Iron Metal Based Positive Electrodes for Metal Fluoride High Energy Lithium Batteries

Lithium-ion batteries are at the forefront of energy storage, ranging from wearables to the automotive and aviation industry, but their performance, safety, and renewability have much room for improvement. Metal fluoride conversion materials, particularly iron fluorides, provide an avenue for growth by improving cost and power densities. A challenge to these materials has been their lack of an intrinsic supply of lithium which must be accommodated by having lithium at the negative electrode or other means. This study presents a novel pathway involving Fe and LiF within a glass forming fluoride to enable the use of metal fluoride in its lithiated state. The LiF composite enhances the kinetics of the Li+ and F- transport required to form FeF3 in-situ. Although presently only in low areal capacity construction, this proof of concept was successfully demonstrated in thin-film form utilizing a backbone of LLZO based solid state electrolyte, in a full solid state battery, that showed over 2 years of cycling and little capacity loss. Furthermore, this clean and isolated system confirmed the formation of FeF3 by X-ray photoelectron spectroscopy, providing insights on the ion transport of Fe2+ and F- to enable the in-situ formation of FeF3.