Electrochemical investigation of the role of MnO2 nanorod catalysts in water containing and anhydrous electrolytes for Li–O2 battery applications

Abstract

The electrochemical behaviour of MnO₂ nanorod and Super P carbon based Li–O₂ battery cathodes in water-containing sulfolane and anhydrous DMSO electrolytes are shown to be linked to specific discharge product formation. During discharge, large layered spherical agglomerates of LiOH were characteristically formed on the MnO₂ cathodes while smaller, toroidal, spherical Li₂O₂ particles and films were formed on the Super P cathodes. In an anhydrous DMSO based electrolyte the LiOH structures were also found on cathodes discharged in the anhydrous electrolyte, suggesting that MnO₂ initiates electrochemical decomposition of the DMSO electrolyte to form LiOH via H₂O reactions with Li₂O₂. The LiOH crystals are uniquely formed on MnO₂, and segregated to this phase even in mixed oxide–carbon cathodes. In contrast, no Li₂O₂ toroids were noted on Super P cathodes discharged in the DMSO based electrolytes. Instead, the morphology varied from smaller sheets (at high discharge current) to much larger agglomerates (at low discharge currents). In mixed carbon–MnO₂ nanorod cathodes, the use of PVDF initiates H₂O formation that affects discharge products and an overall mechanism governing phase formation at MnO₂ in sulfolane and anhydrous DMSO with and without PVDF binder is presented. This work highlights the importance of careful consideration of electrolyte–cathode material–discharge product interactions in the search for more stable Li–O₂ systems.