Tuning the Electrochemical Performance of Covalent Organic Framework Electrode in Lithium-Ion Battery: Role of Pore Electrostatic Potential.

Covalent organic frameworks (COFs), an emerging class of layered, porous framework materials, have garnered significant recognition as electrode materials in metal-ion batteries. The electrostatic potential of the COF's pore is a fundamental yet underexplored aspect in the context of its role in electrochemical energy storage. Using density functional theory simulations, we have studied a set of experimentally relevant triazine-based COFs, considering 1,4-benzene, 1,4-naphthalene, 2,6-naphthalene, and 4,4'-biphenyl as linkers, which differ by aromaticity and connectivity, to quantify the effect of pore electrostatic potential (ESP) on the electrochemical performances of a Li-ion battery. Our results reveal that, upon tuning the linkers' aromaticity, the ESP of the pore can be tuned up to ∼2 eV, with a concomitant voltage modulation as high as 0.4 V. Our results also suggest that, due to the presence of different heteroatom-based binding motifs, the intercalation mechanism in the COF is significantly different compared to that of a conventional graphite electrode. Furthermore, we have investigated COF systems with pore walls functionalized by -F, -CN, and -OH groups, revealing a strong dependency of ESP of the pore on the electron-donating or -withdrawing substituent group, resulting in further modulation of voltage. We find that, while such thermodynamically controlled electrochemical behavior is determined by the ESP of the COF's pore, the Li-ion migration barrier is independent of ESP. Overall, our study provides an in-depth understanding of the impact of pore ESP in triazine-based COFs in determining their electrochemical energy storage performance, opening up a route map in linker engineering aspects of the COFs.