Nonplanar tertiary-N extended nitrobenzene enables insoluble and low-energy-barrier organic small-molecule cathodes for high-performance aqueous batteries

Abstract

Organic small molecules with a high mass content ratio of redox-active sites are promising high-capacity cathode materials for aqueous zinc batteries, but their strong interaction with aqueous electrolytes causes serious dissolution and limited cycling life. Here, we demonstrate nonplanar tertiary-N extended nitrobenzene, which harnesses its strong intramolecular π–π interaction beyond the H₂O dissociation energy, to create an insoluble and low-energy-barrier nitroarene (TNB) small-molecule cathode. Two rotating tert-N linkages bring the extended π-aromatic nonplanar configuration of TNB, exhibiting a maximum negative intramolecular potential energy of −35.8 kcal mol⁻¹ compared to its large repulsive force of 15.1 kcal mol⁻¹ in H₂O medium. Consequently, the intramolecular π–π interactions within TNB are significantly stronger than its interactions with H₂O molecules, thereby suppressing dissolution in the aqueous electrolyte and extending the battery lifespan to the state-of-the-art level (180 000 cycles). Meanwhile, the nonplanar structure of TNB allows for 98.9% utilization of nitro/tert-N motifs with low activation energy (0.23 eV), liberating superior capacity (430 mAh g⁻¹) and large-current tolerance (100 A g⁻¹). Significantly, this nonplanar molecular design shows promising preliminary generalizability to develop versatile insoluble carboxylic, cyano, and imine compounds. These proof-of-concept results suggest a potential paradigm for highly active and ultrastable organic molecules towards better aqueous batteries.