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Abstract

The realization of electrochemical energy storage devices combining high energy and power density places high demands on the electrode materials. It remains difficult to provide high metal storage capacity and rate capability at the same time in one and the same material. By decoupling metal storage and electron transport in different phases of a nanostructured electrode composed of nitrogen-rich carbon nanoparticles which are embedded into a conductive mesoporous carbon matrix, this dilemma can be minimized. The composite material has a remarkable performance for sodium storage with a reversible capacity of 343 mAh g-1 at 0.1 A g-1 and capacity retention of 124 mAh g-1 at 20 A g-1. This work shows that a properly designed nanocomposite material can fulfill both requirements and sheds new light on resolving the seemingly conflicting energy/power density demands in current electrochemical energy storage devices.