Asymmetric Coordination of Metal-Organic Frameworks with Enhanced Metal-Oxygen Hybridization for Li-O2 Batteries

Abstract

Aprotic Li-O2 batteries have drawn considerable attention owning to their high theoretical energy density, but their sluggish cathode reaction kinetics leads to large overvoltages and poor cycling stability. Herein, freestanding one-dimensional Ni-DABDT (2,5-diaminobenzene-1,4-dithiol) metal-organic frameworks with asymmetric coordination configuration (Ni-N2S2) are synthesized as catalyst cathodes for Li-O2 batteries. The asymmetric Ni-N2S2 stabilizes the low-spin state of Ni center, and it promotes O2 chemisorption and the hybridization between the Ni 3dz 2 orbital and π* orbital of O2. This accelerates oxygen redox kinetics and promotes the formation of small-sized toroidal Li2O2 particulates on Ni-N2S2 during discharge, and hence facilitates their reversible decomposition. These enable the Li-O2 batteries to work with low overvoltage of 0.61 V, superior rate performance and long-term stability over 450 cycles, as well as a pouch cell of 50 mAh with good cycle stability. This work highlights the importance of coordination environment regulation in electrocatalysts for Li-O2 batteries.