In order to improve safety and volumetric energy density, the current solid-liquid Li-ion battery will be gradually changed into a future all solid-state battery. For such battery, since there is no restriction of the decomposition voltage of an organic liquid electrolyte, i.e. typically 5.0 V vs. Li/Li+, the cathode material with high working voltage (Vw) is available. Note that Vw for the current solid-liquid Li-ion battery ranges below 4.2 V vs. Li/Li+. Also, it is the easiest way to increase Vw in order for increasing the energy density of a battery. This proposal describes a muSR experiment on a spinel-type Li[Ni1/2Mn3/2]O4 cathode material with Vw=4.7 V to determine a diffusion coefficient (DLi) and clarify the relationship between DLi and cation distribution in the spinel lattice.