N, S co-doped porous carbon microtubes with high charge/discharge rates for sodium-ion batteries

Pseudocapacitance, typically occurring on the surface of the electrode material, plays a crucial role in improving the charge/discharge rate of sodium ion batteries (SIBs). In this work, N, S co-doped porous carbon microtubes (SNCTs) are prepared through modified in situ polymerization and subsequent annealing with sublimed sulphur in a nitrogen atmosphere. The one-dimensional porous hollow structure enhances the electrolyte penetration and shortens the sodium-ion diffusion pathway, while the N, S doping improves the electrical conductivity of carbon and offers excess reaction sites for sodium-ion storage. The electrode reactions are dominated by a pseudocapacitive process, which can effectively shorten the sodium-ion diffusion pathway and provide extra capacity, resulting in high-rate capability. When used as anodes for SIBs, SNCTs demonstrate good cycling stability (222 mA h g−1 at 2000 mA g−1 after 800 cycles) and superior rate performance (288 and 252 mA h g−1 at 1000 and 2000 mA g−1, respectively). A room-temperature full cell SIB is further assembled using the SNCT as the anode and commercial Na3V2(PO4)3 as the cathode, which exhibits a high specific capacity of 186.1 mA h g−1 after 50 cycles at 50 mA g−1. This work should provide new insights into carbon-based anode materials as high-performance anodes for SIBs.