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.
High capacity energy storage batteries are needed in applications involving renewable energy and also with resepct to the creation and storing of conventional electrical energy. This NSF funded project was focused on examining a new electrode material class, lithium-magnesium alloy as possible anode material for developing Lithium ion batteries that have capacities beyind that are available in the market today. The results obtained in this research program have met the objectives set out and have clearly validated the original hypothesis of the research and certainly supports continued investigations/development of this system. This reseach has successfully made solid lithium-magnesium alloys that are of high quality required for electrochemical investigations. In electrochemical experiments, we have shown that phase transitions occur at room temperature electrochemical conditions as was hypothesized--this is an important sciencetific component of this research. It was also demonstrated that the reverse phase transformation can be made to occur, during charging of the electrode. This research showns that it is possible to make Li-Mg alloys that can pontentially serve as anodes in ultra-high-capacity Li-ion cells. The research also provided important educational training of a PhD graduate student and an undergraduate student who functioned as assistant to the graduate student. The students have engaged in designing and calculating electrochemical experiments and processes and have developed a hands-on experience in battery electro chemistry. They were also invovled in explaining the principles and operation of batteries to several high school students.
