Three-Dimensional Au Microlattices as Positive Electrodes for Li–O₂Batteries

We demonstrate the feasibility of using a 3-dimensional gold microlattice with a periodic porous structure and independently tunable surface composition as a Li-O2 battery cathode. The structure provides a platform for studying electrochemical reactions in architected Li-O2 electrodes with large (300 μm) pore sizes. The lack of carbon and chemical binders in these Au microlattices enabled the investigation of chemical and morphological processes that occur on the surfaces of the microlattice during cycling. Li-O2 cells with Au microlattice cathodes were discharged in 0.5 M lithium-bis(trifluoromethane)sulfonamide (LiTFSI) in a 1,2-dimethoxyethane (DME) electrolyte, with lithium metal foil as the anode. SEM analysis of microlattice cathodes after first discharge revealed the presence of toroidal-shaped 500-700 nm particles covering the surface of the electrode, which disappeared upon subsequent charging. Raman and FTIR spectroscopy analysis determined these particulates to be Li2O2. The morphology of discharge products evolved with cycling into micrometer-sized clusters of arranged "platelets", with a higher amount of side reaction products such as Li2CO3 and LiOH. This work shows that properly designed 3-dimensional architected materials may provide a useful foundation for investigating fundamental surface electrochemistry while simultaneously enabling mechanical robustness and enhancing the surface area over a factor of 30 compared with a thin film with the same foot print.