Low-cost lignite-derived hard carbon for high-performance sodium-ion storage

Sodium-ion batteries are regarded as the most promising alternative candidates for lithium-ion batteries. Hard carbon, as a kind of anode materials, has been demonstrated to deliver high specific capacity and stable cycling performance. However, it is still difficult to strike the balance between the relatively high cost and the superior electrochemical performance. We successfully fabricated low-cost lignite-derived hard carbons (a-LCs) with easy scale-up method. The microstructure, morphology and surface information of the obtained a-LCs are evaluated by X-ray diffraction, Raman spectrum and Fourier transform infrared spectrometer. By changing carbonization temperature, a-LCs’ microstructure and defect composition can be tuned and quite different sodium-ion storage behaviors can be seen. When carbonization temperature increases, the carbon microcrystallites grow and defects decay, resulting in a decrease in defect absorption capacity and an increase in graphitic-like nanodomain intercalation capacity. Particularly, a-LC carbonized at 1200 °C (a-LC-1200) can deliver a high capacity of 256 mAh g⁻¹ with the initial Coulombic efficiency of 82%. Besides, it also exhibits a superior rate performance of 210, 197, 180, 168 and 146 mAh g⁻¹ at current rates of 1, 2, 5, 10 and 20C (defined that 1C = 200 mA g⁻¹), respectively. It solves the above problems very well and displays great commercial value.