Preparation method of multi-network hydrogel applied to flexible zinc ion battery

Abstract

Rapid development of wearable portable devices urgently requires high performance flexible supercapacitors and batteries. As a core component of a flexible energy storage device, hydrogel electrolyte has aroused wide attention. According to the invention, the PBAx composite hydrogel (x represents the PVA content, and the values are 0, 0.5, 1 and 1.5) is prepared through chain crosslinking of sodium polyacrylate (PANa), polyvinyl alcohol (PVA) and bacterial cellulose (BC). The PVA component can effectively regulate and control intramolecular crosslinking among PANa molecular chains through hydrogen-bond interaction, so that the optimized PBA0.5 hydrogel forms a porous structure, the structure shows remarkably enhanced water holding capacity and mechanical strength, and the ultimate compressive strength reaches 258.4 kPa. By utilizing the ionic conductivity characteristic of 4.607 S m <-1 > of the material, the specific capacity of a basic zinc battery assembled by the material reaches 171.3 mAh g <-1 >, and the material shows excellent rate capability. The hydrogel electrolyte can effectively protect the zinc negative electrode and guarantee the cycling stability of the battery. In addition, due to the excellent anti-freezing performance of the PBA0.5 hydrogel, the specific capacity of the battery in a low-temperature environment of-40 DEG C can still be kept at 83.1 mAh g <-1 >.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible zinc ion batteries, and in particular to a hydrogel electrolyte, a manufacturing method thereof, and a flexible zinc ion battery. Background Art

[0002] With the rapid development of wearable and portable devices, the demand for flexible supercapacitors and batteries is becoming increasingly urgent. Hydrogel electrolytes, as key components of flexible energy storage devices, have attracted widespread attention due to their inherent safety, environmental friendliness, and direct compatibility with the human body and clothing. Compared with traditional liquid electrolytes, hydrogel electrolytes can significantly improve the device's voltage window and antifreeze performance, making them particularly suitable for applications that require deformation.

[0003] However, existing hydrogel electrolytes still face the following key challenges: insufficient mechanical properties: flexible devices need to be repeatedly deformed, and the mechanical strength of single polymer hydrogels (such as polyacrylamide and polyacrylic acid) is difficult to meet actual needs, and structural failure is prone to occur; poor water retention: in low humidity environments, hydrogels are prone to water loss, resulting in a decrease in ionic conductivity, affecting battery cycle stability; limited low-temperature performance: the free water in conventional hydrogels freezes at low temperatures, hindering ion migration and causing a sharp decline in battery capacity; structural design contradictions: improving mechanical strength usually requires increasing cross-linking density, but this will sacrifice the porous structure, thereby reducing ionic conductivity and electrolyte adsorption capacity.

[0004] Current improvement strategies focus on introducing biopolymers (such as bacterial cellulose) to construct multi-network structures, or improving water retention by adding hydrophilic groups. However, these methods are difficult to take into account the coordinated optimization of mechanical strength, pore regulation and low-temperature performance. For example, although excessive cross-linking enhances mechanical properties, it will block ion transport channels; and simply relying on hydrophilic groups to lock water cannot effectively suppress the low-temperature freezing problem. Therefore, the development of a hydrogel electrolyte that can dynamically regulate the hydrogen bond network and balance the porous structure and antifreeze properties is the key to improving the reliability of flexible zinc batteries. Summary of the Invention

[0005] In response to the problems of insufficient mechanical strength, poor low-temperature performance, and weak water retention in existing hydrogel electrolytes, the present invention aims to provide a multi-network cross-linked hydrogel electrolyte that optimizes the pore structure by regulating the hydrogen bond network to achieve high mechanical strength, excellent water retention, and antifreeze properties.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: a multi-network hydrogel electrolyte, which is composed of bacterial cellulose (BC), sodium polyacrylate (PANa) and polyvinyl alcohol (PVA), wherein the content of PVA is x (x = 0g, 0.5g, 1g or 1.5g) in mass fraction, denoted as BPA x ; Its preparation method comprises the following steps:

[0007] (1) Dissolve PVA (preferably 0.5 g) in deionized water, heat and stir to dissolve, and then degas;

[0008] (2) Mixing acrylic acid (AA) solution and NaOH solution in an ice bath, adding initiator ammonium persulfate (APS) and cross-linking agent N,N'-methylenebisacrylamide (MBAA), and stirring thoroughly to prepare PANa prepolymer solution;

[0009] (3) Add the BC solution to the PANa prepolymer solution, stir thoroughly, then add the PVA solution and mix. Continue stirring. Transfer a certain amount of the mixed solution to a culture dish and cure at 65°C for two hours.

[0010] (4) Immerse the solidified hydrogel in 6MKOH+0.2MZnAc electrolyte and allow it to swell fully to obtain a hydrogel electrolyte.

[0011] The hydrogel electrolyte is composed of bacterial cellulose (BC), sodium polyacrylate (PANa) and polyvinyl alcohol (PVA).

[0012] Wherein, the content x of the PVA in step (1) is 0g, 0.5g, 1g or 1.5g.

[0013] Furthermore, the heating temperature in step (1) is 95°C.

[0014] Furthermore, the degassing method in step (1) is to stand at room temperature for 1 hour.

[0015] Furthermore, the acrylic acid (AA) solution in step (2) is prepared by adding 10 ml of deionized water to 7.2 ml of acrylic acid (AA).

[0016] Furthermore, the NaOH solution in step (2) is prepared by ultrasonically dissolving 4 g of sodium hydroxide (NaOH) in 10 ml of deionized water.

[0017] Furthermore, the mixing method under ice bath conditions in step (2) is to add the acrylic acid solution dropwise to the NaOH solution under ice bath conditions.

[0018] Furthermore, the mass of ammonium persulfate (APS) added in step (2) is 110 mg.

[0019] Furthermore, the mass of N,N'-methylenebisacrylamide (MBAA) added in step (2) is 4 mg.

[0020] Furthermore, the sufficient stirring time in step (2) is 30 minutes.

[0021] Furthermore, the concentration of the BC solution in step (3) is 1.05 wt%.

[0022] Furthermore, the stirring time in step (3) is continued for 10 minutes.

[0023] Furthermore, the volume of the certain amount of mixed solution in step (3) is 15 ml.

[0024] Meanwhile, the culture dish in step (3) is circular and has a diameter of 90 mm.

[0025] Furthermore, the curing condition in step (3) is to maintain a constant temperature of 65° C. for two hours.

[0026] Furthermore, the volume of the electrolyte in step (4) is 15 ml.

[0027] Wherein, the electrolyte in step (4) is an alkaline aqueous solution containing 6M KOH and 0.2M zinc acetate (ZnAc).

[0028] A flexible zinc-ion battery using BPA x The hydrogel electrolyte comprises: positive electrode: nickel cobalt layered double hydroxide (NiCo-LDH), conductive carbon black and polytetrafluoroethylene mixed in a mass ratio of 8:1:1 and loaded on nickel foam; negative electrode: zinc foil; the battery structure is a positive electrode / hydrogel electrolyte / zinc foil sandwich configuration.

[0029] Nickel-cobalt layered double hydroxide (NiCo-LDH) was prepared by mixing Ni(NO₃)₂6H₂O (6.65 g, 22.19 mmol), Co(NO₃)₂ (2.85 g, 9.51 mmol), BDC (6 g, 36 mmol), and Ina (3.6 g, 30 mmol) with N,N-dimethylformamide (DMF, 240 ml) and ethylene glycol (EG, 240 ml). The mixture was sealed in a 1-liter glass bottle with a wire cap. After heating at 140°C for 3 days, the mixture was cooled to room temperature. The resulting precipitate was washed with ethanol and then dried at 60°C overnight.

[0030] Furthermore, nickel cobalt layered double hydroxide (NiCo-LDH), carbon black and polytetrafluoroethylene (PTFE) were mixed in a mass ratio of 8:1:1, ground until uniform, and then extracted with ethanol at 60°C for 12 hours.

[0031] Furthermore, the zinc foil and nickel foam were cut into rectangular strips (4x1.5cm 2) The hydrogel electrolyte was cut into square pieces (2x2 cm 2 ).

[0032] Among them, the electrode material (2.5 mg cm -2) is sandwiched between two sheets of nickel foam and pressed under a pressure of 15 MPa.

[0033] The benefits of the multi-network hydrogel, flexible zinc ion battery, and preparation method and application thereof of the present invention are as follows:

[0034] BPA prepared by the present invention 0.5 The hydrogel has high mechanical properties (ultimate stress 192.52 kPa, ultimate strain 690.58%) and high ionic conductivity (4.607 S / m). It also exhibits excellent antifreeze and moisture retention properties (water retention rate 76.8% (24 hours) at 25°C / 40% humidity) and excellent anti-dendritic ability: it effectively inhibits dendrite growth at the zinc negative electrode.

[0035] The present invention assembles a flexible zinc ion battery based on the prepared hydrogel. The battery has a wide voltage window (2.0V), high rate performance (specific capacity 80.1mAh / g at 7A / g) and long cycle life (5Ag-1, 2000 cycles specific capacity retention rate 95.5%). At the same time, the battery has excellent low temperature resistance and flexibility. At -40°C, it still has a specific capacity of 83.1mAhg -1 (2Ag -1 ) high specific capacity and long cycle life (5Ag -1 The specific capacity retention rate is 61.3% after 3000 cycles) and it maintains high specific capacity after bending 180° (specific capacity 60.67 mAhg-1 at 2Ag-1). BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0037] Figure 1 Synthesis mechanism diagram of the multi-network hydrogel prepared in Example 1 of the present invention

[0038] Figure 2 ad is BPA0, BPA 0.5 , BPA1 and BPA 1.5 Scanning electron microscopy image of the hydrogel. The inset is a magnified image to better illustrate the hydrogel structure.

[0039] Figure 2 ef is BPA x FTIR spectra of hydrogel before and after adsorption of KOH aqueous solution.

[0040] Figure 2g is BPA0, BPA 0.5 , BPA1 and BPA 1.5 X-ray diffraction curve of .

[0041] Figure 3 ac is BPA 0.5 Pictures of bending, twisting, and lifting heavy objects.

[0042] Figure 3 d is different BPA x Strain-stress diagram of the hydrogel electrolyte.

[0043] Figure 3 e is BPA 0.5 Strain-stress diagram of cyclic tension.

[0044] Figure 3 f is different BPA x Ultimate stress / strain diagram of the hydrogel electrolyte.

[0045] Figure 3 gBPAx hydrogel electrolyte at 25℃ and BPA 0.5 Water retention capacity of hydrogel electrolyte at -20°C.

[0046] Figure 4 a is the situation where the battery lights up the parallel LED lights.

[0047] Figure 4 b is the use of BPA x Cyclic voltammetry (CVs) of flexible zinc-ion batteries prepared with hydrogel electrolyte.

[0048] Figure 4 c is the use of BPA x Galvanostatic charge-discharge curves (GCDs) of flexible zinc-ion batteries prepared with hydrogel electrolyte (current density of 2Ag -1 ).

[0049] Figure 4 d is the calculated specific capacity of all devices.

[0050] Figure 4 ef is the use of BPA x Images of electrochemical impedance spectroscopy and cycling performance of flexible zinc-ion batteries prepared with hydrogel electrolytes.

[0051] Figure 5 For use of BPA x Impedance fitting results of flexible zinc-ion batteries prepared with hydrogel electrolyte.

[0052] Figure 6 ac is the use of BPA 0.5Zinc foil cathode with hydrogel (b) and liquid hydrogel (c) before (a) and after cycling.

[0053] Figure 6 de is obtained using BPA at different scan speeds and current densities. 0.5 CVs and GCDs images of flexible zinc-ion batteries prepared with hydrogel electrolyte under deformation.

[0054] Figure 6 f is the use of BPA 0.5 Schematic diagram of deformation of flexible zinc-ion battery prepared with hydrogel electrolyte.

[0055] Figure 6 g for the use of BPA 0.5 CV images of flexible zinc-ion batteries prepared with hydrogel electrolyte at -40°C.

[0056] Figure 6 h for the use of BPA 0.5 GCD image of flexible zinc-ion battery prepared with hydrogel electrolyte at -40°C.

[0057] Figure 6 i is calculated using BPA 0.5 Specific capacity of flexible zinc-ion batteries prepared with hydrogel electrolyte at -40°C.

[0058] Figure 7 BPA at -40°C 0.5 Electrochemical impedance spectroscopy (EIS) curves of hydrogels.

[0059] Figure 8 BPA 0.5 Rate curve of hydrogel-assembled flexible zinc battery at a bending angle of 180°.

[0060] Figure 9 BPA at -40°C 0.5 DSC curve of .

[0061] Figure 10 BPA 0.5 Cycling curves of hydrogel-assembled flexible zinc batteries at -40 °C.

[0062] Figure 11 BPA for use at -40°C x Impedance fitting results of flexible zinc-ion batteries prepared with hydrogel electrolyte.

[0063] Figure 12 A Python code was developed to evaluate the porosity of hydrogels based on scanning electron microscopy (SEM) images. Increasing the polyvinyl alcohol (PVA) content resulted in a decrease in porosity and pore size.

[0064] Figure 13 This is a diagram showing the synthesis mechanism of PBAx multi-network hydrogel and the characterization of its important properties. DETAILED DESCRIPTION

[0065] Based on the accompanying drawings, the following will clearly and completely explain the technical solutions in the application examples. It should be noted that the described embodiments only represent some examples of the present application, rather than all possible implementation plans. All other embodiments that can be obtained by a person of ordinary skill in the art based on the embodiments disclosed in this application without inventive effort shall fall within the scope of protection claimed in this application.

[0066] In order to more clearly illustrate the technical solutions and advantages, the specific implementation methods of this application will be described in more detail below with reference to the accompanying drawings.

[0067] In the first aspect, the present application provides a multi-network hydrogel with excellent mechanical properties, good frost resistance and water retention, the synthesis scheme of which is as follows Figure 1 As shown. First, sodium polyacrylate (PANa) was prepared using ammonium persulfate (APS) as an initiator and N,N'-methylenebisacrylamide (MBAA) as a cross-linking agent. Then bacterial cellulose (BC) and polyvinyl alcohol (PVA) were added to the solvent and gelled to obtain a hydrogel. Different samples of BPA were obtained by changing the amount of PVA. x (x = 0, 0.5, 1 and 1.5). A KOH / zinc acetate (ZnAc) aqueous solution was adsorbed into the hydrogel to prepare a hydrogel electrolyte. The specific preparation method is as follows:

[0068] (1) PVA (0 g, 0.5 g, 1 g or 1.5 g, preferably 0.5 g) was dissolved in deionized water, heated and stirred at 95°C to dissolve, and then allowed to stand at room temperature for one hour to degas;

[0069] (2) Acrylic acid (AA) solution (7.2 ml of acrylic acid (AA) was added to 10 ml of deionized water) and NaOH solution (4 g of sodium hydroxide (NaOH) was ultrasonically dissolved in 10 ml of deionized water) were added dropwise to the NaOH solution under ice bath conditions and mixed. Then, 110 mg of ammonium sulfate (APS) as an initiator and 4 mg of N,N'-methylenebisacrylamide (MBAA) as a cross-linking agent were added and stirred for 30 minutes to prepare a PANa prepolymer solution.

[0070] (3) BC (1.05 wt%) solution was added to the PANa prepolymer solution, stirred thoroughly, and then the PVA solution was added and mixed. Stirring was continued for 10 minutes. 15 ml of the mixed solution was transferred to a Petri dish (round with a diameter of 90 mm) and cured at 65°C for 2 hours.

[0071] (4) The solidified hydrogel was immersed in 15 ml of 6MKOH + 0.2MZnAc electrolyte and fully swelled to obtain a hydrogel electrolyte.

[0072] The porous structures of all electrolytes were observed in SEM images ( Figure 2 ) is clearly visible. BPA0 presents a layered structure ( Figure 2 a), the layers are arranged in parallel and weakly connected, indicating that the binding between BC and PANa is relatively weak. 0.5 Shown as Figure 2 b shows a framework-like porous network. This porous structure is expected to provide space and pathways for electrolyte storage and ion transport. BPA containing more PVA 1.0 With a woven structure ( Figure 2 c), which may be due to the enhanced bonding between PVA and the hydroxyl groups on the BC chains. Further addition of PVA resulted in a less porous structure, e.g. Figure 2 The hydrogel exhibits a dense structure with wrinkles, which is related to the high interconnection between PVA and BC chains.

[0073] The porosity of the hydrogel is Figure 12 As shown in Figure 2, the increase in PVA content leads to a decrease in porosity and pore size.

[0074] Fourier transform infrared spectroscopy (FTIR) was used to further study the structure of the hydrogel before and after electrolyte adsorption. Figure 2 The spectrum of the BPA0 sample shows typical carboxylate characteristics at 1534 cm -1 and 1400cm -1 There are strong peaks at 3000 to 3700 cm, corresponding to the symmetric and asymmetric stretching vibrations of carboxyl groups. -1 The broad peak at 2800 cm -1 The weak peak near 1450cm can be attributed to associated water. -1 and 1300cm -1 The nearby peaks are derived from bacterial cellulose (BC).

[0075] The introduction of PVA resulted in a significant change in the spectrum. 0.5 , BPA1 and BPA 1.5 The peak corresponding to the associated water of the sample is significantly enhanced, indicating that its ability to capture water is improved. At the same time, a strong peak related to the carboxyl group appears: 1750cm -1 The C=O stretching vibration peak at 1250 cm -1 The CO stretching vibration peak at 100 nm indicates that the Na-O bond in PANa is weakened. This is attributed to the hydroxyl groups on PVA and the Na+ In addition, in BPA 0.5 , BPA1 and BPA 1.5 The 1400 cm-1 spectral region can also be clearly observed in the sample. -1 and 1100cm -1 OH bending vibration peak nearby.

[0076] The X-ray diffraction (XRD) pattern of the hydrogel is as follows: Figure 2 As shown in g. It is obvious that higher PVA content leads to higher crystallinity of hydrogel, which is related to the enhanced cross-linking inside the hydrogel. Therefore, we can conclude that PVA is essential for building a multiple network structure. The abundant hydroxyl groups on the PVA chain combine with PANa and BC chains through hydrogen bonds to form a physically cross-linked multiple network structure. With the increase of PVA content, the cross-linking is enhanced, and BPA x The morphology of hydrogels has undergone changes from loose framework, dense framework, network interweaving to dense solid, such as Figure 2 a-2d and Figure 12 shown.

[0077] BPA after water adsorption x FTIR spectrum of hydrogel Figure 2 f. As expected, the peaks associated with the carboxyl groups disappear, indicating that they are associated with water molecules. At the same time, the peaks between 2800 and 3700 cm -1 The broad peak of the hydrogel is greatly enhanced, further proving that the hydrogel has a significant water absorption capacity. These properties are crucial for the application of hydrogel electrolytes.

[0078] Different compositions of BPA x Hydrogels exhibit different mechanical properties and water retention characteristics due to their structural differences. Figure 3 a-3c shows the prepared BPA 0.5 The photo of the hydrogel in a deformed state shows its good flexibility. Its mechanical strength is shown by Figure 3 The strain / stress curves shown in d to 3f are illustrated. As expected, higher PVA content leads to higher stress and smaller strain, which is consistent with its structure and Figure 2 The XRD results shown are consistent. Due to its loose structure and easy to stretch, the ultimate tensile stress of BPA0 is 176.5KPa, corresponding to a strain of 853%. BPA with skeleton and woven structures 0.5 and BPA1, due to the multi-network structure formed by physical cross-linking between hydroxyl groups, show slightly higher stress tolerance, while the strain limit is reduced. 1.5It shows a significant increase in ultimate stress, reaching 258.4 kPa, with the corresponding minimum strain of only 245%, which is attributed to its dense structure - the hydroxyl-rich PVA chains are highly cross-linked on the BC chains. Figure 3 e shows BPA 0.5 The cyclic tensile properties of the hydrogel. The clearly visible hysteresis loop is attributed to the stress delay during strain changes, known as the Bauschinger effect. After repeated elastic deformation, the stress only decreases slightly, indicating good elastic properties and fatigue resistance.

[0079] In addition, the water retention of the hydrogel was also tested. x The electrolyte was placed in an environment with a temperature of 25°C and a relative humidity of 40%. Figure 3 As shown in g, compared with other components, BPA 0.5 Shows significantly higher water retention. After the first 24 hours, BPA 0.5 It can still retain 76.8% of its initial mass, while BPA0 can only retain 67.9% of its initial mass. We believe that the number of hydroxyl groups and the porous structure related to the PVA content are the key reasons. For BPA0 with a layered structure, although it also has water storage space, the limited hydroxyl groups cannot lock water molecules. The low-temperature water retention of the hydrogel was further evaluated by placing it at a low temperature of -20°C. The change in the mass of the hydrogel is negligible, indicating that even below the freezing point, water molecules can still be well locked in the framework structure.

[0080] On the other hand, BPA1 and BPA 1.5 It exhibits relatively poor water retention, and its scanning electron microscopy (SEM) images confirm its limited water storage space. 0.5 The appropriate PVA content ensures that it has both sufficient space and sufficient hydroxyl groups, thus showing the best water retention capacity. It is worth mentioning that the mass of all electrolytes slightly recovered to about 80% of the initial mass within the subsequent 30 hours. This can be attributed to the hydrophilicity imparted by the abundant hydroxyl groups inside the hydrogel, which enables it to further capture water molecules from the air.

[0081] In summary, the present application provides a multi-network hydrogel with excellent mechanical properties, good frost resistance and water retention.

[0082] In the second aspect, the present application provides a BPA-based x A preparation method and application of a hydrogel flexible zinc ion battery, the preparation method comprising:

[0083] A flexible zinc-ion battery using BPA xThe hydrogel electrolyte comprises: positive electrode: nickel cobalt layered double hydroxide (NiCo-LDH), conductive carbon black and polytetrafluoroethylene mixed in a mass ratio of 8:1:1 and loaded on nickel foam; negative electrode: zinc foil; the battery structure is a positive electrode / hydrogel electrolyte / zinc foil sandwich configuration.

[0084] Nickel-cobalt layered double hydroxide (NiCo-LDH) was prepared by mixing Ni(NO₃)₂6H₂O (6.65 g, 22.19 mmol), Co(NO₃)₂ (2.85 g, 9.51 mmol), BDC (6 g, 36 mmol), and Ina (3.6 g, 30 mmol) with N,N-dimethylformamide (DMF, 240 ml) and ethylene glycol (EG, 240 ml). The mixture was sealed in a 1-liter glass bottle with a wire cap. After heating at 140°C for 3 days, the mixture was cooled to room temperature. The resulting precipitate was washed with ethanol and then dried at 60°C overnight.

[0085] Furthermore, nickel cobalt layered double hydroxide (NiCo-LDH), carbon black and polytetrafluoroethylene (PTFE) were mixed in a mass ratio of 8:1:1, ground until uniform, and then extracted with ethanol at 60°C for 12 hours.

[0086] Furthermore, the zinc foil and nickel foam were cut into rectangular strips (4x1.5cm 2 ), the hydrogel electrolyte was cut into square pieces (2x2 cm 2 ).

[0087] Among them, the electrode material (2.5 mg cm -2 ) is sandwiched between two sheets of nickel foam and pressed under a pressure of 15 MPa.

[0088] Use of BPA x As the hydrogel electrolyte, NiCo-LDH as the positive electrode, and zinc foil as the negative electrode, a flexible alkaline zinc battery was assembled to further study the electrochemical performance of the hydrogel electrolyte. Figure 4 As shown in a, two BPA 0.5 The device made of hydrogel electrolyte can successfully light up 14 LED lights. Figure 4 b shows the cyclic voltammetry curve. Compared with the corresponding electrolyte, BPA 0.5 It shows the largest redox peak current. In addition, its oxidation current at 2.0V is significantly smaller than that of BPA0 and BPA1, indicating that it has a wider operating voltage window. 1.5 The minimum oxidation current is shown at 2.0 V, but its small redox peak current indicates that its energy storage capacity is poor. Based on the Fourier transform infrared spectroscopy (FTIR) results, we believe that the hydroxyl groups of PVA and the Na +Ionic bonding releases the carboxyl groups of PANa; these carboxyl groups further combine with water molecules, effectively inhibiting the oxygen evolution reaction (OER). Figure 4 c and 4d show the constant current charge-discharge (GCD) curves and the calculated specific capacity. 0.5 , BPA1 and BPA 1.5 In 1Ag -1 A wide potential window of 2.0 V can be achieved at current densities of 2Ag, which is consistent with the CV results. -1 At the same current density, all devices except BPA0 have similar specific capacity: BPA 0.5 171.3 mAh g -1 , BPA1 is 160.4 mAh g -1 , BPA 1.5 163.6 mAh g -1 However, the use of BPA 0.5 The device showed much better rate performance and coulombic efficiency than other electrolytes. -1 At a current density of 0.5 Still able to show 80.1mAh g -1 The specific capacity of BPA1 and BPA 1.5 Only 34.6mAh g -1 and 12.27mAh g -1 .

[0089] We believe that its ideal pore structure leads to BPA 0.5 The rapid internal ion migration is the main reason, and the EIS results further support this conclusion. Figure 4 e) and -40℃( Figure 7 ) and then tested after discharge. Figure 4 As shown in e, BPA 0.5 The arc region shows a significantly smaller radius. The fitting results based on the EIS spectrum are listed in Figure 5 BPA 0.5 It shows a significantly reduced Rs value (0.413Ω), corresponding to an ionic conductivity of 4.607Sm -1 , which is related to its unique framework-like porous structure that helps promote ion migration. In addition, BPA 0.5 It also shows lower Rct, Wo-R and Wo-T values. Generally, a smaller Rct is associated with a faster redox reaction at the electrolyte / electrode interface, while smaller Wo-R and Wo-T are associated with smaller mass transfer resistance. Therefore, we can conclude that BPA 0.5The better interaction between the electrolyte and the electrode can enhance the electrochemical reaction activity and thus improve the device performance. -1 The cycle stability was tested at a charge and discharge current density of Figure 4 f. The capacity of all devices increased in the initial stage, which was due to the (electrolyte) wetting process of the electrode. 0.5 It still showed significantly better performance, maintaining a capacity retention rate of 95.5% after 2000 cycles.

[0090] Compared with liquid electrolytes, hydrogel electrolytes have unique advantages in the application of basic aqueous zinc batteries. Figure 6 a-6c demonstrates the use of BPA 0.5 SEM (Scanning Electron Microscope) images of zinc foil cathodes with electrolyte and liquid electrolyte before and after cycling. 0.5 It can effectively prevent the growth of zinc dendrites and improve the safety and service life of the device.

[0091] The flexibility of the device Figure 6 As shown in d-6f. Figure 8 As shown, in the 180° bending state, the device -1 It can still provide 60.67mAh g -1 The decrease in capacity is related to the insufficient contact between the electrode and the electrolyte.

[0092] A significant advantage of hydrogel electrolytes over liquid electrolytes is the protective antifreeze ability conferred by their bound water molecules. Therefore, DSC (differential scanning calorimetry) tests were conducted in the temperature range of -60 to 10°C to examine BPA. x Antifreeze properties (such as Figure 9 Clearly, no peaks associated with freezing exotherm were observed. 0.5 Electrochemical testing of the device at -40°C further confirmed its antifreeze performance. Figure 6 The CV (cyclic voltammetry) curve shown in g shows symmetrical redox peaks, indicating good coulombic efficiency. Figure 6 h shows the GCD (constant current charge and discharge) curve and Figure 6 The calculated specific capacity shows that the device can -1 It can still provide 83.1mAh g -1 The capacity drop can be attributed to reduced ion diffusion efficiency and increased interfacial impedance. As shown in the GCD curve, the 0.2V IR drop (ohmic internal resistance drop) is significantly greater than the GCD curve measured at 25°C. Figure 7The EIS (electrochemical impedance spectroscopy) spectrum of the hydrogel at -40 ° C is shown as well as Figure 11 The fitting results in further show that Rs (solution / bulk resistance) increases due to the decrease in temperature. Figure 10 The device was demonstrated to be -40℃, 5A g -1 Cycling performance under current density. After 3000 cycles ( Figure 10 ), the specific capacity can still maintain 61.3% of the initial capacity, which further proves that BPA 0.5 Antifreeze properties of hydrogel electrolytes.

[0093] In summary, this application provides a BPA-based x Preparation method and application of hydrogel flexible zinc ion battery

[0094] The beneficial effects of the present invention are:

[0095] BPA was synthesized using bacterial cellulose (BC), sodium polyacrylate (PANa) and polyvinyl alcohol (PVA) x Hydrogel. Its performance can be improved by optimizing the content of PVA. The hydroxyl groups of PVA can react with the Na + Ionic bonding strengthens the cross-linking between polymer chains in the hydrogel, thereby improving mechanical strength and regulating the porous structure. 0.5 The hydrogel exhibits ideal water retention capacity and mechanical strength, and is expected to be used as a hydrogel electrolyte for basic aqueous zinc batteries. 0.5 Devices assembled with hydrogel electrolytes at 2Ag -1 The current density was 171.3 mAh g -1 The specific capacity of 7Ag -1 The current density still maintains 80.1 mAh g -1 In addition, the hydrogel electrolyte exhibits significant protection for the zinc cathode and excellent antifreeze properties, indicating its broad application potential.

[0096] For those skilled in the art, after understanding and practicing the contents of this specification, it is natural to think of other implementations of this application. Our protection intends to cover all modifications, different uses, or adaptive adjustments based on the core concept of this application, even if these adjustments use techniques known in the art but not described here. The examples in this specification are only for facilitating understanding.

[0097] It should be emphasized that the scope of this application is not limited to the specific structures described in the text or shown in the drawings. As long as it is within the spirit of this application, various modifications are permitted. The sole basis for determining whether there is infringement is the content of the claims.

Claims

1. A multi-network hydrogel electrolyte, characterized in that The invention relates to a composite of bacterial cellulose (BC), sodium polyacrylate (PANa) and polyvinyl alcohol (PVA), wherein the content of PVA is x (x=0 g, 0.5 g, 1 g or 1.5 g) by mass and is denoted as BPAx. The preparation method comprises the following steps: (1) PVA (preferably 0.5 g) was dissolved in deionized water, heated and stirred at 95°C to dissolve, and then allowed to stand at room temperature for 1 hour for degassing; (2) Acrylic acid (AA) solution (7.2 ml acrylic acid (AA) was added to 10 ml deionized water) and NaOH solution (4 g sodium hydroxide (NaOH) was ultrasonically dissolved in 10 ml deionized water) were mixed in an ice bath. 110 mg initiator ammonium persulfate (APS) and 4 mg cross-linker N,N'-methylenebisacrylamide (MBAA) were added and stirred for 30 minutes to prepare PANa prepolymer solution. (3) BC solution (1.05 wt%) was added to the PANa prepolymer solution, stirred thoroughly, and then the PVA solution was added and mixed. Stirring was continued for 10 minutes. 15 ml of the mixed solution was transferred to a Petri dish (round and 90 mm in diameter) and cured at 65°C for 2 hours. (4) The solidified hydrogel was immersed in 15 ml of 6M KOH + 0.2M ZnAc electrolyte solution and fully swelled to obtain a hydrogel electrolyte.

2. The hydrogel electrolyte according to claim 1, characterized in that The electrolyte in step (4) is an alkaline aqueous solution containing 6M KOH and 0.2M zinc acetate (ZnAc).

3. A multi-network hydrogel electrolyte prepared by the preparation method according to any one of claims 1-2.

4. A flexible zinc ion battery, characterized in that: It uses BPAx hydrogel electrolyte and includes: positive electrode: nickel cobalt layered double hydroxide (NiCo-LDH), conductive carbon black and polytetrafluoroethylene mixed in a mass ratio of 8:1:1 and loaded on nickel foam; negative electrode: zinc foil: the battery structure is a positive electrode / hydrogel electrolyte / zinc foil sandwich configuration.

5. The flexible zinc ion battery according to claim 4, characterized in that: Nickel-cobalt layered double hydroxide (NiCo-LDH) was prepared by mixing Ni(NO₃)₂6H₂O (6.65 g, 22.19 mmol), Co(NO₃)₂ (2.85 g, 9.51 mmol), BDC (6 g, 36 mmol), and Ina (3.6 g, 30 mmol) with N,N-dimethylformamide (DMF, 240 ml) and ethylene glycol (EG, 240 ml). The mixture was sealed in a 1-liter glass bottle with a wire cap. After heating at 140°C for 3 days, the mixture was cooled to room temperature. The resulting precipitate was washed with ethanol and then dried at 60°C overnight.

6. The flexible zinc ion battery according to claim 4, characterized in that Nickel cobalt layered double hydroxide (NiCo-LDH), carbon black and polytetrafluoroethylene (PTFE) were mixed in a mass ratio of 8:1:1, ground until uniform, and then extracted with ethanol at 60°C for 12 hours.

7. The flexible zinc ion battery according to claim 4, characterized in that: Cut the zinc foil and nickel foam into rectangular strips (4x1.5cm 2 ), hydrogel electrolyte was cut into square pieces (2x2cm 2 ).

8. The flexible zinc ion battery according to claim 4, characterized in that: When preparing the positive electrode, the electrode material (2.5 mg-cm -2 ) is sandwiched between two sheets of nickel foam and pressed under a pressure of 15 MPa.

9. Use of the multi-network hydrogel electrolyte according to claim 3 in the preparation of flexible zinc ion batteries.

Images