Al Doping for Mitigating the Capacity Fading and Voltage Decay of Layered Li and Mn-Rich Cathodes for Li-Ion Batteries
P. K. Nayak, J. Grinblat, M. Levi, E. Levi, S. Kim, J. W. Choi, D. Aurbach
Li and Mn-rich layered cathodes, despite their high specific capacity, suffer from capacity fading and discharge voltage decay upon cycling. Both specific capacity and discharge voltage of Li and Mn-rich cathodes are stabilized upon cycling by optimized Al doping. Doping Li and Mn-rich cathode materials Li1.2Ni0.16Mn0.56Co0.08O2 by Al on the account of manganese (as reflected by their stoichiometry) results in a decrease in their specific capacity but increases pronouncedly their stability upon cycling. Li1.2Ni0.16Mn0.51Al0.05Co0.08O2 exhibits 96% capacity retention as compared to 68% capacity retention for Li1.2Ni0.16Mn0.56Co0.08O2 after 100 cycles. This doping also reduces the decrease in the average discharge voltage upon cycling, which is the longstanding fatal drawback of these Li and Mn-rich cathode materials. The electrochemical impedance study indicates that doping by Al has a surface stabilization effect on these cathode materials. The structural analysis of cycled electrodes by Raman spectroscopy suggests that Al doping also has a bulk stabilizing effect on the layered LiMO2 phase resulting in the better electrochemical performance of Al doped cathode materials as compared to the undoped counterpart. Results from a prolonged systematic work on these cathode materials are presented and the best results that have ever been obtained are reported.