Revealing and Quantifying Carbon Corrosion in Aqueous Manganese-Based Batteries

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.