In situ forming of ternary metal fluoride thin films with excellent Li storage performance by pulsed laser deposition

Abstract

In the field of lithium ion battery, conversion-based metal fluoride cathodes are attractive for their excellent theoretical capacity and high voltage. However, the utilization of binary metal fluorides is severely hindered by irreversibility and large voltage hysteresis. The introduction of ternary metal fluorides, like AgCuF3 and CuxFe1-xF2, brings hope to address these shortcomings. To better understand the basic mechanism of conversion reaction in ternary metal fluoride cathodes, the Cu–Fe–F (CFF) thin films were successfully grown in situ by pulsed laser deposition in this work. The physico-chemical properties and electrochemical performance were discussed. Such a CFF solid solution phase presented great cycle stability (82% capacity remains after 100 cycles at current density of 285 mA g−1) and higher energy efficiency (71.8%), which can be attributed to the reversible structural rearrangement after the delithiation process disclosed by ex situ XPS, high-resolution TEM, and selected-area electron diffraction.