Quasi-solid-state deep eutectic gel electrolyte-based thermal battery

Abstract

The invention relates to the technical field of thermal batteries, and discloses a quasi-solid-state deep eutectic gel electrolyte-based thermal battery, which comprises electrodes and a quasi-solid-state deep eutectic gel electrolyte arranged between the electrodes. The electrolyte is prepared by carrying out solvent replacement on polyvinyl alcohol hydrogel in a mixed soaking solution containing a deep eutectic solvent and a ferricyanate aqueous solution, wherein the deep eutectic solvent is composed of ethylene glycol and choline chloride. Through a solvent replacement strategy, a deep eutectic solvent is used for inducing polymer molecular chain rearrangement and regulating and controlling a solvation shell layer of redox couple ions. The prepared electrolyte has excellent tensile and compression mechanical strength, high thermoelectric force and good anti-fatigue property. The battery solves the problem that mechanical and thermoelectric properties of traditional gel electrolyte are difficult to consider, and is suitable for flexible wearable heat energy collection devices.

Description

Technical Field

[0001] This invention relates to the field of thermal battery technology, specifically to a quasi-solid-state deep eutectic gel electrolyte-based thermal battery. Background Technology

[0002] Thermal batteries, as devices capable of directly converting low-grade heat energy into electrical energy, have attracted widespread attention due to their simple structure, low cost, and ability to utilize vast environmental waste heat resources. While traditional liquid thermal batteries possess high thermoelectric conversion efficiency, the inherent drawbacks of liquid electrolytes, such as easy leakage, volatility, and difficulty in encapsulation, severely limit their application in portable and wearable electronic devices.

[0003] To overcome the limitations of liquid electrolytes, researchers have developed quasi-solid-state gel electrolytes based on polymer matrices, attempting to immobilize redox ions within the gel network to address leakage issues. However, existing hydrogel electrolytes generally face the challenge of balancing mechanical and thermoelectric properties. On one hand, traditional hydrogel matrices are primarily composed of abundant free water and a sparse polymer network, resulting in low mechanical strength and poor tensile and compressive strength. They are prone to fracture or structural damage under complex mechanical deformations caused by human movement, leading to device failure. On the other hand, redox couples in pure water environments are limited by the solvation shell of water molecules, resulting in a small reaction entropy difference and a low Seebeck coefficient, thus restricting the device's output voltage and power density.

[0004] Although existing studies have attempted to modify gel electrolytes by introducing organic solvents or inorganic fillers, it is often difficult to simultaneously achieve high mechanical strength and excellent thermoelectric chemical response. For example, simply increasing the crosslinking density can improve strength, but it often hinders ion transport; while simply pursuing high ionic conductivity can easily lead to an overly soft gel. Therefore, how to construct a quasi-solid-state electrolyte material that possesses both excellent mechanical strength and significantly improved thermoelectric conversion performance by controlling the electrolyte's microstructure and solvation environment is a pressing technical challenge in the field of flexible thermal batteries. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a quasi-solid-state deep eutectic gel electrolyte-based thermal battery, which solves the problems of low mechanical strength and easy fracture failure that are common in existing quasi-solid-state gel electrolytes, as well as the problem that the thermoelectric potential is low due to the limitation of pure water solvation environment, making it difficult to simultaneously achieve excellent mechanical properties and efficient thermoelectric conversion performance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a quasi-solid-state deep eutectic gel electrolyte-based thermal battery, comprising electrodes and a quasi-solid-state deep eutectic gel electrolyte disposed between the electrodes; The quasi-solid deep eutectic gel electrolyte is prepared by solvent replacement after immersing polyvinyl alcohol hydrogel in a mixed soaking solution. The mixed soaking solution is a mixture of a deep eutectic solvent and an aqueous solution of ferricyanide; The deep eutectic solvent is composed of ethylene glycol and choline chloride; The aqueous solution of ferricyanide contains dissolved potassium ferricyanide and potassium ferrocyanide.

[0007] Preferably, the volume ratio of the deep eutectic solvent to the ferricyanide aqueous solution in the mixed soaking solution is 2:8 to 9.5:0.5.

[0008] Preferably, the molar ratio of ethylene glycol to choline chloride in the deep eutectic solvent is 2:1; the concentration of potassium ferricyanide and the concentration of potassium ferrocyanide in the ferricyanide aqueous solution are both 0.2M and 0.2M, respectively.

[0009] Preferably, the battery is a flexible device, consisting of multiple units containing the quasi-solid-state deep eutectic gel electrolyte connected in series by wires.

[0010] A method for preparing a quasi-solid-state deep eutectic gel electrolyte includes the following steps: S1. Preparation of polyvinyl alcohol hydrogel: Polyvinyl alcohol is dissolved in deionized water, heated and stirred to allow the polyvinyl alcohol to fully swell and dissolve, and after defoaming treatment, it is poured into a mold and polyvinyl alcohol hydrogel is obtained by repeated freeze-thaw cycles. S2. Preparation of deep eutectic solvent: Ethylene glycol and choline chloride are mixed and heated and stirred until a clear and transparent liquid deep eutectic solvent is formed. S3. Preparation of mixed soaking solution: Dissolve potassium ferricyanide and potassium ferrous ferricyanide in deionized water to obtain an aqueous solution of ferricyanide, and mix the deep eutectic solvent with the aqueous solution of ferricyanide to obtain a mixed soaking solution; S4. Preparation of quasi-solid deep eutectic gel electrolyte: The polyvinyl alcohol hydrogel obtained in step S1 is immersed in the mixed immersion solution obtained in step S3 for solvent replacement to obtain quasi-solid deep eutectic gel electrolyte. S5. Battery assembly: The quasi-solid-state deep eutectic gel electrolyte obtained in step S4 is sandwiched between the two electrodes for encapsulation.

[0011] Preferably, in step S1, the polyvinyl alcohol has a mass fraction of 20 wt% in deionized water; the heating and stirring is carried out at 95°C for 1.5 h; the defoaming treatment is carried out at room temperature for 3 h and then reheated to 65°C; the repeated freeze-thaw cycle is 3 times between freezing at -18°C and thawing at room temperature.

[0012] Preferably, in step S2, the molar ratio of ethylene glycol to choline chloride is 2:1, and the heating and stirring temperature is 75°C.

[0013] Preferably, in step S3, the volume ratio of the deep eutectic solvent to the ferricyanide aqueous solution in the mixed soaking solution is 2:8 to 9.5:0.5.

[0014] Preferably, in step S3, the volume ratio of the deep eutectic solvent to the ferricyanide aqueous solution in the mixed soaking solution is 9.5:0.5.

[0015] Preferably, in step S4, the mixed soaking solution is replaced every 6 hours during the solvent replacement process, for a total of 3 times.

[0016] This invention provides a quasi-solid-state deep eutectic gel electrolyte-based thermal battery. It possesses the following beneficial effects: 1. This invention introduces a deep eutectic solvent into the polyvinyl alcohol hydrogel network through solvent displacement; the interaction between DES and PVA molecular chains causes the PVA molecular chains to rearrange, forming a more compact and ordered polymer network structure, thereby significantly enhancing the modulus of the gel; compared with pure PVA hydrogel, the tensile strength of the obtained deep eutectic gel electrolyte is significantly improved, reaching up to 7.17 MPa, which is about 30 times that of pure PVA hydrogel.

[0017] 2. This invention solves the problem that mechanical strength and ion transport thermoelectric properties often restrict each other in traditional gel electrolytes by adjusting the volume ratio of DES to ferricyanide aqueous solution in the mixed soaking solution. This specific ratio can ensure the maximum molecular chain rearrangement to obtain the highest strength, and maintain the best ion solvation environment to obtain the highest thermoelectric potential, thus achieving the simultaneous improvement of both in a single material system.

[0018] 3. The quasi-solid deep eutectic gel electrolyte prepared by this invention has high strength while maintaining the flexibility of hydrogel, and solves the leakage problem compared with liquid electrolyte. Flexible thermal battery devices assembled based on this electrolyte can adapt to complex mechanical deformations such as bending and stretching, and can maintain stable thermoelectric conversion efficiency and power output even when worn by the human body or under harsh stress environment. Detailed Implementation

[0019] 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.

[0020] Example: Example 1: This embodiment provides a method for preparing a quasi-solid-state deep eutectic gel electrolyte, wherein the volume ratio of the deep eutectic solvent to the ferricyanide aqueous solution in the mixed soaking solution is an intermediate value of 5:5. The specific steps are as follows: Preparation of polyvinyl alcohol hydrogel: Polyvinyl alcohol powder was added to deionized water to prepare a mixture with a mass fraction of 20 wt%. The mixture was first stirred at 300 rpm for 30 minutes at room temperature to allow initial swelling. Then, it was sealed and heated and stirred in an oil bath at 95°C for 1.5 hours until completely dissolved to form a homogeneous sol. The sol was allowed to stand at room temperature for 3 hours to defoam, then reheated to 65°C to maintain fluidity, and poured into a glass mold. The mold was frozen at -18°C for 12 hours, then thawed at room temperature for 6 hours. This freeze-thaw cycle was repeated three times to obtain the formed PVA hydrogel.

[0021] Preparation of deep eutectic solvents: Ethylene glycol and choline chloride were mixed in a beaker at a molar ratio of 2:1. The beaker was placed in an oil bath at 75°C and heated with continuous stirring until the solid completely disappeared, yielding a clear and transparent deep eutectic solvent.

[0022] Preparation and solvent replacement of the mixed soaking solution: Weigh out potassium ferricyanide and potassium ferrocyanide separately and dissolve them in deionized water to prepare ferricyanide aqueous solutions with a concentration of 0.2M for potassium ferricyanide and 0.2M for potassium ferrocyanide.

[0023] Measure 50 mL of the deep eutectic solvent prepared above and mix it with 50 mL of ferricyanide aqueous solution (i.e., volume ratio of 5:5), and stir evenly to obtain a mixed soaking solution.

[0024] The PVA hydrogel prepared in step 1 was cut and immersed in the mixed soaking solution, and solvent replacement was performed under sealed conditions at room temperature. The gel was removed every 6 hours, and fresh mixed soaking solution of the same ratio was used to replace it, for a total of 3 times. After removal, the surface liquid was wiped dry to obtain the quasi-solid deep eutectic gel electrolyte.

[0025] Example 2: This embodiment provides a method for preparing a quasi-solid-state deep eutectic gel electrolyte, wherein the volume ratio of the deep eutectic solvent to the ferricyanide aqueous solution in the mixed soaking solution is 2:8, which is the lower limit of the scope of the claims, and the lower limit of the process parameter range is also adopted. The specific steps are as follows: Preparation of polyvinyl alcohol hydrogel: Polyvinyl alcohol powder was added to deionized water to prepare a mixture with a mass fraction of 18 wt%. After stirring at room temperature for 40 min, the mixture was sealed and placed in an oil bath at 90℃ and stirred for 2 h to ensure complete dissolution at a lower temperature. After defoaming treatment, the mixture was heated to 60℃ and poured into a mold. Freeze-thaw cycles were performed: freezing at -15℃ for 16 h, thawing at room temperature for 8 h, and repeating the cycle 3 times to obtain PVA hydrogel.

[0026] Preparation of deep eutectic solvents: Ethylene glycol and choline chloride were mixed in a molar ratio of 2:1. The mixture was heated and stirred at 70°C until a homogeneous, transparent liquid was formed.

[0027] Preparation and solvent replacement of the mixed soaking solution: Prepare an aqueous solution of ferricyanide with a concentration of 0.2M potassium ferricyanide and 0.2M potassium ferrocyanide.

[0028] Measure 20 mL of deep eutectic solvent and mix it with 80 mL of ferricyanide aqueous solution (i.e., volume ratio of 2:8) to prepare a mixed soaking solution.

[0029] The PVA hydrogel was immersed in the mixed soaking solution, and the solution was changed every 5 hours for a total of 3 times, so that a small amount of DES component could penetrate into the gel network to obtain a quasi-solid deep eutectic gel electrolyte.

[0030] Example 3: This embodiment provides a method for preparing a quasi-solid-state deep eutectic gel electrolyte, wherein the volume ratio of the deep eutectic solvent to the ferricyanide aqueous solution in the mixed soaking solution is the upper limit of the scope of the claims, 9.5:0.5, and the upper limit of the process parameter range is also adopted. The specific steps are as follows: Preparation of polyvinyl alcohol hydrogel: Polyvinyl alcohol powder was added to deionized water to prepare a mixture with a mass fraction of 22 wt%. After stirring at room temperature for 20 min, the mixture was sealed and placed in an oil bath at 98℃ and heated and stirred for 1 h to rapidly dissolve the polyvinyl alcohol. After defoaming, the mixture was heated to 70℃ and poured into a mold. Freeze-thaw cycles were performed: freezing at -20℃ for 10 h, thawing at room temperature for 4 h, and repeating the cycle 3 times to obtain PVA hydrogel.

[0031] Preparation of deep eutectic solvents: Ethylene glycol and choline chloride were mixed in a molar ratio of 2:1. The mixture was heated and stirred at 80°C to accelerate the dissolution process until a clear and transparent liquid was formed.

[0032] Preparation and solvent replacement of the mixed soaking solution: Prepare an aqueous solution of ferricyanide with a concentration of 0.2M potassium ferricyanide and 0.2M potassium ferrocyanide.

[0033] Measure 95 mL of deep eutectic solvent and mix it with 5 mL of ferricyanide aqueous solution (i.e., volume ratio of 9.5:0.5) to prepare a mixed soaking solution with high DES content.

[0034] PVA hydrogel was immersed in the mixed soaking solution, and the solution was changed every 6 hours for a total of 3 times. The high concentration of DES environment forced the PVA molecular chains to rearrange to the maximum extent and adjusted the solvation shell of the ions, ultimately resulting in a quasi-solid deep eutectic gel electrolyte with high mechanical strength and high thermoelectric potential.

[0035] Comparative Example 1: Compared with Example 3, the difference is that in step 3, no deep eutectic solvent was added, but 100 mL of ferricyanide aqueous solution was directly used as the soaking solution. The other steps and parameters are the same.

[0036] Comparative Example 2: Compared with Example 3, the difference is that in steps 2 and 3, an equal volume of pure ethylene glycol is used instead of the deep eutectic solvent. That is, the mixed soaking solution is made by mixing 95 mL of ethylene glycol with 5 mL of ferricyanide aqueous solution. The mixed solution does not contain choline chloride. The remaining steps and parameters are the same.

[0037] Comparative Example 3: Compared to Example 1, the difference lies in the use of a one-pot method, eliminating the solvent replacement process in step 3. Specifically, in step 1, PVA powder, water, DES, and ferricyanide are directly mixed and dissolved, heated to form a sol, poured into a mold, and subjected to freeze-thaw cycles to directly obtain a gel. The total proportions of the remaining raw materials remain the same.

[0038] Comparative Example 4: Compared with Example 2, the difference is that in step 3, the volume ratio of deep eutectic solvent to ferricyanide aqueous solution in the mixed soaking solution is adjusted to 1:9, while the other steps and parameters are the same.

[0039] Test Example 1: Tensile Mechanical Property Test Experimental description: This test case aims to determine and compare the tensile mechanical properties of quasi-solid gel electrolytes prepared in different examples and comparative examples.

[0040] Sample preparation: The quasi-solid-state gel electrolytes prepared in Examples 1, 2, and 3, as well as Comparative Examples 1, 2, 3, and 4, were used as test samples. Each group of samples was cut into dumbbell-shaped specimens using a standard cutting tool, with a gauge length of 20 mm, a width of 4 mm, and a uniform thickness of 1.0 mm ± 0.1 mm.

[0041] Test equipment: Uniaxial tensile tests were conducted using a universal testing machine equipped with a 100N force sensor.

[0042] Test steps: Clamp the two ends of the cut dumbbell-shaped specimen into the upper and lower clamps of the universal testing machine, respectively, and adjust the clamp spacing to ensure that the specimen is under no pretension in its natural state and that its axis coincides with the tensile direction.

[0043] Set the stretching rate to 50 mm / min.

[0044] The tensile procedure was initiated under ambient conditions of room temperature and relative humidity of 50%±5%, applying a uniaxial tensile load to the specimen until the specimen fractured.

[0045] The system automatically records stress and strain data during the stretching process.

[0046] Based on the stress-strain curve, the tensile strength at break, elongation at break, and Young's modulus of the specimen were read and calculated. Each group of samples was tested in parallel five times, and the arithmetic mean was taken after removing the maximum and minimum values ​​as the final test result.

[0047] Experimental data: The table below lists the mechanical property data of each group of samples under the above test conditions: Table 1: Tensile mechanical properties test results of each group of gel electrolytes

[0048] Results analysis: As shown in Table 1, the gel electrolyte prepared in Example 3 exhibited the highest tensile strength, significantly higher than that of Comparative Example 1. This difference in mechanical properties stems from the rearrangement of the polyvinyl alcohol (PVA) molecular chain conformation by the deep eutectic solvent. During solvent replacement, the deep eutectic solvent molecules penetrate into the gel network, and the interaction forces between them and the PVA molecular chains lead to a localized, orderly arrangement of the PVA molecular chains, forming a denser and more ordered polymer network structure. This rearranged network can effectively disperse external stress, thereby significantly improving the material's modulus and tensile strength.

[0049] Although Comparative Example 2 introduced ethylene glycol solvent, its tensile strength was significantly lower than that of Example 3, which contained choline chloride at the same volume ratio. This indicates that ethylene glycol alone cannot induce polyvinyl alcohol molecular chains to form a network of equal strength, suggesting that the deep eutectic system formed by choline chloride and ethylene glycol specifically contributes to molecular chain rearrangement and subsequent mechanical enhancement. Furthermore, a comparison between Example 1 and Comparative Example 3 shows that, at the same ratio, the strength of the sample prepared by solvent replacement is significantly better than that prepared by one-pot method. This confirms that the process route of first forming a physically cross-linked hydrogel matrix and then introducing a deep eutectic solvent through solvent replacement is a key step in achieving effective molecular chain rearrangement and obtaining high mechanical properties.

[0050] The data from Comparative Example 4 show that when the content of the deep eutectic solvent is below a certain threshold, its effect on inducing molecular chain rearrangement is limited, resulting in a slightly higher tensile strength than pure hydrogel, but with limited improvement. Only when the content of the deep eutectic solvent is within the range defined by this invention can the gel network undergo sufficient structural evolution, exhibiting a significant mechanical reinforcement effect. The data from Examples 1 to 3 show that as the proportion of deep eutectic solvent increases, both tensile strength and elongation at break increase, verifying the regulatory effect of the mixed soaking solution ratio on the final mechanical properties of the material.

[0051] Test Example 2: Compression Mechanical Properties Test Experimental description: This test case aims to determine the compressive strength and structural stability of gel electrolytes obtained under different component ratios and preparation processes when subjected to large deformation compressive loads.

[0052] Sample preparation: The gel electrolytes prepared in Examples 1, 2, 3, and Comparative Example 1 were selected as the test objects. The gel samples were cut into cylindrical specimens using a dedicated punch. The specimen dimensions were controlled as follows: diameter 10 mm ± 0.5 mm, height 8 mm ± 0.5 mm. The actual diameter and height of each specimen were measured and recorded before testing for subsequent stress calculations.

[0053] Test equipment: The compression test module of the universal testing machine is equipped with a flat pressure plate clamp.

[0054] Test steps: Place the cylindrical specimen at the center of the lower pressure plate of the universal testing machine, ensuring that the specimen end face is parallel to the surface of the pressure plate.

[0055] Adjust the position of the upper pressure plate so that it just contacts the upper surface of the sample, and reset the load reading at this point to zero as the starting point of the test.

[0056] The compression rate is set to 5 mm / min.

[0057] Initiate the compression program to apply an axial compressive load to the specimen until the specimen height is compressed to 50% of its initial height.

[0058] The system records the load displacement data during the compression process in real time and converts the load into engineering stress based on the initial cross-sectional area of ​​the specimen.

[0059] The stress value corresponding to 50% compressive strain is recorded as the 50% compressive strength. Five specimens are tested repeatedly for each group of samples, and the arithmetic mean is taken.

[0060] Experimental data: The table below records the compressive strength data of each group of samples at 50% compressive strain: Table 2: Test results of compressive mechanical properties of each group of gel electrolytes

[0061] Results analysis: The experimental data in Table 2 reveal the influence of deep eutectic solvent content on the compressive strength of the gel electrolyte. The sample in Example 3, with a volume ratio of 9.5:0.5, achieved a 50% compressive strength of 8.99 MPa, while the comparative example 1, without solvent replacement, only achieved 0.36 MPa, a difference of orders of magnitude. This strength improvement is attributed to the transformation of the gel's internal microstructure during solvent replacement. In a high-concentration deep eutectic solvent environment, the hydrogen bonding interactions between polyvinyl alcohol molecular chains are enhanced, promoting the transformation of amorphous regions into crystalline regions or the formation of a denser physical cross-linked network. This dense network structure restricts the relative slippage of molecular chain segments, thereby endowing the material with higher deformation resistance under external compressive loads.

[0062] As the proportion of deep eutectic solvent in the mixed soaking solution decreased, the compressive strength of the samples showed a decreasing trend. The compressive strength of Example 1 was 5.12 MPa, and that of Example 2 was 2.84 MPa, both significantly higher than that of Comparative Example 1. This indicates that even at lower deep eutectic solvent contents, the solvent replacement process can still induce a certain degree of shrinkage and solidification in the gel network, eliminating the molecular chain relaxation phenomenon caused by swelling in pure water. The introduction of deep eutectic solvent molecules fills the gaps in the polymer network, constructing a more rigid supporting framework, enabling the gel to transform from a soft hydrated state to a high-modulus state with quasi-solid characteristics.

[0063] Comparative analysis shows that the compressive strength of the gel electrolyte is positively correlated with the density of the hydrogen bond network within the system. In the pure water environment of Comparative Example 1, the presence of a large number of water molecules acts as a plasticizer, weakening the interaction forces between polymer chains, leading to large deformation and low stress levels during compression. In Examples 1 to 3, the ethylene glycol and choline chloride components in the deep eutectic solvent replace some or most of the free water, increasing the crosslinking density of the network nodes by forming multiple hydrogen bonds with the hydroxyl groups of polyvinyl alcohol. This enhanced physical crosslinking not only improves the stiffness of the material but also effectively dissipates the mechanical energy input during compression, ensuring the structural integrity of the material under large strain.

[0064] Test Example 3: Thermochemical Performance Test Experimental description: This test case aims to determine the thermoelectric conversion capability of the gel electrolytes prepared in the examples and comparative examples, and to calculate the Seebeck coefficient by measuring the open-circuit voltage at different temperature differences. .

[0065] Sample preparation: The gel electrolytes prepared in Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2 were used. Each sample was cut into strips of uniform size, with dimensions of 20 mm in length, 10 mm in width, and 1 mm in thickness.

[0066] Test equipment: A self-made thermoelectric performance testing platform was used. The platform mainly consists of two independently temperature-controlled copper bases, a high-precision temperature controller, two platinum electrode plates, and a digital nanovoltmeter.

[0067] Test steps: The cut strip of gel sample is laid flat between two copper bases on the test platform, ensuring that both ends of the sample cover the surfaces of the two bases respectively.

[0068] Platinum electrode sheets were placed between the sample and the copper base and fixed with insulating clamps to ensure close contact between the electrode and the gel surface, thus eliminating errors caused by contact resistance.

[0069] Connect the positive and negative probes of the digital nanovoltmeter to the two platinum electrode plates, respectively.

[0070] The temperature of the cooling end is set to be constant at 298K.

[0071] Gradually adjust the temperature of the heating end to establish a stable temperature difference between the two ends of the sample. The set temperature gradients are 5K, 10K, 15K, 20K, 25K, and 30K.

[0072] Maintain a constant temperature for 5 minutes at each set temperature difference point. After the voltage reading displayed on the digital nanovoltmeter stabilizes, record the open-circuit voltage at that temperature difference. .

[0073] With temperature difference The x-axis represents the open-circuit voltage. Plot a curve on the ordinate and perform a linear fit. The slope of the fitted line is the Seebeck coefficient for that sample. The unit is mVK -1 .

[0074] Experimental data: The table below records the Seebeck coefficients for each group of samples calculated using linear fitting: Table 3: Test results of thermoelectric properties of gel electrolytes in each group

[0075] Results analysis: Table 3 shows the modulating effect of the deep eutectic solvent composition and its concentration on the thermoelectric potential of the redox couple of ferrocyanate. The Seebeck coefficient in Example 3 is as high as 1.68 mVK. -1 It is significantly higher than the 0.82 mVK of Comparative Example 1. -1 This performance improvement stems from the solvation effect altering the entropy change of the redox reaction. In electrolytes containing high concentrations of deep eutectic solvents, the choline cations in choline chloride and ethylene glycol molecules reconstruct the ferricyanide ion through hydrogen bonding and electrostatic interactions. and ferricyanide ions The surrounding solvated shell. This reconfiguration leads to an increase in the configurational entropy difference between oxidized and reduced ions, thus according to the definition of thermoelectric potential ( ,in (This is the reaction entropy), which directly increases the thermoelectric potential of the material.

[0076] Comparing the data from Example 3 and Comparative Example 2, it can be seen that, under the same organic solvent content, the thermoelectric potential of the system lacking choline chloride was not significantly improved. This confirms that the simple organic solvent effect is not the dominant factor in increasing the thermoelectric potential, but rather that specific components in the deep eutectic solvent play a key role. Choline chloride, as a hydrogen bond acceptor, may preferentially adsorb onto the surface of polyvalent anions through stronger electrostatic interactions, altering the effective charge density and solvation radius of the ions, thereby amplifying the entropy change of the reaction.

[0077] The trends from Examples 2 and 1 to Example 3 show that the Seebeck coefficient monotonically increases with the increase of the volume ratio of deep eutectic solvent in the mixed soaking solution. This indicates that the deeper the solvent replacement, the more deep eutectic solvent components reside within the gel network, and the more significant the reshaping effect on the ion solvation environment. Under the conditions of Example 3, most of the free water is replaced, and the system is in a quasi-solid-state environment rich in deep eutectic solvent, maximizing the utilization of the solvent effect to improve thermoelectric conversion efficiency. This result verifies the feasibility of optimizing thermoelectric performance by controlling the solvent ratio.

[0078] Test Example 4: Output Power Performance Test of Flexible Devices Experimental description: This test case aims to verify the actual energy output capability of flexible thermoelectric chemical devices assembled from gel electrolytes prepared based on the examples and comparative examples under bending conditions.

[0079] Component assembly: The gel electrolytes prepared in Example 3 and Comparative Example 1 were selected. The gel electrolytes were cut into 10mm × 10mm × 1mm square pieces. Carbon nanotube paper was selected as the electrode material and cut into the same size. A "sandwich" structure was adopted, sandwiching one piece of gel electrolyte between two pieces of carbon nanotube paper electrodes to form a single power generation unit. Twelve identical single power generation units were prepared and connected in series end-to-end using copper wires. Finally, the series-connected device array was encapsulated using a flexible polyurethane film to obtain a flexible thermal battery device.

[0080] Test equipment: The test platform consists of a heating platform, a cooling platform, a semi-cylindrical mold with a curvature radius of 2cm, a variable resistance box, a digital multimeter, and a data acquisition system.

[0081] Test steps: The encapsulated flexible device is attached and fixed to the curved surface of a semi-cylindrical mold, so that the device is in a bent state to simulate the force situation when the human body wears it.

[0082] Adjust the mold position so that one side of the device contacts the heating source and the other side contacts the cooling source.

[0083] Adjust the temperatures of the heating and cooling sources to establish a stable temperature difference environment between the hot and cold ends of the device. The set temperature difference point... The corresponding values ​​are 10K, 20K, and 30K.

[0084] Under each temperature difference condition, the variable resistor box is connected to the output circuit of the device.

[0085] Adjust the load resistance value of the rheostat in stages. Simultaneously record the output voltage in the circuit. and current .

[0086] According to the formula Calculate the output power under different loads and plot the power-resistance curve. The peak value of the curve is taken as the maximum output power at that temperature difference. .

[0087] Experimental data: The table below records the maximum output power data of the devices assembled in Example 3 and Comparative Example 1 under different temperature differences in a bent state: Table 4: Test results of maximum output power of flexible devices under bending conditions

[0088] Results analysis: The test results in Table 4 show that the flexible device assembled based on the quasi-solid-state deep eutectic gel electrolyte prepared in Example 3 has a significantly higher output power than the pure hydrogel device based on Comparative Example 1. At a temperature difference of 30 K, the maximum output power of the device in Example 3 reaches 514.55 nW, approximately four times that of Comparative Example 1. This power increase is mainly driven by a significant increase in thermoelectric potential. According to the power formula... The output power is proportional to the square of the open-circuit voltage. Because the electrolyte in Example 3 modulates the solvation environment of the ions through a deep eutectic solvent, it significantly increases the thermoelectric potential, resulting in a higher cumulative voltage output across the series battery pack, ultimately leading to a non-linear increase in output power.

[0089] The experiment was conducted with a bending radius of 2 cm, and the data confirmed that the device of Example 3 maintained high energy output even under mechanical deformation. This is attributed to the high mechanical strength and fatigue resistance of the gel electrolyte imparted by the solvent replacement process. During bending, the gel network of Example 3 effectively absorbed mechanical stress, maintained tight contact between the electrode and electrolyte interface, and prevented a sharp increase in internal resistance caused by interface peeling or gel breakage. In contrast, the pure hydrogel of Comparative Example 1 had lower mechanical strength and was more prone to deformation mismatch under bending conditions, leading to increased contact resistance and thus limiting its power output performance.

[0090] Furthermore, the introduction of the deep eutectic solvent creates a quasi-solid-state ion transport channel by replacing free water. This structure not only solves the leakage problem that easily occurs in traditional liquid electrolytes when flexible devices are bent and compressed, but also ensures the long-term operational stability of the device under temperature difference conditions by suppressing water evaporation. In Example 3, the device exhibited stable power response under different temperature gradients, and the power value increased systematically with increasing temperature difference, verifying the practical application potential of this quasi-solid-state deep eutectic gel electrolyte system in the field of flexible wearable thermal energy harvesting.

Claims

1. A quasi-solid-state deep eutectic gel electrolyte-based thermal battery, characterized in that, Includes electrodes and a quasi-solid-state deep eutectic gel electrolyte disposed between the electrodes; The quasi-solid deep eutectic gel electrolyte is prepared by solvent replacement after immersing polyvinyl alcohol hydrogel in a mixed soaking solution. The mixed soaking solution is a mixture of a deep eutectic solvent and an aqueous solution of ferricyanide; The deep eutectic solvent is composed of ethylene glycol and choline chloride; The aqueous solution of ferricyanide contains dissolved potassium ferricyanide and potassium ferrocyanide.

2. The quasi-solid-state deep eutectic gel electrolyte-based thermal battery according to claim 1, characterized in that, The volume ratio of the deep eutectic solvent to the ferricyanide aqueous solution in the mixed soaking solution is 2:8 to 9.5:0.

5.

3. The quasi-solid-state deep eutectic gel electrolyte-based thermal battery according to claim 1, characterized in that, The molar ratio of ethylene glycol to choline chloride in the deep eutectic solvent is 2:1; the concentration of potassium ferricyanide and potassium ferrocyanide in the ferricyanide aqueous solution is 0.2M.

4. A quasi-solid-state deep eutectic gel electrolyte-based thermal battery according to claim 1, characterized in that, The battery is a flexible device, consisting of multiple units containing the quasi-solid deep eutectic gel electrolyte connected in series by wires.

5. A method for preparing a quasi-solid-state deep eutectic gel electrolyte, comprising a quasi-solid-state deep eutectic gel electrolyte-based thermal battery according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Preparation of polyvinyl alcohol hydrogel: Polyvinyl alcohol is dissolved in deionized water, heated and stirred to allow the polyvinyl alcohol to fully swell and dissolve, and after defoaming treatment, it is poured into a mold and polyvinyl alcohol hydrogel is obtained by repeated freeze-thaw cycles. S2. Preparation of deep eutectic solvent: Ethylene glycol and choline chloride are mixed and heated and stirred until a clear and transparent liquid deep eutectic solvent is formed. S3. Preparation of mixed soaking solution: Dissolve potassium ferricyanide and potassium ferrous ferricyanide in deionized water to obtain an aqueous solution of ferricyanide, and mix the deep eutectic solvent with the aqueous solution of ferricyanide to obtain a mixed soaking solution; S4. Preparation of quasi-solid deep eutectic gel electrolyte: The polyvinyl alcohol hydrogel obtained in step S1 is immersed in the mixed immersion solution obtained in step S3 for solvent replacement to obtain quasi-solid deep eutectic gel electrolyte. S5. Battery assembly: The quasi-solid-state deep eutectic gel electrolyte obtained in step S4 is sandwiched between the two electrodes for encapsulation.

6. The method for preparing a quasi-solid-state deep eutectic gel electrolyte according to claim 5, characterized in that, In step S1, the polyvinyl alcohol has a mass fraction of 20 wt% in deionized water; the heating and stirring is carried out at 95°C for 1.5 h; the defoaming treatment is carried out at room temperature for 3 h and then reheated to 65°C; the repeated freeze-thaw cycle is 3 times between freezing at -18°C and thawing at room temperature.

7. The method for preparing a quasi-solid-state deep eutectic gel electrolyte according to claim 5, characterized in that, In step S2, the molar ratio of ethylene glycol to choline chloride is 2:1, and the heating and stirring temperature is 75°C.

8. The method for preparing a quasi-solid-state deep eutectic gel electrolyte according to claim 5, characterized in that, In step S3, the volume ratio of the deep eutectic solvent to the ferricyanide aqueous solution in the mixed soaking solution is 2:8 to 9.5:0.

5.

9. The method for preparing a quasi-solid-state deep eutectic gel electrolyte according to claim 8, characterized in that, In step S3, the volume ratio of the deep eutectic solvent to the ferricyanide aqueous solution in the mixed soaking solution is 9.5:0.

5.

10. The method for preparing a quasi-solid-state deep eutectic gel electrolyte according to claim 5, characterized in that, In step S4, the mixed soaking solution is replaced every 6 hours during the solvent replacement process, for a total of 3 times.

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