First-principles study of ZIF-8 as anode for Na and K ion batteries

Zeolitic imidazolate frameworks (ZIFs) have been investigated experimentally as anodes for Na and K ion bat-teries. In this work, atomic ZIF-8 models with Zn vacancies have been constructed and the adsorption and diffusion properties of alkali metal atoms are analyzed by density functional theory (DFT) calculations. Zinc vacancies have strong adsorption energy for alkali metal atoms, especially when the first atom is inserted. Additionally, the intercalation of alkali metal atoms would reduce energy band gap of ZIF-8 from 4.85 eV to 4.31 eV for Na and 3.82 eV for K. Moreover, alkali metal atoms can diffuse smoothly in ZIF-8, and the energy barriers are 0.10 eV for Li, 0.45 eV for Na and 0.66 eV for K, respectively. This work deeply explores the interaction mechanism between alkali metals and ZIF-8 theoretically, and provides a reference for the future design of porous carbon materials as anodes for metal ion batteries.