Self-supporting flexible hydrogel electrode and preparation method thereof, coplanar all-hydrogel zinc ion battery and preparation method and application of coplanar all-hydrogel zinc ion battery

Abstract

The invention discloses a self-supporting flexible hydrogel electrode and a preparation method thereof, and a coplanar all-hydrogel zinc ion battery and a preparation method and application thereof. According to the electrode, an electrochemical active filler and a conductive filler are uniformly mixed with a polyacrylic acid hydrogel precursor to form a self-supporting hydrogel electrode membrane with a porous structure. The electrode shows the elongation at break of more than 300% and the tensile strength of more than 50 kPa, and forms a stable interface with the polyvinyl alcohol hydrogel electrolyte through hydrogen-bond interaction, so that the interface impedance is remarkably reduced, and the ion transmission path is optimized. The constructed all-hydrogel coplanar battery has the high area specific capacity of 1.2 mAh / cm < 2 > under a voltage window of 0.2-1.8 V, the capacity retention rate exceeds 80% after 200 times of circulation, and stable power supply is still kept after 120 times of circulation under 40% tensile deformation. The battery is suitable for wearable equipment and can continuously work under complex deformation such as bending and twisting.

Description

Technical Field

[0001] This invention relates to an electrode material and its preparation method, a zinc-ion battery and its preparation method and application, and particularly to a self-supporting flexible hydrogel electrode and its preparation method, a coplanar fully hydrogel zinc-ion battery and its preparation method and application. Background Technology

[0002] The rapid development of wearable electronic devices has placed increasingly stringent demands on their supporting energy storage devices. An ideal flexible energy storage system not only needs to overcome the mechanical limitations of traditional rigid electrochemical systems under dynamic deformations such as bending and stretching, but also needs to achieve synergistic optimization among energy density, power density, cycle life, and intrinsic safety. Hydrogel materials, due to their high safety profile caused by their rich aqueous electrolyte content, along with their large specific surface area, abundant ion transport channels, good biocompatibility, tissue-like flexibility, and large tensile deformation capacity, are considered ideal matrix materials for constructing next-generation flexible energy storage devices.

[0003] To meet the long battery life requirements of wearable devices, flexible zinc-ion batteries typically use zinc metal, which has a battery-like energy storage mechanism, as the negative electrode. However, zinc foil itself has poor ductility and is prone to fatigue cracks under repeated deformation, making it difficult to meet the electrode tensile strength requirements of wearable devices. Early research attempted to replace brittle zinc foil by compositing zinc metal powder with hydrogels in order to improve flexibility. However, the high activity and specific surface area of ​​zinc powder in this strategy exacerbate side reactions with water in the hydrogel, easily leading to corrosion and hydrogen evolution, resulting in new problems such as poor cycle stability.

[0004] Existing hydrogel electrode technologies mainly follow two paths: First, simply coating or physically mixing electrochemically active materials onto the surface of a pre-fabricated hydrogel matrix. This approach heavily relies on the hydrogel matrix for flexibility, while the active material layer itself is brittle and prone to detachment from the matrix or breakage under dynamic deformation, leading to electrical contact failure. Second, constructing functionalized electronically conductive hydrogels. The theoretical advantage lies in connecting active materials through a three-dimensional conductive network, utilizing a porous structure to promote ion transport, and leveraging the viscoelasticity of the polymer network to buffer volume changes. However, existing methods struggle to achieve high-activity material loading while maintaining the structural integrity and interfacial stability of the electrode under repeated stretching deformation.

[0005] Furthermore, existing flexible zinc-ion batteries mostly employ a stacked structure of "electrode sheet-gel electrolyte," resulting in poor solid-solid interface contact between the electrode and the non-fluid electrolyte. This makes them prone to interfacial delamination during bending, stretching, and other deformation processes, increasing interfacial impedance and leading to battery failure. Therefore, developing a fully hydrogel electrode and battery structure capable of achieving high-activity material loading, excellent tensile strength and electrochemical performance, and maintaining a stable interface under dynamic operating conditions has become a critical issue urgently needing to be addressed in the field of flexible energy storage. Summary of the Invention

[0006] Objectives of the invention: The first objective of this invention is to provide a self-supporting flexible hydrogel electrode with high tensile strength and high tensile strength; the second objective of this invention is to provide a method for preparing the above-mentioned self-supporting flexible hydrogel electrode.

[0007] The third objective of this invention is to provide a coplanar fully hydrogel zinc-ion battery with high areal capacity, excellent rate performance and high environmental stability; the fourth objective of this invention is to provide a method for preparing the above-mentioned coplanar fully hydrogel zinc-ion battery.

[0008] The fifth objective of this invention is to provide the application of coplanar hydrogel zinc-ion batteries in wearable electronic devices.

[0009] Technical solution: The self-supporting flexible hydrogel electrode of the present invention comprises a polyacrylic acid-based hydrogel with a network structure, an electrochemically active filler and a conductive filler loaded on the polyacrylic acid-based hydrogel network structure; the polyacrylic acid-based hydrogel is formed by thermally or photoinitiated polymerization of acrylic monomers in a mixed solvent composed of water and a polar organic co-solvent in the presence of a crosslinking agent and an initiator; the loading amount of the electrochemically active filler is 50-300 mg / mL; the loading amount of the conductive filler is 10-100 mg / mL.

[0010] Wherein, the electrochemically active filler is at least one of vanadate, manganese oxide, and molybdenum oxide; the conductive filler is at least one of silver nanosheets, silver nanowires, carbon nanotubes, and graphene; the acrylic monomer is at least one of acrylic acid, methacrylic acid, and acrylamide; the crosslinking agent is at least one of N,N'-methylenebisacrylamide and polyethylene glycol diacrylate; the initiator is at least one of ammonium persulfate, potassium persulfate, and azobisisobutyronitrile; and the polar organic cosolvent is at least one of ethylene glycol, glycerol, and dimethyl sulfoxide.

[0011] The above-mentioned method for preparing a self-supporting flexible hydrogel electrode includes the following steps:

[0012] (S1) Water and a polar organic co-solvent are mixed to obtain a mixed solvent, and then acrylic monomers, crosslinking agents and initiators are added and stirred to form a precursor solution;

[0013] (S2) Add electrochemically active filler and conductive filler to the precursor solution obtained in step (S1), mix them evenly, and then cast them into a film. Thermally initiated polymerization is then used to form a self-supporting flexible hydrogel electrode.

[0014] In step (S1), the volume ratio of water to polar organic co-solvent is 1:1 to 1:3.

[0015] In step (S1), an alcohol solvent is added to delay gelation; the alcohol solvent is ethanol and / or isopropanol; the amount of alcohol solvent added is 40%-60% of the total volume of the precursor solution.

[0016] In step (S1), the volume percentage of acrylic monomers in the mixed solvent is 20%-40%; the mass ratio of acrylic monomers to crosslinking agents is 100:1-200:1; the mass ratio of acrylic monomers to initiators is 50:1-150:1; and the stirring and dissolving time is 30-120 min.

[0017] In step (S2), the mixing time is 2-10 min; the temperature for thermally initiated polymerization is 40-80℃, and the polymerization time is 2-24 h.

[0018] The coplanar hydrogel zinc-ion battery of the present invention includes a positive electrode and a negative electrode, both of which are self-supporting flexible hydrogel electrodes obtained by the above method; the positive and negative electrodes are arranged coplanarly on a hydrogel electrolyte substrate, and the upper surfaces of the positive and negative electrodes are also covered with the hydrogel electrolyte, so that the positive and negative electrodes are encapsulated by the hydrogel electrolyte; the hydrogel electrolyte is a polyvinyl alcohol-based hydrogel electrolyte.

[0019] The above-mentioned method for preparing a coplanar fully hydrogel zinc-ion battery includes the following steps:

[0020] (T1) Using the above method, a self-supporting flexible hydrogel positive / negative electrode is obtained. The positive and negative electrodes are then attached in parallel to the polyvinyl alcohol hydrogel electrolyte substrate, with an insulating gap in between.

[0021] (T2) A polyvinyl alcohol hydrogel precursor solution is coated on the surfaces of the positive and negative electrodes and then frozen crosslinked to achieve a fully hydrogel integrated encapsulation; the polyvinyl alcohol hydrogel precursor solution is prepared by dissolving polyvinyl alcohol in a mixed solution of water containing zinc salt and a polar organic co-solvent.

[0022] The polyvinyl alcohol hydrogel electrolyte is prepared by dissolving polyvinyl alcohol in a mixed solution of water containing zinc salt and a polar organic co-solvent, and then crosslinking it through a freeze-thaw cycle. The zinc salt includes at least one of zinc trifluoromethanesulfonate, zinc sulfate, and zinc chloride. The polar organic co-solvent includes at least one of ethylene glycol, glycerol, and dimethyl sulfoxide. The concentration of the zinc salt solution is 0.5-2.0 mol / L. The volume ratio of water to polar organic co-solvent is 1:1-1:3. The freezing temperature is -20℃ to -60℃, and the freeze-crosslinking time is 2-12 h.

[0023] In step (T1), an alcohol solvent is added to delay gelation; the alcohol solvent is ethanol and / or isopropanol; the amount of alcohol solvent added is 40%-60% of the total volume of the precursor solution.

[0024] In step (T1), the electrochemically active filler of the positive electrode hydrogel electrode is ammonium vanadate with a loading of 50-200 mg / mL; the electrochemically active filler of the negative electrode hydrogel electrode is zinc vanadate with a loading of 100-300 mg / mL; and the insulation gap is 0.1-0.5 mm.

[0025] The above-mentioned coplanar hydrogel zinc-ion batteries are used in wearable electronic devices.

[0026] Invention principle:

[0027] To address issues such as the intrinsic flexibility and electrochemical performance of electrode materials, the instability of the electrode-electrolyte interface under deformation, the balance between high-activity material loading and electrode structural integrity, and the compatibility of material systems and processes in flexible zinc-ion batteries, this invention provides a method for preparing flexible hydrogel electrodes. This method constructs a coplanar fully hydrogel zinc-ion battery with a stable interface and establishes a process window for scalable fabrication. This enables the battery to provide stable power in practical wearable scenarios, thereby promoting the application of fully hydrogel zinc-ion batteries in wearable systems such as flexible displays, electronic skin, and health monitoring.

[0028] This invention constructs a flexible electrode with both excellent electronic conductivity and ion transport channels by integrating electrochemically active fillers and silver-based conductive fillers into a polyacrylic acid hydrogel network. The hydrogen bonds formed between the hydroxyl groups on the surface of the active filler and the polyacrylic acid network significantly enhance the mechanical properties of the hydrogel, allowing it to maintain a high elongation at break of 300% and a tensile strength of 50 kPa while achieving a high loading of active materials. Silver nanosheets form a highly efficient percolating conductive network within the gel, significantly reducing the electrode sheet resistance from 1.580 kΩ to 307.4 mΩ. More importantly, the polyacrylic acid-based electrode and the polyvinyl alcohol-based electrolyte achieve tight interfacial adhesion through abundant hydrogen bonding, greatly reducing interfacial impedance and optimizing the ion transport path. Through a coplanar battery architecture and full hydrogel encapsulation technology, the problem of easy delamination between the metal electrode and electrolyte interface in traditional flexible batteries is eliminated, enabling the battery to adapt to multi-directional deformation and maintain stable electrochemical performance under bending, stretching, and torsion conditions.

[0029] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0030] (1) The hydrogel electrode prepared by this invention has both high tensile strength (elongation at break greater than 300%) and high strength (tensile strength greater than 50 kPa), and its mechanical properties are superior to those of the hydrogel matrix without added active filler. (2) The coplanar fully hydrogel battery constructed by this invention has high areal capacity and excellent rate performance, at 0.5 mA cm⁻¹ -2 The current density achieves a capacity of 1.2 mAh cm⁻¹. -2 Energy density reaches 1070 µWh cm⁻¹ -2 (3) The battery of the present invention maintains excellent performance stability under harsh working conditions. After 120 cycles under 40% tensile deformation, the capacity retention rate is still over 80%; after 200 cycles at room temperature, the capacity retention rate is over 80%. (4) The battery of the present invention has excellent environmental stability. Using the hydrogel electrolyte itself as the encapsulation layer, the mass loss is only 0.041% after being placed under environmental conditions for 288 hours, showing good water retention capacity. (5) The preparation method of the present invention is simple and reliable, and has broad application prospects in the fields of flexible display, electronic skin and wearable health monitoring. Attached Figure Description

[0031] Figure 1 The images show the hydrogel slurry prepared in Example 1 and its physical appearance after heating and gelation, as well as the microstructure obtained by scanning electron microscopy after drying.

[0032] Figure 2 Comparison of cyclic voltammetry curves of hydrogel electrodes obtained in Examples 1 and 3 at different electrode material concentrations;

[0033] Figure 3 Comparison of stress-strain curves of hydrogel negative electrode, hydrogel positive electrode, and hydrogel matrix obtained in Example 1, Comparative Example 1, and Example 3;

[0034] Figure 4 The cyclic voltammetry curve and constant current charge-discharge curve of the coplanar fully hydrogel zinc-ion battery obtained in Example 4 are shown.

[0035] Figure 5 The graph shows the cycle capacity retention and coulombic efficiency trends of the coplanar fully hydrogel zinc-ion battery obtained in Example 4 at a current density of 0.1 mA / cm2.

[0036] Figure 6 The tensile test curves of the adhesion force between the hydrogel electrode substrate and the hydrogel electrolyte obtained in Comparative Example 1 and Example 4 are shown.

[0037] Figure 7 This is a graph showing the trend of water content variation in the coplanar fully hydrogel zinc-ion battery obtained in Example 4.

[0038] Figure 8 The graph shows the capacity retention and cyclic voltammetry curve changes of the coplanar fully hydrogel zinc-ion battery obtained in Example 4 under 40% stretching cycles.

[0039] Figure 9 The charge-discharge curves and open-circuit voltage curves of the series coplanar fully hydrogel zinc-ion battery module obtained in Example 5 are shown in Figure 5.

[0040] Figure 10 This is a physical demonstration of the series coplanar hydrogel zinc-ion battery module obtained in Example 5, which powers an LED light sign and undergoes bending and twisting deformation. Detailed Implementation

[0041] The present invention will now be described in further detail.

[0042] Example 1

[0043] (1) Mix ethylene glycol and water at a volume ratio of 2:1 to obtain 35 mL of mixed solvent. Add 15 mL of acrylic acid, 20 mg of N,N'-methylenebisacrylamide (MBAA) and 150 mg of ammonium persulfate (APS) to the mixture and stir magnetically for 30 min until fully dissolved. Then add 25 mL of ethanol to delay spontaneous gelation and obtain polyacrylic acid (PAA) precursor solution.

[0044] (2) Take three 10 mL portions of the above precursor solution, add 400 mg of silver nanosheets to each, and then add 1 g, 2 g, and 3 g of zinc vanadate (ZVO) respectively, with corresponding concentrations of 100, 200, and 300 mg / mL. Stir magnetically for 20 min and then ultrasonically disperse for 5 min to obtain a uniform negative slurry.

[0045] (3) Pour the negative electrode slurry into a petri dish and let it stand at 60°C for 12 h to obtain self-supporting hydrogel negative electrodes with different concentrations of negative electrode materials; wherein the concentrations of the negative electrode materials are 100 mg / mL, 200 mg / mL and 300 mg / mL respectively.

[0046] Hydrogel sample preparation process as follows Figure 1 As shown, SEM morphology observation reveals that the electrode possesses a porous three-dimensional network structure, which is beneficial for active material loading and ion transport. Cyclic voltammetry results for this electrode group are as follows... Figure 2 As shown, when the ZVO addition reaches 300 mg / mL, it exhibits the largest capacity, and the redox peak shape of the electrode is closest to the intrinsic properties of the ZVO material, indicating that its electrochemical behavior is fully preserved, possessing optimal reaction reversibility and electrochemical activity. Figure 3The performance test results of this group of electrodes showed that when the ZVO addition amount was 300 mg / mL, the tensile strength of the electrode was 123.8 kPa and the elongation at break was 316.1%. This indicates that 300 mg / mL is the optimal value for the active material loading in the ZVO anode system.

[0047] Comparative Example 1

[0048] The preparation process is the same as in Example 1, except that no electrochemically active fillers or conductive fillers are added, and only PAA precursor solution is used to polymerize and form a pure hydrogel matrix.

[0049] like Figure 3 Mechanical property tests on the sample showed that its elongation at break was 226.5%, and its tensile strength was only 23.3 kPa, far lower than that of the composite hydrogel electrode with added active fillers. Electrochemical tests indicated that the pure hydrogel matrix had no obvious redox peaks and lacked electrochemical activity. This comparative example demonstrates that a simple hydrogel matrix cannot meet the dual requirements of strength and electrochemical function for flexible electrodes; the addition of appropriate fillers is key to achieving functionalization. Furthermore, the addition of fillers not only achieves electrochemical function but also synergistically enhances its mechanical properties.

[0050] Comparative Example 2

[0051] The preparation process is the same as in Example 1, except that silver nanosheets were not added as conductive fillers.

[0052] The sheet resistance of the electrode increased significantly from 307.4 mΩ to 1.580 kΩ. This indicates that conductive fillers are crucial for constructing an efficient percolation conductive network, and that an appropriate amount of silver nanosheets can significantly reduce the internal resistance of the electrode and improve electron transport efficiency.

[0053] Comparative Example 3

[0054] The preparation process is the same as in Example 1, except that silver nanosheets are replaced with an equal mass of conductive carbon black.

[0055] The resulting black slurry failed to gel and solidify smoothly during the heating polymerization process, ultimately forming loose and uneven lumps that could not form a film. This indicates that the surface properties of carbon black are poorly compatible with the PAA precursor, which may interfere with the free radical polymerization process, or that its particle size and morphology prevent it from forming a stable dispersion in the gel network, highlighting the irreplaceable role of silver nanosheets in this system.

[0056] Comparative Example 4

[0057] The preparation process is the same as in Example 1, except that the ZVO addition amount is increased to 400 mg / mL. As before, a higher active material loading will further increase the electrode capacity.

[0058] However, the gel cracked during polymerization, failing to form a complete self-supporting membrane. This indicates that excessive active filler can disrupt the continuity of the hydrogel network and affect structural integrity.

[0059] Example 2

[0060] Based on Example 1, the difference is that the volume ratio of ethylene glycol to water is 3:2, which does not affect the film-forming effect of the gel and has similar electrochemical and mechanical properties to Example 1.

[0061] Example 3

[0062] (1) The preparation process of the PAA precursor solution is the same as step (1) in Example 1;

[0063] (2) Take three 10 mL portions of the above precursor solution, add 400 mg of silver nanosheets to each, and then add 0.6 g, 1.0 g, and 2.0 g of ammonium vanadate (NVO) respectively, with corresponding concentrations of 60, 100, and 200 mg / mL. Stir magnetically for 20 min and then ultrasonically disperse for 5 min to obtain a uniform positive electrode slurry.

[0064] (3) Pour the positive electrode slurry into a petri dish and let it stand at 60°C for 12 h to obtain self-supporting hydrogel positive electrodes with different concentrations of positive electrode materials; wherein the concentrations of positive electrode materials are 60 mg / mL, 100 mg / mL, and 200 mg / mL.

[0065] Performance testing of this electrode group showed that when the NVO addition level was 200 mg / mL, the tensile strength of the electrode was 86.0 kPa, and the elongation at break was 449.5%. Cyclic voltammetry testing results for this electrode group are as follows: Figure 6 As shown in Figure c, the electrode exhibits the highest capacity when the NVO addition is 200 mg / mL, and its CV curve most closely matches the intrinsic properties of the NVO material, with the most prominent redox peak, indicating that its electrochemical activity is fully preserved and side reactions are minimized. This suggests that 200 mg / mL is the optimal value for active material loading in the NVO cathode system.

[0066] Comparative Example 5

[0067] The preparation process was the same as in Example 3, but the NVO addition was increased to 250 mg / mL. As previously observed, a higher active material loading would further increase the electrode capacity. However, cracking occurred during the gelation process, preventing the formation of a complete electrode film. This again confirmed the existence of an upper limit for the concentration of active filler; excessive loading would sacrifice the structural integrity and processability of the electrode.

[0068] Example 4

[0069] (1) The hydrogel positive electrode prepared in Example 3 and the hydrogel negative electrode prepared in Example 1 were cut into strip-shaped hydrogel electrode films of 10 mm × 25 mm respectively;

[0070] (2) Add 1 mol / L zinc trifluoromethanesulfonate to 40 mL of a solvent in which water and ethylene glycol are mixed at a volume ratio of 1:2. After stirring evenly, add 4.5 g of polyvinyl alcohol (PVA) powder and stir at 90°C until completely dissolved to obtain a PVA precursor solution. Cast the solution into a petri dish and freeze crosslink at -40°C for 6 h to form a transparent self-supporting PVA hydrogel electrolyte membrane with a thickness of about 1.0 mm.

[0071] (3) The strip-shaped hydrogel positive electrode film and the strip-shaped hydrogel negative electrode film obtained in step (1) are arranged in parallel on the transparent self-supporting PVA hydrogel electrolyte membrane substrate, with a 0.2 mm insulating gap in between.

[0072] (3) The second layer of PVA precursor solution was poured and covered on the electrode strip and the substrate surface, and then frozen crosslinked at -40℃ for 6h to achieve full hydrogel integrated encapsulation and obtain a coplanar full hydrogel zinc-ion battery.

[0073] Electrochemical performance tests of the battery, such as Figure 4 As shown. Cyclic voltammetry tests exhibited stable redox peaks within a voltage window of 0.2–1.8 V. Constant current charge-discharge tests were performed at 0.5 mA cm⁻¹. -2 It showed a current density of 1.2 mAh cm⁻¹. -2 High area capacity. Figure 5 Long-cycle testing showed that the battery retained more than 80% of its capacity after 200 cycles.

[0074] The interfacial adhesion test of the battery is as follows: Figure 6 As shown, after the PAA-based hydrogel electrode matrix material and the PVA-based hydrogel electrolyte are bonded at the ends, tensile deformation is applied, and the deformation reaches 200% with a strength of 25 kPa. No separation occurs at the interface between the two parts, indicating excellent interfacial adhesion and stability.

[0075] Environmental stability tests of the battery, such as Figure 7 As shown, using its own hydrogel electrolyte as the encapsulation layer, after standing for 288 hours under environmental conditions, the mass loss is only 0.041%, demonstrating excellent water retention capacity and operational stability.

[0076] The tensile deformation stability of the battery is as follows Figure 8 As shown, after being subjected to 40% tensile deformation and undergoing 120 stretch-release cycles, the battery capacity retention rate still exceeds 80%, demonstrating excellent mechanical-electrochemical synergistic stability.

[0077] Example 5

[0078] Three coplanar hydrogel batteries prepared in Example 4 were connected in series using flexible conductive tape to construct a battery module with improved output voltage. Figure 9 As shown, this module has a stable open-circuit voltage of 2.5V after charging. Figure 10 As shown, the module can continuously power LED electronic light signs under bending and stretching conditions, and maintain stable voltage output under various deformations, proving its feasibility for application in practical wearable devices.

Claims

1. A self-supporting flexible hydrogel electrode, characterized by, The self-supporting flexible hydrogel electrode comprises a polyacrylic acid-based hydrogel with a network structure, an electrochemically active filler loaded on the network structure of the polyacrylic acid-based hydrogel, and a conductive filler; the polyacrylic acid-based hydrogel is formed by thermal initiation or photo-initiated polymerization of an acrylic monomer in a mixed solvent composed of water and a polar organic cosolvent in the presence of a crosslinking agent and an initiator; the loading amount of the electrochemically active filler is 50-300 mg / mL; and the loading amount of the conductive filler is 10-100 mg / mL.

2. The self-supporting flexible hydrogel electrode of claim 1, wherein, The electrochemically active filler is at least one of vanadate, manganese oxide, and molybdenum oxide; the conductive filler is at least one of silver nanosheet, silver nanowire, carbon nanotube, and graphene; the acrylic monomer is at least one of acrylic acid, methacrylic acid, and acrylamide; the crosslinking agent is at least one of N,N'-methylenebisacrylamide and polyethylene glycol diacrylate; the initiator is at least one of ammonium persulfate, potassium persulfate, and azobisisobutyronitrile; and the polar organic cosolvent is at least one of ethylene glycol, glycerol, and dimethyl sulfoxide.

3. A method of preparing the self-supporting flexible hydrogel electrode of claim 1, wherein, The method comprises the following steps: (S1) mixing water and a polar organic cosolvent to obtain a mixed solvent, and then adding an acrylic monomer, a crosslinking agent, and an initiator to stir to form a precursor solution; (S2) adding an electrochemically active filler and a conductive filler to the precursor solution obtained in step (S1), uniformly mixing, and then casting into a film to form a self-supporting flexible hydrogel electrode by thermal initiation polymerization.

4. The method of claim 3, wherein the self-supporting flexible hydrogel electrode is prepared by the steps of: In step (S1), the volume ratio of the water to the polar organic cosolvent is 1:1-1:

3.

5. The method of claim 3, wherein the self-supporting flexible hydrogel electrode is prepared by the steps of: In step (S1), an alcohol solvent is added to delay gelation; the alcohol solvent is ethanol and / or isopropanol; and the addition amount of the alcohol solvent is 40%-60% of the total volume of the precursor solution.

6. The method of claim 1, wherein the self-supporting flexible hydrogel electrode is prepared by the steps of: In step (S2), the thermal initiation polymerization temperature is 40-80℃, and the polymerization time is 2-24 h.

7. A co-planar all-aqueous gel zinc-ion battery comprising a positive electrode, a negative electrode, characterized in that, The positive electrode and the negative electrode are both self-supporting flexible hydrogel electrodes obtained by the method of claim 1; the positive electrode and the negative electrode are arranged in a coplanar manner on a hydrogel electrolyte substrate, and the upper surfaces of the positive electrode and the negative electrode are also covered with the hydrogel electrolyte, so that the positive electrode and the negative electrode are encapsulated by the hydrogel electrolyte; and the hydrogel electrolyte is a polyvinyl alcohol-based hydrogel electrolyte.

8. A method of preparing the co-planar all-aqueous gel zinc ion battery of claim 7, wherein, The method comprises the following steps: (T1) obtaining a self-supporting flexible hydrogel positive electrode / negative electrode by the method of claim 1, and adhering the positive electrode and the negative electrode in parallel to a polyvinyl alcohol hydrogel electrolyte substrate with an insulating gap left in between; (T2) covering the surfaces of the positive electrode and the negative electrode with a polyvinyl alcohol hydrogel precursor solution, and achieving all-hydrogel integrated encapsulation by freeze-crosslinking; the polyvinyl alcohol hydrogel precursor solution is prepared by dissolving polyvinyl alcohol in a mixed solution of water and a polar organic cosolvent containing a zinc salt.

9. The method of co-planar all-aqueous gel zinc-ion battery of claim 8, wherein, The polyvinyl alcohol hydrogel electrolyte is prepared by dissolving polyvinyl alcohol in a mixed solution containing a zinc salt and a polar organic cosolvent, and then cross-linking by freeze-thaw cycles; the zinc salt includes at least one of zinc trifluoromethane sulfonate, zinc sulfate, and zinc chloride; the polar organic cosolvent includes at least one of ethylene glycol, glycerol, and dimethyl sulfoxide; the freezing temperature is-20℃ to-60℃, and the freezing cross-linking time is 2-12h.

10. Use of the co-planar full hydrogel zinc ion battery of claim 7 in a wearable electronic device.