Integrated thermoelectric conversion and electric energy storage device and preparation method therefor

Abstract

An integrated thermoelectric conversion and electric energy storage device and a preparation method therefor, which relate to the preparation of an NVO electrode and the assembly of a thermoelectric conversion device. The preparation of an NVO electrode comprises the following preparation steps: S1, dissolving NH4VO3 in water, then mixing same with an auxiliary material, and then adding an acid solution for reaction to obtain a mixed solution; S2, subjecting the mixed solution to a hydrothermal reaction, then collecting a precipitate, and washing and drying the precipitate to obtain an NVO material; S3, mixing the NVO material, a conductive agent, and a binder, adding a solvent, and stirring to obtain a slurry; and S4, applying the slurry to carbon cloth, and performing vacuum drying to then obtain an NVO electrode. The NVO electrode and a counter electrode are respectively arranged on two surfaces of a hydrogel-based ion conductor, and are assembled to obtain a thermoelectric conversion device. By means of the coordination of the thermoelectric conversion effect and electric energy storage, the thermoelectric conversion device can implement thermoelectric conversion, store electric energy obtained from the thermoelectric conversion, perform thermal charging in a non-operating state, and, after being connected to an external circuit, release the electric energy stored in the non-operating state.

Description

A thermoelectric conversion and electric energy storage integrated device and its preparation method Technical Field

[0001] The present invention relates to the technical field of thermoelectric conversion, and in particular to a thermoelectric conversion and electric energy storage integrated device and a preparation method thereof. Background Art

[0002] Ionic thermoelectric materials, with their high Seebeck coefficient, low cost, easy processing, low environmental pollution, and self-healing properties, have become a popular choice for next-generation thermoelectric materials. Ionic thermoelectric materials have a completely different thermoelectric conversion mechanism from inorganic thermoelectric materials: unlike inorganic thermoelectric materials, which use electrons and holes as charge carriers, ionic thermoelectric materials use ions as charge carriers. Obviously, ions cannot enter the external circuit through the interface between the ion conductor and the electrode material. This results in the ions concentrating at the interface, either generating an open-circuit voltage through the double-layer effect to supply power to the external circuit, or converting charge carriers at the interface through a redox reaction—where ions on the ion conductor side are converted to electrons on the electrode side through a redox reaction. This conversion is ultimately influenced by two factors: the apparent rate of the redox reaction and the carrier migration rate on the ion conductor side. At present, the electrical conductivity of various types of ionic conductors is generally low, especially lower than that of most (electronic) conductors. Under the premise of comparable carrier concentration, this also means that the mobility of carriers in ionic conductors - the ion migration rate - is much lower than the migration rate of electrons in the conductor. Therefore, in general, the carrier migration rate on the ionic conductor side is considered to directly limit the upper limit of the external output of the thermoelectric conversion device.

[0003] Compared with the carriers that can undergo redox reactions in ionic conductors, electrode materials that can undergo redox reactions are less affected by the carrier migration rate on the ionic conductor side. Therefore, after combining them with ionic conductors, the overall thermoelectric conversion efficiency of the device is expected to be higher than that of pure ionic conductor-type thermoelectric materials. Moreover, because they constitute a sandwich-type battery structure, such devices can combine thermoelectric conversion functions with secondary battery functions. In the non-working state, the electrical energy obtained by thermoelectric conversion of ionic conductors can be stored through the redox function of the electrodes (chemical energy storage), thereby improving the voltage, current and power under working conditions, and better meeting the energy needs of the Internet of Things and wearable devices when they are away from the power grid.

[0004] Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the purpose of the present invention is to propose an integrated thermoelectric conversion and electric energy storage device and its preparation method. By modifying the electrode, it has the dual functions of thermoelectric conversion and electric energy storage. The electric energy obtained by thermoelectric conversion is stored with the help of the electrode material, so that the thermoelectric conversion device is not limited by the instantaneous power of the device's own thermoelectric conversion before the stored electric energy is exhausted. This strategy solves the problem of low output power currently faced by thermoelectric conversion devices.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of the present invention provides a method for preparing an NVO electrode, comprising the following steps:

[0008] S1: dissolving NH4VO3 in water, then mixing it with auxiliary materials, and then adding acid to react to obtain a mixed solution;

[0009] S2: After the mixed solution is subjected to a hydrothermal reaction, the precipitate is collected, washed, and dried to obtain NVO material;

[0010] S3: After mixing the NVO material, the conductive agent and the binder, water is added and stirred to obtain a slurry;

[0011] S4: The slurry is applied on carbon cloth and vacuum dried to obtain an NVO electrode.

[0012] In some embodiments, in step S1, the dissolution temperature is 60°C, the auxiliary material is β-cyclodextrin, the acid solution is selected from at least one of oxalic acid, citric acid, phytic acid, and lactic acid, the molar ratio of NH4VO3 to the auxiliary material is 10:1-3, and the molar ratio of NH4VO3 to the acid solution is 2:1-3.

[0013] In some embodiments, in step S2, the container is a stainless steel autoclave lined with polytetrafluoroethylene, the hydrothermal reaction temperature is 120-180°C, and the hydrothermal reaction time is 10-15 hours.

[0014] In some embodiments, in step S3, the conductive agent is selected from at least one of acetylene black, Ketjen black, and graphite, the binder is selected from at least one of carboxymethyl cellulose, polyvinylidene fluoride, and Nafion, and the mass ratio of NVO material, conductive agent, and binder is 7:2:1 or 6:3:1.

[0015] In some embodiments, in step S4, the vacuum drying temperature is 60-100° C., and the vacuum drying time is 9-12 h.

[0016] A second aspect of the present invention is to provide an NVO electrode.

[0017] A third aspect of the present invention provides an integrated thermoelectric conversion and energy storage device, comprising an NVO electrode, a counter electrode, and a hydrogel-based ion conductor. The NVO electrode and the counter electrode are disposed on opposite surfaces of the hydrogel-based ion conductor. The thermoelectric conversion device provided by the present invention can be used to provide a stable power source for wearable devices and Internet of Things systems.

[0018] In the present invention, the preparation method of the ionic hydrogel is described in the patent "ZL202011544475.9 A Thermoelectric Conversion Material and Thermoelectric Conversion Device", which includes the following steps: mixing a hydrogel monomer, a solvent, a cross-linking agent, and an accelerator, performing a polymerization reaction under ultraviolet light to obtain a hydrogel, and placing the hydrogel in an acid solution for dialysis to obtain a hydrogel-based ionic conductor. The hydrogel monomer can be selected from at least one of acrylamide, sodium acrylate, potassium acrylate, and polyvinyl alcohol; the solvent can be selected from at least one of water, ethanol, isopropyl alcohol, glycerol, ethylene glycol, ether, acetone, and ethyl acetate; the cross-linking agent can be selected from at least one of methylenebisacrylamide and ethylene glycol dimethacrylate; the accelerator is an amine, such as tetramethylethylenediamine; and the acid solution can be selected from at least one of sulfuric acid, hydrochloric acid, phosphoric acid, trichloroacetic acid, and trinitrobenzenesulfonic acid.

[0019] In some embodiments, the preparation method of the counter electrode includes the following steps: mixing activated carbon with a conductive agent and a binder, adding water and stirring to obtain a slurry, applying the slurry on a carbon cloth, and vacuum drying to obtain the counter electrode.

[0020] In some embodiments, the conductive agent is selected from at least one of acetylene black, Ketjen black, and graphite, the binder is selected from at least one of carboxymethyl cellulose, polyvinylidene fluoride, and Nafion, and the mass ratio of activated carbon to the conductive agent and the binder is 8:1:1 or 6:3:1.

[0021] In some embodiments, the vacuum drying temperature is 60-100° C., and the time is 9-12 h. Beneficial effects:

[0022] (1) The present invention proposes an NVO electrode and hydrogel-based ion conductor assembly device with redox reaction function, which combines the thermoelectric conversion effect based on the gel ion conductor and the thermoelectrochemical effect based on the electrode to achieve thermoelectric conversion and store the electrical energy converted from thermoelectricity.

[0023] (2) The thermoelectric conversion method proposed in the present invention can not only improve the power density and energy density of thermoelectric devices at relatively low temperature differences near room temperature, but also utilize the redox reaction function of the electrode to act as a secondary battery, storing electrical energy converted from thermal energy, realizing the integration of thermoelectric conversion and electrical energy storage, and providing a stable power supply for wearable devices and Internet of Things systems.

[0024] (3) The present invention increases the redox effect on the electrode, which on the one hand regulates the open circuit voltage and operating voltage of the device, and on the other hand regulates the carrier conversion process at the interface between the electrode and the ion conductor, thereby improving the operating voltage, current and output power. The secondary battery and the thermoelectric conversion battery are combined to realize thermal charging of the thermoelectric conversion device in the non-working state, store the electrical energy in the non-working state, and improve the operating voltage, current, output power and continuous working time. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the open circuit voltage-time curve of the thermoelectric conversion device under different temperature differences;

[0026] FIG2 is a current-voltage curve and a power curve of a thermoelectric conversion device under a temperature difference of 5K;

[0027] FIG3 is a diagram showing the output power of a thermoelectric conversion device under different load resistances;

[0028] FIG4 is a diagram showing the energy density output by the thermoelectric conversion device of FIG3 under different loads.

[0029] Figure 5 shows the thermoelectric conversion device under different temperature differences, using a current of 0.9 mA (current density of about 0.51 mA / cm -2 )Charge and discharge voltage-time curve of constant current charge and discharge test. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to the accompanying drawings. The embodiments described with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be understood as limiting the present invention.

[0031] Example 1

[0032] (1) Preparation of hydrogel-based ion conductors:

[0033] Weigh 3.75g of acrylamide and 6.25g of potassium acrylate in a clean beaker, add 18mL of deionized water, 0.5mL of N,N'-methylenebisacrylamide solution, and then continue to add 0.3mL of tetramethylethylenediamine. After rapid stirring to remove bubbles, pour the mixed solution into a mold and irradiate under ultraviolet light for 13 minutes. After free radical polymerization, place it in 0.5mol / L hydrochloric acid and dialyze for three days to obtain a hydrogel-based ion conductor.

[0034] (2) Preparation of NVO electrode:

[0035] 2.5 mmol NH4VO3 was dissolved in 35 mL deionized water at 60°C, and then 0.3 mmol cyclodextrin was added. After stirring for 1 hour, 3.75 mmol anhydrous oxalic acid was added and reacted for 10 minutes to obtain a mixed solution. The mixed solution was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and subjected to a hydrothermal reaction at 120°C for 10 hours. The precipitate was collected by filtration, washed several times with ethanol and deionized water, and then dried in an oven at 80°C for 8 hours to obtain NVO material.

[0036] NVO material, acetylene black and carboxymethyl cellulose were mixed in a mass ratio of 7:2:1, deionized water was added and stirred thoroughly. After stirring for 12 hours, the mixed slurry was evenly brushed on the carbon cloth. The slurry-coated carbon cloth was placed in a vacuum drying oven and dried at 60°C for 12 hours to remove residual moisture and ensure that the electrode was dry. The slurry and carbon cloth were bonded together to obtain the NVO working electrode.

[0037] (3) Preparation of counter electrode:

[0038] Activated carbon, acetylene black and carboxymethyl cellulose were mixed in a mass ratio of 8:1:1, deionized water was added and stirred thoroughly. After stirring for 12 hours, the mixed slurry was evenly brushed on the carbon cloth. The slurry-coated carbon cloth was placed in a vacuum drying oven and dried at 60°C for 12 hours to remove residual moisture, ensure that the electrode was dry, and the slurry was bonded to the carbon cloth to obtain a counter electrode.

[0039] (4) The NVO electrode and the counter electrode are respectively arranged on the two surfaces of the hydrogel-based ion conductor and assembled into a sandwich structure to obtain a thermoelectric conversion device.

[0040] The performance test of the thermoelectric conversion device provided in Example 1 was carried out to test the open circuit voltage of the device under different temperature differences and the output power under different load resistances:

[0041] As can be seen from Figure 1, the open circuit voltage of the device was tested at different temperature differences (5K, 10K and 15K). It can be seen that the device can reach above 0.4V in two hours under different temperature differences, and the greater the temperature difference, the faster the open circuit voltage reaches above 0.4V, indicating that the thermoelectric conversion device provided by the present invention has excellent performance.

[0042] As can be seen from Figure 2, the short-circuit current density of the thermoelectric conversion device provided by the present invention can reach 20A / m at a temperature difference of 5K. 2 , the corresponding power density can reach 2.5W / m 2 When the temperature difference exceeds 15K, the power density of the device's electrical energy output exceeds 4.0W / m 2 .

[0043] As shown in Figure 3, the device can maintain an output voltage of approximately 0.1V for a long time within the external circuit resistance range of 0.5-2.5kΩ, and has good thermoelectric conversion capabilities and continuous power output capabilities.

[0044] As can be seen from Figure 4, the energy output of the thermoelectric converter provided by the present invention reaches 400 J / m within two hours. 2 , excellent performance.

[0045] As can be seen from Figure 5, the thermoelectric converter provided by the present invention shows a relatively obvious platform in the constant current charge and discharge test, proving that the electrode can realize the function of storing electrical energy by undergoing redox reaction. Obviously, its electrical energy storage capacity is higher than the capacitive discharge mode of conventional ion conductors. Moreover, the NVO electrode prepared by this patent can cooperate with the ion conductor, and the ability to store electrical energy under different temperature differences also shows differences. The stored electrical energy increases with the increase of temperature difference (the constant current discharge time is prolonged with the increase of temperature difference).

[0046] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the inventive concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A method for preparing an NVO electrode, characterized in that, It includes the following preparation steps: S1: Dissolve NH4VO3 in water, then mix it with auxiliary materials, and then add an acid to react to obtain a mixed solution; S2: After subjecting the mixed solution to a hydrothermal reaction, collect the precipitate and wash and dry it to obtain the NVO material; S3: Mix the NVO material, a conductive agent, and a binder, and add water and stir to obtain a slurry; S4: Apply the slurry onto carbon cloth and dry it under vacuum to obtain the NVO electrode.

2. The preparation method of the NVO electrode according to claim 1, wherein In the step S1, the auxiliary material is β-cyclodextrin, the acid is selected from at least one of oxalic acid, citric acid, phytic acid, and lactic acid, the molar ratio of NH4VO3 to the auxiliary material is 10:1-3, and the molar ratio of NH4VO3 to the acid is 2:1-3.

3. The preparation method of the NVO electrode according to claim 1, characterized in that, In the step S2, the hydrothermal reaction temperature is 120-180 °C, and the hydrothermal reaction time is 10-15 h.

4. The preparation method of the NVO electrode according to claim 1, characterized in that, In the step S3, the conductive agent is selected from at least one of acetylene black, Ketjen black, and graphite, the binder is selected from at least one of carboxymethyl cellulose, polyvinylidene fluoride, and Nafion, and the mass ratio of the NVO material, the conductive agent, and the binder is 7:2:1 or 6:3:

1.

5. The preparation method of the NVO electrode according to claim 1, wherein In the step S4, the vacuum drying temperature is 60-100 °C, and the vacuum drying time is 9-12 h.

6. The NVO electrode prepared by the preparation method according to any one of claims 1 to 5.

7. An integrated device for thermoelectric conversion and electrical energy storage, characterized in that, It includes the NVO electrode according to claim 6, a counter electrode, and a hydrogel-based ion conductor, and the NVO electrode and the counter electrode are respectively arranged on two surfaces of the hydrogel-based ion conductor.

8. The integrated device for thermoelectric conversion and electrical energy storage according to claim 7, characterized in that, The preparation method of the counter electrode includes the following steps: Mix activated carbon, a conductive agent, and a binder, add water and stir to obtain a slurry, apply the slurry onto carbon cloth, and dry it under vacuum to obtain the counter electrode.

9. The integrated device for thermoelectric conversion and electrical energy storage according to claim 8, characterized in that, The conductive agent is selected from at least one of acetylene black, Ketjen black, and graphite, the binder is selected from at least one of carboxymethyl cellulose, polyvinylidene fluoride, and Nafion, and the mass ratio of the activated carbon, the conductive agent, and the binder is 8:1:1 or 6:3:

1.

10. The integrated device for thermoelectric conversion and electrical energy storage according to claim 8, wherein, The vacuum drying temperature is 60-100 °C, and the time is 9-12 h.

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