Structural and Electrochemical Investigations of Monovalent and Divalent Aqueous Rechargeable Batteries

Abstract

Several stringent laws and regulations have been enforced by various National/International agencies for the adoption of sustainable methods for energy production and usage. In recent times, electric grids based on alternative renewable sources such as solar, tidal, geothermal, and biomass have witnessed an upsurge. However, the intermittent nature of renewable resources and the sub-optimal electricity distribution/transmission calls for corrective measures leading to enhancement in the efficiency of electricity utilization. It is now widely recognized that energy storage via rechargeable batteries can be an efficient strategy in making the process(es) of electricity production and utilization from the grid to the end-user. Lithium-ion batteries are considered one of the most promising candidates with their outreach in various sectors, such as portable electronics, electric mobility, and grid storage applications. While advanced LiBs may offer good power and energy density, these are unlikely to meet the stiff scale-up targets concerning performance, cost, and safety in large-scale applications such as electric vehicles and the grid. Lithium reserves are limited and distributed heterogeneously. Additionally, conventional Li-ion uses expensive and flammable organic liquid electrolytes Aqueous rechargeable batteries (both monovalent and multivalent) are considered safer alternatives to state-of-the-art LIB technology and other non-aqueous battery chemistries owing to several advantages based on higher safety, cost-effectiveness, and higher ionic conductivity. As water is the solvent, aqueous rechargeable batteries do not require a sophisticated cell assembly line. One of the significant challenges that hinder their wide-scale application is the choice of suitable electrode materials that can work in the aqueous environment. In this thesis, various electrode materials with optimized electrolyte compositions for both aqueous monovalent and multivalent metal-ion rechargeable batteries have been explored. Chapter 3 explores the aqueous rechargeable mixed ion batteries we have developed using a NASICON anode and an olivine cathode in mixed ion electrolytes. The interesting phenomenon of selective ion insertion by the host structure in the presence of more than one cation in the electrolyte is probed in detail. In Chapters 4 to 7, we have explored various host materials (redox-active 2-D covalent organic frameworks, transition metal oxides, Prussian blue analogs) for the aqueous rechargeable divalent metal ion batteries (Zn, Ca, and Mg). The electrochemical characterizations of the materials are performed in detail to account for their redox behavior. The effect of electrolyte composition on the electrochemical performance of the cell is studied in detail. The thesis also probes the underlying mechanism of the battery operation associated with the structural/phase evolution of the electrode structure (with successive cycling) in detail with the help of various post-cycling ex-situ measurements.