An Open-Structured Matrix as Oxygen Cathode with High Catalytic Activity and Large Li2O2 Accommodations for Lithium–Oxygen Batteries

The nonaqueous lithium–oxygen (Li–O 2 ) battery is considered as one of the most promising candidates for next-generation energy storage systems because of its very high theoretical energy density. However, its development is severely hindered by large overpotential and limited capacity, far less than theory, caused by sluggish oxygen redox kinetics, pore clogging by solid Li 2 O 2 deposition, inferior Li 2 O 2 /cathode contact interface, and difficult oxygen transport. Herein, an open-structured Co 9 S 8 matrix with sisal morphology is reported for the first time as an oxygen cathode for Li–O 2 batteries, in which the catalyzing for oxygen redox, good Li 2 O 2 /cathode contact interface, favorable oxygen evolution, and a promising Li 2 O 2 storage matrix are successfully achieved simultaneously, leading to a significant improvement in the electrochemical performance of Li–O 2 batteries. The intrinsic oxygen-affinity revealed by density functional theory calculations and superior bifunctional catalytic properties of Co 9 S 8 electrode are found to play an important role in the remarkable enhancement in specific capacity and round-trip efficiency for Li–O 2 batteries. As expected, the Co 9 S 8 electrode can deliver a high discharge capacity of ≈6875 mA h g −1 at 50 mA g −1 and exhibit a low overpotential of 0.57 V under a cutoff capacity of 1000 mA h g −1 , outperforming most of the current metal-oxide-based cathodes.