Sulfur-doping biomass based hard carbon as high performance anode material for sodium-ion batteries

The intercalation/deintercalation of Na+ in the hard carbon (HC) has been widely investigated for the construction of high performances sodium-ion batteries (SIBs). In this work, a variety of sulfur-doped HCs were obtained by simple pyrolysis of the sublimated sulfur and the camphor tree (S-Cmph) derived material. When used as anode for SIBs, the S-Cmph-700 (pyrolyzed at 700celcius) delivered a capacity of 616.7 mAh/g with an ICE of 66.61 %, high than that of the untreated material pyrolyzed at 1500celcius (50.11 %) (Cmph-1500). Furthermore, excellent rate performance with specific capacities of 372.3, 323, 282.6, 252.6, 221, 181.2 mAh/g at 40, 80, 200, 400, 800 and 2000 mA g-1 can be achieved, respectively. When the current density returned at 40 mA g-1, the anode recovered a specific capacity of 356.8 mAh/g. In addition, the as-acquired anode material exhibited good cycling performance with a reversible capacity of 145.6 mAh/g over 500 cycles at 2000 mA g-1. The improved electrochemical performances of Cmph-HC anode can be attributed to the benefit of the S-doping, leading to the increase of the interlayer spacing of the anode material, which facilitates the intercalation/deintercalation of Na+ ions in the interlayer spacing of the HC material, and provided more active sites in the Cmph-HC anode for the Na+ ions storage. In addition, sulfur can reversibly react with Na+, limiting the irreversible consumption of Na+ and increase the intercalation rate of Na+ inside the anode material. This work presents a low cost, simple and effective way to synthesize a high performances anode material for the commercialization of SIBs.