Electric vehicles powered by lithium‐ion batteries are viewed as a vital green technology required to meet CO₂ emission targets as part of a global effort to tackle climate change. Positive electrode (cathode) materials within such batteries are rich in critical metals—particularly lithium, cobalt, and nickel. The large‐scale mining of such metals, to meet increasing battery demands, poses concerns surrounding material exhaustion in addition to further environmental, social, and governance (ESG) issues. In particular, unethical mining practices and political instability within the Democratic Republic of the Congo (the world's largest cobalt producer) have prompted research into cobalt‐low and cobalt‐free alternatives. This review aims to provide a holistic view of lithium‐ion cathode development and inform advancements by highlighting the interdependencies across mining, material development, and end‐of‐life management. While material sustainability is reported through supply and demand projections, the potential socioenvironmental impacts of lithium‐ion battery technology represent a hugely underresearched area among the aforementioned themes. Notably, the lack of attention paid toward future implications of increased nickel use across material management and development disciplines is also discussed.

Conventional intercalation cathodes for lithium batteries store charge in redox reactions associated with the transition metal cations, e.g. Mn3+/4+ in LiMn2O4, and this limits the energy storage of Li-ion batteries. Compounds such as Li[Li0.2Ni0.2Mn0.6]O2 exhibit a capacity to store charge in excess of the transition metal redox reactions. The additional capacity occurs at and above 4.5 V vs. Li+/Li. The capacity at 4.5 V is dominated by oxidation of the O2- anions accounting for ~0.43 e-/formula unit, with an additional 0.06 e-/formula unit being associated with O loss from the lattice. In contrast, the capacity above 4.5 V, is mainly O loss, ~ 0.08 e-/formula. The O redox reaction involves the formation of localized hole states on O during charge, which are located on O coordinated by (Mn4+/Li+). The results have been obtained by combining operando electrochemical mass spec on 18O labelled Li[Li0.2Ni0.2Mn0.6]O2 with XANES, soft X-ray spectroscopy, Resonant Inelastic X-ray spectroscopy and Raman spectroscopy. Finally the general features of O-redox are described with discussion about the role of comparatively ionic (less covalent) 3d metal-oxygen interaction on anion redox in lithium rich cathode materials.

Layered sodium transition metal oxides with the P2 structure, e.g. Na_2/3[Ni_1/3Mn_2/3]O₂, are regarded as candidates for Na-ion battery cathodes. On charging, extraction of Na destabilizes the P2 phase (ABBA oxide ion stacking) in which Na⁺ is in trigonal prismatic coordination, resulting in layer gliding and formation of an O2 phase (ABAC stacking) with octahedral coordination. However, many related compounds do not exhibit such a simple P2 to O2 transition but rather form a so called “Z”-phase. Substituting Ni by Fe in Na_2/3[Ni_1/3Mn_2/3]O₂ is attractive as it reduces cost. The Fe containing compounds, such as Na_2/3[Ni_1/6Mn_1/2Fe_1/3]O₂, form a “Z”-phase when charged above 4.1 V vs. Na⁺/Na. By combining ex situ and operando X-ray diffraction with scanning transmission electron microscopy and simulated diffraction patterns, we demonstrate that the “Z”-phase is most accurately described as a continuously changing intergrowth structure which evolves from P2 to O2 through the OP4 structure as an intermediate. On charging, Na⁺ removal results in O-type stacking faults within the P2 structure which increase in proportion. At 50% O-type stacking faults, the ordered OP4 phase forms and on further charging more O-type stacking faults are formed progressing towards a pure O2 structure. This gives the superficial appearance of a solid solution. Furthermore, in contrast to some previous studies, we did not detect Fe migration at any state-of-charge using ⁵⁷Fe-Mössbauer spectroscopy. It was, however, found that the Fe-substitution serves to disrupt cation ordering in the material.

Magnesium substituted P2-structure Na_0.67Ni_0.3Mn_0.7O₂ materials have been prepared by a facile solid-state method and investigated as cathodes in sodium-ion batteries. The Mg-doped materials described here were characterized by X-ray diffraction (XRD), ²³Na solid-state nuclear magnetic resonance (SS-NMR), and scanning electron microscopy (SEM). The electrochemical performance of the samples was tested in half cells vs Na metal at room temperature. The Mg-doped materials operate at a high average voltage of ca. 3.3 V vs Na/Na⁺ delivering specific capacities of ∼120 mAh g^–1, which remain stable up to 50 cycles. Mg doping suppresses the well-known P2–O2 phase transition observed in the undoped composition by stabilizing the reversible OP4 phase during charging (during Na removal). GITT measurements showed that the Na-ion mobility is improved by 2 orders of magnitude with respect to the parent P2–Na_0.67Ni_0.3Mn_0.7O₂ material. The fast Na-ion mobility may be the cause of the enhanced rate performance.