In this study, we developed an attractive synthesis approach for the incorporation of PO43− polyanions during the co-precipitation of Li(Ni0.90Co0.05Mn0.05)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 Px-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 P0.7-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+).​