The earliest studied oxide cathode is the layered LiCoO 2 . With the rising prices for cobalt and the geopolitical issues with its supply, nickel became a popular ingredient for cathodes since it is cheaper and more abundant. This led to the discoveries of ternary Li-Ni-O compounds such as LiNiO 2 and Li 2 NiO 3 which eliminate the use of Co (see Figure ). The composition and structure of several Li-Ni-O phases have very specific growth conditions. A subtle change in the Li/Ni ratio and oxygen partial pressure can lead to different structures. This is because: (1) many of those structures are related as they are based on the same oxygen cubic close-packed (ccp) sublattice; (2) Ni 3+ and Ni 4+ are difficult to stabilize and can be easily converted to Ni 2+ (e.g. via disproportionations); (3) cation mixing becomes more favorable due to the similar ionic radii of Ni 2+ (0.69 Å) and Li + (0.76 Å) and the magnetic frustration/interactions. The superexchange interaction between neighboring Ni cations that are bridged by O anions is stronger in a (linear) interplane fashion between the antisite Ni 2+ (upon Ni 2+ /Li + exchange) and Ni cations in the TM layer, compared to the 90° intraplane superexchange between Ni in the TM layer. The interplane superexchange also relieves the magnetic frustration that arises from the intraplane interaction within the TM layer by providing different exchange paths. Many more (meta)-stable structures could have been generated during (electro)-chemical processes. Some of them may exist in small quantities, which becomes difficult to isolate. However, there have been successful discoveries of new phases in this way. For example, the metastable P3 " m1 The phase stability at 0 K was calculated using the PBEsol+U functional in VASP. The LiNiO 2 , Li 2 NiO 2 and Li 2 NiO 3 are the experimentally known ternary phases.