Li-O2 batteries are a promising alternative to Li-ion batteries as they theoretically provide the highest possible specific energy density and take advantage of the freely available ambient air as the oxidizer. In Li-O2 batteries, the anode consists of the Li metal which oxidizes into the electrolyte, while emitting electrons into the external electric circuit. Meanwhile, in the cathode, molecular oxygen receives these electrons and reduces to oxygen anions. Over a course of a multistage process, these oxygen anions produced from the cathode, react with Li cations produced from the oxidation of the Li anode, thus forming lithium-oxygen compounds LiO2 (lithium superoxide) and Li2O2 (lithium peroxide) as discharge products. Although the solvation properties of the electrolyte ultimately determine which of the oxide compounds is produced, the resulting compound is predominantly Li2O2. Bulk Li2O2 is an electronic insulator and the precipitation of this compound on the cathode is thought to be the main limiting factor in achieving high capacities in lithium-oxygen cells. SEM and TEM observations frequently reveal crystallite morphologies of Li2O2 compounds, rather than uniform layers covering the electrode surface. The shapes and crystallite morphologies of LiO2 and Li2O2 particles, as well as their extent of contact with the electrode, may all affect the capacity, rechargeability and generally the electrochemistry of the cell. The precise morphologies and their effects, however, remain largely undetermined. In this work we use DFT calculations and ab initio thermodynamics to study the stability of various LiO2 and Li2O2 surfaces, and their crystallite morphologies. PBE and Revised-PBE exchange-correlational functionals are used in conjunction with dispersion and orbital delocalization corrections (DFT+U) to allow for a more complete and accurate analysis. Surface-state analyses are also employed to gain insight into the electronic structure of these oxides.

Cu/CeO2 hybrid nanocrystals with tunable size and interface ratio as electrocatalysts for CO2 reduction reaction

ACS Fall 2020 Virtual Meeting

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