Imaging Cycle-Induced Damage of MnO2 Microparticles

Abstract

MnO2 has been proposed as an electrode material in electrochemical energy storage devices. However, poor cycle life, especially in aqueous electrolytes, remains a detriment to commercialization. Prior studies have suggested a number of explanations for this capacity loss; however, experiments aimed at elucidating the details of the degradation process (es) are sparse. We describe here a microtube-membrane construct that allows for electrodeposition of monodisperse MnO2 microparticles distributed across the membrane surface, and for subsequent electrochemical cycling of these MnO2 particles. This allowed for a detailed analysis of the effect of cycling on the MnO2, by simply imaging the membrane surface before and after cycling. When an aqueous electrolyte was used, gross changes in particle shape, size and morphology were observed over the course of 500 cycles. Partial dissolution occurred as well. No such changes were observed when the MnO2 particles were cycled (up to 500 times) in a propylene carbonate electrolyte solution.