Semi-interpenetrating network structure hydrogel with high water retention rate as well as preparation method and application of semi-interpenetrating network structure hydrogel

Abstract

The invention discloses a semi-interpenetrating network structure hydrogel with a high water retention rate as well as a preparation method and application of the semi-interpenetrating network structure hydrogel. The hydrogel is prepared through a free radical polymerization method, guar gum is used for constructing a high-water-retention framework, a large number of hydrophilic functional groups are provided, hydrogen bonds are formed between the hydrophilic functional groups and water molecules, and the water retention capacity of the hydrogel is enhanced. In addition, by introducing the hygroscopic ionic liquid, the water retention effect is further enhanced, a large number of ion transport channels are provided, and a chemical crosslinking-semi-interpenetrating network-ionic liquid enhanced stable network structure is formed. The hydrogel electrolyte shows excellent water retention capacity, and when the hydrogel electrolyte is applied to the flexible zinc-air battery, the service life of the battery can be remarkably prolonged, the specific capacity of the battery can be remarkably improved, and the peak power density of the battery can be enhanced. The method is simple in process and environment-friendly, and has a good application prospect in wearable energy storage equipment.

Description

Technical Field

[0001] This invention relates to the field of flexible zinc-air battery technology, specifically to a semi-interpenetrating network structure hydrogel with high water retention, its preparation method, and its application. Background Technology

[0002] Flexible zinc-air batteries offer numerous advantages, including high theoretical energy density, high environmental compatibility, low cost, and stable voltage output, making them an ideal choice for designing wearable flexible power supplies. The electrolyte, a crucial intermediary between the zinc negative electrode and the air positive electrode, plays a vital role in ion transport and maintaining ionic conductivity and battery stability. The gel polymer electrolyte, existing in an intermediate state between liquid and solid, avoids electrolyte leakage and effectively enhances the safety of zinc-air batteries.

[0003] However, due to the semi-open structure of zinc-air batteries exposed to air, the water in the hydrogel evaporates rapidly, causing electrolyte dehydration and shrinkage, leading to a decrease in properties such as ionic conductivity and tensile strength, and even electrolyte failure. Currently, there is limited research on water-retaining hydrogel electrolytes, and those that exist have drawbacks such as rapid water loss, poor water retention, and low ionic conductivity. To address the aforementioned issues, researchers have improved the water retention of hydrogels by introducing inorganic salts, organic substances, and ionic liquids. For example, in the patent "A High Water Retention Dual-Network Hydrogel Electrolyte and Its Preparation Method and Application" (application number CN202410300114.1), high-concentration sodium chloride is added during the hydrogel preparation process to enhance its water retention. The hydrogel with added sodium chloride, after being left at room temperature for 140 hours, maintained a water retention rate of approximately 85%, an increase of about 1% compared to the sample without sodium chloride. In the patent "A Ternary Composite Hydrogel Electrolyte Reinforced by Hyaluronic Acid and Its Application in Flexible Zinc-Air Batteries" (application number CN202510681215.2), hyaluronic acid is introduced to enhance the electrolyte performance of the hydrogel. Due to the hydrogen bond network formed by the oxygen-containing functional groups in hyaluronic acid, the hydrogel electrolyte retains 56.8% water content after 48 hours, effectively suppressing electrolyte water evaporation. In the paper "A multifunctional ILhydrogel electrolyte for zinc anode-stabilized flexible...", further research is conducted. In the paper "zinc-air batteries over a wide temperature range" (DOI: 10.1016 / j.est.2025.116985), 1-butyl-3-methylimidazolium bromide was added to the hydrogel electrolyte. Due to the hydrophilicity of the ionic liquid, the prepared hydrogel electrolyte had a water retention rate of 81.2% after 50 h, indicating relatively limited improvement in water retention performance and significant room for further optimization. In the paper "Superstretchability and satisfactory water retention capacity via a dual-crosslinked hydrogel electrolyte for wide-temperature flexible zinc-airbatteries" (DOI: 10.1016 / j.cej.2024.155539), k-carrageenan was integrated into a polyacrylic acid network to develop a chemical-physical dual-crosslinked network hydrogel electrolyte. After 107 h of exposure to air, the water retention rate exceeded 60%. However, the key hydrophilic site in k-carrageenan—OSO3—remains unreliable. -It readily binds to cations in electrolytes, weakening its hydration capacity. Furthermore, its water retention mainly relies on the initial moisture retained in the hydrogel, and it cannot actively acquire moisture from the environment. Therefore, its improvement in water retention performance is relatively limited and further optimization is still needed.

[0004] This invention proposes a high water-retention semi-interpenetrating network hydrogel, its preparation method, and its application. By introducing guar gum to refine the hydrogel's pore structure and adding a hygroscopic imidazole ionic liquid, the hydrogel actively captures moisture from the air through ion-pair interactions between its anions and cations and water molecules, forming a multi-type, high-density synergistic hydrophilic network. This enhances the effective hydration capacity per unit volume, thereby significantly improving the hydrogel's water retention. After 484 hours in a constant temperature and humidity chamber (20℃, 30% relative humidity), the water retention rate was 90.14%, an increase of 11.65% compared to the 78.65% water retention rate of the hydrogel without guar gum and the hygroscopic imidazole ionic liquid. Even after 5 days at room temperature, the ionic conductivity remained at 180.51 mS / cm, demonstrating excellent water retention and ionic conductivity. This hydrogel was applied in a zinc-air battery, achieving a cycle life of 245 hours and a power density of 231 mW / cm². 2 The discharge specific capacity reaches 745 mAh / g, providing technical support for the practical application of flexible zinc-air batteries. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a semi-interpenetrating network structured hydrogel with high water retention, its preparation method, and its applications. The preparation method uses a polyacrylamide / sodium acrylate chemical cross-linked network as the basic structural framework. Guar gum is added as a semi-interpenetrating network, and a hygroscopic imidazole ionic liquid is introduced to conduct a free radical polymerization reaction. Utilizing a simple process and natural, environmentally friendly raw materials, this method achieves the preparation of a hydrogel electrolyte with excellent water retention.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a semi-interpenetrating network structure hydrogel with high water retention, characterized by comprising the following preparation steps: Substrate synthesis: Acrylamide was added to deionized water and stirred to prepare an acrylamide solution. Then, sodium hydroxide solution was slowly added dropwise to liquid acrylic acid under ice bath conditions and magnetically stirred to obtain a sodium acrylate solution. The two solutions were mixed to obtain an acrylamide-sodium acrylate hydrogel substrate.

[0007] Construction of the semi-interpenetrating network structure: Guar gum powder was heated and stirred in deionized water to prepare a guar gum presol. The guar gum presol cooled to room temperature and a hygroscopic ionic liquid were added to an acrylamide-sodium acrylate hydrogel substrate. Subsequently, a crosslinking agent and an initiator were added. After a free radical polymerization crosslinking reaction was carried out under vacuum conditions, the substrate was immersed in an alkaline electrolyte to swell. After swelling was completed, a layer of hygroscopic ionic liquid was brushed onto the surface of the hydrogel to obtain a polyacrylamide / sodium acrylate-guar gum-ionic liquid semi-interpenetrating network hydrogel.

[0008] Preferably, the concentration of the guar gum solution is 0.005~0.05 g / mL, and the temperature during heating and stirring is 60~90℃; The concentration of the sodium acrylate solution is 30-60 wt%, and the concentration of the acrylamide solution is 10-40 wt%. The molar ratio of acrylamide to sodium acrylate in the acrylamide-sodium acrylate hydrogel substrate is 1:2 to 3:1. The hygroscopic ionic liquid includes one or more of 1-ethyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride, 1-octyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate, 1-hexyl-3-methylimidazolium acetate, 1-octyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium bromide, 1-hexyl-3-methylimidazolium bromide, and 1-octyl-3-methylimidazolium bromide.

[0009] Preferably, the mass ratio of the added guar gum to the hygroscopic ionic liquid is 1:5 to 1:15.

[0010] The method for preparing the high water retention semi-interpenetrating network structure hydrogel electrolyte is characterized in that the crosslinking agent is N,N'-methylenebisacrylamide, and the amount added is 0.03-0.16 wt% of the total hydrogel. The initiator is one or more of ammonium persulfate, potassium persulfate, and sodium persulfate, and the amount added is 0.05~0.3 wt% of the total hydrogel. The reaction temperature during the free radical polymerization crosslinking reaction is 40–80°C, and the reaction time is 5–12 h. The alkaline electrolyte is a mixed solution of 5-7M NaOH and 0.1-0.3M (CH3COO)2Zn; This invention provides a semi-interpenetrating network hydrogel electrolyte with high water retention prepared by the method described in the above technical solution. The semi-interpenetrating network hydrogel has a water retention rate of 90.14% and an ionic conductivity of 226.38 mS / cm after being placed in a constant temperature and humidity chamber (20℃, 30% relative humidity) for 484 h. After being placed at room temperature for 5 days, the ionic conductivity still reaches 180.51 mS / cm. The initial tensile strain of the hydrogel is 705%, and after being placed at room temperature for 5 days, the tensile strain still reaches 586%, which is 83% of the initial tensile strain.

[0011] In this invention, the system's ability to bind water molecules is enhanced through multi-component synergistic effects, endowing the hydrogel with excellent water retention capacity. The high water retention rate semi-interpenetrating network structure hydrogel electrolyte utilizes multiple mechanisms—chemical cross-linking network, semi-interpenetrating physical network, and ionic liquid reinforcement—to collectively improve the hydrogel's water retention effect. Acrylamide and sodium acrylate undergo free radical polymerization under the action of an initiator, with the cross-linking agent N,N'-methylenebisacrylamide providing covalent cross-linking sites to form a three-dimensional network structure. In the polyacrylamide / sodium acrylate substrate, the carboxyl anion (—COO) of sodium acrylate... - As a strongly hydrophilic site, guar gum can adsorb the hydrogen terminals of water molecules. The amide group (-CONH2) of acrylamide forms a hydrogen bond network with water molecules and the carboxyl group of sodium acrylate through hydrogen bonds. The semi-interpenetrating network is the entanglement between the guar gum macromolecular chain and the acrylamide-sodium acrylate crosslinking system. As a semi-interpenetrating network, it runs through the main network. The introduction of guar gum plays a key role in the hydrogel. Guar gum contains a large number of hydroxyl groups, which can bind to water molecules through hydrogen bonds and firmly bind to the free water in the hydrogel, converting it into bound water that is not easy to "escape". In addition, guar gum and polyacrylamide / sodium acrylate form a large number of hydrogen bonds and entangle with each other to construct a semi-interpenetrating hydrogel with smaller pore size and denser structure, which reduces the formation of large-sized water transport channels and prolongs the "escape" path of water molecules. Furthermore, ionic liquids also play a positive role in water retention. In this invention, imidazole ionic liquids with good hygroscopicity are selected as functional additives. Their molecular structure includes a positively charged imidazole ring and an anion. The nitrogen atom on the imidazole ring and the alkyl chain endow the cation with a certain polarity, giving the ionic liquid a high hydration capacity. Compared with the limited passive water retention function of traditional hydrogels, hygroscopic imidazole ionic liquids can actively capture moisture from the air, breaking the limitation of hydrogels relying on moisture retention. At the same time, ionic liquids are molten salts themselves, providing a large number of ion transport channels, which enhances the water retention of hydrogels while giving them excellent ionic conductivity.

[0012] The semi-interpenetrating network structure hydrogel electrolyte with high water retention capacity described in this invention effectively improves the performance of flexible zinc-air batteries. Its features include an operating voltage of 1.6 V, a cycle life of 245 h, a specific capacity of 744.98 mAh / g, and a power density of 231 mW / cm³. 2 .

[0013] The preparation method described in this invention is simple, low-cost, and environmentally friendly. It effectively constructs the water-retention properties of hydrogels and effectively solves the problems of rapid water loss, short working life, and complex processes in traditional methods for semi-solid electrolytes in zinc-air batteries. Attached Figure Description

[0014] Figure 1 This is an optical image of the high water retention semi-interpenetrating network structure hydrogel described in Example 2; Figure 2 These are 10-day shape monitoring photos of the high water retention semi-interpenetrating network structure hydrogel described in Example 2; Figure 3 The water retention rate monitoring curves of the five hydrogels described in Comparative Examples 1-2 and Examples 1-3 within 484 h are shown. Figure 4 The AC impedance spectra of the five hydrogels described in Comparative Examples 1-2 and Examples 1, 2, and 4 are shown. Figure 5 The diagram shows the ionic conductivity of the five hydrogels described in Comparative Examples 1-2 and Examples 1, 2, and 4. Figure 6 This is the AC impedance spectrum of the high water retention semi-interpenetrating network structure hydrogel described in Example 2 after 5 days of storage. Figure 7 This is a graph showing the change in ionic conductivity of the high water retention semi-interpenetrating network structure hydrogel described in Example 2 after 5 days of storage. Figure 8 The displacement-tensile strength curves were measured for the four hydrogel tensile fracture states described in Comparative Examples 1-2 and Examples 1-2. Figure 9 This is the displacement-tensile strength curve of the high water retention semi-interpenetrating network structure hydrogel described in Example 2, measured after 5 days of tensile fracture. Figure 10 The constant current charge-discharge curves of zinc-air batteries using the five types of hydrogels as electrolytes as described in Comparative Examples 1-2 and Examples 1, 2, and 4 are shown. Figure 11 The open-circuit voltage curves of zinc-air batteries using the three hydrogels described in Comparative Example 1, Comparative Example 2, and Example 2 as electrolytes are shown. Figure 12The constant current discharge curves of zinc-air batteries using the three hydrogels described in Comparative Example 1, Comparative Example 2, and Example 2 as electrolytes are shown. Figure 13 The power density curves of zinc-air batteries using the four hydrogels described in Comparative Example 1, Comparative Example 2, Example 2, and Example 4 as electrolytes are shown. Detailed Implementation

[0015] The technical solution provided by the present invention will be further described clearly and completely below with reference to the accompanying drawings and embodiments.

[0016] This invention provides a method for preparing a semi-interpenetrating network structure hydrogel with high water retention, characterized by comprising the following preparation steps: Substrate synthesis: Acrylamide was added to deionized water and stirred to prepare an acrylamide solution. Then, sodium hydroxide solution was slowly added dropwise to liquid acrylic acid under ice bath conditions and magnetically stirred to obtain a sodium acrylate solution. The two solutions were mixed to obtain an acrylamide-sodium acrylate hydrogel substrate.

[0017] Construction of the semi-interpenetrating network structure: Guar gum powder was heated and stirred in deionized water to prepare a guar gum presol. The guar gum presol cooled to room temperature was mixed with a hygroscopic ionic liquid and added to an acrylamide-sodium acrylate hydrogel substrate. Subsequently, a crosslinking agent and an initiator were added. After a free radical polymerization crosslinking reaction was carried out under vacuum conditions, the substrate was immersed in an alkaline electrolyte to swell. Then, an ionic liquid was brushed onto the surface of the hydrogel to obtain a polyacrylamide / sodium acrylate-guar gum-ionic liquid semi-interpenetrating network hydrogel.

[0018] In this invention, the concentration of the guar gum solution is 0.005~0.05 g / mL, and a guar gum pre-solution is obtained by heating and stirring in a water bath at a temperature of 60~90℃; the concentration of the sodium acrylate solution is 20~50 wt%, and the concentration of the acrylamide solution is 10~40 wt%; the molar ratio of acrylamide to sodium acrylate in the acrylamide-sodium acrylate hydrogel substrate is 1:2~3:1; preferably, the mass ratio of the added guar gum to the hygroscopic ionic liquid is 1:10~1:30; the crosslinking agent is N,N'-methylenebisacrylamide, and the amount added is 0.03~0.16 wt% of the total hydrogel; the initiator is one or more of ammonium persulfate, potassium persulfate, and sodium persulfate, and the amount added is 0.05~0.3 wt% of the total hydrogel. In this invention, the hygroscopic ionic liquid includes one or more of 1-ethyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride, 1-octyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate, 1-hexyl-3-methylimidazolium acetate, 1-octyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium bromide, 1-hexyl-3-methylimidazolium bromide, and 1-octyl-3-methylimidazolium bromide.

[0019] In this invention, the steps of ice bath stirring, heating and dissolving, cooling, and drying are not particularly limited, and processes well known to those skilled in the art can be used. In this invention, the reaction temperature during the free radical polymerization crosslinking reaction is 40-80℃, and the reaction time is 5-12 h; the alkaline electrolyte is a mixed solution of 5-7M NaOH and 0.1-0.3M (CH3COO)2Zn.

[0020] The present invention does not impose any particular limitation on the application method of the high water retention semi-interpenetrating network structure hydrogel. The application method of hydrogel in zinc-air battery electrolyte materials that is well known to those skilled in the art can be used.

[0021] The following detailed description, in conjunction with embodiments, illustrates a method for preparing a high water-retention semi-interpenetrating network structure hydrogel according to the present invention. These embodiments are only some examples of the present invention and do not include all examples. All other embodiments obtained by those skilled in the art based on these embodiments without inventive effort are within the scope of protection of the present invention.

[0022] Comparative Example 1 (1) Dissolve 2.77 g of sodium hydroxide in 10 mL of deionized water to obtain a sodium hydroxide solution. Add 5 g of acrylic acid dropwise under ice bath conditions and stir at high speed for 1 h to avoid excessive temperature caused by the exothermic reaction of acid-base neutralization, so as to obtain a sodium acrylate pre-solution with a concentration of 36.7 wt%.

[0023] (2) Dissolve 3 g of acrylamide monomer in 15 mL of deionized water and stir for 30 min to ensure that the acrylamide is more uniformly dispersed in the system, and obtain a pre-solution of acrylamide with a concentration of 16.7 wt%.

[0024] (3) Mix the solutions obtained in steps (1) and (2) and stir the mixture on a magnetic stirrer for 4 hours to ensure thorough stirring.

[0025] (4) Add 1 mL of 0.25 Mn, N'-methylenebisacrylamide pre-solution to the mixed solution obtained in step (3) and continue stirring for 2 h to disperse it evenly. Transfer the well-mixed reaction solution to a special petri dish, then add 1 mL of 0.35 M ammonium persulfate pre-solution and gently shake to mix.

[0026] (5) Nitrogen gas was introduced for 5 min to remove dissolved oxygen, and the reaction was allowed to stand in a vacuum oven at 60℃ for 8 h. After the reaction was completed, a transparent hydrogel with good elasticity was obtained. It was taken out and the surface of the hydrogel was gently rinsed with deionized water to remove unreacted monomers and impurities, and finally a pure polyacrylamide-sodium acrylate hydrogel was obtained.

[0027] Comparative Example 2 (1) 0.1 g of guar gum powder was dispersed in 15 mL of deionized water under vigorous stirring, and heated and stirred in an 80°C water bath for 2 h to allow it to fully swell, resulting in a homogeneous guar gum pre-solution with a concentration of 0.0067 g / mL. This step was intended to pre-dissolve the guar gum molecular chains to avoid clumping when directly mixed with monomers.

[0028] (2) Dissolve 2.77 g of solid sodium hydroxide in 10 mL of deionized water to obtain a sodium hydroxide solution. Add 5 g of acrylic acid dropwise under ice bath conditions and stir at high speed for 1 h to reduce the excessive temperature caused by the exothermic reaction of acid-base neutralization, thereby obtaining a pre-solution of acrylamide with a concentration of 16.7 wt%. Dissolve 3 g of acrylamide monomer in 15 mL of deionized water and stir for 30 min to ensure that the acrylamide is more uniformly dispersed in the system, thereby obtaining a pre-solution of acrylamide with a concentration of 16.7 wt%.

[0029] (3) The sodium acrylate pre-solution obtained in step (2) is mixed with the acrylamide pre-solution, and the mixture is continuously stirred on a magnetic stirrer for 4 hours to ensure thorough stirring.

[0030] (4) After the guar gum pre-solution in step (1) is cooled to room temperature, it is added to the mixed solution obtained in step (3) to obtain an acrylamide / sodium acrylate-guar gum mixed solution. The mixed solution is continuously stirred on a magnetic stirrer for 4 h to ensure that the acrylamide, sodium acrylate and guar gum molecular chains are fully mixed and pre-assembled.

[0031] (5) Add 1 mL of 0.25 M N,N'-methylenebisacrylamide (MBAA) pre-solution to the mixed solution obtained in step (4) and continue stirring for 30 min to disperse it evenly. Transfer the well-mixed reaction solution to a special petri dish, then add 1 mL of 0.35 M ammonium persulfate pre-solution and gently shake to mix.

[0032] (6) Immediately introduce high-purity nitrogen gas for 5 min to remove dissolved oxygen from the system, and let it stand in a vacuum oven at 60℃ for 8 h. After the reaction is complete, a transparent hydrogel with good elasticity is obtained. Take it out and gently rinse the surface with deionized water to remove unreacted monomers and impurities, and finally obtain a pure polyacrylamide / sodium acrylate-guar gum semi-interpenetrating network hydrogel.

[0033] Example 1 (1) Disperse 0.1 g of guar gum powder in 15 ml of deionized water under vigorous stirring, and heat and stir in an 80°C water bath for 2 h to ensure that the guar gum powder is fully swollen, so as to obtain a guar gum pre-solution with a concentration of 0.0067 g / mL.

[0034] (2) Dissolve 2.77 g of solid sodium hydroxide in 10 mL of deionized water to obtain a sodium hydroxide solution. Add 5 g of acrylic acid dropwise under ice bath conditions and stir at high speed for 1 h to obtain a sodium acrylate pre-solution with a concentration of 36.7 wt%. Dissolve 3 g of acrylamide monomer in 15 mL of deionized water and stir for 30 min to ensure that the acrylamide is more uniformly dispersed in the system to obtain an acrylamide pre-solution with a concentration of 16.7 wt%.

[0035] (3) Mix the sodium acrylate pre-solution obtained in step (2) with the acrylamide pre-solution, and stir the mixture on a magnetic stirrer for 4 hours to ensure thorough stirring.

[0036] (4) Add the guar gum pre-solution cooled to room temperature in step (1) and 0.5 g of ionic liquid (1-ethyl-3-methylimidazolium chloride) as a functional additive to the mixed solution obtained in step (3) to obtain an acrylamide / sodium acrylate-guar gum-ionic liquid mixed solution. Stir the mixed solution on a magnetic stirrer for 4 h to ensure that the acrylamide, sodium acrylate, ionic liquid and guar gum molecular chains are fully mixed and pre-assembled.

[0037] (5) Add 1 mL of 0.25 Mn, N'-methylenebisacrylamide pre-solution to the mixed solution obtained in step (4) and continue stirring for 30 min to disperse it evenly. Transfer the well-mixed reaction solution to a special petri dish, then add 1 mL of 0.35 M ammonium persulfate pre-solution and gently shake to mix.

[0038] (6) Immediately introduce high-purity nitrogen gas for 5 min to remove dissolved oxygen from the system, and let it stand in a vacuum oven at 60℃ for 8 h. After the reaction is complete, a transparent hydrogel with good elasticity is obtained. Take it out and gently rinse the surface with deionized water to remove unreacted monomers and impurities, and finally obtain a pure polyacrylamide / sodium acrylate-guar gum-ionic liquid semi-interpenetrating network hydrogel.

[0039] Example 2 (1) Disperse 0.1 g of guar gum powder in 15 ml of deionized water under vigorous stirring, and heat and stir in an 80°C water bath for 2 h to ensure that the guar gum powder is fully swollen, so as to obtain a guar gum pre-solution with a concentration of 0.0067 g / mL.

[0040] (2) Dissolve 2.77 g of solid sodium hydroxide in 10 mL of deionized water to obtain a sodium hydroxide solution. Add 5 g of acrylic acid dropwise under ice bath conditions and stir at high speed for 1 h to obtain a sodium acrylate pre-solution with a concentration of 36.7 wt%. Dissolve 3 g of acrylamide monomer in 15 mL of deionized water and stir for 30 min to ensure that the acrylamide is more uniformly dispersed in the system to obtain an acrylamide pre-solution with a concentration of 16.7 wt%.

[0041] (3) Mix the sodium acrylate pre-solution obtained in step (2) with the acrylamide pre-solution, and stir the mixture on a magnetic stirrer for 4 hours to ensure thorough stirring.

[0042] (4) Add the guar gum pre-solution cooled to room temperature in step (1) and 1 g of ionic liquid ((1-ethyl-3-methylimidazolium chloride)) as a functional additive to the mixed solution obtained in step (3) to obtain an acrylamide / sodium acrylate-guar gum-ionic liquid mixed solution. Stir the mixed solution on a magnetic stirrer for 4 h to ensure that the acrylamide, sodium acrylate, ionic liquid and guar gum molecular chains are fully mixed and pre-assembled.

[0043] (5) Add 1 mL of 0.25 Mn, N'-methylenebisacrylamide (MBAA) pre-solution to the mixed solution obtained in step (4) and continue stirring for 30 min to disperse it evenly. Transfer the well-mixed reaction solution to a special petri dish, then add 1 mL of 0.35 M ammonium persulfate pre-solution and gently shake to mix.

[0044] (6) Immediately introduce high-purity nitrogen gas for 5 min to remove dissolved oxygen from the system, and let it stand in a vacuum oven at 60℃ for 8 h. After the reaction is complete, a transparent hydrogel with good elasticity is obtained. Take it out and gently rinse the surface with deionized water to remove unreacted monomers and impurities, and finally obtain a pure polyacrylamide / sodium acrylate-guar gum-ionic liquid semi-interpenetrating network hydrogel.

[0045] Example 3 (1) Disperse 0.1 g of guar gum powder in 15 ml of deionized water under vigorous stirring, and heat and stir in an 80°C water bath for 2 h to ensure that the guar gum powder is fully swollen, so as to obtain a guar gum pre-solution with a concentration of 0.0067 g / mL.

[0046] (2) Dissolve 2.77 g of sodium hydroxide in 10 mL of deionized water to obtain a sodium hydroxide solution. Add 5 g of acrylic acid dropwise under ice bath conditions and stir at high speed for 1 h to obtain a sodium acrylate pre-solution with a concentration of 36.7 wt%. Dissolve 3 g of acrylamide monomer in 15 mL of deionized water and stir for 30 min to ensure that the acrylamide is more uniformly dispersed in the system to obtain an acrylamide pre-solution with a concentration of 16.7 wt%.

[0047] (3) Mix the sodium acrylate pre-solution obtained in step (2) with the acrylamide pre-solution, and stir the mixture on a magnetic stirrer for 4 hours to ensure thorough stirring.

[0048] (4) Add the guar gum pre-solution cooled to room temperature in step (1) and 1.5 g of ionic liquid ((1-ethyl-3-methylimidazolium chloride)) as a functional additive to the mixed solution obtained in step (3) to obtain an acrylamide / sodium acrylate-guar gum-ionic liquid mixed solution. Stir the mixed solution on a magnetic stirrer for 4 h to ensure that the acrylamide, sodium acrylate, ionic liquid and guar gum molecular chains are fully mixed and pre-assembled.

[0049] (5) Add 1 mL of 0.25 Mn, N'-methylenebisacrylamide (MBAA) pre-solution to the mixed solution obtained in step (4) and continue stirring for 30 min to disperse it evenly. Transfer the well-mixed reaction solution to a special petri dish, then add 1 mL of 0.35 M ammonium persulfate pre-solution and gently shake to mix.

[0050] (6) Immediately introduce high-purity nitrogen gas for 5 min to remove dissolved oxygen from the system, and let it stand in a vacuum oven at 60℃ for 8 h. After the reaction is complete, a transparent hydrogel with good elasticity is obtained. Take it out and gently rinse the surface with deionized water to remove unreacted monomers and impurities, and finally obtain a pure polyacrylamide / sodium acrylate-guar gum-ionic liquid semi-interpenetrating network hydrogel.

[0051] Example 4 (1) Disperse 0.15 g of guar gum powder in 15 ml of deionized water under vigorous stirring, and heat and stir in an 80°C water bath for 2 h to ensure that the guar gum powder is fully swollen, so as to obtain a guar gum pre-solution with a concentration of 0.01 g / mL.

[0052] (2) Dissolve 2.77 g of sodium hydroxide in 10 mL of deionized water to obtain a sodium hydroxide solution. Add 5 g of acrylic acid dropwise under ice bath conditions and stir at high speed for 1 h to obtain a sodium acrylate pre-solution with a concentration of 36.7 wt%. Dissolve 3 g of acrylamide monomer in 15 mL of deionized water and stir for 30 min to ensure that the acrylamide is more uniformly dispersed in the system to obtain an acrylamide pre-solution with a concentration of 16.7 wt%.

[0053] (3) Mix the sodium acrylate pre-solution obtained in step (2) with the acrylamide pre-solution, and stir the mixture on a magnetic stirrer for 4 hours to ensure thorough stirring.

[0054] (4) Add the guar gum pre-solution cooled to room temperature in step (1) and 1 g of ionic liquid ((1-ethyl-3-methylimidazolium chloride)) as a functional additive to the mixed solution obtained in step (3) to obtain an acrylamide / sodium acrylate-guar gum-ionic liquid mixed solution. Stir the mixed solution on a magnetic stirrer for 4 h to ensure that the acrylamide, sodium acrylate, ionic liquid and guar gum molecular chains are fully mixed and pre-assembled.

[0055] (5) Add 1 mL of 0.25 Mn, N'-methylenebisacrylamide (MBAA) pre-solution to the mixed solution obtained in step (4) and continue stirring for 30 min to disperse it evenly. Transfer the well-mixed reaction solution to a special petri dish, then add 1 mL of 0.35 M ammonium persulfate pre-solution and gently shake to mix.

[0056] (6) Immediately introduce high-purity nitrogen gas for 5 min to remove dissolved oxygen from the system, and let it stand in a vacuum oven at 60℃ for 8 h. After the reaction is complete, a transparent hydrogel with good elasticity is obtained. Take it out and gently rinse the surface with deionized water to remove unreacted monomers and impurities, and finally obtain a pure polyacrylamide / sodium acrylate-guar gum-ionic liquid semi-interpenetrating network hydrogel.

[0057] Example 5 (1) Disperse 0.1 g of guar gum powder in 15 ml of deionized water under vigorous stirring, and heat and stir in an 80°C water bath for 2 h to ensure that the guar gum powder is fully swollen, so as to obtain a guar gum pre-solution with a concentration of 0.0067 g / mL.

[0058] (2) Dissolve 2.77 g of sodium hydroxide in 10 mL of deionized water to obtain a sodium hydroxide solution. Add 5 g of acrylic acid dropwise under ice bath conditions and stir at high speed for 1 h to obtain a sodium acrylate pre-solution with a concentration of 36.7 wt%. Dissolve 3 g of acrylamide monomer in 15 mL of deionized water and stir for 30 min to ensure that the acrylamide is more uniformly dispersed in the system to obtain an acrylamide pre-solution with a concentration of 16.7 wt%.

[0059] (3) Mix the sodium acrylate pre-solution obtained in step (2) with the acrylamide pre-solution, and stir the mixture on a magnetic stirrer for 4 hours to ensure thorough stirring.

[0060] (4) Add the guar gum pre-solution cooled to room temperature in step (1) and 1 g of ionic liquid (1-ethyl-3-methylimidazolium acetate) as a functional additive to the mixed solution obtained in step (3) to obtain an acrylamide / sodium acrylate-guar gum-ionic liquid mixed solution. Stir the mixed solution on a magnetic stirrer for 4 h to ensure that the acrylamide, sodium acrylate, ionic liquid and guar gum molecular chains are fully mixed and pre-assembled.

[0061] (5) Add 1 mL of 0.25 Mn, N'-methylenebisacrylamide (MBAA) pre-solution to the mixed solution obtained in step (4) and continue stirring for 30 min to disperse it evenly. Transfer the well-mixed reaction solution to a special petri dish, then add 1 mL of 0.35 M ammonium persulfate pre-solution and gently shake to mix.

[0062] (6) Immediately introduce high-purity nitrogen gas for 5 min to remove dissolved oxygen from the system, and let it stand in a vacuum oven at 60℃ for 8 h. After the reaction is complete, a transparent hydrogel with good elasticity is obtained. Take it out and gently rinse the surface with deionized water to remove unreacted monomers and impurities, and finally obtain a pure polyacrylamide / sodium acrylate-guar gum-ionic liquid semi-interpenetrating network hydrogel.

[0063] Test case The hydrogels prepared in Examples 1-5, Comparative Example 1, and Comparative Example 2 were used to assemble flexible zinc-air batteries, and the battery performance was tested. The core components of the flexible zinc-air battery are: positive electrode - quasi-solid-state electrolyte - negative electrode.

[0064] The positive electrode was prepared by the following method: (1) 60 mg of Co3O4 catalyst, 30 mg of conductive carbon black and 300 μL of 5% Nafion solution were added to 10 mL of anhydrous ethanol and ultrasonically dispersed to obtain catalyst ink; (2) the catalyst ink was uniformly sprayed onto carbon cloth cut to the desired shape and size, dried at 60°C and weighed to obtain a mass loading of 2 mg / cm.2 Carbon cloth-based flexible air cathode.

[0065] The preparation method of flexible zinc-air battery is as follows: (1) Polish high-purity zinc sheet with sandpaper and cut it into specific size; (2) Soak hydrogel in a mixed solution of 6 mol / L potassium hydroxide and 0.2 mol / L zinc acetate for 24 h, take it out and brush a layer of hygroscopic imidazole ionic liquid on the surface of hydrogel; (3) Assemble into a sandwich structure in the order of zinc foil negative electrode, hydrogel electrolyte, and carbon cloth catalyst.

[0066] Performance testing like Figure 1 As shown, the hydrogel described in Example 2 exhibits a colorless, transparent, and uniform physical morphology, and demonstrates high transparency, indicating the formation of a uniform three-dimensional network structure.

[0067] Figure 2 Optical images showing that the surface area of ​​the hydrogel described in Example 2 did not shrink significantly after being left at room temperature for 10 days. Figure 3 The water retention curves of the hydrogels after being placed in a constant temperature and humidity chamber (20℃, 30% relative humidity) for 484 h are shown. The water retention rate of the hydrogel in Comparative Example 1 is 78.65%, while the water retention rate of the hydrogel in Comparative Example 2 is 87.96% after the addition of guar gum. After the introduction of hygroscopic imidazole ionic liquid, the water retention rates of Examples 1, 2 and 3 are 88.54%, 91.04% and 91.52% respectively.

[0068] Figure 4 The AC impedance spectra of each hydrogel sample are shown. The ohmic impedance of the hydrogel in Comparative Example 1 is 2.11 Ω, and the ohmic impedances of the hydrogels in Examples 1, 2 and 4 are 0.87 Ω, 0.26 Ω and 0.35 Ω, respectively. Figure 5 The ionic conductivity of the five hydrogels described in Comparative Examples 1-2, Examples 1-2, and Example 4 is as follows: the ionic conductivity of the hydrogels described in Comparative Examples 1 and 2 is 169.82 mS / cm and 198.46 mS / cm, respectively; and the ionic conductivity of the hydrogels described in Examples 1, 2, and 4 is 214.59 mS / cm, 226.38 mS / cm, and 223.17 mS / cm, respectively.

[0069] Figure 6 The crosslinking impedance diagram of the hydrogel sample described in Example 2 is shown to change after being placed at room temperature for five days. The initial ohmic impedance of the hydrogel sample described in Example 2 was 0.26 Ω, and after 5 days, the ohmic impedance increased to 0.36 Ω. Figure 7The trend of ionic conductivity change of the hydrogel sample described in Example 2 after being placed at room temperature for five days is shown. The ionic conductivity on the first day was 226.38 mS / cm, and after five days, the ionic conductivity was 180.48 mS / cm.

[0070] like Figure 8 The tensile properties of the hydrogels are shown. The hydrogel described in Comparative Example 1 can withstand a stress of 113 kPa and a strain of 502%, while the hydrogel described in Comparative Example 2 can withstand a stress of 162 kPa and a strain of 592%. The hydrogel described in Example 2 can withstand a stress of 204 kPa and a strain of 710%.

[0071] Figure 9 The tensile strain-strength change curves of the hydrogel sample described in Example 2 after being placed at room temperature for five days are shown. The hydrogel described in Example 2 can withstand a stress of 204 kPa and a strain of 710%. After one day, the hydrogel described in Example 2 can withstand a stress of 192 kPa and a strain of 678%. After five days, the hydrogel described in Example 2 can withstand a stress of 166 kPa and a strain of 586%. The stress and strain remain at 81% and 83% of their initial values, respectively.

[0072] Figure 10 The constant current charge-discharge curves of the flexible zinc-air battery assembled based on the hydrogel of this invention are shown. At 2 mA / cm²... 2 At the specified current density, the cycle time of the flexible zinc-air battery with hydrogel as electrolyte in Comparative Example 1 was 175 h, and the cycle time of the flexible zinc-air battery with hydrogel as electrolyte in Comparative Example 2 was 216 h. The flexible zinc-air batteries assembled with hydrogel electrolytes in Examples 1, 2, and 4 could operate for 226 h, 245 h, and 248 h respectively after continuous charging for 10 min and discharging for 10 min, corresponding to 678, 735, and 744 cycles respectively. Specifically, the charge / discharge plateau voltages of the flexible zinc-air battery assembled with hydrogel as electrolyte in Example 1 were 1.24 V and 1.86 V, with a cycle efficiency of 66.67%; the charge / discharge plateau voltages of the flexible zinc-air battery assembled with hydrogel as electrolyte in Example 2 were 1.23 V and 1.81 V, with a cycle efficiency of 67.96%; and the charge / discharge plateau voltages of the flexible zinc-air battery assembled with hydrogel as electrolyte in Example 4 were 1.20 V and 1.89 V, with a cycle efficiency of 63.49%.

[0073] like Figure 11As shown, the open-circuit voltage of the flexible zinc-air battery assembled with hydrogel electrolyte in Comparative Example 1 is 1.26V, the open-circuit voltage of the flexible zinc-air battery assembled with hydrogel electrolyte in Comparative Example 2 is 1.46V, and the open-circuit voltage of the flexible zinc-air battery assembled with hydrogel electrolyte in Example 2 is 1.61V.

[0074] like Figure 12 As shown, the flexible zinc-air battery assembled with the hydrogel electrolyte described in Example 2 achieved a specific capacity of 744.98 mAh / g, which is very close to the theoretical specific capacity (820 mAh / g). At 2 mA / cm² 2 At the specified current density, it discharged continuously at 1.2V for 121.45 h. The specific capacity of the flexible zinc-air battery assembled with the hydrogel electrolyte described in Comparative Example 1 was 589.12 mAh / g, and the specific capacity of the flexible zinc-air battery assembled with the hydrogel electrolyte described in Comparative Example 2 was 717.43 mAh / g. Figure 13 As shown, the power density of the flexible zinc-air battery assembled with the hydrogel electrolyte described in Example 2 reaches 240.97 mW / cm². 2 The power density of the flexible zinc-air battery assembled with the hydrogel electrolyte described in Example 4 reached 217.27 mW / cm². 2 The power density of the flexible zinc-air battery assembled with the hydrogel electrolyte described in Comparative Example 1 is 124.32 mW / cm². 2 .

[0075] The performance of the high water retention hydrogels of Comparative Examples 1-2 and Examples 1-2, and the zinc-air batteries assembled with them, were tested at 2 mA / cm². 2 The constant current charge-discharge lifetime under current density is summarized in Table 1 below.

[0076] Table 1 Test performance of hydrogels with high water retention rates in Comparative Examples 1-2 and Examples 1-2

[0077] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a semi-interpenetrating network structure hydrogel with high water retention, characterized in that, The preparation steps include the following: Substrate synthesis: Acrylamide was placed in deionized water and stirred to prepare an acrylamide solution. Then, acrylic acid was added to sodium hydroxide solution under ice bath conditions and magnetically stirred to obtain sodium acrylate solution. The two solutions were mixed to obtain an acrylamide-sodium acrylate hydrogel substrate. Construction of the semi-interpenetrating network structure: Guar gum powder was heated and stirred in deionized water to prepare a guar gum presol. The guar gum presol cooled to room temperature and a hygroscopic ionic liquid were added to an acrylamide-sodium acrylate hydrogel substrate. Subsequently, a crosslinking agent and an initiator were added. After a free radical polymerization crosslinking reaction was carried out under vacuum conditions, the substrate was immersed in an alkaline electrolyte to swell. After swelling was completed, a layer of hygroscopic ionic liquid was brushed onto the surface of the hydrogel to obtain a polyacrylamide / sodium acrylate-guar gum-ionic liquid semi-interpenetrating network hydrogel.

2. The method for preparing a high water-retention semi-interpenetrating network structure hydrogel according to claim 1, characterized in that, The concentration of the guar gum solution is 0.005~0.05 g / mL, and the temperature during heating and stirring is 60~90℃.

3. The method for preparing a high water-retention semi-interpenetrating network structure hydrogel according to claim 1, characterized in that, The concentration of sodium acrylate solution is 30-60 wt%, and the concentration of acrylamide solution is 10-40 wt%.

4. The method for preparing a high water-retention semi-interpenetrating network structure hydrogel according to claim 1, characterized in that, The molar ratio of acrylamide to sodium acrylate in the acrylamide-sodium acrylate hydrogel substrate is 1:2 to 3:

1.

5. The method for preparing a high water-retention semi-interpenetrating network structure hydrogel according to claim 1, characterized in that, The mass ratio of guar gum to hygroscopic ionic liquid is 1:5 to 1:

15. Hygroscopic ionic liquids include one or more of 1-ethyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride, 1-octyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate, 1-hexyl-3-methylimidazolium acetate, 1-octyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium bromide, 1-hexyl-3-methylimidazolium bromide, and 1-octyl-3-methylimidazolium bromide.

6. The method for preparing a high water-retention semi-interpenetrating network structure hydrogel according to claim 1, characterized in that, The crosslinking agent is N,N'-methylenebisacrylamide, and the amount added is 0.03 to 0.16 wt% of the total hydrogel. The initiator is one or more of ammonium persulfate, potassium persulfate, and sodium persulfate, and the amount added is 0.05~0.3 wt% of the total hydrogel.

7. The method for preparing a high water-retention semi-interpenetrating network structure hydrogel according to claim 1, characterized in that, The reaction temperature during the free radical polymerization crosslinking reaction is 40–80℃, and the reaction time is 5–12 h.

8. The method for preparing a high water-retention semi-interpenetrating network structure hydrogel according to claim 1, characterized in that, The alkaline electrolyte is a mixed solution of 5-7M NaOH and 0.1-0.3M (CH3COO)2Zn.

9. A semi-interpenetrating network structure hydrogel with high water retention capacity prepared by the preparation method according to any one of claims 1-8, characterized in that, The hydrogel had a water retention rate of 90.14% after being placed in a constant temperature and humidity environment (20℃, 30% relative humidity) for 484 h, an initial ionic conductivity of 226.38 mS / cm, and an initial tensile strain of 705%.

10. The application of the high water retention semi-interpenetrating network structure hydrogel of claim 9, characterized in that, It is used in flexible zinc-air batteries.

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