Anti-freeze self-healing hydrogel electrolyte and zinc-ion battery

Abstract

This invention relates to an antifreeze self-healing hydrogel electrolyte and a zinc-ion battery, belonging to the field of flexible electronics and low-temperature energy storage technology. The hydrogel is formed by the polymerization reaction of polymer monomers, boron nitride nanosheets, a photoinitiator, and water. The hydrogel is then immersed in a zinc salt solution to obtain the antifreeze self-healing hydrogel electrolyte. The boron nitride nanosheets have a lateral dimension of less than 500 nm. Based on the total mass of polymer monomers, boron nitride nanosheets, photoinitiator, and water (100%), the mass fraction of polymer monomers is 20%–50%, the mass fraction of boron nitride nanosheets is 0.5%–10%, and the mass fraction of photoinitiator is 0.1%–2%. This hydrogel retains its self-healing function at low temperatures. After healing, the severed interface recovers most of its mechanical strength and ionic conductivity, enabling the assembled self-healing battery to operate stably at -30°C, greatly improving the durability and reliability of the device in low-temperature environments.

Description

Technical Field

[0001] This invention relates to antifreeze self-healing hydrogel electrolytes and zinc-ion batteries, belonging to the field of flexible electronics and low-temperature energy storage technology. Background Technology

[0002] Hydrogels are soft materials composed of a three-dimensional polymer network and a large number of water molecules. Due to their bio-tissue-like flexibility, high ionic conductivity, and good biocompatibility, they show great promise for applications in flexible electronics, wearable sensors, soft robots, and energy storage devices. However, the high water content (typically 50-90 wt%) in traditional hydrogels makes them extremely prone to freezing in sub-zero environments. The formation of ice crystals disrupts the polymer network, causing the hydrogel to change from tough to brittle. Ion transport channels are blocked, leading to a sharp decline or even failure of its mechanical and electrical properties at low temperatures. This severely limits the application of hydrogel-based devices in cold regions.

[0003] Currently, conventional strategies for improving the antifreeze properties of hydrogels mainly involve introducing high concentrations of salts, polyols (such as ethylene glycol and glycerol), or deep eutectic solvents into the hydrogel network as cryoprotectants to lower the freezing point through colligative effects. However, these methods often suffer from problems such as easy solvent leakage, potential toxic side effects, and significant weakening of the hydrogel's mechanical strength, which limits their reliability in practical applications.

[0004] In addition, zinc-ion batteries (ZIBs) have attracted widespread attention as a safe, low-cost, and environmentally friendly aqueous battery system. However, their aqueous electrolytes also face the risk of freezing at low temperatures, leading to a decrease in ionic conductivity and a deterioration in battery performance. Simultaneously, the zinc anode is prone to dendrite formation during cycling, which may puncture the separator, causing a short circuit and affecting the battery's cycle life and safety. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide an antifreeze self-healing hydrogel electrolyte and a zinc ion battery.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] An antifreeze self-healing hydrogel electrolyte is provided, wherein the hydrogel is formed by polymerization of polymer monomers, boron nitride nanosheets, photoinitiator and water, and the hydrogel is immersed in zinc salt solution to obtain the antifreeze self-healing hydrogel electrolyte; wherein the lateral size of the boron nitride nanosheets is less than 500 nm, and based on the total mass of polymer monomers, boron nitride nanosheets, photoinitiator and water as 100%, the mass fraction of polymer monomers is 20%~50%, the mass fraction of boron nitride nanosheets is 0.5%~10%, and the mass fraction of photoinitiator is 0.1%~2%.

[0008] Preferably, the boron nitride nanosheets are two-dimensional hexagonal boron nitride nanosheets (h-BN) or cubic boron nitride nanosheets (c-BN).

[0009] Preferably, the lateral dimension of the boron nitride nanosheets is 50~150 nm.

[0010] Preferably, the boron nitride nanosheets have a mass fraction of 1% to 5%.

[0011] Preferably, the polymer monomers are N,N-dimethylacrylamide (DMAA) and methacrylic acid (MAA) in a molar ratio of 1 to 10:1.

[0012] Preferably, the mass fraction of the polymer monomer is 25% to 40%.

[0013] Preferably, the photoinitiator is 2,2-diethoxyacetophenone.

[0014] Preferably, the zinc salt is one or more of zinc trifluoromethanesulfonate, zinc sulfate, zinc perchlorate, and zinc chloride, and the zinc salt concentration is 1M to 4M.

[0015] The present invention discloses a method for preparing an antifreeze self-healing hydrogel electrolyte, the method comprising the following steps:

[0016] Polymer monomers, photoinitiators, and boron nitride nanosheets were added sequentially to deionized water, mixed and dispersed evenly, and then injected into a mold. The mixture was irradiated under 50-200W ultraviolet light for 10-60 minutes to obtain a hydrogel. The hydrogel was immersed in a zinc salt solution for more than 12 hours. After the immersion was completed, the hydrogel electrolyte was obtained.

[0017] A zinc-ion battery, the battery comprising a positive electrode, a negative electrode, and the antifreeze self-healing hydrogel electrolyte described in this invention.

[0018] Preferably, the positive electrode sheet includes a positive current collector and a positive active material, ammonium intercalated vanadium oxide.

[0019] Preferably, the negative electrode is zinc.

[0020] Beneficial effects This invention introduces polar boron nitride nanosheets into a hydrogel electrolyte. The strong interfacial polar field on the nanosheets orients neighboring water molecules and enhances the interaction between water molecules and polymer chains, thereby converting a large amount of free water into bound water. This bound water layer can adsorb onto the initial ice nucleus, inhibiting its growth. Combined with the geometric confinement effect provided by the nanosheets and polymer network, the hydrogel exhibits no noticeable freezing phenomenon over a wide temperature range of -150°C to 20°C. Even at extremely low temperatures of -80°C, the hydrogel maintains high toughness, stretchability, and puncture resistance, avoiding the embrittlement problem of traditional hydrogels. This hydrogel electrolyte maintains high ionic conductivity at low temperatures, ensuring the normal operation of zinc-ion batteries in frigid environments. Simultaneously, the introduction of h-BN helps guide the uniform deposition of zinc ions, effectively inhibiting the growth of zinc anode dendrites and significantly extending battery cycle life. This hydrogel retains its self-healing function at low temperatures. After healing, the severed interface recovers most of its mechanical strength and ionic conductivity, enabling the assembled self-healing battery to operate stably at -30°C, significantly improving the device's durability and reliability in low-temperature environments. This invention does not rely on complex monomer designs or toxic reagents, providing a scalable platform for developing low-temperature resistant flexible materials. Attached Figure Description

[0021] Figure 1 The images show the ice crystal morphology of pure water (Comparative Example 1), h-BN aqueous solution (Comparative Example 2), P(DMAA-co-MAA) hydrogel (Comparative Example 1), and P(DMAA-co-MAA) / h-BN composite hydrogel provided in Example 1.

[0022] Figure 2 The graph shows the growth rate of ice crystals at different supercooling conditions for Control Example 1 (pure water), Control Example 2 (h-BN aqueous solution), Comparative Example 1 (P(DMAA-co-MAA) hydrogel), and the P(DMAA-co-MAA) / h-BN composite hydrogel provided in Example 1.

[0023] Figure 3 Differential scanning calorimetry normal plots of pure water (Comparative Example 1) and P(DMAA-co-MAA) / h-BN composite hydrogels provided in Examples 1-2 and Comparative Examples 2-5, respectively.

[0024] Figure 4 The DSC curves are for comparison example 1, example 2 and example 1.

[0025] Figure 5 The stress-strain curves of pure water and P(DMAA-co-MAA) / h-BN composite hydrogel provided in Example 1 during freeze-thaw cycles are shown in the control example 1.

[0026] Figure 6The graph shows the long-term cyclic charge-discharge specific capacity of the zinc-ion battery composed of the hydrogels provided in Comparative Example 1 and Example 1.

[0027] Figure 7 A scanning electron microscope image of the zinc anode of a zinc-ion battery composed of the hydrogels provided in Comparative Example 1 and Example 1.

[0028] Figure 8 Voltage-time graph of constant current cycling of zinc-ion battery composed of hydrogel provided in Example 1.

[0029] Figure 9 The bar chart shows the change in the full-cell discharge specific capacity of the zinc-ion battery composed of hydrogel provided in Example 1 as a function of self-healing time. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to specific embodiments.

[0031] The first aspect of the present invention provides an antifreeze self-healing hydrogel electrolyte, which is formed by polymerization of polymer monomers, boron nitride nanosheets, photoinitiator and water to form an antifreeze self-healing hydrogel; wherein the polymer monomer is a mixture of N,N-dimethylacrylamide (DMAA) and methacrylic acid (MAA), and the photoinitiator is 2,2-diethoxyacetophenone.

[0032] In this embodiment, when the hydrogel is immersed in zinc salt completely dissolved in water, it can absorb a large number of active zinc ions. These zinc ions, as the main source of charge carriers in the hydrogel electrolyte, migrate within the gel network and participate in redox reactions occurring at the positive and negative electrodes, thereby achieving charge transfer and energy conversion. The electrolyte formed in this way is an aqueous zinc ion hydrogel electrolyte.

[0033] In hydrogel electrolyte systems, ionic conductivity is a key performance parameter for measuring ion migration capability, directly determining the charge carrier transport efficiency and thus affecting the energy conversion efficiency and overall system stability of zinc-ion batteries. There is a significant dependence between the ionic conductivity of the hydrogel electrolyte and the zinc salt concentration: when the zinc salt concentration is too low, although zinc ions have a high diffusion coefficient in the electrolyte, the overall ion migration rate is still limited due to the insufficient number of charge carriers per unit volume capable of conducting electricity; conversely, if the zinc salt concentration is too high, the electrolyte viscosity will increase sharply, leading to increased resistance to zinc ion migration, which will also cause a decrease in ionic conductivity. Therefore, in practical applications, the zinc salt concentration needs to be optimized and controlled to achieve a balance between carrier concentration and migration resistance, thereby achieving optimal electrochemical performance. Considering the influence of zinc salt concentration on the electrolyte and other performance aspects of the zinc-ion battery composed of the electrolyte, in this embodiment, the molar concentration range of the zinc salt solution is 1M~4M. More preferably, the molar concentration range of the zinc salt solution is 2M.

[0034] To optimize the dissolution kinetics and chemical stability of the electrolyte, this implementation scheme features a targeted design for the selection of zinc salts, preferably one or a combination of zinc trifluoromethanesulfonate, zinc sulfate, zinc perchlorate, and zinc chloride. These zinc salts, due to their excellent water solubility, can completely dissolve in the aqueous phase, forming a homogeneous and stable electrolyte system, providing a reliable medium for ion migration. In terms of electrochemical performance, the zinc ions generated by their dissociation act as core charge carriers, ensuring high ionic conductivity in the electrolyte. Specific anions, by regulating the solvation structure or forming competitive hydrogen bonds, effectively suppress side reactions such as hydrogen evolution, thereby significantly improving the coulombic efficiency and cycle stability of the battery. Furthermore, these zinc salts have significant advantages in terms of commercial availability and low raw material costs, providing economic feasibility for the large-scale application of zinc-ion battery technology. It should be noted that the selection of zinc salts can be flexibly adjusted according to actual application scenarios (such as wide temperature range, high rate capability, etc.) and specific performance requirements; this implementation scheme does not impose other restrictions.

[0035] To address the potential issues of hydrogel electrolyte freezing and deterioration of mechanical properties, as well as the possible dendrite growth in the zinc anode, when aqueous zinc-ion batteries are used in low-temperature environments, this embodiment improves and resolves these problems to some extent by adding boron nitride nanosheets to the hydrogel electrolyte. The boron nitride nanosheets, through the synergistic effect of their polar lattice and functional groups on the polymer chains, generate a continuous bound water layer that penetrates both the surface of the boron nitride nanosheets and the polymer chain segments. Simultaneously, the topological confinement formed by the nanosheets in the network reduces the scale and connectivity of the free water region. This bound water layer passivates the surface of ice nuclei, while the boron nitride-polymer network hinders ice crystal expansion. Together, these two mechanisms effectively suppress freezing and dendrite formation and growth at the network scale, ensuring the normal migration of zinc ions in the electrolyte.

[0036] To further improve the antifreeze properties of the electrolyte with added boron nitride nanosheets and enhance the zinc ion transport efficiency, in this embodiment, the mass concentration of boron nitride nanosheets in the hydrogel ranges from 0.5 wt% to 10 wt%. More preferably, the mass concentration ranges from 1 wt% to 5 wt%. The lateral dimensions of the boron nitride nanosheets are below 500 nm, more preferably 50 nm to 150 nm.

[0037] A second aspect of the present invention also provides a zinc-ion battery comprising a positive electrode, a negative electrode, and the hydrogel electrolyte provided in this embodiment. During the charging and discharging process of the battery, zinc ions repeatedly insert and extract between the positive and negative electrode. The hydrogel electrolyte is disposed between the positive and negative electrode, serving to isolate the positive and negative electrode and conduct ions between them.

[0038] In this embodiment, the positive electrode of the zinc-ion battery includes a positive current collector and a positive active material. The positive current collector acts as a carrier for electron conduction, conducting electrons generated by the active material out of or into the external circuit. Typically, the positive current collector is made of a material with good conductivity and mechanical strength; no specific limitations are imposed here. In this embodiment, titanium foil is preferably used as the positive current collector, and ammonium intercalated vanadium oxide is preferably used as the positive active material. Furthermore, the negative electrode of the zinc-ion battery is preferably made of pure zinc.

[0039] Example 1 This embodiment provides an antifreeze self-healing hydrogel electrolyte, the preparation process of which is as follows: (1) Add 1.1 g MAA and 1.36 g DMAA to a glass bottle in sequence and sonicate for 10 minutes.

[0040] (2) Add 2.5 mL of deionized water and continue sonicating for 10 minutes to make the mixture homogeneous.

[0041] (3) Add 5 mg of photoinitiator 2,2-diethoxyacetophenone and sonicate for 10 minutes to dissolve it.

[0042] (4) Add 0.25 g of h-BN nanosheets with a transverse dimension of about 100 nm to the above solution and disperse them thoroughly.

[0043] (5) Inject the mixed solution into the mold and irradiate it under 100 W ultraviolet light for 35 minutes to complete the polymerization reaction and obtain P(DMAA-co-MAA) / h-BN composite hydrogel.

[0044] Example 2 This embodiment uses h-BN nanosheets with a lateral dimension of 500 nm, and the rest is the same as in Example 1.

[0045] Example 3 In this embodiment, the amount of h-BN nanosheets added is 50 mg, and the rest is the same as in Example 1.

[0046] Comparative Example 1 In this comparative example, boron nitride nanosheets were not added, and the rest was the same as in Example 1. P(DMAA-co-MAA) hydrogel was obtained by polymerization.

[0047] Comparative Example 2 In this comparative example, h-BN nanosheets with a lateral dimension of 1 μm were used, and the rest were the same as in Example 1.

[0048] Comparative Example 3 In this comparative example, h-BN nanosheets with a lateral dimension of 5 μm were used, and the rest were the same as in Example 1.

[0049] Comparative Example 4 In this comparative example, h-BN nanosheets with a lateral dimension of 15 μm were used, and the rest were the same as in Example 1.

[0050] Comparative Example 5 This comparative example uses cubic boron nitride (c-BN) nanosheets with a lateral dimension of 1 μm, and the rest is the same as in Example 1.

[0051] Compare with Example 1 This Comparative Example 1 contains only pure water and is used to compare the freezing process and ice crystal morphology of pure water with that of the P(DMAA-co-MAA) / h-BN composite hydrogel from Example 1.

[0052] Compare with Example 2 Comparative Example 2 contains only a pure aqueous solution (5 wt%) of 100 nm h-BN nanosheets, used to compare the freezing process and ice crystal morphology of pure water with that of the P(DMAA-co-MAA) / h-BN composite hydrogel from Example 1.

[0053] The hydrogel electrolytes of Example 1 and Comparative Example 1 were used in the preparation of zinc-ion batteries.

[0054] In this embodiment of the invention, the zinc-ion battery includes a positive electrode, a negative electrode, and the hydrogel electrolyte provided in this embodiment. The preparation method of the zinc-ion battery in this embodiment of the invention is as follows: (1) Preparation of the positive electrode sheet: 1 g of NH4VO3 was placed in a tube furnace at 300 °C and calcined for 2 h under argon atmosphere to obtain black powder NH4. + -V₂O₅. (The NH₄) + V₂O₅, Super P, and polyvinylidene fluoride (PVDF) were added to a mortar in a 7:2:1 ratio and ground for 15 minutes. After grinding, 260 μL of N-methylpyrrolidone (NMP) was added, and grinding continued for another 15 minutes to obtain a black slurry, which is the positive electrode active material. The slurry was evenly coated onto a 15 μm thick titanium foil using a 60 μm coater and dried in an oven at 80 ℃ for 12 h to obtain the positive electrode sheet. The sheet was cut into 12 mm diameter circles for later use. The positive electrode active material loading was 0.75~1.25 mg / cm³. 2 .

[0055] (2) Preparation of negative electrode sheet: Commercial zinc sheets with a thickness of 100 μm were cut into 12 mm circles, ultrasonically washed with isopropanol for 15 min, and then air-dried for later use.

[0056] (3) The obtained hydrogel was soaked in 2 M zinc perchlorate solution for 12 hours to prepare a hydrogel electrolyte for zinc ion batteries.

[0057] (4) Preparation of zinc-ion full cells: The CR2032 model negative electrode battery casing, spring sheet, gasket, negative electrode plate, hydrogel electrolyte, positive electrode plate, and positive electrode battery casing are assembled in sequence, and finally packaged by a button cell battery packaging machine to obtain a button cell battery for battery performance testing.

[0058] (5) Preparation of zinc-ion half-cells: The CR2032 model negative electrode battery casing, spring sheet, gasket, negative electrode plate, hydrogel electrolyte, negative electrode plate, and positive electrode battery casing are assembled in sequence, and finally packaged by a button cell battery packaging machine to obtain a button cell battery for battery performance testing.

[0059] The modification morphology and grain size of ice crystals by the hydrogel materials provided in the examples were monitored, and the performance of zinc-ion batteries assembled from the hydrogel electrolytes provided in Example 1 and Comparative Example 1 were tested. The monitoring and test results are shown in [reference]. Figures 1-9 The testing method is as follows: (1) Evaluation of antifreeze performance: The composite hydrogel material provided in Example 1 was placed in the silicone oil of the sample holder, and then rapidly cooled to freeze the droplets. The temperature was then slowly increased to melt the droplets. When only a small ice crystal remained, the temperature was adjusted to maintain this small ice crystal for 20 seconds without growth or melting. This temperature was recorded as the melting point temperature (T). m Then the temperature is lowered to a target temperature (T). f That is, the degree of supercooling ΔT = T m -T f The entire process was observed and recorded using a high-speed camera to measure and record the morphology and growth rate of the ice crystals. Additionally, control example 1, using pure water as the test subject, and control example 2, using an h-BN aqueous solution as the test subject, were also included in the test.

[0060] Figure 1 The morphological characteristics of individual ice crystals are shown in untreated water and in pure water after modification with equal amounts of boron nitride nanosheets provided in Example 1. The polar h-BN / polymer interface, through a strong interfacial field, orients and binds neighboring water molecules, converting them from free water to bound water. Simultaneously, the h-BN nanosheets and polymer network together constitute multi-scale geometric confinement (nanochannels between the polymer mesh and nanosheets), physically restricting the formation and growth space of the ice crystal embryo. The bound water layer passivates the edges of the initial ice nucleus, while the tortuous BN-polymer network hinders the expansion of the ice front, thus synergistically inhibiting freezing. Therefore, the more non-circular the ice crystal morphology, i.e., the more inhibited the growth rate, the stronger the antifreeze activity of the boron nitride nanosheets. (Reference) Figure 1 Comparing the growth morphology of ice crystals, Example 1 showed the most significant control over the ice crystal structure, with its ice crystals exhibiting the most obvious asymmetric and non-circular characteristics.

[0061] Figure 2 The ice crystal growth rate of pure water and the P(DMAA-co-MAA) / h-BN composite hydrogel of Example 1 were compared under different supercooling conditions. Linear fitting of the data revealed that the ice crystal growth rate in pure water was 225.00 μm·s. -1 ·℃ -1 The growth rate of Example 1 decreased significantly to 13.43 μm·s. -1 ·℃ -1 This indicates that it has the strongest inhibitory effect on ice crystal growth.

[0062] (2) DSC evaluation: Approximately 6 mg of Comparative Example 1, Control Example 1, Control Example 2, and Example 1 were accurately weighed and sealed in an aluminum sample pan to prevent moisture evaporation. The sample pan and blank reference pan were placed in a DSC furnace, and a temperature program was executed under a high-purity nitrogen atmosphere (flow rate 50 mL / min): first, after equilibration at 25 °C, the temperature was lowered to -150 °C at a rate of 5 °C / min, and then raised back to 25 °C at the same rate. The freezing behavior of the samples was determined by analyzing the heat flow-temperature curves during the cooling process. The exothermic freezing peak of the hydrogel during cooling was used as the evaluation index, considering both the temperature at which the exothermic peak appeared and its peak area: the lower the temperature at which the exothermic peak appeared and the smaller the peak area, the lower the content of freezeable free water inside, and the better the antifreeze performance. This result provides key thermodynamic evidence for its application at low temperatures. Figure 3 The DSC curves are for Comparative Example 1, Control Example 1, Control Example 2 and Example 1. Figure 4 The DSC curves are for comparison example 1, example 2 and example 1.

[0063] Combination Figure 3 The exothermic peaks in the DSC curves of pure water in Examples 1-2, Comparative Examples 2-5, and Control Example 1 revealed that the unmodified P(DMAA-co-MAA) hydrogel exhibited a significant exothermic peak at approximately -23°C, indicating that a large amount of free water within it had frozen. In contrast, the freezing behavior of the material was fundamentally altered after incorporating hexagonal boron nitride (h-BN) nanosheets: as the lateral size of the h-BN nanosheets decreased from 15 μm to 100 nm, the exothermic peak on its DSC curve was significantly weakened and eventually disappeared. In particular, when using h-BN with a particle size of 100 nm, no thermodynamic phase transition signal was detected over a wide temperature range from -150°C to 20°C. This phenomenon demonstrates that the introduction of h-BN, through the synergistic effect of its polar interface and polymer network, effectively converts free water within the system into unfrozen bound water, thereby achieving complete inhibition of ice crystal nucleation and growth at the molecular level. As a key control, the sample using 1 μm cubic boron nitride (c-BN) retained a distinct freezing peak, which ruled out the interference of simple nanoscale effects and confirmed that interfacial polarity is the main physical mechanism for inducing antifreeze properties. This further verified that the boron nitride nanosheets of the specific size used in Example 1 have excellent inhibitory effects on the freezing of free water.

[0064] according to Figure 4As shown in the DSC cooling curves of Comparative Example 1, Example 2, and Example 1, Comparative Example 1 exhibits a sharp and large-area exothermic crystallization peak at approximately -23°C, indicating the presence of a large amount of freezeable free water within it, and that ice crystal nucleation and growth are not significantly inhibited. The exothermic peak in Example 2 is significantly weakened, the peak area is greatly reduced, and the freezing initiation temperature shifts to a lower temperature, indicating that the introduction of h-BN effectively inhibits ice crystal formation. In contrast, almost no exothermic signal is detected on the DSC curve of Example 1, and the freezing peak is difficult to distinguish from the baseline, indicating that the crystallizable water in the system has been converted to non-freezing bound water to the maximum extent, thus exhibiting excellent antifreeze performance on a macroscopic scale. These results demonstrate that with the increase of h-BN content, ice crystal nucleation and growth of the hydrogel are gradually inhibited, with Example 1 showing the most significant antifreeze effect.

[0065] (3) Evaluation of low-temperature mechanical properties: The hydrogels from Example 1 and Comparative Example 1 were prepared into standard dog bone-shaped specimens (gauge length 12 mm, width 2 mm). A Gotech AI-7000-MUG universal testing machine equipped with a high and low temperature chamber was used. After equilibration at the set temperature (20, 0, -20, -40, -60, -80 °C) for ≥10 minutes, tensile tests were performed at a rate of 100 mm / min until fracture. Stress-strain curves were recorded, and Young's modulus (E) and tensile strength (σ) were calculated. b Elongation at break (ε) b ) and fracture work (W) f For each condition, n≥3 samples are tested.

[0066] Figure 5 The uniaxial tensile curves visually demonstrate the superior mechanical toughness of the composite hydrogel of this invention at low temperatures. The composite hydrogel containing 5 wt% h-BN in Example 1 exhibited significant smooth plastic deformation across a wide temperature range of 20°C to -80°C. Even at the extremely low temperature of -80°C, its elongation at break far exceeded 200%, and the stress-strain curve showed typical toughness characteristics, indicating that the material maintained a rubber-like elastic network. In stark contrast, the blank hydrogel in Comparative Example 1 showed a catastrophic decline in mechanical properties when the temperature dropped below 0°C. The curve rapidly reached a peak and then plummeted, with extremely low fracture strain, exhibiting typical brittle fracture, which was caused by the freezing of the internal water phase. The direct comparison of the two figures strongly confirms that the introduction of h-BN nanosheets, by stabilizing bound water and preventing the glass transition of polymer chains, enables the hydrogel to maintain excellent ductility and damage tolerance even under extreme low-temperature environments, overcoming the freeze-brittleness problem of traditional hydrogels.

[0067] (4) Low-temperature performance evaluation of aqueous zinc-ion batteries: All full-cell performance tests were conducted in a LAND CT3002A 5V system under the following conditions: current density 1 A / g and charge / discharge voltage window 0.2–1.6 V. All low-temperature tests were performed in a high / low temperature and humidity chamber (SME-64PF-70, -70–150°C). After battery operation, the battery was disassembled using a pellet mill and by removing the full-cell assembly. The zinc anode was then removed for scanning electron microscopy to observe its surface morphology after battery operation.

[0068] Figure 6 The graphs show the long-term charge-discharge specific capacity of aqueous zinc-ion batteries assembled using the electrolytes provided in Example 1 and Comparative Example 1, respectively. (Reference) Figure 7 The test results shown indicate that, in Comparative Example 1, the hydrogel without boron nitride nanosheets resulted in a rapidly failing aqueous zinc-ion battery at -30°C due to electrolyte freezing. However, in the electrolyte provided in Example 2, with the addition of h-BN nanosheets at a mass concentration of 5 wt%, the zinc-ion battery exhibited excellent low-temperature performance at -30°C. Specifically, the zinc-ion battery using the electrolyte from Example 1 could cycle for over 2500 cycles (approximately 45 days) at a current density of 1 A / g.

[0069] Figure 7 Scanning electron microscopy (SEM) images of the zinc anode of aqueous zinc-ion batteries assembled with the electrolytes provided in Example 1 and Comparative Example 1, respectively, after 20 hours of operation, are shown. The comparison reveals that the aqueous zinc-ion battery composed of the hydrogel electrolyte without added boron nitride nanosheets (Comparative Example 1) exhibits a large number of dendrites on the zinc anode after 20 hours of operation, significantly reducing battery life and affecting battery performance. In contrast, the zinc-ion battery composed of the electrolyte with added h-BN nanosheets (Example 1) shows significantly suppressed dendrite growth on the zinc anode after 20 hours of operation, exhibiting a relatively smooth surface. This indicates that h-BN nanosheets can effectively modify the zinc anode, thereby mitigating battery short circuits caused by zinc dendrites and optimizing battery performance.

[0070] (4) Evaluation of the low-temperature self-healing performance of aqueous zinc-ion batteries: All half-cell performance tests were conducted using a LAND CT3002A 5V system under test conditions of 0.5mA cm⁻¹. -1 / 0.25mAh cm -1All full-cell performance tests were conducted in a LAND CT3002A 5V system under the following conditions: current density 1 A / g and charge / discharge voltage window 0.2–1.6 V. All low-temperature tests were performed in a high / low temperature and humidity chamber (SME-64PF-70, -70–150°C). After battery operation, the battery was disassembled using a tablet press and by removing the full-cell assembly. The hydrogel electrolyte was removed and cut off. After several hours of contact healing, the battery was reassembled, and its performance at -30°C was tested.

[0071] Figure 8 The results show that the half-cell composed of the composite hydrogel of Example 1, after being cut and re-healed for 24 hours, can operate stably for over 500 hours after reassembly, with a flat voltage-time curve and minimal fluctuations. This result demonstrates that even after cutting and re-healing, this function ensures that energy storage devices made of the materials of this invention can recover most of their performance through a simple self-healing process after mechanical damage in cold environments.

[0072] Figure 9 Quantitative data visually demonstrates the excellent self-recovery capability of the hydrogel electrolyte of this invention in terms of its electrochemical function after damage. The figure shows the discharge specific capacity recovery of the full battery composed of the composite hydrogel of Example 1 after different periods of room temperature self-healing. The test results clearly show that the battery's discharge specific capacity steadily increases with increasing self-healing time. After a 24-hour self-healing process, the battery's discharge capacity can recover to approximately 93% of the original battery. This data strongly indicates that the hydrogel electrolyte of this invention can not only achieve physical repair of the macroscopic structure but also effectively rebuild the efficient ion transport channels in its microscopic three-dimensional network, thereby restoring its key electrochemical function as an electrolyte. This reliable functional self-recovery characteristic ensures that energy storage devices made of this material can significantly recover their performance through a simple self-healing process after mechanical damage, greatly improving the durability and reliability of the devices in complex application scenarios such as flexible wearables, representing a significant breakthrough in the field of low-temperature flexible energy storage devices.

[0073] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. An antifreeze self-healing hydrogel electrolyte, characterized in that: The hydrogel is formed by the polymerization reaction of polymer monomers, boron nitride nanosheets, photoinitiator and water. The hydrogel is immersed in zinc salt solution to obtain antifreeze self-healing hydrogel electrolyte. The lateral size of the boron nitride nanosheets is less than 500 nm. Based on the total mass of polymer monomers, boron nitride nanosheets, photoinitiator and water as 100%, the mass fraction of polymer monomers is 20%~50%, the mass fraction of boron nitride nanosheets is 0.5%~10%, and the mass fraction of photoinitiator is 0.1%~2%.

2. The antifreeze self-healing hydrogel electrolyte as described in claim 1, characterized in that: The boron nitride nanosheets are either two-dimensional hexagonal boron nitride nanosheets or cubic boron nitride nanosheets.

3. The antifreeze self-healing hydrogel electrolyte as described in claim 1, characterized in that: The lateral dimensions of the boron nitride nanosheets are 50~150 nm.

4. The antifreeze self-healing hydrogel electrolyte as described in claim 1, characterized in that: The boron nitride nanosheets have a mass fraction of 1% to 5%.

5. The antifreeze self-healing hydrogel electrolyte as described in claim 1, characterized in that: The polymer monomers are N,N-dimethylacrylamide and methacrylic acid in a molar ratio of 1 to 10:

1.

6. The antifreeze self-healing hydrogel electrolyte as described in claim 1, characterized in that: The mass fraction of the polymer monomer is 25% to 40%.

7. The antifreeze self-healing hydrogel electrolyte as described in claim 1, characterized in that: The photoinitiator is 2,2-diethoxyacetophenone; And / or, the zinc salt is one or more of zinc trifluoromethanesulfonate, zinc sulfate, zinc perchlorate, and zinc chloride, and the zinc salt concentration is 1M to 4M.

8. A method for preparing an antifreeze self-healing hydrogel electrolyte according to any one of claims 1 to 7, characterized in that: The method steps include: Polymer monomers, photoinitiators, and boron nitride nanosheets were added sequentially to deionized water, mixed and dispersed evenly, and then injected into a mold. The mixture was irradiated under 50-200W ultraviolet light for 10-60 minutes to obtain a hydrogel. The hydrogel was immersed in a zinc salt solution for more than 12 hours. After the immersion was completed, the hydrogel electrolyte was obtained.

9. A zinc-ion battery, characterized in that: The battery includes a positive electrode, a negative electrode, and an antifreeze self-healing hydrogel electrolyte as described in any one of claims 1 to 7.

10. A zinc-ion battery as described in claim 9, characterized in that: The positive electrode sheet includes a positive current collector and a positive active material, ammonium intercalated vanadium oxide. And / or, the negative electrode is zinc.

Images