Yogesh Surendranath, Assistant Professor, Department of Chemistry
Li-O2 batteries are poised to transform the consumer electronic and electric vehicle markets because they possess a theoretical energy density of 3,213 W h/kg, three fold larger than the current state of the art. This dramatic boost in energy density is provided by the carbon-based Li-O2 cathode, at which O2 is reduced to Li2O2 upon cell discharge. However, the insoluble Li2O2 precipitates indiscriminately on the surface of the carbon cathode, inhibiting subsequent reduction of O2, leading to diminished capacity, poor rate capability, and poor round-trip efficiency. These challenges could be overcome if the surfaces of carbon cathodes can be modified to discourage the indiscriminate nucleation and growth of Li2O2 crystallites. We hypothesize that Li2O2 nucleation occurs via Li+ coordination to oxidic surface functionalities including ketones, carboxylic acids, and alcohols, which are known to be prevalent on carbon surfaces. Thus, we will apply well-known oxygen protecting group (PG) chemistries (e.g. silylation, benzylation, alkylation) to carbon electrodes to impede the nucleation of Li2O2 crystallites. By reducing the nucleation site density, fewer, larger Li2O2 crystallites will be favored, leaving the majority of the electrode surface available to sustain rapid O2 reduction, thereby, enabling high energy and power densities.