Li-ion batteries are interesting because they offer high power and, as a consequence, they are preferred to aqueous-based batteries for traction applications e.g. hybrid electric vehicles (HEV). Several electrochemically active structures as cathode for Li-ion batteries have been proposed in the past years as an alternative to LiCoO2. In order to understand the factors that promote or hinder their performance as electrode materials and in situ neutron diffraction is an excellent technique due to its higher sensitivity to detect light elements compared to X-ray. We plan to investigate LiCoO2 and LiMn2O4 by in situ neutron diffraction using an electrochemical cell specifically designed for Polaris and extract relevant structural of the materials while battery cycling.