Enhanced cycling stability of LiNiO2 cathodes through a Mg/W dual-cation modification strategy

LiNiO2 cathodes for lithium-ion batteries offer the prospect of high specific capacities; however, a plethora of structural and surface instabilities occur during cycling, which can limit their lifetime and impinge on their safety. Structural and surface modification strategies such as cation-doping have been shown to stabilise cycling performance and prolong cathode lifetimes, yet they often tackle either surface or bulk driven degradation processes. Here, we present a dual-cation substitution approach for the LiNiO2 cathode which produces a coat-doped cathode in a single step. Judicious selection of cation substituents enables the targeted stabilisation of both bulk- and surface-originating instabilities, in this case magnesium and tungsten, respectively. While the addition of tungsten as a sole substituent promotes a rock-salt surface layer which typically reduces the observable capacity, we demonstrate that the incorporation of Mg into W-containing compositions can mitigate these structural transformations. These coat-doped Mg/W-LiNiO2 cathodes exhibit superior cycling stabilities compared to unmodified LiNiO2 and singly-substituted Mg- or W-LiNiO2. X-ray diffraction computed tomography methods complement these findings, providing spatially resolved structural information on the location and heterogeneity of the coat-doped cathodes, guiding synthetic pathways to optimised materials that outperform undoped LiNiO2 even in high-mass loading cell environments.