Molecular tuning of sulfur doped quinoline oligomer derived soft carbon for superior potassium storage

Soft carbon has been considered as one of the most promising high-performance potassium-ion battery anodes owing to the advantages of high carbon crystallinity and conductivity. Nevertheless, the lack of microstructure tunning strategy for soft carbon generally leads to low interlayer spacing and limited active sites, which results in relatively low storage capacity and sluggish kinetics. Herein, sulfur doped quinoline oligomer derived soft carbon nanosheets (SNC) have been successfully fabricated with expanded interlayer spacing, modest defects, and relatively ordered carbon clusters. These favorable characteristics can not only contribute to a high potassium storage capacity, but also shorten the diffusion spacing for both electrons and ions. Hence, SNC displays an extremely high capacity (456 mA h g−1 at 0.05 A g−1) and long cyclability (189 mA h g−1 at 2.0 A g−1 after 1000 cycles), superior to most of recently reported carbon anodes. Kinetic analyses demonstrate that sulfur doped quinoline oligomer derived soft carbon can significantly boost the potassium diffusion. Additionally, the enlarged interlayer spacing and modest defect sites benefitted from high sulfur doping could further enhance potassium storage properties. This study provides a facile molecular tuning and large-scale production strategy for soft carbon anodes with high capacity and long life.