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.

Initial stages of Li-O₂battery discharge are characterized by high supersaturation of lithium peroxide in highly solvating media. It leads to homogeneous nucleation of Li₂O₂nanoplates instantly assembled into mesocrystals in the solution bulk.

Many obstacles impede the development of Li–air batteries for practical applications. In particular, there is lack of understanding of the dynamics of processes occurring in porous air electrodes during discharge, including oxygen transport limitations, pore clogging and electrode passivation by both insulating discharge and parasitic reaction products. Here, using small-angle neutron scattering, which provides information on the whole electrode adequate to electrochemical data, we uncover the mechanisms limiting the Li–O₂ porous carbon electrode capacity by analysis of the cathode pore filling in highly and poorly solvating media – dimethyl sulfoxide and acetonitrile. The results obtained allowed us suppose that in both cases the cell death is mainly triggered by blocking of oxygen transport pathways inside carbon black particle agglomerates. Total discharge capacities are, indeed, higher in highly solvating solutions due to a higher discharge intermediate lifetime and longer diffusion distance, which enable Li₂O₂ formation outside the carbon black agglomerates, which are, as we demonstrated, in fact mesocrystals that are confirmed by the appearance of a diffraction peak in scattering curves.