A method for in situ preparation of polyacrylamide hydrogel electrolyte at room temperature

Abstract

The application discloses a method for in-situ preparation of polyacrylamide hydrogel electrolyte at room temperature. The method directly utilizes the inherent reducibility of anode metal zinc, guides ammonium persulfate in a gel precursor solution placed between two zinc sheets or zinc sheets and positive electrode sheets to generate free radicals, so as to initiate a polymerization reaction. Compared with a conventional thermal polymerization and photopolymerization method for preparing hydrogel, the method can be completed in a short time at room temperature, and the prepared hydrogel electrolyte has good combination capacity with electrodes, and the stability of a battery is significantly improved.

Description

Technical Field

[0001] This invention relates to an in-situ preparation method of polyacrylamide hydrogel polymer electrolyte, belonging to the field of zinc-ion battery technology. Background Technology

[0002] Lithium-ion battery technology is one of the most promising devices for energy storage applications, widely used due to its excellent energy density. However, the relatively low abundance of lithium metal, high cost, and potential safety issues arising from the use of organic electrolytes limit its application in large-scale energy storage. New types of rechargeable batteries with abundant metal resources, such as sodium-ion and zinc-ion batteries, have emerged to address these challenges, aiming to promote the application of environmentally friendly and sustainable energy storage technologies to alleviate the energy and environmental problems brought about by social development.

[0003] However, the commercialization of aqueous zinc-ion batteries still faces many challenges. For example, side reactions such as dendrite growth and hydrogen evolution on the zinc anode side may cause short circuits, and the generation and accumulation of H2 in the battery are also potential safety hazards.

[0004] Hydrogel electrolytes, due to their limited active water molecules, have been shown to suppress side reactions such as anodic dendrite growth and hydrogen evolution to a certain extent. However, compared to aqueous electrolytes, the preparation and battery assembly of hydrogel electrolytes are more complex and time-consuming. Typically, the hydrogel electrolyte is prepared first and then manually clamped between the two electrodes, which easily introduces air bubbles between the electrodes and the gel electrolyte, leading to poor contact interfaces, increased interfacial impedance, and affecting battery stability and performance. Furthermore, repeated electroplating / stripping processes can also easily trigger related side reactions. Therefore, an important way to improve the performance of hydrogel electrolyte batteries is to enhance the bonding ability of the electrode-electrolyte interface. Summary of the Invention

[0005] The purpose of this invention is to provide a method for in-situ preparation of polyacrylamide-based hydrogels, which can simplify the preparation process of gel electrolytes and improve the surface bonding ability of electrodes and electrolytes.

[0006] The technical solution to achieve the purpose of this invention is as follows:

[0007] In a first aspect, the present invention provides a method for in-situ preparation of polyacrylamide hydrogel electrolytes, comprising the following steps:

[0008] (1) Weigh 1.818g acrylamide (AM) and 8.630g zinc sulfate heptahydrate, dissolve them in a mixed solution of 8.460g glycerol and deionized water, add 400μL acetonitrile, stir thoroughly, add 140μL N,N-methylenebisacrylamide solution as a crosslinking agent, and then add 230μL ammonium persulfate solution as an initiator to form a gel precursor solution;

[0009] (2) Drop the precursor solution onto the surface of a zinc sheet, and then place another zinc sheet so that the precursor solution is located between two zinc sheets of the same size. After standing for a period of time, the precursor solution gels to form an in-situ hydrogel electrolyte for a zinc-zinc symmetric battery.

[0010] Secondly, the present invention provides a method for in-situ preparation of polyacrylamide hydrogel electrolytes, comprising the following steps:

[0011] (1) Weigh 1.818g acrylamide (AM) and 8.630g zinc sulfate heptahydrate, dissolve them in a mixed solution of 8.460g glycerol and deionized water, add 400μL acetonitrile, stir thoroughly, add 140μL N,N-methylenebisacrylamide solution as a crosslinking agent, and then add 230μL ammonium persulfate solution as an initiator to form a gel precursor solution;

[0012] (2) Drop the precursor solution onto the surface of a zinc plate, and then place another positive electrode plate so that the precursor solution is located between the positive electrode plate and the zinc plate. After standing for a period of time, the precursor solution gels to form the in-situ hydrogel electrolyte of the full cell.

[0013] Preferably, in the mixed solution of glycerol and deionized water, the mass ratio of glycerol to deionized water is 1:5.

[0014] Preferably, the concentration of the N,N-methylenebisacrylamide solution is 10 mg·mL. -1 .

[0015] Preferably, the concentration of the ammonium persulfate solution is 20 mg / mL. -1 .

[0016] Preferably, the zinc sheet is a round sheet with a diameter of 14 mm and a thickness of 0.1 mm.

[0017] Preferably, the precursor solution is allowed to stand for 10–30 minutes to gel.

[0018] Preferably, the positive electrode is a sodium vanadate positive electrode, which is a circular disc with a diameter of 12 mm and a thickness of 0.2 mm. The positive electrode is subjected to 3.6 mmol·L⁻¹ -1 FeSO4 and 2 mol·L -1 Soak in a mixed solution of ZnSO4 for 6 hours.

[0019] Compared with the prior art, the effects and advantages of this invention are:

[0020] Compared to non-in-situ polymerization hydrogel methods, the preparation method of this invention is simpler and faster, with lower requirements for preparation conditions. Non-in-situ methods require light or heat stimulation, while the preparation method of this invention only needs to be carried out at room temperature and can be completed in as little as 10 minutes. Compared with non-in-situ methods, the in-situ preparation process of this invention enhances the bonding ability of the electrode-electrolyte interface, and the cycle stability of the battery is significantly improved. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the in-situ preparation process of ZGA hydrogel according to the present invention.

[0022] Figure 2 The infrared spectra of the acrylamide powder and the ZGA hydrogel prepared by both in-situ and non-in-situ methods according to the present invention are shown.

[0023] Figure 3 The in-situ and non-in-situ symmetrical cells of the present invention are at 0.2 mA·cm -2 0.2mAh·cm -2 Long-cycle performance at current density.

[0024] Figure 4 The in-situ and in-situ full cells of the present invention are at 1.0 A·g -1 Full cell performance graph at current density. Detailed Implementation

[0025] In-situ preparation of hydrogels is an effective method to solve interfacial problems such as poor contact between solid electrolytes and electrodes and interfacial side reactions. (See attached image) Figure 1 As shown, in-situ hydrogel preparation involves first contacting the hydrogel precursor solution with the electrode. The liquid precursor solution can fully penetrate the solid electrode, and then directly polymerizes on the electrode surface to form a hydrogel. Batteries assembled using this method exhibit a good electrode-electrolyte interface, and the formation of hydrogen bonds in the gel electrolyte inhibits the activity of water molecules, thereby suppressing related side reactions. The in-situ preparation method of hydrogel electrolytes is quite feasible in addressing interface issues.

[0026] This invention adds glycerol to the hydrogel precursor solution to enhance the surface tension of the liquid, enabling it to stand upright between two metal sheets. This method directly utilizes the inherent reducing properties of zinc anolyte to guide the generation of free radicals from ammonium persulfate in the gel precursor solution placed between two zinc sheets, or between a zinc sheet and a positive electrode, thereby initiating a polymerization reaction. Compared to conventional thermal and photopolymerization methods for preparing hydrogels, this method can be completed quickly at room temperature. The polymerized hydrogel electrolyte exhibits excellent bonding between the electrolyte and the electrode, significantly improving battery stability. For in-situ full cells, the positive electrode needs to be immersed in a solution containing Fe... 2+ The precursor solution was immersed in the solution for 6 hours, and then placed between the soaked positive electrode plate and zinc plate. The specific process is as follows:

[0027] (1) Weigh acrylamide and zinc sulfate heptahydrate separately and dissolve them in a mixed solution of glycerol and deionized water;

[0028] (2) After mixing evenly, add acetonitrile, stir thoroughly, then add N,N-methylenebisacrylamide solution as a crosslinking agent, and then add ammonium persulfate aqueous solution as an initiator to form a gel precursor solution.

[0029] (3) The precursor solution is dropped onto the surface of the zinc sheet, and zinc sheets of the same size are placed on the droplet to form a “Zn / precursor solution / Zn” structure. After standing, the precursor solution between the zinc sheets gels and is directly converted into in-situ ZGA gel, forming a “Zn / In situ ZGA / Zn” structure. This structure is then assembled with the positive and negative electrode shells, springs, and gaskets of the battery for symmetrical battery testing.

[0030] (4) Add V2O5 to a NaCl solution, heat in a water bath, wash and dry the resulting reddish-brown precipitate to obtain sodium vanadate cathode material powder.

[0031] (5) Dissolve and stir polyvinylidene fluoride with N-methylpyrrolidone to obtain a binder solution, mix it with sodium vanadate cathode material powder and acetylene black to grind it into a slurry, coat it on carbon paper, dry it and cut it into round pieces to obtain the cathode sheet NVO.

[0032] (6) Immerse the positive electrode in a mixed solution of FeSO4 and ZnSO4.

[0033] (7) Drop the gel precursor solution onto the surface of the Zn sheet, and place the soaked positive electrode sheet on the droplet to form a sandwich structure. Allow it to stand until the precursor solution polymerizes in situ into a gel, and then assemble it with the positive and negative electrode shells, spring sheets and gaskets of the battery for full cell testing.

[0034] Example 1

[0035] (1) First, weigh 1.818 g AM and 8.630 g zinc sulfate heptahydrate, and dissolve them in a mixed solution of 8.460 g glycerol and deionized water (glycerol:H2O = 1:5). After mixing thoroughly, add 400 μL acetonitrile, stir well, and then add 140 μL N,N-methylenebisacrylamide solution (10 mg·mL⁻¹). -1 As a crosslinking agent, 230 μL of ammonium persulfate solution (20 mg·mL⁻¹) was added. -1 ( ) acts as an initiator to form a gel precursor solution.

[0036] (2) 150 μL of precursor solution was dropped onto the surface of a zinc sheet (14 mm in diameter, 0.1 mm thick), and a zinc sheet of the same size was placed on top of the droplet to form a "Zn / precursor solution / Zn" structure. After standing for 10 minutes, the precursor solution between the zinc sheets gelled, directly transforming into in-situ ZGA gel, forming a "Zn / In situ ZGA / Zn" structure. The amount of precursor solution added is related to the thickness of the gel electrolyte; the more added, the thicker the gel electrolyte. In this embodiment, the thickness of the gel electrolyte is approximately 1 mm. This structure was further assembled into a symmetrical battery with a positive electrode shell, a negative electrode shell, a spring plate, and a gasket for subsequent electrochemical testing. See attached... Figure 1 As shown.

[0037] Comparative Example

[0038] The other processes are the same as in Example 1, except that in step (2), the precursor solution is placed in a culture dish so that the thickness of the precursor solution in the culture dish is about 2 mm, and the culture dish is placed in a vacuum drying oven at 60°C for 2 h to obtain an in-situ ZGA gel.

[0039] Figure 2 The infrared spectra of gels prepared by in-situ and non-in-situ methods are shown. They have the same structure, which confirms the feasibility of the in-situ method.

[0040] The symmetrical batteries prepared in Example 1 and the comparative example were subjected to cyclic charge-discharge tests, and the results are as follows: Figure 3 As shown, in-situ ZGA hydrogels can enhance the long-cycle stability of batteries.

[0041] Example 2

[0042] (1) Same as step (1) in Example 1.

[0043] (2) Add 3g of V2O5 to 90mL of 2mol / L NaCl solution, heat in a water bath at 25℃ for 72h, wash the resulting reddish-brown precipitate with ethanol and deionized water using a medium-low speed centrifuge, and dry the product overnight in a vacuum drying oven at 60℃ to obtain sodium vanadate cathode material.

[0044] (3) Polyvinylidene fluoride (PVDF) was dissolved and stirred with N-methylpyrrolidone to obtain a binder solution. This solution was then mixed with the cathode material powder and acetylene black and ground into a slurry. The mass ratio of sodium vanadate cathode material, acetylene black, and PVDF was 7:2:1. The carbon paper coated with the slurry was dried overnight in a vacuum drying oven at 60°C. The cathode sheet was cut into round pieces with a diameter of 12 mm (thickness of 0.2 mm).

[0045] (4) Immerse the positive electrode in a solution with a concentration of 3.6 mmol·L⁻¹ -1 FeSO4 and 2 mol·L -1 A mixed solution of ZnSO4 was prepared for 6 hours.

[0046] (5) A 150 μL precursor solution was dropped onto the surface of a zinc sheet (14 mm in diameter and 0.1 mm thick), and the positive electrode was placed on the droplet to form a "Zn / precursor solution / Zn" structure. After standing for 10 minutes, the precursor solution gelled, directly transforming into in-situ ZGA gel, forming a "Zn / In situ ZGA / NVO" structure. This structure was then assembled with the battery's positive and negative electrode shells, spring contacts, and gaskets, and a full-cell test was performed. The results are as follows: Figure 4 As shown, there was no significant difference in performance between the full-cell and full-cell batteries.

Claims

1. A method for in-situ preparation of polyacrylamide hydrogel electrolyte at room temperature, characterized in that, Includes the following steps: (1) Weigh 1.818 g acrylamide and 8.630 g zinc sulfate heptahydrate, dissolve them in a mixed solution of 8.460 g glycerol and deionized water, add 400 μL acetonitrile, stir thoroughly, add 140 μL N,N-methylenebisacrylamide solution as a crosslinking agent, and then add 230 µL ammonium persulfate solution as an initiator to form a gel precursor solution; (2) Drop the precursor solution onto the surface of a zinc sheet, and then place another zinc sheet so that the precursor solution is located between two zinc sheets of the same size. After standing for a period of time, the precursor solution gels to form an in-situ hydrogel electrolyte for a zinc-zinc symmetric battery.

2. A method for in-situ preparation of polyacrylamide hydrogel electrolyte at room temperature, characterized in that, Includes the following steps: (1) Weigh 1.818 g acrylamide and 8.630 g zinc sulfate heptahydrate, dissolve them in a mixed solution of 8.460 g glycerol and deionized water, add 400 μL acetonitrile, stir thoroughly, add 140 μL N,N-methylenebisacrylamide solution as a crosslinking agent, and then add 230 µL ammonium persulfate solution as an initiator to form a gel precursor solution; (2) Drop the precursor solution onto the surface of a zinc plate, and then place another positive electrode plate so that the precursor solution is located between the positive electrode plate and the zinc plate. After standing for a period of time, the precursor solution gels to form the in-situ hydrogel electrolyte of the full cell.

3. The method as described in claim 1 or 2, characterized in that, In a mixed solution of glycerol and deionized water, the mass ratio of glycerol to deionized water is 1:

5.

4. The method as described in claim 1 or 2, characterized in that, The concentration of the N,N-methylenebisacrylamide solution was 10 mg·mL. -1 .

5. The method as described in claim 1 or 2, characterized in that, The concentration of the ammonium persulfate solution is 20 mg·mL. -1 .

6. The method as described in claim 1 or 2, characterized in that, The zinc sheet is a round sheet with a diameter of 14 mm and a thickness of 0.1 mm.

7. The method as described in claim 1 or 2, characterized in that, Let stand for 10-30 minutes to allow the precursor solution to gel.

8. The method as described in claim 2, characterized in that, The positive electrode is a sodium vanadate positive electrode, which is a circular disc with a diameter of 12 mm and a thickness of 0.2 mm. The positive electrode is subjected to 3.6 mmol·L⁻¹. -1 FeSO4 and 2 mol·L -1 Soak in a mixed solution of ZnSO4 for 6 hours.

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