Preparation of low water activity hydrogel membrane and its application in proton battery electrolyte

Abstract

The present application relates to a kind of preparation of low water activity hydrogel film and its application in proton battery electrolyte: with commercial crosslinking agent as monomer, it is dispersed in acidic aqueous solution, ultrasonic removes the bubble in it, then corresponding initiator is added and placed in film mold, after heating / illumination polymerization, low water activity hydrogel film is obtained.The low water activity hydrogel film, the content of acidic aqueous solution is less than 60wt%, to ensure that the prepared hydrogel film has excellent mechanical properties without rupture;Low content of water in hydrogel film makes it anchor on the hydrophilic group of monomer by forming hydrogen bond, so as to avoid the corrosion and dissolution of active material and battery device by acidic aqueous solution flowing out;Using inorganic strong acidic aqueous solution can make hydrogel film provide high proton conductivity at lower water content.Using low water activity hydrogel film as electrolyte is expected to make proton battery simultaneously have capacity retention rate, cycle stability and rate performance.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology, specifically relating to the preparation and application of a low-water-activity hydrogel membrane. Background Technology

[0002] As the proportion of renewable energy sources such as wind and solar power in the energy market increases year by year, there is a need to develop large-scale energy storage technologies with high-efficiency energy storage and conversion capabilities. Proton batteries, due to their low cost, safety, and environmentally friendly technological advantages, have come into the research field. A proton battery is a device that uses protons (H+) as its energy source. + A novel type of secondary battery using protons as charge carriers. Protons have the smallest molar mass of 1 g·mol⁻¹. -1 With its extremely small ionic radius of 0.89 fm and unique transport mechanism, the battery system based on the reversible electrochemical reaction of protons is expected to achieve high specific energy and high specific power.

[0003] To meet the demands for high proton conductivity and low cost, proton batteries typically use acidic aqueous solutions as electrolytes. However, acidic aqueous solutions can cause dissolution and corrosion of electrode active materials and battery devices. Furthermore, the narrow electrochemical window (1.23V) in aqueous systems limits the operating voltage of proton batteries. To address the corrosion and dissolution issues in acidic aqueous electrolytes, researchers have employed materials such as acetonitrile solutions of phosphoric acid, anhydrous polyphosphoric acid, and modified covalent organic frameworks as proton battery electrolytes. However, these electrolytes introduce new problems, such as the low proton conductivity of acetonitrile solutions of phosphoric acid and anhydrous polyphosphoric acid at room temperature, and the high cost of modified covalent organic frameworks. Therefore, there is an urgent need to develop a proton battery electrolyte that balances high proton conductivity, low cost, safety, and environmental friendliness.

[0004] Hydrogels, as a type of three-dimensional network structure material polymerized from hydrophilic monomers, possess low cost and high proton conductivity. Simultaneously, the hydrophilic monomers can confine water within the structure through hydrogen bonds, preventing water loss and ensuring the long-term effectiveness of the electrolyte, making them a promising candidate for use as quasi-solid-state electrolytes in proton batteries. Current research shows that high water-activity hydrogel electrolytes, due to their large content of free water, still exhibit strong corrosive and soluble properties. Therefore, it is necessary to reduce the water activity in hydrogels, i.e., to develop low-water-activity hydrogel electrolytes to reduce the dissolution and corrosion of active materials and battery devices. Summary of the Invention

[0005] The purpose of this invention is to provide a low-water-activity hydrogel membrane for preparation and its application in proton battery electrolytes. The three-dimensional structure formed by the polymerization of hydrophilic monomers provides a connected network to accommodate acidic proton carriers; simultaneously, the filling of the pores with an inorganic strong acid aqueous solution provides high proton conductivity; finally, the low water activity in the hydrogel and the fixation of water in the pores by the hydrophilic groups on the monomers effectively mitigate the damage to active materials and battery devices caused by the loss of active water during cycling. Therefore, when this hydrogel membrane is used as a proton battery electrolyte, the prepared proton battery is expected to exhibit superior capacity retention, cycle stability, and rate performance.

[0006] A method for preparing a low-water-activity hydrogel membrane, characterized in that the low-water-activity hydrogel membrane comprises the following three parts: a crosslinking agent, an initiator, and an acidic aqueous solution. By controlling the type of crosslinking agent and the mass ratio of the crosslinking agent to the acidic aqueous solution, low-water-activity hydrogel membranes with different network structures and water contents can be prepared. Specifically, the method includes the following steps:

[0007] (1) Mix the crosslinking agent and acidic aqueous solution in a certain proportion and remove the air bubbles in the resulting liquid by ultrasonication;

[0008] (2) Add the initiator to the liquid obtained in step (1) in a certain proportion and stir quickly. After mixing evenly, pour it into the film forming mold and polymerize under certain conditions to obtain a low water activity hydrogel film.

[0009] (3) The membrane obtained in step (2) is placed in a vacuum drying oven for heat treatment to remove the water adsorbed on the surface of the low water activity hydrogel membrane.

[0010] The prepared low-water-activity hydrogel membrane should contain less than 60 wt% acidic aqueous solution after heat treatment to ensure that the acidic aqueous solution will not be lost and corrode or dissolve the active materials and battery devices when used as a proton battery electrolyte.

[0011] The crosslinking agent selected in step (1) is one or a mixture of two or more of the following: polyvinyl alcohol, acrylamide, acrylic acid, methacrylic acid, [(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 2-acrylamido-2-methylpropanesulfonic acid, N,N-methylenebisacrylamide, and polyethylene glycol dimethacrylate (more preferably, polyvinyl alcohol, acrylamide, methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, N,N-methylenebisacrylamide, and acrylic acid).

[0012] The acidic aqueous solution selected in step (1) is an aqueous solution of sulfuric acid, nitric acid, hydrochloric acid, or phosphoric acid (more preferably, sulfuric acid), with a concentration of 0.1 mol·L⁻¹. -1 ~4mol·L -1(Further preferred, 2–3 mol·L⁻¹) -1 );

[0013] In step (1), the mass ratio of crosslinking agent to acidic aqueous solution is 2 to 10:3 (more preferably, 2 to 5:3);

[0014] The ultrasound time in step (1) is 0.2 to 1 hour (more preferably, 0.2 to 0.6 hours);

[0015] The initiator selected in step (2) is one of glutaraldehyde, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, 2-oxo-1,5-glutaric acid, benzoyl peroxide, azobisisobutyronitrile, ammonium persulfate or potassium persulfate (more preferably, glutaraldehyde, 2-oxo-1,5-glutaric acid, ammonium persulfate or potassium persulfate);

[0016] In step (2), the mass ratio of initiator to liquid obtained in step (1) is 1:100 to 2000 (more preferably, 1:200 to 1500);

[0017] The polymerization in step (2) can be classified into photopolymerization, thermal polymerization, and catalytic polymerization according to the reaction conditions. The conditions used for polymerization are determined by the selected initiator. Photopolymerization is carried out under ultraviolet or visible light for 0.5 to 4 hours (more preferably, 1 to 3 hours); thermal polymerization is carried out under heating conditions at a heat treatment temperature of 40 to 110°C (more preferably, 70 to 100°C) for 0.5 to 12 hours (more preferably, 3 to 6 hours); catalytic polymerization is carried out at room temperature for 5 to 50 hours (10 to 30 hours).

[0018] In step (3), the heat treatment temperature is 50-100℃ (more preferably, 60-80℃), and the heat treatment time is 4-24h (more preferably, 5-10h).

[0019] The low-water-activity hydrogel membrane prepared by this invention, when used as a proton battery electrolyte, provides numerous interconnected channels for proton transport through the three-dimensional structure formed by chemical bonds or intertwined polymer chains between crosslinking agents in a three-dimensional structure. Furthermore, the formed hydrogel membrane possesses certain strength and flexibility, capable of withstanding certain impacts and shearing without rupture. Finally, the three-dimensional channels are filled with a small amount of strongly acidic aqueous solution, enabling high cycle stability and rate performance under low-water-activity conditions. The advantages of this invention lie in its low raw material cost, mild reaction conditions, controllable parameters, good reproducibility, simple and mature process, and mass production capability. The proportion of crosslinking agents and the concentration of acid can be controlled by adjusting process parameters to simultaneously achieve high proton conductivity and low corrosive solubility. Therefore, this low-water-activity hydrogel membrane is expected to become a strong competitor to proton battery electrolytes, promoting the practical application of proton batteries in the field of energy storage batteries.

[0020] This invention uses a commercially available crosslinking agent as a monomer, disperses it in an acidic aqueous solution, and ultrasonically removes air bubbles. A suitable initiator is then added, and the mixture is placed in a film-forming mold. After heating / photopolymerization, a low-water-activity hydrogel membrane is obtained. The low-water-activity hydrogel membrane contains less than 60 wt% acidic aqueous solution to ensure excellent mechanical properties without cracking. The low water content allows the hydrogel membrane to anchor to the hydrophilic groups of the monomer through hydrogen bonding, thus preventing corrosion and dissolution of the active materials and battery devices by the acidic aqueous solution. Furthermore, the use of an inorganic strongly acidic aqueous solution allows the hydrogel membrane to provide high proton conductivity at a low water content. Therefore, using a low-water-activity hydrogel membrane as an electrolyte is expected to enable proton batteries to simultaneously possess capacity retention, cycle stability, and rate performance. Attached Figure Description

[0021] Figure 1 This is the charge-discharge curve of Example 1;

[0022] Figure 2 This is a charge-discharge cycle diagram of Example 1;

[0023] Figure 3 This is the charge-discharge curve of Example 2;

[0024] Figure 4 This is a charge-discharge cycle diagram of Example 2;

[0025] Figure 5 This is the charge-discharge curve of Example 3;

[0026] Figure 6 This is a charge-discharge cycle diagram of Example 3;

[0027] Figure 7 This is the charge-discharge curve of Example 4;

[0028] Figure 8 This is a charge-discharge cycle diagram of Example 4. Detailed Implementation

[0029] The following embodiments are further illustrations of the present invention, but are not intended to limit the scope of the invention.

[0030] Example 1

[0031] Weigh 15g of polyvinyl alcohol and disperse it in 20g of 3mol·L⁻¹ solution. -1 The dispersion was ultrasonicated in an aqueous H2SO4 solution for 0.5 h, and then mechanically stirred in an 80°C oil bath for 1 h to form a homogeneous liquid. The transparent, viscous liquid was then gradually heated to 100°C in an oil bath, and 30 mg of glutaraldehyde was added as a chemical initiator. After stirring for 0.5 h, the mixture was poured into a mold, cooled to room temperature, and dried in an 80°C vacuum drying oven for 5 h to obtain a low-water-activity hydrogel film with a thickness of 0.2 mm.

[0032] Assembly and testing of coin cells: 0.8 g of α-MoO3 and 0.1 g of SuperP (conductive carbon black) were added to 2 g of polyvinylidene fluoride (PVDF, 5% by mass) solution. Using 2 ml of N-methylpyrrolidone as solvent, the mixture was ground for 0.5 h. A 400-micron doctor blade was used to coat the mixture onto titanium foil to form a film. The film was then dried in a 75°C forced-air drying oven for 4 h, followed by overnight drying in a 100°C vacuum drying oven. The film was then sliced, weighed, and prepared as a coin cell. The electrode sheet is used as the negative electrode. Weigh out Cu[Fe(CN)6]. 0.63 · 0.8 g of 3,4H₂O and 0.1 g of SuperP were added to 2 g of polyvinylidene fluoride (PVDF, 5%) solution. Following the above method (using 2 ml of N-methylpyrrolidone as solvent, grinding for 0.5 h, then coating onto titanium foil with a 400 μm doctor blade, drying in a 75°C forced-air drying oven for 4 h, then transferring to a 100°C vacuum drying oven for overnight drying, slicing, weighing, and preparing the final product). An α-MoO3 electrode sheet was used as the positive electrode. A three-electrode system was assembled using an α-MoO3 electrode sheet as the working electrode, a Pt wire as the counter electrode, and a Hg / Hg2SO4 electrode as the reference electrode to protonate the α-MoO3, ensuring full proton embedding within the α-MoO3 material. Subsequently, the protonated α-MoO3 electrode sheet was used as the negative electrode, along with Cu[Fe(CN)6]. 0.63 • 3.4H2O electrode sheet is the positive electrode; the low-water-activity hydrogel membrane prepared in this embodiment (cut into…) Using a quasi-solid-state electrolyte, coin cells were assembled at 0.2 A·g -1(Calculated based on the mass of α-MoO3) The charge-discharge rate was used for testing within a voltage range of 0.2–1.4V. The corresponding charge-discharge curves are shown below. Figure 1 As shown, the results indicate that the full battery exhibits a capacity of 199 mAh·g. -1 The discharge specific capacity is [value missing], and the coulombic efficiency is 99.2%. The cycle performance curves are shown below. Figure 2 As shown, after 20 cycles, the discharge specific capacity is 190 mAh·g. -1 The capacity retention rate was 95.5% (calculated based on the discharge specific capacity in the second week).

[0033] Example 2

[0034] Weigh out 10g of acrylamide, 3g of 2-acrylamide-2-methylpropanesulfonic acid, and 60mg of N,N-methylenebisacrylamide, and disperse them in 14ml of 3mol·L⁻¹ solution. -1 After sonicating in an aqueous solution of H2SO4 for 0.5 h, 20 mg of 2-oxo-1,5-glutaric acid was added as a photoinitiator and stirred until homogeneous. The resulting dispersion was then poured into a mold, and the reaction was initiated with ultraviolet light. After irradiation for 2 h, the resulting hydrogel membrane was dried in a vacuum drying oven at 60 °C for 10 h to obtain a low-water-activity hydrogel membrane with a thickness of 0.2 mm.

[0035] The assembly and testing of the button cell were the same as in Example 1, except that the charge / discharge rate was 0.4 A·g. -1 (Calculated based on the mass of α-MoO3). The corresponding charge-discharge curves are as follows: Figure 3 As shown, the results indicate that the full battery exhibits a capacity of 182 mAh·g. -1 The discharge specific capacity is [value missing], and the coulombic efficiency is 94.2%. The cycle performance curves are shown below. Figure 4 As shown, after 40 cycles, the discharge specific capacity is 162 mAh·g. -1 The capacity retention rate was 89.0% (calculated based on the discharge specific capacity in the second week).

[0036] Example 3

[0037] Weigh out 20g of methacrylic acid and 0.4g of N,N-methylenebisacrylamide and disperse them in 20ml of 3mol·L⁻¹ solution. - 1 The mixture was sonicated in an aqueous solution of H2SO4 for 0.5 h, and 0.2 g of ammonium persulfate was added as a chemical initiator. After stirring evenly, the mixture was poured into a mold and placed in an oil bath at 70 °C for 6 h. The resulting hydrogel was then dried in a vacuum drying oven at 80 °C for 8 h to obtain a low-water-activity hydrogel film with a thickness of 0.2 mm.

[0038] The assembly and testing of the button cell were the same as in Example 1, except that the charge / discharge rate was 0.4 A·g.-1 (Calculated based on the mass of α-MoO3). The corresponding charge-discharge curves are as follows: Figure 5 As shown, the results indicate that the full battery exhibits a capacity of 186 mAh·g. -1 The discharge specific capacity is [value missing], and the coulombic efficiency is 94.6%. The cycle performance curves are shown below. Figure 6 As shown, after 50 cycles, the discharge specific capacity is 157 mAh·g. -1 The capacity retention rate was 84.4% (calculated based on the discharge specific capacity in the second week).

[0039] Example 4

[0040] Weigh out 15g of polyvinyl alcohol and 15g of acrylic acid and disperse them in 30ml of 3mol·L⁻¹ solution. -1 The mixture was sonicated in an aqueous H₂SO₄ solution for 1 hour, and 0.15 g of ammonium persulfate was added as a chemical initiator. The resulting dispersion was mechanically stirred in a 90°C oil bath for 1 hour to form a homogeneous liquid. Then, the concentrated liquid was poured into a mold and reacted in a 50°C oil bath for 2 hours. The resulting hydrogel was dried in a vacuum drying oven at 80°C for 5 hours to obtain a low-water-activity hydrogel film with a thickness of 0.2 mm.

[0041] The assembly and testing of the button cell were the same as in Example 1, except that the charge / discharge rate was 0.4 A·g. -1 (Calculated based on the mass of α-MoO3), the charge / discharge voltage range is 0.2–1.5V. The corresponding charge / discharge curves are as follows: Figure 7 As shown, the results indicate that the full battery exhibits a capacity of 191 mAh·g. -1 The discharge specific capacity is [value missing], and the coulombic efficiency is 93.1%. The cycle performance curves are shown below. Figure 8 As shown, after 15 cycles, the discharge specific capacity is 183 mAh·g. -1 The capacity retention rate was 95.8% (calculated based on the discharge specific capacity in the first week).

Claims

1. A method for preparing a low-water-activity hydrogel membrane, characterized in that: Includes the following steps: Step 1: Mix the crosslinking agent and the acidic aqueous solution to remove air bubbles from the resulting liquid; Step 2: Add the initiator to the liquid obtained in Step 1, stir and mix evenly, then pour into a film forming mold and polymerize to obtain a low-water-activity hydrogel film; Step 3: Dry and heat treat the membrane obtained in Step 2.

2. The preparation method according to claim 1, characterized in that: The crosslinking agent selected in step 1 is one or a mixture of two or more of polyvinyl alcohol, acrylamide, acrylic acid, methacrylic acid, [(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 2-acrylamido-2-methylpropanesulfonic acid, N,N-methylenebisacrylamide, and polyethylene glycol dimethacrylate; more preferably, it is one or more of polyvinyl alcohol, acrylamide, methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, N,N-methylenebisacrylamide, and acrylic acid.

3. The preparation method according to claim 1, characterized in that: The acidic aqueous solution selected in step 1 is one or more of sulfuric acid, nitric acid, hydrochloric acid, or phosphoric acid aqueous solution; sulfuric acid is more preferred. The concentration is 0.1 mol·L -1 ~4mol·L -1 Further optimization of 2-3 mol·L -1 .

4. The preparation method according to claim 1, 2, or 3, characterized in that: In step 1, the mass ratio of crosslinking agent to acidic aqueous solution is 2 to 10:3, more preferably 2 to 5:

3.

5. The preparation method according to claim 1, characterized in that: In step 1, the bubbles in the obtained liquid are removed by ultrasonic treatment for 0.2 to 1 hour, preferably 0.2 to 0.6 hours.

6. The preparation method according to claim 1, characterized in that: The initiator selected in step 2 is one or more of glutaraldehyde, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, 2-oxo-1,5-glutaric acid, benzoyl peroxide, azobisisobutyronitrile, ammonium persulfate, or potassium persulfate, and is more preferably one or more of glutaraldehyde, 2-oxo-1,5-glutaric acid, ammonium persulfate, or potassium persulfate; the mass ratio of initiator to liquid obtained in step 1 in step 2 is 1:100 to 2000, and is more preferably 1:200 to 1500.

7. The preparation method according to claim 1 or 6, characterized in that: The polymerization in step 2 can be classified into one or more of photopolymerization, thermal polymerization or catalytic polymerization, depending on the reaction conditions. The conditions used for polymerization are determined by the initiator selected. Photopolymerization is carried out under ultraviolet or visible light conditions for 0.5 to 4 hours (more preferably 1 to 3 hours). The thermal polymerization is carried out under heating conditions, with a heat treatment temperature of 40–110°C (more preferably, 70–100°C) and a heat treatment time of 0.5–12 h (more preferably, 3–6 h). Catalytic polymerization was carried out at room temperature, and the polymerization time was 5–50 h (10–30 h).

8. The preparation method according to claim 1, characterized in that: In step 3, the drying heat treatment temperature is 50-100℃ (more preferably, 60-80℃), and the heat treatment time is 4-24h (more preferably, 5-10h).

9. A low-water-activity hydrogel membrane prepared by the preparation method of claim 1.

10. The application of the low-water-activity hydrogel membrane of claim 9 as a proton battery electrolyte.

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