Preparation Of The Porous Nickel Yarns For Flexible Wire-shaped Supercapacitor Electrodes

With the development of flexible wearable electronic sand its huge growth in market,flexible linear supercapacitors have been step into our daily life.Flexible wearable electronic devices bring new requirements to energy system,and it is a frontier topic to develop flexible,lightweight,high-capacity batteries and supercapacitors.Specifically,wire-shaped flexible devices have been widely investigated due to their wearability and flexibility in all dimensions.The core part of wire-shaped supercapacitors is their linear electrodes,mainly including carbon fibers,carbon nanotube（CNT）fibers,graphene fibers and metal wires decorated with active materials.Compared with carbon-based fibers,metals wires owning better conductivity and mechanical properties,is suitable for large-scale preparation and knitting manufacture by machines.However,commercial metal wires bear large density,smooth surface and small specific surface area,bring much difficulty to deposite active materials and lowing the capacity of the whole electrodes.In this thesis,porous nickel-foam yarns（PNYs）have developed to low the density and increase the specific surface area of the wire-shaped current collectors.The PNYs with hollow structure were prepared using nylon yarns as template through chemical nickel-plating,nickel electroplating and the post-process of high temperature reduction calcination.Taking the advantage of capillary action possessed by the PNYs,CNTs and graphene were deposited onto the Ni yarns by solution adsorption.The so-constructed supercapacitor electrodes were assembled into all-solid wire-shaped devices.Our works bring a novel route to prepare high-quality current collectors and electrodes.1.The special porous and hollow structure of PNYs features its intrinsic capillary action,allowing CNTs deposited to the surface or pores of PNYs via a facile solution imbibition to form CNTs-PNY electrodes.The CNT loading could reach 33 mg m^-1 due to the high efficient adsorption of CNTs by PNYs.The CNTs-PNY composite electrodes showed outstanding electrochemical property,excellent mechanical durability and flexibility.The volume capacitance of the wire electrode can reach 28.04 F cm^-3 at a current density of 0.2 A cm^-3.2.Graphene were deposited onto PNY substrate by the heating reduction of graphene oxide.Then MnO₂ nanosheet were grown on graphene by hydrothermal process to form MnO₂-Graphene-PNY composite electrodes.The MnO₂-Graphene layer tightly bonded with PNY substrate.The incorporation of MnO₂ significantly increase the capacitance of the wire-shaped electrodes.The volume capacitance of MnO₂-Graphene-PNY composite electrode is 34 F cm^-3 at current density of 0.2 A cm^-3,five times of that of Graphene-PNY electrode.The electrodes show a capacitance retention of above 82.3% over 1000 cycles,revealing its outstanding electrochemical stability.