LDH or CoFeAl-LDH.

[0008] In the second aspect of the present application, a preparation method of the composite material of the multi-metal hydroxide and iodine described in the first aspect is provided. The preparation method includes the following steps:

[0009] Mix the multi-metal hydroxide powder, the porous conductive substrate, the binder and the solvent, and then coat the mixture on the surface of the current collector, and dry to obtain the multi-metal hydroxide-porous substrate composite material;

[0010] Contact and adsorb the multi-metal hydroxide-porous substrate composite material with an aqueous solution of iodide under light-shielded conditions to obtain the composite material of the multi-metal hydroxide and iodine.

[0011] Preferably, the mass ratio of the multi-metal hydroxide powder, the activated carbon and the binder is (2-7):(7-2):1.

[0012] Preferably, the solvent is N-methylpyrrolidone or water.

[0013] Preferably, the drying condition is drying at 80-120 °C for 8-12 h.

[0014] Preferably, the current collector is selected from: carbon cloth, titanium foil, stainless steel mesh or nickel foam.

[0015] Preferably, the binder is selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC).

[0016] Preferably, the preparation method of the multi-metal hydroxide powder is the co-precipitation method.

[0017] Preferably, the preparation method of the multi-metal hydroxide powder includes the following steps:

[0018] Mix a divalent metal salt and a trivalent metal salt with water to obtain a metal salt solution;

[0019] Mix sodium hydroxide and sodium carbonate with water to obtain an alkali solution;

[0020] Drop the obtained metal salt solution and the alkali solution into a water-containing container simultaneously, and keep the pH value in the container at 8.5-12; age the obtained suspension for 12-24 h, centrifuge to collect the precipitate, and dry to obtain the multi-metal hydroxide powder;

[0021] The divalent metal salt is selected from one or two of divalent nickel salts and divalent cobalt salts;

[0022] The trivalent metal salt is selected from one or two of trivalent iron salts and trivalent aluminum salts.

[0023] Preferably, the aqueous iodide solution contains at least one of ZnI2, NH4I or KI, and the iodide concentration is 0.1 - 0.5 mol / L; the adsorption temperature is 20 - 40 °C, and the adsorption time is 6 - 12 h.

[0024] In the third aspect of the present application, an electrolyte for an aqueous zinc-iodine battery based on a four-electron conversion reaction is provided. The electrolyte includes a zinc source and an anchoring agent, and the anchoring agent is one or both of zinc bromide or zinc chloride.

[0025] Preferably, the molar concentration of zinc bromide is 0.1 - 0.3 M. The zinc source is zinc sulfate, and the molar concentration is 1 - 2 M.

[0026] In the fourth aspect of the present application, an aqueous zinc-iodine battery based on a four-electron conversion reaction is provided. The aqueous zinc-iodine battery includes: a positive electrode, a negative electrode, a separator, and an electrolyte;

[0027] Wherein, the positive electrode includes the multi-metal hydroxide and iodine composite material described in the first aspect, and the electrolyte is the electrolyte described in the third aspect.

[0028] In the fifth aspect of the present application, the use of the multi-metal hydroxide and iodine composite material according to any one of the first aspect as a positive electrode material for an aqueous zinc-iodine battery is provided.

[0029] Preferably, the active loading amount of iodine species on the positive electrode material is 2.0 - 15.0 mg cm -2 .

[0030] Specifically:

[0031] When the multi-metal hydroxide is a NiFe-LDH material, its preparation method includes the following steps:

[0032] Mix the ferric salt and nickelous salt in a molar ratio of (1 - 3):1 to obtain a metal salt solution; mix sodium hydroxide and sodium carbonate to obtain an alkali solution; simultaneously drip the obtained metal salt solution and alkali solution into a water-containing container, and maintain the pH value in the container at 8.5 - 12; age the obtained suspension for 12 - 24 h, centrifuge to collect the precipitate, and dry to obtain NiFe-LDH powder;

[0033] Preferably, the ferric salt is FeCl3·6H2O, and the nickelous salt is NiCl2·6H2O.

[0034] The concentration of sodium hydroxide in the mixed alkali solution is 1.0 - 2.0 mol / L, and the concentration of sodium carbonate is 0.5 - 1.0 mol / L.

[0035] The negative electrode of the battery is a metal zinc foil. The thickness of the metal zinc foil is 30 to 100 microns, and it is hermetically assembled into a CR2032 battery under a pressure of 50 to 70 MPa for electrochemical performance testing.

[0036] When the multi-metal hydroxide is CoFeAl-LDH, the metal salts are divalent cobalt salt, trivalent iron salt and trivalent aluminum salt, and their molar ratio is Co 2+ :Fe 3+ :Al 3+ =(1.5 to 3):1:1.

[0037] Preferably, the divalent cobalt salt is Co(NO3)2·6H2O, the trivalent iron salt is Fe(NO3)3·9H2O, and the trivalent aluminum salt is Al(NO3)3·9H2O.

[0038] The technical solution of this application has the following advantages compared with the prior art:

[0039] 1. This application provides a positive electrode material for an aqueous zinc-iodine battery based on the chemical adsorption of multi-metal hydroxide and the synergistic four-electron reaction mechanism. Through the layered structure and surface positive charge characteristics of the multi-metal hydroxide, this application realizes the efficient chemical adsorption of negatively charged iodine species, and combines with the three-dimensional conductive network constructed by activated carbon to significantly inhibit the dissolution and shuttle effect of polyiodide ions. Specifically, the strong electrostatic interaction and interlayer nano-confinement effect of the multi-metal hydroxide can reduce the dissolution rate of polyiodide ions to less than 5%.

[0040] 2. Preferably, this application can use an electrolyte containing zinc bromide or zinc chloride. In this way, bromide ions - or chloride ions are introduced as the anchor of iodine intermediate state (I + ), and the obtained intermediate products (taking bromide ions as an example, the intermediate products are [I2Br] - and [IBr2] - ) can also be adsorbed by the multi-metal hydroxide, activating the four-electron redox reaction of iodine (I - / I 0 / I + ). This enables iodine species to be well fixed on the positive electrode material throughout the four-electron redox reaction of iodine, improving the utilization rate of iodine and increasing the theoretical capacity to about 422 mAh / g, thus realizing an aqueous zinc-iodine battery with high capacity, high energy density and long cycle life. During this process, iodine species can be well fixed on the positive electrode material, improving the utilization rate of iodine, increasing the theoretical capacity to about 422 mAh / g, and thus realizing an aqueous zinc-iodine battery with high capacity, high energy density and long cycle life.

[0041] The synergistic effect of this chemical adsorption and four-electron reaction mechanism effectively solves the problems of active material loss, slow reaction kinetics and capacity decay in traditional zinc-iodine batteries, providing an innovative solution for realizing an aqueous zinc-iodine battery with high energy density and long cycle life.

[0042] 3. Traditional carbon-based host materials only rely on physical adsorption to fix iodine species, unable to effectively inhibit the dissolution and shuttling of polyiodide ions, resulting in a high loss rate of active substances during the cycling process. At the same time, the iodine redox reaction usually only involves two-electron transfer (I - →I 0 ), leading to an actual capacity basically lower than 200 mAh g -1 .

[0043] The technical solution of this application has the following characteristics:

[0044] The materials of this application can improve the specific capacity and cycling stability of aqueous zinc-iodine batteries. Specifically manifested as: Figure 8 It can be seen that under the condition of a current density of 2 A g -1 , after 600 charge-discharge cycles, the capacity retention rate of the positive electrode material of Example 4 (legend NiFe-I) is as high as 96%; its specific capacity is as high as 430 mAh g -1 , showing extremely excellent cycling stability. Figure 9 , 10 It can be seen that the average discharge capacities of the positive electrode material of Example 1 at 1.0, 2.0, 3.0, 5.0, and 10 A g -1 are 451.5, 409.4, 381.6, 349.9, and 302.7 mAh g -1 respectively. Overall, it shows an excellent trend of high-capacity output and relatively stable change with the current density. Compared with the electrode of Comparative Example 1 of unmodified similar materials (legend AC-I), its rate performance advantage is significant. Figure 6 It can be known that under 2 A g -1 , compared with the AC@I positive electrode material, the NiFe-AC@I positive electrode material shows excellent stability. From Figure 7 it can be seen that under a large current density of 5 A g -1 , the positive electrode material of Example 1 still shows amazing long cycling stability. After undergoing up to 6,000 charge-discharge cycles, its capacity retention rate can still be as high as 89%, the battery can still maintain excellent stability, and its specific capacity can also be maintained at a good level. Figure 11 It can be seen that under a current density of 10 A g-1, the positive electrode material of Example 1 can still maintain a capacity of 220 mAh g after up to 30,000 cycles -1 , which fully reflects the excellent performance of this positive electrode material under high-current working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Scanning electron microscope images of NiFe-LDH and CoFeAl-LDH provided in Examples 1-2 of this application;

[0046] Figure 2 EDS diagrams of CoFeAl-LDH and NiFe-AC@I cathode materials provided for Examples 1-2 of this application;

[0047] Figure 3 XRD patterns of NiFe-LDH and the material of NiFe-LDH composite with iodine in Example 1;

[0048] Figure 4 I3d XPS diagrams of the cathode material provided for Example 1 of this application in different states;

[0049] Figure 5 Raman spectra of the cathode material provided for Example 1 of this application in different states;

[0050] Figure 6 Charge-discharge long cycle diagrams of the electrode materials provided for Examples 1-2 and Comparative Example 1 of this application as the cathode of zinc-ion battery at a current density of 2 A g -1 (abbreviated as @2.0A g

[0051] Figure 7 Charge-discharge long cycle comparison diagrams of the electrode material provided for Example 1 of this application as the cathode of zinc-ion battery at a current density of 5 A g -1 (abbreviated as @5A g

[0052] Figure 8 Electrochemical rate performance diagrams of the electrode materials provided for Example 1 and Comparative Example 1 of this application as the cathode of zinc-ion battery, and the current densities are 1.0, 2.0, 3.0, 5.0, 10.0A g -1 ;

[0053] Figure 9 Charge-discharge curves of the electrode material provided for Example 1 of this application as the cathode of zinc-ion battery, and the current densities adopted for constant current charge-discharge are 1.0, 2.0, 3.0, 5.0, 10.0A g -1 ;

[0054] Figure 10 Charge-discharge curves of the electrode materials provided for Examples 1, 3, 4 and Comparative Example 1 of this application as the cathode of zinc-ion battery at a current density of 2 A g -1 (abbreviated as @2A g

[0055] Figure 11For Example 1 of this application and Comparative Example 1, the electrode materials provided are used as the positive electrode of a zinc-ion battery at a current density of 10 A g -1 ) for the charge-discharge long-cycle comparison diagram;

[0056] Figure 12 For Examples 5-6 of this application and Comparative Example 1, the electrode materials provided are used as the positive electrode of a zinc-ion battery at a current density of 6.5 mA cm-2 for the charge-discharge cycle comparison diagram.

[0057] Figure 13 It is a cycle comparison diagram of a zinc-ion battery containing the positive electrode material of Example 1 and the electrolyte provided in Example 7 at a current density of 2 A g. Detailed implementation manners

[0058] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts shall fall within the scope of protection of this application.

[0059] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in this application can be obtained through market purchases or can be prepared by existing methods. The experimental methods without specific conditions noted in the following examples are usually determined according to national standards. If there are no corresponding national standards, they are carried out according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0060] Example 1

[0061] A preparation method of a positive electrode material, the method includes

[0062] S1. Dissolve ferric salt (FeCl3·6H2O) and nickelous salt (NiCl2·H2O) in a molar ratio of 1:1 in 40 mL of deionized water to obtain a metal salt solution; dissolve 0.068 mol of sodium hydroxide and 0.021 mol of sodium carbonate in 40 mL of deionized water to obtain an alkali solution; simultaneously drop the obtained metal salt solution and alkali solution into a beaker containing 40 mL of deionized water, and keep the pH value in the beaker at 8.5; age the obtained suspension for 12 h, centrifuge to collect the precipitate, and dry to obtain NiFe-LDH powder.

[0063] S2. Mix the obtained NiFe-LDH: activated carbon: binder (polyvinylidene fluoride, PVDF) in a mass ratio of 2:7:1, add N-methylpyrrolidone (NMP), grind and mix evenly, then coat it on a carbon cloth current collector, and dry it at 80 °C for 24 h to obtain the NiFe-AC composite electrode material.

[0064] S3. Immerse the obtained NiFe-Ac composite electrode material in 500 μL of 0.1 M aqueous ZnI2 solution, soak it for 12 h under dark conditions at room temperature of 20 °C, and after soaking, dry it at 80 °C for 8 h to obtain the NiFe-AC@I modified electrode material. Avoid light because zinc iodide is unstable under light conditions. After calculation, in the NiFe-AC@I modified electrode material, the mass ratio of the loaded iodine to the polymetallic hydroxide is 1.5:1.

[0065] Example 2

[0066] S1. Dissolve a divalent cobalt salt (Co(NO3)2·6H2O), a trivalent iron salt (Fe(NO3)3·9H2O), and a trivalent aluminum salt (Al(NO3)3·9H2O) in a molar ratio of 2:1:1 in 40 mL of deionized water to obtain a metal salt solution; dissolve 0.068 mol of sodium hydroxide and 0.021 mol of sodium carbonate in 40 mL of deionized water to obtain an alkali solution; simultaneously drop the obtained metal salt solution and alkali solution into a beaker containing 40 mL of deionized water, and maintain the pH value in the beaker at 8.5; age the obtained suspension for 12 h, centrifuge to collect the precipitate, and dry to obtain CoFeAl-LDH powder.

[0067] S2. Mix the obtained CoFeAl-LDH: activated carbon: binder (polyvinylidene fluoride, PVDF) in a mass ratio of 2:7:1, add N-methylpyrrolidone (NMP), grind and mix evenly, then coat it on a carbon cloth current collector, and dry it at 80 °C for 24 h to obtain the CoFeAl-AC composite electrode material.

[0068] S3. Immerse the obtained CoFeAl-Ac composite electrode material in 500 μL of 0.1 M aqueous ZnI2 solution, soak it for 6 h under dark conditions at 40 °C, and after soaking, dry it at 80 °C for 8 h to obtain the CoFeAl-AC@I modified electrode material. After detection, in the CoFeAl-AC@I modified electrode material, the mass ratio of the loaded iodine to the polymetallic hydroxide is 1.5:1.

[0069] Example 3

[0070] S1. Dissolve ferric salt (FeCl3·6H2O) and nickelous salt (NiCl2·H2O) in deionized water at a molar ratio of 1:1 to obtain a metal salt solution. Dissolve 0.068 mol of sodium hydroxide and 0.021 mol of sodium carbonate in 40 mL of deionized water to obtain an alkali solution. Drop the obtained metal salt solution and alkali solution into a beaker containing 40 mL of deionized water simultaneously, and maintain the pH value in the beaker at 8.5. Age the obtained suspension for 12 h, centrifuge to collect the precipitate, and dry to obtain NiFe-LDH powder.

[0071] S2. Mix the NiFe-LDH, activated carbon, and binder (polyvinylidene fluoride, PVDF) obtained in Example 1 S1 at a mass ratio of 7:2:1, add N-methylpyrrolidone (NMP), grind and mix evenly, then coat it on a carbon cloth current collector and dry at 80 °C for 24 h to obtain a NiFe-AC composite electrode material.

[0072] S3. Immerse the obtained NiFe-Ac composite electrode material in 500 μL of 0.1 M ZnI2 aqueous solution, soak it for 12 h under dark conditions at 25 °C, and after soaking, dry it at 80 °C for 8 h to obtain a NiFe-AC@I modified electrode material. After testing, in the NiFe-AC@I modified electrode material, the mass ratio of the loaded iodine to the polymetallic hydroxide is 1.5:1.

[0073] Example 4

[0074] S2. Mix the NiFe-LDH, activated carbon, and binder (polyvinylidene fluoride, PVDF) obtained in Example 1 S1 at a mass ratio of 5:4:1, add N-methylpyrrolidone (NMP), grind and mix evenly, then coat it on a carbon cloth current collector and dry at 80 °C for 24 h to obtain a NiFe-AC composite electrode material.

[0075] S3. Immerse the obtained NiFe-Ac composite electrode material in 500 μL of 0.1 M ZnI2 aqueous solution, soak it for 12 h under dark conditions at 20 °C (room temperature), and after soaking, dry it at 80 °C for 8 h to obtain a NiFe-AC@I modified electrode material. After testing, in the NiFe-AC@I modified electrode material, the mass ratio of the loaded iodine to the polymetallic hydroxide is 1.5:1.

[0076] Example 5

[0077] S2. Mix the NiFe-LDH, activated carbon, and binder (polyvinylidene fluoride, PVDF) obtained in Example 1 S1 at a mass ratio of 7:2:1, add N-methylpyrrolidone (NMP), grind and mix evenly, then coat it on a carbon cloth current collector and dry at 80 °C for 24 h to obtain a NiFe-AC composite electrode material.

[0078] S3. Immerse the obtained NiFe-Ac composite electrode material in 500 μL of 0.5 M ZnI₂ aqueous solution, soak it for 12 h under dark conditions at room temperature of 20 °C, and then dry it at 80 °C for 8 h to obtain the NiFe-AC@I modified electrode material. After testing, in the NiFe-AC@I modified electrode material, the mass ratio of the loaded iodine to the poly-metal hydroxide is 5.5:1.

[0079] Example 6

[0080] S2. Mix the CoFeAl-LDH: activated carbon: binder (polyvinylidene fluoride, PVDF) obtained in Example 2 S1 in a mass ratio of 2:7:1, add N-methylpyrrolidone (NMP), grind and mix evenly, then coat it on the carbon cloth current collector, and dry it at 80 °C for 24 h to obtain the CoFeAl-AC composite electrode material.

[0081] S3. Immerse the obtained CoFeAl-AC composite electrode material in 500 μL of 0.5 M ZnI₂ aqueous solution, soak it for 12 h under dark conditions at room temperature of 20 °C, and then dry it at 80 °C for 8 h to obtain the CoFeAl-AC@I modified electrode material. After testing, in the CoFeAl-AC@I modified electrode material, the mass ratio of the loaded iodine to the poly-metal hydroxide is 5.5:1.

[0082] Example 7

[0083] Selection of electrolyte type

[0084] Mix the poly-metal hydroxide (LDH), activated carbon and binder in a mass ratio of 2:7:1, and prepare the material as the positive electrode of the battery in the manner of Example 1. Select 2 M ZnSO₄·7H₂O as the zinc source for the electrolyte, and select 0.2 M zinc bromide and 0.2 M zinc chloride as the + anchoring agents for I.

[0085] Figure 13 is the cycle comparison diagram of the zinc-ion battery containing the positive electrode material of Example 1 and the electrolyte provided in Example 7 at a current density of 2 A / g. It can be Figure 13 seen that different results are obtained by using zinc bromide and zinc chloride as the anchoring agents in this application. The positive electrode system anchored with zinc bromide shows an initial specific capacity of 420 mAh g⁻¹, and the Coulomb efficiency is maintained at 96%, while the positive electrode system anchored with zinc chloride shows an initial specific capacity of 360 mAh g -1 and the average Coulomb efficiency is 91%. This shows that both zinc bromide and zinc chloride can be used as anchoring agents to anchor I⁺ ions, but zinc bromide as the anchoring agent can significantly improve the redox reversibility and cycle stability of iodine species.

[0086] Comparative Example 1

[0087] S1. Activated carbon and binder (polyvinylidene fluoride, PVDF) were added in a mass ratio of 9:1, ground and mixed evenly with NMP, then coated on carbon cloth and dried at 80 °C for 24 h to obtain the AC electrode material.

[0088] S2. The obtained AC positive electrode material was immersed in 500 μL of 0.1 M ZnI₂ aqueous solution and soaked for 12 h under dark conditions at room temperature of 20 °C. After soaking, it was dried at 80 °C for 8 h to obtain the AC@I electrode material.

[0089] Material characterization and performance testing:

[0090] The positive electrode materials provided in Examples 1 to 3 were subjected to scanning electron microscopy testing. Since the results were similar, only the test results of Example 1 are used for illustration below.

[0091] Figure 1 Scanning electron micrographs of NiFe-LDH and CoFeAl-LDH provided for Example 1 and Example 2. The metal hydroxide exhibits an obvious nanosheet structure. These sheet-like structures aggregate with each other, stack layer by layer, have a large surface area and a rich pore structure, improving the adsorption capacity.

[0092] Figure 2 EDS diagrams of the CoFeAl-LDH material provided for Example 2 (left) and the NiFe-AC@I positive electrode material of Example 1 (right). Figure 2 The successful synthesis of CoFeAl-LDH can be seen in the left figure of the CoFeAl-LDH material. Figure 2 In the right figure, the loading signal of I can be seen, proving the successful loading of I.

[0093] Figure 3 XRD patterns of NiFe-LDH and the composite material of NiFe-LDH and iodine (NiFe-AC@I, corresponding legend NiFeLDH+ZnI₂) in Example 1. This pattern proves the successful preparation of NiFe-LDH. For the composite material, there is no obvious shift in the peak position at 2θ = 11.4°. According to Bragg's equation 2dsinθ = nλ, it can be inferred that the interlayer spacing has no obvious increase. Therefore, iodide ions are not in the interlayer of NiFe-LDH, and iodide ions are adsorbed on its surface by positively charged NiFe-LDH. It is speculated that the adsorption of metal hydroxide plays a key role in the electrochemical performance of the material.

[0094] Figure 4I3d XPS spectra of the cathode material (NiFe-AC@I) provided in Example 1 of this application in different states; this spectrum confirms the four-electron redox process of iodine during the reaction (I - →I 0 →I + ). Specifically, initially, iodine exists in the form of I - . As the charging potential rises from the initial value to 1.2 V and 1.85 V, characteristic signals of I 0 and I + appear respectively; during the discharging process, when the potential drops from 1.85 V to 1.2 V and 0.5 V, the iodine species sequentially transform into I 0 and I - , clearly demonstrating the good reversibility of this redox reaction.

[0095] Figure 5 Raman spectra of the cathode material (NiFe-AC@I) provided in Example 1 of this application in different states; the peak appearing at 160 - 170 cm-1 is [IBr2] - , which also confirms the successful excitation of the four-electron reaction of iodine, thereby achieving a relatively high theoretical specific capacity (422 mAh g -1 ).

[0096] Using the electrode materials provided in Examples 1 to 3 and Comparative Example 1 as the cathode, zinc foil as the anode, and the electrolyte being 2 M ZnSO4 and 0.2 M ZnBr2, charge-discharge tests and long charge-discharge cycle tests were conducted on the battery, and the results are as Figures 8 to 13 shown.

[0097] For the cathode materials provided in Examples 1 to 3, long charge-discharge cycle tests were carried out. Since the results are similar, only the test results of Example 1 are used for illustration below. Figure 6 shows the long charge-discharge cycle conditions of the cathode materials provided in Example 1 and Comparative Example 1 as the cathode of a zinc-ion battery at a current density of 2 A g -1 . As can be Figure 6 seen, under the condition of a current density of 2 A g -1 , after 600 charge-discharge cycles, the capacity retention rate of the cathode material of Example 1 (legend: NiFe-AC@I) is as high as 97%; its specific capacity is as high as 430 mAh g -1 , showing extremely excellent cycle stability. In contrast, the performance of the electrode material of Comparative Example 1 (legend: AC@I) is much inferior. The capacity retention rate during the same period can only reach 67%, and the corresponding specific capacity is only 198 mAh g -1 . At a current density of 2 A g -1Under the condition of [condition not specified in the original], after 420 charge-discharge cycles, the capacity retention rate of the cathode material of Example 2 (legend: CoFeAl-AC@I) is as high as 92%; its specific capacity is as high as 380 mAh g -1 , and it also shows extremely excellent cycle stability.

[0098] Charge-discharge tests were carried out on the cathode materials provided in Examples 1 to 5. Since the results are similar, only the test results of Example 4 are used for illustration below.

[0099] Figure 8 This is the electrochemical rate performance diagram of the electrode materials provided in Example 1 and Comparative Example 1 of this application as the positive electrode of a zinc-ion battery, and the current densities are 1.0, 2.0, 3.0, 5.0, 10.0 A g -1 . Figure 8 It can be seen that: the cathode material of Example 1 has average discharge capacities of 451.5, 411.0, 381.6, 349.9, and 302.7 mAh g -1 at 1.0, 2.0, 3.0, 5.0, and 10 A g -1 respectively. Overall, it shows an excellent trend of high-capacity output and relatively stable change with the current density. Compared with the electrode material of Comparative Example 1 of the unmodified similar material, its rate performance advantage is significant. Figure 8 It can be known that at 2 A g -1 , compared with the AC@I cathode material, the NiFe-AC@I cathode material shows excellent stability.

[0100] Figure 7 This is the charge-discharge cycle diagram of the electrode material of Example 1 as the zinc-ion positive electrode material at a current density of 5 A g -1 . Figure 7 It can be known that at a large current density of 5 A g -1 , the cathode material of Example 1 still shows amazing long-cycle stability. After undergoing up to 6,000 charge-discharge cycle tests, its capacity retention rate can still be as high as 89%, the battery can still maintain excellent stability, and its specific capacity can also be maintained at a good level.

[0101] Figure 10 This is for Example 1 (NiFeLDH:AC:PVDF = 2:7:1), Example 3 (NiFeLDH:AC:PVDF = 7:2:1), Example 4 (NiFeLDH:AC:PVDF = 5:4:1) of this application, and the electrode material provided in Comparative Example 1 (AC:PVDF = 9:1) as the positive electrode of a zinc-ion battery at a current density of 2 amperes per gram (abbreviated as @2 A g -1 ). From Figure 10It can be seen that when the mass ratio of NiFe-LDH is 10-30% (i.e., Example 1), the electrode material exhibits a relatively high discharge specific capacity and has a relatively high discharge plateau; while when the proportion of NiFe-LDH exceeds 50% (i.e., Examples 3 and 4), due to the hindered ion diffusion caused by the densification of the layered structure stacking, the discharge specific capacity drops to 300 mAh g-1. The above results indicate that when the ratio of NiFe LDH to activated carbon is within a suitable range, the synergistic effect of the chemisorption of NiFe LDH and the physical confinement of activated carbon can reach the optimal state.

[0102] Figure 11 For Example 1 of this application, the electrode materials provided in Comparative Example 1 were used as the positive electrode of a zinc ion battery at a current density of 10 amperes per gram (abbreviated as @10.0 A g -1 ) of the charge-discharge long cycle comparison diagram;

[0103] Figure 11 At a high current density of 10 A g -1 , the positive electrode material of Example 1 still showed amazing long cycle stability. After undergoing up to 30,000 charge-discharge cycles, its capacity retention rate was still as high as 88%, the battery could still maintain excellent stability, and its specific capacity could also be maintained at a good level, which fully demonstrated the excellent performance of this positive electrode material under high current conditions.

[0104] Figure 12 For Examples 5-6 of this application, the electrode materials provided in Comparative Example 1 were used as the positive electrode of a zinc ion battery at a current density of 6.5 mA cm -2 of the charge-discharge cycle comparison diagram. This diagram shows the areal capacity exhibited by the prepared positive electrode material at a current density of 6.5 mA cm-2 when the mass ratio of the loaded iodine to the polymetallic hydroxide is 5.5:1. It can be seen that NiFe-AC@I and CoFeAl-AC@I have relatively similar areal capacities, with an average of up to 1.45 mAh cm -2 , while AC@I is only 0.85 mAh cm -2 . This fully demonstrates that even under a relatively high loading state, compared with Comparative Example 1, the battery of this application can still exhibit excellent areal capacity advantages, which provides a possibility for large-scale application.

Claims

1. A composite material of multimetal hydroxide and iodine, characterized in that: The composite material comprises: a multi-metal hydroxide supported by a porous conductive substrate and iodine ions adsorbed on the surface of the multi-metal hydroxide.

2. The multi-metal hydroxide and iodine composite material according to claim 1, characterized in that: The mass ratio of the iodine to the polymetallic hydroxide is (1.2-5.5):

1.

3. The multi-metal hydroxide according to claim 1 is selected from: NiFe-LDH or CoFeAl-LDH.

4. A method for preparing the composite material of multi-metal hydroxide and iodine according to claim 1, characterized in that: The preparation method comprises the following steps: The multi-metal hydroxide powder, the porous conductive substrate, the binder and the solvent are mixed and coated on the surface of the current collector, and dried to obtain the multi-metal hydroxide-porous substrate composite material; The multi-metal hydroxide-porous substrate composite material is brought into contact with an iodide aqueous solution for adsorption under light-proof conditions to obtain a multi-metal hydroxide and iodine composite material.

5. The method for preparing the composite material of multi-metal hydroxide and iodine according to claim 4, characterized in that: The preparation method of the multi-metal hydroxide powder is a co-precipitation method.

6. The method for preparing the composite material of multi-metal hydroxide and iodine according to claim 5, characterized in that: The preparation method of the multi-metal hydroxide powder comprises the following steps: Mixing a divalent metal salt and a trivalent metal salt with water to obtain a metal salt solution; Mixing sodium hydroxide and sodium carbonate with water to obtain an alkaline solution; The obtained metal salt solution and alkaline solution are simultaneously added dropwise to a container containing water, and the pH value in the container is maintained at 8.5 to 12; the obtained suspension is aged for 12 to 24 hours, and the precipitate is collected by centrifugation and dried to obtain a multi-metal hydroxide powder; The divalent metal salt is selected from one or both of divalent nickel salt and divalent cobalt salt; The trivalent metal salt is selected from: one or two of trivalent iron salts and trivalent aluminum salts.

7. The preparation method according to claim 4, characterized in that: The iodide aqueous solution contains at least one of ZnI2, NH4I or KI, and the iodide concentration is 0.1-0.5 mol / L; the adsorption temperature is 20-40°C, and the adsorption time is 6-12h.

8. An electrolyte for an aqueous zinc-iodine battery based on a four-electron conversion reaction, characterized in that: The electrolyte includes a zinc source and an anchoring agent, and the anchoring agent is one or both of zinc bromide and zinc chloride.

9. An aqueous zinc-iodine battery based on a four-electron conversion reaction, characterized in that: The aqueous zinc-iodine battery comprises: a positive electrode, a negative electrode, a separator and an electrolyte; Wherein, the positive electrode comprises the multimetal hydroxide and iodine composite material according to any one of claims 1 to 3, and the electrolyte is the electrolyte according to claim 9.

10. Use of the multimetal hydroxide and iodine composite material according to any one of claims 1 to 2 as a positive electrode material for aqueous zinc-iodine batteries.

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