Flexible free-standing air electrode with bimodal pore architecture for long-cycling Li-O-2 batteries

Abstract

Li-O-2 batteries have been proposed as next-generation energy-storage devices, but this technology is hindered by serious problems including parasitic reactions, degradation, and leakage of the electrolyte. Li-O-2 batteries are also currently designed to have a rigid bulky structure, which cannot satisfy the flexibility demands of modern electronics. Herein, we report the significant enhancement of the electrochemical performance and flexibility of a Li-O-2 battery by introducing a free-standing, binder-free carbon nanotube cathode with a bimodal pore architecture. This electrode structure imparted stability to active sites during the recovery of discharge products to the initial state, providing long-term cyclability of more than 100 cycles in a tetraethylene glycol dimethyl ether electrolyte system. The O-2 transportation and conductivity were also improved, yielding an increased discharge capacity of 5500 mAh g(-1) (nearly twice that of a non-porous cathode) and minimizing parasitic reactions. This novel bimodal-pore cathode exhibited an increased tri-phase boundary for the Li-O-2 reactive zone in the interconnected CNT network. The small pore structures (similar to 50 nm) accommodated Li2O2, and the large pore structures (similar to 385 nm) enabled effective oxygen diffusion without clogging the pores. Moreover, Li+ and oxygen diffusion were facilitated by the two independent channels provided by the pore structures. (C) 2017 Elsevier Ltd. All rights reserved.