Heteroatom screening and microcrystal regulation of coal-derived hard carbon promises high-performance sodium-ion batteries

Coal is a cost-effective and high-yield precursor for the carbon anode of sodium-ion batteries (SIBs). To enhance Na+ storage behavior, it is crucial to prevent long-range graphitization of microcrystals within the coal structure during high-temperature carbonization. Herein, we present a strategy to inhibit graphitized microcrystals of anthracite-derived carbon, which reveals the correlations between the initial Coulombic efficiency (CE) and heteroatom/defects. By introducing NH3 during the carbonization process of anthracite, it is possible to effectively remove the heteroatoms (O, S, etc.) in anthracite, while also expanding the spacing of carbon layers derived from anthracite. This results in obtaining high capacity and high initial CE. Using Nitrogen-doped anthracite hard carbon (N-AC-1200) as an anode material for SIBs, a high reversible capacity of 220 mA h g−1 at 0.1 A g−1 is achieved. Furthermore, a full cell assembled by Na2/3Ni1/3Mn2/3O2 (NNMO) cathode and N-AC-1200 anode delivers a high capacity of 76 mA h g−1 at 5C. The insights provided by this work will help guide the design of heteroatom-controlled hard carbon microcrystalline environment and provide new ideas for practical hard carbon electrode design principles.