Flexible Solid-state Supercapacitors Based On Hydrogel Electrolytes:Key Materials And Devices

In recent years,with the rapid development of portable and wearable electronic devices,such as human-machine interfaces,electronic skins,wireless communication devices,and intelligent robots,there is an urgent need for matched energy storage devices to provide power and energy for them,which makes higher requirements for energy storage devices.In order to meet practical applications,energy storage devices are required to have high energy density,high power density,high security and wearability.Flexible solid-state supercapacitors have attracted attention due to their high safety,high power density,long cycle lifetime,and good mechanical properties.However,most of the flexible solid-state supercapacitors reported in the literature only have single dimensional flexibility(such as bendability),and cannot adapt to applications in all wearable scenarios.Therefore,research on flexible solid-state supercapacitors with stretchability,compressibility,and even arbitrarily deformable is necessary;yet the exploration for these supercapacitors is still in its infancy,and relevant reports are limited.At present,most of the gel electrolytes used in solid-state supercapacitors are polyvinyl alcohol-based hydrogel electrolytes,while these electrolytes are not stretchable and compressible.Therefore,it is significant to develop new-type hydrogel electrolytes with good electrochemical performances,excellent mechanical properties and high safety.This dissertation deals with key materials such as hydrogel electrolytes and carbon electrode materials for flexible solid-state supercapacitors,and studies on flexible solid-state supercapacitors,planar miniature supercapacitors,and zinc-ion hybrid capacitors based on hydrogel electrolytes and carbon electrode materials.The preparation technology,electrochemical performances and mechanical properties of self-powered systems were also investigated.The main research contents are as follows:First,kelp activated carbon electrode materials with unique 3D structure and hierarchical pore structure,and novel sodium alginate hydrogel electrolyte materials were synthesized using kelp as precursor.The effects of the 3D structure and carbon pore structure on the storage characteristics of electric double layer capacitors and the electrochemical performances of sodium alginate hydrogel electrolyte were studied.The research results show that sodium alginate hydrogel electrolyte has high ionic conductivity,suitable electrochemical window,high safety and biocompatibility.The assembled all-kelp solid-state supercapacitors have high specific capacitance,high energy density,low equivalent series resistance and interface resistance,and good high-temperature electrochemical stability.Then,in order to improve the mechanical flexibility and toughness of the sodium alginate hydrogel,solid-state electrolyte and electrode materials based on the sodium alginate/polyacrylamide dual-networks hydrogel substrate were prepared.The microstructure and mechanical tensile/compressive properties of the dual-networks hydrogel electrolyte and electrode materials,as well as the arbitrary deformation function and electrochemical performances of the assembled all-hydrogel supercapacitors were studied.The research results show that the device has excellent electrochemical stability under a variety of severe deformation conditions(such as: stretching,compression,twisting,knotting,folding,rolling,crumpling,etc.)due to the strong interface adhesion between the electrode and the electrolyte.Finally,to further increase the energy density of the supercapacitors,zinc-ion hybrid capacitors were prepared using kelp activated carbon as cathode active material,zinc foil as anode,and zinc trifluoromethanesulfonate aqueous solution as electrolyte.The ion sieving effect of kelp activated carbon,the energy storage mechanism,electrode reactions and electrochemical performances of zinc-ion hybrid capacitors were investigated.In addition,employing screen printing technology and zinc trifluoromethanesulfonate hydrogel as solidstate electrolyte,miniature and flexible solid-state zinc-ion hybrid capacitors with planar interdigital electrode structure were prepared.The capacitance storage characteristics and mechanical properties were also studied.By integrating the miniature zinc-ion hybrid capacitors with solar cells,the obtained flexible self-powered system exhibits good photoelectric performances,mechanical flexibility,electrochemical stability,and wearability.In this dissertation,the electrode components,hydrogel electrolyte components,and energy storage mechanism of flexible solid-state supercapacitors are systematically studied.It is significant for the preparation of flexible solid-state supercapacitors with high performances and other solid-state energy storage devices.