Electrochemical characteristics of pyrrhotine as anode material for lithium-ion batteries

Micron-sized pyrrhotine particles with a standard hexagonal structure were prepared by simple precipitation and subsequent heat treatment and were investigated as anode material for lithium-ion batteries. The as-prepared Fe7S8 electrode delivered a highly reversible capacity of 604.1 mAh/g with a voltage range of 2.5-0.05 V. X-ray diffraction, scanning electronic microscopy and X-ray photoelectron spectroscopy were employed to characterize the reaction products at different stages, and a possible two-step reaction mechanism was proposed. The electrochemical test results demonstrated that the discharge/charge voltage range had a remarkable influence on the capacity retention and coulombic efficiency, which could be associated with the decomposability of lithiation products and volume change. Additionally, the dissolution of Li2Sx (2 < x < 8) in electrolyte was found to cause severe capacity loss as well. Thus a proper coating layer and cycling voltage range were essential for this kind of electrode material to achieve practical application in lithium-ion batteries.