Two-component electrolyte additive and application thereof in zinc-iodine battery

Abstract

The invention discloses a two-component electrolyte additive and application thereof in a zinc-iodine battery. The two-component electrolyte additive is prepared from dicyandiamide and N, N-dimethylacetamide according to the mass ratio of (0.10 to 2.10) to (1.74 to 5.22). Dicyandiamide and N, N-dimethylacetamide can be coupled with I < + > ions at the same time, attack of water molecules to I < + > is prevented, and the stability of I < + > is improved; in addition, dicyandiamide and N, N-dimethylacetamide can also be coupled with I3-, and dissolution and shuttling of iodine are inhibited. Through use of dicyandiamide and N, N-dimethylacetamide, the four-electron reaction of iodine can be effectively excited, and stable operation of the zinc-iodine battery under an extreme temperature condition is realized. The application method comprises the following steps: dissolving dicyandiamide, N, N-dimethylacetamide and zinc sulfate in deionized water to obtain the aqueous zinc-iodine battery electrolyte solution. The method has the advantages of low cost, easiness in manufacturing, no corrosion and the like.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology for aqueous zinc-iodine batteries, specifically to a two-component electrolyte additive, dicyandiamide (DCD) and N,N-dimethylacetamide (DMAC), and their application in zinc-iodine batteries. Background Technology

[0002] Aqueous zinc-iodine batteries are a new type of rechargeable battery developed in recent years. They possess advantages such as high efficiency, safety, non-toxicity, low cost, and simple manufacturing process, making them highly valuable and promising for large-scale energy storage. Traditional iodine cathodes primarily undergo a 2-electron reaction, resulting in a theoretical capacity of only 211 mAh / g and an operating voltage of only ~1.3 V, leading to low energy and power densities and insufficient competitiveness in zinc-iodine batteries. Therefore, it is necessary to stimulate a 4-electron reaction in the iodine cathode, which could double the theoretical capacity (422 mAh / g) and achieve a higher operating voltage (~1.8 V). However, the I₂ generated by the 4-electron reaction... + Ions are thermodynamically unstable and easily hydrolyzed, which makes it difficult for the 4-electron reaction at the iodine cathode to proceed.

[0003] To effectively drive the four-electron reaction at the iodine cathode, electrolyte additives have become one of the more successful strategies. For example, patent application CN119542575A proposes an electrolyte system composed of zinc chloride, zinc sulfate, polyiodine ion complexing agent polyvinyl alcohol, and diluent dimethylacetamide, which mainly stabilizes I- through zinc chloride. + Chloride ions are converted into four electrons for iodine conversion. However, this type of system has a significant drawback: chloride ions are highly corrosive to battery metal components. Another invention patent application, CN117458003A, reports a deep eutectic electrolyte, which is based on the coordination of molecules containing amide groups (such as dimethylacetamide) and sulfone functional groups (such as dimethyl sulfoxide) with zinc salts, thereby inhibiting the action of water molecules on I₂ by reducing the activity of water molecules. + However, these deep eutectic electrolytes typically require high-concentration salts, which are not only costly but also have low ionic conductivity, making it difficult to support charge-discharge reactions under high currents. To date, developing a dilute aqueous electrolyte that can both promote four-electron iodine reactions and possess halogen-free properties remains a critical challenge in this field. Summary of the Invention

[0004] To address the aforementioned technical problems and shortcomings in this field, the present invention provides a two-component electrolyte additive and its application in zinc-iodine batteries. The present invention offers advantages such as low cost, ease of manufacture, and non-corrosiveness.

[0005] The specific technical solution is as follows: In a first aspect, the present invention provides a two-component electrolyte additive, which is composed of dicyandiamine and N,N-dimethylacetamide in a mass ratio of (0.10-2.10):(1.74-5.22).

[0006] Applying the above-mentioned two-component electrolyte additive to a zinc sulfate aqueous solution yields a halogen-free dilute aqueous electrolyte that can stabilize I... + And adsorb I3 - It enables a reversible 4-electron iodine conversion reaction and allows for stable operation of 4-electron zinc-iodine batteries over a wide temperature range.

[0007] Furthermore, the two-component electrolyte additive consists of dicyandiamine and N,N-dimethylacetamide in a mass ratio of (0.84~2.02):3.48, for example 1.34:3.48.

[0008] For example, dicyandiamine, N,N-dimethylacetamide, and zinc sulfate can be dissolved in deionized water to obtain an aqueous zinc-iodine battery electrolyte solution.

[0009] In a second aspect, the present invention provides an electrolyte solution, wherein the electrolyte solution uses water as a solvent and contains dicyandiamine, N,N-dimethylacetamide and zinc sulfate; In the electrolyte solution, the concentration of dicyandiamine is 0.06-1.25 M, such as 0.5 M, 0.8 M, 1.2 M, etc., and the concentration of N,N-dimethylacetamide is 1-3 M, such as 2 M, etc.

[0010] Furthermore, the zinc sulfate concentration in the electrolyte solution is 1-3 M, for example, 2 M.

[0011] Furthermore, the electrolyte solution is halogen-free.

[0012] Thirdly, the present invention provides the application of the two-component electrolyte additive described in the first aspect or the electrolyte solution described in the second aspect in zinc-iodine batteries.

[0013] Fourthly, the present invention provides an aqueous zinc-iodine battery, comprising a negative electrode zinc, a positive electrode iodine, a separator, and the electrolyte solution described in the second aspect.

[0014] Furthermore, the method for preparing the positive electrode iodine includes: After mixing iodine and activated carbon, the mixture is sealed in a glass tube using a tube sealing machine. Then, it is heated to 60-100℃ (e.g., 80℃) and kept at that temperature for 2-10 hours (e.g., 5 hours). Finally, it is cooled to room temperature to obtain the activated carbon@iodine composite material. Activated carbon@iodine composite material, polyvinylpyrrolidone and carbon (such as Super P) are mixed and N-methyl-2-pyrrolidone is used as a solvent to form a slurry. The slurry is then coated onto carbon paper and dried to obtain an iodine positive electrode sheet.

[0015] Furthermore, the mass ratio of iodine to activated carbon is 2:8 to 6:4, for example, 4:6, etc.

[0016] Furthermore, the mass ratio of activated carbon@iodine composite material, polyvinylpyrrolidone, and carbon is 8:1:1.

[0017] Furthermore, the drying temperature is 35-45°C, for example, 40°C.

[0018] Furthermore, the drying time is 8-20 hours, for example, 12 hours.

[0019] Furthermore, the diaphragm includes a glass fiber membrane.

[0020] This invention can significantly stabilize I + Preventing I3 - The shuttle effect improves the reversibility and stability of the 4-electron conversion reaction at the iodine cathode, resulting in an aqueous 4-electron zinc-iodine battery with excellent cycle performance and outstanding performance over a wide temperature range.

[0021] Compared with the prior art, the beneficial effects of this invention are as follows: 1) DCD binds I through its amino and imine bidentate groups. + DMAC chelates I from the other side via its carbonyl oxygen. + This forms a unique molecular sandwich structure, and the multidentate chelation enhances the interaction between DCD and DMAC and I. + The bonding strength. DCD and DMAC constitute two physical barriers, effectively isolating water molecules from I from both sides. + Furthermore, each DMAC molecule contains three hydrophobic methyl groups, effectively restricting water molecules from entering the complex structure and further enhancing I... + Stability.

[0022] 2) Although DCD and DMAC can chelate I when used alone. + Improve I + It has stability, but its effectiveness is limited. Because I + The other side of the ion remains exposed to the aqueous solution, making it susceptible to hydrolysis due to attack by water molecules. Neither DCD nor DCD, nor DMAC nor DMAC can simultaneously chelate I from both sides. + This is mainly due to their conflicting spatial configurations. However, DCD and DMAC can couple I from both sides simultaneously. +This allows for minimal steric hindrance, and theoretical calculations also show that this structure has the most negative binding energy, namely DCD-I. + The molecular sandwich structure of -DMAC is stable. In general, the two additive molecules simultaneously couple I... + It is highly selective, and there is no universal formula for reference.

[0023] 3) Hydrogen bond networks in aqueous solutions have difficulty penetrating DCD-I + -DMAC molecular clips, with their hydrophobic outer shells, reach the inner shells of the complex and interact with I. + Interaction. DCD-I + -DMAC molecular clamp coordination saturation state makes I + The loss of spatial proximity and the electronic driving force required for mutual approach inhibits the interaction with I. + Various side reactions are involved.

[0024] 4) DCD and DMAC can also chelate I3 from both sides simultaneously. - It effectively inhibits the dissolution and shuttle of iodine.

[0025] 5) Due to DCD and DMAC chelating I from both sides + Stable I + Its effect is very significant, enabling the iodine cathode to undergo a 4-electron conversion reaction at both low temperatures of -20℃ and high temperatures of 60℃, giving the zinc-iodine battery the special ability to charge and discharge stably under extreme temperature conditions. Attached Figure Description

[0026] Figure 1 The UV-Vis spectra of ZDD-0.8 prepared in Example 1, ZDCD-0.8 prepared in Comparative Example 1, and ZS electrolyte prepared in Comparative Example 3 after the addition of ICl.

[0027] Figure 2 Cyclic voltammetry curves of zinc-iodine batteries assembled with ZDD-0.8 prepared in Example 1, ZDCD-0.8 prepared in Comparative Example 1, and ZDMAC-2 prepared in Comparative Example 2 electrolytes.

[0028] Figure 3 Cyclic voltammetry curves of the zinc-iodine battery assembled with the ZS electrolyte prepared in Comparative Example 3.

[0029] Figure 4 The ZDD-0.8 electrolyte prepared in Example 1 was used in an H-type electrolytic cell with I3. - Diagram of the shuttle experiment.

[0030] Figure 5 The UV-Vis spectrum of the solution of the ZDD-0.8 electrolyte prepared in Example 1 in the right container of the H-type electrolytic cell.

[0031] Figure 6 Cyclic performance graphs of ZDD-0.8 prepared in Example 1 and ZDCD-0.8 prepared in Comparative Example 1 at 25°C and a current density of 10 A / g.

[0032] Figure 7 The cycling performance of ZDMAC-2 prepared for Comparative Example 2 at 25 °C and a current density of 10 A / g is shown in the figure.

[0033] Figure 8 Cyclic performance graphs of ZDD-0.8 prepared in Example 1 and ZDCD-0.8 prepared in Comparative Example 1 at 60°C and current density of 5 A / g.

[0034] Figure 9 The cycling performance of ZDD-0.8 prepared in Example 1 at -20°C and a current density of 5 A / g is shown in the graph. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0036] Example 1: 1.34 g DCD, 3.48 g DMAC and 11.5 g ZnSO4·7H2O (99%) were dissolved in deionized water, and then the mixed solution was diluted to 20 mL to obtain a mixed solution with ZnSO4 concentration of 2 M, DCD concentration of 0.8 M and DMAC concentration of 2 M. This solution was named ZDD-0.8.

[0037] Comparative Example 1: To prepare a comparative solution ZDCD-0.8, 1.34 g of DCD and 11.5 g of ZnSO4·7H2O (99%) were dissolved in deionized water, and then the mixed solution was diluted to 20 mL to obtain a mixed solution ZDCD-0.8 with a ZnSO4 concentration of 2 M and a DCD concentration of 0.8 M.

[0038] Comparative Example 2: To prepare a control solution ZDMAC-2, 3.48 g of DMAC and 11.5 g of ZnSO4·7H2O (99%) were dissolved in deionized water. The mixed solution was then diluted to 20 mL to obtain a mixed solution ZDMAC-2 with a ZnSO4 concentration of 2 M and a DMAC concentration of 2 M.

[0039] Comparative Example 3: To prepare a control solution ZS, 11.5 g of ZnSO4·7H2O (99%) was dissolved in deionized water, and then the mixed solution was diluted to 20 mL to obtain a ZnSO4 concentration of 2 M solution ZS.

[0040] The solutions obtained in the above examples were used as electrolytes and injected into a button-type CR2025 aqueous zinc-iodine battery. The aqueous zinc-iodine battery also includes a negative electrode pure zinc sheet (purity 99.9%), a positive electrode iodine, and a glass fiber membrane separator. The positive electrode iodine was prepared by mixing 40 mg of iodine and 60 mg of activated carbon, sealing the mixture in a glass tube using a sealing machine, heating it to 80°C, holding it at that temperature for 5 h, and then cooling it to room temperature to obtain an activated carbon@iodine composite material. Then, 40 mg of the activated carbon@iodine composite material, 5 mg of polyvinylpyrrolidone, and 5 mg of carbon (Super P) were mixed and mixed into a slurry using N-methyl-2-pyrrolidone as a solvent. This slurry was coated onto carbon paper and then dried at 40°C for 12 h to obtain the iodine positive electrode sheet.

[0041] The prepared iodine positive electrode, pure zinc negative electrode, and separator were assembled into a CR2025 button-type zinc-iodine battery in air. The prepared electrolyte solutions were then added, and the charge-discharge performance and cycle performance of the zinc-iodine battery were tested using a Newway battery testing system.

[0042] ICl was added to ZDD-0.8, ZDCD-0.8, and ZS respectively to achieve an ICl concentration of 0.1 mol / L. After mixing, the solutions were allowed to stand for 1 h, and the mixed solution was detected using UV-Vis spectroscopy. Figure 1 As shown, in the ZS electrolyte, only a broad absorption peak appears around 460 nm, corresponding to I₂. No I₂ was observed. + The signal indicates that I + The disproportionation reaction was carried out, and the decomposition was complete. For ZDCD-0.8, two clear peaks were detected at 345 nm and 451 nm, corresponding to I... + And I2. This indicates that DCD can stabilize most I + However, there are still a small number of I + It can still be converted to I2 through disproportionation and hydrolysis. In contrast, the ZDD-0.8 electrolyte shows a significantly stronger I2 conversion. + The peak is observed, while the I2 signal is significantly weaker. This indicates that DCD and DMAC can provide a synergistic coordination environment, more effectively suppressing I. + Hydrolysis improves its stability.

[0043] Figure 2These are the cyclic voltammetry (CV) curves of zinc-iodine batteries using ZDMAC-2, ZDCD-0.8, and ZDD-0.8 electrolytes. ZDMAC-2 exhibits a pair of distinct redox peaks at 1.27 / 1.16 V, and very weak peaks at 1.70 V and 1.39 V, indicating that it uses I0.8 electrolytes. - / I 0 The two-electron reaction is the main one, I 0 / I + The reaction was very weak. ZDCD-0.8 showed a pair of redox peaks at 1.25 / 1.27 V and 2.01 / 1.88 V, indicating that a 4-electron reaction could occur. However, the redox peaks at the higher voltage positions were atypical and asymmetrical, suggesting that I... 0 / I + The reaction was still not complete. ZDD-0.8 also showed two pairs of peaks at similar positions, indicating that the 4-electron reaction could also proceed; and the redox peaks near the high voltage were prominent and symmetrical, indicating that I 0 / I + The reaction proceeds efficiently and fully. The CV curves demonstrate a significant synergistic enhancement effect when DCD and DMAC are used together. In contrast, the ZS solution, without any additives, shows only a pair of redox peaks near 1.2 V in its CV curve, corresponding to I... - / I 0 Two-electron reaction ( Figure 3 ).

[0044] Diffusion experiments were conducted in an H-type electrolytic cell. The right-hand container of the H-type electrolytic cell contained a colorless ZDD-0.8 solution, while the left-hand container contained an equal volume of a brownish-yellow ZDD-0.8 solution (containing 0.2 mol / L I3). - The two sections were separated using a glass fiber membrane. The solution in the right-hand container remained colorless throughout the 90-minute period. Figure 4 ), indicating I3 - I3 was adsorbed by DCD and DMAC, limiting its diffusion behavior. UV-Vis spectroscopy analysis of the solution in the right-hand container did not detect I3. - signals ( Figure 5 This demonstrates that DCD and DMAC effectively limit I3. - The shuttle behavior. In contrast, when using ZS solution, the solution in the right container turned yellow rapidly, and after 90 minutes, the colors of the solutions on both sides were basically the same. UV-Vis spectroscopy detection showed that after 30, 60, and 90 minutes, I3... - The peak rises rapidly. Using ZDCD-0.8 solution, the solution in the right-hand container remains essentially colorless, but a weak I3 peak is detected by UV-Vis spectroscopy after 90 minutes. -The peak indicates that ZS solution can hardly restrict iodine shuttle; DCD can restrict most iodine shuttle, but a small amount of iodine will still shuttle; the best effect is achieved when DCD and DMAC are used together.

[0045] Figure 6 This describes the cycling performance of ZDD-0.8 at 25°C and a current density of 10 A / g. After 7908 cycles, ZDD can release 128 mAh / g of capacity. In comparison, ZDCD-0.8's capacity decreased to 119 mAh / g after 2159 cycles. ZDMAC-2's capacity decreased to 57 mAh / g after 400 cycles. Figure 7 ).

[0046] Figure 8 The cycling performance of ZDD-0.8 at 60℃ and a current density of 5 A / g is as follows: after 900 cycles, the capacity can reach 237 mAh / g, while ZDCD-0.8 releases a capacity of 231 mAh / g after 297 cycles and then fails.

[0047] Figure 9 The cycling performance is at -20°C and a current density of 5 A / g. After 1200 cycles, ZDD-0.8 released 171 mAh / g of capacity, while ZDCD was frozen at -20°C and could not function properly.

[0048] ZDD-0.8 exhibits superior cycle performance compared to the 121 mAh / g of the zinc-iodine battery assembled with a composite solid electrolyte as disclosed in patent application CN120999093A after 3000 cycles at 1 A / g, superior to the 140 mAh / g of the L-tyrosine additive as disclosed in patent application CN121097234A after 3000 cycles, superior to the ~135.8 mAh / g of the amino acid additive as disclosed in patent application CN120709535A after 1000 cycles at 1 A / g, and superior to the ~125.5 mAh / g of the phenol additive as disclosed in patent application CN120357053A after 800 cycles at 1 A / g.

[0049] Example 2: 0.84 g DCD, 3.48 g DMAC and 11.5 g ZnSO4·7H2O (99%) were dissolved in deionized water, and then the mixed solution was diluted to 20 mL to obtain a mixed solution with ZnSO4 concentration of 2 M, DCD concentration of 0.5 M and DMAC concentration of 2 M. This solution was named ZDD-0.5.

[0050] The subsequent processes are the same as in Example 1.

[0051] The assembled zinc-iodine battery maintained a discharge capacity of 113 mAh / g after 8,100 cycles at 25°C and a current density of 10 A / g.

[0052] Example 3: 2.02 g DCD, 3.48 g DMAC and 11.5 g ZnSO4·7H2O (99%) were dissolved in deionized water, and then the mixed solution was diluted to 20 mL to obtain a mixed solution with ZnSO4 concentration of 2 M, DCD concentration of 1.2 M and DMAC concentration of 2 M. This solution was named ZDD-1.2.

[0053] The subsequent processes are the same as in Example 1.

[0054] The assembled zinc-iodine battery maintained a discharge capacity of 104 mAh / g after 8,100 cycles at 25°C and a current density of 10 A / g.

[0055] In summary, dicyandiamine and N,N-dimethylacetamide of the present invention can be simultaneously coupled to I + Ions, preventing water molecules from reacting with I + Attacks, improve I + Stability; furthermore, dicyandiamine and N,N-dimethylacetamide can also be coupled with I3. - This inhibits the dissolution and shuttle of iodine. The use of dicyandiamine and N,N-dimethylacetamide effectively stimulates the four-electron reaction of iodine, enabling stable operation of the zinc-iodine battery under extreme temperature conditions.

[0056] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A two-component electrolyte additive, characterized in that, It is composed of dicyandiamine and N,N-dimethylacetamide in a mass ratio of (0.10-2.10):(1.74-5.22).

2. An electrolyte solution, characterized in that, The electrolyte solution uses water as a solvent and contains dicyandiamine, N,N-dimethylacetamide and zinc sulfate; The electrolyte solution contains dicyandiamine at a concentration of 0.06-1.25 M and N,N-dimethylacetamide at a concentration of 1-3 M.

3. The electrolyte solution according to claim 2, characterized in that, The zinc sulfate concentration in the electrolyte solution is 1-3 M.

4. The application of the two-component electrolyte additive according to claim 1 or the electrolyte solution according to claim 2 or 3 in zinc-iodine batteries.

5. An aqueous zinc-iodine battery, characterized in that, It includes a negative electrode zinc, a positive electrode iodine, a diaphragm, and the electrolyte solution as described in claim 2 or 3.

6. The aqueous zinc-iodine battery according to claim 5, characterized in that, The method for preparing the positive electrode iodine includes: After mixing iodine and activated carbon, the mixture is sealed in a glass tube using a tube sealing machine. Then, it is heated to 60-100℃, kept at that temperature for 2-10 hours, and cooled to room temperature to obtain the activated carbon@iodine composite material. Activated carbon@iodine composite material, polyvinylpyrrolidone and carbon are mixed, and N-methyl-2-pyrrolidone is used as a solvent to form a slurry. The slurry is then coated onto carbon paper and dried to obtain an iodine positive electrode sheet.

7. The aqueous zinc-iodine battery according to claim 6, characterized in that, The mass ratio of iodine to activated carbon is 2:8 to 6:

4.

8. The aqueous zinc-iodine battery according to claim 6, characterized in that, The mass ratio of activated carbon@iodine composite material, polyvinylpyrrolidone, and carbon is 8:1:

1.

9. The aqueous zinc-iodine battery according to claim 6, characterized in that, The drying temperature is 35-45℃; The drying time is 8-20 hours.

10. The aqueous zinc-iodine battery according to claim 5, characterized in that, The diaphragm includes a glass fiber membrane.

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