Low-Activation-Energy Bipolar Organic Nanostructures for High-Capacity and Ultralong-Life Aqueous Calcium-Ion Batteries

Abstract

Rechargeable aqueous calcium-ion batteries (CIBs) provide a promising solution to large-scale energy storage due to their divalent-electron transfer, resource abundance, and high capacity. However, their advancement is challenged by suboptimal anode materials with low exposure of redox-active motifs in dense-stacked and disorganized structures due to high spatial energy barriers, resulting in limited capacity and durability. Here we design low-activation-energy bipolar organic nanostructures (BONs) through integrating dual-electron benzoquinone and 4,4'-azodianiline units into extended π-conjugated polymeric skeletons through multi-intermolecular H-bonds (N−H···O) and π-π interactions. The well-organized rod geometries of BONs deliver consecutive electron delocalization paths to fully expose built-in multi-redox carbonyl/azo/amine motifs and strengthen the anti-dissolution ability in aqueous electrolytes. Consequently, a stable 4 e− Ca2+/H+/OTF− storage is initiated in BONs anode with an ultralow activation energy (0.22 eV), liberating the state-of-the-art capacity (302 mAh g−1) and lifespan (100,000 cycles) among all reported organics in CIBs. Besides, BONs anode can be further leveraged to design advanced BONs||KCoFe(CN)6 full battery with superior capacity (210 mAh g−1), high energy density (221 Wh kg−1 anode) and long-lasting cycling stability (20,000 cycles). This work constitutes a major advancement in designing multi-redox organic nanostructures for better CIBs.