Impact of Cathodic Electric Double Layer Composition on the Performance of Aprotic Li-O2 Batteries

Abstract

One of the difficulties limiting the development of high capacity Li-O2 batteries is the positive electrode passivation by the discharge product Li2O2 which is deposited mostly due to the second electron transfer of oxygen reductionwhich requires the presence of Li+ in the Stern layer. To suppress the passivation and shift the reaction zone of Li2O2 formation towards the electrolyte bulk, we propose to use additional cations in the electrolyte. Using molecular dynamics simulations, we investigate the ability of various cations to replace Li+ ions in the first cation layers near the electrode, with EMI+ (1-ethyl-3-methylimidazolium) and PP13+ (N-methyl-N-propylpiperidinium) showing pronounced effects. However, our experimental studies including cycling voltammetry and discharge capacity measurements in high and low donor number solvents reveal practically no effect of such addition. Therefore, Li+ should be fully eliminated from electron transfer zone, and this is possible by anchoring of additional cations according to the simulations. We optimized the surface density for these cations, although the experimental support of this approach looks challenging.