Atomic layer deposition (ALD) of lithium fluoride (LiF) protective film on Li-ion battery LiMn_1.5Ni_0.5O₄ cathode powder material

A protective lithium fluoride (LiF) film was deposited onto individual grains of LiMn_1.5Ni_0.5O₄ (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 TiF₄. 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 TiF₄ 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.