Redox chemistry of nitrogen-doped CNT-encapsulated nitroxide radical polymers for high energy density and rate-capability organic batteries

To enhance the electrochemical performance and identify the redox reaction of a nitroxide radical-based organic battery, poly(2,2,6,6-tetramethylpiperidinyloxy-4-vinylmethacrylate) (PTMA) as nitroxide radical polymer is synthesized and used to fill the central pore of nitrogen-doped carbon nanotubes (NCNTs). The PTMA-filled NCNTs demonstrate high rate capability, stable cycling, and high electrode stability, owing to their high charge transfer and ion diffusion; further, they prevent the dissolution of organic active material. The nitrogen doping on CNTs improves the electrochemical properties by created defects. The PTMA-filled NCNT cells have a high reversible capacity of 199.8 mAh g⁻¹ and high energy density of 489.4 Wh kg⁻¹ on electrode level at 0.2C with a two-step redox couple. Moreover, the cells with the two-step redox couple exhibit excellent stable cycle performance with high capacity retention and Coulombic efficiency for 3000 cycles. The nitroxide radical of PTMA can be converted to either an oxoammonium cation or an aminoxy anion; further, the redox reaction of each step exhibits different performance. The nitroxide radical–oxoammonium cation redox step in NCNTs shows a high rate capability owing to the high charge transfer rate and ion diffusion coefficient. The unusual results will help further improve the properties and commercialization of rechargeable organic batteries.