Reversible Lithium Uptake by FeP_2

摘要

The electrochemical reaction of lithium with the metal phosphide FeP_2 is reported. Li uptake in this material was investigated using electrochemical studies combined with X-ray diffraction, X-ray absorption spectroscopy, and magnetic measurements. The uptake of six Li during the first discharge leads to a specific capacity of 1365 mAh/g, and an amorphous phase retaining substantial Fe-P bonding that displays superparamagnetic behavior and an extremely low transition temperature. Upon charge, 5.5 lithium can be extracted from this metastable ternary "Li-Fe-P" phase, leading to a reversible capacity of 1250 mAh/g. The low (ca. 10-15 percent) irreversibility exhibited by FeP_2 makes it an interesting candidate in the search for new negative electrode materials.