Lithium-ion batteries are an important foundation for moving towards sustainable energy production, electric mobility and energy storage, and they have a key role to play in the future energy transition. Phase separation during the lithiation of redox-active materials is a critical factor affecting battery performance, including energy density, charging rates, and cycle life. Accurate physical descriptions of these materials are necessary for understanding underlying lithiation mechanisms, performance limitations, and optimizing energy storage devices. A team led by Prof. Alexandros Vasileiadis from the Department of Radiation Science and Technology, Faculty of Applied Sciences, Delft University of Technology, The Netherlands, has extended the theory of canonical solutions to explain and predict the behavior of olivine phosphate cathodes. The introduction of multiple sublattices and their interactions provides an elegant explanation for the variation of the redox potential and the phase separation behavior. The formalization of mean-field theory provides an intuitive understanding of these phenomena, which can facilitate the study of novel active materials. This approach can serve as a valuable alternative to computationally intensive ab initio calculations, providing clear insights starting from simple concepts. Mathematically derived phenomenological descriptions suggest that changes in redox potentials are caused by interactions of non-reactive sublattices. In addition, the authors found that redox platforms previously shown to be phase-separated can be transformed into solid solution phases. This transformation is due to a reduction in the number of nearest neighbors within the same sublattice, which reduces the effective interaction of the intercalated species. Application of the model to materials that have been extensively studied, such as LFMP, LFCP, and LFMCP and their possible compositions, demonstrates how quantitative and accurate this theory can be even when considering complex systems. Subsequent applications in the phase-field framework are able to reproduce and explain a variety of experimental results, the interpretation of which was previously incomplete and lacked mathematical support. Firm conclusions about the absence of phase separation in LFMP with low manganese content still need to be confirmed experimentally. However, the proposed mechanism used to explain the operational XRD peak shifts reveals the importance of considering multiparticle behavior when experimenting with a collective system such as a half-cell. Finally, the model strongly points to an optimal composition for high power cathodes, demonstrating that LiMn0.4Fe0.6PO4 may be an excellent candidate due to its solid solution behavior and low transport-induced inhomogeneities. Further experiments are needed to validate this argument and the use of a two-dimensional model to capture the known transport limitations in the particles is suggested. The interaction between the two sublattice concentrations may play an important role in explaining the nonequilibrium behavior, opening the way to optimize the (discharge) process to take advantage of these effects. The authors anticipate that the proposed theory may be applicable to other popular active materials such as LiMn1.5Ni0.5O4 (LMNO) or NMC with different compositions, explaining the effect of metal ratio on the performance. To do so would require consideration of structural modifications occurring in spinel or lamellar structures that have not been considered in current theories. Ultimately it is hoped that overcoming these limitations may extend the field of the theory so that particle size, porosity and thickness as well as the composition of the material can all be used as part of optimizing cell design parameters to improve cycle life and energy efficiency.