Tautomerization-driven charge delocalization in organic cathodes for fast cation storage in aqueous Zn batteries

The quinone-based cathode material, tri-(pyrene-4,5,9,10-tetraone)-di-(tetraamino-p-benzoquinone) (TPDT), for aqueous zinc batteries incorporates extended π-conjugation, cation-radical states, and dynamic tautomerization, resulting in continuous charge-transfer pathways. Therefore, the TPDT composite cathode shows excellent electrochemical performance with only 5% KB additive. Organic small molecules are promising cathode materials for aqueous zinc batteries due to their structural tunability and sustainability. However, their intrinsically poor electrical and ionic conductivities seriously hinder the rate capability. To compensate, organic electrode preparation usually requires the addition of a large amount of carbon agents, typically ≥30%, which adds processing complexity and limits the practical energy density of the system. To address these very important limitations, we design and synthesize a fully conjugated quinone molecule, tri-(pyrene-4,5,9,10-tetraone)-di-(tetraamino-p-benzoquinone) (TPDT), featuring multiple redox-active sites with unique dynamic tautomerization. Experimental and theoretical analyses reveal that TPDT possesses extended π-conjugation, cationic radical stabilization, and π-π stacking interactions, which together promote efficient through-plan and through-space charge transport. Remarkably, the partially reduced TPDT isomers with different C=O or C=N reaction sites exhibit low energy differences, enabling dynamic tautomerization at room temperature. This equilibrium facilitates charge redistribution and continuous charge-transfer pathways across the molecular framework. As a result, TPDT exhibits excellent electrical and ionic conductivities and outstanding electrochemical performance. The composite with graphene oxide further ensures stable cycling. With only 5% Ketjen black (KB) additive, the composite cathode delivers a high capacity of 313 mAh g −1 at 0.1 A g −1 and retains 81 mAh g −1 at 50 A g −1 together with 92% capacity retention after 20,000 cycles. At the low temperature of −20 °C, it still maintains 128 mAh g −1 at 5 A g −1 over 5400 cycles. This work highlights the importance of structural dynamics in designing organic cathodes and has a guiding significance for developing high-performance zinc-organic batteries.