In this study a modified solid state synthesis (auto-ignition method) is used to form nanosized spinel type material LiMg0.05Ni0.45Mn1.5O4. This material presents a high voltage plateau at 4.75V vs. Li/Li+. Structural and electrochemical characterisations have been performed using a wide range of techniques (TEM, neutron diffraction, galvanostatic measurements, and impedance spectroscopy). Besides, in situ XAS has been performed to monitor the evolution of Ni and Mn oxidation state during Li intercalation. The material presents an ordered cubic spinel structure, good capacity retention upon cycling (131mAhg−1 at C/10 and 117mAhg−1 at 1C) and good electronic conductivity (10−6 Scm−1 at RT). The simultaneous presence of Mn3+/Mn4+ in the structure has been investigated and explained by inclusion of disordered nanodomains in the structure.