Thermal vapor sulfurization modified micro-sized red phosphorus/activated carbon composite anode for sodium-ion batteries

High-capacity red phosphorus/activated carbon (P/C) composites are promising anode materials for next-generation sodium-ion batteries. However, the poor conductivity and significant volume effect of red phosphorus inevitably deposited on the outer surface of P/C composites may incur significant capacity decay and structural degradation. This work reports a method for preparing surface-modified micro-sized P/C composites with built-in nanoscale features. Through thermal vapor sulfurization, the obtained micron-sized sulfur-modified P/C (S-P/C) composites not only fulfill the requirements of the battery manufacture but also maintain their nano-in-micro structure. It can eliminate the detrimental red phosphorus on the outer surface of P/C composites and convert it into the ion conductive layer of Na3PS4, limiting its volume effect and significantly promoting ion conduction. As a result, S-P/C composites exhibit excellent cyclic stability in a half cell (610 mAh/g at 0.2 A/g and capacity retention of 94.2 % after 100 cycles) and reach a high areal capacity level (1.99 mAh cm−2) in a full cell.