Abstract We investigate the reversible and irreversible transformations, the Li, Mn spinel undergoes under different atmospheres (air, O 2, and N 2) when heated up to 1050 °C. In air and O 2, a substantial reversible cation exchange occurs. For T≥800 °C, Mn 2+ ions substitute Li + at the tetrahedral (8a) position, and Li + shifts to interstitial octahedral (16c) site. Charge balance is achieved by a decrease in the Mn 3+ fraction, which is partially reduced to Mn 2+ in the regular octahedral (16d) site, according to the charge distribution (Li 1−2 y +Mn 2 y 2+) 8a[Li 3 y +] 16c[Mn 5 y 2+Mn 1−5 y 3+Mn 1 4+] 16dO 4 ( y increases with T). Under N 2 flow, a first decomposition occurs between 600 and 800 °C and yields Mn 3O 4, orthorhombic LiMnO 2 and O 2. A minor O 2 release occurs when heating above 900 °C, which is accompanied by the transformation of o-LiMnO 2 into a cubic Li x Mn 1− x O solid solution ( x≤0.5), consistent with a decrease in the average oxidation state of Mn ions. This cubic phase is stable at high temperature and decomposes upon cooling (T≤800 ° C) leaving just the Mn 3O 4 and o-LiMnO 2 phases.