Metastable Rocksalt Oxide Mediated Synthesis of High-Density Dual-Protected M@NC for Long-life Rechargeable Zinc-Air Batteries with Record Power Density.

Creating high-density durable bifunctional active sites in air electrode is essential, but still challenging for long-life rechargeable zinc-air battery with appealing power density. Herein, we discover a general strategy mediated by metastable rocksalt oxides for achieving high-density well-defined transition metal nanocrystals encapsulated in N-doped carbon shells (M@NC) which are anchored on substrate by porous carbon network as highly-active and durable bifunctional catalytic sites. Well-dispersed Co2Fe1@NC in a small uniform size (15 ± 5 nm) and high density (metal loading up to 54.0 wt%) offers zinc-air battery a record power density of 423.7 mW cm-2. The dual protection from the complete graphitic carbon shells and the anchoring of outer carbon network makes Co2Fe1@NC chemically and mechanically durable, giving the battery a long cycling life. Systematic in-situ temperature-dependent characterizations as well as DFT modelling rationalize the rocksalt-oxide mediated process and its indispensable role in achieving high-density nanosized M@NC. These findings open up opportunities for designing efficient electrocatalysts towards high-performance Zn-air batteries and diverse energy devices.