Preparation And Thermal Performances Of Carbon Material-based All-solid-state Supercapacitors

With the rapid growth of demand for clean energy and new intelligent electronic products,the development of energy storage technology plays an important role in ensuring efficient and sustainable energy supply.The supercapacitor as an efficient electrochemical energy storage device has attracted more and more attention due to its outstanding advantages such as high power density,fast charge and discharge rate,long cycle life and no pollution.However,temperature has a great influence on the performance of supercapacitors,especially in the environment of high temperature or extreme low temperature.Therefore,exploring the impact of ambient temperature on the performance of supercapacitors is critical to its practical application.In addition,effective thermal management of supercapacitors for reducing the effect of temperature on their electrochemical performance is of great significance to improve the safety,performance and life of practical applications.In view of this,two high-performance all-solid supercapacitors were fabricated using the flexible carbon materials（carbon cloth and carbon nanotube film）,carbon cloth/polypyrrole（CC/PPy）and carbon nanotube film（CNF）/reduced graphene oxide（r GO）/polyaniline（PANI）as the electrodes,respectively,and their electrochemical performances at various temperatures were studied.A simple electrochemical co-deposition method was used to embed phase change microcapsules（MPCMs）with high latent heat into a CNF-based porous electrode to realize the in-situ thermal management of the supercapacitor.The detailed research contents of this thesis were shown as follows:（1）The carbon cloth/polypyrrole electrode was prepared by a facile electrochemical deposition method,and the all-solid-state supercapacitor was assembled with the PVA-H₃PO₄gel electrolyte.The impact of deposition time（100s,200s,300s,400s,500s）on the performances of both the CC/PPy electrode and the all-solid-state supercapacitor were investigated.The electrochemical performances of CC/PPy supercapacitors at various ambient temperatures（0℃,20℃,40℃,60℃）were studied.The experimental results show that the areal specific capacitance of the CC/PPy electrode was 341.78 m F cm^-2 with the deposition time of 400s,and the areal specific capacitance of the CC/PPy supercapacitor reaches to 110.6 m F cm^-2.The electrochemical test at various ambient temperatures show that the capacitance of the CC/PPy supercapacitor elevates and the internal resistance decreases with the increase of ambient temperature,however,when the temperature varies from 40℃to60℃,the capacitance decreases due to the aging of the electrolyte.In addition,the rise of temperature will accelerate the self-discharge of the supercapacitor,and thus the device is not suitable to work at high temperature for a long time.（2）We,for the first time,implanted MPCMs into the three-dimensional porous reduced graphene oxide/polyaniline（GP）framework based on the flexible CNF substrate by one-pot electrochemical co-deposition process.The supercapacitor was assembled using the prepared hybrid electrode and PVA-H₂SO₄ gel electrolyte.The results show that the CNF/GP/MPCMs supercapacitor has a enthalpy of 24.8 J g^-1.At the various ambient temperatures（15～45℃）,the implantation of MPCMs makes the capacitance fluctuation rate of supercapacitor decrease by 0.16 m F cm^-2℃^-1,which improves the electrochemical stability of the supercapacitor.The areal specific capacitance of CNF/GP/MPCMs supercapacitor can reach to 66.34 m F cm^-2 at a scan rate of 5 m V s^-1.After 6000 charge/discharge cycles,the capacitance can still maintains90.2%.Moreover,under various bending angles,the capacitance nearly unchanged,and 94.1%of the initial capacitance can be retained after 500 times of repeated bending,indicative of excellent mechanical properties.