Superior high voltage LiNi0.6Co0.2Mn0.2O2 cathode using Li3PO4 coating for lithium-ion batteries

Lithium phosphate (Li3PO4) is a well-known solid electrolyte for lithium-ions. In this study, we analyzed the effects of Li3PO4 coating on the electrochemical performance of LiNi0.6Co0.2Mn0.2O2 (NCM), a nickel-rich cathode. In particular, the coated materials exhibited enhanced cycle stability at high voltages and possessed superior rate capability. Among the cathodes with different coating levels (0.5–3 wt%), the one with 2 wt% of Li3PO4 provided the best rate capability, possibly because it is a moderate coating level at which the formation of an excessive cathode electrolyte interface (CEI) is suppressed. Thus, an optimal coating was achieved such that the inhibition in the ionic conduction by the excessive CEI is avoided, while the thickness of the coating layer, which can hinder the ionic transport as well, is minimal. The coated NCM effectively suppressed the formation of CEI, especially LiOH component with insulating nature, as revealed by X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. As a result, the coated NCM retained more than 70% of the relative capacity, while pristine NCM retained only 35.1% relative capacity after cycling at 3.0–4.9 V vs. Li/Li+ for 200 cycles. This study demonstrates that an artificial CEI layer is effective for enhancing the high-voltage stability and rate capability of Ni-rich NCM cathodes.