Flexible Stretchable Ionic Thermoelectric Supercapacitors

As one of the most common energy sources in nature,thermal energy mostly is produced by the sun,the burning of fossil fuels,and the cooling of equipment.Among them,low-grade thermal energy,such as the temperature difference between the human body and the surrounding environment and the heat generated during the use of micro-equipment,are easily dissipated and difficult to collect and reuse.In recent years,the rise of thermoelectric materials and their devices show the great application potential in the field of thermal energy harvesting.However,the existing problems still hinder their practical application:such as,the traditional electronic thermoelectric materials have low Seebeck coefficient,that is,the thermal voltage generated under a certain temperature difference cannot meet the voltage demand of most electrical devices,and the output power is insufficient.In addition,most inorganic semiconductor thermoelectric materials lack the flexibility,which limits their application of flexible,wearable or portable electronic devices.Although the available thermoelectric devices could convert the thermal energy into electricity,they are difficult to storage the produced electricity.In view of the above problems,ionic thermoelectric gel electrolytes,two tungsten sulfide(WS₂)/carbon nanotube(CNTs)thin film electrodes and extensible CNTs hydrogel electrodes were prepared.Based on this,this thesis constructed flexible all solid-state supercapacitors and stretchable ionic thermoelectric supercapacitors.We also studied the electrochemical properties of high-performance hybrid film electrodes,thermoelectric properties of ionic thermoelectric hydrogel electrolytes,and the synergistic feasibility of ionic thermoelectric supercapacitors in energy conversion and storage.The work mainly includes the following three parts:CNTs were introduced into the Two-Dimentional Transition Metal Sulfide WS₂.A hybrid thin film electrode for WS₂/CNTs with an anti-stack skeleton structure was constructed by self-assembly of extraction filtration and freeze-drying.The thin film electrode has good flexibility and decent electrochemical performance.When the scanning rate is 20 m V/s,the maximum specific capacitance could reach up to 752.53 m F/cm².After 10000 cycles,the capacitance only loses 1.28%.The specific capacitance of the corresponding flexible supercapacitor is 574.65 m F/cm²,after 10000cycles of charging and discharging under bending state,and the capacitance loss is 23.12%.A polyacrylamide-carboxymethyl cellulose sodium double network hydrogel was constructed by physical and chemical crosslinking.This ionic thermoelectric hydrogel has excellent thermoelectric properties,with a high seebeck coefficient of 17.1 m V/K,high ionic conductivity of26.1 m S/cm and low thermal conductivity was 0.21 W/m K.In addition,the tensile ionic thermoelectric electrolyte has good mechanical properties and transparency.The optimum elongation at break is 235%and the corresponding tensile strength is 0.71 MPa.Under the tensile strength of 150%,the Seebeck coefficient(10.4 m V/K)and conductivity(22.6 m S/cm)of the ion thermoelectric hydrogel electrolyte were maintained at a good level.High performance stretchable hydrogel electrodes were prepared by introducing the CNTs into polyacrylamide hydrogels.A flexible stretchable ionic thermoelectric supercapacitor was constructed using the ionic thermoelectric hydrogel electrolyte prepared in Chapter 2 and CNTs hydrogel electrode.The supercapacitor firstly performs the thermal to electrical conversion by the ionic thermoelectric electrolyte,and then stores the electricity within a CNTs hydrogel electrode.When the temperature difference between the human body and the environment is 2 K,the output voltage of the ionic thermoelectric supercapacitor can reach up to 30 m V.In addition to being an energy converter,the supercapacitor can also be used as a high-performance energy storage device.The voltage window of a single supercapacitor can reach 2 V.This is due to the excellent capacitance characteristics of CNTs hydrogel electrode and high concentration electrolyte.