High Energy Density CNT/NaI Composite Cathodes for Sodium-Ion Batteries

The Na-iodine system has potential as a positive electrode in sodium-ion batteries due to its fast reaction kinetics and high energy density. Here, the fabrication of a NaI-loaded carbon nanotube (CNT) mat cathode is presented and the use of NaI as a Na-ion battery cathode is reported for the first time. Freestanding electrodes show a capacity retention of 92% after 100 cycles at 100 mA h g⁻¹ and a high specific energy density (≈473 W h kg⁻¹, second discharge basis vs Na metal) and small hysteresis (0.03 V). Adding a CNT mat interlayer between the NaI composite cathode and the separator, and fluoroethylene carbonate to the electrolyte significantly suppresses shuttling of active materials during cycling. Using ex situ X-ray photoelectron spectroscopy and Raman data, an understanding of the relevant processes occurring during cycling of the CNT/NaI cathode is developed.