Na-doped layered LiNi 0.8 Co 0.1 Mn 0.1 O 2 with improved rate capability and cycling stability

We have prepared LiNi0.8Co0.1Mn0.1O2 (LNMCO) doped with Na+ and studied its properties using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), SEM, galvanostatic cycling, and AC impedance spectroscopy. XRD analysis indicates that an appropriate amount of Na doping benefits the formation of sound layered structure, while reducing the potential for cation-disorder occurrence. Electrochemical measurements demonstrate that Na-doped LNMCOs deliver a rate capability and cycling stability at high cutoff voltages of 4.3 and 4.5 V that are more effective than those of undoped LNMCO. 0.2 wt% Na-doped LNMCO exhibits a discharge capacity and capacity-retention rate that are higher than those of undoped LNMCO after 100 cycles (132.0 mAh g−1 and 69.1% vs. 90.6 mAh g−1 and 49.5%). Electrochemical impedance spectroscopy (EIS) measurement demonstrates that Na doping lowers both the impedance of the solid electrolyte interface layer and the charge transfer. We attribute the superior electrochemical performances of Na-doped LNMCOs to a pillared structure that simultaneously favors Li+ mobility and the improvement of cycling stability.