Electrochemical Physics for the Precision Engineering of Next-Generation Batteries

Dr. Peng Bai, Energy, Environmental and Chemical Engineering, Washington University
September 25, 2017 at 11:00 am
206 Crow
Event Description 

Next-generation batteries with higher energy density, longer cycle life, lower cost and zero safety risk are essential to a more sustainable energy future. While the chemistry of materials determines the energy density and initial cost, the physics at the electrochemical interfaces controls the efficiency and safety during operation. In the lithium metal anode, which is the master key to the next-generation Li-O2, Li-S and Li-IC (intercalation compounds) rechargeable batteries, whisker-like electrodeposits are long believed to be the cause of internal shorts and even fires and explosions thereafter. In situ observations in capillary cells and liquid-TEM cells reveal that the solid-electrolyte interphase (SEI) layer is the reason of the root-growing whiskers, which fortunately can be blocked by nanoporous ceramic separators. The most dangerous tip-growing dendritic lithium that occurs at diffusion limitation can be avoided by keeping the operation currents below the intrinsic diffusion-limited current during battery cycling. The transition of growth mechanisms helps identify a clear safety constraint (Sand’s capacity) for the rational engineering of next generation rechargeable metal batteries. In the porous cathode made of carbon-coated intercalation compounds (IC), our mathematical model of a single nanoparticle reveals that the solid-state phase transformation in the bulk can be suppressed by electrochemical reaction at the particle surface. Such a surprising behavior could lead to strong dynamic heterogeneity throughout the electrode, which necessitates the precision extraction of the true local reaction rates for consistent Tafel analysis. Our combined theoretical and experimental research suggests the need of better carbon coating to improve the electron transfer at the solid-solid (core-shell) interfaces, and smarter cycling protocol to maximize the efficiency of the electrode.