Etch-driven N, P co-doped hierarchical porous carbon embedded with Ni nanoparticles as an efficient dynamic carrier for room-temperature Na-S battery

Shuttle effect in Room temperature sodium-sulfur (RT NaS) batteries in ether-based electrolyte is difficult to avoid and reduces the cycle performance. Small molecule sulfur with short chain structure (e.g. S-2 similar to 4) can avoid shuttle effect but low conductivity. In this paper, a N, P co-doped hierarchical porous carbon embedded with Ni nanoparticles (Ni@NPC) is developed by heat-treatment method using commercially phosphorus-containing chelating resin for waste water as the precursor, which adsorb Ni2+ by both physical and chemical process. The micro-pores in the Ni@NPC composite provide the matrix for S-2 similar to 4, the mesoporous-macropore are conductive to the transmission of electrolyte and the carbon skeleton together with Ni nano-particles facilitate the electron transport. As a result, Ni@NPC/S cathode exhibits a sodium diffusion coefficient of the order of 10(-7)- 10(-9), which is better than reported literatures. Similarly, Ni@NPC/S has excellent cycling performance (maintained at a specific capacity of 231.5 mAh g(-1) after 7000 cycles at 5 A g(-1), with an average decay rate of 0.004 % per cycle) and rate performance (258.3 mAh g(-1) at a high current density of up to 10 A g(-1)).