Tailoring the Electrochemical Properties of Two-Dimensional Bis(diimino)metal Coordination Frameworks by Introducing Co/Ni Heterometallic Structures

Bis­(diimino)­metal coordination frameworks (MDI, M = transition metal), which are a class of metal organic frameworks with two-dimensional anisotropy, high electric conductivity, and redox activity, are attractive platforms for tailoring electrochemical properties by introducing a heterometallic composition. In this study, we synthesized heterometallic Co x Ni1–x DI coordination frameworks for electrochemical energy storage applications and investigated their electrochemical properties by experimental and theoretical techniques. Ni atoms were embedded into CoDI, and the crystal structure of Co x Ni1–x DI was modified, especially along the interlayer axis, which activated the kinetically impeded redox reactions accompanied by PF6 – insertion/extraction. Furthermore, upon charge/discharge with Li+ transport, Co x Ni1–x DI with a specific composition exhibited higher specific capacity (248 mAh g–1) than CoDI and NiDI in the potential window of 1.0–3.5 V versus Li+/Li. Density functional theory calculations indicate that the energy levels of the antibonding orbitals around the metals and interlayer spaces are important factors in tailoring the electrochemical properties of Co x Ni1–x DI.