Ionic gel material, carbon micron tube ion thermoelectric supercapacitor and preparation method and application of carbon micron tube ion thermoelectric supercapacitor

Abstract

The invention provides an ionic gel material, a carbon micron tube ionic thermoelectric supercapacitor and a preparation method and application of the carbon micron tube ionic thermoelectric supercapacitor, and belongs to the technical field of electrical materials.The preparation method comprises the steps that carbon micron tube dispersion liquid, gelatin and potassium chloride are evenly mixed according to the proportion, formed and dried, and CMTs / KCl / gelatin ionic thermoelectric gel with the thermoelectric pressure and temperature multifunctional sensing characteristic is prepared; and the flexible stretchable ion thermoelectric supercapacitor is assembled by taking the CMTs / KCl / gelatin ion thermoelectric gel as an electrolyte and taking the CMTs / MnO2 / foamy copper electrode. The CMTs / KCl / gelatin ion thermoelectric gel has thermoelectric effect and temperature and pressure sensing monitoring capability, and the prepared capacitor can be used as an energy storage device, has good electrochemical performance, realizes conversion and storage from heat energy to electric energy, especially realizes thermal voltage output under low temperature gradient, and has wide application prospect. The device can be used for converting low-order heat energy into electric energy and storing and utilizing the electric energy in real time.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical materials. More specifically, the present invention relates to an ionic gel material, a carbon microtube ionic thermoelectric supercapacitor, and a preparation method and application thereof. Background Art

[0002] The energy shortage caused by insufficient fossil fuel supply and growing consumption is one of the most important problems faced by mankind. One of the fundamental reasons for the severe energy situation lies in the low energy utilization efficiency, and the effective utilization of waste heat helps to improve the current energy situation. The relatively backward power generation technology restricts the effective utilization of waste heat or other thermal energy. The thermoelectric conversion technology based on the Seebeck effect has been widely applied, namely thermoelectric generators (TEGs) and thermogalvanic cells (TGCs). Although researchers have conducted in-depth studies and made significant progress in thermoelectric performance, these thermoelectric devices have a low Seebeck coefficient under low-grade waste heat (usually at a temperature below 200°C), resulting in poor thermoelectric conversion performance of these thermoelectric devices under low-grade waste heat (usually at a temperature below 200°C). Moreover, the expensive chemicals and complex designs involved in these devices always limit their further applications. In addition, this thermoelectric conversion does not have an energy storage function.

[0003] Carbon nanotubes (CNTs) are known for their special structure, unique electro-mechanical and chemical properties and their various applications. However, their relatively small inner diameter hinders the entry of large-diameter reaction species or reactants, and the potential of CNTs as reactors or channels is greatly limited. Therefore, carbon microtubes (CMTs) with a larger inner spacing are potential conductive materials for preparing ionic thermoelectric gel materials, with good thermoelectric performance, non-toxicity, flexible stretchability, temperature sensitivity and pressure sensitivity. Therefore, how to design an ionic gel material with multifunctional sensing characteristics and a capacitor with high thermoelectric conversion performance by using these common materials, especially to improve the thermoelectric conversion performance under low-grade waste heat (usually at a temperature below 200°C) and have an energy storage function, is of great significance for promoting the development and application of carbon microtubes. Summary of the Invention

[0004] Aiming at the above problems, the present invention provides an ionic gel material, a carbon microtube ionic thermoelectric supercapacitor, and a preparation method and application thereof. A CMTs / KCl / gelatin ionic thermoelectric gel with pressure-temperature multifunctional sensing characteristics is prepared, and a flexible and stretchable ionic thermoelectric supercapacitor is assembled with the CMTs / KCl / gelatin ionic thermoelectric gel as the electrolyte and the CMTs / MnO2 / foam copper electrode. This capacitor can be used as an energy storage device, has good electrochemical performance, and realizes the conversion and storage of thermal energy into electrical energy. Especially, it can output a thermal voltage under a low temperature gradient, and can be used to convert low-grade thermal energy into electrical energy and store and utilize it in real time.

[0005] To achieve these objects and other advantages according to the present invention, a method for preparing an ionic gel material is provided, including:

[0006] Preparing a carbon nanotube dispersion, mixing the carbon nanotube dispersion, gelatin and potassium chloride uniformly, and forming and drying to obtain the ionic gel material; wherein, the ratio of carbon nanotubes, gelatin and potassium chloride is: 20-40 mg: 25-30 wt%: 0.8 M.

[0007] Preferably, in the method for preparing the ionic gel material, the ratio of carbon nanotubes, gelatin and potassium chloride is: 30 mg: 30 wt%: 0.8 M.

[0008] Preferably, in the method for preparing the ionic gel material, it specifically includes:

[0009] (1) Dispersing carbon nanotubes in deionized water, slowly adding sodium dodecylbenzenesulfonate as a surfactant, and stirring until dissolved; continuing to add HCl, and performing ultrasonic dispersion and cell disruption treatment to obtain a carbon nanotube dispersion;

[0010] (2) Mixing the above carbon nanotube dispersion, gelatin and potassium chloride in a ratio of 30 mg: 30 wt%: 0.8 M, and stirring in an oil bath at 60 °C, taking out to obtain a uniformly mixed ionic gel; pouring the ionic gel into a mold to cool and form, taking out the solidified gel, and drying at room temperature in air to obtain the ionic gel material.

[0011] An ionic gel material is prepared by any of the above preparation methods.

[0012] An application of an ionic gel material prepared by any of the above preparation methods in a temperature sensor and / or a pressure sensor.

[0013] A method for preparing a carbon nanotube ionic thermoelectric supercapacitor, using the ionic gel material prepared by any of the above preparation methods as an electrolyte, and assembling with electrodes to form the carbon nanotube ionic thermoelectric supercapacitor.

[0014] Preferably, in the method for preparing the carbon nanotube ionic thermoelectric supercapacitor, preparing carbon nanotubes loaded with MnO2, then coating on the surface of the electrode, and then assembling with the ionic gel material to form the carbon nanotube ionic thermoelectric supercapacitor.

[0015] Preferably, in the method for preparing the carbon nanotube ionic thermoelectric supercapacitor, the thickness of the ionic gel is 1-1.5 mm.

[0016] A carbon nanotube ionic thermoelectric supercapacitor prepared by any of the above methods for preparing a carbon nanotube ionic thermoelectric supercapacitor.

[0017] Application of a carbon nanotube ionic thermoelectric supercapacitor prepared by the preparation method of any one of the above carbon nanotube ionic thermoelectric supercapacitors as a device for collecting low-grade thermal energy at room temperature and in cold environments; or as an application of a device that completes electrical energy storage while realizing thermal energy conversion.

[0018] The present invention has at least the following beneficial effects:

[0019] 1. The present invention proposes a flexible and stretchable CMTs / KCl / gelatin composite material with thermoelectric effect and temperature and pressure sensing and monitoring capabilities. The prepared CMTs / KCl / gelatin composite material has a Seebeck coefficient of 4 mV / K and a tensile strength of 1.7 MPa, and has the advantages of flexibility, stretchability, and response to temperature and pressure. In addition, the CMTs / potassium chloride / gelatin sensor can also detect the temperature difference on the material surface in contact and non-contact modes and respond to pressure stimuli. When stimulated by both pressure and temperature signals at the same time, the CMTs / potassium chloride / gelatin sensor will respond to both signals, and the detected voltage is significantly higher than the voltage generated only by pressure induction. In addition, in practical applications, the CMTs / potassium chloride / gelatin sensor can also monitor the movement of the human body (finger, arm) and the temperature difference between the human body and the environment. These findings provide a new strategy for the production and utilization of flexible sensors with multi-signal detection functions.

[0020] 2. The present invention uses the CMTs / KCl / Gelatin composite material as a solid electrolyte, in-situ synthesizes CMTs / MnO2 active material with carbon nanotubes CMTs, and uses copper foam as a current collector to prepare a capacitor electrode, and assembles a new type of ionic thermoelectric supercapacitor. By adding CMTs / MnO2 to the electrode, the electrochemical performance of the capacitor is improved, and the ionic conductivity reaches a maximum of 14.2 mS / cm. When the sweep rate is 50 mV / s, the areal specific capacitance can reach 152.2 mF / cm 2 . In addition to electrochemical energy storage, the ionic thermoelectric supercapacitor can also convert low-grade thermal energy into electrical energy. The assembled ionic thermoelectric supercapacitor realizes an output of a relatively high ionic thermal voltage of 81.6 mV at ΔT = 20 K, and the capacitor generates a Seebeck coefficient of 4.12 mV / K. In addition, the ionic thermoelectric supercapacitor can also output the converted electrical energy to the external circuit in real time to light up the LED, proving that the ionic thermoelectric supercapacitor has great potential in the field of thermal energy-electricity conversion.

[0021] Other advantages, objectives, and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. Description of the Drawings

[0022] Figure 1 Structural characterization of the ionic gel material in Example 1 of the present invention;

[0023] Figure 2 Mechanical property results of different ionic gel materials of the present invention;

[0024] Figure 3 Thermoelectric properties of different ionic gel materials of the present invention;

[0025] Figure 4 Seebeck coefficients of different CMTs / KCl / gelatin composites of the present invention and the thermal voltage at each temperature gradient;

[0026] Figure 5 Temperature sensor application of the CMTs / potassium chloride / gelatin composite prepared in Example 1 of the present invention;

[0027] Figure 6 Pressure sensor application of the CMTs / potassium chloride / gelatin composite prepared in Example 1 of the present invention;

[0028] Figure 7 SEM image and EDS energy spectrum of the material in Example 4 of the present invention;

[0029] Figure 8 XPS image and spectrum of the material in Example 4 of the present invention;

[0030] Figure 9 Result graph of testing the electrochemical properties of the capacitor using a two - electrode system in the present invention;

[0031] Figure 10 CV curves and areal specific capacitance of ionic thermoelectric supercapacitors with different components in the present invention;

[0032] Figure 11 CV curves, GCD curves and Seebeck coefficients of ionic thermoelectric supercapacitors with different electrolyte thicknesses in the present invention;

[0033] Figure 12 Seebeck coefficients, ionic conductivities, thermal conductivities, power factors and ZT i values;

[0034] Figure 13 Working principle diagram of the carbon nanotube ionic thermoelectric supercapacitor in Example 4 of the present invention;

[0035] Figure 14 Thermal charging curves of the carbon nanotube ionic thermoelectric supercapacitor in Example 4 of the present invention under different temperature difference conditions;

[0036] Figure 15 Charge transfer amount and charge transfer efficiency of charge and discharge of carbon nanotube ion thermoelectric supercapacitor in Example 4 of the present invention under different temperature gradients;

[0037] Figure 16 Practical application diagram of the ion thermoelectric supercapacitor of Example 4 of the present invention. Detailed implementation manners

[0038] The present invention will be further described in detail below with reference to the accompanying drawings, so that those skilled in the art can implement it according to the description in the specification.

[0039] It should be understood that terms such as "having", "comprising" and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0040] It should be noted that the experimental methods described in the following embodiments are all conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified; in the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected" and "set" should be understood in a broad sense. For example, they can be fixedly connected and set, or detachably connected and set, or integrally connected and set. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations. The orientation or positional relationship indicated by terms such as "transverse", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0041] The main experimental materials of the present invention are as follows:

[0042] Table 1 Experimental materials

[0043]

[0044] Example 1

[0045] A preparation method of an ion gel material, comprising:

[0046] (1) Preparation of carbon nanotube dispersion: 0.1 g of carbon nanotubes (CMTs) was dispersed in 20 mL of deionized water, and 0.1 g of sodium dodecylbenzenesulfonate (SDBS) was slowly added as a surfactant and stirred until completely dissolved. An appropriate amount of concentrated hydrochloric acid (HCl) was further added to the carbon nanotube mixture to functionalize the carbon nanotubes. The dispersion system was ultrasonically treated for 30 min and cell-crushed for 1 h on an ultrasonic cleaner to initially obtain a well-dispersed CMTs dispersion.

[0047] (2) Preparation of ionogel material: Gelatin and carbon nanotubes (CMTs) were used as the main raw materials, and KCl was used as a dopant. Specifically, the above carbon nanotube dispersion, gelatin, and potassium chloride were mixed in a certain proportion and stirred in an oil bath at 60 °C for 2 h, and then taken out to obtain a uniformly mixed ionogel. Subsequently, the ionogel was poured into a polytetrafluoroethylene mold to cool and form. The cured gel was taken out and dried at room temperature in air for 4 h to obtain an ionogel material (CMTs / KCl / gelatin composite material) with an appropriate moisture content, which was formed into different thicknesses as needed. In this example, the ratio of the carbon nanotube dispersion (CMTs solid content), gelatin, and potassium chloride was 30 mg: 30 wt%: 0.8 M.

[0048] Example 2

[0049] I. Comparative experiment design:

[0050] 1. The dosage of the carbon nanotube dispersion (CMTs solid content) in step (2) of the example was changed (5 mg, 10 mg, 20 mg, 30 mg, 40 mg, etc.), and other operations remained unchanged to prepare ionogel materials with different carbon nanotube contents.

[0051] 2. The gelatin ratio in step (2) of the example was changed (20 wt%, 25 wt%, 30 wt%, 35 wt%), and other operations remained unchanged to prepare ionogel materials with different gelatin ratios.

[0052] 3. The KCl content in step (2) of the example was changed (0.4 M, 0.6 M, 0.8 M, 1.0 M), and other operations remained unchanged to prepare ionogel materials with different KCl contents.

[0053] 4. At the same time, as a control, ionogel materials with different components were also prepared, including: ionogel materials without CMTs and KCl (Gel), ionogel materials without CMTs (Gel-KCl), and other operations were the same as in Example 1.

[0054] 5. Copper sheet electrodes were placed at both ends of the above ion gel material to assemble a sensor, and pressure and temperature sensing tests were carried out to examine the voltage generated when the sample was subjected to different stimuli; the relationship curves between pressure and voltage, and temperature and voltage were plotted; the temperature sensing ability and pressure sensing ability were measured.

[0055] II. Effect Data Analysis

[0056] (I) Structural Characterization of the Ion Gel Material in Example 1

[0057] Figure 1 (a) Macroscopic morphology diagram of carbon microtubes; (b) SEM image of carbon microtubes; (c), (d) SEM images of ion gel; (e) Infrared spectrum diagram of ion gelatin.

[0058] From Figure 1 (a), we can observe the macroscopic morphology of the synthesized CMTs. The CMTs have an aerogel-like structure. Individual CMTs have a relatively long aspect ratio. Adding them to the CMTs / KCl / gelatin composite material can obtain a lightweight, low-density and soft conductive network. As Figure 1 (b) shows, the maximum length of the CMTs diameter can reach dozens of micrometers, and its diameter is 500 nm. In addition, the surface structure of the CMTs presents a bamboo joint-like morphology, and the convex parts can greatly increase the surface roughness and specific surface area of the CMTs. As Figure 1 (c) shows, the microstructure surface of the composite material is rough, and the precipitated KCl is evenly distributed on the surface of the composite material. From Figure 1 (d), it can be observed that the CMTs shuttle through the gel network. The shown bamboo joint structure can enhance the contact interface between the CMTs and the gel matrix and the adsorption of ions by the CMTs, so as to obtain a high-performance CMT / KCl / gelatin composite material. The CMTs / KCl / gelatin composite material has a rich pore structure. In addition, the CMTs are wrapped by gelatin and shuttle through the voids of the gel matrix, which is beneficial to improving the mechanical and conductive properties of the CMTs / KCl / gelatin composite material.

[0059] We carried out infrared spectrum tests on the prepared CMTs / KCl / gelatin composite material and KCl / gelatin composite material, and the results are as Figure 1 (e) shows. In the Fourier transform infrared spectrum of the CMTs / KCl / gelatin composite material, the peak at 1633 cm -1 is the stretching vibration of the amide I band (C=O) of the gelatin molecule, the peak at 1536 cm -1 is attributed to the bending vibration of its amide II band (N-H), and the peak at 1242 cm -1 is the stretching vibration of the amide III band (C-H). The CMTs / potassium chloride / gelatin composite material is at 3305 cm -1There is a wide absorption peak here, which is the -OH stretching vibration of the CMTs / KCl / gelatin composite material. In addition, the CMTs / potassium chloride / gelatin composite material shows two peaks near 2926 cm -1 and 2854 cm -1 These two peaks are related to the stretching vibration of the carbon nanotube -CH2 group.

[0060] (II) Mechanical property results of different ion gel materials

[0061] Figure 2 (a) Tensile and twisting of ion gelatin; (b) Stress-strain curves of ion gels with different KCl contents; (c) Stress-strain curves of ion gels with different gelatin ratios; (d) Stress-strain curves of ion gels with different carbon nanotube contents.

[0062] Flexible performance is one of the most important performances of flexible sensors, directly affecting the wear resistance, reliability and durability of the sensor sensing performance. To evaluate the flexibility of the CMTs / KCl / gelatin composite material, tensile, torsion and bending tests were carried out on the CMTs / KCl / gelatin composite material. As Figure 2 (a) shows, the CMT / potassium chloride / gelatin composite material can be stretched from 4 cm to 8 cm without breaking, and can be easily folded and bent without cracking, which shows excellent toughness and flexible performance. In addition, as Figure 2 (b) shows, we also further quantified the effects of different potassium chloride concentrations, gelatin mass fractions and CMTs addition amounts on the mechanical properties of the CMTs / KCl / gelatin composite material through tensile tests. With the increase of potassium chloride concentration, the mechanical properties of the CMTs / KCl / gelatin composite material show a downward trend. Since the addition of potassium chloride can improve the thermoelectric properties of the CMTs / KCl / gelatin composite material, 0.8 M potassium chloride was selected as the concentration of the subsequent research material after comprehensively considering the mechanical properties and thermoelectric properties of the CMTs / KCl / gelatin composite material. As Figure 2 (c) shows, with the increase of gelatin mass fraction, the tensile strength and elongation at break of the CMTs / KCl / gelatin composite material increase significantly. This phenomenon is due to the fact that gelatin contains abundant active groups, which can combine with the groups on the surface of CMTs, thus improving the mechanical properties of the CMTs / KCl / gelatin composite material. At the same time, in Figure 2 (d), with the increase of the addition amount of CMTs from 10 mg to 40 mg, the tensile strength of the CMT / potassium chloride / gelatin composite material increases significantly from 0.55 MPa to 1.7 MPa, and the elongation at break increases monotonically from 460% to 1200%, because CMTs have a large aspect ratio.

[0063] (III) Thermoelectric properties of different ion gel materials

[0064] Figure 3 (a) Seebeck coefficients of ion gel materials with different components Figure 3 (b) Ionic conductivities of ion gel materials with different components. Among them, Gel: ion gel material without CMTs and KCl; Gel-KCl: ion gel material without CMTs; Gel-KCl-CMTs: CMTs / KCl / gelatin composite material.

[0065] The temperature sensing of the CMTs / KCl / gelatin composite material is based on the thermal diffusion effect of the CMTs / KCl / gelatin composite material. Therefore, studying the thermoelectric properties of the CMTs / KCl / gelatin composite material helps to optimize its temperature sensing performance and improve the sensing accuracy. From Figure 3 (a) We observed that the Seebeck coefficient of the ion gel prepared only by gelatin is only 0.56 mV / K. Adding KCl to the gelatin, the Seebeck coefficient of the ion gel increases from 0.56 mV / K to 1.5 mV / K. This is because the chloride salts in the system provide a large number of mobile cations and anions, thus generating a thermal diffusion effect. The temperature gradient drives the cations and anions to migrate from the hot side to the cold side, resulting in the accumulation of net charge and the internal electric field that generates voltage, thus generating a large thermoelectric potential and improving the thermoelectric performance of the system. In addition, adding the previously prepared carbon microtubes to the system further increases the Seebeck coefficient of the system. The Seebeck coefficient of the CMTs / KCl / gelatin system can reach 4.0 mV / K. As Figure 3 (b) shown, adding KCl and CMTs to gelatin can significantly increase the ionic conductivity of the system. The cations and anions ionized by potassium chloride can increase the ionic mobility of the system, and the excellent conductivity and structure of CMTs further enhance the conductive ability of the gel.

[0066] Figure 4 Among them, (a) Seebeck coefficients of CMTs / KCl / gelatin composite materials with different KCl concentrations; (b) thermal voltages of CMTs / KCl / gelatin composite materials with different KCl concentrations at each temperature gradient; (c) Seebeck coefficients of CMTs / KCl / gelatin composite materials with different gelatin mass fractions; (d) thermal voltages of CMTs / KCl / gelatin composite materials with different gelatin mass fractions at each temperature gradient; (e) Seebeck coefficients of CMTs / KCl / gelatin composite materials with different CMTs added; (f) thermal voltages of CMTs / KCl / gelatin composite materials with different CMTs added at each temperature gradient.

[0067] From Figure 4It can be seen that after adding potassium chloride and CMT to gelatin, both the Seebeck coefficient and conductivity of the CMT / potassium chloride / gelatin composite material are significantly improved. The thermal diffusion of KCl in gelatin exhibits a p-type thermopower. Initially, all mobile ions K + , Cl - , H + are evenly distributed in the KCl / CMTs / gelatin material, and there is no electromotive force in the system. During the thermal charging process, a temperature difference is applied across the battery. Due to the mismatch in the thermal mobilities of cations and anions, compared with Cl - , more K + will accumulate on the cold side, resulting in a net positive charge density and a negative charge density near the cold electrode and the hot electrode, respectively. Such a net charge density distribution induces a built-in electric field pointing from the cold side to the hot side, thus generating a voltage. Therefore, we evaluated the Seebeck coefficients of the CMTs / KCl / gelatin composite materials at different KCl concentrations. As can be seen from Figure 4 (a-b), as the KCl concentration increases, the content of mobile cations in the CMTs / KCl / gelatin composite material also increases, resulting in an increase in the Seebeck coefficient of the CMTs / KCl / gelatin composite material. This is because when the KCl concentration is too high, KCl will weaken the Debye length of the surface charge of the polymer, and the result tends to the Seebeck coefficient value of a pure KCl solution. In addition, as can be seen from Figure 4 (c-d), by changing the mass fraction of gelatin in the CMTs / KCl / gelatin composite material, the Seebeck coefficient of the CMTs / KCl / gelatin composite material can be increased from 1.75 mV / K to 4 mV / K. However, excessive gelatin will cause a decrease in the moisture content in the CMTs / KCl / gelatin composite material, thus inhibiting the ion mobility and the thermoelectric performance of the CMTs / KCl / gelatin composite material.

[0068] In addition, we also measured the Seebeck coefficients of the composite materials with different CMTs addition amounts to evaluate the effect of CMTs on the thermoelectric performance of the CMTs / potassium chloride / gelatin composite materials. As shown in Figure 4As shown in (e-f), with the increase in the addition amount of CMTs, the Seebeck coefficient of the CMTs / KCl / gelatin composite first increases and then shows a downward trend, reaching a peak after adding 30 mg of CMTs. The increase in the active groups of CMTs will lead to an increase in the concentration difference between cations and anions in the CMTs / KCl / gelatin composite, thereby resulting in an increase in the Seebeck coefficient. However, when CMTs are added to a certain extent, aggregation of CMTs appears in the CMTs / KCl / gelatin composite. The aggregation of CMTs will affect the ion transport in the CMTs / KCl / gelatin composite, and further affect the thermoelectric performance of the system. At the same time, the aggregation of CMTs will also inhibit the formation of the CMTs / KCl / gelatin composite and reduce the stability of the gel structure.

[0069] Example 3

[0070] Application of CMTs / potassium chloride / gelatin composite (temperature sensor + pressure sensor)

[0071] Figure 5 In (a) is a schematic diagram of the temperature sensing test of CMTs / potassium chloride / gelatin prepared in Example 1; (b) is a schematic diagram of the temperature sensing mechanism of CMTs / potassium chloride / gelatin; (c) is a schematic diagram of the skin temperature sensing test; (d) is the voltage response of the sensor to different temperature differences; (e) is the corresponding thermoelectric voltage of the sensor on the skin surface; (f) is the voltage response of sensors with different thicknesses to a 1K temperature difference; (g) is a schematic diagram of the non-contact temperature sensing test and the actual non-contact temperature sensing test diagram; (h) is the voltage-time curve of non-contact skin temperature sensing.

[0072] The CMTs / potassium chloride / gelatin composite has stable thermoelectric properties and is an ideal temperature sensor material. Therefore, we assembled the CMTs / KCl / gelatin composite into a temperature sensor to explore its potential application in human body temperature detection. As Figure 5 (a) shows, we assembled a temperature sensor with the CMTs / KCl / gelatin composite as the electrolyte and copper foil as the electrode. The temperature sensing mechanism of the sensor is as Figure 5 (b) shows. Based on the thermal diffusion effect, the cations and anions in the CMTs / potassium chloride / gelatin composite move under the influence of the temperature difference at both ends. The asynchronous movement of cations and anions leads to the uniform distribution of ions in the composite, thereby forming a potential difference at both ends of the sensor. Therefore, the CMTs / potassium chloride / gelatin sensor can display the thermal condition of the sensing area. As Figure 5As shown in (d), when different temperature differences are applied on both sides of the sensor, the voltage change of the CMTs / potassium chloride / gelatin sensor is uniform, indicating that the CMTs / KCl / gelatin sensor has good stability. When the temperature difference on both sides is eliminated, the voltage on both sides of the sensor will return to the original value, and the sensor shows good responsiveness to temperature changes. The sensor voltage is positively correlated with the temperature difference on both sides, that is, the greater the temperature difference, the higher the sensor voltage. In addition, in Figure 5 (e), the sensor can also generate a stable voltage change according to the temperature difference between the skin and the air. As Figure 5 (c) shows, according to the Seebeck coefficient of the CMTs / potassium chloride / gelatin composite material, the voltage generated by the temperature difference on both sides of the sensor is close to the actual voltage value measured on both sides of the sensor, indicating that the sensor can accurately detect the temperature difference on both sides of the sensor. The thickness of the CMTs / KCl / gelatin composite material is an important factor affecting temperature sensing. As can be seen from Figure 5 (f), when the temperature difference is 1 K, the thicker the thickness, the greater the voltage change and the higher the sensitivity of the sensor.

[0073] To further verify the reliability of the CMTs / KCl / gelatin composite material in temperature sensing, we measured the temperature sensing of the palm non-contact with the sensor. The palm was placed 1 cm above the sensor, and the temperature on both sides of the sensor was monitored by thermal imaging technology Figure 5 (g). As can be seen from Figure 5 (h), a voltage response was successfully obtained in the experiment. The temperature difference measured by thermal imaging technology was 0.8 K, which was basically the same as the temperature corresponding to the thermal voltage generated in the experiment, indicating that the temperature sensing of the CMTs / KCl / gelatin sensor has high accuracy. The reason for this phenomenon is that the heat diffusion of the human skin raises the temperature of the upper surface of the CMTs / KCl / gelatin sensor. The temperature difference prompts the CMTs / KCl / gelatin sensor to generate a thermal voltage, enabling the sensor to achieve non-contact temperature sensing. Therefore, the temperature responsiveness of the CMTs / KCl / gelatin sensor provides the possibility for detecting human body temperature.

[0074] Figure 6 Among them, (a) Schematic diagram of CMTs / KCl / gelatin pressure sensing test; (b) Pressure sensing mechanism of CMTs / KCl / gelatin sensor; (c) Voltage response of the sensor to different pressures; (d) Voltage response of sensors with different thicknesses under a 100 g weight; (e) Voltage response of the sensor when the finger is bent 90°; (f) Voltage response of the sensor when the arm is bent; (g) Schematic diagram of the sensor bent 90° test; (h) Voltage response of the sensor when bent 90° under the condition of a temperature difference of 1 K.

[0075] Due to the good electrical conductivity and mechanical flexibility of the CMTs / KCl / gelatin composite, we evaluated its potential application in flexible wearable pressure sensor devices. Figure 6 (a) is a schematic diagram of the pressure sensing test of CMTs / KCl / gelatin, and its main structure is a sandwich structure of copper foil - CMTs / KCl / gelatin composite - copper foil. The pressure sensing mechanism of the CMTs / KCl / gelatin sensor is as Figure 6 (b) shows. As the pressure increases, the voltage across the capacitor also increases and returns to the original value after the pressure is released. According to the voltage sensitivity of the CMTs / KCl / gelatin sensor to external forces, different weights were placed on the surface of the CMTs / KCl / gelatin sensor to evaluate its responsiveness and stability to different external forces. As Figure 6 (c) shows, when the load weight gradually increases from 10 g to 100 g, the sensor shows a higher voltage response. In addition, the thickness of the CMTs / KCl / gelatin composite also has a significant impact on the performance of the sensor. Figure 6 (d) shows that the sensor with a smaller thickness has a larger voltage change when loaded with 100 g. Considering the influence of thickness on temperature sensing and pressure sensing, the CMTs / KCl / gelatin composite with a thickness of 1.5 mm was assembled with copper foil and adhered to the skin (such as fingers and elbows) to test its ability to monitor human movement in real time.

[0076] The CMTs / KCl / gelatin sensor can generate local deformation with the movement of fingers and elbows, which leads to the movement of CMTs in the CMTs / KCl / gelatin composite. The movement of CMTs changes the internal conductive network of the CMT / potassium chloride / gelatin composite, causing a change in the voltage signal, thereby realizing the real-time detection of human movement. Therefore, as Figure 6 (e - f) shows, the voltage signal of the CMTs / KCl / gelatin sensor changes with the movement of fingers and elbows, and it has good sensitivity. In addition, when repeatedly bending the fingers and elbows of the tester, the CMTs / KCl / gelatin sensor shows regular and effective voltage response signals. This phenomenon indicates that the CMTs / KCl / gelatin sensor has good pressure sensing ability and great potential in flexible wearable materials.

[0077] In addition, we also evaluated the response ability of the CMTs / KCl / gelatin sensor when used as both a temperature and a pressure sensor. As Figure 6As shown in (g), after applying different temperatures on both sides of the sensor and bending the sensor by 90°, the voltage signal of the sensor changed significantly, indicating that the sensor can respond to both pressure and temperature difference simultaneously. Meanwhile, the voltage generated by sensing pressure and temperature difference is greater than that generated by sensing pressure alone, indicating that part of the voltage response of the CMTs / KCl / gelatin sensor comes from temperature sensing. This phenomenon proves the feasibility of the developed CMTs / KCl / gelatin sensor for applications in temperature monitoring and pressure sensing. In addition, the CMTs / KCl / gelatin sensor was also compared with other similar sensors (Table 2). It is not difficult to find that the CMTs / KCl / gelatin sensor can monitor temperature and pressure simultaneously, which is not available in similar sensors. In addition, all the materials used in the CMTs / KCl / gelatin sensor are cheaper, easier to obtain, non-toxic to the human body and have little environmental impact. In short, this flexible and stretchable CMTs / KCl / gelatin sensor that can monitor both temperature and pressure provides the possibility for broadening flexible wearable sensing devices.

[0078] Table 2 The present invention was compared with other similar sensors

[0079]

[0080] The above-mentioned literature is as follows:

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[0082] Literature 2: Cho H, Lee H, Lee S, et al. Reduced graphene oxide-based wearable and bio-electrolyte triggered pressure sensor with tunable sensitivity[J]. Ceramics International, 2021, 47(12): 17702 - 17710.

[0083] Literature 3: Zhou J, Hsieh Y L. Conductive Polymer Protonated Nanocellulose Aerogels for Tunable and Linearly Responsive Strain Sensors[J]. ACS Appl Mater Interfaces, 2018, 10(33): 27902 - 27910.

[0084] Literature 4: Liu Q, Tai H, Yuan Z, et al. A High-Performances Flexible Temperature Sensor Composed of Polyethyleneimine / Reduced Graphene Oxide Bilayer for Real-Time Monitoring[J]. Advanced Materials Technologies, 2019, 4(3): 1800594.

[0085] Literature 5: Li J, Gai L, Li H, et al. A high sensitivity temperature sensor based on packaged microfibre knot resonator[J]. Sensors and Actuators A: Physical, 2017, 263: 369 - 372.

[0086] Literature 6: Jang H, Yoon H, Ko Y, et al. Enhanced performance in capacitive force sensors using carbon nanotube / polydimethylsiloxane nanocomposites with high dielectric properties[J]. Nanoscale, 2016, 8(10): 5667 - 75.

[0087] It can be seen that the Seebeck coefficient of the CMTs / KCl / gelatin composite prepared in Example 1 is 4 mV / K, the tensile strength is 1.7 MPa, and it has the advantages of flexibility, stretchability, and responses to temperature and pressure.

[0088] In addition, the CMTs / potassium chloride / gelatin sensor can also detect the temperature difference on the material surface in contact and non-contact modes in real time and respond to pressure stimuli. When stimulated by both pressure and temperature signals simultaneously, the CMTs / potassium chloride / gelatin sensor will respond to both signals, and the detected voltage is significantly higher than the voltage generated only by pressure induction. In addition, in practical applications, the CMTs / potassium chloride / gelatin sensor can also monitor the movement of the human body (fingers, arms) and the temperature difference between the human body and the environment. These findings provide a new strategy for the production and utilization of flexible sensors with multi-signal detection functions.

[0089] Example 4

[0090] A preparation method of a flexible and stretchable carbon microtube ion thermoelectric supercapacitor, using the ion gel material (CMTs / KCl / gelatin composite material) prepared in Example 1 as the electrolyte and CMTs / MnO2 / foamed copper as the electrode to assemble a flexible and stretchable carbon microtube ion thermoelectric supercapacitor. The specific operation steps are as follows:

[0091] (1) Preparation of carbon microtube dispersion: Disperse 0.1 g of carbon microtubes (CMTs) in 20 mL of deionized water, slowly add 0.1 g of sodium dodecylbenzenesulfonate (SDBS) as a surfactant, and stir until completely dissolved. Continue to add an appropriate amount of concentrated hydrochloric acid (HCl) to the carbon microtube mixture to functionalize the carbon microtubes. Perform ultrasonic treatment on the dispersion system for 30 min and cell disruption treatment for 1 h on an ultrasonic cleaner to initially obtain a well-dispersed CMTs dispersion.

[0092] (2) Preparation of ion gel material: Using gelatin (Gelatin) and carbon microtubes (CMTs) as the main raw materials and KCl as the dopant. Specifically, it includes: Mix the above carbon microtube dispersion, gelatin, and potassium chloride in a certain proportion, and stir in an oil bath at 60 °C for 2 h, then take out to obtain a uniformly mixed ion gel. Subsequently, pour the ion gel into a polytetrafluoroethylene mold to cool and form, take out the solidified gel, and dry it at room temperature in air for 4 h to obtain an ion gel material (CMTs / KCl / gelatin composite material) with an appropriate moisture content, and form it into different thicknesses as needed. In this example, the ratio of the carbon microtube dispersion (CMTs solid content), gelatin, and potassium chloride is 30 mg: 30 wt%: 0.8 M. The formed thickness in this example is 1 mm.

[0093] (3)MnO₂ supported on carbon microtubes: 10 mg of carbon microtubes (CMTs) and KMnO₄ were mixed at a mass ratio of 1:2, placed in a 250 ml round-bottom flask, 100 ml of water was added, and ultrasonically treated at room temperature for 30 min. 10 ml of glacial acetic acid was pipetted and transferred to an oil bath at 70 °C and stirred and refluxed until the purple color of KMnO₄ faded completely. After cooling to room temperature, it was filtered by suction, rinsed repeatedly with ethanol and deionized water, and the product was dried in a vacuum drying oven at 70 °C to obtain a mixture of CMTs and potassium permanganate.

[0094] (4) Preparation of carbon microtube electrodes and assembly of supercapacitors: The prepared mixture of CMTs and potassium permanganate, acetylene black, and PTFE were added to a mortar at a ratio of 8:1:1. A certain amount of absolute ethanol was added dropwise to the mixture of CMTs and potassium permanganate and ground thoroughly until the sample was evenly dispersed to obtain a slurry. The obtained slurry was coated on a copper foam substrate to form an electrode, and the coating area was 10 mm × 10 mm. Then it was transferred to an oven at 80 °C and dried thoroughly. The dried electrode was placed on a tablet press and pressed into a thin sheet at a pressure of 10 MPa to obtain a carbon microtube electrode. The loading amount of the electrode material was calculated by the difference method. Using the ion gel material (CMTs / KCl / gelatin composite material) prepared in Example 1 as the electrolyte, it was bonded to the working electrode to form a carbon microtube ion thermoelectric supercapacitor, and its electrochemical performance was tested.

[0095] Example 5

[0096] Comparative experiment design

[0097] 1. The dosage of the carbon microtube dispersion (CMT solid content) in step (2) of Example 4 was changed (0 mg, 10 mg, 30 mg, 50 mg), and other operations were the same. Ion gel materials with different carbon microtube addition amounts were prepared, and then capacitors with different CMT addition amounts were prepared according to the method of Example 4 and were respectively denoted as: Gelatin(0 mg), Gelatin-0.1CMTs(10 mg), Gelatin-0.3CMTs(30 mg), Gelatin-0.5CMTs(50 mg).

[0098] 2. The ion gel material (CMTs / KCl / gelatin composite material) was prepared as the electrolyte according to the method of Example 4; the carbon microtube supported MnO₂ in step (3) was not set; in step (4), acetylene black and PTFE were added to the mortar at a ratio of 1:1, and the mixture of CMTs and potassium permanganate was not added. Other operations were the same as those in Example 4. The ion gel material (CMTs / KCl / gelatin composite material) was bonded to the working electrode to prepare a Gelatin / CMTs capacitor as a comparative sample.

[0099] 3. The carbon nanotube ion thermoelectric supercapacitor was prepared according to the method of Example 4, denoted as Gelatin / CMTs / MnO2 capacitor.

[0100] 4. The Gelatin capacitor, Gelatin / CMTs capacitor, and Gelatin / CMTs / MnO2 capacitor were compared as capacitor devices with different components.

[0101] 5. According to the method of Example 4, ion gel materials (CMTs / KCl / gelatin composites) with thicknesses of 0.5 mm, 1 mm, and 1.5 mm were formed to prepare corresponding supercapacitors with different electrolyte thicknesses for comparison.

[0102] II. Performance Testing

[0103] Figure 7 Figures are SEM images and EDS spectra. Among them, (a-c) are SEM images of CMTs and CMTs loaded with MnO2 samples, and (e-f) are EDS spectra. Figure 7 (a) The CMTs exhibit regular tubular structures with smooth surfaces and no other impurities. While in Figure 7 (b), the surface of CMTs doped with MnO2 is no longer smooth, and it is obvious that the products decomposed by microwaves are attached. Its appearance is similar to cracked bark and does not have a specific shape. This uniformly dispersed nanostructure is beneficial to the transport of electrolyte ions, can increase the connection between the electrolyte and the electrode material, thereby improving the material utilization rate by 150. This unique structure can not only provide sufficient electrochemically active sites on the surface of CMTs, but also increase the effective liquid-solid interface area, providing a fast channel for the insertion and extraction of electrolyte ions, thus promoting the Faraday reaction. Moreover, the ordered and dense distribution of CMTs can increase the effective area of the active material, promoting the transfer of electrons, the insertion and extraction of ions. In addition, the EDS spectra ( Figure 7 (e-f)) contain elements C, Mn, and O, and the atomic ratio of Mn to O is close to 1:2. These results all indicate that MnO2 is uniformly distributed on CMTs.

[0104] Figure 8 Among them, (a) XPS image of CMTs loaded with MnO2 sample; (b) high-resolution spectrum in the C 1s region; (c) high-resolution spectrum in the O1s region; (d) high-resolution spectrum in the Mn 2p region.

[0105] Figure 8(a) is the XPS curve of MnO2 / CMTs. Chemical composition and element valence. The full spectrum proves the presence of C, N, and Mn elements in the composite material. The proportions of C1s, O1s, and Mn2p are 76.8%, 17.4%, and 5.8% respectively. The atomic ratio of Mn and O in the metal metal oxide is about 1:2, indicating that MnO2 has been successfully prepared. Figure 8 (d) is the high-resolution analysis chart of manganese, where there are three types of peaks: the Mn2p3 / 2 peak at 642.2 eV, the Mn2p1 / 2 peak at 653 eV, and the Mn2p 1 / 2 satellite peak at 662.8 eV. The satellite peak of Mn2p1 / 2 is at 662.8 eV. This corresponds to the specific peak of manganese element. The results show that the main form of manganese existence is Mn 4+ . Figure 8 (b) is the XPS spectrum of high-resolution C1s. The XPS peaks correspond to C (284.1 eV), C (284.9 eV), CO (285.4 eV), and CO (288.9 eV) respectively. As Figure 8 (c) shows, the O1s signal in the XPS spectrum further confirms the presence of manganese dioxide in the composite material. In the XPS spectrum of the MnO2 / CMTs composite material, the peaks located at 529.9 eV and 532.4 eV are attributed to O-Mn-O and O-H respectively. The C-OH bond and Mn-OH bond are prone to etherification at high temperatures to form a C-O-Mn band, thereby binding MnO2 and CMTs together. Making the binding of MnO2 and CMTs more firm. These results show that the main form of manganese existence is Mn 4+ , and MnO2 is amorphous. The formation of the C-O-Mn band is beneficial to the stability of the material.

[0106] The two-electrode system is used to test the electrochemical performance of the capacitor, and the results are as Figure 9 shown. Figure 9 In (a), the CV curves of the ionic thermoelectric supercapacitor at different scanning rates in Example 4; (b) the GCD curves of the ionic thermoelectric supercapacitor at different scanning rates; (c) the area specific capacitance curves of the ionic thermoelectric supercapacitor at different scanning rates and current densities; (d) the EIS curves of the ionic thermoelectric supercapacitor with different CMTs addition amounts in Example 5.

[0107] Figure 9(a) shows the cyclic voltammetry characteristic curves of the carbon nanotube ion thermoelectric supercapacitor at scanning rates from 5 mV / s to 100 mV / s. Each CV curve exhibits excellent symmetry, with the oxidation and reduction currents being close. The response current increases with the increase in the scanning rate, indicating that the device has obvious and reversible pseudocapacitance characteristics. There are no oxidation-reduction peaks in the curves because the oxidation-reduction reaction of MnO2 occurs continuously between -0.6 V and 0.6 V, so no single oxidation-reduction peak can be observed. At 5 mV / s, the specific capacitance of the capacitor is 528.6 mF cm -2 , and as the scanning rate increases to 200 mV / s, the specific capacitance gradually decreases to 54.9 mF cm -2 . This is because when the scanning rate is too fast and the scanning time is extremely short, the ions in the electrolyte do not have enough time to react with all the active materials. K + can only approach the outer surface of the electrode and react only with the surface materials, resulting in a decrease in the charge storage capacity and a downward trend in the specific capacitance. At large scanning rates such as 100 and 200 mV / s, although the capacitor shows certain resistance behavior, at the voltage boundaries of -0.6 V and 0.6 V, the current can respond quickly and change, so the CV curve still maintains a good rectangular-like shape, indicating that the electrode has excellent reversibility. To further study the rate performance and charge-discharge characteristics of the capacitor, the charge-discharge current density is set to 2 - 10 cm -2 , and the charge-discharge test is carried out. The results are as shown in Figure 9 (b). At 2 mA cm -2 , the discharge time is slightly shorter than the charging time, probably because the set current is too small, resulting in insufficient charging power and a long time to reach the set voltage of 0.6 V. As the current density increases, the GCD curve becomes more and more symmetrical triangular shape, and there is a very small voltage drop in the discharge part, indicating that the capacitor has low impedance and excellent reversibility. Figure 9 (c) shows the relationship between the specific capacitance of the carbon nanotube ion thermoelectric supercapacitor and the scanning rate or current density. At current densities of 2, 4, 6, 8, 10 mA cm -2 , the specific capacitances of the capacitor are 417.2, 304.8, 285.3, 253.7, 225.8 mF cm -2 , and the retention rate is 54.1%. Figure 9(d) is the frequency impedance response EIS graph of the Gelatin, Gelatin-0.1CMTs, Gelatin-0.3CMTs, and Gelatin-0.5CMTs capacitors prepared in Example 5. In the high-frequency region, the curve presents a semicircular shape. The Nyquist graph of the capacitor is mainly composed of a semicircle in the high-frequency region and a straight line in the low-frequency region, which respectively show the charge transfer resistance and internal ion diffusion resistance of the sample. Among them, the diameter of the semicircle in the high-frequency region represents the charge transfer resistance R ct , which represents the resistance between the electrode material and the current collector. The smaller the semicircle diameter, the smaller the charge transfer resistance. Among them, the internal resistance of the electrolyte with the addition of CMTs will be reduced. The electrodes or capacitors prepared using foam copper as the current collector are further reduced by adding CMTs active materials doped with MnO2 to improve the conductivity of the current collector. By improving the electrodes of the capacitor, its internal resistance is further reduced. Compared with the Gelatin capacitor, the semicircle diameter of the capacitor with the addition of CMTs is reduced in the high-frequency region, and the charge transfer resistance R of Gelatin-0.5CMTs is ct It is 7.3Ω, which is significantly smaller than the charge transfer resistance of gelatin (20.8Ω); this indicates that the introduction of CMTs enhances the conductivity of the electrolyte and reduces the resistance between it and the electrolyte. The slope of the oblique line in the low-frequency region is also greater than that of Gelatin, indicating that the pore structure and high conductivity of active CMTs reduce the ion transmission resistance. Among them, Gelatin-0.5CMTs has the fastest ion diffusion process, so the capacitance performance is the best, which is consistent with the CV and GCD curves.

[0108] Figure 10 In the figure, (a) is the CV curve of the ionic thermoelectric supercapacitor with different components in Example 5; (b) is the CV curve of the ionic thermoelectric supercapacitor with different components; (c) is the area specific capacitance of the ionic thermoelectric supercapacitor with different components.

[0109] Comparison of electrochemical properties of capacitors prepared under different component conditions in Example 5 Figure 10 shown. Figure 10 (a) is the CV image of capacitors with different components at 50mV / s. The area enclosed by the CV curves of Gelatin / CMTs / MnO2 capacitors and Gelatin / CMTs capacitors is much larger than that of Gelatin capacitors, which indicates that the capacitance contribution mainly comes from the addition of CMTs and MnO2. Figure 10 (b) is 4 mA cm -2GCD characteristic curves of each of the following electrodes. Each curve shows a symmetric triangular shape. Similarly, by adding CMTs and MnO2 active materials, the discharge time of the capacitor has increased significantly, and the Gelatin / CMTs / MnO2 capacitor has the longest discharge time. CMTs have a very high specific surface area, and their unique tubular structure provides a fast transmission channel for ions and electrons, improving the conductivity and carrier migration rate of the capacitor. MnO2 has the advantages of a high voltage window, low price, environmental friendliness, and large theoretical specific capacity, and is one of the ideal active materials for capacitors. The contribution of pure Gelatin capacitors to the specific capacitance is almost negligible. Among capacitors with different components, the Gelatin / CMTs / MnO2 capacitor has the largest specific capacitance. As Figure 10 (c) shows, the areal specific capacitance of the Gelatin / CMTs / MnO2 capacitor is 152.2 mF cm -1 . This may be because the Gelatin / CMTs / MnO2 capacitor has a large specific surface area, and the combination of CMTs and MnO2 has a good synergistic effect. The two synergistically successfully improve the problems of poor conductivity and insufficient charge transfer channels of the single-crystal MnO2 electrode, thereby improving the electrochemical performance of the electrode. In addition, the pore structure distribution in the electrode is suitable with rich pores and contains a large number of functional groups, which is conducive to the rapid transfer and storage of ions, and the ion transport resistance is small. Therefore, the Gelatin / CMTs / MnO2 capacitor has the best electrochemical performance.

[0110] Figure 11 In, (a) CV curves of ionic thermoelectric supercapacitors with different electrolyte thicknesses in Example 5; (b) GCD curves of ionic thermoelectric supercapacitors with different electrolyte thicknesses; (c) Seebeck coefficients of ionic thermoelectric supercapacitors with different electrolyte thicknesses.

[0111] As in Example 5, we prepared ionic thermoelectric supercapacitors with electrolyte thicknesses of 0.5 mm, 1.0 mm, and 1.5 mm respectively, and tested their electrochemical performance. Figure 11 (a) are the CV curves of capacitors with different thicknesses at a scanning rate of 50 mV / s in the voltage window of -0.6 to 0.6 V. From Figure 11 (c), it can be seen that as the electrolyte thickness increases from 0.5 mm to 1.5 mm, the area of the CV curve of the capacitor gradually becomes smaller, and the areal specific capacitance of the capacitor decreases from 189.2 mF cm -2 to 86.6 mF cm -2 . In addition, we carried out constant current charge and discharge tests on these three supercapacitors with different electrolyte thicknesses in the voltage range of -0.6 to 0.6 V and a current density of 4 mA cm -2 , as Figure 11(b). The areal specific capacitances of supercapacitors with electrolyte thicknesses of 0.5 mm, 1.0 mm, and 1.5 mm are 356.3, 304.8, and 253.2 mF cm -2 . It can be found that as the electrolyte thickness increases, the areal specific capacitance of the capacitor significantly shows a downward trend. From Figure 11 (d), the relationship between the electrolyte thickness and the Seebeck coefficient of the CMTs ion thermoelectric supercapacitor can be intuitively observed. As the electrode thickness increases, the Seebeck coefficient of the capacitor first increases and then decreases. When the electrolyte thickness is 1.0 mm, the Seebeck coefficient of the capacitor reaches the maximum value. Considering the comprehensive electrochemical and thermoelectric performances of the capacitor, when the electrolyte thickness is 1.0 mm, the comprehensive performance of the capacitor is the best.

[0112] Figure 12 . Among them, (a) Seebeck coefficient and ionic conductivity of ion thermoelectric supercapacitors with different CMTs addition amounts in Example 5; (b) thermal conductivity of ion thermoelectric supercapacitors with different CMTs addition amounts; (c) power factor of ion thermoelectric supercapacitors with different CMTs addition amounts; (d) ZT i value.

[0113] The addition amount of CMTs has a significant impact on the Seebeck coefficient of the ion thermoelectric supercapacitor, as shown in Figure 12 (a). After multiple Seebeck coefficient measurements, the Seebeck coefficient of the ion thermoelectric supercapacitor without CMTs addition is only 1.54 mV / K, while the Seebeck coefficient of the ion thermoelectric supercapacitor with CMTs addition is greatly improved. When the CMTs addition amount is 30 mg, the Seebeck coefficient of the ion thermoelectric supercapacitor is 4.12 mV / K, with the best performance. As the CMTs addition amount increases, the ionic conductivity of the capacitor also increases significantly, and the ionic conductivity increases from 4.77 mS / cm to 14.2 mS / cm. At the same time, from Figure 12 (b - c), the thermal conductivity and power factor of the ion thermoelectric supercapacitor also increase with the increase of the CMTs addition amount. The minimum thermal conductivity value observed in the capacitor without CMTs addition is 0.21 W m -1 K -1 , and the thermal conductivity of the capacitor reaches 0.44 W m -1 K -1 when the CMTs addition amount is 50 mg; the power factor of the capacitor without CMTs addition is 34.6 μW m -1 K -1, when the addition amount of CMTs is 50 mg, the power factor of the capacitor is 322.17 μW m -1 K -1 . In addition, as Figure 12 (d) shows, the ZT i value of the ionic thermoelectric supercapacitor first increases and then decreases with the increase of the addition amount of CMTs. When no CMTs are added, the thermoelectric figure of merit ZT i of the capacitor is 0.012. When the addition amount of CMTs is 30 mg, the thermoelectric figure of merit ZT i of the capacitor is about 0.018. After that, with the increase of the addition amount of CMTs, the thermoelectric figure of merit ZT i gradually decreases, which indicates that the addition of CMTs promotes the improvement of the thermoelectric figure of merit of the capacitor.

[0114] As Figure 13 shown is the working principle diagram of the carbon nanotube ionic thermoelectric supercapacitor of Embodiment 4 of the present invention.

[0115] The ionic thermoelectric supercapacitor can complete the storage of electrical energy while realizing thermal energy conversion. That is, in the presence of a temperature difference, the low-grade thermal energy in the human body or the environment is collected and converted into electrical energy and stored in the supercapacitor. Figure 13 shows four stages of the ionic thermoelectric supercapacitor converting thermal energy into electrical energy and storing it. Stage Ⅰ is the directional thermal diffusion of K + ions in the presence of a temperature difference. When heat is applied to one end of the capacitor, the temperature difference (ΔT) between the two electrodes causes the moving K + to diffuse to the cold side, leaving immobile anions (Cl - ) on the hot side. Therefore, the concentration difference of K + between the cold electrode and the hot electrode generates a thermally induced voltage, as shown in the figure. The concentration difference at both ends of the electrolyte is caused by ion migration, and the existence of the concentration difference leads to the formation of a potential difference. This open-circuit voltage is called the thermal voltage. Due to the potential imbalance between the interfaces, charge transfer cannot be completed between the electrode and the electrolyte interface without forming a path. At this time, in Stage Ⅱ, the temperature difference is kept constant and the external circuit is connected. When there is a load (a 5 kΩ resistor in this experiment), electrons will flow from the hot side to the cold side. Due to the potential difference, electrons flow from the hot side to the cold side through the external circuit and accumulate electrons in the electrode. Electrons accumulate in the cold electrode until the transferred electrons and the K +Equilibrium. However, due to the temperature difference, the ion concentration difference at both ends of the electrolyte still exists, and a double electric layer is formed between the electrode and the electrolyte interface. In Stage III, the temperature difference is removed, and at the same time, the connection between the two electrodes is disconnected. Since the temperature difference is eliminated, the thermally diffused ions on the cold side return to their initial state, and the thermodiffusion effect gradually disappears. The ion concentration difference at both ends of the electrolyte is eliminated. However, at this time, the charge on the cold-side electrode cannot be transferred due to the formation of an open circuit, resulting in the supercapacitor finally showing a negative voltage opposite to the thermal voltage initially formed by ion thermodiffusion. In Stage IV, a load resistor is connected. By connecting the load resistor, the electrons accumulated on the cold-side electrode are released, and the electron charge flows back from the cold-side electrode to the hot-side electrode, and the voltage tends to balance.

[0116] Figure 14 Thermal charging curves of the carbon nanotube ion thermoelectric supercapacitor of Example 4 under different temperature differences; (a) 5K; (b) 10K; (c) 15K; (d) 20K.

[0117] By testing the thermal charging conditions of the ion thermoelectric supercapacitor under different temperature gradients, we prove that the ion thermoelectric supercapacitor can meet the actual needs in real application scenarios such as the field of intelligent manufacturing and human skin under different temperature conditions. Figure 14 (a-d) show the thermal charging curves of the ion thermoelectric supercapacitor when the temperature difference increases from 0K to 20K. It can be seen from the figure that the ion thermoelectric supercapacitor can exhibit stable thermoelectric output performance under various temperature conditions and can operate effectively under large temperature differences. In addition, as the temperature difference of the ion thermoelectric supercapacitor increases, the thermal voltage output by the capacitor also almost increases linearly, and its maximum output voltage can reach 81.6 mV.

[0118] Figure 15 Among them, (a) Charge transfer amount of the carbon nanotube ion thermoelectric supercapacitor of Example 4 during charge and discharge under different temperature gradients; (b) Charge transfer efficiency of the ion thermoelectric supercapacitor during charge and discharge under different temperature gradients.

[0119] To better evaluate the charge storage and transfer capabilities during the operation of the carbon nanotube ion thermoelectric supercapacitor, by deforming the charge and discharge curves of the capacitor in the equivalent circuit into current-time curves and integrating the current-time curves, the charge stored during the charging process and the charge transferred during the discharging process are calculated respectively. It should be emphasized that the equivalent circuit can only approximately represent the circuit conditions when the ion thermoelectric supercapacitor operates and is not exactly the same. As Figure 15 (a) shows, as the temperature difference increases, the amount of charge transferred during the charge and discharge process also increases. In addition, the amount of charge transferred during discharge is usually less than that during charge. This is mainly due to the self-discharge phenomenon of the supercapacitor during the charge balance time and the voltage drop consumed by the internal series resistance load. Figure 15(b), at relatively low temperature differences, the output voltage of the ionic thermoelectric supercapacitor is almost linearly related to the temperature gradient. When the temperature difference is 2K and the output voltage is 8mV,

[0120] Q discharging / Q charging = 94.2%, when the temperature difference is 12K and the output voltage is 40mV, Q discharging / Q charging = 82.4%.

[0121] Figure 16 In (a), it is the actual application diagram of the ionic thermoelectric supercapacitor of Embodiment 4 of the present invention; (b) is the photo of the ionic thermoelectric supercapacitor lighting the LED under the condition of 11K; (c) is the infrared thermal imager picture and the measured picture of the ionic thermoelectric supercapacitor.

[0122] To demonstrate the potential application of the ionic thermoelectric supercapacitor prepared in Example 4 in collecting low-grade thermal energy at room temperature and in cold environments, we connected the capacitor with a light-emitting diode to form a circuit, and then placed the capacitor between two thermocouples. By stimulating the temperature difference, we observed whether the capacitor could convert thermal energy into an electrical signal. As Figure 16 shown, when there is no temperature gradient, the diode has no brightness, indicating that no voltage signal is generated. When the capacitor is in a temperature gradient of about 11K (T c = 23.8°C, T h = 34.6°C), the cations and anions in the electrolyte of the capacitor move towards the two electrodes respectively under the drive of the temperature difference, generating a thermal diffusion effect. The ions accumulate on the two electrodes of the capacitor, and then a voltage difference is generated. A potential is generated inside the capacitor. Under a constant temperature gradient, the capacitor outputs voltage and current, and the output voltage and current reach a stable state. Then, the capacitor can continuously light the LED lamp tube through a voltage amplifier. When the temperature gradient gradually disappears, the voltage and current decrease, and the LED goes out. The results show that the ionic thermoelectric supercapacitor can continuously collect low-grade thermal energy. In a low-temperature environment, the ionic thermoelectric supercapacitor shows great potential in powering soft and stretchable electronic devices during polar and space exploration. For the future development of high-efficiency ionic thermoelectric supercapacitors in various application scenarios, it is also helpful to combine the solar thermal effect, meta-structure design and passive radiative cooling technology.

[0123] Therefore, the present invention uses a CMTs / KCl / gelatin composite material as a solid electrolyte, in-situ synthesizes carbon microtube / manganese dioxide (CNTs / MnO2) active material using CMTs, prepares a capacitor electrode with copper foam as the current collector, and assembles a novel ion thermoelectric supercapacitor. The CMTs / KCl / Gelatin electrolyte is used to convert thermal energy into electrical energy and then store charges simultaneously. By adding CMTs / MnO2 to the electrode, the disadvantage of the low conductivity of the capacitor is greatly improved. This capacitor has good electrochemical energy storage characteristics, with a voltage window of up to 1.2 V, an ionic conductivity of up to 14.2 mS / cm, and an areal specific capacitance of up to 152.2 mF / cm² when the scan rate is 50 mV / s. 2 Meanwhile, as an electrochemical energy storage device, the ion thermoelectric supercapacitor can also convert low-grade thermal energy into electrical energy and store and utilize it in real time. The assembled ion thermoelectric supercapacitor achieved a relatively high output of 81.6 mV of ion thermal voltage at ΔT = 20 K, and at this time, the capacitor had a Seebeck coefficient of 4.12 mV / K. In addition, the ion thermoelectric supercapacitor can light up an LED and provide a stable voltage output.

[0124] The number of devices and the scale of processing described here are used to simplify the description of the present invention. Applications, modifications, and variations of the present invention will be apparent to those skilled in the art.

[0125] Although the embodiments of the present invention have been disclosed as above, it is not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and the illustrated and described examples here.

Claims

1. A method for preparing an ionic gel material, characterized in that, Comprising: Preparing a carbon nanotube dispersion liquid, mixing the carbon nanotube dispersion liquid, gelatin and potassium chloride evenly, and forming and drying to obtain the ion gel material; wherein, the ratio of carbon nanotubes, gelatin and potassium chloride is: 20 - 40 mg: 25 - 30 wt%: 0.8 M.

2. The preparation method of the ionic gel material according to claim 1, characterized in that, The ratio of carbon nanotubes, gelatin and potassium chloride is: 30 mg: 30 wt%: 0.8 M.

3. The preparation method of the ionic gel material according to claim 1, characterized in that, Specifically including: 1) Disperse carbon nanotubes in deionized water, slowly add sodium dodecylbenzenesulfonate as a surfactant, and stir until dissolved; continue to add HCl, and perform ultrasonic dispersion and cell disruption treatment to obtain a carbon nanotube dispersion liquid; 2) Mix the above carbon nanotube dispersion liquid, gelatin and potassium chloride in a ratio of 30 mg: 30 wt%: 0.8 M, and stir in an oil bath at 60 °C, take out to obtain a uniformly mixed ion gel; pour the ion gel into a mold to cool and form, take out the solidified gel, and dry it under air room temperature conditions to obtain the ion gel material.

4. An ionic gel material, characterized in that, Prepared by any one of the preparation methods of claims 1 - 3.

5. Application of an ion gel material prepared by any one of the preparation methods of claims 1 - 3 in a temperature sensor and / or a pressure sensor.

6. A preparation method of a carbon nanotube ion thermoelectric supercapacitor, characterized in that, Using the ion gel material prepared by any one of the preparation methods of claims 1 - 3 as an electrolyte, and assembling it with electrodes to form the carbon nanotube ion thermoelectric supercapacitor.

7. The preparation method of the carbon nanotube ion thermoelectric supercapacitor according to claim 6, characterized in that, Prepare carbon nanotubes loaded with MnO2, then coat it on the surface of the electrode, and then assemble it with the ion gel material to form a carbon nanotube ion thermoelectric supercapacitor.

8. The preparation method of the carbon nanotube ion thermoelectric supercapacitor according to claim 7, characterized in that, The thickness of the ion gel is 1 - 1.5 mm.

9. A carbon nanotube ion thermoelectric supercapacitor prepared by the preparation method of any one of the carbon nanotube ion thermoelectric supercapacitors of claims 6 - 8.

10. Application of a carbon nanotube ion thermoelectric supercapacitor prepared by the preparation method of any one of the carbon nanotube ion thermoelectric supercapacitors of claims 6 - 8 as a device for collecting low-grade heat energy at room temperature and in cold environments; or as an application of a device for simultaneously realizing heat energy conversion and completing electrical energy storage.

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