Thermal stability in the blended lithium manganese oxide – Lithium nickel cobalt manganese oxide cathode materials: An in situ time-resolved X-Ray diffraction and mass spectroscopy study

• Thermal stability of blended LiMn2O4(LMO)–LiNi1/3Co1/3Mn1/3O2(NCM) is studied.
• Blending of LMO with NCM leads to lower gas releasing temperature of CO2 and O2.
• During heating the NCM decomposes first followed by the LMO.
• MnO, NiO and possibly CoO were formed at temperatures higher than 500 °C.

Thermal stabilities of a series of blended LiMn2O4 (LMO)–LiNi1/3Co1/3Mn1/3O2 (NCM) cathode materials with different weight ratios were studied by in situ time-resolved X-ray diffraction (XRD) combined with mass spectroscopy in the temperature range of 25 °C–580 °C under helium atmosphere. Upon heating, the electrochemically delithiated LMO changed into Mn3O4 phase at around 250 °C. Formation of MnO with rock-salt structure started at 520 °C. This observation is in contrast to the previous report for chemically delithiated LMO in air, in which a process of λ-MnO2 transforming to β-MnO2 was observed. Oxygen peak was not observed in all cases, presumably as a result of either consumption by the carbon or detection limit. CO2 profile correlates well with the phase transition and indirectly suggests the oxygen release of the cathode. Introducing NCM into LMO has two effects: first, it makes the high temperature rock-salt phase formation more complicated with more peaks in CO2 profile due to different MO (M = Ni, Mn, Co) phases; secondly, the onset temperature of CO2 release is lowered, implying lowered oxygen release temperature. Upon heating, XRD patterns indicate the NCM part reacts first, followed by the LMO part. This confirms the better thermal stability of LMO over NCM.