Effect of Cu/Fe addition on the microstructures and electrical performances of Ni-Co-Mn oxides

The reliability of negative temperature coefficient (NTC) thermistors is one of the important factors for the excellent performance of the battery management system in electric vehicles. The electrical properties of the thermistor can be explained by the indirect electron jump between Mn3+ and Mn4+ at the Bsites in a spinel-type thermistor. Additionally, different types of dopants, such as Fe, Cu, Zn, Cr, and Mn, are considered as electrical modifiers that can further improve the electrical properties of the thermistor. For example, Cu is often added to NTC thermistors, occupying the octahedral sites in a spinel-type thermistor, which can play an important role in conduction with the Mn cations. Addition of Fe is also widely used in NTC thermistors owing to its high sensitivity, B constant, and stability. In this study, composition-dependent structural and electrical properties of Cu-0.2/Fe-co-doped Ni(0.3)Mn(a-x-y)Co(0.9)o(4) (NMC) are investigated. Cu/Fe-co-doped NMC shows the R-25 and B-25/85 constant values of 4490-12730 Omega and 3185-3490 K, respectively, exhibiting a typical rho-T curve of NTC thermistors. Higher B constant and reliable electrical stability are observed for Cu/Fe-co-doped NMC. Based on the relationship between the cationic oxidation states and electrical properties of Cu/Fe-co-doped NMC, the hopping conduction mechanism is discussed. (C) 2020 Elsevier B.V. All rights reserved.