Pre-doping iodine to restrain formation of low-active graphitic-N in hard carbon for significantly boosting sodium storage performance

Nitrogen doping can improve the electrocatalysis performance of hard carbon (HC) as a promising anode material in sodium-ion batteries, but is very challenging to controllably decrease the content of low-active graphitic-N in C–N configurations for raising the HC anode performance. Here an iodine-predoping approach is used to effectively restrain graphitic-N formation and its mechanism is further revealed, in which iodine preferentially occupies the vacancy sites of graphitic-type carbon to directionally induce nitrogenous species bonding with the vacancy sites of pyridinic- and pyrrolic-type. Experimental characterizations and theoretical calculations solidly confirm the mechanism. As expected, the controllably constructed HC anode exhibits the highest reversible capacity of 483.1 mAh g−1 at 30 mA g−1 among all reported HC works, while delivering a long lifespan up to 6000 cycles decaying only 0.0096% per cycle at 1 A g−1. This work sheds light on viable fundamentals for controllably constructing desired C–N configuration for host materials.