Optimizing surface residual alkali and enhancing electrochemical performance of LiNi 0.8 Co 0.15 Al 0.05 O 2 cathode by LiH 2 PO 4

Abstract LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA), a promising ternary cathode material of lithium-ion batteries, has widely attracted attention due to its high energy density and excellent cycling performance. However, the presence of residual alkali (LiOH and Li 2 CO 3 ) on the surface will accelerate its reaction with HF from LiPF 6 , resulting in structural degradation and reduced safety. In this work, we develop a new coating material, LiH 2 PO 4 , which can effectively optimize the residual alkali on the surface of NCA to remove H 2 O and CO 2 and form a coating layer with excellent ion conductivity. Under this strategy, the coated sample NCA@0.02Li 3 PO 4 (P2-NCA) provides a capacity of 147.8 mAh g −1 at a high rate of 5 C, which is higher than the original sample (126.5 mAh g −1 ). Impressively, the cycling stabilities of P2-NCA under 0.5 C significantly improved from 85.2% and 81.9% of pristine-NCA cathode to 96.1% and 90.5% at 25 °C and 55 °C, respectively. These satisfied findings indicate that this surface modification method provides a feasible strategy toward improving the performance and applicability of nickel-rich cathode materials.