The MnO2/Mn2+ cathode chemistry represents a promising avenue for high-energy-density and low-cost aqueous batteries. However, its practical application for grid-scale storage is limited by insufficient cycling stability. Extensive reports have highlighted the poor reversibility of MnO2 deposition and stripping. Here, we reveal an overlooked source of capacity loss under typical operating conditions: corrosion of the carbon current collector. Using gas chromatography, we show that carbon corrosion can account for up to ∼25% of initial capacity losses and can cause thickness losses approaching 200 nm in the first cycle. Corrosion-induced thickness losses are largest under acidic and near-neutral conditions. Corroborating our corrosion measurements, X-ray photoelectron spectroscopy and scanning electron microscopy results indicate the formation of surface oxygen species and carbon fiber degradation after cycling. Our work provides a quantitative understanding of carbon corrosion in aqueous batteries that can inform strategies for extending their cycle life.
Keywords: MnO2 cathode; aqueous batteries; carbon corrosion; gas chromatography; grid-scale storage.