Electrochemical Behavior of Mn-based Oxide Cathode Materials for Alkali-ion Batteries: Study of Cationic and Anionic Redox Reactions

Abstract

Better batteries are being developed in response to the growing demand for clean energy in order to replace conventional fossil fuels with renewable energy for affordable and long-term energy storage. Lithium-ion batteries have long dominated the markets for electronic goods and electric vehicles. Alternative monovalent (Na+/K+) metal-ion batteries are being investigated in light of the diminishing Li sources. The discovery of suitable cathode materials with effective electrochemical performance is essential for the development of these post-Li- ion batteries. A variety of oxide materials have been investigated in this effort because of their high specific capacities, environmental friendliness, and simplicity of synthesis. Oxide compounds can be found in a variety of structures, including layered structures, spinel structures, and tunnels with one to three-dimensional diffusion pathways. My research focuses on examining different insertion compounds for secondary batteries that are based on oxides. Here, a thorough investigation of various oxide cathodes for metal-ion batteries will be presented, demonstrating the connection between electrochemical performance and phase transition. The work is presented in three chapters. Phase pure Na0.44MnO2 compound was synthesized by using facile solution combustion method taking low-cost nitrates and urea as precursors. This compound has a 3D tunnel structure and was studied as a host for Li-, Na-, and K-ion batteries. Following that, phase pure Li0.44MnO2 was synthesized using molten salt and underlying redox mechanism were explained. The electrochemical activity of layered P2- oxides type [Na0.7Mn0.6Ni0.3Co0.1O2, Na0.7(Li1/18Mn11/18Ni3/18Fe2/181/18)O2-xNa2MoO4] will be reported. High reversible capacity over 140 mAh/g, involving both cationic and anionic redox activity, will be demonstrated along with the effect of cation doping in improving overall performance. Many oxides exhibit polymorphic phase transition. Li0.44MnO2 was found to undergo tunnel to spinel phase transition upon annealing with onset point of 463 °C. This phase transition will be depicted combining in-situ X-ray diffraction, in-situ Raman spectroscopy and in-situ transmission electron microscopy.