Study On The Construction And Performance Of Compressible Electrochemical Capacitors Based On Sponge Substrate

Electrochemical capacitors?ECs?are a low-carbon,green,and energy-efficient energy storage devices.In recent years,consumer electronics that smaller,wearable,foldable,compressible,and portable have emerged and developed rapidly,the light,and flexible energy storage devices ECs that can provide energy are receiving attention.Polypyrrole?PPy?as one of the conductive polymers has become a promising active electrode material due to its inherent flexibility,non-toxicity,good electrical conductivity,and ease of synthesis.In this paper,carbon fibers?CFs?were embedded in melamine sponge?MS?,and composite materials were prepared by galvanostatic deposition and in-situ gas-phase polymerization.The capacitance properties of the flexible and compressible ECs were studied.?1?Here the melamine sponge?MS?has been chosen as the carrier to integrate the electrodes of capacitors because of its compressible and porous structure.Two bunches of carbon fibers sewn into the middle of the MS are used as electrodes to electrochemically deposit the polypyrrole doped with anion of dodecyl benzene sulfonate,then the symmetric capacitors are obtained after the gel electrolyte of LiClO₄/polyvinyl alcohol?LiClO₄/PVA?is added into the pores of the MS.The performances of the electrochemical capacitor with electrodes integrated in the MS have been evaluated by electrochemical methods in different electrolytes.The results show that the capacitors exhibit better performance in LiClO₄/PVA than in LiCl/PVA,and that the optimal capacitor can retain 98.2%capacitance after 10000 cycles,and the capacitances of the capacitors become slightly bigger under bending and compressing states compared with their normal state.The capacitors connected in parallel and series show a good electrical relationship,four cells connected in series can turn on a light emission device after being charged,indicating that the flexible capacitor exhibits potential practical application.?2?Polypyrrole?PPy?doped with phosphate ions has been electrochemically deposited on the carbon fibers?CFs?embedded in melamine sponge?MS?to obtain the flexible integrated electrochemical capacitors?ECs?electrodes?PPy-CFs/MS/PPy-CFs?.The ECs prepared from the PPy-CFs/MS/PPy-CFs based on H3PO4/polyvinyl alcohol?PVA?gel electrolyte exhibit good performance and excellent cyclic stability.In order to get high output potential difference in single EC device with aqueous electrolyte,the devices with internal tandem structure have been fabricated through alternately dividing and insulating the PPy-CFs electrodes embedded in MS.The measurements of cyclic voltammetry and galvanostatic charge/discharge reveal that the devices containing two,three,four and five ECs internally connected in series have a good electric relationship,and single device containing five internal tandem ECs can easily achieve 3.0 V output potential difference and light up a light emitting diode.Furthermore,under compressing,bending and twisting conditions,the performances of the devices are almost unchanged compared with those under normal state.This method will open a new strategy to fabricate flexible and compressible energy storage devices with relatively high voltage output and compact structure.?3?The CFs/MS-PPy electrode was prepared by in-situ gas-phase polymerization,which use MS embedded with CFs?CFs/MS?as the flexible substrate and iron p-toluenesulfonate as the oxidant.Further more,compressible ECs ECs-CFs/MS-PPy-70 was successfully assembled.When there is no compression deformation,ECs-CFs/MS-PPy-70 has good capacitance performance and can retain 90.4%of the initial capacitance after10000 cycles.When the compression deformation gradually increases from0%to 60%,the ECs-CFs/MS-PPy-70 can still work normally,and at larger scan rates and current densities,the capacitance value gradually increases,indicating the improvement of the rate capability of ECs-CFs/MS-PPy-70,demonstrating the great promise of this type of compressible ECs.