A Pyrazine-Pyridinamine Covalent Organic Framework as a Low Potential Anode for Highly Durable Aqueous Calcium-Ion Batteries

Abstract

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.