Electrochemical activation, voltage decay and hysteresis of Li-rich layered cathode probed by various cobalt content

The high capacity of Li-rich layered cathode materials have attracted great attention for the greater energy density lithium ion (Li-ion) batteries, but the understanding of knowledge associated with electrochemical behaviours are still needed to improve their performances further. In this study, different amount of Co content is designed in Li-rich layered compounds (0.5Li2MnO3·0.5LiMn0.5-xNi0.5-xCo2xO2, 0 ≤ x ≤ 0.2), and the stepwise electrochemical activation process is applied to explore the features. We discover that the substitution of Co3+ ions can accelerate the electrochemical activation of Li2MnO3 component, and the Co-doped compound delivers much higher capacities even they suffer an apparent voltage decay comparing to the Co-free one. Besides, a fast metal ions migration exists (e.g., from the metastable tetrahedral site to the lower energy cubic site) in initial dozens of cycles (e.g., 30 cycles at 0.1C); thereafter, they likely return to the original octahedral site, as demonstrated in the voltage decay and hysteresis analysis. [Display omitted] •Spherical and high tap-density Li-rich cathodes with varied Co content are prepared.•The stepwise electrochemical activation strategy is applied to study the Li-rich cathode.•The differences of electrochemical behaviors are monitored as varying the Co content.•Co-doped cathode delivers much higher capacities and energy densities.•A relationship of the voltage decay, hysteresis and metallic ions migration trend is presented.