A stretchable hydrogel thermal battery with a high elastic limit and a preparation method thereof

Abstract

The present invention discloses a stretchable hydrogel thermal battery with a high elastic limit and a preparation method thereof. The hydrogel thermal battery is prepared by in-situ free radical polymerization through the "one-pot method" using an amide monomer, deionized water, and a cross-linking agent as raw materials to obtain a hydrogel, and then performing solution exchange on the hydrogel in an electrolyte solution. Among them, due to the very low content of the cross-linking agent used, the prepared hydrogel network has a low cross-linking density and highly entangled polymer chains, thus having good stretchability and a high elastic limit, and also having good thermoelectric performance after solvent exchange in the electrolyte solution, so it has broad application prospects in the fields of self-powered, flexible power generation devices, temperature sensors, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a stretchable hydrogel thermal battery material, and more particularly to a stretchable hydrogel thermal battery with a high elastic limit and a preparation method thereof. Background Art

[0002] A thermal battery uses the temperature dependence of the electrochemical oxidation-reduction potential for thermoelectric conversion, and can continuously convert thermal energy into electrical energy. With the development of science and technology, the research on traditional liquid thermal batteries has become mature, and the emergence of various redox electrolytes has further promoted the research on thermal batteries. However, traditional liquid electrolytes have problems such as difficult encapsulation, easy leakage, poor mechanical properties, and electrolyte instability. To solve the above problems and apply thermal batteries to fields such as flexible devices, researchers have proposed the means of quasi-solidifying electrolytes.

[0003] A hydrogel is a three-dimensional network that can swell but not dissolve in water, and is a hydrophilic polymer with a physical or chemical cross-linked structure. Hydrogels have advantages such as good hydrophilicity, ultra-high molecular designability and composability, good flexibility and elasticity, etc., and can well meet the requirements of the quasi-solid electrolyte matrix. However, many single-network hydrogels have low mechanical strength and are easily damaged during actual use; in addition, although introducing a double network into the hydrogel can improve its strength, due to the short chains in the double network structure being easily broken during stretching and unable to return to their original state, it cannot withstand multiple cyclic loads. Therefore, to meet the strict requirements for the long-term stable operation of hydrogel thermal batteries, researchers hope that hydrogels have properties such as excellent fatigue resistance, good mechanical properties, and good thermoelectric properties.

[0004] The present invention prepares a hydrogel from amide monomers, deionized water and a cross-linking agent, and then prepares a hydrogel thermal battery by performing solution exchange on the hydrogel in an electrolyte solution. Among them, the hydrogel has good thermoelectric properties after completing solvent exchange in the electrolyte solution; and due to the very low content of the cross-linking agent used, the prepared hydrogel network has a low cross-linking density and the polymer chains are highly entangled, so it has a high elastic limit and excellent fatigue resistance, thereby greatly expanding its application range. Summary of the Invention

[0005] The present invention aims to develop a stretchable hydrogel thermal battery with a high elastic limit and a preparation method thereof. The prepared hydrogel has excellent fatigue resistance due to its low cross-linking density and highly entangled polymer chains, can bear multiple cyclic loads, and has a high elastic limit, good tensile properties and good thermoelectric properties, and has broad application prospects in fields such as self-powered, flexible power generation devices, and temperature sensors.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A stretchable hydrogel thermal battery with a high elastic limit is prepared by using an amide monomer as the initial raw material, in-situ free radical polymerization under photoinitiation to synthesize the hydrogel, and then performing solvent exchange of the obtained hydrogel in an electrolyte solution. The specific preparation method is to uniformly mix the amide monomer, deionized water, crosslinking agent, and photoinitiator to form a transparent precursor solution; then inject it into a mold and irradiate it with ultraviolet light for 3 - 5 h to form a hydrogel, and then place the obtained hydrogel after peeling in an electrolyte solution for 24 h of solvent exchange to obtain the product.

[0008] Further, the amide monomer is any one or two of acrylamide, methacrylamide, N-isopropylacrylamide, N-methyl-2-acrylamide, N-ethylacrylamide, 3-butenamide, and preferably acrylamide ( ).

[0009] Further, the molar ratio of the amide monomer to deionized water used is 1:(3 - 25), and preferably 1:3.

[0010] When the crosslinking density is the same, the water content determines the entanglement density of polymer chains, thereby affecting the hardness of the hydrogel. When the water content is low, the prepared hydrogel network is densely entangled and remains hard after full swelling; when the water content is high, the prepared hydrogel network is loose and becomes soft and flabby after full swelling, with poor mechanical properties. Therefore, reasonably adjusting the ratio of monomer to water can control the hardness of the hydrogel.

[0011] Further, the crosslinking agent used is N,N'-methylenebisacrylamide, and its dosage ratio to the amide monomer used is (0.1 - 10 -5 ):1, and preferably 10 -4 :1.

[0012] There is a conflict between the hardness and toughness of the hydrogel polymer network. Entanglement affects strength, and toughness is affected by the crosslinking density. When the crosslinking density is high, the hydrogel becomes hard but also brittle, with low toughness; when the crosslinking density is low, due to the existence of dense entanglement, the hydrogel is still hard, but because the polymer chains are long and the number of crosslinking points is small, the energy can dissipate along the long chains during stretching without breaking, so the toughness is high. Therefore, reasonably adjusting the ratio of monomer to crosslinking agent can control the toughness of the hydrogel.

[0013] Further, the photoinitiator is α-hydroxyisobutyrophenone, and its dosage ratio to the amide monomer used is 4×10 -5 :1.

[0014] Further, the electrolyte solution is ferrocyanide / ferricyanide [Fe(CN)6] 4 / 3- , iron (II / III) (Fe 2+ / 3+ ), iodide / triiodide (I - / I3 - ), tin (IV / II) (Sn 4+ / 2+ ), and cobalt (II / III) (Co 2+ / 3+ ), preferably ferrocyanide / ferricyanide [Fe(CN)6] 4 / 3- , with a concentration of 0.05 - 0.4 mol / L.

[0015] Under preferred conditions, the chemical structural formula of the obtained hydrogel is ( ). The hydrogel has good tensile properties, elastic limit, and excellent fatigue resistance, and can be used to prepare flexible power generation devices.

[0016] Through reasonable molecular design, the present invention prepares an anti-fatigue hydrogel thermal battery with excellent tensile properties and high elastic limit. Due to the very low content of the cross-linking agent used, the prepared hydrogel network has a low cross-linking density and highly entangled polymer chains, thus having good stretchability and a high elastic limit; and its thermoelectric properties can also be optimized by changing the type and concentration of the electrolyte solution.

[0017] The monomers selected in the present invention are inexpensive, the process is simple, the controllability is high, expensive equipment is not required, and large-scale production can be carried out. The obtained hydrogel thermal battery has high stretchability, high elastic limit, and good thermoelectric properties, and has broad application prospects in the fields of self-powered, flexible power generation devices, temperature sensors, etc.

[0018] The beneficial effects of the present invention are reflected in:

[0019] (1) The preparation process of the hydrogel thermal battery provided by the present invention is simple, the controllability is high, expensive equipment is not required, the raw materials are inexpensive, and it is easy to carry out large-scale production.

[0020] (2) The hydrogel of the present invention is copolymerized from acrylamide monomers and a cross-linking agent, and its polymer chains are long and dense, and the cross-linking density is low, so it has a high elastic limit and good fatigue resistance.

[0021] (3) The fracture strength of the hydrogel thermal battery prepared by the present invention is 146 kPa, and the elongation at break is 480%. At the same time, it has high thermoelectric properties at different electrolyte solution concentrations. Description of the Drawings

[0022] Figure 1 It is a schematic structural diagram of the hollow mold used in the examples.

[0023] Figure 2UV-Vis spectrum of the hydrogel thermal battery prepared in Example 4.

[0024] Figure 3 Thermopower diagrams of the hydrogel thermal batteries prepared with different electrolyte concentrations in Examples 1-5.

[0025] Figure 4 Conductivity diagrams of the hydrogel thermal batteries prepared with different electrolyte concentrations in Examples 1-5.

[0026] Figure 5 Stress-strain curve diagram of the hydrogel thermal battery prepared in Example 4.

[0027] Figure 6 Cyclic stress-strain curve diagrams of the hydrogel thermal battery prepared in Example 4 under different strains.

[0028] Figure 7 Cyclic stress-strain curve diagrams of the hydrogel thermal battery prepared in Example 4 under the same strain. Detailed implementation manners

[0029] A stretchable hydrogel thermal battery with a high elastic limit is prepared by mixing an amide monomer, deionized water, a crosslinking agent, and a photoinitiator and stirring evenly to form a transparent precursor solution; then injecting the obtained precursor solution into a hollow mold, irradiating with ultraviolet light for 3-5 h, and peeling it off from the hollow mold to obtain a hydrogel; and subjecting the obtained hydrogel to solvent exchange in an electrolyte solution for 24 h.

[0030] The amide monomer is any one or two of acrylamide, methacrylamide, N-isopropylacrylamide, N-methyl-2-acrylamide, N-ethylacrylamide, and 3-butenamide.

[0031] The molar ratio of the acrylamide monomer used to deionized water is 1:(3-25).

[0032] The crosslinking agent is N,N'-methylenebisacrylamide, and its dosage to the molar ratio of the amide monomer used is (0.1-10 -5 ):1.

[0033] The photoinitiator is α-hydroxyisobutyrophenone, and its dosage to the molar ratio of the amide monomer used is 4×10 -5 :1.

[0034] The electrolyte solution is ferrocyanide / ferricyanide [Fe(CN)6] 4 / 3- , iron (II / III) (Fe 2+ / 3+ ), iodide / triiodide (I - / I3 - ), tin (IV / II) (Sn4+ / 2+ ), cobalt (II / III) (Co 2+ / 3+ ), with a concentration of 0.05 - 0.4 mol / L.

[0035] As Figure 1 , the hollow mold includes a first glass layer and a second glass layer. An annular rubber layer is provided between the first glass layer and the second glass layer. A receiving cavity for receiving the precursor solution is formed on the inner circumference of the annular rubber layer. A channel for injecting the precursor solution into the receiving cavity is provided on the annular rubber layer. The thickness of the annular rubber layer is 0.5 - 1 mm.

[0036] To make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0037] Example 1

[0038] 3.554 g (0.05 mol) of acrylamide monomer, 2.7 mL (0.15 mol) of deionized water, 0.77 mg (0.005 mmol) of crosslinking agent N,N'-methylenebisacrylamide, and 0.33 mg (0.002 mmol) of photoinitiator α-hydroxyisobutyrophenone were mixed and stirred evenly to form a transparent precursor solution; then it was injected into the hollow mold, and after ultraviolet irradiation for 3 - 5 h, the hydrogel obtained by peeling from the hollow mold; 0.921 g of potassium ferrocyanide and 0.823 g of potassium ferricyanide were dissolved in deionized water to prepare a 50 mL 0.05 mol / L electrolyte solution; finally, the obtained hydrogel was placed in the electrolyte solution for solvent exchange for 24 h to obtain a hydrogel thermal battery.

[0039] Example 2

[0040] 3.554 g (0.05 mol) of acrylamide monomer, 2.7 mL (0.15 mol) of deionized water, 0.77 mg (0.005 mmol) of crosslinking agent N,N'-methylenebisacrylamide, and 0.33 mg (0.002 mmol) of photoinitiator α-hydroxyisobutyrophenone were mixed and stirred evenly to form a transparent precursor solution; then it was injected into the hollow mold, and after ultraviolet irradiation for 3 - 5 h, the hydrogel obtained by peeling from the hollow mold; 1.842 g of potassium ferrocyanide and 1.646 g of potassium ferricyanide were dissolved in deionized water to prepare a 50 mL 0.1 mol / L electrolyte solution; finally, the obtained hydrogel was placed in the electrolyte solution for solvent exchange for 24 h to obtain a hydrogel thermal battery.

[0041] Example 3

[0042] 3.554 g (0.05 mol) of acrylamide monomer, 2.7 mL (0.15 mol) of deionized water, 0.77 mg (0.005 mmol) of crosslinker N,N'-methylenebisacrylamide, and 0.33 mg (0.002 mmol) of photoinitiator α-hydroxyisobutyrophenone were mixed and stirred evenly to form a transparent precursor solution; subsequently, it was injected into a hollow mold, and after ultraviolet irradiation for 3 - 5 h, the hydrogel obtained by peeling from the hollow mold; 3.684 g of potassium ferrocyanide and 3.292 g of potassium ferricyanide were added to deionized water to prepare a 50 mL 0.2 mol / L electrolyte solution; finally, the obtained hydrogel was placed in this electrolyte solution for solvent exchange for 24 h to obtain a hydrogel thermal battery.

[0043] Example 4

[0044] 3.554 g (0.05 mol) of acrylamide monomer, 2.7 mL (0.15 mol) of deionized water, 0.77 mg (0.005 mmol) of crosslinker N,N'-methylenebisacrylamide, and 0.33 mg (0.002 mmol) of photoinitiator α-hydroxyisobutyrophenone were mixed and stirred evenly to form a transparent precursor solution; subsequently, it was injected into a hollow mold, and after ultraviolet irradiation for 3 - 5 h, the hydrogel obtained by peeling from the hollow mold; 5.526 g of potassium ferrocyanide and 4.939 g of potassium ferricyanide were added to deionized water to prepare a 50 mL 0.3 mol / L electrolyte solution; finally, the obtained hydrogel was placed in this electrolyte solution for solvent exchange for 24 h to obtain a hydrogel thermal battery.

[0045] Example 5

[0046] 3.554 g (0.05 mol) of acrylamide monomer, 2.7 mL (0.15 mol) of deionized water, 0.77 mg (0.005 mmol) of crosslinker N,N'-methylenebisacrylamide, and 0.33 mg (0.002 mmol) of photoinitiator α-hydroxyisobutyrophenone were mixed and stirred evenly to form a transparent precursor solution; subsequently, it was injected into a hollow mold, and after ultraviolet irradiation for 3 - 5 h, the hydrogel obtained by peeling from the hollow mold; 7.368 g of potassium ferrocyanide and 6.585 g of potassium ferricyanide were added to deionized water to prepare a 50 mL 0.4 mol / L electrolyte solution; finally, the obtained hydrogel was placed in this electrolyte solution for solvent exchange for 24 h to obtain a hydrogel thermal battery.

[0047] Figure 2 It is the UV-visible spectrum of the hydrogel thermal battery obtained in Example 4. From Figure 2 it can be seen that its transparency is about 93%.

[0048] The hydrogel thermal batteries obtained in Examples 1-5 were cut into thin slices of 10×15 mm, placed on a glass slide, and the Peltier patch was used as the cold end and the hot end. After applying thermal conductive silicone grease, it was placed on an aluminum heat sink and connected to a Keithley 2601B system source meter through platinum wire electrodes with copper wires. The V-T mode was selected to record the voltage change, and then a thermocouple was connected to a UNI-T UT-325 thermometer to record the temperature difference change. Keeping the current of the source meter constant and changing the power of the Peltier patch, different temperature differences can be generated. According to the measured voltage and temperature difference values, the thermoelectric potential of each sample can be fitted, and the results are shown in Figure 3 . From Figure 3 It can be seen that the thermoelectric potential of the obtained hydrogel thermal battery decreases with the increase of the concentration of the electrolyte solution. When the concentration of the ferrous / ferricyanide solution is 0.05 mol / L, the thermoelectric potential reaches the highest value of 1.60 mV / K.

[0049] The hydrogel thermal batteries obtained in Examples 1-5 were cut into thin slices of 10×15 mm, placed on a glass slide, and the Peltier patch was used as the cold end and the hot end. After applying thermal conductive silicone grease, it was placed on an aluminum heat sink and connected to a Keithley 2601B system source meter through platinum wire electrodes with copper wires. The V-T mode was selected to record the voltage change, and then a thermocouple was connected to a UNI-T UT-325 thermometer to record the temperature difference change. Keeping the power of the Peltier patch constant and maintaining a fixed temperature difference, the current value of the source meter was changed. According to the measured voltage and the fitted I-V curve, the conductivity of the sample can be calculated, and the results are shown in Figure 4 . From Figure 4 It can be seen that the conductivity of the obtained hydrogel thermal battery increases with the increase of the concentration of the electrolyte solution. When the concentration of the ferrous / ferricyanide solution is 0.4 mol / L, the conductivity reaches the highest value of 1.36 S / m.

[0050] By comprehensively considering the thermoelectric potential and conductivity of the hydrogel thermal batteries in Examples 1-5, it was determined that when the concentration of the ferrous / ferricyanide solution in Example 4 was 0.3 mol / L, the hydrogel thermal battery with a thermoelectric potential of 1.41 mV / K and a conductivity of 1.11 S / m was the best example.

[0051] Using a multi-functional testing machine, the mechanical properties of the hydrogel obtained in Example 4 were measured at a tensile rate of 50 mm / min, and the results are shown in Figure 5 . It can be Figure 5 seen that its fracture strength was 146 kPa and the elongation at break was 480%. This shows that the hydrogel thermal battery prepared by the present invention has good mechanical properties.

[0052] During the cyclic loading-unloading process of the hydrogel prepared in Example 4, different strains of 50-350% were applied to study the elasticity of the obtained hydrogel thermal battery, and the results are as shown in Figure 6 shown. It can beFigure 6 It can be found that there is no hysteresis in the stress-strain curves of the hydrogel under different strains during the loading-unloading cycle. Thus, it can be known that the hydrogel thermal battery has a high elastic limit.

[0053] A fixed strain of 200% was applied to the hydrogel prepared in Example 4 during the loading-unloading process, and the cycle was repeated 500 times to further study the fatigue resistance of the obtained hydrogel thermal battery. The results are as Figure 7 shown. Figure 7 It can be found that there is no hysteresis in its stress-strain curve during the loading-unloading cycle and they all overlap. Thus, it can be known that the hydrogel thermal battery has excellent fatigue resistance.

[0054] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A preparation method of a stretchable hydrogel thermal battery material with a high elastic limit, characterized in that: Using an amide monomer as the initial raw material, in-situ free radical polymerization is carried out by photoinitiation to synthesize a hydrogel, and then the obtained hydrogel is subjected to solvent exchange in an electrolyte solution to prepare the hydrogel thermal battery material; Specifically, an amide monomer, deionized water, a crosslinking agent, and a photoinitiator are mixed and stirred evenly to form a transparent precursor solution; then it is injected into a mold and irradiated with ultraviolet light for 3-5 h to form a hydrogel, and then the obtained hydrogel is peeled off and placed in an electrolyte solution for solvent exchange for 24 h; Among them, the amide monomer is any one or two of acrylamide, methacrylamide, N-isopropylacrylamide, N-methyl-2-acrylamide, N-ethylacrylamide, 3-butenamide; The molar ratio of the amide monomer and deionized water used is 1:(3-25); The crosslinking agent used is N,N'-methylenebisacrylamide, and the molar ratio of its dosage to the amide monomer used is (0.1~10 -5 ):1; The photoinitiator is α-hydroxyisobutyrophenone, and the molar ratio of its dosage to the amide monomer used is 4×10 -5 :

1.

2. The preparation method of a stretchable hydrogel thermal battery material with a high elastic limit according to claim 1, characterized in that: The electrolyte solution is ferrous / ferricyanide.

3. A stretchable hydrogel thermal battery material with a high elastic limit prepared by the method according to claim 1.

4. Application of a stretchable hydrogel thermal battery material with a high elastic limit according to claim 3 in the preparation of flexible power generation devices.

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