Delocalized Redox Framework of Indanthrone Enables Low-Strain and Durable Mn²⁺/H⁺ Storage in Aqueous Batteries

Aqueous manganese batteries (AMBs) are promising alternatives to lithium-ion systems due to their safety and cost-effectiveness. However, organic cathodes often face challenges regarding material dissolution and slow ion kinetics. In this work, we introduce indanthrone (IDT) as a strategic organic cathode for high-performance Mn²⁺/H⁺ batteries. IDT features a massive eight-ring π-conjugated framework that enables extensive electronic delocalization. Unlike systems with excessively concentrated active groups, the IDT framework provides a more dispersed distribution of redox-active sites. This arch\itecture promotes smooth ion transport through enhanced charge delocalization across the extended aromatic system. The IDT electrode delivers a high specific capa\city of 194.8 mAh/g at 0.1 A/g, while the Mn-IDT full-cell exhibits 85.5% capacity retention after 3000 cycles at 0.3 A/g. Spectroscopic and crystallographic analyses confirm a low-strain pathway, where b-axis expansion (2.09%) is effectively compensated by minor contractions in the a and c-axes. This unique anisotropic response leads to minimal overall volume fluctuation, ensuring structural integrity during prolonged operation. This work provides a molecular-level design principle for constructing low-strain organic cathodes for high-voltage aqueous multivalent batteries.