Design And Synthenis Of Flexible Electrode And The Application In Supercapacitors

Flexible supercapacitor is a kind of high power density,long cycle life,cheap and safety of new type energy storage device.With the development of flexible electronics,flexible supercapacitor has great application prospect in flexible energy storage system.This paper scientific summarized the research progress of supercapacitor,and introduces the research status of flexible electrode for flexible supercapacitor.We focused on design,synthsis of bimetal oxides,porous carbon and freestanding carbon foam electrode and explored their applications in flexible supercapacitors,flexible all solid state supercapacitor and compressible supercapacitor.The main works are listed as follows:（1）Amorphous honeycomb-like NiMoO₄ ultrathin nanosheets were synthesized on flexible Ni foam substrate via a facile electrochemical method followed by thermal treatment process.The as-prepared honeycomb-like NiMoO₄ nanosheets with interconnecting nanoscale pore channels and an ultrathin structure provide a large electrochemical active area,which facilitates electrolyte immersion and ion transport and provides effective pathways for electron transport.The ultrathin mesoporous NiMoO₄ NSs on Ni foam with strong adhesion were directly evaluated as a binder-free electrode for SCs,resulting in the high specific capacity(1694 F g^-1 at 1 A g^-1 and 1220 F g^-1 at 50 A g^-1)with outstanding rate performance and excellent cycling stability（92.7% after 9000 cycles）.Moreover,a high energy density(43.5 Wh kg^-1 at 500 W kg^-1)was obtained for the symmetric supercapacitor composed of two pieces of NiMoO₄ electrode.（2）A new kind of high-performance nitrogen-doped nanoporous carbon electrode with large surface area and abundant micropores/mesoporous was derived from a conveniently available fruits waste（shaddock peels）and commercial melamine as nitrogen source via a facile pyrolysis process.Electrochemical measurements show that the as-synthesized NPC electrodes possessed a remarkably large capacitance of 321.7 F g^-1 with good rate capability and excellent long-term cycling stability.Such the excellent electrochemical performance was achieved by shortening the diffusion distance,increasing electrode-electrolyte contact area and improving the electron conductivity of NPC electrode arising from its nanoporous architecture and nitrogen doping.As a prototype,an all-solid-state ASC device based on the NPC negative electrode and a MnO₂ positive electrode achieved an ultrahigh energy density of 82.1 Wh Kg^-1 at a power density of 899 W Kg^-1.Moreover,the as-prepared devices display outstanding flexibility and mechanical properties under bend and fold states.（3）A new type of foam-like nitrogen-doped carbon with high resiliency and stability for high-performance electrodes in compressible SCs.Benefiting from the rich nitrogen content,electrodes prepared from NCFs exhibited extraordinary wettability.Furthermore,the resulting NCFs can bear a compressive strain as high as 80% and show no obvious volume reduction under at a constant strain of 55% after 100 cycles of compression due to its superior structural flexibility and high porosity.When evaluated as an electrode material for SCs,the NCF electrodes exhibited a remarkable areal and specific capacitance of 332 m F cm^-2 and 52 F g^-1 at a current density of 1 m A cm^-2,respectively.An integrated all solid-state symmetric supercapacitor evice based on NCF electrodes can be compressed arbitrarily under 60% strain without significant changes in electrochemical performance.（4）Based on previous work,we reported a smart etching and catalytic process to distinctly enhance the degree of graphitization and specific surface area of NCF electrodes using commercial KMnO₄ as the etchant and catalyst precursor.Our strategy to improve the electrochemical performance by etching the NCF electrode can be grouped as follows: i)a melamine sponge（MS）precursor was etched with KMnO₄ solution,yielding an ENCF consisting of exfoliated carbon fibers with more ion-accessible surface area sites;ii)MnO₂（derived from the pyrolysis of KMnO₄）as a graphitization catalyst can improve the degree of graphitization of ENCF,and thus contribute to high electric conductivity;iii)a small quantity of MnO₂ nanoparticles embedded in ENCF can produce extra pseudocapacitance.and iv)hierarchical micro-,meso-,and macropores channels formed a rapid ion and electron transport network for further improvement in the rate performance.