Surface modification with Li3PO4 enhances the electrochemical performance of LiNi0.9Co0.05Mn0.05O2 cathode materials for Li-Ion batteries

Although high-nickel cathodes (Ni ≥ 90%) have immense potential for use in lithium-ion batteries (LIBs) because of their high energy densities and low material costs. However, structural instability and poor cycling performance have hampered their applications. In this study, we synthesized LiNi0.9Co0.05Mn0.05O2 (denoted "NCM9055″) cathode materials and coated them with Li3PO4 by using a wet-chemical method. We employed X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy to investigate the effects of Li3PO4 surface modification. The (NH4)2HPO4 precursors reacted with the surface residual lithium compounds of NCM9055 to form amorphous Li3PO4 and this active coating layer improved the chemical stability at the electrode-electrolyte interface by suppressing deleterious surface side reactions. Accordingly, the Li+ ion conductivity, rate capability, and long-term cycling performance of the material improved significantly. Measurements of the electrochemical performance revealed that after 200 cycles at a rate of 1 C and a cut-off voltage of 2.7–4.3 V, the 1 mol% Li3PO4–coated NCM9055 (denoted "1P@NCM9055") cathode retained 90.2% of its initial discharge capacity (ca. 192.9 mA h g–1), whereas the pristine (NCM9055) retained 74.2% of its initial discharge capacity (ca. 196.8 mA h g–1) at room temperature. Our findings should encourage the development and applications of our as-prepared Ni-rich cathode materials in commercial LIBs.