EAGER: Exploiting Electrochemically-induced Phase Transformations in Mg-Li Thin Film Electrodes for Ultra-high Capacity Energy Storage

University Of Utah, Salt Lake City UT

Investigators

Abstract

TECHNICAL SUMMARY: Research is proposed to understand the mechanism of reversible phase transformations in Mg-Li phase-changing anodes during electrochemical insertion/removal of Li in Mg thin films during the charging/discharging processes. The key concept of this research is that starting with a pure Mg anode, a phase change from HCP Mg to BCC Li-Mg can be induced in the anode during Li charging (and the reverse during discharging). The key question is how the thin film microstructural variables affect the reversibility of the electrochemically-induced phase transformations. The size and intercolumnar spacing of the columnar grains, as well as the grain orientation, are the primary variables affecting the phase transformation. The hypothesis is that there could be an optimum grain size and intercolumnar spacing that accommodates the volume change of the phase transition, fully allowing maximization of Li storage and removal without the destruction of the electrode. This is a high-risk research, because it is not certain that the reversibility of phase transformation and volume change accommodation is repeatable over the sufficient number of cycles required in batteries. Specifically, the research involves making Mg films of various thicknesses with ultrafine and columnar grain structures, either by sputtering or PVD, micromachining using MEMS fabrication techniques to extend the intercolumnar spacing, testing electrochemical cells to understand the nature of the reversible phase change from HCP Mg to BCC Li-Mg and vice-versa during charging/discharging and experimental determination of the capacity, cyclability and stability of the performance during the charge/discharge cycles. NON-TECHNICAL SUMMARY: Next-generation electric vehicles, as well as effective utilization of renewable energy from solar cells and windmills, will require major technological breakthroughs in electrical energy storage and retrieval. A high-risk and high-payoff research poject is proposed to exploit phase transformations in lithium-magnesium alloy anodes to help develop ultra-high-capacity energy storage batteries with capacities much larger than those currently under consideration for electric vehicles. The research could potentially lead to new electrode materials and structures for a new generation of reliable and high-capacity batteries, which could in turn accelerate the development of low-cost plug-in electric vehicles. The project will employ a graduate student and one or more undergraduate students, provide education and training in the area of battery materials science research, and develop outreach/recruitment presentations aimed at senior high school students. The research will be integrated into class lectures on battery materials science for a graduate course on Energy Science and Engineering. Public outreach presentations, under the theme of "energy materials science", to high school students and parents during University Science Day recruitment events, will also be made.