Method for inhibiting reduction of output performance of battery at low temperature by using anti-freezing gel

Abstract

The invention relates to the field of hydrogel materials, and discloses a method for inhibiting reduction of output performance of a battery at low temperature by using an anti-freezing gel, the anti-freezing gel comprises a dual-network polymer matrix which is formed by interpenetrating sodium alginate and polyacrylamide and has physical crosslinking and chemical crosslinking at the same time; a mixed solvent system of water and a deep-eutectic solvent composed of choline chloride and ethylene glycol; the two-dimensional Ti < 3 > C < 2 > TXMXene nanosheets are uniformly dispersed in the matrix. Wherein the eutectic solvent effectively inhibits crystallization of water through strong hydrogen-bond interaction; the double-network structure provides excellent stretchability and toughness through synergistic energy dissipation. The hydrogel is directly coated on the surface of the battery through the self-adhesion of the hydrogel to form a thermal buffer layer, so that the temperature drop rate of the battery in a low-temperature environment is effectively slowed down, the reduction of the output voltage of the battery and the attenuation of the discharge capacity are further remarkably inhibited, and a simple, convenient and efficient battery low-temperature protection method is provided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of hydrogel materials, in particular to a method for inhibiting the decline of battery output performance at low temperature by using anti-freezing gel. BACKGROUND

[0002] Hydrogel is a kind of three-dimensional network structure gel with strong hydrophilicity. It can swell rapidly in water and maintain a large volume of water in the swollen state without dissolving. There are three forms of water in hydrogel, namely free water, weakly bound water and strongly bound water. Generally, free water accounts for the majority in hydrogel, which means that when it is in a subzero temperature environment, the free water will freeze, causing the hydrogel to become hard and brittle, losing its inherent mechanical properties, electrical conductivity and other properties, greatly limiting the scope of application of hydrogel. Therefore, it is urgent to solve the problem of freezing of free water in hydrogel and improve the anti-freezing performance of hydrogel.

[0003] Battery is an indispensable "mobile energy heart" in modern society, from smartphones, electric vehicles to medical devices, renewable energy storage, it provides portable power for daily life, drives technology convenience and green future. However, the ambient temperature has a significant impact on the output performance of the battery, especially in low temperature environment, the activity of the battery electrolyte and electrode will decrease, which will cause the performance of the battery to deteriorate in terms of discharge capacity, output power, charging efficiency and service life. Currently, the research strategy for anti-freezing battery mainly focuses on the improvement of electrolyte and electrode materials, including the introduction of anti-freezing additives into the electrolyte, the development of low temperature adaptive electrode and the design of battery heating technology to compensate for the deterioration of battery output performance in low temperature environment. However, the above design optimization of materials and structure of each part of the battery all have the problems of complex process and difficult mass production. Therefore, it is urgent to find a simple and convenient method to protect the battery in low temperature environment that can meet the mass production conditions. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a method for inhibiting the decline of battery output performance at low temperature by using anti-freezing gel, which solves the problem that traditional hydrogel loses its flexibility and functionality due to the freezing of internal free water in low temperature environment, resulting in limited application, and the problem that the existing protection method has complex process and is difficult to achieve convenient and low-cost application in view of the deterioration of battery performance at low temperature.

[0005] To achieve the above purpose, the present application realizes the following technical solutions: The present application provides an anti-freezing conductive hydrogel in the first aspect.

[0006] The internal structure of the anti-freezing conductive hydrogel comprises a sodium alginate-polyacrylamide double network polymer matrix, which contains a mixed solvent system composed of a deep eutectic solvent and water, and uniformly dispersed two-dimensional Ti3C2T X MXene nanosheets.

[0007] Specifically, the double network polymer matrix is composed of a first network and a second network. The first network is a physical crosslinking network formed by ionic interaction, which is composed of sodium alginate. The second network is a chemical crosslinking network formed by covalent crosslinking, which is composed of polyacrylamide polymerized from acrylamide monomers, and the covalent crosslinking is formed by N,N'-methylenebisacrylamide as a crosslinking agent. The synergistic effect of this double network interpenetrating structure gives the hydrogel excellent mechanical tensile and compression resistance.

[0008] The mixed solvent system is the basis for the hydrogel to work at low temperature. The deep eutectic solvent in the system is composed of a hydrogen bond acceptor choline chloride and a hydrogen bond donor ethylene glycol, and the molar ratio of the two is 1:2 to 1:4. The strong hydrogen bond interaction between choline chloride and ethylene glycol molecules effectively destroys the regular arrangement of water molecules and inhibits the formation and growth of ice crystals, thereby reducing the freezing point of the entire solvent system to a level much lower than 0℃. In the mixed solvent system, the volume ratio of the deep eutectic solvent to water is 4:1 to 9:1.

[0009] The two-dimensional Ti3C2T X Ti3C2T X As a conductive filler, MXene nanosheets have metallic conductivity, which can be connected in the polymer matrix to form a continuous electron transport path. At the same time, the ions (such as chloride ions and choline cations) in the mixed solvent system provide an ion transport path. The synergistic effect of the electron path and the ion path gives the hydrogel a composite conductive property.

[0010] In a specific embodiment, based on the total volume of the hydrogel, the concentration of sodium alginate is 1-3% (w / v), the concentration of acrylamide monomers is 10-25% (w / v), and the concentration of two-dimensional Ti3C2T X The solid content of MXene nanosheets is 0.1-1.0% (w / v). In addition, the polar functional groups of carboxyl and amide groups present on the polymer chains of the hydrogel enable the surface to form hydrogen-bonding intermolecular forces with a variety of material substrates, thereby exhibiting self-adhesion properties without the need for additional adhesives.

[0011] The second aspect of the present application provides a method for preparing an anti-freezing conductive hydrogel as described above.

[0012] The core of the preparation method lies in employing a strategy of in-situ polymerization initiated by ultraviolet light to achieve rapid gel formation. This method specifically includes the following steps: First, the functional components are pre-prepared. The eutectic solvent is prepared by heating and stirring choline chloride and ethylene glycol at 70-90°C until a homogeneous, transparent liquid is formed. (Two-dimensional Ti3C2T) X The MXene nanosheet dispersion was prepared by acid etching of Ti3AlC2MAX phase powder to remove the Al layer, followed by ultrasonic exfoliation.

[0013] Next, the gel precursor solution was prepared. Sodium alginate, acrylamide monomer, crosslinking agent N,N'-methylenebisacrylamide, photoinitiator, and pre-prepared two-dimensional Ti3C2T were added. X The MXene nanosheet dispersion was sequentially added to a eutectic solvent-water mixed solvent system and stirred until homogeneous to obtain a uniform gel precursor solution.

[0014] Finally, the gel is cured by light. The gel precursor solution is injected into a mold and irradiated under a UV light source. The light is applied at a center wavelength of 365 nm and a power density of 3-10 mW / cm². 2 Under ultraviolet light, the photoinitiator is excited to generate free radicals, which in turn initiate the free radical polymerization of acrylamide monomers, forming a chemically cross-linked network of polyacrylamide. This network interpenetrates with the pre-dissolved sodium alginate physical network, ultimately forming an antifreeze conductive hydrogel with a specific morphology. Two-dimensional Ti3C2T X In this process, in addition to serving as a conductive filler, MXene nanosheets can absorb some light energy and convert it into heat through photothermal effects, thereby locally increasing the system temperature and promoting the polymerization reaction rate.

[0015] A third aspect of the present invention provides a method for suppressing the decline in battery output performance at low temperatures using an antifreeze gel.

[0016] The method involves directly coating the antifreeze conductive hydrogel described in the first aspect onto the surface of the battery. This coating process utilizes the self-adhesive properties of the hydrogel, allowing it to adhere tightly to the battery casing without the need for any additional adhesive materials, making the process simple.

[0017] The mechanism of this method lies in the fact that the antifreeze conductive hydrogel layer coating the battery surface constitutes a thermal buffer layer. Because the gel contains a high concentration of eutectic solvent and water, its thermal capacity allows it to slow down heat transfer between the battery and the low-temperature external environment. When the ambient temperature drops sharply, this gel layer can slow down the rate of temperature decrease of the battery itself, allowing the battery to maintain a relatively high operating temperature range for a longer period.

[0018] When applied to energy storage devices such as lithium batteries, this method effectively alleviates the problems of increased electrolyte viscosity, reduced ion migration rate, and sluggish lithium insertion / extraction kinetics caused by low temperatures by maintaining the battery's operating temperature at low temperatures. The final technical effect is to suppress the drop in output voltage plateau and the decay of usable discharge capacity in the low temperature range of -50℃ to 0℃.

[0019] This invention provides a method for suppressing the decline in battery output performance at low temperatures using antifreeze gel. It has the following beneficial effects: 1. The antifreeze conductive hydrogel provided by this invention exhibits excellent ultra-low temperature antifreeze properties. By introducing a eutectic solvent composed of choline chloride and ethylene glycol as the main solvent system, the strong hydrogen bonds formed between its components effectively disrupt the regular arrangement of water molecules, fundamentally inhibiting the formation and growth of ice crystals. This allows the hydrogel to maintain its inherent flexibility and elasticity even in extreme low-temperature environments such as -50°C or even lower, avoiding the hardening and brittleness problems caused by freezing in traditional hydrogels.

[0020] 2. The hydrogel prepared by this invention exhibits high conductivity. This conductivity stems from the synergistic effect of ionic and electronic conductivity. On one hand, the eutectic solvent itself contains freely moving ions, providing an efficient ion transport pathway; on the other hand, the two-dimensional Ti3C2T uniformly dispersed in the polymer matrix... X The interconnected MXene nanosheets form a continuous electron transport network. This composite conductivity mechanism endows the hydrogel with excellent overall electrical properties, laying the foundation for its application in flexible electronics and sensing.

[0021] 3. The hydrogel of this invention possesses excellent mechanical properties. It employs a dual-network structure formed by the interpenetration of a sodium alginate physical cross-linking network and a polyacrylamide chemical cross-linking network. When subjected to external forces, the physical cross-linking network can effectively dissipate energy through the reversible breaking and recombination of ionic bonds, while the chemical cross-linking network provides a stable structural framework to ensure the material's resilience. The synergistic effect of the two networks gives the hydrogel high tensile strength, high toughness, and good fatigue resistance, enabling it to withstand repeated bending, compression, or stretching while maintaining structural integrity.

[0022] 4. The preparation method of this invention is simple, with mild and highly controllable reaction conditions. Employing ultraviolet light-initiated in-situ polymerization, the gel formation process, compared to traditional thermally initiated polymerization, allows the reaction to be completed rapidly within minutes at room temperature, avoiding the impact of high temperatures on material activity and resulting in low energy consumption. This method is easy to operate; by controlling the duration and area of ​​light irradiation, precise control over the gel shape and size can be achieved, providing feasibility for large-scale, customized production.

[0023] 5. The battery low-temperature protection method provided by this invention is convenient to operate and highly effective. Utilizing the self-adhesive properties of the hydrogel, it can be directly and tightly coated onto the battery surface without any additional adhesives or complex encapsulation processes. This gel layer, as a highly efficient thermal buffer layer, effectively slows down the rate of heat loss from the battery in low-temperature environments, maintaining the battery body at a relatively high operating temperature. This significantly suppresses the drop in output voltage and capacity decay caused by low temperatures, ensuring the reliable operation of energy storage devices in cold environments. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating the relative change in output current of the battery without antifreeze gel coating in a low-temperature environment of -10℃ to 50℃ in an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the relative change in output current of the antifreeze gel-coated battery in a low-temperature environment of -10℃ to 50℃ in an embodiment of the present invention; Figure 3 This is a schematic diagram comparing the data after normalization for cases with and without antifreeze gel coating. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1: Preparation of the antifreeze gel of the present invention Preparation of the eutectic solvent (DES): Weigh 13.96 g of choline chloride (ChCl) and 18.63 g of ethylene glycol (EG) to a molar ratio of 1:3. Add both to a round-bottom flask and place it in a constant-temperature oil bath at 80°C. Stir magnetically at 500 rpm for 3 hours until a homogeneous, clear, and transparent liquid is formed. After cooling to room temperature, the eutectic solvent is obtained and sealed for later use.

[0027] Ti3C2T XPreparation of MXene nanosheet dispersion: 2.8 g of lithium fluoride (LiF) was slowly dissolved in 40 mL of 9 M hydrochloric acid (HCl) solution. 2.0 g of Ti3AlC2MAX phase powder was added in batches to the LiF-HCl mixed solution under ice-water bath conditions. The suspension was then transferred to a constant temperature water bath at 40 °C and reacted for 24 hours. After the reaction, the product was repeatedly washed with deionized water by centrifugation (4000 rpm) until the pH of the supernatant was neutral. The resulting precipitate was redispersed in deionized water and subjected to probe sonication for 1 hour under ice-water bath conditions. Finally, the sonicated suspension was centrifuged at 10000 rpm for 30 minutes, and the supernatant was collected to obtain Ti3C2T with a concentration of 5 mg / mL. X MXene nanosheet dispersion.

[0028] Preparation of the gel precursor solution: In a 50 mL beaker, measure 14.0 mL of the eutectic solvent prepared in step 1 and add 2.0 mL of deionized water, mixing thoroughly. Add 0.4 g of sodium alginate (SA) and 4.0 g of acrylamide (AM) monomer to this mixed solvent, stirring magnetically until completely dissolved. Then, add 0.0026 g of N,N'-methylenebisacrylamide (MBAA) and 0.0125 g of photoinitiator Irgacure2959 to the solution. Continue stirring under light-protected conditions, and slowly add 4.0 mL of the Ti3C2T prepared in step 2. X MXene nanosheet dispersion. Continue stirring in the dark for 1 hour to obtain a homogeneous gel precursor solution.

[0029] Photocuring to form a gel: The above-mentioned gel precursor solution was placed in a vacuum drying oven and evacuated for 30 minutes to remove air bubbles. The precursor solution was then injected into a mold consisting of two glass plates and a 2mm thick silicone gasket. The mold was placed in a UV curing chamber at a center wavelength of 365nm and a light power density of 5mW / cm². 2 Irradiate with ultraviolet light for 10 minutes. After curing, remove the gel from the mold to obtain the target antifreeze conductive hydrogel.

[0030] Comparative Example 1: Preparation of conventional hydrogels without eutectic solvents The preparation method is basically the same as in Example 1, except that in step 3, "Preparation of the gel precursor solution", a eutectic solvent is not used. The solvent system consists of 16.0 mL of deionized water. All other components, including sodium alginate (0.4 g), acrylamide (4.0 g), N,N'-methylenebisacrylamide (0.0026 g), photoinitiator Irgacure2959 (0.0125 g), and Ti3C2T X The amount and order of addition of the MXene nanosheet dispersion (4.0 mL) were the same as in Example 1.

[0031] Comparative Example 2: Preparation of antifreeze hydrogels without MXene nanosheets The preparation method is basically the same as in Example 1, except that Ti3C2T is not added in step 3, "Preparation of gel precursor solution". X MXene nanosheet dispersion. To maintain a constant total volume, 4.0 mL of Ti3C2T... X The MXene nanosheet dispersion was replaced with 4.0 mL of deionized water. The amounts and order of addition of all other components, including the eutectic solvent (14.0 mL), sodium alginate (0.4 g), acrylamide (4.0 g), N,N'-methylenebisacrylamide (0.0026 g), and photoinitiator Irgacure2959 (0.0125 g), were consistent with those in Example 1.

[0032] Comparative Example 3: Preparation of Single-Network Antifreeze Conductive Hydrogel The preparation method is basically the same as in Example 1, except that sodium alginate (SA) is not added in step 3, "Preparation of gel precursor solution". All other components, including the eutectic solvent (14.0 mL), deionized water (2.0 mL), acrylamide (4.0 g), N,N'-methylenebisacrylamide (0.0026 g), photoinitiator Irgacure 2959 (0.0125 g), and Ti3C2T... X The amount and order of addition of the MXene nanosheet dispersion (4.0 mL) were the same as in Example 1.

[0033] Test Example 1: Mechanical Performance Test This test case aims to evaluate the impact of different network structures on the mechanical properties of hydrogels.

[0034] 1. Experimental Procedure (1) Sample preparation: The antifreeze conductive hydrogel prepared in Example 1 and the single-network antifreeze conductive hydrogel prepared in Comparative Example 3 were respectively placed at room temperature for 2 hours to equilibrate.

[0035] Samples used for tensile testing are cut using a standard dumbbell-shaped cutter (3 mm wide at the narrowest point).

[0036] The samples used for compression testing were cut into cylindrical shapes using a 12mm diameter circular sampler.

[0037] (2) Tensile property test: The dumbbell-shaped sample is clamped at both ends onto the fixtures of the universal testing machine, with an initial gauge length set to 20 mm. The sample is stretched at a constant tensile rate of 100 mm / min until it fractures. The system automatically records the stress-strain data during the stretching process and calculates the elongation at break and tensile strength of the sample accordingly.

[0038] (3) Compression performance test: A cylindrical sample is placed between two parallel compression platforms of a universal testing machine. The sample is compressed at a constant rate of 10 mm / min until the strain reaches 70%. The system records the stress-strain data during compression and reads the compressive strength corresponding to 70% strain.

[0039] 2. Experimental Results The above mechanical property tests were performed on the hydrogel samples of Example 1 and Comparative Example 3. Each group of samples was tested three times, and the average value of the results was recorded in Table 1.

[0040] Table 1: Mechanical property test data of hydrogels from Example 1 and Comparative Example 3 As shown in Table 1, the hydrogel prepared in Example 1 has significantly higher elongation at break, tensile strength, and compressive strength than the hydrogel prepared in Comparative Example 3.

[0041] The differences in the aforementioned mechanical properties stem from the different internal network structures of the hydrogels. The hydrogel of Example 1 possesses a dual-network structure where a sodium alginate physical cross-linking network and a polyacrylamide chemical cross-linking network interpenetrate each other. When the material is subjected to external tensile force, the physical cross-linking points of the ionic bonds between the sodium alginate chains can undergo reversible breakage and recombination. This process effectively dissipates the externally applied energy, enabling the gel to withstand greater deformation without breaking. Simultaneously, the stable polyacrylamide chemical cross-linking network, acting as a structural framework, maintains the overall integrity and resilience of the gel.

[0042] In contrast, the hydrogel in Comparative Example 3 consists only of a single chemically cross-linked network formed by polyacrylamide. This structure lacks the energy dissipation mechanism of the aforementioned physical network. When subjected to external force, the stress acts directly on the irreversible covalent backbone, leading to stress concentration and rapidly reaching the material's fracture limit. Therefore, its tensile strength and elongation at break are both limited. This structural difference also results in different compressive properties; the dual-network structure can more effectively disperse and withstand compressive stress.

[0043] Test Example 2: Electrical Performance Test This test case aims to evaluate the two-dimensional Ti3C2T. X The effect of MXene nanosheets on the electrical properties of hydrogels.

[0044] 1. Experimental Procedure (1) Sample preparation: Take the antifreeze conductive hydrogel prepared in Example 1 and the antifreeze hydrogel prepared in Comparative Example 2 respectively. Cut the hydrogel samples into cuboid strips with dimensions of 20mm×10mm×2mm.

[0045] (2) Conductivity test: Electrochemical impedance spectroscopy (EIS) was used for the test. The two ends of the cuboid sample were brought into close contact with the electrodes (stainless steel electrodes) of the electrochemical workstation. At room temperature (25°C), a sinusoidal AC voltage of 10 mV was applied, and the scanning frequency range was 100 kHz to 0.1 Hz. Based on the impedance spectrum data obtained from the test, the bulk resistance (R) of the sample was determined by the intersection of the high-frequency region and the real axis in the Nyquist plot.

[0046] (3) Data calculation: The conductivity (σ) of the sample is calculated according to the formula σ=L / (R×S). Where L is the distance between the two electrodes (i.e. the sample length, 20mm) and S is the cross-sectional area of ​​the sample (10mm×2mm).

[0047] 2. Experimental Results The above-mentioned electrical performance tests were performed on the hydrogel samples of Example 1 and Comparative Example 2. Each group of samples was tested three times, and the average value of the results was recorded in Table 2.

[0048] Table 2: Electrical property test data of hydrogels from Example 1 and Comparative Example 2 Data shows that the conductivity of the hydrogel prepared in Example 1 is significantly different by orders of magnitude compared to that of the hydrogel prepared in Comparative Example 2.

[0049] The aforementioned differences in conductivity directly reflect the different electrical conduction mechanisms within the hydrogels. The hydrogel prepared in Comparative Example 2 does not contain two-dimensional Ti3C2T. X The conductivity of MXene nanosheets originates entirely from the directional migration of chloride ions and choline cations present in the eutectic solvent system. These ions move within channels formed by the polymer network, creating a single ionic conductivity pathway, the efficiency of which is limited by ion concentration and mobility.

[0050] The hydrogel prepared in Example 1 constructed a composite conductive model. In addition to the ionic conductivity pathways provided by the eutectic solvent, two-dimensional Ti3C2T uniformly dispersed in the polymer matrix... XDue to their inherent metallic properties, MXene nanosheets overlap or tunnel together to form a continuous electron transport network within the system. Therefore, the overall conductivity of this hydrogel is the result of the synergistic effect of both ionic and electronic conduction mechanisms. The introduction of electron transport pathways provides an additional path for rapid charge migration, which is the fundamental reason why its conductivity is significantly higher than that of the comparative hydrogel (Example 2), which relies solely on ionic conduction.

[0051] Test Example 3: Antifreeze Performance Test This test case aims to evaluate the effect of eutectic solvent systems on the low-temperature performance of hydrogels.

[0052] 1. Experimental Procedure (1) Differential Scanning Calorimetry (DSC) Test: The antifreeze conductive hydrogel prepared in Example 1 and the conventional hydrogel prepared in Comparative Example 1 were taken respectively. 5-10 mg of sample was accurately weighed and sealed in an aluminum crucible. The sample was placed in the sample chamber of the differential scanning calorimeter and cooled from room temperature (25 °C) to -100 °C at a cooling rate of 10 °C / min under a nitrogen protective atmosphere, and then heated to 30 °C at the same rate. The heat flow curves during the cooling and heating processes were recorded, the presence of an exothermic peak during freezing was observed, and the glass transition temperature (Tg) of the material was determined.

[0053] (2) Low-temperature physical state observation: The hydrogel samples of Example 1 and Comparative Example 1 were cut into rectangular strips (40mm×10mm×2mm). The strips were placed in a low-temperature test chamber at -50℃ and kept at a constant temperature for 2 hours. After the samples were taken out of the low-temperature chamber, they were immediately bent 180° within 1 second, and their physical state and response to mechanical deformation were objectively recorded.

[0054] 2. Experimental Results The hydrogel samples of Example 1 and Comparative Example 1 were subjected to the above-mentioned antifreeze performance test, and the results are recorded in Table 3.

[0055] Table 3: Test data on the antifreeze properties of the hydrogels of Example 1 and Comparative Example 1 As shown in Table 3, the hydrogels of Example 1 and Comparative Example 1 exhibit fundamentally different performance at low temperatures. The sample of Example 1 did not show an exothermic freezing peak during cooling, its glass transition temperature was much lower than the test temperature, and it maintained good flexibility at -50℃. In contrast, the sample of Comparative Example 1 showed a significant exothermic freezing peak below 0℃ and completely lost its flexibility at -50℃, exhibiting a hard and brittle state.

[0056] The fundamental reason for the aforementioned performance differences lies in the composition of the solvent system within the hydrogel. In the hydrogel of Comparative Example 1, the solvent is pure water. When the ambient temperature is below its freezing point, water molecules arrange themselves into a regular hexagonal crystal structure through hydrogen bonding, forming ice crystals. This phase transition process releases a large amount of latent heat, which manifests as a sharp exothermic peak on the DSC curve. The formation and growth of ice crystals permeate the entire polymer network, leading to overall hardening of the material, thus exhibiting macroscopic hardness and brittleness.

[0057] In the hydrogel of Example 1, the solvent system consisted of a eutectic solvent and water. Choline chloride acted as a hydrogen bond acceptor, and ethylene glycol as a hydrogen bond donor, forming strong hydrogen bond interactions with water molecules. This strong intermolecular interaction disrupted the original hydrogen bond network between water molecules, hindering the orderly arrangement and crystallization of water molecules towards ice crystal nuclei. Therefore, the water crystallization process was effectively suppressed, and no exothermic peak was observed on the DSC curve. The system did not crystallize at low temperatures but instead transformed into an amorphous glassy state, thus maintaining the mobility of the polymer network at the molecular scale, which macroscopically manifested as the material retaining its flexibility at -50°C.

[0058] Test Example 4: Adhesion Performance Test This test case aims to quantitatively evaluate the adhesion ability of the hydrogel prepared in Example 1 to substrates of different materials.

[0059] 1. Experimental Procedure (1) Sample and substrate preparation: Take the antifreeze conductive hydrogel prepared in Example 1 and cut it into square samples with a size of 20mm×20mm×2mm. Prepare standard test substrate plates with a size of 75mm×25mm, including stainless steel plates, glass plates and polypropylene (PP) plates. Clean the surface of all substrate plates with ethanol and deionized water in sequence, and dry them for later use.

[0060] (2) Preparation of overlapping shear specimen: Lay a substrate plate flat and attach half of the area (20mm × 10mm) of the square hydrogel sample to one end of the substrate plate. Then, cover the other half of the exposed area of ​​the hydrogel with another substrate plate of the same material to form a shear specimen with an overlapping area of ​​20mm × 20mm. Apply a fixed weight (e.g., 50g) to the overlapping area for 30 seconds to ensure sufficient contact.

[0061] (3) Shear strength test: Clamp both ends of the lapped shear specimen onto the tensile fixtures of the universal testing machine. Stretch the specimen at a constant rate of 10 mm / min until the two substrate plates are completely separated. Record the maximum load (F_max) during the separation process.

[0062] (4) Data Calculation: Calculate the shear strength (τ) according to the formula τ=Fmax / A. Where Fmax is the maximum load and A is the adhesion overlap area (20mm×20mm=400mm). 2 ).

[0063] 2. Experimental Results The adhesion properties of the hydrogel sample from Example 1 on different substrates were tested as described above. Each test was repeated three times, and the average value of the results was recorded in Table 4.

[0064] Table 4: Adhesion performance test data of hydrogel on different substrates in Example 1 The test results in Table 4 show that the hydrogel prepared in Example 1 exhibits adhesion properties to a variety of surfaces with different properties, among which the adhesion strength to polar surfaces such as stainless steel and glass is relatively high.

[0065] This adhesive property stems from the chemical composition and molecular structure of the hydrogel. The sodium alginate and polyacrylamide polymer chains that form the hydrogel's dual-network framework are densely packed with numerous polar functional groups, primarily including carboxyl groups on sodium alginate and amide groups on polyacrylamide. These functional groups can act as hydrogen bond donors or acceptors, forming multi-point, reversible hydrogen bond intermolecular interactions with polar sites on the substrate surface (such as hydroxyl groups on glass surfaces or oxide layers on metal surfaces).

[0066] These intermolecular forces formed at the interface collectively constitute the adhesion between the hydrogel and the substrate. When a shear force is applied, these numerous intermolecular forces must be broken to separate the interface, which macroscopically manifests as the material's adhesive strength. For non-polar surfaces like polypropylene, the adhesive strength is relatively low due to the lack of sites for strong interactions. This self-adhesive property, requiring no additional adhesive, is an inherent property of this material, facilitating its direct application for device surface coating.

[0067] Test Example 5: Battery Low Temperature Protection Application Test This test case aims to evaluate the effect of the hydrogel prepared in Example 1 on suppressing the output performance of lithium-ion batteries under low-temperature conditions.

[0068] 1. Experimental Procedure (1) Test preparation: Two commercially available 18650 lithium-ion batteries of identical model, batch, and capacity were selected. Both batteries were charged to full capacity using a battery testing system at 25°C (charged to 4.2V, then constant voltage charging until the current was less than 0.02C).

[0069] Experimental group: Take a fully charged battery and use the antifreeze conductive hydrogel prepared in Example 1 to uniformly and tightly coat the entire cylindrical surface of the battery using its self-adhesive properties.

[0070] Control group: Another fully charged battery, without any treatment.

[0071] (2) Low-temperature environment simulation and discharge test: Both the experimental and control group batteries were placed in a programmable high and low temperature controlled chamber and connected to a battery testing system. The temperature control program was set to cool from 25°C to -40°C at a rate of 3°C / min, and then hold at -40°C for 45 minutes to ensure that the battery temperature reached equilibrium with the ambient temperature.

[0072] In a constant temperature environment of -40℃, the two batteries were discharged at a constant current rate of 0.5C using a battery testing system until the discharge cutoff voltage (2.75V) was reached.

[0073] (3) Data Recording: The system automatically records the voltage-capacity curves of both batteries throughout the entire discharge process. After the test, the total discharge capacity released by each battery at -40℃ is recorded, and its average discharge voltage is calculated.

[0074] 2. Experimental Results The experimental and control group batteries were subjected to the above-mentioned low-temperature discharge test, and the results are recorded in Table 5.

[0075] Table 5: Battery discharge performance test data at -40℃ As shown in Table 5, at a low temperature of -40℃, the experimental group batteries coated with the hydrogel of Example 1 discharged significantly more electricity than the control group batteries that did not undergo any treatment. Simultaneously, the average discharge voltage of the experimental group batteries remained at a high level throughout the entire discharge process.

[0076] The test results above demonstrate that the encapsulated hydrogel layer effectively suppresses the degradation of battery output performance at low temperatures. This effect stems from the physical properties of the hydrogel. The hydrogel layer acts as a thermal buffer, isolating the battery from the external low-temperature environment. Because the gel system (primarily a eutectic solvent and water) has a certain heat capacity, it slows down the rate at which the battery body loses heat to the external environment. Therefore, even in an external environment of -40℃, the actual internal operating temperature of the encapsulated battery is maintained at a relatively high level.

[0077] The electrochemical performance of a battery is directly related to its operating temperature. For the control group battery, low temperature leads to a sharp increase in electrolyte viscosity, increased resistance to lithium-ion migration, and a decrease in charge transfer reaction kinetics on the electrode material surface. These factors collectively result in a rapid increase in internal resistance, ultimately manifesting macroscopically as a significant reduction in the output voltage plateau and a severe decrease in usable capacity. In contrast, the experimental group battery, due to the thermal buffering effect of the hydrogel, maintains a relatively favorable operating temperature, effectively mitigating the aforementioned problems caused by low temperature, thus enabling it to release more capacity and maintain a higher operating voltage.

Claims

1. An antifreeze gel, characterized in that, include: (a) Sodium alginate-polyacrylamide dual-network polymer matrix; (b) A mixed solvent system consisting of a eutectic solvent of choline chloride and ethylene glycol and water; (c) Two-dimensional Ti3C2T dispersed in the matrix X MXene nanosheets; Wherein, based on the total volume of the gel, the concentration of sodium alginate is 1-3% (w / v), the polyacrylamide is polymerized from acrylamide monomer at a concentration of 10-25% (w / v), and the Ti3C2T X The solid content of MXene nanosheets is 0.1-1.0% (w / v).

2. The antifreeze gel according to claim 1, characterized in that, In the eutectic solvent, the molar ratio of choline chloride to ethylene glycol is 1:2 to 1:

4.

3. The antifreeze gel according to claim 1, characterized in that, The dual-network polymer matrix is ​​formed by crosslinking N,N'-methylenebisacrylamide as a crosslinking agent.

4. The antifreeze gel according to claim 1, characterized in that, In the mixed solvent system, the volume ratio of the eutectic solvent to water is 4:1 to 9:

1.

5. A method for preparing an antifreeze gel as described in any one of claims 1-4, characterized in that, Includes the following steps: (a) Sodium alginate, acrylamide monomer, crosslinking agent, photoinitiator, and two-dimensional Ti3C2T X The MXene nanosheet dispersion was mixed with a eutectic solvent-water mixed solvent system to obtain a gel precursor solution; (b) The gel precursor solution is subjected to ultraviolet light treatment to initiate in-situ polymerization of the acrylamide monomer, which interpenetrates with the sodium alginate network to form the antifreeze conductive hydrogel.

6. The method for preparing the antifreeze gel according to claim 5, characterized in that, The preparation steps of the gel precursor solution include: heating and stirring choline chloride and ethylene glycol at 70-90°C to prepare the eutectic solvent.

7. The method for preparing the antifreeze gel according to claim 5, characterized in that, The preparation step of the gel precursor solution further includes: preparing the two-dimensional Ti3C2T by acid etching of Ti3AIC2MAX phase powder and ultrasonic exfoliation. X MXene nanosheet dispersion.

8. The method for preparing the antifreeze gel according to claim 5, characterized in that, The ultraviolet light used in the ultraviolet irradiation treatment has a center wavelength of 365nm and a power density of 3-10mW / cm². 2 .

9. A method for suppressing the decline in battery output performance at low temperatures using an antifreeze gel, characterized in that, The method includes directly coating the surface of the battery with the antifreeze gel as described in any one of claims 1-4, by means of its self-adhesion.

10. The suppression method according to claim 9, characterized in that, The battery is a lithium battery, and the coating effectively mitigates the reduction in output voltage and capacity decay of the lithium battery in the temperature range of -50℃ to 0℃.

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