High performance supercapacitors using non-aqueous electrolytes

Abstract

This thesis deals with a central theme on “development of non-aqueous electrolytes for supercapacitor devices”. Selecting appropriate salts compatible with non-aqueous solvents to prepare the final electrolytes while understanding the chemistry of the charge storage is the skeleton of the research. Addition of desired additives to further improve the electrochemical performance with a strong electrode-electrolyte interaction has been the driving force for successful implementation of the planned research. Choosing active electrode materials from different families of materials such as metal based manganese ferrites as well as metal-free nanoporous polymeric frameworks proved the versatility of the designed electrolytes. The thesis comprises of seven chapters. The chapter I includes the path to design the objectives of the present research. A thorough literature review of the existing literatures was conducted to assess the recent advancements in supercapacitors (SCs). Based on the understanding, research gap has been identified. High power density, fast charge-discharge cycles, and long operational lifetime made SC as a potential charge storage device. Despite these advantages, their widespread adoption in high-energy-demand applications remains constrained by limitations, including low energy density, faster self-discharge rates, suboptimal electrode fabrication techniques, and inefficiencies associated with electrolyte performance. This chapter presents a comprehensive investigation of the literatures and chalked out a plan to address some of these through an understanding of non-aqueous electrolyte design and its interaction with various classes of active electrode materials. Chapter II listed the materials used in this research. Further it elaborates working principles of state-of-the-art instruments used in this research such as FTIR, Raman, XPS, XRD, FESEM, TEM, TGA, N2 sorption analysis, along with various electrochemical techniques such as, CV, GCD, and EIS, employed for understanding the supercapacitor performance. In Chapter III, a series of transition-metal-substituted manganese ferrites, Mn0.95M0.05Fe2O4 (M: Co, Cu, and Zn), was synthesized by combustion method. All of these ferrites are used as active electrode materials for SC applications. SC device fabricated using best performing active electrode material, Mn0.95Zn0.05Fe2O4, with a redox-active non-aqueous electrolyte (LiClO4/PC/TEA-BF4/KI) exhibited high Csp of 186 F g-1, Esp of 77.5 W h kg-1, and Psp of 900 W kg-1 measured at 0.5 A g-1. The device has demonstrated stability up to 8000 charge-discharge cycles with an initial Csp retention of ∼80% and high coulombic efficiencies of ∼97–100%, at 2 A g-1.