Tracking Formation and Decomposition of Abacus-Ball-Shaped Lithium Peroxides in Li-O2 Cells

Study of formation and decomposition of Li2O2 during operations of Li-O-2 cells is essential for understanding the reaction mechanism and finding solutions to improve the cell performance. Using vertically aligned carbon nanotubes (VACNTs) directly grown on stainless steel meshes as the cathodes in the Li-O-2 cells with dimethoxyethane (DME) electrolytes, nucleation, growth, and decomposition processes of the Li2O2 in the first cycle are clearly visualized. Through cycles with the controlled discharge and charge capacities, the abacus-ball-shaped Li2O2 and the rust-like carbonates simultaneously formed around the VACNTs are further identified. It is indicated that the increasing coverage of carbonates on the cathode surface suppresses the formation of Li2O2, which maintains the shape of abacus ball. When the VACNT surfaces are predominantly covered by the carbonates, the cells tend to terminate.