Recent works on lithium deficient LixNi1/3Mn1/3Co1/3O2 (x < 1) (NMC) cathode material has shown promises as a high voltage and high-temperature cathode material. In this work, the structure of such materials was studied with in situ XRD, DSC, and Raman spectroscopy. Moreover, to extend the understanding to higher nickel cathodes, LixNi0.6Mn0.2Co0.2O2 (x < 1) and LixNi0.8Mn0.1Co0.1O2 (x < 1) were studied together with the LixNi1/3Mn1/3Co1/3O2 (x < 1). In situ XRD results showed the lithium deficient cathode materials to be in rhombohedral (R-3m) phase at above 840 degrees C. A higher cation mixing is observed with increasing nickel content in the NMC cathode materials. Raman spectroscopy has indicated that Mn-O bonding spinel phase peak detected around 630 cm(-1) and found much higher intensity for NMC111 compared to the NMC622 and NMC811. It concludes that the formation of trace spinel phase in lithium deficient NMC materials is not due to cation mixing which mostly discussed in such a high nickel content cathode materials.