Spherical Carbon as a New High-Rate Anode for Sodium-ion Batteries

• Autogenic synthesis route is used to make monodisperse, dense carbon microspheres.
• Spherically shaped carbon material provides a good high rate anode for Na batteries yielding 40 mAhg−1 specific capacity at a 10C rate.
• 23Na solid state MAS NMR was used to determine that graphene regions in the carbon material are responsible for the high-rate capability.

Ambient temperature sodium-ion batteries are emerging as a new chemistry platform for energy storage technologies. Anodes that consist of carbon have been used for this application due to their highly stable and reversible Na cycling nature. In the search of new carbon materials with various microstructure morphologies, we have synthesized spherical carbon particles via an autogenic process. 23Na MAS solid-state NMR characterization method as a function of the state of charge of carbon was used to determine that these spherical carbon anodes show pure, reversible Na intercalation into graphene regions: these materials are devoid of nanocavity or nanopore filling of Na. This feature and the spherical morphology create low reactivity behavior with the electrolyte which assists in the material's highly reversible (de)sodiation. Specific capacity is 40 mAhg−1 at a high-rate of 10C (1.5 Ag−1) thus demonstrating that the graphene element in hard carbons contributes largely to the rate capability.