Water-based electrolyte and preparation method and application thereof

Abstract

The invention discloses a water-based electrolyte as well as a preparation method and application thereof. The water-based electrolyte is an aqueous solution containing gamma-cyclodextrin, graphene oxide and zinc sulfate. The zinc-zinc symmetric battery assembled by using the water-based electrolyte has a highly reversible cycle life of more than 5000 hours under the condition of 1mA cm <-2 > / 1mAh cm <-2 >, and still keeps a dendrite-free compact deposition morphology after being cycled for 400 hours under the high current density of 5mA cm <-2 > / 5mAh cm <-2 >. And the water-based electrolyte can enable the Zn / V2O5 total battery to circulate for more than four thousand times under 5Ag <-1 >, and a small bulb can be lightened under the clamping of two soft package batteries.

Description

Technical Field

[0001] The present invention relates to an aqueous electrolyte and its preparation method and application, and particularly relates to a γ-cyclodextrin synergistic graphene oxide composite aqueous electrolyte for aqueous zinc-ion batteries, its preparation method, and its application in the preparation of aqueous zinc-ion batteries, belonging to the field of aqueous zinc-ion batteries. Background Art

[0002] Aqueous zinc-ion batteries have characteristics such as high specific capacity, high safety, and good economy, and have become one of the most promising new-generation electrochemical energy storage devices. However, side reactions such as dendrite growth and surface corrosion of the zinc anode severely limit its cycle life and practical applications. In the prior art, the optimization of the electrolyte is the key to improving the performance of aqueous zinc-ion batteries. Common electrolyte additives include inorganic salts, organic molecules, and polymers, etc., but the effects of these additives in inhibiting zinc dendrite growth and improving electrolyte stability are limited. Therefore, developing a new type of electrolyte system to solve the above problems has important research significance and application value. Summary of the Invention

[0003] Object of the Invention: The first object of the present invention is to provide an aqueous electrolyte, the second object of the present invention is to provide a preparation method of the aqueous electrolyte, and the third object of the present invention is to provide the application of the aqueous electrolyte in the preparation of aqueous zinc-ion batteries.

[0004] Technical Solution: An aqueous electrolyte according to the present invention, the aqueous electrolyte is an aqueous solution including γ-cyclodextrin, graphene oxide, and zinc salt, wherein the concentration of γ-cyclodextrin in the electrolyte is below 20 mmol / L, preferably below 15 mmol / L, most preferably 15 mmol / L, the concentration of graphene oxide is 1 - 4 mg / mL, preferably 3 mg / mL, and the concentration of zinc salt in the electrolyte is 1 - 3 mol / L, preferably 2 mol / L.

[0005] Further, the zinc salt is zinc sulfate, zinc trifluoromethanesulfonate, or zinc acetate.

[0006] The preparation method of the aqueous electrolyte according to the present invention includes the following steps:

[0007] Add graphene oxide powder into water, stir and disperse, then add γ-cyclodextrin and zinc salt solution, and stir to dissolve.

[0008] Further, stir and disperse the graphene oxide powder in water for more than 2 h.

[0009] The application of the aqueous electrolyte according to the present invention in the preparation of aqueous zinc-ion batteries.

[0010] Furthermore, the aqueous zinc-ion battery is a zinc-zinc symmetric battery or a Zn / V2O5 full battery.

[0011] Furthermore, the zinc-zinc symmetric battery includes the water-based electrolyte described in the present invention as the electrolyte, and two zinc foils are used as the positive electrode and the negative electrode respectively, and are assembled into a coin battery.

[0012] Furthermore, the Zn / V2O5 full battery is a coin battery or a soft-pack battery.

[0013] Furthermore, the positive electrode of the Zn / V2O5 full battery includes using a titanium foil loaded with V2O5 as the positive electrode sheet, a zinc foil as the negative electrode sheet, and the water-based electrolyte described in the present invention as the electrolyte, and is assembled into a coin battery in the order of the negative electrode shell, the shrapnel, the gasket, the negative electrode sheet, the glass fiber separator, the positive electrode sheet, and the positive electrode shell.

[0014] Furthermore, the positive electrode of the Zn / V2O5 full battery includes using a titanium foil loaded with V2O5 as the positive electrode sheet, a zinc foil as the negative electrode sheet, the water-based electrolyte described in the present invention as the electrolyte, and the zinc foil and the titanium foil are used as the electrode tabs respectively, and are encapsulated into a soft-pack battery.

[0015] The mechanism of the present invention is as follows: Cyclodextrin has been proven to be able to effectively induce uniform deposition of Zn. However, in the case of increasing current density and capacity, the cycle life will be reduced. Therefore, the present invention adopts a simple dual electrolyte additive strategy. By adding γ-cyclodextrin and graphene oxide to the zinc sulfate electrolyte together, a more highly stable zinc anode is obtained. The hydrophobic cavity and rich hydroxyl groups of γ-cyclodextrin can effectively change the ability of the solvation structure of zinc ions, enabling the charge level to be adsorbed on the surface of the zinc negative electrode, making the charge on the electrode surface evenly distributed, thereby regulating the diffusion path and deposition site of zinc ions; while graphene oxide can utilize its large specific surface area and good electrical conductivity to provide more active sites and electron transport channels for the deposition of zinc ions. At the same time, the graphene oxide layer can also self-assemble on the zinc surface to form a reduced graphene oxide layer, which can promote the desolvation process and accelerate the reaction kinetics. Cyclodextrin and graphene oxide can also be closely linked together through functional groups to make them more stable in the zinc sulfate electrolyte, so that γ-cyclodextrin and graphene oxide jointly guide the directional deposition of zinc ions, significantly improving the cycle stability and Coulomb efficiency of the zinc negative electrode.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0017] (1) The present invention provides a γ-cyclodextrin co-oxidized graphene composite aqueous electrolyte and an aqueous zinc-ion battery based on the aqueous electrolyte. The aqueous electrolyte of the present invention can effectively inhibit the generation of by-products. The large cavity and internal hydrophobic structure in γ-cyclodextrin and its abundant hydroxyl groups can effectively change the desolvation ability of zinc ions, thereby inhibiting hydrogen evolution and side reactions. Graphene oxide can self-assemble into a reduced graphene oxide layer on the zinc surface, which is beneficial to promoting the desolvation process and accelerating the reaction kinetics. Under the synergistic modulation of the two, progressive nucleation and directional deposition of zinc ions can be achieved, making the deposition of zinc ions dense and uniform. Thereby, the service life of the battery can be extended. The synergistic effect of the two can greatly improve the cycling performance of the aqueous zinc-ion battery and ensure the safety of the battery.

[0018] (2) The zinc-zinc symmetric battery assembled based on the aqueous electrolyte of the present invention has a highly reversible cycle with a cycle life exceeding 5000 hours under the conditions of 1 mA cm -2 / 1 mAh cm -2 , and a reversible cycle exceeding 400 hours at a high current density of 5 mA cm -2 / 5 mAh cm -2 .

[0019] (3) The Zn / V2O5 full battery assembled based on the aqueous electrolyte of the present invention cycles more than 4000 times under the condition of 5 A g -1 , and two Zn / V2O5 soft-pack batteries can light up a 0.3 W small light bulb. Description of the Drawings

[0020] Figure 1 XRD spectrum of graphene oxide prepared in Example 2.

[0021] Figure 2 Electrolyte photos prepared in Example 1 with different concentrations of γ-cyclodextrin (γ-CD) as additives. a-d are γ-cyclodextrin concentrations: 5 mmol / L, 10 mmol / L, 15 mmol / L, and 20 mmol / L respectively.

[0022] Figure 3 Cycling performance graph of zinc-zinc symmetric batteries with different concentrations of γ-cyclodextrin (γ-CD) additives prepared in Example 1 at a current density of 10 mA cm -2 .

[0023] Figure 4 Impedance graph of zinc-zinc symmetric batteries with different concentrations of graphene oxide (GO) added prepared in Example 2.

[0024] Figure 5Impedance diagrams of the zinc-zinc symmetric batteries prepared in Example 3 and Comparative Examples 1-2 after standing for 24 hours.

[0025] Figure 6 Impedance diagrams of the zinc-zinc symmetric batteries prepared in Example 3 and Comparative Examples 1-2 at a current density of 1 mA cm -2 Cyclic voltammograms of the zinc anode of the zinc-zinc symmetric batteries prepared in Example 3 and Comparative Examples 1-2 at a current density of 50 C.

[0026] Figure 7 Cycling performance diagrams of the zinc-zinc symmetric batteries prepared in Example 3 and Comparative Examples 1-2 at a current density of 1 mA cm -2 Current density.

[0027] Figure 8 Cycling performance diagrams of the zinc-zinc symmetric batteries prepared in Example 3 and Comparative Examples 1-2 at a current density of 5 mA cm -2 Current density.

[0028] Figure 9 Cycling performance diagrams of the zinc-zinc symmetric batteries prepared in Comparative Example 3 at a current density of 5 mA cm -2 Current density.

[0029] Figure 10 Cycling performance diagrams of the Zn / V2O5 full batteries based on the electrolytes prepared in Example 3 and Comparative Examples 1-2 at 5 A / g.

[0030] Figure 11 Cyclic voltammograms of the zinc anode after cycling of the Zn / V2O5 full batteries based on the electrolytes prepared in Example 3 and Comparative Examples 1-2 at 5 A / g.

[0031] Figure 12 Digital photos of the Zn / V2O5 soft-pack battery based on the electrolytes prepared in Example 3 and Comparative Examples 1-2 lighting a bulb. Detailed implementation mode

[0032] The technical solutions of the present invention will be further described below with reference to the accompanying drawings.

[0033] Example 1

[0034] 1. Prepare a pure zinc sulfate solution: First, weigh 2.87 g of ZnSO4·(H2O)7 (ZS), then transfer it to a glass bottle, add deionized water thereto, and adjust the concentration of the pure zinc sulfate solution to 2 mol / L.

[0035] 2. Preparation of electrolyte: Disperse γ-cyclodextrin (γ-CD) into a pure zinc sulfate solution to obtain an electrolyte containing γ-cyclodextrin. Among them, the concentration of zinc sulfate in the electrolyte is 2 mol / L, and the concentrations of γ-cyclodextrin are 5 mmol / L, 10 mmol / L, 15 mmol / L, and 20 mmol / L respectively. The 4 groups of electrolytes obtained are as Figure 2 shown. It can be Figure 2 seen that when the concentration of the γ-cyclodextrin additive is 20 mmol / L, a small amount of γ-cyclodextrin can be clearly observed to precipitate. Therefore, we use 5 mmol / L, 10 mmol / L, and 15 mmol / L as the concentration gradient of the single γ-cyclodextrin additive for comparison. At the same time, a comparison is made with the electrolyte without adding γ-cyclodextrin (0 mmol / L).

[0036] 3. Encapsulation of zinc-zinc symmetric battery: Use two zinc foils with a diameter of 1.6 cm and a thickness of 50 μm as the two electrodes of the positive and negative electrodes, and use a glass fiber separator and 150 μL of the aqueous electrolytes with different concentrations of γ-cyclodextrin (concentrations are 0 mmol / L, 5 mmol / L, 10 mmol / L, 15 mmol / L) prepared in step 3 to assemble the symmetric battery in a 2032 coin cell, and 4 groups of zinc-zinc symmetric batteries are obtained respectively.

[0037] Perform cyclic performance tests on the 4 groups of zinc-zinc symmetric batteries prepared in this example at a current density of 10 mA cm -2 , and the results are as Figure 3 shown. It can be Figure 3 seen that when the concentration of γ-cyclodextrin is 15 mmol / L, the cyclic performance of the battery is the best. Therefore, the concentration of γ-cyclodextrin as an additive is determined to be 15 mmol / L.

[0038] Example 2

[0039] 1. The preparation of the pure zinc sulfate solution is the same as step 1 in Example 1.

[0040] 2. Preparation of graphene oxide: Synthesize graphene oxide (GO) from graphite powder by the improved Hummers method. First, put 1.25 g of graphite powder and 0.75 g of NaNO3 in a 1000 mL beaker, add 30 mL of concentrated H2SO4 to the above beaker, and stir for 0.5 h under ice bath conditions. Then, slowly add 5 g of KMnO4 at low temperature. After the addition, react the above system at room temperature for 2 h. Then, add 150 mL of deionized water to the beaker, raise the temperature to 95 °C and react for 1 h. Finally, when the temperature drops to about 60 °C, add 3.75 mL of 30% hydrogen peroxide solution. Then, wait until it cools to room temperature, centrifuge and wash, and freeze-dry. Graphene oxide (GO) is prepared.

[0041] XRD analysis was performed on the graphene oxide prepared in this example, and the results are as Figure 1 shown. As can be seen from Figure 1 , an obvious characteristic peak of graphene oxide was observed, which proved the successful preparation of graphene oxide.

[0042] 3. Preparation of aqueous electrolyte: The prepared graphene oxide powder was added to deionized water, and then stirred for 2 h to obtain a uniform dispersion liquid containing graphene oxide dispersion. Subsequently, pure zinc sulfate solution and γ-cyclodextrin (γ-CD) were added to the dispersion liquid containing graphene oxide dispersion to obtain an aqueous electrolyte containing modified electrolyte. The concentration of γ-cyclodextrin in the aqueous electrolyte was 15 mmol / L, the concentration of zinc sulfate was 2 mol / L, and the concentrations of graphene oxide were 1 mg / mL, 2 mg / mL, 3 mg / mL, and 4 mg / mL, respectively. Four groups of aqueous electrolytes were prepared.

[0043] 4. Encapsulation of zinc-zinc symmetric cells: Follow the steps in Example 1, step 3, to prepare 4 zinc-zinc symmetric cells respectively.

[0044] The 4 groups of zinc-zinc symmetric cells prepared in this example were subjected to EIS impedance test on a Chenhua electrochemical workstation, and the results are as Figure 4 shown. As can be seen from Figure 4 , when the concentration of graphene oxide was 3 mg / mL, the impedance was the smallest, that is, the conductivity was the largest. Thus, the concentration of graphene oxide as an additive was determined to be 3 mg / mL.

[0045] Example 3

[0046] 1. Preparation of pure zinc sulfate solution and graphene oxide: Follow the steps 1 and 2 in Example 2.

[0047] 2. Preparation of aqueous electrolyte: Follow the steps 3 in Example 2. Among them, the concentration of γ-cyclodextrin in the aqueous electrolyte was 15 mmol / L, the concentration of zinc sulfate was 2 mol / L, and the concentration of graphene oxide was 3 mg / mL. An aqueous electrolyte was prepared and denoted as ZS + γ-CD + GO.

[0048] 3. Encapsulation of zinc-zinc symmetric cells: Follow the steps 4 in Example 2 to prepare zinc-zinc symmetric cells.

[0049] Comparative Example 1

[0050] The preparation of pure zinc sulfate solution was the same as step 1 in Example 1. The pure zinc sulfate solution was used as the electrolyte to encapsulate the zinc-zinc symmetric cell. The encapsulation process was the same as step 3 in Example 1 to prepare a zinc-zinc symmetric cell, denoted as ZS.

[0051] Comparative Example 2

[0052] The preparation of the pure zinc sulfate solution was the same as in Step 1 of Example 1. Subsequently, the pure zinc sulfate solution and γ-cyclodextrin were mixed and dispersed to obtain an electrolyte solution. The concentration of zinc sulfate in the electrolyte solution was 2 mol / L, and the concentration of γ-cyclodextrin was 15 mmol / L. The zinc-zinc symmetric battery was encapsulated in the same way as in Step 3 of Example 1 to obtain a zinc-zinc symmetric battery, denoted as ZS+γ-CD.

[0053] The impedance analysis of the zinc-zinc symmetric batteries prepared in Example 3 and Comparative Examples 1-2 was carried out after standing for 24 hours, and the results are as Figure 5 shown. It can be Figure 5 seen that the impedance of the zinc-zinc symmetric batteries prepared using the aqueous electrolyte is smaller than that of the symmetric batteries using pure zinc sulfate and adding only γ-cyclodextrin. The impedance of the zinc-zinc symmetric battery prepared with the aqueous electrolyte in Example 3 is the smallest.

[0054] The cyclic voltammetry analysis of the zinc anodes of the zinc-zinc symmetric batteries prepared in Example 3 and Comparative Examples 1-2 was carried out at a current density of 1 mA cm -2 for 50 cycles, and the results are as Figure 6 shown. It can be Figure 6 seen that there are many rampant dendrites on the surface of the zinc anode of the symmetric battery using pure zinc sulfate as the electrolyte. With the addition of γ-cyclodextrin, the number of dendrites decreases. In the case of the co-addition of γ-cyclodextrin and graphene oxide, the surface of the zinc anode is relatively smooth.

[0055] The cycling performance analysis of the zinc-zinc symmetric batteries prepared in Example 3 and Comparative Examples 1-2 was carried out at a current density of 1 mA cm -2 , and the results are as Figure 7 shown. It can be Figure 7 seen that the cycling time of the zinc-zinc symmetric battery with the aqueous electrolyte in Example 3 is as long as 5000 h, which is more than three times that of Comparative Example 1 with the addition of cyclodextrin additive, effectively proving the synergistic effect of γ-cyclodextrin and graphene oxide additives.

[0056] The cycling performance analysis of the zinc-zinc symmetric batteries prepared in Example 3 and Comparative Examples 1-2 was carried out at a current density of 5 mA cm -2 , and the results are as Figure 8 shown. It can be Figure 8 seen that at a relatively large current density, the symmetric battery with the aqueous electrolyte prepared in Example 3 can still have a cycling time of up to 400 h, indicating that the synergistic effect of γ-cyclodextrin and graphene oxide effectively inhibits the growth of zinc dendrites and prolongs the cycling performance of the battery.

[0057] Comparative Example 3

[0058] The preparation of the pure zinc sulfate solution and graphene oxide was the same as steps 1 and 2 in Example 2. Subsequently, the pure zinc sulfate solution was mixed and dispersed with graphene oxide to prepare an electrolyte. The concentration of zinc sulfate in the electrolyte was 2 mol / L, and the concentration of graphene oxide was 3 mg / mL. The zinc-zinc symmetric battery was encapsulated in the same way as step 4 in Example 2 to obtain a zinc-zinc symmetric battery, denoted as ZS+GO.

[0059] The cyclic performance of the zinc-zinc symmetric battery prepared in this example was analyzed at a current density of 5 mA cm -2 . The results are as Figure 9 shown. It can be Figure 9 seen that only when γ-cyclodextrin and graphene oxide are used as additives together can the performance be maximized.

[0060] Example 4

[0061] 1. Preparation of V2O5 positive electrode sheet: Commercial V2O5 was used as the active material. A slurry containing the active material, conductive carbon (Super P), and polyvinylidene fluoride (PVDF) binder in a mass ratio of 7:2:1 was fully mixed and cast on a titanium foil to prepare the V2O5 positive electrode material. The prepared electrode sheet was placed in a vacuum oven and dried at 70 °C for 12 h to remove the residual solvent. The active mass loading was adjusted to approximately 1.5 mg / cm 2 .

[0062] 2. The electrode liquids were respectively the aqueous electrolytes in Example 3, that is, the concentration of γ-cyclodextrin in the aqueous electrolyte was 15 mmol / L, the concentration of zinc sulfate was 2 mol / L, and the concentration of graphene oxide was 3 mg / mL. An aqueous electrolyte was prepared and compared with a pure zinc sulfate solution.

[0063] 3. Encapsulation of Zn / V2O5 full battery: A zinc foil with a diameter of 1.6 cm and a thickness of 50 μm was used as the negative electrode, and a titanium foil with a diameter of 1.6 cm and a thickness of 30 μm loaded with V2O5 was used as the positive electrode. They were assembled in a 2032 coin cell in the order of negative electrode shell, shrapnel, gasket, negative electrode sheet, glass fiber separator, positive electrode sheet, and positive electrode shell. 150 μL of the electrolyte was dropped in each case, and 2 groups of Zn / V2O5 full batteries were obtained, denoted as ZS-γ-CD-GO (aqueous electrolyte) and ZS' (electrolyte is pure zinc sulfate solution) respectively.

[0064] 4. Encapsulating the Zn / V2O5 soft-pack battery: Using a 3×3 cm, 30-μm-thick titanium foil loaded with V2O5 as the positive electrode, and a 3×3 cm, 50-μm-thick zinc foil as the negative electrode. The current collectors are 8-cm-long, 0.8-mm-wide zinc foil and titanium foil respectively, and are each pasted on the back of the positive and negative electrodes through conductive adhesive. Using a 3.5×3.5 cm glass fiber separator and 3 mL of aqueous electrolyte, it is encapsulated in a 6×8 cm pure aluminum foil vacuum bag soft-pack battery seal to obtain the Zn / V2O5 soft-pack battery.

[0065] The cycle performance analysis of 2 groups of Zn / V2O5 full batteries prepared in this example at 5 A / g is as follows Figure 10 shown. It can be seen from Figure 10 this that the Zn / V2O5 full battery prepared with the aqueous electrolyte enables the full battery to achieve a cycle life of more than 4000 times. This proves the synergistic effect and effective protection function of the γ-cyclodextrin and graphene oxide additives.

[0066] The scanning analysis of the zinc anode after cycling of 2 groups of Zn / V2O5 full batteries prepared in this example at 5 A / g is as follows Figure 11 shown. It can be seen from Figure 11 this that in the case of pure zinc sulfate as the electrolyte, the surface of the zinc anode is full of dendrites and pits, while under the condition of adding the aqueous electrolyte, the surface of the zinc anode is smooth and dense. This effectively proves the effective inhibition of dendrites by the addition of the composite additive (γ-cyclodextrin + graphene oxide).

[0067] Using two Zn / V2O5 soft-pack batteries prepared in this example to light a 0.3 W light bulb, the result is as follows Figure 12 shown. It can be seen from Figure 12 this that the Zn / V2O5 soft-pack battery prepared in this example can light the light bulb.

Claims

1. A water-based electrolyte, characterized in that, The aqueous electrolyte is an aqueous solution comprising γ-cyclodextrin, graphene oxide, and a zinc salt, wherein the concentration of γ-cyclodextrin in the electrolyte is 20 mmol / L or less, the concentration of graphene oxide is 1-4 mg / mL, and the concentration of the zinc salt in the electrolyte is 1-3 mol / L.

2. The aqueous electrolyte according to claim 1, characterized in that, The zinc salt is zinc sulfate, zinc trifluoromethanesulfonate, or zinc acetate.

3. The preparation method of the aqueous electrolyte according to claim 1 or 2, characterized in that, It includes the following steps: Add graphene oxide powder to water, stir and disperse it, then add γ-cyclodextrin and zinc salt solution, and stir to dissolve.

4. The preparation method according to claim 3, wherein Add graphene oxide powder to water and stir and disperse for 2 h or more.

5. Use of the aqueous electrolyte according to claim 1 or 2 in the preparation of an aqueous zinc-ion battery.

6. The application according to claim 5, characterized in that, The aqueous zinc-ion battery is a zinc-zinc symmetric battery or a Zn / V2O5 full battery.

7. The application according to claim 6, wherein The zinc-zinc symmetric battery includes the aqueous electrolyte according to claim 1 or 2 as the electrolyte, and two zinc foils are used as the positive electrode and the negative electrode respectively to assemble a coin battery.

8. The application according to claim 6, characterized in that, The Zn / V2O5 full battery is a coin battery or a pure soft-pack battery.

9. The application according to claim 8, wherein The positive electrode of the Zn / V2O5 full battery includes using a titanium foil loaded with V2O5 as the positive electrode sheet, a zinc foil as the negative electrode sheet, and the aqueous electrolyte according to claim 1 or 2 as the electrolyte, and is encapsulated into a coin battery in the order of negative electrode case, shrapnel, gasket, negative electrode sheet, glass fiber separator, positive electrode sheet, and positive electrode case.

10. The application according to claim 8, characterized in that The positive electrode of the Zn / V2O5 full battery includes using a titanium foil loaded with V2O5 as the positive electrode sheet, a zinc foil as the negative electrode sheet, the aqueous electrolyte according to claim 1 or 2 as the electrolyte, and the zinc foil and the titanium foil are used as the electrode tabs respectively to be encapsulated into a soft-pack battery.

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