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 LiNi_0.6Co_0.2Mn_0.2O₂ (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.

磷酸锂（Li ₃ PO ₄）是众所周知的锂离子固体电解质。在这项研究中，我们分析了Li ₃ PO ₄涂层对富镍阴极LiNi _0.6 Co _0.2 Mn _0.2 O ₂（NCM）的电化学性能的影响。特别地，经涂覆的材料在高压下表现出增强的循环稳定性并且具有优异的倍率能力。在具有不同涂层水平（0.5–3 wt％）的阴极中，具有2 wt％的Li ₃ PO ₄的阴极之所以能够提供最佳的倍率性能，可能是因为它具有适中的涂覆水平，在该水平上可以抑制过量阴极电解质界面（CEI）的形成。因此，获得了最佳的涂层，从而避免了过量CEI对离子传导的抑制，同时也可以阻碍离子迁移的涂层厚度最小。如X射线光电子能谱和电化学阻抗谱所揭示的，涂覆的NCM有效地抑制了CEI的形成，特别是具有绝缘性质的LiOH组分的形成。结果，在相对于Li / Li ^+的电压为3.0–4.9 V循环后，涂层的NCM保留了相对容量的70％以上，而原始的NCM仅保留了35.1％的相对容量。持续200个周期。这项研究表明，人工CEI层对于增强富Ni的NCM阴极的高压稳定性和倍率能力有效。