The overarching goal of this proposal is to understand, predict, and ultimately control ion transport and topotactic phase transition (TPT) processes occurring in structurally ordered transition metal oxide (TMO) thin films. The fundamental science we propose is highly relevant to energy conversion and storage technologies, as such fundamental processes govern the mass-transport properties and failure mechanisms of widely used electrode and electrolyte materials. TPTs occurring at the forefront of many catalytic reactions and electrode/electrolyte interfaces are often responsible for many of the challenges (e.g., safety concern due to volume expansion and capacity decrease after cycling due to loss of desired structure/phase) found in lithium ion batteries and solid oxide fuel cells.
We will investigate structurally and compositionally well-defined complex oxide films and thin-film based devices that will enable the facile intercalation of either small cations (e.g., Li+, Na+, and Ca2+) or oxygen anions (O2-). Our team will bring together 1) state-of-the-art synthesis of oxide thin film heterostructures and devices; 2) detailed in situ/in operando characterization of the superstructures, film/substrate, film/film, film/vacuum, and film/solvent interfaces, and their evolution as a function of interfacial strain, doping level, and processing conditions; and 3) ab initio modeling of defect formation, structural ordering, and phase transition pathways and kinetics within the studied materials. The specific aims of this research are to: 1) correlate atomic-scale structural evolution, mesoscale topotactic phase transition, and macroscopic mass transport characteristics as TPTs occur; 2) understand how doping and interfacial strain can be used to modify the onset (e.g., temperature, electrochemical potential), dynamics, intermediate states, and trajectories of TPTs.
The unique and powerful synthesis, characterization, and high performance computing capabilities in EMSL will allow us to establish defensible structure-stability-property relationships. By controlling the onset and trajectories of the TPTs, metastable phases with desired functional properties can be designed, synthesized, stabilized, and harnessed for technological benefits. The fundamental insights gained through this work are of direct relevance to the catalysis, solid oxide fuel cell, and battery research. This DOE funded project is well aligned with EMSL's mission as the "molecular level discoveries will translate to predictive understanding and accelerated solutions for national energy and environmental challenges".