Zinc ion battery hydrogel electrolyte as well as preparation method and application thereof

Abstract

The invention discloses a zinc ion battery hydrogel electrolyte as well as a preparation method and application thereof, and relates to the technical field of hydrogel electrolytes. The preparation method of the hydrogel electrolyte comprises the following steps: preparing a chitin material loaded with carbon dots in situ by a hydrothermal method, and dissolving by using a potassium hydroxide / urea aqueous solution as a solvent through a freeze thawing method to obtain a mixed solution; then, epoxy chloropropane and ethyl alcohol are used for chemical crosslinking and physical crosslinking in sequence to prepare chitin hydrogel loaded with the carbon dots in situ; and finally, the chitin hydrogel is soaked in a zinc sulfate solution to obtain the chitin hydrogel electrolyte loaded with the carbon dots in situ. The preparation process of the hydrogel electrolyte is simple, green, safe and low in cost. According to the invention, the carbon dots are loaded on the chitin in situ, so that the ionic conductivity and mechanical property of the chitin hydrogel electrolyte are improved, the introduction of the carbon dots can induce the uniform deposition of zinc ions, thereby effectively inhibiting the growth of zinc dendrites, and finally obtaining the zinc ion battery with excellent cycle stability.

Description

Technical Field

[0001] The invention relates to the technical field of hydrogel electrolytes, and in particular to a zinc ion battery hydrogel electrolyte and a preparation method and application thereof. Background Art

[0002] In recent years, the over-exploitation of non-renewable energy sources such as fossil fuels has caused serious energy crises and environmental pollution problems, making the development of green, clean and highly safe renewable energy a necessary trend to achieve global green and sustainable development. Among the many energy storage devices, electrochemical energy storage and conversion devices occupy a very important position. Among them, lithium-ion batteries (LIBs) have the advantages of high energy density and long life and have been widely used in commercial energy storage. However, their practical application is still limited by limited lithium resources, high production costs, and organic electrolytes that are prone to safety accidents.

[0003] Aqueous zinc-ion batteries (AZIBs) have the advantages of abundant reserves, high theoretical capacity (820mAh / g), low redox potential (-0.76Vvs.SHE) and non-toxic aqueous electrolytes, and are considered to be an energy storage device with broad application prospects. However, zinc-ion batteries still have problems such as liquid electrolyte leakage, zinc dendrite growth and side reactions, which seriously affect the actual performance and application of zinc-ion batteries. Hydrogel electrolytes are usually composed of hydrophilic polymer networks and liquid electrolytes. Their structures contain abundant hydrophilic functional groups, which can bind water molecules in their three-dimensional network structures through hydrogen bonds, thereby reducing the active water content and effectively avoiding problems such as liquid electrolyte leakage. On the other hand, hydrophilic functional groups and three-dimensional network structures provide additional zinc ion transfer sites and ion transport channels, which effectively promote the diffusion and transport of metal ions, making them have higher ionic conductivity.

[0004] Bio-based materials such as cellulose, sodium alginate, gelatin, chitosan, etc. are ideal hydrogel raw materials. They are rich in resources, low in price, environmentally friendly, biocompatible, green and safe, and have been widely used to prepare hydrogel electrolytes. The structure of bio-based hydrogel electrolytes usually contains one or more functional groups, which makes them easy to be modified. Therefore, the actual needs of high-performance zinc-ion batteries can be met through reasonable bio-based hydrogel design. The current optimization strategies mainly include double / multi-network structure, functional group regulation, doping nanofillers, etc., which are used to improve the mechanical properties of bio-based hydrogel electrolytes, poor interface contact, poor conductivity, and the inevitable zinc dendrite growth and side reactions during battery charging and discharging. Among them, carbon quantum dots, as a zero-dimensional carbon-based nanomaterial, are rich in oxygen-containing functional groups such as hydroxyl and carboxyl groups on their surface. They have excellent optical and electrochemical properties and have been widely used as electrolyte additives for zinc-ion batteries. The rich functional groups and inherent excellent conductivity of carbon dots give them significant advantages in hydrogel electrolytes in terms of enhancing ionic conductivity, improving mechanical properties, inhibiting zinc dendrite growth, and improving electrochemical stability, thereby effectively improving the electrochemical performance of zinc ion batteries.

[0005] Therefore, developing a green and safe hydrogel electrolyte with simple preparation process and excellent electrochemical performance is of great significance to further promote the development of high-performance zinc-ion batteries. Summary of the invention

[0006] Based on the existing technical problems, the present invention provides a zinc ion battery hydrogel electrolyte and a preparation method and application thereof. The technical solution is as follows:

[0007] The present invention provides a method for preparing a zinc ion battery hydrogel electrolyte, comprising the following steps:

[0008] (1) weighing chitosan and urea, adding them to deionized water, and mixing them by magnetic stirring to obtain a mixed solution;

[0009] (2) transferring the mixed solution of step (1) into a polytetrafluoroethylene liner, sealing it and performing a hydrothermal reaction;

[0010] (3) After the hydrothermal reaction is completed, the mixed solution is completely cooled to room temperature to obtain a chitosan mixed solution with in-situ carbon dots loaded thereon;

[0011] (4) adding potassium hydroxide and urea to the mixed solution of step (3), stirring magnetically until dissolved, and then performing a freeze-thaw cycle at low temperature until completely dissolved;

[0012] (5) adding epichlorohydrin to the solution obtained in step (4), stirring with a magnetic stirrer until the mixture is uniformly mixed, then pouring the mixture into a glass mold and placing the mixture in a refrigerator to react, thereby obtaining a hydrogel;

[0013] (6) immersing the hydrogel obtained in step (5) in an ethanol solution to allow physical crosslinking;

[0014] (7) The hydrogel obtained in step (6) is rinsed with deionized water and then immersed in a zinc salt solution to obtain a hydrogel electrolyte.

[0015] Preferably, in step (1), the mass concentration of chitosan is 3%, and the mass concentration of urea is 1%.

[0016] Preferably, in step (2), the hydrothermal temperature is 140°C, 160°C, or 180°C.

[0017] Preferably, in step (4), the mass concentration ratio of the added potassium hydroxide and urea to the deionized water in step (1) is 20:4:76.

[0018] Preferably, in step (5), the molar ratio of the added epichlorohydrin to the chitosan structural unit in step (1) is 6:1, and the cross-linking time is 12 to 48 hours.

[0019] Preferably, in step (6), the volume concentration of ethanol is 80% and the cross-linking time is 6 to 8 hours.

[0020] Preferably, in step (7), the zinc salt is a combination of one or more of zinc sulfate, zinc chloride, zinc acetate, and zinc trifluoromethanesulfonate, the solution concentration is 2 mol / L, and the immersion time is 12 to 48 h.

[0021] Another object of the present invention is to provide a hydrogel electrolyte prepared according to the zinc ion battery hydrogel electrolyte and its preparation method and application.

[0022] Another object of the present invention is to provide an aqueous zinc ion battery prepared according to the hydrogel electrolyte.

[0023] The hydrogel electrolyte prepared by the technical solution provided by the present invention has the following beneficial effects:

[0024] The present invention prepares a chitosan hydrogel electrolyte loaded with carbon dots in situ by in-situ growth of carbon dots on the surface of chitosan through a hydrothermal reaction. The carbon dots have excellent electrical conductivity and strong zinc affinity, which can improve the ionic conductivity of the hydrogel electrolyte, and regulate zinc ion transmission as nucleation sites, inducing uniform deposition of zinc ions on the negative electrode surface, thereby improving zinc dendrite growth; the surface of the carbon dots has abundant oxygen-containing functional groups, which can form hydrogen bond interactions with the chitosan matrix, thereby improving mechanical properties. The zinc ion battery prepared by the chitosan hydrogel electrolyte loaded with carbon dots in situ has excellent cycle stability.

[0025] The in-situ carbon dot-loaded hydrogel electrolyte prepared by the preparation method of the present invention has high ionic conductivity and excellent mechanical properties, promotes zinc ion transmission, ensures the structural integrity of the hydrogel electrolyte during the cycle, and effectively improves problems such as zinc dendrite growth, thereby improving the cycle stability of the zinc ion battery.

[0026] The preparation method of the hydrogel electrolyte for zinc ion batteries of the present invention has a simple preparation process, uses readily available biomass chitosan as a raw material, uses potassium hydroxide / urea as a green solvent, has a low preparation cost, and the preparation process is green and safe, and is suitable for large-scale production; and the hydrogel electrolyte can effectively improve the electrochemical performance of zinc ion batteries, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a transmission electron microscope (TEM) image of the chitosan-based carbon dots in the present invention;

[0028] Figure 2 X-ray photoelectron spectroscopy (XPS) diagram of chitosan and chitosan loaded with in-situ carbon dots in the present invention;

[0029] Figure 3 is an electrochemical impedance spectroscopy (EIS) diagram of the hydrogel electrolyte with in-situ carbon dots loaded in the present invention;

[0030] Figure 4 The graph is a voltage-time curve of a zinc symmetric battery with a hydrogel electrolyte in situ loaded with carbon dots at different current densities in the present invention. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below in conjunction with the accompanying drawings and examples. The technical scheme of the present invention is further illustrated below by specific implementation methods. Those skilled in the art should understand that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0032] Example 1

[0033] The method for preparing the zinc ion battery hydrogel electrolyte provided by the embodiment of the present invention comprises:

[0034] (1) adding 3% chitosan and 1% urea to deionized water, and mixing by magnetic stirring to obtain a mixed solution;

[0035] (2) transferring the mixed solution of step (1) into a polytetrafluoroethylene liner, sealing it and performing a hydrothermal reaction at 140° C.;

[0036] (3) After the hydrothermal reaction is completed, the mixed solution is completely cooled to room temperature to obtain a chitosan mixed solution with in-situ carbon dots loaded thereon;

[0037] (4) adding potassium hydroxide and urea to the mixed solution of step (3) in a mass ratio of potassium hydroxide: urea: deionized water = 20:4:76, stirring magnetically until dissolved, and then performing a freeze-thaw cycle at low temperature until completely dissolved;

[0038] (5) adding epichlorohydrin to the solution obtained in step (4) at a molar ratio of chitosan structural unit: epichlorohydrin = 1:6, stirring with a magnetic stirrer until the mixture is uniform, then pouring the mixture into a glass mold, and placing the mixture in a refrigerator to react, thereby obtaining a hydrogel;

[0039] (6) immersing the hydrogel obtained in step (5) in an ethanol solution with a concentration of 80% to allow physical crosslinking;

[0040] (7) The hydrogel obtained in step (6) was rinsed with deionized water, and then immersed in a 2 mol / L zinc sulfate solution to obtain the hydrogel electrolyte of Example 1.

[0041] The hydrogel electrolyte prepared by the above method was used to assemble a zinc symmetric battery and the battery cycle stability test was carried out. -2 The current density is 0.2 mAh cm -2 It can maintain a stable cycle of up to 760 hours at an area capacity of 1.547 W.

[0042] Example 2

[0043] The method for preparing the zinc ion battery hydrogel electrolyte provided by the embodiment of the present invention comprises:

[0044] (1) adding 3% chitosan and 1% urea to deionized water, and mixing by magnetic stirring to obtain a mixed solution;

[0045] (2) transferring the mixed solution of step (1) into a polytetrafluoroethylene liner, sealing it and performing a hydrothermal reaction at 160° C.;

[0046] (3) After the hydrothermal reaction is completed, the mixed solution is completely cooled to room temperature to obtain a chitosan mixed solution with in-situ carbon dots loaded thereon;

[0047] (4) adding potassium hydroxide and urea to the mixed solution of step (3) in a mass ratio of potassium hydroxide: urea: deionized water = 20:4:76, stirring magnetically until dissolved, and then performing a freeze-thaw cycle at low temperature until completely dissolved;

[0048] (5) adding epichlorohydrin to the solution obtained in step (4) at a molar ratio of chitosan structural unit: epichlorohydrin = 1:6, stirring with a magnetic stirrer until the mixture is uniform, then pouring the mixture into a glass mold, and placing the mixture in a refrigerator to react, thereby obtaining a hydrogel;

[0049] (6) immersing the hydrogel obtained in step (5) in an ethanol solution with a concentration of 80% to allow physical crosslinking;

[0050] (7) The hydrogel obtained in step (6) was rinsed with deionized water, and then immersed in a 2 mol / L zinc sulfate solution to obtain the hydrogel electrolyte of Example 2.

[0051] The hydrogel electrolyte prepared by the above method was used to assemble a zinc symmetric battery and the battery cycle stability test was carried out. -2 The current density is 0.2 mAh cm -2 It can maintain a stable cycle of up to 1500h at an area capacity of 1.547 W.

[0052] Example 3

[0053] The method for preparing the zinc ion battery hydrogel electrolyte provided by the embodiment of the present invention comprises:

[0054] (1) adding 3% chitosan and 1% urea to deionized water, and mixing by magnetic stirring to obtain a mixed solution;

[0055] (2) transferring the mixed solution of step (1) into a polytetrafluoroethylene liner, sealing it and performing a hydrothermal reaction at 180° C.;

[0056] (3) After the hydrothermal reaction is completed, the mixed solution is completely cooled to room temperature to obtain a chitosan mixed solution with in-situ carbon dots loaded thereon;

[0057] (4) adding potassium hydroxide and urea to the mixed solution of step (3) in a mass ratio of potassium hydroxide: urea: deionized water = 20:4:76, stirring magnetically until dissolved, and then performing a freeze-thaw cycle at low temperature until completely dissolved;

[0058] (5) adding epichlorohydrin to the solution obtained in step (4) at a molar ratio of chitosan structural unit: epichlorohydrin = 1:6, stirring with a magnetic stirrer until the mixture is uniform, then pouring the mixture into a glass mold, and placing the mixture in a refrigerator to react, thereby obtaining a hydrogel;

[0059] (6) immersing the hydrogel obtained in step (5) in an ethanol solution with a concentration of 80% to allow physical crosslinking;

[0060] (7) The hydrogel obtained in step (6) was rinsed with deionized water, and then immersed in a 2 mol / L zinc sulfate solution to obtain the hydrogel electrolyte of Example 3.

[0061] The hydrogel electrolyte prepared by the above method was used to assemble a zinc symmetric battery and the battery cycle stability test was carried out. -2The current density is 0.2 mAh cm -2 It can maintain a stable cycle of up to 2000h at an area capacity of 1.547 W.

[0062] Comparative Example

[0063] The method for preparing the zinc ion battery hydrogel electrolyte provided by the embodiment of the present invention comprises:

[0064] (1) Weighing potassium hydroxide and urea in a mass ratio of potassium hydroxide: urea: deionized water = 20:4:76, adding them to deionized water, and mixing them with magnetic stirring until dissolved to prepare a potassium hydroxide / urea aqueous solution;

[0065] (2) adding 3% by mass concentration of the shell to the mixed solution obtained in step (1), mixing by magnetic stirring to obtain a mixed solution, and then subjecting the mixed solution to a freeze-thaw cycle at a low temperature until the mixed solution is completely dissolved;

[0066] (3) adding epichlorohydrin to the solution obtained in step (2) at a molar ratio of chitosan structural unit: epichlorohydrin = 1:6, stirring with a magnetic stirrer until the mixture is uniform, then pouring the mixture into a glass mold, and placing the mixture in a refrigerator to react, thereby obtaining a hydrogel;

[0067] (4) immersing the hydrogel obtained in step (3) in an ethanol solution with a concentration of 80% to allow physical crosslinking;

[0068] (5) The hydrogel obtained in step (4) was rinsed with deionized water, and then immersed in a 2 mol / L zinc sulfate solution to obtain a hydrogel electrolyte of a comparative example.

[0069] The hydrogel electrolyte prepared by the above method was used to assemble a zinc symmetric battery and the battery cycle stability test was carried out. -2 The current density is 0.2 mAh cm -2 It can also maintain a 1500h cycle at an area capacity of , but its cycle curve polarization voltage fluctuates greatly and has poor stability.

[0070] The microscopic morphology, chemical structure, AC impedance and cycle performance of the assembled batteries of the above embodiments and comparative examples were tested and characterized:

[0071] The mixed solution obtained in step (3) of Example 1-3 was subjected to ultrasound, dialysis purification, and freeze-drying to obtain separated carbon dot powder, and the carbon dots were subjected to TEM and infrared tests. Figure 1As shown, it is a transmission electron microscopy (TEM) image of the chitosan-based carbon dots obtained in Examples 1-3. It can be seen that the carbon dots are evenly distributed in the solution, and their particle sizes are approximately 1.48, 1.53, and 2.69 nm, respectively. The particle size of the carbon dots increases with the increase of the hydrothermal reaction temperature; the carbonization degree of the chitosan-based carbon dots prepared in Example 1 is low, and there are no obvious lattice fringes. As the temperature increases, obvious lattice fringes belonging to the graphite (100) crystal plane appear.

[0072] Figure 2 It is a comparison chart of infrared spectra of the chitosan-based carbon dots and chitosan with in-situ carbon dots obtained in Examples 1-3 and chitosan in the comparative example. Figure 3 The XPS comparison diagram of the chitin with in-situ carbon dots obtained in Examples 1-3 and the chitin in the comparative example. Figure 2 and Figure 3 It can be seen that with the increase of hydrothermal reaction temperature, the carbonization degree of chitin increases; and there is a shift of the OH bond absorption peak to a low wave number in the infrared spectrum, which is due to the hydrogen bond formed by the carbon dots and chitin, proving the in-situ loading of the carbon dots; and the structure of the carbon dots contains hydroxyl, amide groups, C=C and pyrrole N / graphite N structures, which can provide a large number of zinc ion active sites, promote zinc ion transfer and diffusion, regulate zinc ion deposition behavior, and induce its uniform deposition, thereby improving ionic conductivity and zinc dendrite growth. In addition, the rich oxygen-containing functional groups can improve the mechanical properties by increasing the hydrogen bonding effect in the chitin hydrogel network. Therefore, the zinc ion battery using the chitin hydrogel electrolyte with in-situ carbon dot loading exhibits excellent electrochemical performance.

[0073] like Figure 3 As shown, it is the AC impedance spectrum of the stainless steel / / stainless steel symmetrical battery assembled with the hydrogel electrolyte prepared in the comparative example and Examples 1-3. The impedance values ​​of the hydrogel electrolytes prepared in the comparative example and Examples 1-3 are 2.38, 1.90, 1.63, and 2.22Ω, respectively. The presence of carbon dots reduces the impedance of the hydrogel electrolyte, accelerates the diffusion of zinc ions, and improves the ionic conductivity of the hydrogel electrolyte, thereby improving the electrochemical performance of the zinc ion battery. Compared with other embodiments, the impedance of the hydrogel electrolyte prepared in Implementation 3 is larger. This is because the content of carbon dot-related groups in the chitin in situ loaded with carbon dots in Example 3 is higher, and the affinity for zinc ions is stronger, which hinders the transfer and transmission of zinc ions to a certain extent.

[0074] The zinc symmetric cells assembled with the hydrogel electrolytes prepared in the comparative example and Examples 1-3 were tested at 0.2 mA cm -2 The current density is 0.2 mAh cm -2The cycle stability test was carried out under the area capacity of , and the test results of the battery hydrogel electrolyte prepared under different conditions are shown in Table 1.

[0075] Table 1 Battery cycle stability performance (0.2 mA cm) of Examples 1-3 and Comparative Examples -2 , 0.2mAh cm -2 )Test Results

[0076]

[0077] From the cycle results of Examples 1-3 and the comparative example in Table 1, the presence of carbon dots in the hydrogel electrolyte contributes to the cycle stability of the battery. Although the cycle life of the comparative example can reach 1500h, the fluctuation of the polarization voltage during the cycle is obvious, and the cycle stability is relatively poor, with poor zinc plating / stripping reversibility. Compared with other embodiments, the polarization voltage of the hydrogel electrolyte in Example 1 is 85mV, and it has a stable cycle life of 760h, which may be due to the low degree of carbonization of the carbon dots, resulting in insufficient improvement in its performance. In Example 3, the carbon dots in the hydrogel electrolyte have more characteristic functional groups and stronger zinc affinity, which is conducive to inducing uniform zinc deposition and improving interface side reactions. Although the impedance is increased to a certain extent, the electrochemical performance is still better than that of the hydrogel electrolyte in the comparative example, so that the zinc ion battery assembled with the hydrogel electrolyte has excellent cycle stability.

[0078] like Figure 4 The figure shows the rate cycling performance of zinc symmetric batteries assembled with hydrogel electrolytes prepared in the comparative example and in Examples 1-3 at different current densities. Compared with the comparative example, the hydrogel electrolytes prepared in Examples 1-3 all exhibited excellent stable cycling performance.

[0079] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a zinc ion battery hydrogel electrolyte, characterized in that: The steps include: (1) weighing chitosan and urea, adding them to deionized water, and stirring them magnetically to obtain a mixed solution; (2) transferring the mixed solution of step (1) into a polytetrafluoroethylene liner, sealing it and performing a hydrothermal reaction at a high temperature; (3) After the hydrothermal reaction is completed, the mixed solution is completely cooled to room temperature to obtain a chitosan mixed solution with in-situ carbon dots loaded thereon; (4) adding potassium hydroxide and urea to the solution of step (3), stirring magnetically until dissolved, and then performing a freeze-thaw cycle at low temperature until completely dissolved; (5) adding epichlorohydrin to the solution obtained in step (4), stirring with a magnetic stirrer until the mixture is uniformly mixed, then pouring the mixture into a glass mold and placing the mixture in a refrigerator to react, thereby obtaining a hydrogel; (6) immersing the hydrogel obtained in step (5) in an ethanol solution to allow it to undergo physical crosslinking; (7) The hydrogel obtained in step (6) is rinsed with deionized water and then immersed in a zinc salt solution to obtain a hydrogel electrolyte.

2. The method for preparing a zinc ion battery hydrogel electrolyte according to claim 1, wherein: In the step (1), the mass concentration of chitosan is 3%, and the mass concentration of urea is 1%.

3. The method for preparing a zinc ion battery hydrogel electrolyte according to claim 1, wherein: In the step (2), the temperature of the hydrothermal reaction is 140°C, 160°C, or 180°C.

4. The method for preparing a zinc ion battery hydrogel electrolyte according to claim 1, characterized in that: In the step (4), the mass concentration ratio of the added potassium hydroxide and urea to the deionized water in the step (1) is 20:4:

76.

5. The method for preparing a zinc ion battery hydrogel electrolyte according to claim 1, characterized in that: In the step (5), the molar ratio of epichlorohydrin to the chitosan structural unit in the step (1) is 6:1, and the cross-linking time is 12 to 48 hours.

6. The method for preparing a zinc ion battery hydrogel electrolyte according to claim 1, characterized in that: In the step (6), the volume concentration of ethanol is 80% and the cross-linking time is 6 to 8 hours.

7. The method for preparing a zinc ion battery hydrogel electrolyte according to claim 1, characterized in that: In the step (7), the zinc salt is a combination of one or more of zinc sulfate, zinc chloride, zinc acetate, and zinc trifluoromethanesulfonate, the solution concentration is 2 mol / L, and the soaking time is 12 to 48 hours.

8. A hydrogel electrolyte prepared according to the method for preparing a zinc ion battery hydrogel electrolyte according to any one of claims 1 to 7.

9. A zinc ion battery prepared according to the hydrogel electrolyte of claim 8.

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