Investigating the Effects of Magnesium Doping in Various Ni-Rich Positive Electrode Materials for Lithium Ion Batteries

This work studies the effect of Mg doping in LiMO 2 (M = Ni, Ni+Al, Ni+Co+Al, Ni content >0.8) at a dopant level of less than 5%. Synthesized materials were all single phase and contained no appreciable amount of surface or bulk impurities. Structural and electrochemical characterization of the materials was carried out to understand how Mg affects the materials and whether the presence of Al or Co influences the dopant effects of Mg. All synthesized materials, even those without Co, were found to contain a small amount of Ni in the Li layer. Increases in the Mg content of the material reduced the initial capacity of the materials but improved the capacity retention. The capacity reduction was related to the amount of Li trapped by electrochemically inactive Al and Mg. The capacity retention was related either to the number of Ni ions substituted by electrochemically inactive dopants or to the amount of Li trapped by those dopants. Mg helped improve capacity retention by reducing the growth of polarization during cycling. No synergistic effects were found to exist from co-doping materials containing Co and/or Al with Mg.