Electric vehicles are one alternative for reducing fossil fuel consumption and greenhouse gas production for sustainable transportation needs. Electric vehicles require rechargeable batteries that balance the electrical energy storage and power delivery needs, and these batteries must have a life span sufficient to reduce cost and achieve true carbon footprint reduction. Furthermore, batteries should be manufactured from sustainable materials to minimize environmental impact. Towards these ends, this research seeks to advance the sustainability of lithium-ion (Li-ion) battery technology through life-span improvements of electrodes made from sustainable materials based on lithium-manganese oxide mixtures. A unique aspect of the research plan is to study battery materials made from single "nanowires" to better understand the fundamental processes that reduce lithium-ion battery lifespan. If successful, this research will advance energy storage technology for future clean energy needs, particularly in the transportation sector. The education and outreach programs associated with this award will extend the impact of the research outcomes into the broader, STEM educational ecosystem in the Richmond, Virginia region. Educational activities include K-12 outreach programs delivered through the ?NanoFellows Institute and Summer Regional Governor's School initiatives at the Math Science Innovation Center (MSiC), and through the Richmond Area Program for Minorities in Engineering (RAPME). These initiatives will introduce students to exciting opportunities that exist for delivering societal impact as future scientists and engineers to the area of sustainable energy.
The overall technical goal of this CAREER award is to gain a fundamental understanding of intrinsic storage capacity in Li-ion batteries through a focused analysis on single intercalation nanowire cathodes made from sustainable lithium/manganese oxide composites. Towards this end, the first research objective is to measure the lithium storage capacity of a single alpha-phase manganese dioxide (MnO2) nanowire cathode with a resolution better than 0.03 Li atoms per host molecule. Single MnO2 nanowires will be subjected to different electrochemical cycling depths in order to reveal the correlation between crystal changes and capacity retention. The second objective test the hypothesis that the intrinsic capacity fading in these intercalation cathodes will be improved by minimizing the structural and electronic conductivity changes, which occur within their host crystal during reversible ionic intercalation. This will be achieved by the use of controlled lithia-doping and further ammonia treatment to stabilize the 2x2 tunnel structure of the host crystal through alleviation of Jahn-Teller distortions. Experimentally, lithium/manganese dioxide nanowire cells will be integrated with nanoelectromechanical resonators to quantify the lithium capacity of the nanowire through its electrochemically-induced mass changes. Four electrochemically-correlated measurements will be performed on this single nanowire at specific charge-discharge cycle numbers that are spread over its cycle-life: (1) TEM imaging to characterize the microstructure, (2) electronic conductivity measurements, (3) contact-mode AFM to study nanomechanical softening, and (4) charge capacity measurement using in-situ electron microscopy-based dynamic resonance measurements. Since capacity fading with progressive cycling is a key failure mode that is common to diverse electrode material systems as well as to different ionic intercalation systems, the new scientific knowledge and other advanced experimental capabilities, which will emerge from this effort, have the potential to go beyond the lithium-MnO2 system and to transform the electrode design strategies for future electrochemical energy storage systems.
