In-situ SEM Construction And Study Of Micro-supercapacitor

Minimization of the energy storage and conversion devices has been widely considered a notable feature of current technology trends.Supercapacitor has attracted great attention as a typical energy-storage technology with high power density,long cycling life,etc.Carbon nanomaterials are well known as ideal electrode materials due to their high conductivity,specific surface area,as well as excellent mechanical strength.However,energy capacities of conventional supercapacitor cells are far below the theoretical expectations due to low transferability of charge carriers in the randomly overlaid graphene electrodes.In this thesis,by using in-situ electron microscopy,we for the first time,construct the world's smallest supercapacitor consisting of single carbon nanofiber or few layers graphene as electrodes and tiny all solid PVA/H2SO4 or ionic liquid EMIMBF4 as electrolytes inside a SEM.We explore the limits of their supercapacitor performances,such as specific capacity,energy density and power density.Such in-situ experiments also offer the platform for direct visualization of the interactions between graphene electrodes and the electrolyte ions,thus opening up different avenues for deeper understanding and developing high-performance supercapacitors.The main results of this thesis are summarized as follows:By using the EDS elemental mapping technique,we are able to "see" the diffusion process of the electrolyte ions on the surface of graphene electrodes.Moreover,we find the solidification of solid the ionic liquid electrolyte can indeed block the channels for ion transport.By conducting in-situ SEM electrochemical tests,we obtained nearly rectangular cyclic volt-ampere curves,indicating typical characteristic of double-layer capacitor of these tiny supercapacitors.The specific capacity of the carbon nano-electrodes with different sizes were tested by galvanostatic charge-discharge curve in ionic liquid EMIMBF4 electrolyte,and the maximum values of 284.55F/g and 220.59F/g were calculated from carbon nanofiber and graphene electrode respectively.We also find the specific capacity decreases with the increasing current density.Due to the solidification of the electrolytes and the difficulty in the mirco-supercapacitor construction,the measured the specific capacity are still far below the expectations.Nevertheless,we believe this pioneering attempt will offer extremely valuable visions for the study of future supercapacitors.