P-doped hard carbon material for anode of sodium ion battery was prepared by using polyphosphoric acid modified petroleum asphalt as precursor

The practical value of hard carbon anode in sodium ion batteries has garnered significant attention. Asphalt-derived hard carbon offers lower cost and scale advantages compared to expensive resin and bio-based hard carbon materials. However, the synthesis of asphalt-derived hard carbon with significantly enhanced reversible capacity remains challenging. This study focuses on synthesizing P-doped hard carbon material using polyphosphoric acid-modified petroleum asphalt as a precursor and the pre-oxidation method. Doping P elements in hard carbon induces deformation of the molecular layer structure within the pseudo-graphite domains, expanding graphite layer spacing and increasing the number of internal closed micropores, thereby enhancing the sodium storage capacity of the matrix. The reversible capacity of P-doped hard carbon (PHC-1300) increased from 240.3 mA h g−1 to 359.9 mA h g−1 during the initial charge-discharge cycle at a rate of 0.05 C compared to undoped hard carbon (HC-1300). Moreover, phosphate exhibits higher reduction ability than adjacent carbon atoms, generating electron holes that partially compensate for limited electron conduction capability in hard carbon material. The electronic conductivity of the material increases from 26.1114 S cm−1 to 36.6418 S cm−1, demonstrating a significant enhancement compared to high graphitized soft carbon (SC-1300).Therefore, the practical significance of employing this straightforward precursor modification method to prepare P-doped hard carbon warrants attention.