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Rechargeable aqueous calcium‐ion batteries (CIBs) are promising for reliable large‐scale energy storage. However, they face significant challenges, primarily stemming from suboptimal anodes, resulting in unfavorable voltage profiles, limited capacity, and diminished durability, all of which hinder the development of CIBs. Here, a covalent organic framework (PTHAT‐COF) featuring repeated pyrazine and pyridinamine units, employed as the anode material for aqueous CIBs, is introduced. This innovative approach results in a remarkably flat ultralow potential plateau ranging from −0.6 to −1.05 V (vs Ag/AgCl), attributed to the high level of the lowest unoccupied molecular orbital. Furthermore, the PTHAT‐COF anode exhibits outstanding rate performance (152.3 mAh g−1 @ 1 A g−1), exceptional long‐term cycling stability, and remarkable capacity retention (10 000 cycles with 89.9% retention). Mechanistic studies, including experimental and theoretical calculations, reveal that C═N active sites reversibly trap Ca2+ ions via chemisorption during the discharging/charging process. The PTHAT‐COF demonstrates exceptional structural stability throughout cycling. Finally, by pairing PTHAT‐COF with a high‐voltage manganese‐based Prussian blue cathode, a complete aqueous CIB with a voltage interval of 2.2 V is achieved, exhibiting extraordinary durability (10 000 cycles with 83.6% retention). This research illuminates the potential of organic anode materials in aqueous batteries to achieve higher battery voltages. [ABSTRACT FROM AUTHOR]

Due to the high abundance of their components, low cost, and high safety, zinc‐based batteries open up new vistas for large‐scale energy storage. However, their stability, lifetime, and reversibility are impaired by passivation and dendrite growth of the Zn anode. Here, this challenge is circumvented by an iodine post‐functionalized zeolitic imidazolate framework‐90 (ZIF‐90‐I) additive, in which the polycation absorbed on Zn anode can regulate solid–electrolyte interphase (SEI) formation in the 1 m Zn(TFSI)2 electrolyte and induce Zn2+ uniform deposition. Moreover, the I3−/I− redox can rejuvenate dead Zn and inhibit dendrites. With the ZIF‐90‐I additive, Zn plating/stripping at 99.5% Coulombic efficiency for 120 cycles is obtained in Zn||Ti cells at 20 mA cm−2/1 mAh cm−2. In addition, Zn||Zn cells show steady cycling for 1200 h at 5 mA cm−2/1 mAh cm−2 with stable overpotentials. The utilization rate of Zn reaches up to 68.6%. In situ optical microscopy reveals smooth, uniform Zn plating, and the Zn‐rejuvenated function from the I3−/I− redox couple. The refreshed SEI with the increase of Zn‐rich complexes, and nitrides from adsorbed polycations, are uniform and ZnF2‐rich in the Zn(TFSI)2 + ZIF‐90‐I electrolyte. The full Zn||air cells in Zn(TFSI)2 + ZIF‐90‐I electrolyte exhibit excellent cycling stability with stable polarization voltage at 0.1 mA/0.05 mAh cm−2. [ABSTRACT FROM AUTHOR]