Ni-rich layered oxide positive electrode active materials are promising for high-energy non-aqueous lithium-based batteries, but their poor structural stability limits their high-power applications. Here, to address this issue, we propose a two-step doping strategy for the synthesis of Ni-rich positive electrode active materials. This involves an initial lithiation of the hydroxide precursor at an intermediate temperature, followed by cooling, dopant mixing and high-temperature calcination. This approach yields positive electrode active materials with nanoscale primary particles, thereby improving mechanical stability and suppressing intergranular cracking. Moreover, the material prepared via a two-step doping strategy exhibits a layered–rocksalt nanostructured multiphase, which reversibly transforms into a layered-spinel nanostructured multiphase upon cell charging, facilitating lithium-ion diffusion. As a result, the nanostructured Nb-doped Ni-rich multiphase positive electrode active material enables improved high-rate performance when tested in both Li metal coin cell and Li-ion pouch cell configurations, also applying electric vertical take-off and landing testing protocols.