On the Composition of LiNi_(0.5)Mn_(1.5)O_4 Cathode Active Materials

摘要

LiNi_(0.5)Mn_(1.5)O_4 (LNMO) cathode active materials for lithium-ion batteries havebeen investigated for over 20 years. Despite all this effort, it has not been possibleto transfer their favorable properties into applicable, stable battery cells. Tomake further progress, the research perspective on these spinel type materialsneeds to be updated and a number of persisting misconceptions on LNMOhave to be overcome. Therefore, the current knowledge on LNMO is summarizedand controversial points are addressed by detailed considerations on thecomposition and crystallography of LNMO. The findings are supported by anin-situ high temperature X-ray diffraction study and the investigation of fourdifferent types of LNMO materials, including Mn(Ⅲ) rich ordered LNMO, anddisordered LNMO with low Mn(Ⅲ) content. It is shown that the importanceof cation order is limited to a small composition range. Furthermore, newevidence contradicting the idea of oxygen defects in LNMO is presented andan enhanced classification of LNMO based on the Ni content of the spinelphase is proposed. Moreover, a balanced chemical equation for the formationof LNMO is presented, allowing for comprehensive calculations of key propertiesof LNMO materials. Finally, suitable target compositions and calcinationprograms are suggested to obtain better LNMO materials.