Iodine positive electrode material with protective coating, method for preparing same and zinc-iodine battery

Abstract

This invention discloses an iodine cathode material with a protective coating, its preparation method, and a zinc-iodine battery, belonging to the field of electrode material technology. This invention uses an iodine cathode material as a substrate and coats the substrate surface with a protective material to form an iodine cathode material with a protective coating. This can inhibit the dissolution of iodine species and their diffusion to the negative electrode side, effectively improving the ability of the iodine cathode material with a protective coating to confine active iodine and the adsorption of polyiodides, thereby effectively suppressing the dissolution of active iodine and the shuttle problem of polyiodides.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology. Specifically, it relates to iodine cathode materials with protective coatings, their preparation methods, and zinc-iodine batteries. Background Technology

[0002] Intrinsically safe aqueous batteries represent an important development direction for building high-energy-density and high-safety energy storage systems. Among them, aqueous zinc batteries, which employ high-capacity metallic zinc anodes (820mAh / g) and have good compatibility with aqueous electrolytes in their operating voltage window, have become a current research hotspot.

[0003] Traditional zinc-based batteries mostly employ intercalation-type cathode materials. These materials have limited zinc storage capacity and slow kinetics, making it difficult to match the high-capacity characteristics of zinc anodes, thus limiting the full potential of aqueous zinc batteries. Developing novel high-capacity, fast-kinetic cathode materials has become crucial for advancing this field. Halogen electrode reactions, with their rapid conversion reaction characteristics based on a dissolution-deposition mechanism, exhibit excellent kinetic prospects. Zinc-iodine batteries utilize this mechanism for energy storage, overcoming the limitations of traditional zinc-ion batteries that rely on ion intercalation / deintercalation, thereby avoiding the problem of cathode material structural collapse. Furthermore, iodine has advantages such as abundant resources, low cost, and diverse valence states, and its theoretical cathode specific capacity is relatively high (211 mAh / g), making zinc-iodine batteries a highly promising next-generation clean and efficient energy storage device.

[0004] However, the practical application of zinc-iodine batteries still faces severe challenges, mainly manifested in the polyiodide shuttle effect of the iodine cathode material and the resulting insufficient stability of the zinc anode. The root cause lies in the solid-liquid-solid phase transition that occurs during the charging and discharging process of the iodine cathode: solid iodine molecules are reduced to soluble iodide ions, which then react with iodine molecules to generate polyiodide intermediates soluble in the electrolyte (such as I3). - These dissolved polyiodides diffuse into the zinc anode and undergo irreversible side reactions with zinc, leading to zinc anode corrosion and continuous loss of active iodine, which severely restricts the cycle life and practical usability of the battery. Summary of the Invention

[0005] To address the technical problems of polyiodide shuttle effect and its resulting insufficient stability in zinc anodes faced by existing iodine cathode materials, this invention provides an iodine cathode material with a protective coating, its preparation method, and a zinc-iodine battery. This invention uses an iodine cathode material as a substrate and coats the surface of the substrate with a protective material to obtain an iodine cathode material with a protective coating. The protective coating acts as a selective barrier, effectively improving the iodine-loaded cathode's ability to confine active iodine and its adsorption of polyiodides, thereby effectively inhibiting the dissolution of active iodine and polyiodide shuttle.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] The first objective of this invention is to provide an iodine cathode material with a protective coating, wherein the iodine cathode material with the protective coating is formed by coating a protective material onto the surface of an iodine cathode material as a substrate.

[0008] The protective material accounts for 4% to 7% of the total mass of the iodine cathode material containing the protective coating.

[0009] The protective material is polyethyleneimine (molecular weight 70,000 Da), chitosan (degree of deacetylation 95%), gelatin (molecular weight 50,000 Da to 100,000 Da), or sodium alginate (molecular weight 222 Da).

[0010] In a preferred embodiment, the protective material accounts for 5% of the mass of the iodine cathode material containing the protective coating.

[0011] A second objective of this invention is to provide a method for preparing an iodine cathode material with a protective coating, comprising the following steps: The protective material is dispersed in a solvent to form a coating solution, which is then coated onto the surface of the iodine cathode material to form a protective coating. After drying, the iodine cathode material with the protective coating is obtained.

[0012] In a preferred embodiment, the mass concentration of the coating solution is 2wt% to 7wt%.

[0013] In a preferred embodiment, the mass concentration of the coating solution is 5 wt%.

[0014] In a preferred embodiment, the solvent is water or an aqueous solution of acetic acid.

[0015] For coating materials with poor water solubility, such as gelatin or chitosan, adding a certain amount of acetic acid to water can help dissolve the polymer. If other organic solvents are used, the iodine in the iodine-supported carbon is easily dissolved during stirring of the positive electrode slurry. In the acetic acid aqueous solution, the mass ratio of acetic acid to water is 1–20:100.

[0016] In a preferred embodiment, the drying process is performed at 25°C to 35°C for 0.5 hours.

[0017] In a preferred embodiment, the iodine cathode material is obtained by mixing iodine-loaded carbon black, Ketjen black and sodium alginate to obtain an iodine cathode slurry, and coating the iodine cathode slurry onto a current collector.

[0018] The third objective of this invention is to provide a zinc-iodine battery that uses the iodine cathode material with a protective coating as described in claim 1 as the cathode.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention uses iodine cathode material as a substrate and coats a protective material onto the surface of the substrate to obtain an iodine cathode material with a protective coating. The iodine cathode material with a protective coating provided by this invention avoids the formation of a continuous insulating film inside the electrode, thereby minimizing damage to the entire electrode's electronic conductivity network and allowing electrons to still transport smoothly within the electrode; polyiodides (I3) - After dissolving from the positive electrode material, the iodine must pass through the coating to enter the bulk electrolyte and shuttle to the negative electrode. The protective coating, acting as a selective barrier, captures and "repatriates" the iodine before it leaves the electrolyte, effectively improving the iodine-loaded positive electrode's ability to confine active iodine and adsorb polyiodides, thereby effectively inhibiting the dissolution of active iodine and the shuttle movement of polyiodides. Furthermore, the protective molecules in the coating are distributed at the reaction interface, resulting in higher utilization, less material usage, and a more concentrated effect compared to mixing them into the overall electrode. Attached Figure Description

[0020] Figure 1 Figure a shows the iodine cathode material obtained in Comparative Example 1 and the iodine cathode material with protective coating obtained in Example 1. Figure b shows the iodine cathode material obtained in Comparative Example 1 and the iodine cathode material with protective coating obtained in Example 1.

[0021] Figure 2 Figure 1 shows a comparison of the electrochemical performance of the zinc-iodine battery obtained in Comparative Example 1 and the zinc-iodine battery obtained in Example 1. Specifically, Figure 1a shows the 10C cycle test results of the zinc-iodine batteries obtained in Comparative Example 1 and Example 1; Figure 2b shows the 2C cycle test results of the zinc-iodine batteries obtained in Comparative Example 1 and Example 1; Figure 3c shows the rate performance of the zinc-iodine batteries obtained in Comparative Example 1 and Example 1; and Figure 4d shows the CV characteristic curves of the zinc-iodine batteries obtained in Comparative Example 1 and Example 1 at 0.1 mV / s.

[0022] Figure 3 The graph shows the 10C cycle test results of the zinc-iodine battery obtained in Comparative Example 1 and the zinc-iodine battery obtained in Example 2.

[0023] Figure 4 The PEI and I3 in the iodine cathode material with protective coating obtained in Example 1 of this invention - A diagram illustrating strong chemisorption. Detailed Implementation

[0024] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention is further described below with reference to specific embodiments. However, the embodiments are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0025] The practical application of zinc-iodine batteries faces severe challenges, mainly including the polyiodide shuttle effect of iodine cathode materials and insufficient stability of zinc anodes. The root cause lies in the solid-liquid-solid phase transition that occurs in the iodine cathode during charging and discharging: solid iodine molecules are reduced to soluble iodide ions, which then react with iodine molecules to form polyiodide intermediates soluble in the electrolyte (such as I3). - These dissolved polyiodides diffuse into the zinc anode and undergo irreversible side reactions with zinc, leading to zinc anode corrosion and continuous loss of active iodine, severely limiting the battery's cycle life and practical usability. Based on the above problems, this invention provides an iodine cathode material with a protective coating, its preparation method, and its application.

[0026] The technical solution of the present invention will be analyzed in detail below.

[0027] This invention provides an iodine cathode material with a protective coating, wherein the iodine cathode material with a protective coating is formed by coating a protective material onto the surface of an iodine cathode material as a substrate. The protective material accounts for 4% to 7% of the mass of the iodine cathode material with the protective coating; the protective material is polyethyleneimine, chitosan, gelatin, or sodium alginate.

[0028] In the above technical solution, the iodine cathode material with a protective coating avoids the formation of a continuous insulating film inside the electrode, thereby minimizing damage to the entire electrode's electronic conductivity network and allowing electrons to still transport smoothly inside the electrode; polyiodides (I3) - After dissolving from the positive electrode material, the iodine must pass through the coating to enter the bulk electrolyte and shuttle to the negative electrode. The protective coating, acting as a selective barrier, captures and redirects the iodine before it leaves the electrode, effectively enhancing the iodine-carrying positive electrode's ability to confine active iodine and adsorb polyiodides, thereby effectively inhibiting the dissolution of active iodine and the shuttle movement of polyiodides. Furthermore, the protective molecules in the coating are distributed at the reaction interface, resulting in higher utilization, less material usage, and a more concentrated effect compared to mixing them into the overall electrode.

[0029] The technical solution of the present invention will be further illustrated below through the following embodiments and comparative examples.

[0030] Example 1 A method for preparing an iodine cathode material with a protective coating includes the following steps: S1, Preparation of iodine-loaded carbon black: Weigh activated carbon for supercapacitors and elemental iodine in a mass ratio of 1:1, grind them in a mortar for about 2 minutes until fine, take them out and put them into a glass sample bottle, put them in a forced-air drying oven and heat them at 120℃ for 6 hours to allow the elemental iodine to sublimate and embed into the activated carbon, thus obtaining iodine-loaded carbon black, denoted as I2@CB.

[0031] S2, Preparation of iodine cathode material: Weigh iodine-loaded carbon black, Ketjen black, and sodium alginate in a solid mass ratio of 7:2:1, grind them in a mortar for 8 minutes, gradually adding 1.5 mL of pure water during the process, and wet grind for 3 minutes to obtain iodine cathode slurry. Scrape about 8 mg of iodine cathode slurry onto a stainless steel mesh and dry it in an oven at 25°C for 2 hours to obtain iodine cathode material with a diameter of 12 mm.

[0032] S3, Preparation of iodine cathode material with protective coating: Prepare a PEI (molecular weight of 70000 Da) solution with a mass concentration of 5 wt%. Add the PEI solution (the mass percentage of PEI is 5% based on the mass of the iodine cathode material with protective coating) dropwise to the surface of the iodine cathode material in S2, uniformly cover the surface of the iodine cathode material, and dry in an oven at 25°C for 0.5 h to allow the solvent to evaporate. The PEI solution forms a coating on the surface of the iodine cathode material, thus obtaining the iodine cathode material with protective coating.

[0033] Example 2 A method for preparing an iodine cathode material with a protective coating includes the following steps: S1, Preparation of iodine-loaded carbon black: Weigh activated carbon for supercapacitors and elemental iodine in a mass ratio of 1:1, grind them in a mortar for about 2 minutes until fine, take them out and put them into a glass sample bottle, put them in a forced-air drying oven and heat them at 120℃ for 6 hours to allow the elemental iodine to sublimate and embed into the activated carbon, thus obtaining iodine-loaded carbon black, denoted as I2@CB.

[0034] S2, Preparation of iodine cathode material: Weigh iodine-loaded carbon black, Ketjen black, and sodium alginate (SA) in a solid mass ratio of 7:2:1, place them in a mortar and grind for 8 minutes, gradually adding 1.5 mL of pure water during the process, and wet grind for 3 minutes to obtain iodine cathode slurry. Scrape about 8 mg of iodine cathode slurry onto a stainless steel mesh and dry it in an oven at 25°C for 2 hours to obtain iodine cathode material with a diameter of 12 mm.

[0035] S3, Preparation of iodine cathode material with protective coating: Weigh 1g of SA (molecular weight 222Da) powder and add it to 20mL of water and stir thoroughly to prepare a 5wt% SA solution. Drop the SA solution (based on the mass of the iodine cathode material with protective coating, the mass percentage of SA is 5%) onto the surface of the iodine cathode material in S2, and evenly cover the surface of the iodine cathode material. Dry in an oven at 25℃ for 0.5h to allow the solvent to evaporate. The SA solution forms a coating on the surface of the iodine cathode material, thus obtaining the iodine cathode material with protective coating.

[0036] Comparative Example 1 A method for preparing an iodine cathode material includes the following steps: S1, Preparation of iodine-loaded carbon black: Weigh activated carbon for supercapacitors and elemental iodine in a mass ratio of 1:1, grind them in a mortar for about 2 minutes until fine, take them out and put them into a glass sample bottle, place them in a forced-air drying oven at 60°C and heat for 6 hours to allow the elemental iodine to sublimate and embed into the activated carbon, thus obtaining iodine-loaded carbon black, denoted as I2@CB.

[0037] S2, Preparation of the iodine cathode: Weigh out iodine-loaded carbon black, Ketjen black, and sodium alginate in a solid mass ratio of 7:2:1, grind them in a mortar for 8 minutes, gradually adding 1.5 mL of pure water during the process, and wet grind for 3 minutes to obtain an iodine cathode slurry. Scrape about 8 mg of the iodine cathode slurry onto a stainless steel mesh and dry it in an oven at 25°C for 2 hours to obtain the iodine cathode material.

[0038] Application Example 1 Take the iodine positive electrode material with protective coating prepared in Example 1 and place it in the center of the positive electrode shell. Add 50 μL of 2M ZnSO4 electrolyte, insert the glass fiber separator, and continue to add 50 μL of electrolyte until it is wetted. Take a zinc foil disc, align it with the position of the positive electrode sheet, and insert it into the battery shell. Place the gasket and spring sheet, and seal it with a battery sealing machine to obtain a zinc-iodine battery.

[0039] Application Example 2 Take the iodine positive electrode material with protective coating prepared in Example 2 and place it in the center of the positive electrode shell. Add 50 μL of 2M ZnSO4 electrolyte, put in the glass fiber separator, and continue to add 50 μL of electrolyte until it is wetted. Take a zinc foil disc, align it with the position of the positive electrode sheet, and put it into the battery shell. Place the gasket and spring sheet, and seal it with a battery sealing machine to obtain a zinc-iodine battery.

[0040] Application Comparative Example 1 Take the iodine positive electrode material prepared in Comparative Example 1 and place it in the center of the positive electrode shell. Add 50 μL of 2M ZnSO4 electrolyte, insert a glass fiber separator, and continue to add 50 μL of electrolyte until it is wetted. Take a zinc foil disc, align it with the position of the positive electrode, and insert it into the battery shell. Place a gasket and a spring sheet, and seal it with a battery sealing machine to obtain a zinc-iodine battery.

[0041] In the iodine cathode material with a protective coating prepared in Example 1 of this invention, the electron-rich amino group (-NH2) on the PEI chain acts as an electron donor and undergoes charge transfer with iodine (as an electron acceptor) to form a stable PEI-I2 or PEI-I3. - Charge-transfer complexes can chemically immobilize soluble iodine species onto polymer chains. Additionally, by selecting [a specific compound], I3 [can be inhibited]. - PEI material with shuttle effect is used as a coating for iodine cathode material to improve the electrochemical performance of zinc-iodine batteries. In the acidic environment of battery operation (especially after charging), some amino groups of PEI become protonated and positively charged (-NH3). + ), positively charged PEI and negatively charged I3 - Strong Coulomb attraction is generated, ion pairs are formed, and I3 is significantly reduced. - The zinc-iodine battery prepared in Example 1 exhibits excellent self-discharge resistance, high coulombic efficiency, cycle stability, and long cycle life, thanks to these advantages.

[0042] The performance of the zinc-iodine batteries prepared in Application Example 1 and Comparative Example 1 was tested, and the results are as follows: Figure 2As shown, it is evident that the zinc-iodine battery prepared using Example 1 exhibits better cycle performance than the zinc-iodine battery prepared using Comparative Example 1. As shown in Figure a, after 2000 charge-discharge cycles at 10C at room temperature, the discharge specific capacity of the zinc-iodine battery prepared using Example 1 is 148 mAh / g, while the discharge specific capacity of the zinc-iodine battery prepared using Comparative Example 1 is only 122 mAh / g. As shown in Figure b, after 430 charge-discharge cycles at 2C, the discharge specific capacity of the zinc-iodine battery prepared using Example 1 is 139 mAh / g, while the discharge specific capacity of the zinc-iodine battery prepared using Comparative Example 1 is only 106 mAh / g. As shown in Figure c, the rate performance of the zinc-iodine battery prepared using Example 1 is also significantly improved, and the capacity decay of the zinc-iodine battery prepared using Example 1 is slower. At current density gradients of 1C, 3C, 5C, 10C, 25C, and 50C, the average discharge specific capacity of the zinc-iodine battery in Application Example 1 was approximately 190 mAh / g, 170 mAh / g, 160 mAh / g, 140 mAh / g, 120 mAh / g, and 90 mAh / g, respectively. In contrast, the average discharge specific capacity of the zinc-iodine battery in Comparative Example 1 was approximately 180 mAh / g, 160 mAh / g, 145 mAh / g, 125 mAh / g, 105 mAh / g, and 80 mAh / g, respectively. It can be seen that the discharge specific capacity of the zinc-iodine battery in Application Example 1 was significantly higher than that of the zinc-iodine battery in Comparative Example 1 at all current densities. Meanwhile, as the current density increased from 1C to 50C, the capacity of the zinc-iodine battery in Application Example 1 decreased by approximately 52.6%, while the capacity of the zinc-iodine battery in Comparative Example 1 decreased by approximately 55.6%, indicating a smaller capacity decay in the zinc-iodine battery in Application Example 1. When the current density gradually decreased from 50C to 1C, the capacity of the zinc-iodine battery in Application Example 1 recovered to approximately 180 mAh / g, a better recovery than that of the zinc-iodine battery in Comparative Example 1 (approximately 160 mAh / g), further demonstrating that the zinc-iodine battery prepared in Application Example 1 possesses superior rate performance and capacity recovery capability. As shown in Figure d, the CV characteristic curves show that the zinc-iodine battery prepared in Application Example 1 has higher oxidation and reduction peak currents, exhibiting better reaction kinetics and lower charge transport impedance. The smaller voltage difference between the oxidation and reduction peaks indicates a lower degree of polarization, suggesting a reduced interfacial impedance between the electrode material and the electrolyte.

[0043] Figure 3 To conduct a 10C cycle test on the zinc-iodine battery obtained in Comparative Example 1 and the zinc-iodine battery obtained in Application Example 2, after 200 cycles of 10C charge-discharge at room temperature, the discharge specific capacity of the zinc-iodine battery obtained in Application Example 2 was 142.29 mAh / g, while the discharge specific capacity of the zinc-iodine battery obtained in Comparative Example 1 was only 123.25 mAh / g.

[0044] PEI, as an iodine cathode coating, inhibits I3 by forming a protective layer. - The ion shuttle effect, which gives the battery higher specific capacity, longer cycle life, and better reaction kinetics, is due to its ability to form a physical barrier on the surface of the iodine cathode, thereby hindering the formation of I3. - Diffusion at the iodine cathode, and with I3 - It has strong chemisorption properties, and the results are as follows: Figure 4 As shown, PEI aqueous solution reacts with yellowish-brown I3 - After the solutions are mixed, the solution becomes colorless, indicating that charge transfer has occurred. This allows the iodine species to be chemically fixed onto the polymer chain, thus suppressing I3 in zinc-iodine batteries. - The shuttle effect improves the cycle performance of the battery.

[0045] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. An iodine cathode material with a protective coating, characterized in that, The iodine cathode material with protective coating is formed by coating the protective material onto the surface of the iodine cathode material as a substrate. Based on the mass of the iodine cathode material containing the protective coating, the protective material accounts for 4% to 7% of the total mass. The protective material is polyethyleneimine, chitosan, gelatin, or sodium alginate.

2. The iodine cathode material with a protective coating according to claim 1, characterized in that, The protective material accounts for 5% of the total mass of the iodine cathode material containing the protective coating.

3. A method for preparing an iodine cathode material with a protective coating as described in claim 1, characterized in that, Includes the following steps: The protective material is dispersed in a solvent to form a coating solution, which is then coated onto the surface of the iodine cathode material to form a protective coating. After drying, the iodine cathode material with the protective coating is obtained.

4. The method for preparing the iodine cathode material with a protective coating according to claim 3, characterized in that, The mass concentration of the coating solution is 2wt% to 7wt%.

5. The method for preparing the iodine cathode material with a protective coating according to claim 4, characterized in that, The mass concentration of the coating solution is 5 wt%.

6. The method for preparing the iodine cathode material with a protective coating according to claim 3, characterized in that, The solvent is water or an aqueous solution of acetic acid.

7. The method for preparing the iodine cathode material with a protective coating according to claim 3, characterized in that, The drying process involves drying at 25℃~35℃ for 0.5h.

8. The iodine cathode material with a protective coating according to claim 1, characterized in that, The iodine cathode material is obtained by mixing iodine-loaded carbon black, Ketjen black and sodium alginate to obtain an iodine cathode slurry, and coating the iodine cathode slurry onto a current collector.

9. A zinc-iodine battery, characterized in that, The iodine cathode material with a protective coating as described in claim 1 is used as the cathode.

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