Synergistic effects of low-level magnesium and chromium doping on the electrochemical performance of LiNiO2 cathodes

LiNiO2 cathode materials with magnesium and chromium doping were prepared using a simple low - cost and efficient co - precipitation and lithiation procedure. During this procedure, both magnesium and chromium form a concentrated core particle, unto which nickel hydroxide precipitates. During lithiation, the elements in question will redistribute themselves and form a homogenous mixture. Magnesium - containing materials exhibit an excellent electrochemical performance, due to phase stabilizing effects, while for chromium - containing materials, performance remains poor. Rietveld refinement reveals that there is a possible upper limit for Mg doping (similar to 2.5 mol %) as a pilar dopant. Washing of the lithiated materials was explored, and it is proposed that this can improve capacity retention in prolonged cycling. However, the inevitable loss of lithium from the surface layer remains a challenge. Two sources for the chromium facilitated capacity decay are proposed, both owing to the highly irreversible redox reaction of hexavalent chromium possibly blocking lithium pathways.