Atomic Layer Deposition of Stable LiAlF₄ Lithium Ion Conductive Interfacial Layer for Stable Cathode Cycling

Modern lithium ion batteries are often desired to operate at a wide electrochemical window to maximize energy densities. While pushing the limit of cutoff potentials allows batteries to provide greater energy densities with enhanced specific capacities and higher voltage outputs, it raises key challenges with thermodynamic and kinetic stability in the battery. This is especially true for layered lithium transition-metal oxides, where capacities can improve but stabilities are compromised as wider electrochemical windows are applied. To overcome the above-mentioned challenges, we used atomic layer deposition to develop a LiAlF₄ solid thin film with robust stability and satisfactory ion conductivity, which is superior to commonly used LiF and AlF₃. With a predicted stable electrochemical window of approximately 2.0 ± 0.9 to 5.7 ± 0.7 V vs Li⁺/Li for LiAlF₄, excellent stability was achieved for high Ni content LiNi_0.8Mn_0.1Co_0.1O₂ electrodes with LiAlF₄ interfacial layer at a wide electrochemical window of 2.75-4.50 V vs Li⁺/Li.