Enhanced Performance of LiFePO4 Cathodes with Alumina Nanocoating by Atomic Layer Deposition: Insights from Electrochemical, Operando X-ray Diffraction, and X-ray Photoelectron Spectroscopy Analyses

This study investigates the application of ultrathin Al2O3 (alumina) coatings, deposited via atomic layer deposition (ALD), to improve the electrochemical performance of LiFePO4 cathodes in lithium-ion batteries. Using 2–20 ALD cycles, we explore how these alumina layers impact rate capability, long-term cycling, and stability under various conditions, including high C-rates and elevated temperature. Cathodes coated with 5 ALD cycles exhibited significantly enhanced capacity at high charge/discharge rates compared to uncoated samples. Electrochemical impedance spectroscopy (EIS) revealed a lower charge transfer resistance for the 5 ALD cycle alumina-coated sample compared with the pristine sample. Full-cell configurations with coated LiFePO4 also demonstrated superior performance and cycle life for the ALD-coated cathodes. Additionally, X-ray photoelectron spectroscopy (XPS) measurements conducted before and after electrochemical tests revealed differences in the composition of the cathode electrolyte interphase (CEI) layer. Operando X-ray diffraction (XRD) measurements confirmed the protective nature of ALD alumina layers by showcasing the reversibility of the LiFePO4 to FePO4 phase transition during charging/discharging.