Enhanced multi-network hydrogel electrolyte and preparation method and application thereof

Abstract

The invention discloses an enhanced multi-network hydrogel electrolyte as well as a preparation method and application thereof, and belongs to the field of aqueous zinc ion batteries. Firstly, oxygen terminal nano-diamond is uniformly dispersed in deionized water to form a mixed solution, then sodium alginate is added to be fully dissolved, and the mixed solution is uniformly dispersed; the oxygen terminal nano-diamond-sodium alginate homogeneous solution is obtained. The solution is mixed with a polyvinyl alcohol solution which is completely molten through water bath heating and a proper amount of glycerol, and all the components are ensured to be uniformly distributed through sufficient stirring. And then, through repeated freezing and thawing and zinc ion cross-linking and curing effects, the oxygen terminal nano-diamond enhanced hydrogel electrolyte with a multi-network structure is finally formed. The oxygen terminal nano-diamond is highly uniformly dispersed in the hydrogel electrolyte, dendritic crystal growth and side reaction are effectively inhibited through a triple synergistic mechanism of enhancing the mechanical strength, reducing the free water content and increasing the zinc ion transference number by surface functional groups, and the super-long cycle stability is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of aqueous zinc-ion batteries, and particularly relates to an oxygen-terminal nanodiamond-reinforced multi-network hydrogel electrolyte as well as a preparation method and application thereof. BACKGROUND

[0002] As a new energy storage technology, aqueous zinc-ion batteries have broad application prospects in large-scale energy storage and flexible wearable devices due to their excellent safety, low cost, environmental friendliness, and high power density. Compared with lithium-ion batteries, zinc resources are abundant and widely distributed, which can effectively avoid energy crisis. However, the commercialization process of zinc-ion batteries still faces significant challenges. The energy density of zinc metal anode is generally lower than that of lithium-ion batteries, which limits its application in high-end scenarios such as electric vehicles; more importantly, the short cycle life is the core bottleneck, which is mainly due to the side reactions such as dendrite growth, hydrogen evolution and corrosion of zinc anode during charging and discharging, leading to short circuit, capacity decay and even failure of the battery. The traditional uniform structure electrolyte or separator cannot meet the differentiated needs of the positive and negative electrodes for water molecule activity, often sacrificing the capacity of the positive electrode while suppressing the negative electrode side reactions, so that the overall performance of the battery is not optimal.

[0003] In the specific form selection of zinc anode, zinc powder anode shows unique application potential compared to the common zinc foil anode. Zinc powder anode has the advantages of large specific surface area, flexible control of zinc utilization, easy large-scale production, and better suitability for flexible devices. In particular, its large specific surface area helps to reduce the local current density, theoretically improving the uniformity of zinc deposition and hopefully improving the energy density of the battery. However, zinc powder anode also introduces new technical challenges: the electrode preparation process directly determines the structural stability and electrochemical performance of the electrode. Due to the significantly increased contact area with the electrolyte, zinc powder anode is more prone to water-phase side reactions such as hydrogen evolution and corrosion, which exacerbates electrode polarization and leads to gas production and capacity loss. In addition, zinc powder is difficult to avoid uneven deposition and dendrite problems during the cycle process, causing top-end deposition, bottom-end dissolution and other adverse phenomena, affecting the effective utilization of zinc and the long-term cycle stability of the battery. Therefore, it is particularly important to develop a new electrolyte system that can be well matched with zinc powder anode and cooperatively solve the above problems. SUMMARY

[0004] The purpose of the present application is to propose an oxygen-terminal nanodiamond-reinforced multi-network hydrogel electrolyte and a preparation method thereof in order to solve the problems of serious corrosion and dendrite growth of zinc powder anode. The purpose is to greatly improve the cycle life and stability of zinc powder anode in aqueous zinc-ion batteries.

[0005] The technical solutions adopted by the present application are as follows: The enhanced multi-network hydrogel electrolyte in the application is formed by physical cross-linking and chemical cross-linking of oxygen-terminated nanodiamond, sodium alginate, polyvinyl alcohol, glycerol and zinc salt solution; the thickness of the hydrogel electrolyte is 1-4 mm, the oxygen-terminated nanodiamond is uniformly dispersed in the multi-network hydrogel matrix formed by sodium alginate, polyvinyl alcohol, glycerol and zinc salt, and the mass concentration of the oxygen-terminated nanodiamond is 0.5%-2% of the total mass of the hydrogel.

[0006] The preparation method of the enhanced multi-network hydrogel electrolyte in the application comprises the following specific steps: (1) 1.5~2 mg oxygen-terminated nanodiamond is added to 10 mL deionized water, and the oxygen-terminated nanodiamond is uniformly dispersed by ultrasonic treatment to obtain an oxygen-terminated nanodiamond suspension; (2) 0.1~0.2 g of sodium alginate powder is added to 5 mL of the oxygen-terminated nanodiamond suspension, and the sodium alginate is completely dissolved in the oxygen-terminated nanodiamond suspension to obtain an oxygen-terminated nanodiamond-sodium alginate solution; (3) 0.4-0.6 g of polyvinyl alcohol is added to 5 mL of deionized water and completely dissolved by water bath heating to obtain a polyvinyl alcohol aqueous solution.

[0007] (4) The oxygen-terminated nanodiamond-sodium alginate solution obtained in step (2) and the polyvinyl alcohol aqueous solution obtained in step (3) are mixed, 0.2-0.4 ml of glycerol is added and stirred uniformly to obtain an oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol solution.

[0008] (5) The solution obtained in step (4) is poured into a container, and after standing for 1 h, it is repeatedly frozen and thawed three times.

[0009] (6) The hydrogel obtained in step (5) is soaked in a zinc sulfate solution to complete the cross-linking reaction; after the surface is wiped dry, an oxygen-terminated nanodiamond enhanced multi-network hydrogel electrolyte is obtained.

[0010] Preferably, the oxygen-terminated nanodiamond in step (1) is a detonation nanodiamond treated by ultraviolet irradiation.

[0011] Preferably, after the sodium alginate powder in step (2) is added to the oxygen-terminated nanodiamond suspension, it is stirred for 0.5 h.

[0012] Preferably, in step (3), the temperature of water bath heating is 95°, and the time of water bath heating is 1 h.

[0013] Preferably, in step (5), the size of the container is 100 cm -2 square.

[0014] Preferably, in step (5), the freeze-thaw treatment of the ONDs-SA-PVA solution is freezing at -18° for 12 h and thawing at 25° for 0.5 h.

[0015] Preferably, in step (6), the concentration of the zinc sulfate solution is 1.5-2.5 mol·L -1 , and the soaking time is 72 h.

[0016] The enhanced multi-network hydrogel electrolyte, the preparation method thereof, and the application of the enhanced multi-network hydrogel electrolyte in a water-based zinc ion battery.

[0017] Compared with the prior art, the application has the beneficial effects that: (1) The application forms multiple hydrogen bond cross-linking through the rich oxygen-containing functional groups (carboxyl and hydroxyl) on the oxygen-terminated nanodiamond surface and the hydrogel network, significantly enhances the mechanical strength and structural stability of the electrolyte, effectively inhibits the growth and penetration of zinc dendrites, and enables the symmetrical battery to achieve an ultra-long cycle life of more than 2500 h, which is two orders of magnitude higher than that of a traditional sodium alginate-polyvinyl alcohol electrolyte and is superior to most reported zinc powder negative electrode systems.

[0018] (2) The application endows the electrolyte with excellent flexibility and deformation resistance, and the soft-pack battery assembled therefrom still maintains stable circulation in a bent state, meeting the needs of flexible wearable devices.

[0019] (3) The application adopts a preparation process combining freeze-thaw and ionic cross-linking to convert molecular chains into hydrogels, and has the advantages of simple process, mild conditions, no need for complex equipment or expensive raw materials, and easy scale-up production, thereby providing a feasible path for the industrial application of the water-based zinc ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The scanning electron microscope images of the hydrogel electrolytes in the examples and comparative examples are shown in Figure 1. Figure 2 The scanning electron microscope images of the zinc powder anodes in the examples and comparative examples are shown in Figure 2. Figure 3 The scanning electron microscope images of the hydrogel electrolytes after cycling in the examples and comparative examples are shown in Figure 3. Figure 4 The scanning electron microscope images of the zinc powder negative electrodes after cycling in the examples and comparative examples are shown in Figure 4. Figure 5 The scanning electron microscope images of the copper electrodes after cycling in the examples and comparative examples are shown in Figure 5. Figure 6 The tensile strength diagrams of the examples and comparative examples are shown in Figure 6. Figure 7 The ZnP||ZnP symmetrical battery in the examples and comparative examples at a current density of 1 mA cm -2electrochemical stability performance comparison chart under the following conditions; Figure 8 Half-cells assembled with zinc powder anodes of the examples and comparative examples were tested for long cycle performance at 1 mA cm -2 , 1 mAh cm -2 under the following conditions; Figure 9 Full-cells assembled with zinc powder anodes of the examples and comparative examples were tested for long cycle performance at 10 A g -1 under the following conditions.

[0021] Figure 10 Soft-pack batteries assembled with zinc powder anodes of the examples were used to power a watch under different conditions. DETAILED DESCRIPTION

[0022] The application will be further described in details below with reference to the accompanying drawings and examples, it should be noted that the following examples are intended to facilitate the understanding of the application and do not limit the application in any way. EXAMPLES

[0023] A method for preparing an oxygen-terminated nanodiamond-reinforced multi-network hydrogel electrolyte comprises the following steps: (1) 1.5 mg of oxygen-terminated nanodiamond is added to 10 mL of deionized water, and the oxygen-terminated nanodiamond is uniformly dispersed by ultrasonic treatment to obtain an oxygen-terminated nanodiamond suspension; (2) 0.15 g of sodium alginate powder is added to 5 mL of the oxygen-terminated nanodiamond suspension, and the sodium alginate is completely dissolved in the oxygen-terminated nanodiamond suspension by stirring for 0.5 h to obtain an oxygen-terminated nanodiamond-sodium alginate solution; (3) 0.5 g of polyvinyl alcohol is added to 5 mL of deionized water and completely dissolved by heating in a 95°C water bath for 1 h to obtain a polyvinyl alcohol aqueous solution.

[0024] (4) The oxygen-terminated nanodiamond-sodium alginate solution obtained in step (2) and the polyvinyl alcohol aqueous solution obtained in step (3) are mixed, 0.3 ml of glycerol is added and stirred uniformly to obtain an oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol solution.

[0025] (5) The solution obtained in step (4) is poured into a container and left still for 1 h. Freeze at -18°C for 12 h and then melt at 25°C for 0.5 h, repeating three times.

[0026] (6) The hydrogel obtained in step (5) is soaked in 2 mol·L -1The cross-linking reaction was completed in zinc sulfate solution; after wiping the surface dry, an oxygen-terminated nanodiamond-reinforced multi-network hydrogel electrolyte was obtained.

[0027] Comparative Example The preparation method of a common hydrogel electrolyte includes the following steps: (1) Add 0.15 g sodium alginate powder to 5 mL of deionized water and stir for 0.5 h to completely dissolve the sodium alginate to obtain a sodium alginate solution. (2) Add 0.5 g of polyvinyl alcohol to 5 mL of deionized water and heat it in a 95°C water bath for 1 h to completely dissolve it, thus obtaining a polyvinyl alcohol aqueous solution.

[0028] (3) Mix the sodium alginate solution obtained in step (1) and the polyvinyl alcohol aqueous solution obtained in step (3), add 0.3 ml of glycerol and stir evenly to obtain sodium alginate-polyvinyl alcohol solution.

[0029] (4) Pour the solution obtained in step (3) into a container and let it stand for 1 h. Repeat the process three times by freezing at -18℃ for 12 h and then thawing at 25℃ for 0.5 h.

[0030] (5) Immerse the hydrogel obtained in step (4) in 2 mol·L⁻¹ water. -1 The cross-linking reaction was completed in zinc sulfate solution; after wiping the surface dry, a common hydrogel electrolyte was obtained.

[0031] Effect verification: Different hydrogel electrolytes were cut into discs with a diameter of 16 mm.

[0032] Using a CR2032 button cell casing, two zinc powder anodes with a diameter of 14 mm were used as the positive and negative electrodes of the symmetrical cell, respectively. Different hydrogel electrolytes were used as separators to assemble a ZnP||ZnP symmetrical cell.

[0033] Using a CR2032 button cell casing, a zinc powder anode with a diameter of 14 mm is used as the negative electrode of the symmetrical cell, and a copper sheet with a diameter of 14 mm is used as the positive electrode of the symmetrical cell. Different hydrogel electrolytes are used as separators to assemble a ZnP||Cu half cell.

[0034] Using a CR2032 button cell casing, VO2:acetylene black:PVDF were dispersed evenly in N-methylpyrrolidone at a ratio of 7:2:1 to form a slurry. This slurry was then coated onto carbon paper and dried under vacuum at 60°C for 12 hours to serve as the positive electrode (diameter 12 mm, average active material mass of a single electrode 3.0 mg / cm³). -2), a zinc powder anode with a diameter of 14 mm was used as the negative electrode of the symmetric cell, and different hydrogels were used as electrolytes to assemble the full cell.

[0035] 1. Electron microscopy test: Figure 1 The surface scanning electron micrographs of the hydrogels of the examples and comparative examples show that the scanning images show irregular structures within the sodium alginate-polyvinyl alcohol hydrogel, and the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel shows a more compact pore network and a more uniform hydrogel structure.

[0036] Figure 2 The scanning electron micrograph of the commercial zinc powder negative electrode. The commercial zinc powder negative electrode is composed of a thin film coated on a copper current collector, including zinc powder, conductive carbon additives and binder.

[0037] Figure 3 The scanning electron micrographs of the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel electrolyte and the sodium alginate-polyvinyl alcohol hydrogel electrolyte after 50 cycles are shown. After cycling, the sodium alginate-polyvinyl alcohol hydrogel is severely damaged, forming a layered loose structure, while the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel structure remains stable with no obvious change. This shows that the oxygen-terminated nanodiamond enhances the mechanical properties of the sodium alginate-polyvinyl alcohol hydrogel.

[0038] Figure 4 The scanning electron micrographs of the zinc powder negative electrode using the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel electrolyte and the sodium alginate-polyvinyl alcohol hydrogel electrolyte after 50 cycles are shown. For the comparative example, after cycling, the zinc powder negative electrode surface is uneven because zinc ions are deposited on the zinc powder negative electrode in an agglomeration manner. This rough structure further exacerbates the uneven deposition. The anode of the experimental example has a relatively flat surface, with parallel planes growing on the (002) plane of zinc. This shows that the oxygen-terminated nanodiamond can guide the uniform deposition of zinc ions.

[0039] Figure 5 The scanning electron micrographs of the copper electrode using the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol and sodium alginate-polyvinyl alcohol hydrogel electrolyte after 50 cycles in the corresponding asymmetric cell are shown. The copper electrode surface corresponding to the sodium alginate-polyvinyl alcohol hydrogel electrolyte has a large amount of zinc residue, and the copper electrode surface corresponding to the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel electrolyte is cleaner. This shows that the incorporation of oxygen-terminated nanodiamond makes the deposition and stripping of zinc ions on the copper electrode more complete.

[0040] 2. Mechanical property test: Figure 6The stress-strain curves of oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel and sodium alginate-polyvinyl alcohol hydrogel are shown. The tensile strength of oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel and sodium alginate-polyvinyl alcohol hydrogel is 0.63 MPa and 0.36 MPa, respectively. Oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel exhibits greater tensile strength, thus has excellent mechanical properties, which is attributed to greater polymer chain entanglement within the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel network.

[0041] 3. Symmetric cell test: Figure 7 The electrochemical stability results of ZnP||ZnP symmetric cells assembled with the ZnP||ZnP symmetric cells of the examples and the comparative examples at a current density of 1 mA cm -2 It can be seen that the ZnP||ZnP symmetric cell assembled with the sodium alginate-polyvinyl alcohol hydrogel electrolyte of the comparative example failed only after 26 hours, in comparison, the ZnP||ZnP symmetric cell assembled with the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel electrolyte of the example reached 2500 hours, which is 100 times of the comparative example. These results demonstrate that the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel electrolyte can effectively protect the zinc powder negative electrode, thus achieving longer cycle life.

[0042] 4. Half-cell test: Figure 8 The electrochemical stability results of ZnP||Cu half-cells assembled with the ZnP||Cu half-cells of the examples and the comparative examples at a current density of 1 mA cm -2 The ZnP||Cu half-cell assembled with the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel electrolyte of the example maintained excellent cycle performance throughout the entire cycle process, with minimal fluctuation, and the average cycle efficiency remained at 99.6% after 540 cycles at a current density of 1 mA cm -2 In comparison, the cycle efficiency of the ZnP||Cu half-cell assembled with the sodium alginate-polyvinyl alcohol hydrogel electrolyte of the comparative example decreased sequentially after about 60 cycles. These results highlight the key role of the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel electrolyte in achieving long-term stable electrode deposition / stripping performance.

[0043] 5. Full-cell test: Figure 9 The long cycle performance test results of full cells assembled with the examples and the comparative examples at 10 A g -1 The ZnP||VO2 full cell assembled with the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel electrolyte of the example maintained excellent cycle performance throughout the entire cycle process, with minimal fluctuation, and the average cycle efficiency remained at 99.6% after 540 cycles at a current density of 1 mA cm -1The capacity reached 76 mAh g -1 after 2,000 cycles under the same conditions. Its specific capacity is higher than that of the ZnP || VO2 full cell assembled with the sodium alginate-polyvinyl alcohol hydrogel electrolyte of the comparative example (13 mAh g -1 ), and is more stable. This is attributed to its fast reaction kinetics and optimized Zn 2+ deposition / stripping behavior, thus maintaining excellent rate performance. These results highlight the key role of the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel in stabilizing the zinc powder anode.

[0044] 6. Soft pack battery test: Figure 10 The results of the soft pack battery using the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel electrolyte of the example to power the electronic watch. When the battery can still continuously power the electronic clock under the conditions of normal, pressure, bending and cutting. This verifies the feasibility of the oxygen-terminated nanodiamond-sodium alginate-polyvinyl alcohol hydrogel electrolyte in flexible and wearable electronic devices.

Claims

1. An enhanced multi-network hydrogel electrolyte, characterized in that, It is composed of oxygen-terminated nanodiamonds, sodium alginate, polyvinyl alcohol, glycerol and zinc salt solution through physical and chemical cross-linking; the thickness of the hydrogel electrolyte is 1-4 mm, and the oxygen-terminated nanodiamonds are uniformly dispersed in the multi-network hydrogel matrix formed by sodium alginate, polyvinyl alcohol, glycerol and zinc salt, with a mass concentration of 0.5%-2% of the total mass of the hydrogel.

2. The method for preparing the enhanced multi-network hydrogel electrolyte according to claim 1, characterized in that, The steps of this method are as follows: (1) Add 1.5~2 mg of oxygen-terminated nanodiamond to 5 mL of deionized water and use ultrasound to uniformly disperse the oxygen-terminated nanodiamond to obtain an oxygen-terminated nanodiamond suspension. (2) Add 0.1~0.2 g sodium alginate powder to 5 mL oxygen-terminated nanodiamond suspension and completely dissolve sodium alginate in oxygen-terminated nanodiamond suspension to obtain oxygen-terminated nanodiamond-sodium alginate solution. (3) Add 0.4-0.6 g of polyvinyl alcohol to 5 mL of deionized water and heat in a water bath until completely dissolved to obtain a polyvinyl alcohol aqueous solution; (4) Mix the nanodiamond-sodium alginate solution obtained in step (2) and the polyvinyl alcohol aqueous solution obtained in step (3), and add 0.2-0.4 ml of glycerol and stir evenly to obtain ONDs-SA-PVA solution; (5) Pour the ONDs-SA-PVA solution obtained in step (4) into a container, let it stand for 1 h, and then freeze and thaw it three times to obtain a hydrogel. (6) The hydrogel obtained in step (5) is immersed in zinc sulfate solution to complete the crosslinking reaction; after wiping the surface dry, an oxygen-terminated nanodiamond-reinforced multi-network hydrogel electrolyte is obtained.

3. The method for preparing the enhanced multi-network hydrogel electrolyte according to claim 2, characterized in that, In step (1), the oxygen-terminated nanodiamond is detonated nanodiamond treated with ultraviolet light.

4. The method for preparing the enhanced multi-network hydrogel electrolyte according to claim 2, characterized in that, In step (2), sodium alginate powder is added to oxygen-terminated nanodiamond suspension and stirred for 0.5 h.

5. The method for preparing the enhanced multi-network hydrogel electrolyte according to claim 2, characterized in that, In step (3), the water bath heating temperature is 95°C and the water bath heating time is 1 hour.

6. The method for preparing the enhanced multi-network hydrogel electrolyte according to claim 2, characterized in that, In step (5), the freeze-thaw treatment of the ONDs-SA-PVA solution is to freeze at -18°C for 12 h and then thaw at 25°C for 0.5 h.

7. The method for preparing the enhanced multi-network hydrogel electrolyte according to claim 2, characterized in that, In step (6), the concentration of the zinc sulfate solution is 1.5~2.5 mol·L⁻¹. -1 The soaking time is 72 hours.

8. The application of the enhanced multi-network hydrogel electrolyte according to claim 1 in an aqueous zinc-ion battery.

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