Positive Electrode Passivation by Side Discharge Products in Li-O Batteries.

The development of high specific energy Li-O batteries faces a problem of poor cycling as a result of passivation of the positive electrode by both the discharge product (LiO) and side products (LiCO, etc.). The latter are the result of oxidation of the electrode materials or electrolyte components primarily by discharge intermediate superoxide anions (O) and, in less degree, by LiO.

Lithium peroxide crystal clusters as a natural growth feature of discharge products in Li-O2 cells.

The often observed and still unexplained phenomenon of the growth of lithium peroxide crystal clusters during the discharge of Li-O2 cells is likely to happen because of self-assembling Li2O2 platelets that nucleate homogeneously right after the intermediate formation of superoxide ions by a single-electron oxygen reduction reaction (ORR). This feature limits the rechargeability of Li-O2 cells, but at the same time it can be beneficial for both capacity improvement and gain in recharge rate if a proper liquid phase mediator can be found.