Disordered Rock-Salts materials derived from Li2MnO2F have been extensively studied over the past decade as potential high-energy-density positive electrode materials for Li-ion batteries. At the CEA, our experience with these materials, which are highly sensitive to usage conditions, has enabled us to surpass state-of-the-art performance in full cells incorporating them. Surprisingly, very few studies have been reported on their sodium equivalents and their use in Na-ion batteries, despite their composition being low in critical and expensive materials, making them particularly suitable for this technology. This is likely due to their exacerbated instability compared to the lithiated phases. In a previous internship, we were able to develop synthesis and electrode implementation protocols that allowed us to achieve specific capacities exceeding 220 mAh·g?¹ with a material of this type, which could make it competitive with a LiFePO4-based Li-ion technology. The thesis will therefore focus on optimizing the material's composition and understanding the influence of the synthesis protocol in terms of structure (X-ray diffraction analysis) and material surface state (spectroscopy).