Lignin-based composite hydrogel thermal battery and preparation method and application thereof

Abstract

The application belongs to the technical field of hydrogel thermal batteries, and particularly relates to a lignin-based composite hydrogel thermal battery and a preparation method and application thereof, the preparation method comprising the following steps: defoaming a polyvinyl alcohol aqueous solution, then performing directional freezing and thawing to obtain PVA hydrogel with a directional pore structure; immersing the prepared PVA hydrogel in a sodium lignosulfonate solution to perform first solvent exchange; immersing the PVA hydrogel after the first solvent exchange is completed in a KOH solution to perform second solvent exchange, thereby obtaining a lignin-based hydrogel thermal battery. The prepared lignin-based composite hydrogel thermal battery has excellent thermal stability and good biocompatibility and other characteristics.

Description

Technical Field

[0001] This invention belongs to the field of hydrogel thermal battery technology, specifically relating to a lignin-based hydrogel thermal battery, its preparation method, and its application. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] The global energy structure will gradually be dominated by clean energy. Currently, clean energy faces challenges such as high storage technology costs, low energy density, and limited lifespan, making large-scale application difficult. Furthermore, the efficiency of heat energy utilization is only around 30%, with the remaining heat dissipating into the environment as waste heat, most of which has a temperature below 200°C.

[0004] Lignin is the second most abundant biopolymer in nature after cellulose, and it is mainly found in the cell walls of woody and herbaceous plants. However, most industrial lignin is not fully utilized and is mostly used as a low-grade fuel. Lignin in papermaking black liquor is also often not effectively utilized.

[0005] Liquid thermal batteries generate electricity using the temperature dependence of electrochemical redox potential (Seebeck effect), offering advantages such as low cost, scalability, and high thermoelectric potential, thus possessing broad development prospects. The core component of a liquid thermal battery is the liquid that acts as the redox couple within the battery. Based on the temperature difference-voltage polarity relationship, liquid thermal batteries can be classified into P-type and N-type. However, traditional liquid thermal batteries suffer from problems such as electrolyte leakage, environmental pollution, and low thermoelectric conversion efficiency. Furthermore, they often use petroleum-based chemicals as raw materials, resulting in complex preparation processes that utilize large amounts of chemicals, causing adverse environmental impacts. Simultaneously, their poor mechanical properties and electrical conductivity limit their application in many fields. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a lignin-based hydrogel thermal battery, its preparation method, and its application.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for preparing a lignin-based hydrogel thermal battery, comprising the following steps: After degassing the polyvinyl alcohol aqueous solution, it was subjected to directional freezing and thawing to obtain a PVA hydrogel with a directional pore structure. The prepared PVA hydrogel was immersed in a sodium lignosulfonate solution for the first solvent exchange. After the first solvent exchange, the PVA hydrogel was immersed in KOH solution for a second solvent exchange to obtain a lignin-based hydrogel thermal battery.

[0008] Secondly, the present invention provides a lignin-based hydrogel thermal battery, which is prepared by the aforementioned preparation method.

[0009] Thirdly, the present invention provides the application of the lignin-based hydrogel thermal battery in the preparation of wearable thermoelectric devices or flexible electronics.

[0010] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: This invention provides a lignin-based composite hydrogel thermal battery. PVA hydrogel is prepared using a directional freeze-thaw method. During directional freeze-thaw, PVA forms crystalline regions; with increasing freeze-thaw cycles, the crystallinity increases, creating directional channels. The composite hydrogel thermal battery is prepared through solvent exchange. Sodium lignin sulfonate forms hydrogen bonds with the PVA molecular chains, and the dynamic phenolic quinone transformation on the lignin surface allows sodium lignin sulfonate to act as a redox electron pair, endowing the hydrogel with excellent thermoelectric properties. + and OH - The movement of ions can induce the coordinated movement of other surrounding ions, further enhancing the thermoelectric properties of the gel. Furthermore, the mechanical properties of the composite hydrogel are enhanced through the action of lignin.

[0011] The preparation method of the present invention is simple to operate, low in cost, and environmentally friendly, and endows hydrogel thermal batteries with excellent multifunctional properties, including mechanical properties, electrical conductivity, and thermoelectric properties. Attached Figure Description

[0012] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0013] Figure 1 The conductivity of samples with different concentrations of sodium lignosulfonate added in the embodiments of the present invention; Figure 2 This refers to the conductivity of samples with different concentrations of potassium hydroxide added in the embodiments of the present invention; Figure 3 These are the Seebeck coefficients of samples with different concentrations of sodium lignosulfonate added in the embodiments of the present invention; Figure 4 These are the Seebeck coefficients of samples with different concentrations of potassium hydroxide added in the embodiments of this invention; Figure 5 These are the stress-strain curves of samples with different concentrations of sodium lignosulfonate added in the embodiments of the present invention; Figure 6 These are the stress-strain curves of samples with different concentrations of potassium hydroxide added in the embodiments of the present invention. Detailed Implementation

[0014] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0015] To address the technical problems mentioned in the background art, the present invention provides a method for preparing a lignin-based hydrogel thermal battery, comprising the following steps: After degassing the polyvinyl alcohol aqueous solution, it was subjected to directional freezing and thawing to obtain a PVA hydrogel with a directional pore structure. The prepared PVA hydrogel was immersed in a sodium lignosulfonate solution for the first solvent exchange. After the first solvent exchange, the PVA hydrogel was immersed in KOH solution for a second solvent exchange to obtain a lignin-based hydrogel thermal battery.

[0016] PVA molecules contain numerous hydroxyl groups. During directional freeze-thaw cycles, crystalline regions form between the molecular chains. With each freeze-thaw cycle, the crystallinity increases, creating a three-dimensional network with a directional porous structure. This structure provides the basic framework for the subsequent introduction of other components. PVA molecular chains can form physical cross-links through forces such as hydrogen bonds, enhancing the mechanical properties of the hydrogel. Its hydroxyl groups can also interact with other components, such as forming hydrogen bonds with sodium lignosulfonate molecules, further stabilizing the network structure. The cross-linked network formed by PVA can regulate ion migration behavior; the directional porous structure provides specific pathways for ion migration, influencing ionic conductivity to some extent. Simultaneously, the interaction between PVA molecules and ions also alters ion migration behavior, thus affecting thermoelectric properties.

[0017] Sodium lignosulfonate contains abundant functional groups such as phenolic hydroxyl groups, quinone groups, and sulfonic acid groups. Reversible redox transformations can occur between phenolic hydroxyl and quinone groups, which helps improve the system's charge regulation capability and interfacial polarization effect. Simultaneously, sulfonic acid groups can enhance ion dissociation ability and regulate the ion solvation environment, thereby improving ion thermal diffusion behavior and enhancing ionic thermoelectric properties. Sodium lignosulfonate can promote the rearrangement of PVA molecular chains through hydrogen bonding. At appropriate concentrations, this is beneficial for the formation of PVA microcrystalline regions and improves network stability; however, excessively high sodium lignosulfonate content may interfere with the regular arrangement of PVA segments, leading to a decrease in crystallinity. Its interaction with PVA molecular chains can make the network structure more compact, improving the tensile strength and toughness of the hydrogel. The sulfonic acid groups on the sodium lignosulfonate molecule can dissociate ions, increasing the ion concentration inside the hydrogel and thus improving conductivity. Furthermore, its distribution within the PVA network also affects ion transport paths, further optimizing electrical conductivity.

[0018] K+ dissociated from potassium hydroxide+ and OH - It can act as an ion carrier to significantly improve the ion concentration and ion conductivity of the system. Under the action of a temperature gradient, the two ions undergo thermal diffusion. Due to the difference in migration rate and thermal diffusivity, a potential difference is established across the material, thereby improving the ion thermoelectric properties. K + and OH - The movement of ions can drive the coordinated movement of other ions in the surrounding area, forming an ion flow, which generates stronger charge separation under the temperature gradient and improves the Seebeck coefficient.

[0019] Potassium hydroxide increases the alkalinity of the system, causing partial deprotonation of the phenolic hydroxyl groups in sodium lignosulfonate, enhancing its hydrogen bonding and ionic interactions with PVA, thereby further stabilizing the network structure and giving the hydrogel both toughness and mechanical strength. This dual-network structure can effectively disperse stress and improve the hydrogel's tensile and tear resistance. Potassium hydroxide dissociates to release a large amount of K+. + and OH - This greatly increases the ion concentration inside the hydrogel, thereby significantly improving the ionic conductivity.

[0020] The phenolic quinone redox electron pair of sodium lignosulfonate provides the basis for thermoelectric conversion, while the ions dissociated from potassium hydroxide promote electron transfer and ion migration. The synergistic effect of these two factors significantly enhances the thermoelectric properties of the hydrogel. Simultaneously, the PVA network provides a suitable pathway for ion and electron transport, further optimizing the thermoelectric conversion efficiency.

[0021] The physical cross-linking of PVA, the interaction between sodium lignosulfonate and PVA, and the formation of a double network promoted by potassium hydroxide work together to significantly improve the mechanical properties of the hydrogel. This synergistic effect gives the hydrogel both high tensile strength and good toughness and fatigue resistance.

[0022] The three-dimensional network structure of PVA provides the basic framework for the entire system. Sodium lignosulfonate regulates the arrangement of PVA segments and improves network stability through hydrogen bonding. Potassium hydroxide further optimizes the network structure and ion transport performance by increasing ion concentration, enhancing ion interactions, and promoting the deprotonation of phenolic hydroxyl groups. The synergistic effect of these three components endows the hydrogel with good mechanical properties, high ionic conductivity, and stable ionic thermoelectric properties. This allows the hydrogel to maintain good structural stability under various environmental conditions, such as temperature changes and external forces, while still preserving its performance and structural integrity.

[0023] In some embodiments, the polyvinyl alcohol aqueous solution contains 5-20% polyvinyl alcohol by mass, preferably 8-15%, and more preferably 8-12%.

[0024] The mass percentage of polyvinyl alcohol can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%.

[0025] In some embodiments, the method for preparing the polyvinyl alcohol aqueous solution is as follows: after mixing polyvinyl alcohol with water, soaking for 8-15 hours, stirring at 40-50℃ for 20-40 minutes, and then stirring at 85-100℃ for 1-3 hours to dissolve.

[0026] Polyvinyl alcohol (PVA) molecules contain numerous hydroxyl groups, enabling strong intermolecular hydrogen bonding and resulting in high crystallinity. Therefore, highly hydrolyzed PVA only swells at room temperature and is difficult to completely dissolve, typically requiring heating to promote full dispersion of the molecular chains in water. Soaking allows water molecules to gradually penetrate the PVA particles, forming new hydrogen bonds with the hydroxyl groups and weakening some of the hydrogen bonds between PVA molecular chains, thus causing the particles to gradually swell. This step prevents the formation of a viscous sol layer on the surface of the PVA during subsequent heating, which would hinder further diffusion of water into the particle and prevent the unswelled PVA inside from fully dissolving.

[0027] As the temperature gradually increases, the thermal motion of PVA molecular chains intensifies, and the intermolecular hydrogen bonds weaken further, promoting the gradual extension and diffusion of chain segments into the aqueous phase. Under continuous stirring, the solvent and PVA particles can come into full contact, thereby accelerating the dissolution rate. If the temperature is directly and rapidly increased, a high-viscosity gel layer easily forms on the surface of the PVA particles, hindering the continued diffusion of water into the particle interior, leading to incomplete dissolution and reduced solution homogeneity. Therefore, using a method of first soaking, then slowly heating with continuous stirring, is beneficial for improving the dissolution efficiency of PVA and the quality of the solution, providing a uniform and stable precursor solution for the subsequent preparation of hydrogels.

[0028] In some embodiments, the method of directional freezing and thawing is as follows: pouring a polyvinyl alcohol aqueous solution into a mold, and applying a metal block in contact with liquid nitrogen to one side of the polyvinyl alcohol solution to perform rapid directional freezing; After complete freezing, transfer the mold to an environment of -25~-15℃ and continue freezing for 10-15 hours; Then thaw at 20-30℃. Prepare polyvinyl alcohol hydrogel using the directional freeze-thaw method.

[0029] Preferably, the directional freezing and thawing operation is repeated 2-4 times. For example, it can be repeated once, twice, or three times.

[0030] In some embodiments, the concentration of the sodium lignosulfonate solution is 30-60 wt.%. For example, it can be 30 wt.%, 35 wt.%, 40 wt.%, 45 wt.%, 50 wt.%, 55 wt.%, or 60 wt.%.

[0031] Preferably, the concentration of the sodium lignosulfonate solution is 40-60 wt.%.

[0032] More preferably, the concentration of the sodium lignosulfonate solution is 45-55 wt.%.

[0033] In some embodiments, the first solvent exchange takes 10-15 hours.

[0034] In some embodiments, the concentration of the KOH solution is 2-8 mol / L. For example, it can be 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, or 8 mol / L.

[0035] Preferably, the concentration of the KOH solution is 4-8 mol / L.

[0036] In some embodiments, the second solvent exchange takes 3-7 hours.

[0037] Secondly, the present invention provides a lignin-based hydrogel thermal battery, which is prepared by the aforementioned preparation method.

[0038] Thirdly, the present invention provides the application of the lignin-based hydrogel thermal battery in the preparation of wearable thermoelectric devices or flexible electronics.

[0039] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0040] Example 1 (1) Mix the weighed PVA powder with water to make a solution with a mass fraction of 10%, soak for 12 hours, stir with a magnetic stirrer at 45°C for 30 minutes, and stir at 95°C for 2 hours to obtain a polyvinyl alcohol aqueous solution.

[0041] (2) A polyvinyl alcohol aqueous solution was injected into a polytetrafluoroethylene mold, which was then placed in liquid nitrogen. Half of the Cu steel billet was immersed in the liquid nitrogen, allowing ice to nucleate and grow vertically and form parallel ice columns. The directionally frozen PVA was then thawed at room temperature. The directionally frozen-thaw process was repeated three times to form a PVA hydrogel.

[0042] (3) Prepare a sodium lignosulfonate solution with a mass fraction of 30%. Transfer the prepared sodium lignosulfonate dispersion to a magnetic stirrer and stir for 15 minutes at a speed of 600 rpm to ensure uniform dispersion of the sodium lignosulfonate dispersion. After stirring, the sodium lignosulfonate dispersion was centrifuged for 10 minutes at 10,000 rpm using a high-speed benchtop centrifuge to remove the incompletely dissolved portion and obtain a sodium lignosulfonate solution.

[0043] (4) The PVA hydrogel prepared in step (2) is immersed in the sodium lignosulfonate solution with a concentration of 30 wt.% prepared in step (3) for solvent exchange. After the solvent exchange process lasts for 12 hours, the hydrogel sample is taken out.

[0044] Performance testing: Strain elongation: Select PVA hydrogel and measure the sample dimensions (including length, width, and thickness) using a thickness gauge and ruler. Mount the measured hydrogel sample onto the clamp of the texture analyzer, ensuring the stretching direction of the sample is completely aligned with the stretching direction of the texture analyzer clamp. Set the relevant parameters on the texture analyzer, start the analyzer, and stop the analyzer immediately when the sample fractures, recording the strain elongation during the stretching process.

[0045] Conductivity: Connect the electrochemical workstation to form a complete closed circuit system. Place the hydrogel sample in the circuit system, ensuring good contact between the sample and the electrode. Start the test, use the electrochemical workstation to measure and record the resistance value of the hydrogel. Based on the measured resistance data, calculate the conductivity of the hydrogel according to the conductivity calculation formula, and analyze and process the calculation results.

[0046] The formula for calculating resistivity is as follows: ; Where: ρ is resistivity, in Ω·m; S is the cross-sectional area, in meters. 2 ; R is the resistance value, in Ω; L is the length of the conductor, in meters; The formula for calculating electrical conductivity is: ; Where: σ is the conductivity, in units of S / m; ρ is resistivity, in Ω·m.

[0047] Seebeck coefficient: The prepared hydrogel sample is cut into rectangular specimens of uniform size, and platinum wire electrodes are connected to both ends of the specimen to ensure full contact between the electrodes and the sample and stable contact resistance. The sample is placed in a test device consisting of two independent temperature-controlled platforms, one end as the hot end and the other end as the cold end, and the temperature gradient is controlled by the temperature difference between the hot and cold ends. Thermocouples are used to monitor the temperature at both ends of the sample in real time, and the temperatures of the hot and cold ends are recorded. The temperature difference ΔT is controlled within the range of 5–30 K. After the temperature reaches a steady state, the voltage (ΔV) generated by the sample is recorded. The temperature difference is gradually changed, and the corresponding thermoelectric voltages at different temperature differences are recorded. The Seebeck coefficient is calculated according to the formula.

[0048] The formula for calculating the Seebeck coefficient is as follows: ; The hydrogel prepared in this embodiment has a strain elongation of 225.50%, an electrical conductivity of 2.32 mS / cm, and a Seebeck coefficient of 2.17 mV·K. -1 .

[0049] Example 2 (1) Mix the weighed PVA powder with water to make a solution with a mass fraction of 10%, soak for 12 hours, stir with a magnetic stirrer at 45°C for 30 minutes, and stir at 95°C for 2 hours to obtain a polyvinyl alcohol aqueous solution.

[0050] (2) PVA gel was prepared by directional freezing of polyvinyl alcohol aqueous solution in liquid nitrogen and then freezing the frozen sample at -23°C. This process was repeated three times.

[0051] (3) Prepare a sodium lignosulfonate solution with a mass fraction of 40%. Transfer the prepared sodium lignosulfonate dispersion to a magnetic stirrer and stir for 15 minutes at a speed of 600 rpm to ensure uniform dispersion of the sodium lignosulfonate dispersion.

[0052] After stirring, the sodium lignosulfonate dispersion was centrifuged for 10 minutes at 10,000 rpm using a high-speed benchtop centrifuge to obtain a sodium lignosulfonate solution.

[0053] (4) The PVA hydrogel prepared in step (2) is immersed in the sodium lignosulfonate solution with a concentration of 40 wt.% prepared in step (3) for solvent exchange. After the solvent exchange process lasts for 12 hours, the hydrogel sample is taken out.

[0054] The hydrogel prepared in this embodiment has a strain elongation of 323.34%, an electrical conductivity of 2.53 mS / cm, and a Seebeck coefficient of 3.20 mV·K. -1 .

[0055] Example 3 (1) Mix the weighed PVA powder with water to make a solution with a mass fraction of 10%, soak for 12 hours, stir with a magnetic stirrer at 45°C for 30 minutes, and stir at 95°C for 2 hours to obtain a polyvinyl alcohol aqueous solution.

[0056] (2) PVA gel was prepared by directional freezing of polyvinyl alcohol aqueous solution in liquid nitrogen and then freezing the frozen sample at -23°C. This process was repeated three times.

[0057] (3) Prepare a sodium lignosulfonate solution with a mass fraction of 50%. Transfer the prepared sodium lignosulfonate dispersion to a magnetic stirrer and stir for 15 minutes at a speed of 600 rpm to ensure uniform dispersion of the sodium lignosulfonate dispersion.

[0058] After stirring, the sodium lignosulfonate dispersion was centrifuged for 10 minutes at 10,000 rpm using a high-speed benchtop centrifuge to obtain a sodium lignosulfonate solution.

[0059] (4) The PVA hydrogel prepared in step (2) is immersed in the 50 wt.% sodium lignosulfonate solution prepared in step (3) for solvent exchange. The solvent exchange process lasts for 12 hours, and then the hydrogel sample is taken out.

[0060] The hydrogel prepared in this embodiment has a strain elongation of 430.34%, an electrical conductivity of 5.09 mS / cm, and a Seebeck coefficient of 3.64 mV·K. -1 .

[0061] Example 4 (1) Mix the weighed PVA powder with water to make a solution with a mass fraction of 10%, soak for 12 hours, stir with a magnetic stirrer at 45°C for 30 minutes, and stir at 95°C for 2 hours to obtain a polyvinyl alcohol aqueous solution.

[0062] (2) PVA gel was prepared by directional freezing of polyvinyl alcohol aqueous solution in liquid nitrogen and then freezing the frozen sample at -23°C. This process was repeated three times.

[0063] (3) Prepare a sodium lignosulfonate solution with a mass fraction of 60%. Transfer the prepared sodium lignosulfonate dispersion to a magnetic stirrer and stir for 15 minutes at a speed of 600 rpm to ensure uniform dispersion of the sodium lignosulfonate dispersion.

[0064] After stirring, the sodium lignosulfonate dispersion was centrifuged for 10 minutes at 10,000 rpm using a high-speed benchtop centrifuge to obtain a sodium lignosulfonate solution.

[0065] (4) The PVA hydrogel prepared in step (2) is immersed in the sodium lignosulfonate solution with a concentration of 60 wt.% prepared in step (3) for solvent exchange. After the solvent exchange process lasts for 12 hours, the hydrogel sample is taken out.

[0066] The hydrogel prepared in this embodiment has a strain elongation of 227.69%, an electrical conductivity of 4.45 mS / cm, and a Seebeck coefficient of 3.01 mV·K. -1 .

[0067] Example 5 (1) Mix the weighed PVA powder with water to make a solution with a mass fraction of 10%, soak for 12 hours, stir with a magnetic stirrer at 45°C for 30 minutes, and stir at 95°C for 2 hours to obtain a polyvinyl alcohol aqueous solution.

[0068] (2) PVA hydrogel was prepared by directional freezing of polyvinyl alcohol aqueous solution in liquid nitrogen and freezing the frozen sample at -23℃. The process was repeated three times.

[0069] (3) Prepare a sodium lignosulfonate solution with a mass fraction of 50%. Transfer the prepared sodium lignosulfonate dispersion to a magnetic stirrer and stir for 15 minutes at a speed of 600 rpm to ensure uniform dispersion of the sodium lignosulfonate dispersion.

[0070] After stirring, the sodium lignosulfonate dispersion was centrifuged for 10 minutes at 10,000 rpm using a high-speed benchtop centrifuge to obtain a sodium lignosulfonate solution.

[0071] (4) The PVA hydrogel prepared in step (2) is immersed in the 50 wt.% sodium lignosulfonate solution prepared in step (3) for solvent exchange. The solvent exchange process lasts for 12 hours, and then the hydrogel sample is taken out.

[0072] (5) Immerse the hydrogel sample from step (4) which has undergone solvent exchange with 50 wt.% sodium lignosulfonate solution into a 2 mol / L KOH solution for solvent exchange. The exchange process lasts for 5 hours. Remove the hydrogel sample after 5 hours.

[0073] The hydrogel prepared in this embodiment has a strain elongation of 227%, an electrical conductivity of 24.26 mS / cm, and a Seebeck coefficient of 2.51 mV·K. -1 .

[0074] Example 6 (1) Mix the weighed PVA powder with water to make a solution with a mass fraction of 10%, soak for 12 hours, stir with a magnetic stirrer at 45°C for 30 minutes, and stir at 95°C for 2 hours to obtain a polyvinyl alcohol aqueous solution.

[0075] (2) PVA gel was prepared by directional freezing of polyvinyl alcohol aqueous solution in liquid nitrogen and then freezing the frozen sample at -23°C. This process was repeated three times.

[0076] (3) Prepare a sodium lignosulfonate solution with a mass fraction of 50%. Transfer the prepared sodium lignosulfonate dispersion to a magnetic stirrer and stir for 15 minutes at a speed of 600 rpm to ensure uniform dispersion of the sodium lignosulfonate dispersion.

[0077] After stirring, the sodium lignosulfonate dispersion was centrifuged for 10 minutes at 10,000 rpm using a high-speed benchtop centrifuge to obtain a sodium lignosulfonate solution.

[0078] (4) The PVA hydrogel prepared in step (2) is immersed in the 50 wt.% sodium lignosulfonate solution prepared in step (3) for solvent exchange. The solvent exchange process lasts for 12 hours, and then the hydrogel sample is taken out.

[0079] (5) Immerse the hydrogel sample from step (4) which has undergone solvent exchange with 50 wt.% sodium lignosulfonate solution into a 3 mol / L KOH solution for solvent exchange. The exchange process lasts for 5 hours. Remove the hydrogel sample after 5 hours.

[0080] The hydrogel prepared in this embodiment has a strain elongation of 249%, an electrical conductivity of 34.11 mS / cm, and a Seebeck coefficient of 2.76 mV·K. -1 .

[0081] Example 7 (1) Mix the weighed PVA powder with water to make a solution with a mass fraction of 10%, soak for 12 hours, stir with a magnetic stirrer at 45°C for 30 minutes, and stir at 95°C for 2 hours to obtain a polyvinyl alcohol aqueous solution.

[0082] (2) PVA gel was prepared by directional freezing of polyvinyl alcohol aqueous solution in liquid nitrogen and then freezing the frozen sample at -23°C. This process was repeated three times.

[0083] (3) Prepare a sodium lignosulfonate solution with a mass fraction of 50%. Transfer the prepared sodium lignosulfonate dispersion to a magnetic stirrer and stir for 15 minutes at a speed of 600 rpm to ensure uniform dispersion of the sodium lignosulfonate dispersion.

[0084] After stirring, the sodium lignosulfonate dispersion was centrifuged for 10 minutes at 10,000 rpm using a high-speed benchtop centrifuge to obtain a sodium lignosulfonate solution.

[0085] (4) The PVA hydrogel prepared in step (2) is immersed in the 50 wt.% sodium lignosulfonate solution prepared in step (3) for solvent exchange. The solvent exchange process lasts for 12 hours, and then the hydrogel sample is taken out.

[0086] (5) The hydrogel that underwent solvent exchange with 50 wt.% sodium lignosulfonate solution in step (4) was placed in a 4 mol / L KOH solution for solvent exchange for 5 hours. The hydrogel sample was removed after 5 hours.

[0087] The hydrogel prepared in this embodiment has a strain elongation of 447%, an electrical conductivity of 55.81 mS / cm, and a Seebeck coefficient of 3.94 mV·K. -1 .

[0088] Example 8 (1) Mix the weighed PVA powder with water to make a solution with a mass fraction of 10%, soak for 12 hours, stir with a magnetic stirrer at 45°C for 30 minutes, and stir at 95°C for 2 hours to obtain a polyvinyl alcohol aqueous solution.

[0089] (2) PVA gel was prepared by directional freezing of polyvinyl alcohol aqueous solution in liquid nitrogen and then freezing the frozen sample at -23°C. This process was repeated three times.

[0090] (3) Prepare a sodium lignosulfonate solution with a mass fraction of 50%. Transfer the prepared sodium lignosulfonate dispersion to a magnetic stirrer and stir for 15 minutes at a speed of 600 rpm to ensure uniform dispersion of the sodium lignosulfonate dispersion.

[0091] After stirring, the sodium lignosulfonate dispersion was centrifuged for 10 minutes at 10,000 rpm using a high-speed benchtop centrifuge to obtain a sodium lignosulfonate solution.

[0092] (4) The PVA hydrogel prepared in step (2) is immersed in the 50 wt.% sodium lignosulfonate solution prepared in step (3) for solvent exchange. The solvent exchange process lasts for 12 hours, and then the hydrogel sample is taken out.

[0093] (5) The hydrogel that has undergone solvent exchange with 50 wt.% sodium lignosulfonate solution was placed in a 5 mol / L KOH solution for solvent exchange for 5 hours. The hydrogel sample was removed after 5 hours.

[0094] The hydrogel prepared in this embodiment has a strain elongation of 420%, an electrical conductivity of 74.82 mS / cm, and a Seebeck coefficient of 4.65 mV·K. -1 .

[0095] Example 9 (1) Mix the weighed PVA powder with water to make a solution with a mass fraction of 10%, soak for 12 hours, stir with a magnetic stirrer at 45°C for 30 minutes, and stir at 95°C for 2 hours to obtain a polyvinyl alcohol aqueous solution.

[0096] (2) PVA gel was prepared by directional freezing of polyvinyl alcohol aqueous solution in liquid nitrogen and then freezing the frozen sample at -23°C. This process was repeated three times.

[0097] (3) Prepare a sodium lignosulfonate solution with a mass fraction of 50%. Transfer the prepared sodium lignosulfonate dispersion to a magnetic stirrer and stir for 15 minutes at a speed of 600 rpm to ensure uniform dispersion of the sodium lignosulfonate dispersion.

[0098] After stirring, the solution was centrifuged for 10 minutes at 10,000 rpm using a high-speed benchtop centrifuge to obtain a sodium lignosulfonate solution.

[0099] (4) The PVA hydrogel prepared in step (2) is immersed in the 50 wt.% sodium lignosulfonate solution prepared in step (3) for solvent exchange. The solvent exchange process lasts for 12 hours, and then the hydrogel sample is taken out.

[0100] (5) The hydrogel that has undergone solvent exchange with 50 wt.% sodium lignosulfonate solution was immersed in a 6 mol / L KOH solution for solvent exchange for 5 hours. The hydrogel sample was removed after 5 hours.

[0101] The hydrogel prepared in this embodiment has a tensile strain rate of 875%, an electrical conductivity of 137.6 mS / cm, and a Seebeck coefficient of 5.97 mV·K. -1 .

[0102] Comparative Example 1 The difference from Example 5 is that steps (3) and (4) are omitted, and only the PVA hydrogel is subjected to solvent exchange in KOH solution. Everything else is the same as in Example 5.

[0103] The hydrogel prepared in this comparative example had a strain elongation of 216.41%, an electrical conductivity of 0.84 mS / cm, and a Seebeck coefficient of -0.70 mV·K. -1 .

[0104] like Figure 1 The graph shows a comparison of the conductivity of the hydrogel thermal batteries obtained in Examples 1-4. Figure 1 It can be seen that the conductivity is best when the sodium lignosulfonate content is 50 wt.%, which is 5.09 mS / cm.

[0105] like Figure 2 The graph shows a comparison of the conductivity of the hydrogel thermal batteries obtained in Examples 5-9. Figure 2 It can be seen that the conductivity is best when the potassium hydroxide concentration is 6 mol / L, which is 137.6 mS / cm.

[0106] The hydrogel thermal batteries obtained in Examples 1-9 were placed in the test apparatus, maintaining good contact with both the cold and hot ends. The cold end temperature was kept at room temperature, while the hot end temperature was controlled using a heating device to establish different temperature gradients. After the temperature stabilized, platinum wire electrodes were connected to both ends of the hydrogel thermal battery and a multimeter was connected to record the thermoelectric voltage (ΔV) generated across the sample in an open-circuit state. Simultaneously, thermocouples were placed at both ends of the hydrogel thermal battery, and the hot end temperature, cold end temperature, and temperature gradient were recorded in real time. The above test process was repeated by changing the hot end temperature, recording the thermoelectric voltage corresponding to different temperature gradients, and calculating the Seebeck coefficient according to the formula. The results are shown below. Figure 3 , Figure 4 .

[0107] from Figure 3 It can be seen that the thermoelectric potential of the obtained hydrogel thermal battery changes with the concentration of sodium lignosulfonate solution, reaching a maximum of 3.64 mV / K when the sodium lignosulfonate solution concentration is 50 wt.%. Figure 4 It can be seen that the thermoelectric potential of the obtained hydrogel thermal battery changes with the concentration of potassium hydroxide solution. When the concentration of potassium hydroxide solution is 6 mol / L, the thermoelectric potential reaches a maximum of 5.97 mV / K.

[0108] Based on the combined thermoelectric potential and conductivity of the hydrogel thermal batteries in Examples 1-9, the optimal example was determined to be the hydrogel thermal battery with a thermoelectric potential of 5.97 mV / K and a conductivity of 137.6 mS / cm when sodium lignosulfonate was 50 wt.% and potassium hydroxide was 6 mol / L.

[0109] The mechanical properties of the hydrogels obtained in Examples 1-9 were determined using a multifunctional testing machine. The results are shown in the figure. Figure 5 , Figure 6 .Depend on Figure 5 It can be seen that when sodium lignosulfonate is 50 wt.%, its strain elongation is 430.34%. This indicates that the hydrogel thermal battery prepared in this invention has good mechanical properties. Figure 6It can be seen that when the potassium hydroxide concentration is 6 mol / L, the strain elongation is 875%. This indicates that the hydrogel thermal battery prepared in this invention has good mechanical properties.

[0110] Table 1. Components of Examples and Comparative Examples

[0111] Table 2. Summary of strain, tensile strength, conductivity, and Seebeck coefficient for the examples and comparative models.

[0112] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lignin-based hydrogel thermal battery, characterized in that: Includes the following steps: After degassing the polyvinyl alcohol aqueous solution, it was subjected to directional freezing and thawing to obtain a PVA hydrogel with a directional pore structure. The prepared PVA hydrogel was immersed in a sodium lignosulfonate solution for the first solvent exchange. After the first solvent exchange, the PVA hydrogel was immersed in KOH solution for a second solvent exchange to obtain a lignin-based hydrogel thermal battery.

2. The method for preparing a lignin-based hydrogel thermal battery according to claim 1, characterized in that: The polyvinyl alcohol aqueous solution contains 5-20% polyvinyl alcohol by mass.

3. The method for preparing a lignin-based hydrogel thermal battery according to claim 1, characterized in that: The method for preparing the polyvinyl alcohol aqueous solution is as follows: after mixing polyvinyl alcohol with water, soak for 8-15 hours, stir at 40-50℃ for 20-40 minutes, and then stir at 85-100℃ for 1-3 hours to dissolve.

4. The method for preparing a lignin-based hydrogel thermal battery according to claim 1, characterized in that: The method of directional freezing and thawing is as follows: pour a polyvinyl alcohol aqueous solution into a mold, apply a metal block in contact with liquid nitrogen to one side of the polyvinyl alcohol solution for directional freezing; after complete freezing, transfer the mold to an environment of -25~-15℃ and continue freezing for 10-15 hours; then thaw at 20-30℃.

5. The method for preparing a lignin-based hydrogel thermal battery according to claim 4, characterized in that: The directional freezing and thawing process is repeated 2-4 times.

6. The method for preparing a lignin-based hydrogel thermal battery according to claim 1, characterized in that: The concentration of the sodium lignosulfonate solution is 30-60 wt.%.

7. The method for preparing a lignin-based hydrogel thermal battery according to claim 1, characterized in that: The first solvent exchange takes 10-15 hours; Alternatively, the second solvent exchange may take 3-7 hours.

8. The method for preparing a lignin-based hydrogel thermal battery according to claim 1, characterized in that: The concentration of the KOH solution is 2-8 mol / L.

9. A lignin-based hydrogel thermal battery, characterized in that: It is prepared by any one of the preparation methods described in claims 1-8.

10. The application of the lignin-based hydrogel thermal battery of claim 9 in the preparation of wearable thermoelectric devices or flexible electronics.

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