Comparative studies of zirconium doping and coating on LiNi0.6Co0.2Mn0.2O2 cathode material at elevated temperatures

Layered LiNi0.6Co0.2Mn0.2O2 (NMC) is a promising cathode material for lithium-ion batteries, but structural instability and rapid capacity decay at high voltages and elevated temperatures preclude its large-scale commercialization. Lattice doping and surface coating can address these problems, but the different mechanisms between them are still unclear. Herein, two kinds of cathode materials (Zr-doped NMC and ZrO2-coated NMC) are synthesized and the effects of doping and coating on the structural stability and electrochemical performance of NMC are systematically investigated. Zr-doped NMC exhibits superior electrochemical performance with 98% capacity retention after 50 cycles between 3.0 and 4.5 V at 55 °C. In contrast, pristine and ZrO2-coated NMC suffer continual capacity decay during cycling. Ex situ analyses reveal that the performance improvement originates from the structure stabilizing effects of Zr doping and the robust interfacial film on the cathode surface during cycling. The results suggest that lattice doping is a key factor in obtaining excellent cycling performance at high temperatures. This study provides further insight into the different effects of Zr doping/coating and can be extended to investigate other cathode materials.