Study on lithium storage performance of plum-putting-like CoP nanoparticles embedded in N, P co-doped porous carbon

Metallic cobalt phosphide (CoP) has a higher theoretical capacity than traditional graphite anode due to its unique lithium storage mechanism. However, CoP can not be directly used as anode material because of its insufficient conductivity and serious volume expansion in cycles. Here, CoP was modified by nanocrystallization and carbon compositing methods, and plum-putting-like CoP nanoparticles embedded in nitrogen and phosphorus co-doped porous carbon (CoP@NPPC) were prepared. The successful nanocrystallization strategy leads to the formation of tiny CoP nanodots smaller than 20 nm and nanoparticles smaller than 100 nm, which uniformly disperse in the simultaneously formed N and P co-doped porous carbon. The CoP nanodots and nanoparticles are chemically bonded to carbon by PC bond, which is theoretically proved to bring increased density of states of CoP at Fermi level, responsible for its conductivity improvement. At the same time, the nanocrystallization of CoP also alleviates its volume expansion and particle breakage after numbers of lithiation reactions, thus improving the electrode stability in cycles. Based on the above characteristics, CoP@NPPC achieves a high capacity retention rate of 95.9% and a remaining specific capacity of 380.1 mAh g-1 after 1800 cycles at the current density of 5 A g-1. Moreover, the preparation of CoP@NPPC is achieved by a simple carbothermic treatment using a highly safe flame-retardant material as both P and C sources, which avoids the release of highly toxic phosphine that are usually involved in traditional phosphorization methods.