Three-dimensional N/O co-doped hard carbon anode enabled superior stabilities for sodium-ion batteries

Hard carbons (HCs) with low working potential have been considered one of the most promising anodes for sodium-ion batteries (SIBs), whereas the intrinsic poor rate performance and inferior cyclic stability hindered their practical application. Porosity designing and heteroatom doping are considered essential for high rate performance as well as durability by relieving volume expansion with Na-interaction and providing rapid Na+ diffusion paths. Herein, a three-dimensional N/O co-doped HCs (NOHCs) is synthesized as an anode for ultrastable SIBs. Combining X-ray photoelectron spectroscopy and transmission electron microscopy, we find that the content of pyrrolic-N is positively correlated with carbon interlayer distance, and the CO group could provide more active sites, thus superior reaction kinetics could be observed in NOHCs samples. In-situ Raman and ion diffusion kinetic analysis (GITT and CV) suggest that the integrated strategy of hetero doping and designed pore structure enables highly reversible electrochemical reactions and fast diffusion kinetics. Thus obtained NOHC-2 anode exhibits excellent capacity retention (69.8% after 15,000 cycles, 10.0 A g−1) and rate performance (160.2 mAh g−1 at 10.0 A g−1) with Na metal as the counter electrode. More importantly, the full cell composed of NOHCs anode and Prussian blue cathode delivers a high energy density of 97.3 Wh kg−1 with a power density of 985.7 W kg−1.