Slightly fluorination of Al₂O₃ AlD coating on Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ electrodes: Interface reaction to create stable solid permeable interphase layer

Improving the performance of cathodes by using surface coatings has proven to be an effective method for improving the stability of Li-ion batteries (LIBs), while a high-quality film satisfying all requirements of electrochemical inertia, chemical stability, and lithium ion conductivity has not been found. In this study, a composite film composed of Al₂O₃ and AlF₃ layers was coated on the surface of Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ (Li-rich NMC) based electrodes by atomic layer deposition (ALD). By varying the ratio of Al₂O₃ and AlF₃, an optimal coating was achieved. The electrochemical characterization results indicated that the coating with 1 cycle of AlF₃ ALD on 5 cycles of Al₂O₃ ALD (1AlF₃-5Al₂O₃) significantly improved the cycling stability and alleviated the voltage attenuation problem of Li-rich NMC based electrodes by suppressing side reactions between the electrolyte and electrode, as well as inhibiting the transformation of layered Li₂MnO₃ into a spinel-like phase. After 200 cycles of charge-discharge, the discharge capacity retention of LIB half cells based on 1AlF₃-5Al₂O₃ coated Li-rich NMC electrodes kept at 84%, much higher than that of the uncoated Li-rich NMC (the capacity retention less than 20%).