In lithium-oxygen batteries, although the porous carbon cathodes are widely utilized to tailor the properties of discharged Li2O2, the impact of nanopore size on the Li2O2 formation and decomposition reactions remain incompletely understood. Here, we provide the straightforward elucidation on the effect of pore size in a range of 25-200 nm, using a highly ordered porous cathode matrix based on the carbon-coated anodic aluminum oxide membrane formed on an Al substrate (C/AAO_Al). When the nanopore size is 25 nm, film-like Li2O2 with a thickness of 2-5 nm is formed, possibly via a surface-driven mechanism. When the nanochannel becomes larger, the Li2O2 film thickness saturates at ca. 10 nm, along with crystalline Li2O2 particles possibly formed by a solution-mediated mechanism.
Keywords: charge overpotential; controllable size; lithium peroxide; nanoconfinement; ordered nanoporous cathodes.