Revitalizing nanoscale solid–solid conversion enables ultrastable aqueous batteries

ABSTRACT Aqueous zinc–manganese (Zn–Mn) batteries driven by deposition–dissolution reactions hold significant promise for large-scale grid energy storage. However, their lifetimes are limited by incomplete solid–solid conversion, driven by irreversible pathways forming large-sized solid products—a critical yet overlooked size-dependent challenge. Here, we construct a size-revitalizing layer (SRL) on MnO2 to regulate the interfacial microenvironment via sustained Mn release and strong interaction with solid products. The SRL governs growth kinetics, stabilizing nanoscale products formation. Such small solid products shorten ion-diffusion paths and reduce concentration polarization, enabling a reversible Mn (Ⅱ, l)–Mn (Ⅳ, s) pathway instead of an irreversible Mn (II, l)–Mn (III, s) route. Systematic screening identifies Bi2O3 as the optimal modifier based on its strong p–s (M–Zn) orbital interaction and lattice compatibility, which reduce solid product size from >10 μm to the nanoscale, achieving unparalleled stability and resolving irreversible capacity degradation. With a high-mass-loading cathode (9 mg cm−2), coin cells achieve >1000 cycles at 2 C and scaled iron-plate cells (16 mg cm−2, 26.3 mAh) operate stably for 110 days. This size-controlled solid–solid conversion strategy exhibits broad applicability to diverse electrode materials, highlighting its potential for widespread adoption in advanced energy-storage systems.