Non-Technical Abstract From cellular phones to portable computers, many major technological advances in recent years have relied on the ability to store massive amounts of energy within extremely small batteries. These batteries operate by reversibly inserting and removing Li-ions from electrochemically active host materials. The goal of this work, supported by the Solid State and Materials Chemistry program within the Division of Materials Research, is to build a deeper understanding of what happens at the atomic level of these hosts as Li-ions move through their crystal structures. This fundamental knowledge is crucial for increasing the rate at which batteries can be (dis)charged as well as prolonging their operational lifetime. In parallel, this work seeks to use this understanding to identify new Earth-abundant electrode materials for Na-ion batteries in order to reduce the cost of producing large-scale energy storage systems for electric vehicles and the grid. This project also focuses on encouraging middle school students in the Native American communities located within the Los Angeles area to increase their participation in STEM disciplines. Hands-on teaching demonstrations and experiments are used to demystify the often puzzling world of electricity and energy sciences to engage students in science from an early age.
Polyanionic transition metal compounds (like phosphates, sulfates, and silicates) are of critical importance to energy storage because they do not release oxygen on decomposition, which can exacerbate thermal runaway during cell failure, and are therefore considerably safer than oxide-based electrodes. While a large body of work has been dedicated to optimizing the electrochemical performance of these materials, there is a fundamental lack of understanding about the mechanism for Li-ion transport in these materials. Unlike state-of-the-art oxides, which effectively exhibit isotropic changes in their oxygen sublattice, polyanionic electrodes respond to the removal or insertion of Li through cooperative rotations of their rigid oxoanionic subunits. This work is focused on investigating the mechanism of alkali-ion diffusion in polyanionic intercalation hosts using high-resolution X-ray and neutron diffraction techniques in order to characterize how the framework of these materials changes on charge and discharge. Understanding how these densely packed solids facilitate the motion of positively charged ions through their lattices is critical for accelerating the design of next-generation materials for batteries that can operate based on the transport of larger ions like Na.
