Reversible High-Voltage N‑Redox Chemistry in Metal–Organic Frameworks for High-Rate Anion-Intercalation Batteries

Because
of the capacity limitation in traditional transition-metal
oxide cathodes, the design of novel cathodes is vital for the performance
enhancement in lithium-ion batteries. In this work, we propose a new
anion-intercalation strategy for the design of metal–organic
frameworks that can be used as high-voltage cathodes in lithium-ion
batteries. A novel pcu-topology [Zn4O2(DAnT)3(DMF)4]·(DMF)6 MOF is synthesized
with enriched nitrogen active sites and porous cage structure. When applied
as cathode with LiPF6 based electrolyte, this MOF reaches
the theoretical capacity of ∼60 mAh g–1 at
a current density of 100 mA g–1 within high working
voltage of 2.5–4.0 V versus Li/Li+. Even at a high
current density of 1000 mA g–1 (∼16C), half capacity can still be obtained. The reversible
conversion of N/N+ and adsorption/desorption of PF6– were also examined by a series of ex situ
characterizations including XPS, XRD, and FTIR, which clearly validates
our strategy that permits good electrochemical performance at relatively
high working potential.