Hydrated eutectic electrolyte and preparation method and application thereof

Abstract

The invention provides a hydrated eutectic electrolyte as well as a preparation method and application thereof. The electrolyte comprises water-soluble zinc salt, deionized water and a deep eutectic solution, the deep eutectic solution is formed by mixing zinc perchlorate and a polar deep eutectic solvent and performing deep eutectic crystallization. The electrolyte has the characteristics of low water activity, low freezing point and efficient induction of uniform deposition of zinc, can be compatible with an iodine-loaded positive electrode and can inhibit dissolution of iodine, and the characteristics are beneficial to inhibition of hydrogen evolution reaction, polyiodine shuttling and other side reactions in the battery circulation process, promote uniform deposition of zinc, protect the integrity of an iodine electrode, and improve the electrochemical performance of the battery. The stable operation of the zinc-iodine battery is ensured; the electrolyte is a zinc sulfate solution containing a ZnClO4 / dimethyl sulfoxide deep eutectic solvent, the solution is combined with free water to form a eutectic structure, the eutectic structure participates in construction of a Zn < 2 + > ion solvation shell, extra intramolecular hydrogen bonds are introduced for the electrolyte, meanwhile, hydrogen bonds among water molecules are weakened, so that the internal energy of the electrolyte is enhanced, the freezing point is reduced, and the flowability is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrolyte, in particular to a hydrated eutectic electrolyte and its preparation method and application. BACKGROUND

[0002] Batteries are considered as an ideal choice for large-scale energy storage technology, but the widely used lithium-ion batteries have defects in safety and cost, which limits their application in large-scale energy storage field. At the same time, aqueous batteries are considered as one of the most promising choices in large-scale energy storage technology due to their low cost, high safety, environmental friendliness and long life. However, the current market aqueous batteries, such as nickel-hydrogen batteries and lead-acid batteries, cannot meet the needs of large-scale energy storage technology due to insufficient energy density and short service life.

[0003] Aqueous zinc-iodine batteries have many advantages, including high natural resource abundance of zinc and iodine elements, stable potential platform (1.38 V vs. Zn / Zn 2+ The biggest difference between zinc-iodine battery and traditional zinc-ion battery is that the former is not a rocking chair battery but a secondary ion battery, which theoretically only involves electron exchange between the positive and negative electrodes, avoiding the deformation of energy storage materials caused by ion exchange between the positive and negative electrodes. However, there are still several difficulties that hinder the application of zinc-iodine batteries. The highly reactive hydrated [Zn(OH2)6]²⁺ ions in the aqueous electrolyte can cause serious side reactions to generate Zn4SO4(OH)6*xH2O and uneven deposition of zinc, and even produce dendrites on the surface of zinc electrode, which can pierce the separator and seriously damage the cycle life of the battery; active water can produce hydrogen evolution (HER) and oxygen evolution (OER) under the action of electric field, which can cause the battery to swell and pose a safety hazard; I2 molecules at the positive electrode can also combine with I - form I 3- occur "polyiodide shuttle" to the zinc negative electrode for self-discharge, reducing the capacity of the battery. SUMMARY

[0004] In view of the shortcomings of the prior art, the present application provides a hydrated eutectic electrolyte and its preparation method and application. The present application has the characteristics of low water activity, low freezing point and efficient induction of zinc uniform deposition, and can also inhibit the dissolution of iodine. These characteristics can help to inhibit the hydrogen evolution reaction and polyiodide shuttle side reaction during the cycle of the battery, promote the uniform deposition of zinc, protect the integrity of the iodine electrode, and thus ensure the stable operation of the zinc-iodine battery.

[0005] The technical scheme of the present application is: a hydrated eutectic electrolyte, comprising a water-soluble zinc salt, deionized water and a deep eutectic solution; the deep eutectic solution is formed by mixing zinc perchlorate with a polar deep eutectic solvent to form a deep eutectic solution.

[0006] Preferably, the concentration of the water-soluble zinc salt is 0.1-5.0 mol / L.

[0007] Preferably, the water-soluble zinc salt is at least one of zinc sulfate, zinc acetate, zinc trifluoromethane sulfonate, zinc chloride and zinc tetrafluoroborate.

[0008] Preferably, the deep eutectic solution accounts for 10-40% of the volume of the electrolyte.

[0009] Preferably, the concentration ratio of zinc perchlorate to the polar deep eutectic solvent is 0.5-2.0.

[0010] Preferably, the polar deep eutectic solvent is one or more of dimethyl sulfoxide, sulfolane and dimethyl sulfone.

[0011] Preferably, the application further provides a preparation method of the hydrated eutectic electrolyte, comprising the following steps: S1), dissolving a water-soluble zinc salt in deionized water to obtain a basic electrolyte; S2), mixing zinc perchlorate and a polar deep eutectic solvent in a certain proportion, heating and stirring at 50-90℃ for 3-7h to perform a eutectic reaction, and cooling the formed deep eutectic solution to 28℃; S3), mixing the basic electrolyte and the deep eutectic solution in a volume ratio of 3-5:1, stirring uniformly and standing to obtain the hydrated eutectic electrolyte.

[0012] Preferably, in step S1), the concentration of the water-soluble zinc salt is 0.1-5.0 mol / L.

[0013] Preferably, in step S1), the water-soluble zinc salt is at least one of zinc sulfate, zinc acetate, zinc trifluoromethane sulfonate, zinc chloride and zinc tetrafluoroborate.

[0014] Preferably, in step S2), the polar deep eutectic solvent is one or more of dimethyl sulfoxide, sulfolane and dimethyl sulfone.

[0015] Preferably, the application further provides an application of the hydrated eutectic electrolyte, and the hydrated eutectic electrolyte is used in an aqueous zinc-iodine battery.

[0016] Preferably, the aqueous zinc-iodine battery is a symmetric battery, a half battery or a full battery.

[0017] Preferably, the symmetric battery comprises a zinc foil, a glass fiber separator and the hydrated eutectic electrolyte.

[0018] Preferably, the half-cell comprises a zinc foil, a glass fiber separator, a copper foil, and a hydrated eutectic electrolyte.

[0019] Preferably, the full cell comprises a zinc foil negative electrode, a glass fiber separator, an I2-loaded porous carbon positive electrode, and a hydrated eutectic electrolyte.

[0020] The present application has the following advantages: 1. The present application has the characteristics of low water activity, low freezing point, and efficient induction of uniform zinc deposition, and can inhibit the dissolution of iodine, which helps to inhibit the hydrogen evolution reaction and the polyiodide shuttle effect during the battery cycle, promotes the uniform deposition of zinc, and protects the integrity of the iodine electrode, thereby ensuring the stable operation of the zinc-iodine battery. 2. The electrolyte of the present application is a zinc sulfate solution containing ZnClO4 / dimethyl sulfoxide (DMSO) deep eutectic solvent. The solution forms a eutectic structure in combination with free water, participates in the construction of the Zn2+ ion solvation shell, and introduces additional intramolecular hydrogen bonds into the electrolyte, while weakening the hydrogen bonds between water molecules, thereby increasing the internal energy of the electrolyte, reducing the freezing point, and improving the flowability. 3. The special solvent sheath structure of the deep eutectic solution of the present application utilizes the non-polar solubility of dimethyl sulfoxide to limit the activity of water and enhance the binding energy on the Zn(002) surface, promoting the desolvation kinetics on the Zn(002) surface, achieving reversible dissolution of zinc deposition byproducts, inhibition of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), and reversible uniform deposition of zinc. 4. The deep eutectic solution of the present application can effectively inhibit the "polyiodide shuttle" effect, thereby improving the rate performance and cycle stability of the zinc-iodine battery. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The infrared spectra of the electrolytes prepared in Examples 1-4 and Comparative Examples 1-3 of the present application in the range of 800-1600 m -1 ; Figure 2 The infrared spectra of the electrolytes prepared in Examples 1-4 and Comparative Examples 1-3 of the present application in the range of 2500-3800 cm -1 ; Figure 3 The galvanostatic cycling diagram of the Zn / / Zn symmetric battery made of the electrolytes prepared in Examples 1-4 and Comparative Examples 1-3 of the present application; Figure 4 The coulombic efficiency curve of the zinc-copper half-cell made of the electrolytes prepared in Examples 1-4 and Comparative Examples 1-3 of the present application; Figure 5The long cycle diagram of the zinc-iodine full cell made of the electrolyte prepared in the embodiment 1 and the comparative examples 1, 2 and 3 at a constant current of 4.22 A / g; Figure 6 The SEM diagram of the zinc foil after the constant current cycle of the Zn / / Zn symmetric cell made of the electrolyte prepared in the embodiment 1 and the comparative examples 1, 2 and 3; Figure 7 The XRD spectrum diagram of the zinc foil after the constant current cycle of the Zn / / Zn symmetric cell made of the electrolyte prepared in the embodiment 1 and the comparative examples 1, 2 and 3. DETAILED DESCRIPTION

[0022] The specific embodiments of the present application will be further described below in conjunction with the accompanying drawings: Embodiment 1 The embodiment provides a preparation method of a hydrated eutectic electrolyte, comprising the following steps: S1), dissolving a water-soluble zinc salt, zinc sulfate heptahydrate solid, in deionized water to obtain a basic electrolyte with a concentration of 2 mol / L; S2), mixing 0.528 g of zinc perchlorate with 2 ml of dimethyl sulfoxide, heating and stirring at a high temperature of 60 ℃ for 5 h to perform a eutectic reaction, and cooling the formed deep eutectic solution to 28 ℃; S3), mixing 6 ml of the basic electrolyte with the deep eutectic solution, stirring uniformly, and standing to obtain a hydrated eutectic electrolyte.

[0023] Embodiment 2 The embodiment provides a preparation method of a hydrated eutectic electrolyte, comprising the following steps: S1), dissolving a water-soluble zinc salt, zinc sulfate heptahydrate solid, in deionized water to obtain a basic electrolyte with a concentration of 2 mol / L; S2), mixing 0.634 g of zinc perchlorate with 2 ml of dimethyl sulfoxide, heating and stirring at a high temperature of 60 ℃ for 5 h to perform a eutectic reaction, and cooling the formed deep eutectic solution to 28 ℃; S3), mixing 6 ml of the basic electrolyte with the deep eutectic solution, stirring uniformly, and standing to obtain a hydrated eutectic electrolyte.

[0024] Embodiment 3 The embodiment provides a preparation method of a hydrated eutectic electrolyte, comprising the following steps: S1), dissolving a water-soluble zinc salt, zinc sulfate heptahydrate solid, in deionized water to obtain a basic electrolyte with a concentration of 2 mol / L; S2), mixing 0.423 g of zinc perchlorate with 2 ml of dimethyl sulfoxide, heating and stirring at a high temperature of 60 ℃ for 5 h to perform a eutectic reaction, and cooling the formed deep eutectic solution to 28 ℃; S3), 6 ml of the base electrolyte was mixed with the deep eutectic solution, stirred uniformly, and left to stand to obtain the hydrated eutectic electrolyte.

[0025] Example 4 The present example provides a preparation method of a hydrated eutectic electrolyte, comprising the following steps: S1), dissolving a water-soluble zinc salt, zinc sulfate heptahydrate, in deionized water to obtain a base electrolyte with a concentration of 2 mol / L; S2), mixing 0.211 g of zinc perchlorate with 2 ml of dimethyl sulfoxide, heating and stirring at 60°C for 5 h to perform a eutectic reaction, and cooling the formed deep eutectic solution to 28°C; S3), 6 ml of the base electrolyte was mixed with the deep eutectic solution, stirred uniformly, and left to stand to obtain the hydrated eutectic electrolyte.

[0026] Comparative Example 1 The present example provides a preparation method of an electrolyte, comprising the following steps: S1), dissolving zinc sulfate heptahydrate in deionized water to obtain a base electrolyte with a concentration of 2 mol / L; S2), mixing 2 ml of dimethyl sulfoxide with 6 ml of the base electrolyte, heating and stirring at 60°C for 5 h to perform a eutectic reaction, and leaving to stand to 28°C to obtain the electrolyte.

[0027] Comparative Example 2 The present example provides a preparation method of an electrolyte, comprising the following steps: S1), dissolving zinc sulfate heptahydrate in deionized water to obtain a base electrolyte with a concentration of 2 mol / L; S2), mixing 0.528 g of zinc perchlorate with 8 ml of the base electrolyte, heating and stirring at 60°C for 5 h to perform a eutectic reaction, and leaving to stand to 28°C to obtain the electrolyte.

[0028] Comparative Example 3 The present example provides a preparation method of an electrolyte, comprising the following steps: S1), dissolving zinc sulfate heptahydrate in deionized water to obtain a base electrolyte with a concentration of 2 mol / L; S2), adding 0.211 g of zinc perchlorate to 2 ml of dimethyl sulfoxide, and mixing uniformly with 6 ml of the base electrolyte to obtain the electrolyte.

[0029] Example 5 Performance analysis: The electrolytes of Examples 1-4 and Comparative Examples 1-3 were subjected to Fourier infrared testing (FTIR). As shown in Table 1, the electrolytes of Examples 1-4 have a characteristic peak at 1650 cm-1, which is not present in the electrolytes of Comparative Examples 1-3. Figure 1As shown, the unique separation peaks in Examples 1, 2, 3, and 4 demonstrate the unique hydrated eutectic structure formed by ZnClO4 / dimethyl sulfoxide (DMSO). like Figure 2 As shown, compared with the conventional electrolytes of Comparative Examples 1, 2, and 3, the OH stretching vibrations in the 3100-3400 cm⁻¹ region of the electrolytes obtained in Examples 1, 2, and 3 shift to higher wavenumbers in their FTIR spectra. This indicates that adding a deep eutectic solvent to the base electrolyte to form a hydrated eutectic component has a stronger effect on breaking and rebuilding hydrogen bonds in polyhydrates compared to simply adding DMSO or zinc perchlorate. This weakens the hydrogen bonding between water molecules, thereby reducing the activity of water molecules and inhibiting the hydrogen evolution reaction.

[0030] Solidification and conductivity tests were performed on each electrolyte group at -20℃. As shown in Table 1, dimethyl sulfoxide (DMSO) in the hydrated eutectic electrolyte helps maintain the liquid state of the electrolyte under low-temperature conditions and ensures its stable operation. Meanwhile, the addition of zinc perchlorate also significantly improves the conductivity of the electrolyte at low temperatures.

[0031] Table 1. Electrolyte state and conductivity tests at low temperatures To test the practical performance of the electrolytes prepared in the above embodiments and comparative examples, batteries were assembled and their performance was tested according to the following method: Zinc sheets are placed in the positive electrode shell, an appropriate amount of electrolyte is added, then a glass fiber separator is placed in, an appropriate amount of electrolyte is added, and then the zinc negative electrode, gasket and spring are stacked. The negative electrode shell is then covered, and finally it is placed in a button cell packaging machine to be sealed into a symmetrical cell.

[0032] Symmetrical cells with 1 mA cm electrolytes assembled in Examples 1-4 and Comparative Examples 1-3 -2 and 1mAh cm -2 Constant current cycling under the following conditions Figure 3 As shown.

[0033] Commercial zinc foil was used as the negative electrode and commercial copper foil as the positive electrode. Zn / / Cu half-cells were assembled using the electrolytes of Comparative Example 1 and Example 2, respectively. The copper foil was placed in the positive electrode shell, an appropriate amount of electrolyte was added, then a glass fiber separator was placed in, an appropriate amount of electrolyte was added, the zinc negative electrode was stacked, the negative electrode shell was covered, and finally it was sealed in a button cell packaging machine to form a Zn / / Cu half-cell.

[0034] The coulombic efficiency (CE) curves of zinc-copper half-cells assembled with the electrolytes of Examples 12, 3, 4 and Comparative Examples 1, 2, 3 at 1 mA cm⁻² and 1 mAh cm⁻² are shown below. Figure 4 As shown.

[0035] Commercial zinc foil was used as the negative electrode and I₂ as the positive electrode. Full cells were assembled using the electrolytes from Comparative Example 1 and Example 2, respectively. Porous carbon and elemental iodine were mixed uniformly at a weight ratio of 3:7 and heated at 120°C for 2 hours in a sealed reactor to serve as the active material. An emulsion of active material, conductive carbon black, and PTFE was mixed at a weight ratio of 7:2:1, dispersed in anhydrous ethanol, coated onto a 100-mesh titanium mesh, and dried at 40°C for 20 minutes to serve as the positive electrode. A positive electrode shell was placed inside, and an appropriate amount of electrolyte was added. A glass fiber separator was then placed inside, and an appropriate amount of electrolyte was added. The zinc negative electrode was then stacked, the negative electrode shell was covered, and finally, the cells were sealed in a coin cell packaging machine to form a zinc-iodine full cell. The operating voltage range of the zinc-iodine full cell was 0.6-1.6V, and the current density was set to 4.22A / g. The electrolyte cycling results for Example 1 and Comparative Examples 1-3 are as follows: Figure 5 As shown.

[0036] The battery performance results of Examples 1-4 and Comparative Examples 1-3 are shown in Table 2; Table 2 Electrochemical performance of each electrolyte group in symmetrical cells, half-cells, and full cells. As shown in Table 2, Example 2 suffered from poor battery performance due to excessively high perchlorate concentration, resulting in crystallization. Examples 1, 3, and 4 exhibited longer lifespans due to the formation of hydrated eutectic components, with Example 1 showing the longest lifespan due to its uniform composition. The comparative examples failed to form hydrated eutectic structures, resulting in poor cycle life and low electrochemical capacity. The formation of hydrated eutectic electrolytes has a crucial impact on battery performance. Appropriate perchlorate concentrations and reasonable component ratios can effectively improve stable cycle time, initial coulombic efficiency, and initial specific capacity, thus extending battery life. The inability to form a hydrated eutectic structure leads to poor performance in these key performance indicators.

[0037] The symmetrical cells assembled using the electrolytes of Example 1 and Comparative Examples 1, 2, and 3 achieved a 1 mA cm⁻¹ performance. -2 and 1mAh cm -2 After cycling for 100 hours under the specified conditions, the zinc anode was subjected to scanning electron microscopy (SEM) imaging analysis. Figure 6 As can be seen, electrolytes containing hydrated eutectic components help promote uniform zinc deposition on the negative electrode, while those electrolytes that cannot form hydrated eutectic components show significant dendrite growth. Excessive dendrite growth not only leads to internal short circuits and reduces battery safety, but also continuously reduces the active surface area of ​​the electrode material, further accelerating battery performance degradation. This significant difference once again demonstrates that the hydrated eutectic structure plays a crucial role in suppressing zinc dendrite growth, providing a strong guarantee for the stable operation of zinc-iodine batteries.

[0038] In Example 1 and Comparative Examples 1, 2, 3, symmetric batteries assembled by using different electrolytes were cycled at a current density of 1 mA cm -2 and a capacity of 1 mAh cm -2 for 100 hours, and the X-ray diffraction (XRD) patterns of the zinc anodes were observed as shown in Figure 7 The electrolyte containing the eutectic hydrate component had a lower intensity on the Zn (002) peak, which indicated less zinc deposition, and less Zn4SO4(OH)6*xH2O characteristic peaks, and less byproduct generation. In contrast, the other comparative electrolytes without the eutectic hydrate produced more byproducts on the zinc foil, and the zinc deposition appeared to be disordered. By comparing the relative peak intensity ratio of the (002) and (101) crystal planes, it was found that the zinc deposition under the eutectic hydrate system exhibited a more optimal (002) crystal plane preferred orientation, and this highly ordered layered deposition structure could effectively reduce the electrode / electrolyte interface energy. It is worth noting that a large amount of ZnO (JCPDS No. 36-1451) and Zn(OH)2(JCPDS No. 38-0385) impurity phases were detected in the XRD patterns of the comparative group, which may be due to parasitic reactions triggered by free water molecules. The characteristic diffraction peak at 2θ = 8.5° in the Example 1 sample was highly consistent with the theoretically calculated eutectic hydrate coordination structure, which confirmed that the zinc ions maintained a stable solvation sheath structure during the deposition process. This ordered deposition mode not only reduced the generation of crystal defects, but also significantly reduced the local electric field distortion on the electrode surface, fundamentally inhibiting the nucleation and growth of dendrites.

[0039] The above examples and descriptions in the specification only illustrate the principles and best modes of the present application, and various changes and improvements can be made without departing from the spirit and scope of the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. A hydrated eutectic electrolyte, characterized in that: It includes water-soluble zinc salt, deionized water, and a deep eutectic solution; the deep eutectic solution is formed by deep eutectic reaction of zinc perchlorate and a polar deep eutectic solvent.

2. The hydrated eutectic electrolyte according to claim 1, characterized in that: The deep eutectic solution accounts for 10-40% of the electrolyte volume.

3. The hydrated eutectic electrolyte according to claim 2, characterized in that: The concentration ratio of zinc perchlorate to polar deep eutectic solvent is 0.5-2.

0.

4. The hydrated eutectic electrolyte according to claim 3, characterized in that: The polar deep eutectic solvent is selected from one or more of dimethyl sulfoxide, sulfolane, and dimethyl sulfone.

5. The hydrated eutectic electrolyte according to claim 1, characterized in that: The concentration of the water-soluble zinc salt is 0.1-5.0 mol / L.

6. The hydrated eutectic electrolyte according to claim 5, characterized in that: The water-soluble zinc salt is at least one of zinc sulfate, zinc acetate, zinc trifluoromethanesulfonate, zinc chloride, and zinc tetrafluoroborate.

7. A method for preparing the hydrated eutectic electrolyte according to any one of claims 1-6, characterized in that, Includes the following steps: S1) Dissolve water-soluble zinc salt in deionized water to obtain the basic electrolyte; S2) Mix zinc perchlorate with a polar deep eutectic solvent in a certain proportion, heat and stir at 50-90℃ for 3-7h to carry out eutectic reaction, and cool the formed deep eutectic solution to 28℃. S3) Mix the basic electrolyte and the deep eutectic solution at a volume ratio of 3-5:1, stir evenly, and let stand to obtain the hydrated eutectic electrolyte.

8. The method for preparing the hydrated eutectic electrolyte according to claim 7, characterized in that: The polar deep eutectic solvent is selected from one or more of dimethyl sulfoxide, sulfolane, and dimethyl sulfone.

9. The method for preparing the hydrated eutectic electrolyte according to claim 7, characterized in that: The concentration of the water-soluble zinc salt is 0.1-5.0 mol / L; The water-soluble zinc salt is at least one of zinc sulfate, zinc acetate, zinc trifluoromethanesulfonate, zinc chloride, and zinc tetrafluoroborate.

10. The application of a hydrated eutectic electrolyte, characterized in that: The hydrated eutectic electrolyte according to any one of claims 1-6 is used as the electrolyte in an aqueous zinc-iodine battery; wherein the aqueous zinc-iodine battery is a symmetrical battery, a half-cell, or a full-cell. The symmetrical battery comprises zinc foil, a glass fiber separator, and the hydrated eutectic electrolyte as described in any one of claims 1-6; The half-cell comprises zinc foil, a glass fiber membrane, copper foil, and the hydrated eutectic electrolyte as described in any one of claims 1-6; The full cell comprises a zinc foil negative electrode, a glass fiber separator, an I2-loaded porous carbon positive electrode, and the hydrated eutectic electrolyte as described in any one of claims 1-6.

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