Anchoring Li3PO4 on Li5FeO4 Surface as a Prelithiation Additive for Lithium-Ion Batteries

Antifluorite-type Li 5 FeO 4 is regarded as an important cathode prelithiation material owing to its high specific capacity, yet its air stability needs to be further improved due to the high activity of Li 5 FeO 4 with CO 2 and water in the air. In this article, amorphous Li 3 PO 4 was anchored on the surface of Li 5 FeO 4 through a straightforward method to enhance its air stability. First, Fe 2 O 3 particles were dissolved in a certain concentration of NH 4 H 2 PO 4 solution followed by a drying process and calcination with Li 2 O to obtain Li 3 PO 4 -coated Li 5 FeO 4 . The structure and ingredients were confirmed by Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray Diffraction, Fourier Transform Infrared Spectroscopy, and X-ray Photoelectron Spectroscopy. Furthermore, the electrochemical performances were examined by Galvanostatic charge–discharge, Cyclic Voltammetry, and Electrochemical Impedance Spectroscopy. The results indicate that the final product exhibits a core–shell structure, with Li 5 FeO 4 as the core and Li 3 PO 4 as the shell. This unique structure not only provides better environmental stability for Li 5 FeO 4 but also improves its delithiation performance. Under optimal conditions, the product with 5% NH 4 H 2 PO 4 delivers the most remarkable performance. At a 0.05C current rate, it can deliver a specific capacity of 650.9 mAh –1, which is higher than that of pure Li 5 FeO 4 (612.3 mAh·g –1 ). After 3 h of exposure to air, the optimized sample demonstrates a superior capacity of 498.2 mAh·g –1 while the pure Li 5 FeO 4 retains only 193.9 mAh·g –1 . Moreover, the diffusion coefficient of the optimized sample is also remarkably improved due to the advantage of the fast ion conductivity property of Li 3 PO 4 . Finally, the prelithiation performance was tested through a full battery system employing NCM 811 as the cathode and silicon carbon as the anode, and the results indicate that the as-prepared product is a promising prelithiation additive to enhance capacity retention as well as improve the cyclability of lithium-ion batteries.