Various Ni-rich layered oxide cathodes (above 0.80 Ni content), such as LiNi1−y−zCoyAlzO2 (NCA), are used in electric vehicles (EVs) due to their high capacity (∼200 mAh g−1 for NCA). However, to improve cycle performance and thermal stability and to ensure longer and safer usage, numerous studies have investigated surface modification, coating, and doping of cathode materials. In this study, we have investigated the characteristics of Li[Ni0.85CoxMn0.15−x]O2 with various Mn to Co ratios (x = 0–0.15) synthesized by a coprecipitation method. The discharge capacities of the Li[Ni0.85CoxMn0.15−x]O2 cathodes are similar at around 206 mAh g−1 at room temperature and 213.8 mAh g−1 at 55 °C between 2.7 and 4.3 V at a 0.2C rate, while the cyclability, thermal stability, and rate capability of all samples differ according to the Mn and Co ratio. The Li[Ni0.85Co0.05Mn0.10]O2 cathode shows the most promising electrochemical properties under different conditions among the various cathodes evaluated; it displays a high rate capacity (approximately 163 mAh g−1 at 5C rate) at 25 °C and good thermal stability (main exothermic temperature of 233.7 °C and relatively low heat evolution of 857.3 J g−1).