The development of new electrode materials for Li-ion batteries is primarily focused on two often contradictory objectives: increasing the energy density, and thus the range of vehicles, and reducing the cost of batteries. Disordered NaCl-structured materials, such as Li2MnO2F, thanks to the combination of their Mn-rich, low-cost composition and high Li-ion storage capacity, allow these two aspects to be reconciled. Unfortunately, these materials undergo rapid degradation during cycling, which limits their lifespan. It is therefore necessary to address this degradation to make these materials competitive. Recently, our group has developed a strategy for stabilizing the material by modifying its structure, which is the subject of a patent. The goal of this thesis is to deepen this strategy by improving the understanding of the stabilization mechanism by varying its parameters. The PhD student will have access to all synthesis tools to realize these new materials, as well as electrochemical characterization tools on our battery platform to evaluate their performance. The student will also be required to perform in-depth structural characterizations, notably via various X-ray diffraction methods (including synchrotron).