Synergistic Exploration of Oxide Cathode Materials for Potassium-ion Batteries

Abstract

Since their inception by Sony® in 1991, Li-ion batteries have become dominant in various energy storage applications. However, the ever-growing energy demand coupled with sparsely distributed lithium resources provide impetus to develop alternate post-Li-ion batteries having ideal combination of high energy density, low cost, and operational safety. Unlike sodium and other multivalent systems, potassium-ion batteries (KIBs) possess several distinctive benefits, suitable for potential stationary storage applications. KIBs can offer high-voltage operation due to lower redox potential of K/K+, faster ionic mobility in electrolyte, and a wide potential window of 4.6 V compared to the 4.5 V and 4.2 V potential windows of Li-ion and Na-ion batteries, respectively [1-2]. Thus, KIBs can cater to stationary energy storage technology. Despite the significant advancements in KIB technology, the practical implementation of KIBs relies heavily on the discovery and development of robust positive host frameworks having an ideal combination of materials economy, stability, and efficient K+ (de)insertion ability.

This pursuit has led to the exploration of diverse material categories, including layered transition metal oxides, polyanion compounds, Prussian blue analogs, and organic compounds as potential cathode materials for potassium-ion batteries (KIBs). Among them, layered oxide materials have emerged as promising KIB cathodes due to their ability to facilitate efficient K+ ionic migration within two-dimensional open frameworks, thereby leading to enhanced energy density. Focusing on layered oxides, our work delved into the synthesis and electrochemical characterizations of several potassium-based oxide materials utilizing variety of synthesis routes. These oxides have been explored focusing on their structural, morphological, electronic, and electrochemical properties synergizing experimental tools and first-principles calculations. Specifically, we have adopted theoretical screening approach to survey the chemical space of KxMO2 (M= 3d transition metal) systems. We have identified the ground state configurations, average topotactic voltages, electronic structures, on-site magnetic moments, and thermodynamic stabilities of suites of P2 and P3 type KxMO2 compositions and their depotassiated TMO2 derivatives. Further, we have synthesized several single and mixed transition metal oxides using scalable solid state and wet chemistry routes. These compounds are promising materials for high performance KIB cathodes at room and high temperature (c.a. 40°C and 50°C) with excellent cycling and rate capability. This thesis mainly focuses on the designing novel cathodes and correlation between structure and K+ storage mechanism combining various characterization tools and DFT based calculations [3-10]. This work enriches the oxide cathode database for the development of rechargeable potassium-ion batteries.