Atomic layer deposition (ALD) of lithium fluoride (LiF) protective film on Li-ion battery LiMn1.5Ni0.5O4 cathode powder material

A protective lithium fluoride (LiF) film was deposited onto individual grains of LiMn 1.5 Ni 0.5 O 4 (LMNO) cathode powder material for high voltage Li-ion batteries via an Atomic Layer Deposition (ALD) technique. Lithium Tert-Butoxide (LiOtBut) was used as the Li source, alongside with two different fluoride sources: Hexafluoroacetylacetone (Hfac) and TiF 4 . Protective characteristics of the coatings were studied and examined via scanning electron microscopy (SEM) and inductive coupling plasma (ICP). The films show an improved protection against Mn dissolution. Electrochemical performance of LiF coated powder presented distinctive differences depending on the F source. Analysis of the chemical composition of the coating via X-ray photoelectron spectroscopy (XPS), Time of flight-secondary ion mass spectrometry (TOF-SIMS) and Transmission electron microscopy (TEM) revealed the presence of LiF, as well as carbon-fluoride species (CFx) when using Hfac as the fluorine source. When TiF 4 was utilized as the fluoride source, the film characterizations revealed LiF coating with a partial F doping. Both coatings presented an evidence of Li diffusion into the cathode material. • LiF was deposited on LMNO powder via ALD using two different fluorine sources. • Electrochemical performance was evaluated using CV, EIS and cycling. • Significant differences were observed depending on the fluorine source used. • Diffusion of Li and F ions was observed when TiF 4 was used as fluorine source. • When using Hfac, LiF-CFx layer was formed, facilitating better Li diffusion.