Co-embedded N-doped carbon fibers as highly efficient and binder-free cathode for Na-O2 batteries

High energy density Na-O2 batteries is very promising for large scale energy storage, wherein the critical bottleneck lies in poor energy efficiency and cycle stability stemming from low catalytic activity and unstable structure of cathode. Herein, we propose a highly effective strategy to activate and stabilize low cost while inefficient N-doped carbon fibers by in situ simultaneous Co embedding/coating. Unexpectedly, the obtained binder-free cathode endows Na-O2 battery with superior electrochemical performances, including low charge overpotential, high specific capacity, and especially good cycle stability, which could be attributed to the combined advantages associated with facilitated electron and mass transportation due to fiber shape and binder-free and porous structure, high conductivity and catalytic activity derived from the synergy between N-doped carbon fibers and Co (metallic and partially oxidized Co) as well as the successful tailor of the morphology of discharge products.