Dr Rou Wang

N-doped highly porous carbons (NHPCs) derived from Victorian brown coal (VBC) were prepared through direct KOH activation in the presence of urea as the N source. Different weight ratios of KOH (VBC-urea mixture: KOH=1:0, 1:1, 1:2, and 1:3) have been used to optimize the porosity of NHPCs. Benefiting from the synergistic effect of the high porosity and N doping, the synthesized material with a high specific surface area of 687 m2/g and the N content at ~11 at% exhibited a high specific discharge capacity of 604.6 mAh/g at a current density of 0.1 A/g after 100 cycles and a high-rate performance of 245 mAh/g at 3 A/g. The developed material delivered a reversible capacity of 707.7 mAh/g at 0.05 A/g at the end of rate performance. The long-term cycling test performed at 1 A/g illustrates a stable and reversible capacity of 268 mAh/g after 1000 cycles with a coulombic efficiency of 100% and charge retention of 88%. The hierarchically porous carbon matrix with N doping can increase the Li+ diffusion efficiency and accelerate the charge transfer, thus leading to enhanced high-rate performance, superior reversibility, and high cyclic stability.

A few-layer graphene (FLG) composite material was synthesized using a rich reservoir and low-cost coal under the microwave-assisted catalytic graphitization process. X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were used to evaluate the properties of the FLG sample. A well-developed microstructure and higher graphitization degree were achieved under microwave heating at 1300¿ C using the S5% dual (Fe-Ni) catalyst for 20 min. In addition, the synthesized FLG sample encompassed the Raman spectrum 2D band at 2700 cm-1, which showed the existence of a few-layer graphene structure. The high-resolution TEM (transmission electron microscopy) image investigation of the S5% Fe-Ni sample confirmed that the fabricated FLG material consisted of two to seven graphitic layers, promoting the fast lithium-ion diffusion into the inner surface. The S5% Fe-Ni composite material delivered a high reversible capacity of 287.91 mAhg-1 at 0.1 C with a higher Coulombic efficiency of 99.9%. In contrast, the single catalyst of S10% Fe contained a reversible capacity of 260.13 mAhg-1 at 0.1 C with 97.96% Coulombic efficiency. Furthermore, the dual catalyst-loaded FLG sample demonstrated a high capacity¿up to 95% of the initial reversible capacity retention¿after 100 cycles. This study revealed the potential feasibility of producing FLG materials from bituminous coal used in a broad range as anode materials for lithium-ion batteries (LIBs).