Enhanced Thermal Stability of Aerosol-Synthesized Ni-Rich Li-Ion Battery Cathode Materials via Concentration-Gradient Ca Doping

High-Ni cathode materials such as LiNi0.8Co0.1Mn0.1O2 (NCM811) are replacing low-Ni, high-Co cathode materials in Li-ion batteries. However, the poor thermal stability and long-term cycling performance of high-Ni cathode materials are a barrier to rapid commercial application. Doping is used to optimize the fire safety and electrochemical performance of NCM811. In this work, we synthesized calcium (Ca)-doped NCM811 materials with direct control of the local dopant concentration by using an aerosol synthesis process (rapid metal salt solution aerosol pyrolysis). By identifying the appropriate precursors and controlling the ion concentrations and precursor solubility in solution, we have shown that both a uniform dopant concentration and a unique gradient structure of Ca can be controllably formed within the NCM811 cathode particles. This Ca-doping technique significantly increased the thermal stability of NCM811. In thermal decomposition tests of the delithiated materials, the oxygen release of uniform and gradient Ca-doped NCM811 decreased by 52 and 85%, respectively, as compared to that of the undoped materials. Furthermore, the thermal onset temperature was increased from 498 to 527 K. Herein, we show that rapid formation of a concentration-gradient structure in aerosol synthesis is a promising route to optimize the thermal stability of cathode materials for Li-ion batteries.