Effect of additives on electrochemical performance of lithium nickel cobalt manganese oxide at high temperature

Lithium-nickel-cobalt-manganese oxide, Li[Ni_xCo _yMn_z]O₂ (NCM) is a low-cost cathode material with a high capacity and a moderately high rate capability, however, it still suffers from poor electrochemical performance. In this study, several types of additives are attempted to enhance the surface stability of high-Ni-content (Ni ≥ 60%) cathodes and the most effective additive turns out to be PS. The cycle performance in the presence of 2% PS is much improved at a high temperature of 60 C: (1) 98.9% of its initial capacity is preserved, (2) the increase in thickness is only 17.9%, preventing undesired swellings, and (3) gases are not generated in large amounts with the internal pressure being 56.4 kPa. The FT-IR spectroscopy results suggest that the surface of the cathode in the presence of 2% PS is covered with a film of alkyl sulfone components (RSOSR and RSO ₂SR), which is possibly formed by the electrochemical oxidation of PS. The current results confirm that the electrochemical performance of Ni-rich cathodes can be improved via the appropriate use of additives. They also indicate that among the tested additive candidates in this study, PS is highly desirable for enhancing the electrochemical performance of Ni-rich cathodes.