Nitrogen-Doped Carbon for Sodium-Ion Battery Anode by Self-Etching and Graphitization of Bimetallic MOF-Based Composite

The greater availability of sodium (Na) over lithium (Li) motivates development of a Na-ion battery that can compete with a Li-ion battery. In these batteries, both electrodes consist of hosts into which Li⁺ or Na⁺ can be inserted reversibly. Graphite has been the anode host for Li-ion batteries, but the Na⁺ ion is too large to be inserted easily between the flat graphene layers of common graphite. We report the synthesis and electrochemical performance of N-doped carbon nanofibers and tubules with an organic-liquid electrolyte and a large fraction of graphitic carbon and larger spacing (0.38–0.44 nm) between carbon sheets; the carbon hollow tubules yield ultrastable (10,000 cycles), high-rate capabilities of Na⁺ intercalation and deintercalation with reversible capacities up to 346 mAh g⁻¹.