Optimizing surface residual alkali and enhancing electrochemical performance of LiNi0.8Co0.15Al0.05O2cathode by LiH2PO4.

LiNi0.8Co0.15Al0.05O2(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 Li2CO3) on the surface will accelerate its reaction with HF from LiPF6, resulting in structural degradation and reduced safety. In this work, we develop a new coating material, LiH2PO4, which can effectively optimize the residual alkali on the surface of NCA to remove H2O and CO2and form a coating layer with excellent ion conductivity. Under this strategy, the coated sample NCA@0.02Li3PO4(P2-NCA) provides a capacity of 147.8 mAh g-1at 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.