Carbonyl-staggered covalent organic frameworks for high-rate and stable rechargeable calcium-organic batteries.

Rechargeable calcium batteries are promising for next-generation energy storage devices due to the high crustal abundance of calcium (Ca) and the high-capacity and dendrite-free nature of Ca metal. However, their implementation is hindered by the lack of high-power and high-capacity positive electrodes, largely due to sluggish Ca2+ diffusion in inorganic hosts and limited active-site utilization in organic electrodes. Here we design a series of covalent organic frameworks incorporating different quinone units to construct carbonyl-staggered channels that accelerate Ca2+ hopping, enhance accessibility of deep-layer active sites even at high rates, and facilitate electronic charge transport through in situ conjugation reconstruction at ortho-carbonyl sites during repeated Ca2+ insertion. These combined effects contribute to fast charge-transfer kinetics, endowing the optimized heterogeneous framework with high-rate capability (56.4% capacity retention from 0.05 A g-1 to 2 A g-1) and long cyclability (71.7% capacity retention after 5,000 cycles at 2 A g-1), with further validation in Ca-metal pouch cells. This work highlights carbonyl staggering as a molecular design strategy for regulating Ca-ion transport and improving active-site utilization in calcium-organic batteries.