Asymmetric coordination of metal–organic frameworks with enhanced metal–oxygen hybridization for Li–O2 batteries

Abstract

Aprotic Li–O₂ batteries have drawn considerable attention owing 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 catalytic cathodes for Li–O₂ batteries. The asymmetric Ni–N₂S₂ coordination stabilizes the low-spin state of the Ni center, and it promotes O₂ chemisorption and hybridization between the Ni 3d_z² orbital and the π* orbital of O₂. This accelerates oxygen redox kinetics and promotes the formation of small-sized toroidal Li₂O₂ particles on Ni–N₂S₂ during discharge and hence facilitates their reversible decomposition. As a result, the Li–O₂ batteries exhibit a low overvoltage gap of 0.61 V, superior rate performance and long-term stability over 450 cycles, while a 50 mAh pouch cell also demonstrates good cycle stability. This work highlights the importance of coordination environment regulation in electrocatalysts for Li–O₂ batteries.