UC Santa Barbara

The shift towards greener technologies such as electric vehicles and renewable energy sources generates a rapidly increasing demand for energy storage. This trend underscores the need for the development of sustainable chemistries for rechargeable batteries that do not rely on cobalt (Co) and nickel (Ni), as they are expensive, geographically limited, and unethically sourced (in the case of Co), resulting in complex and unreliable supply chains. Disordered rocksalt (DRX) structures are a promising candidate for next-generation Li-ion batteries, as their close-packed structure and flexible chemistry enables sustainable and earth-abundant manganese (Mn) based cathodes with impressive energy densities. However, practical commercialization of DRX cathodes remains limited by key issues such as rapid capacity and voltage fade along with poor Li conduction necessitating particle downsizing.

This dissertation aims to showcase the rational design of improved DRX cathodes by correlating synthesis parameters, composition, and materials properties, and by leveraging unique reaction pathways to produce novel DRX compositions. First, the ultrafast and energy-efficient microwave synthesis of DRX materials was developed, providing time and energy savings of more than two orders of magnitude compared to standard synthesis routes. Next, to establish compositional limits of fluorine solubility in DRX structures and its impact on electrochemical performance, a joint experimental-computation method was designed to enable accurate determination of DRX stoichiometry. Critically, we observed unexpectedly low fluorine incorporation into the structure, and a diminished impact of fluorination on cycling performance. Instead, higher amounts of redox-active elements such as Mn is more impactful. Finally, following design rules established by the compositional study, a previously unreported class of DRX compositions was synthesized through the novel microwave technique, opening up a large, unexplored compositional space for DRX cathodes. This new class of DRX materials was demonstrated to have superior electrochemical performance over current DRX compositions, representing a significant leap towards practical commercialization of DRX cathodes for sustainable rechargeable batteries.