Using elastin protein to develop highly efficient air cathodes for lithium-O₂ batteries

Transition metal-nitrogen/carbon (M-N/C, M = Fe, Co) catalysts are synthesized using environmentally friendly histidine-tag-rich elastin protein beads, metal sulfate and water soluble carbon nanotubes followed by post-annealing and acid leaching processes. The obtained catalysts are used as cathode materials in lithium-O₂ batteries. It has been discovered that during discharge, Li₂O₂ nanoparticles first nucleate and grow around the bead-decorated CNT regions (M-N/C centres) and coat on the catalysts at a high degree of discharge. The Fe-N/C catalyst-based cathodes deliver a capacity of 12 441 mAh g^-1 at a current density of 100 mA g^-1. When they were cycled at a limited capacity of 800 mAh g^-1 at current densities of 200 or 400 mA g^-1, these cathodes showed stable charge voltages of ∼3.65 or 3.90 V, corresponding to energy efficiencies of ∼71.2 or 65.1%, respectively. These results are considerably superior to those of the cathodes based on bare annealed CNTs, which prove that the Fe-N/C catalysts developed here are promising for use in non-aqueous lithium-O₂ battery cathodes.