Sodium hypophosphite-assist pyrolysis of coal pitch to synthesis P-doped carbon nanosheet anode for ultrafast and long-term cycling sodium-ion batteries

Sodium-ion battery has been considered as an ideal alternative to lithium-ion battery due to the abundant resource of sodium. Hard carbon stands a good chance among most carbons to be the most promising anode material for sodium-ion battery because of its randomly oriented graphite layers. However, the disordered graphite layers display sluggish kinetics of sodium ions thus the high-rate capability of hard carbon in sodium-ion battery is still a big challenge. In this study, extremely ultrafast P-doped carbon nanosheet anode with graphene-like wrinkles and sheet thickness of ca. 8 nm for sodium-ion battery was synthesized by pyrolysis of coal pitch with the assistance of sodium hypophosphite. The ultrathin sheet structure and P-doped property could render pseudocapacitive behavior, as a result, the resultant carbon nanosheet anode delivers high-rate capacity and also the long-term cycling stability (i.e., a high reversible capacity of 189 mA h g−1 at 2 A g−1 after 500 cycles, and an extraordinarily high capacity of 80 mA h g−1 at 20 A g−1 after 10,000 cycles).