A methyl-modified hydrogel electrolyte, a preparation method thereof and application thereof in a zinc battery

Abstract

The application discloses a methyl-modified hydrogel electrolyte, a preparation method thereof and application of the hydrogel electrolyte in a zinc battery, and belongs to the field of secondary batteries. The hydrogel electrolyte is composed of acrylamide, methyl cellulose and zinc sulfate. The preparation method comprises the following steps: adding the methyl cellulose and the acrylamide into a zinc sulfate solution, uniformly mixing, then adding potassium persulfate initiator and a crosslinking agent N,N'-methylene bisacrylamide, finally placing in a double-layer glass plate and sealing, and heat polymerization. The methyl cellulose has zinc affinity, can convert the acrylamide proton polymer into an aprotic polymer, weakens the intermolecular hydrogen bond, so that free hydrogen bond acceptors participate in cation solvation. The solubilization and recrystallization strategy can effectively adjust the gel electrolyte environment, cut off the hydrogen bond of the water donor, participate in the dissolution of the electrolyte salt, thereby improving the electrolyte concentration and inhibiting the salting-out. The gel electrolyte used in the zinc battery can accelerate the migration of zinc ions and realize excellent cycle performance under low-temperature conditions.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of novel battery energy storage, and particularly relates to a methyl-modified hydrogel electrolyte, a preparation method thereof and application thereof in zinc batteries. BACKGROUND

[0002] Aqueous zinc-ion batteries have broad application prospects in large-scale energy storage and flexible wearable electronic products due to high theoretical capacity, abundant material reserves and high safety. However, uncontrollable interface reactions (dendrite, hydrogen evolution, corrosion) seriously hinder the large-scale development of zinc batteries. Hydrogel electrolytes can improve the stability of the electrode-electrolyte interface, but the gel electrolyte usually contains a large amount of free water, which cannot inhibit the disordered growth of zinc dendrites and complex interface reactions. In addition, the reduction of water content in the traditional hydrogel electrolyte will cause a large amount of salt to precipitate, and the ionic conductivity will decrease, thereby limiting the electrochemical performance. Therefore, it is essential to develop a gel electrolyte with high ionic conductivity and maximum salt concentration for long-life zinc batteries.

[0003] Currently, the research on hydrogel electrolytes mainly focuses on two aspects: improving the mechanical strength and mechanical properties and improving the ionic conductivity. In order to improve the mechanical properties and ionic conductivity of the hydrogel electrolyte, a lot of efforts and research have been made, but there is still a large amount of free water in the gel electrolyte in these strategies, which cannot fundamentally solve the interface problem. Increasing the salt concentration can effectively protect the stability of the electrode-electrolyte interface. Therefore, in addition to providing a stable cross-linked network, the polymer in the ideal gel electrolyte should also promote salt dissolution by participating in the solvation of cations. However, the traditional gel electrolyte used in zinc batteries contains both hydrogen bond acceptors and donors, resulting in the formation of a hydrogen bond network within the polymer molecules. Therefore, the polymer in the gel electrolyte hardly participates in the electrolyte dissolution, which leads to serious salt precipitation in the gel electrolyte and an imbalance between free water and bound water. SUMMARY

[0004] In order to overcome the deficiencies in the prior art, the purpose of the present application is to provide a methyl-modified hydrogel electrolyte, a preparation method thereof and application thereof in zinc batteries. The methyl-modified hydrogel electrolyte of the present application is used in zinc batteries, which can regulate the uniform deposition of zinc ions, enhance the interface stability and improve the cycle life of zinc batteries.

[0005] To solve the technical problems of the present application, the technical scheme adopted is as follows:

[0006] A preparation method of a methyl-modified hydrogel electrolyte, the process is as follows:

[0007] 1) Acrylamide and methyl cellulose are dissolved in a zinc sulfate aqueous solution at a mass ratio of (1-3):1, and stirred for 5-10 hours to make them uniformly mixed;

[0008] 2) adding a thermal initiator and a crosslinking agent to the mixed solution of step 1) and stirring for 5-10 minutes;

[0009] 3) coating the mixed solution of step 2) uniformly in a double-layer substrate and sealing, and performing thermal polymerization at 50-70°C to obtain a methyl-modified hydrogel electrolyte.

[0010] Further, the thermal initiator is potassium persulfate or ammonium persulfate, and the crosslinking agent is N,N'-methylenebisacrylamide; the amount of the thermal initiator added is 1-5% of the mass of the acrylamide; and the mass ratio of the thermal initiator to the crosslinking agent is (1-3):1.

[0011] Further, the distance between the double-layer substrates is 0.1-1 mm, and the thermal polymerization time is 2-4 hours.

[0012] Further, the concentration of the zinc sulfate aqueous solution is 1-5 mol / L, and the concentration of the acrylamide in the acrylamide is 0.05-0.1 mg / mL.

[0013] The methyl-modified hydrogel electrolyte prepared by the above preparation method can effectively promote the dissolution of zinc sulfate electrolyte salt, avoid salting out and crystallization in the gel electrolyte, and has good salt dissolution characteristics and electrochemical performance compared with traditional gel electrolytes without methyl cellulose.

[0014] Further, the methyl-modified hydrogel electrolyte is used in a zinc battery.

[0015] Further, a zinc sheet is used as a negative electrode, a zinc vanadate positive electrode or a zinc sheet is used as a positive electrode, a methyl-modified hydrogel electrolyte is prepared as a battery separator and electrolyte, and a quasi-solid zinc battery is assembled.

[0016] Further, the quasi-solid zinc battery is a zinc-zinc symmetric battery or a zinc-zinc vanadate full battery.

[0017] Further, the structure of the zinc-zinc symmetric battery is: a positive electrode shell, a zinc sheet, a methyl-modified gel electrolyte, a zinc sheet, a gasket, and a negative electrode shell; and the structure of the zinc-zinc vanadate full battery is: a positive electrode shell, a zinc vanadate positive electrode, a methyl-modified gel electrolyte, a zinc sheet, a gasket, and a negative electrode shell.

[0018] The preparation process of the zinc vanadate positive electrode is as follows: the vanadium pentoxide is dispersed in a mixture of water and acetone, zinc acetate is added and stirred to dissolve, then transferred to a sealed polytetrafluoroethylene container, incubated at 200±10℃ for 70-75 hours, washed by centrifugation with water, the solid is collected and dried (50-70℃ for 20-24 hours), to obtain zinc vanadate, PVDF is added to NMP and stirred until completely dissolved, the zinc vanadate and acetylene black are ground and poured into the PVDF NMP solution and stirred for 10-15 hours, then coated on the current collector by using a spatula, dried (70-90℃ for 4-6 hours), to obtain the zinc vanadate positive electrode.

[0019] Further, the molar ratio of vanadium pentoxide to zinc acetate is 2:(1-1.5), the volume ratio of water to acetone is (10-20):1, and the mass ratio of zinc vanadate powder, acetylene black and PVDF is (6-8):(1-3):1.

[0020] Further, the current collector is titanium foil or carbon felt.

[0021] Further, the concentration of vanadium pentoxide in the mixture of water and acetone is 10-50 mol / L.

[0022] The beneficial effects of the prior art are:

[0023] First, the structure of the gel electrolyte is regulated to maximize the salt concentration control of salting-out. The gel electrolyte is prepared by using the interaction of methyl cellulose and acrylamide to realize the dissolution and recrystallization of electrolyte salt. This strategy converts the acrylamide proton polymer into an aprotic polymer through methyl cellulose to weaken the intermolecular hydrogen bond. At the same time, the gel electrolyte environment can be effectively adjusted to cut off the hydrogen bond donor to form a hydrogen bond, and release the free hydrogen bond acceptor to participate in Zn 2+ solvation. Compared with traditional hydrogel electrolytes, the methyl-modified hydrogel electrolyte can avoid salting-out, maximize the increase of salt concentration and retain its bound water activity to enhance the ionic conductivity and mechanical properties.

[0024] Second, the electrode-electrolyte interface is stabilized to improve the electrochemical performance of zinc batteries. The hydrogel electrolyte prepared by using the methyl solubilization and recrystallization strategy is applied to zinc batteries, and the specific capacity of the zinc battery is 0.5 mAh cm -2 at a current density of 0.5 mA cm -2Under the condition, the assembled zinc-zinc symmetric battery can achieve more than 8000 hours of plating / peeling cycle life, far exceeding the cycle life of the battery assembled by the traditional gel electrolyte and the water-based liquid battery assembled by using glass fiber separator. At the same time, the gel electrolyte has a low temperature performance, and the zinc-zinc symmetric battery assembled in the environment of-20℃ can achieve more than 2200 hours of cycle stability. The zinc-zinc symmetric battery assembled by the gel electrolyte has a long cycle life, and the capacity remains stable after 400 cycles at 1C rate. Compared with other patents, the technology can achieve long cycle stability, good low temperature antifreeze performance, and long service life.

[0025] Thirdly, the methylation solubilization and recrystallization strategy method is novel, simple to prepare and widely applicable. First, acrylamide and methyl cellulose are dissolved in 2 mol of zinc sulfate aqueous solution at a mass ratio of 2:1 and stirred for 5-10 hours to make them uniformly mixed. Then a small amount of thermal initiator and crosslinking agent are added and stirred for 5-10 minutes. The mixed solution is coated uniformly in a double-layer glass plate and sealed, and then polymerized in a 60℃ oven to prepare a methyl-modified hydrogel electrolyte. The methylation solubilization and recrystallization strategy helps to maximize the electrolyte concentration and maintain the activity of bound water. At the same time, the method is simple to operate, and the film forming technology has been scaled up for application. When applied to zinc batteries, it can greatly improve the cycle life, which provides a new theoretical guidance for the application of flexible batteries. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a schematic diagram of the preparation of the gel electrolyte and the methylation solubilization and recrystallization strategy;

[0027] Figure 2 is the SEM image of the surface morphology of the gel electrolyte of Comparative Example 1 and Example 1;

[0028] Figure 3 is the ternary solubilization equilibrium diagram of the gel electrolyte of Comparative Example 1 and Example 1;

[0029] Figure 4 is the research diagram of the dissolution process of the gel electrolyte of Comparative Example 1 and Example 1;

[0030] Figure 5 is the ion conductivity of the gel electrolyte of Comparative Example 1 and Example 1 and glass fiber separator;

[0031] Figure 6 is the SEM image of the zinc electrode morphology of the zinc-zinc symmetric battery of Comparative Example 2, Comparative Example 3 and Example 2 after cycling;

[0032] Figure 7 is the XRD pattern of the zinc-zinc symmetric battery of Comparative Example 2, Comparative Example 3 and Example 2 after different cycles;

[0033] Figure 8Effect of gel electrolyte and glass fiber separator on the corrosion of electrodes of Comparative Example 1 and Example 1;

[0034] Figure 9 Graph of long cycle test of zinc-zinc symmetric battery of Comparative Example 2, Comparative Example 3 and Example 2 at 25℃;

[0035] Figure 10 Graph of long cycle test of zinc-zinc symmetric battery of Comparative Example 2, Comparative Example 3 and Example 2 at -20℃;

[0036] Figure 11 Comparison of long cycle test results of zinc-zinc symmetric battery (Comparative Example 2, Comparative Example 3 and Example 2) of different separators and electrolytes;

[0037] Figure 12 Graph of cycle of zinc zinc vanadate full battery of Comparative Example 4, Comparative Example 5 and Example 3 at 25℃;

[0038] Figure 13 Graph of cycle of zinc zinc vanadate full battery of Comparative Example 4, Comparative Example 5 and Example 3 at -20℃. DETAILED DESCRIPTION

[0039] The application will be further described below by combining the examples and the drawings.

[0040] Comparative Example 1

[0041] Preparation and structure characterization of traditional hydrogel electrolyte (AM).

[0042] Step 1, preparation of traditional hydrogel electrolyte

[0043] First, 0.8 g of acrylamide was dissolved in 10 mL of 2 mol / L zinc sulfate aqueous solution and stirred for 6 hours to make the mixture uniform; then 10 mg of potassium persulfate and 5 mg of N,N'-methylenebisacrylamide were added and stirred for 10 minutes; the mixed solution was coated uniformly in a double-layer glass plate and sealed, the spacing between the double-layer glass plates was 0.4 mm (i.e. the coating thickness was 0.4 mm), and the traditional hydrogel electrolyte (AM) was prepared by heat polymerization in a 60℃ oven for 2 hours.

[0044] Step 3, structure characterization of traditional hydrogel electrolyte

[0045] The surface morphology was observed by using a focused ion beam scanning electron microscope (SEM) of Zeiss, as shown in FIG. 1. Figure 2 The traditional hydrogel electrolyte showed large-scale salting-out phenomenon on the surface, which indicated that the structure of the traditional hydrogel electrolyte was unstable and the water volatilized quickly.

[0046] Comparative Example 2

[0047] A zinc-zinc symmetric cell was assembled using a hydrophilic glass fiber separator.

[0048] Step 1, Zinc electrode preparation

[0049] A 200 pm thick pure zinc foil (purchased from National Pharmaceutical Chemical Reagents) was ultrasonically cleaned with ethanol (ultrasonic frequency 40 kHz, power 300 W, time 5 minutes) and cut into a 12 mm diameter disk with an area of about 1.13 cm 2 using an electrode slicer. The zinc foil was again ultrasonically cleaned with ethanol (ultrasonic frequency 40 kHz, power 300 W, time 5 minutes) and then dried in a vacuum oven at 40 °C for 1 hour.

[0050] Step 2, Zinc symmetric cell assembly

[0051] The zinc electrode was assembled into a CR2025 type (battery diameter 20.0 mm, thickness 2.5 mm) symmetric cell for cycle stability testing. The components of the cell were in the order of positive shell, zinc disk, separator, zinc disk, stainless steel gasket (diameter 16 mm, thickness 1 mm), negative shell, and the sealing pressure was about 50 kg per cubic centimeter. The cell needed to be rested at room temperature for no less than 2 hours before use. The separator was a glass fiber (produced by Whatman, diameter 110 mm, thickness 260 pm, cut into a 19 mm diameter disk for use). The electrolyte used was a 2 mol / L (or 2 M) zinc sulfate solution, 100 pL of which was added to each cell after the separator was placed. The 2 M zinc sulfate electrolyte was prepared by dissolving ZnS04-7H20 (analytical pure, purchased from National Pharmaceutical Chemical Reagents) in pure water, with a mass ratio of about 5.751:7.48.

[0052] Step 3, Zinc symmetric cell testing

[0053] The long cycle test of the symmetric cell was carried out in a thermostat, which was kept at 25 °C to eliminate the influence of ambient temperature. The battery test used a battery test system from Wuhan LanDian. As shown in Figure 9 , the test parameters were set to constant current discharge and constant current charge, with a current density of 1 mA / cm 2 based on the electrode area and an area capacity of 0.5 mAh / cm 2 . Under this test condition, the symmetric cell using a hydrophilic glass fiber separator had a life of about 355 hours, indicating that the battery life using a hydrophilic glass fiber separator was shorter. At -20 °C, at a current density of 0.5 mA / cm 2 , an area capacity of 0.5 mAh / cm 2 , as shown in Figure 10 , 11 , the symmetric cell had a life of about 27 hours. In addition, under deep discharge conditions, as shown in Figure 11As shown, at 0.5 mA / cm 2 、10mAh / cm 2 Under the same conditions (DOD=68.33%), the symmetrical battery life is 300 hours.

[0054] Step 4: Observation of dendrites on the surface of zinc symmetric battery

[0055] The surface morphology of the zinc electrode after 355 hours of death was observed using a Zeiss focused dual ion beam scanning electron microscope (SEM). Figure 6 As shown, after a long period of zinc deposition and stripping, the electrode surface is covered with disordered and irregular dendrites, which is the main cause of battery short circuit.

[0056] Comparative Example 3

[0057] Assembling Zn-Zn symmetric batteries using conventional hydrogel electrolytes

[0058] Step 1, preparation of traditional hydrogel electrolyte membrane

[0059] Same as step 1 of comparative example 1.

[0060] Step 2, zinc electrode preparation

[0061] Same as step 1 of comparative example 2.

[0062] Step 3, zinc symmetric battery assembly

[0063] Cycling stability testing was performed using zinc electrodes assembled into a symmetrical CR2025-size cell (20.0 mm diameter, 2.5 mm thickness). The battery components consist of the positive electrode casing, zinc sheet, traditional hydrogel electrolyte membrane, zinc sheet, stainless steel gasket (16 mm diameter, 1 mm thickness), and negative electrode casing. The sealing pressure was approximately 50 kg / cm³. The battery was allowed to rest at room temperature for at least two hours before use.

[0064] Step 4, zinc symmetric battery test

[0065] Symmetrical battery long cycle test is carried out in a constant temperature box, and the temperature of the constant temperature box is maintained at 25℃ to eliminate the influence of ambient temperature. Battery test uses the battery test system of Wuhan Landian. Figure 9 As shown, the test parameters are set to constant current discharge and constant current charge, and the current density based on the electrode area is 1 mA / cm 2 , with an area capacity of 0.5 mAh / cm 2 Under this test condition, the life of the symmetrical battery using the traditional hydrogel electrolyte is about 226 hours, which shows that the battery life of the traditional hydrogel electrolyte is short. 2 , with an area capacity of 0.5 mAh / cm 2Tests, such as Figure 10 , 11 show that the symmetric cell has a lifetime of about 240 hours. In addition, under deep discharge conditions, as shown in Figure 11 , the symmetric cell has a lifetime of 460 hours under conditions of 0.5 mA / cm 2 , 10 mAh / cm 2 (DOD = 68.33%).

[0066] Step 5, Observation of Surface Dendrites of Zinc Symmetric Cell

[0067] The surface morphology of the zinc electrode after 226 hours of death was observed using a focused ion beam scanning electron microscope (SEM) from Zeiss. As shown in Figure 6 , after long-term zinc deposition and stripping, the electrode surface is dense deposition, but the dendrites grow irregularly, limiting the cycle life of the cell.

[0068] Comparative Example 4

[0069] Zinc vanadium zinc full cell was assembled using hydrophilic glass fiber separator

[0070] Step 1, Preparation of Zinc Electrode

[0071] The same as Step 1 of Comparative Example 2.

[0072] Step 2, Preparation of Zinc Vanadate Positive Electrode

[0073] 2 mol vanadium pentoxide was dispersed in a mixture of 50 mL water and acetone (volume ratio of water to acetone 15:1), 1.3 mol zinc acetate was added and stirred to dissolve, transferred to a sealed polytetrafluoroethylene container, stored at 200°C for 72 hours, added pure water and centrifuged three times, collected the precipitate, dried at 60°C for 24 hours, to obtain zinc vanadate. In a glass bottle, 3-4 mL NMP and 100 mg PVDF were added and stirred for 6 hours. Then 200 mg acetylene black and 700 mg zinc vanadate were added in a mortar. After grinding for 20 minutes, pour into a glass bottle and stir for 10 hours. Then pour the mixed slurry on carbon felt, evenly spread with a 200 μm spatula, and keep at 80°C for 4 hours, to obtain ZnVO positive electrode.

[0074] Step 3, Full Cell Assembly

[0075] Zinc and zinc vanadate electrodes were assembled into a CR2025 full cell (cell diameter: 20.0 mm, thickness: 1.6 mm). The battery was assembled in the following order: positive electrode casing, zinc vanadate positive electrode sheet, glass fiber separator, zinc electrode, stainless steel gasket (1 mm thick), and negative electrode casing. The sealing pressure was approximately 50 kg / cm³. The battery was allowed to stand at room temperature for 2 hours before use. The separator was glass fiber (manufactured by Whatman, 110 mm diameter, cut into 19 mm discs). The electrolyte used was a 2 mol / L (or 1 M) zinc sulfate solution, with 100 μL added to each cell. The electrolyte was added immediately after the separator was placed.

[0076] Step 4: Zinc vanadate full battery test

[0077] The full battery test uses the battery test system of Wuhan Landian. At room temperature (25℃), the charge and discharge test is carried out at a rate of 10C. Figure 12 As shown, the initial discharge capacity is 150 mAh g -1 , and then showed a downward trend, and the capacity dropped to 75 mAh g after about 1600 cycles. -1 At -20℃, the charge and discharge test was carried out at a rate of 1C. Figure 13 As shown, the battery specific capacity decays rapidly.

[0078] Comparative Example 5

[0079] Assembling zinc vanadate full batteries using traditional hydrogel electrolytes

[0080] Step 1, preparation of traditional hydrogel electrolyte membrane

[0081] Same as step 1 of comparative example 1.

[0082] Step 2: Preparation of zinc electrode.

[0083] Same as step 1 of comparative example 2.

[0084] Step 3, preparation of zinc vanadate positive electrode

[0085] Same as step 2 of comparative example 4.

[0086] Step 4: Full battery assembly

[0087] Zinc and zinc vanadate electrodes were assembled into a CR2025 full cell (cell diameter: 20.0 mm, thickness: 1.6 mm). The battery assembly sequence is: positive electrode casing, zinc vanadate positive electrode sheet, conventional hydrogel electrolyte, zinc electrode, stainless steel gasket (1 mm thick), and negative electrode casing. The sealing pressure was approximately 50 kg / cm³. The battery was allowed to rest at room temperature for 2 hours before use.

[0088] Step 4: Zinc vanadate full battery test

[0089] Full cell test uses battery test system of Wuhan Lan Electric. At room temperature (25℃), charge-discharge test is carried out at 10C rate. As shown in Figure 12 , the initial specific discharge capacity is 150mAh g -1 , and then overcharge after about 900 cycles leads to short circuit of the battery. At -20℃, charge-discharge test is carried out at 1C rate. As shown in Figure 13 , the specific capacity of the battery is only 120mAh g -1 after 400 cycles.

[0090] Example 1

[0091] Preparation of gel electrolyte (AM-CH3) by methyl solubilization and recrystallization strategy

[0092] Step 1, methyl solubilization and recrystallization strategy

[0093] Firstly, the solubilization strategy of methyl cellulose, acrylamide and zinc sulfate aqueous solution mixed in different proportions is studied. First, acrylamide and zinc sulfate are added to water in different proportions and stirred for 5-10 hours to study their solubility. The phase diagram of different proportions is shown in Figure 1 .

[0094] Step 2, preparation of methyl-modified gel electrolyte

[0095] First, 0.8g of acrylamide and 0.4g of methyl cellulose are dissolved in 10mL of 2mol / L zinc sulfate aqueous solution and stirred for 6 hours to make them evenly mixed; then 10mg of potassium persulfate and 5mg of N,N'-methylene bisacrylamide are added and stirred for 10 minutes; the mixed solution is coated evenly in a double-layer glass plate and sealed, with a coating thickness of 0.4mm, and is heated in an oven at 60℃ for 2 hours to prepare the methyl-modified hydrogel electrolyte, as shown in Figure 1 .

[0096] Step 3, structure characterization of methyl-modified hydrogel electrolyte

[0097] The surface morphology is observed by Zeiss focused dual ion beam scanning electron microscope (SEM), as shown in Figure 2 . The surface of the methyl-modified hydrogel electrolyte is smooth, with a small amount of micropores appearing, and no large amount of salt is precipitated. At the same time, the ionic conductivity of the methyl-modified hydrogel electrolyte can reach 20.44 mS cm -1 , which is better than the comparative example, as shown in Figure 5 , which is conducive to the migration of zinc ions. It can be proved by XRD that the methyl-modified hydrogel electrolyte has no obvious sharp peak, showing amorphous state, which indicates that the groups in the gel electrolyte interact with methyl cellulose and electrolyte.

[0098] Example 2

[0099] Methyl-modified gel electrolyte for zinc-zinc symmetric battery

[0100] Step 1, Preparation of methyl-modified gel electrolyte

[0101] The same as Example 1 Step 2.

[0102] Step 2, Zinc electrode preparation

[0103] The same as Comparative Example 2 Step 1.

[0104] Step 3, Methyl-modified gel electrolyte assembly zinc-zinc symmetric battery

[0105] The zinc electrode was assembled into a CR2025 type (battery diameter 20.0 mm, thickness 2.5 mm) symmetric battery for cycle stability test. The battery components were in turn positive electrode shell, zinc electrode, methyl-modified hydrogel electrolyte film, zinc electrode, stainless steel gasket (diameter 16 mm, thickness 1 mm), negative electrode shell, and the sealing pressure was about 50 kg per cubic centimeter. The battery needs to be placed at room temperature for not less than 2 hours before use.

[0106] Step 4, Methyl-modified gel electrolyte assembly zinc-zinc symmetric battery test

[0107] The methyl-modified gel electrolyte assembly zinc-zinc symmetric battery obtained in Step 3 was subjected to cycle test. The battery test used the battery test system of Wuhan Lan Electric. As shown in Figure 9 , the test parameters were set to constant current discharge and constant current charge, and the current density based on electrode area was 1 mA / cm 2 , and the area capacity was 0.5 mAh / cm 2 . Under this test condition, the symmetric battery using methyl-modified hydrogel electrolyte can have a service life of more than 8000 hours, showing super-long cycle and excellent electrochemical performance. At -20℃, at a current density of 0.5 mA / cm 2 , and an area capacity of 0.5 mAh / cm 2 , as shown in Figure 10 , 11 , the symmetric battery service life was about 2150 hours. In addition, under deep discharge conditions, as shown in Figure 11 , at 0.5 mA / cm 2 , 10 mAh / cm 2 (DOD=68.33%), the symmetric battery can still achieve 2600 hours.

[0108] Step 5, Comparison of test results with zinc symmetric battery in comparative example

[0109] Methyl-modified hydrogel electrolyte assembled zinc-zinc symmetric battery at 1 mA / cm 2 , 0.5 mAh / cm 2 and 0.5 mA / cm 2 , 10 mAh / cm 2 Test results under test conditions are as Figure 11 Battery life reached more than 8000 hours and 2600 hours respectively, far exceeding the comparative examples. This fully embodies that the methyl-modified gel electrolyte can significantly improve the battery performance and greatly improve the cycle life.

[0110] Step 6, using SEM to observe the surface morphology of zinc electrode after long-term cycling

[0111] The surface morphology of zinc electrode after the methyl-modified gel electrolyte assembled zinc-zinc symmetric battery is cycled is as Figure 6 shown. It can be seen that the zinc surface presents a dense deposition without obvious dendrites and the surface is flat. Compared with using hydrophilic glass fiber separator, the deposition of zinc is obviously more flat and orderly, which shows that the gel electrolyte can regulate the dense deposition of zinc.

[0112] Step 7, explaining the mechanism of methyl-modified gel electrolyte in zinc battery

[0113] In order to improve the solubility of gel electrolyte and reduce the activity of free water to inhibit its salting-out, the ternary solubilization equilibrium process of AM (or AM-CH3), ZnSO4, H2O was studied, as Figure 3 shown. The solubility of different proportion mixtures is very different. As Figure 4 shown, the dissolution process of gel electrolyte was studied. It can be found that the solubility can be obviously improved in the solution containing methyl cellulose, preventing the electrolyte from salting out. This solubilization strategy is based on the method of methyl modification, which converts the proton polymer acrylamide into an aprotic polymer, weakening the intermolecular hydrogen bond. Through the unoccupied -C=O site in acrylamide participating in Zn 2+ solvation, the electrolyte salt concentration is further improved. During the preparation of gel electrolyte by thermal polymerization, this solubilization recrystallization strategy will retain a small amount of bound water, promoting the crystallization of electrolyte.

[0114] Figure 8 For electrode interface stability research at room temperature, since the methyl-modified hydrogel electrolyte reduces the activity of a large amount of free water and only retains a small amount of bound water, the electrode interface corrosion reaction is reduced, increasing the electrode-electrolyte interface stability; at the same time, methyl cellulose has affinity for zinc, regulating the solvation structure of zinc ions in the electrolyte, inducing uniform deposition of zinc ions, as Figure 7 shown.

[0115] Example 3

[0116] Utilization of methyl-modified gel electrolyte for zinc-zinc vanadate full cell.

[0117] Step 1, Preparation of methyl-modified gel electrolyte

[0118] The same as Example 1 Step 2.

[0119] Step 2, Zinc electrode preparation

[0120] The same as Comparative Example 2 Step 1.

[0121] Step 3, Preparation of zinc vanadate cathode

[0122] The same as Comparative Example 4 Step 2.

[0123] Step 4, Methyl-modified gel electrolyte assembly zinc vanadate full cell

[0124] The zinc electrode and zinc vanadate electrode were assembled into a CR2025 type full cell (the diameter of the battery is 20.0 mm, and the thickness is 1.6 mm). The assembly sequence of the whole battery is cathode shell, zinc vanadate cathode sheet, methyl-modified hydrogel electrolyte, zinc electrode, stainless steel gasket pad (thickness 1 mm), anode shell. The sealing pressure is about 50 kg per cubic centimeter. The battery needs to be placed at room temperature for 2 hours before use.

[0125] Step 5, Methyl-modified gel electrolyte assembly zinc-zinc vanadate full cell test

[0126] The full cell test uses the battery test system of Wuhan Lan Electric. The charge-discharge test was carried out at room temperature (25°C) at a rate of 10C, as shown in Figure 12 , the initial specific discharge capacity is 120 mAh g -1 , and then the specific capacity remains at 110 mAh g -1 above after about 1600 cycles. At -20°C, the charge-discharge test was carried out at a rate of 1C, as shown in Figure 13 , the specific capacity of the battery almost does not decay after 400 cycles, and the capacity retention rate is 98.46%.

[0127] Step 6, Performance comparison of zinc-zinc vanadate full cell in the comparative example

[0128] The zinc vanadium battery assembled using a glass fiber separator rapidly decays in capacity under 10C rate charge-discharge conditions, and is difficult to apply in practice. The zinc vanadium battery assembled using a traditional hydrogel electrolyte is prone to overcharge, short circuit and other failures under 10C rate charge-discharge conditions, which is mainly related to the instability of the interface. The zinc vanadium battery assembled using a methyl-modified hydrogel electrolyte still has excellent specific capacity after 1600 cycles under 10C rate charge-discharge conditions, and has excellent electrochemical performance. In addition, the methyl-modified gel electrolyte still has a wide range of applications in low-temperature environments, and the zinc vanadium battery assembled using the methyl-modified gel electrolyte has almost no capacity decay after 400 cycles, which has good application value in the field of low-temperature flexible batteries.

[0129] Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. The disclosure is intended to cover any variations, uses or adaptations of the disclosure following, in general, the principles of the disclosure and including such departures from the present disclosure that come within known

[0130] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. The patent protection scope of the present application is subject to the claims, and any equivalent structural changes made according to the content of the specification of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a methyl-modified hydrogel electrolyte, characterized by, The process is as follows: 1) Acrylamide and methyl cellulose are dissolved in zinc sulfate aqueous solution at a mass ratio of (1-3):1, and stirred for 5-10 hours to make them uniformly mixed; 2) A thermal initiator and a crosslinking agent are added to the mixed solution of step 1), and stirred for 5-10 minutes; 3) The mixed solution of step 2) is coated uniformly in a double-layer substrate and sealed, and is subjected to thermal polymerization at 50-70°C to obtain a methyl-modified hydrogel electrolyte.

2. The method for preparing a methyl-modified hydrogel electrolyte according to claim 1, wherein: The thermal initiator is potassium persulfate or ammonium persulfate, and the crosslinking agent is N,N'-methylene bisacrylamide; the amount of the thermal initiator added is 1-5% of the mass of acrylamide; the mass ratio of the thermal initiator to the crosslinking agent is (1-3):

1.

3. The method for preparing a methyl-modified hydrogel electrolyte according to claim 1, wherein: The distance between the double-layer substrates is 0.1-1 mm, and the thermal polymerization time is 2-4 hours.

4. The method for preparing a methyl-modified hydrogel electrolyte according to claim 1, wherein: The concentration of the zinc sulfate aqueous solution is 1-5 mol / L, and the concentration of acrylamide in acrylamide is 0.05-0.1 mg / mL.

5. The methyl-modified hydrogel electrolyte prepared by the preparation method of any one of claims 1-4.

6. The use of the methyl-modified hydrogel electrolyte of claim 5 in a zinc battery.

7. Use according to claim 6, characterized in that, A zinc-zinc symmetric battery or a zinc-zinc vanadate full battery is assembled by using a zinc sheet as a negative electrode, a zinc sheet or a zinc vanadate positive electrode as a positive electrode, and the prepared methyl-modified hydrogel electrolyte as a battery separator and electrolyte.

8. Use according to claim 6, characterized in that, The structure of the zinc-zinc symmetric battery is: positive electrode shell, zinc sheet, methyl-modified gel electrolyte, zinc sheet, gasket, and negative electrode shell; and the structure of the zinc-zinc vanadate full battery is: positive electrode shell, zinc vanadate positive electrode, methyl-modified gel electrolyte, zinc sheet, gasket, and negative electrode shell.

9. Use according to claim 7 or 8, characterized in that, The preparation process of the zinc vanadate positive electrode is as follows: vanadium pentoxide is dispersed in a mixture of water and acetone, zinc acetate is added and stirred to dissolve, then transferred to a sealed polytetrafluoroethylene container, and incubated at 200±10°C for 70-75 hours; washed by centrifugation after adding water, and the solid is collected and dried to obtain zinc vanadate; PVDF is added to NMP and stirred until completely dissolved; zinc vanadate and acetylene black are ground and poured into the PVDF NMP solution, stirred for 10-15 hours, and then coated on the current collector using a doctor blade, and dried to obtain a zinc vanadate positive electrode.

10. Use according to claim 9, characterized in that, The molar ratio of vanadium pentoxide to zinc acetate is 2:(1-1.5), the volume ratio of water to acetone is (10-20):1, and the mass ratio of zinc vanadate powder, acetylene black, and PVDF is (6-8):(1-3):1.

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