Experimental study of the phase transition in the lithium-excess lithium–manganese spinel over the pressure range 0–13GPa has shown its suppression. This observation implies that the Li/Mn ratio, associated with the manganese oxidation state, plays an important role in the high-pressure phase transformation of the lithium–manganese spinels. As indicated by the results, the occupation of the octahedral sites with Li+ and Mn4+ ions stabilizes the crystallographic structure of this cubic spinel even at a high pressure.