Metal-organic framework derived ZnO/ZnFe2O4/C nanocages as stable cathode material for reversible lithium-oxygen batteries.

Tremendous efforts have been devoted to exploring various Li-O2 cathode catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, most of the high-activity ORR/OER catalysts can also accelerate side-reactions, such as electrolyte degradation on cycling. To address this issue, we change our strategy from pursuing highly active catalysts to developing stable cathodes that are compatible with the electrolyte. In this work, hierarchical mesoporous ZnO/ZnFe2O4/C (ZZFC) nanocages are synthesized from the templates of metal-organic framework (MOF) nanocages. Such ZZFC nanocages have lower ORR/OER catalytic activity as compared with the widely used catalysts for fuel cells, but they do not catalyze the degradation of organic electrolyte during operation. Furthermore, the optimized porosity and conductivity can fit well the needs of the Li-O2 cathode. When employed in a Li-O2 battery, the ZZFC cathode delivers a primary discharge/charge capacity exceeding 11 000 mAh g(-1) at a current density of 300 mA g(-1) and an improved cyclability with capacity of 5000 mAh g(-1) for 15 cycles. The superior electrochemical performance is ascribed to the hierarchical porosity and little degradation of the organic electrolyte.