Fabrication and characterization of chromium nitride (CrN) based micro-supercapacitors

Abstract

The aim of this thesis work is the elaboration of micro-supercapacitor electrodes based on chromium nitride(CrN)deposited on a silicon current collector.Their electrochemical performance can be improved by increasing their specific surface area and/or porosity for better accessibility of the electrolyte to the active material to improve their charge storage.The first part of the first chapter is devoted to the state of the art on supercapacitors and microsupercapacitors as well as the different energy storage systems,various types and applications of supercapacitors and their storage mechanisms.In the second part,we describe the composition of a supercapacitor as well as materials and electrolytes used for the fabrication of supercapacitors.The second chapter concerns the fabrication of electrodes based on a thin film of chromium nitride(CrN)deposited by bipolar magnetron sputtering at a glancing angle(PVD-GLAD). The use of this new technique allows controlling the morphology of the surface of the electrodes which directly affected their storage capacity.Subsequently,we will describe the fabrication of a micro-device with an inter-digital configuration based on chromium nitride with good electrochemical performances.The third chapter is dedicated to the development of composite electrodes based on silicon nanowires (SiNWs)synthesized via a VLS mechanism and coated with a thin layer of highly pseudo-capacitive material of CrN.Post-coating SiNWs with CrN can offer benefits,such as enhanced faradaic capacitance and electrical conductivity of the composite made of the metal nitride and SiNWs.Furthermore,the double-layer capacitance of the SiNWs with a large specific surface area can be added to that of CrN.The fourth chapter focuses on the development of composites electrodes made with carbon nanowalls (CNW) decorated with CrN.We will describe the benefits of using a template with a large specific urface area on the electrochemical performance of the composites electrodes.The large surface area of CNW and their good electrical conductivity allows improving not only the areal capacitance of CrN based electrodes but also its cycle life.Subsequently,we will describe the fabrication of a micro-device with a staked configuration based on CNW-CrN electrodes with robust electrochemical stability over 30000 cycles.iv Finally, the conclusion summarizes the obtained results during this thesis as well as the prospects envisaged.