Forging a Conductive, Hydrophobic, and Self-Adaptive Trifunctional Interphase on Mn₂O₃ Cathodes for Ultrastable, High-Energy Aqueous Proton Batteries

Manganese oxide cathodes are promising candidates for aqueous batteries owing to their high operating voltage and large capacity. However, they suffer from severe Mn³⁺ disproportionation and Mn²⁺ dissolution in acidic aqueous batteries, hindering their practical applications. Herein, we construct an in situ trifunctional (conductive, hydrophobic, self-adaptive) interphase using PDMS-DE@PANI (epoxypropoxypropyl-terminated polydimethylsiloxane@polyaniline) core–shell nanocapsules for encapsulating Mn₂O₃. The electrochemically driven release of the liquid PDMS-DE core, synergizing with the PANI shell, effectively suppresses Mn²⁺ dissolution while ensuring rapid electron/ion transfer. Consequently, the PD-Mn₂O₃ cathode delivers a record-high capacity of 340 mAh g^–1 at 0.2 A g^–1 and retains 201 mAh g^–1 (92% capacity retention) after 800 cycles at 1 A g^–1. Paired with a HATN anode, the full proton battery achieves an exceptional energy density of 140 Wh kg^–1 with 80% capacity retention over 800 cycles. This dynamic interphase engineering provides a robust strategy for developing high-energy, ultrastable aqueous proton batteries.