The synthesis and electrochemical properties of nanoconfined lithium titanate, titanium oxide, iron fluoride and other compounds

Abstract

Performance and cost of battery cells are most strongly affected by their electrode and electrolyte materials, which are the basis of battery electrochemistry that enabled electrochemical energy storage applications today. This thesis systematically investigates the nanoconfinement of metal oxides and metal fluorides as electrode materials, from material selection, synthesis, characterization, to variable control, and methodology optimization. First, nanoconfined metal oxides were developed for ultra-high-rate performance applications. Uniform lithium titanate particles within 3 nm confined within porous carbon matrix were reported for the first time and delivered up to 12 times higher gravimetric and volumetric capacities than the state-of-the-art activated carbon electrodes. This technique was used to prepare other nanoconfined metal oxides with similar dimensions, including titanium oxide, nickel oxide, manganese oxide, cuprous oxide, among others. Conversion type cathode materials, widely regarded as the most promising candidates for next-generation lithium-ion batteries (LIBs), were studied for high energy density applications. In particular, I focused on metal fluoride (such as iron (III) fluoride, FeF3) nanoparticles confined in carbon. Iron (III) fluoride offers very high theoretical capacity, and better safety and cost advantage over conventional intercalation-type cathode materials that require the expensive nickel and cobalt. The cyclic capacity retention of the composite produced by electrospinning followed by gas phase fluorination exceeded the state of the art by nearly an order of magnitude in cells. Finally, the shell confinement of iron (III) fluoride cathode by in situ cathode electrolyte interphase (CEI) was studied. The CEI properties could be controlled by electrolyte optimization. Post-mortem analysis after cell cycling revealed insights on the mechanisms of CEI formation.