Polyanion incorporation strategy enables stable operation of Ni-rich NCM90 up to 4.5 V with tailored structural and electrochemical performance

In this study, we developed an attractive synthesis approach for the incorporation of PO₄³⁻ polyanions during the co-precipitation of Li(Ni_0.90Co_0.05Mn_0.05)O₂ (NCM90). This strategy effectively mitigates the inherent cycle stability issues at high cut-off voltages while enhancing both specific capacity and rate capability. By incorporating PO₄³⁻ polyanions into the NCM90 structure (denoted as P_x-NCM90, where x = 0.0, 0.5, 0.7, and 0.9, representing the added mole % of PO₄³⁻), the electrochemical performance was significantly improved. The optimized P_0.7-NCM90 delivered a high discharge capacity of ∼230 mAh g⁻¹ at 0.1 C within 3.0–4.5 V (vs. Li/Li⁺) with an initial Coulombic efficiency of ∼93.2 %. It also exhibited high rate capability (∼185 mAh g⁻¹ at 4.0 C) and improved cycling stability, retaining ∼84 % of its capacity after 100 cycles at 1.0 C. Comprehensive physicochemical and electrochemical characterizations, including in-situ X-ray diffraction (XRD), revealed that the highly distributed PO₄³⁻ incorporation stabilizes the NCM90 structure. These findings highlight that PO₄³⁻ addition during co-precipitation is an effective strategy for improving the stability and electrochemical performance of high-Ni layered oxide cathodes at a high cut-off potential of 4.5 V (vs. Li/Li⁺).