Ammonium polyphosphate assisted thermal polymerization of pre-oxidized asphalt to prepare N/P double-doped hard carbon for improved sodium ion storage

The low reversible capacity and electronic conductivity of oxidized asphalt-derived hard carbon are difficult to meet the commercial demand. Heteroatom doped carbon has been shown to modulate graphite-like crystal structure. N/P diatomic doping of hard carbon is designed here, which is realized by ammonium polyphosphate (APP) assisted thermal polymerization. The reversible capacity of N/P double-doped hard carbon (NPHC41-1300) reaches 314 mA h g−1 at 15 mA g−1, after 100 cycles at a current density of 0.3 A g−1, the reversible capacity is measured to be 224.1 mA h g−1, while maintaining a reversible capacity of 116 mA h g−1 at a current density of 1.5 A g−1, indicating excellent cyclic and high rates performance. Moreover, the electronic conductivity of N and P co-doped hard carbon (NPHC41-1300) is 17.0060 S cm−1, exhibiting a remarkable enhancement of 177 % compared to that of undoped hard carbon (HC-1300). Which creates conditions for promoting the practical application of asphalt-derived hard carbon as the negative electrode material of sodium ion battery.