In situ steam oxidation of nickel phosphide/carbon composite nanofibers as anode materials for lithium-ion batteries

The synthesis of self-standing nickel phosphide/carbon (Ni_xP/C) composite nanofibers is accomplished through a one-pot electrospinning and in situ steam oxidation after the carbothermal reduction process. Control over the levels of in situ steam oxidizers in the forms of crystal water and nitrates in the precursor fibers is achieved by systematically adjusting the drying temperature before the high-temperature heat treatment. This led to structural modifications in the final products analyzed through comprehensive characterizations. Mechanistic insights into the in situ steam oxidation process are provided, emphasizing its potential in optimizing electrode materials. Electrochemical assessments reveal significantly improved performance in the sample prepared from the media with optimal content of oxidizers, attributed to a tailored surface oxide layer, electronic configuration, and microstructure, enabling enhanced reaction kinetics and minimizing volume expansion. This results in exceptional cycling stability and notable capacity retention during prolonged charge-discharge cycles. Thus, Ni_xP/C achieves the highest initial charge capacity of 719.5 mAh g⁻¹ with an initial Coulombic efficiency of 61% and maintains a high capacity of 590.7 mAh g⁻¹ after 100 cycles at a current density of 0.1 A g⁻¹.