Tri-sites co-doping: An efficient strategy towards the realization of 4.6V-LiCoO2 with cyclic stability

Abstract

Lithium cobalt oxide (LCO) is extremely attractive for the volumetric and gravimetric energy density at high cut-off voltage, but the degradation issues we are always grappling with becomes much tougher. Here, an unconventional strategy of multi-sites co-doping is proposed using cheap and abundant elements like Na, Si, Al, Fe and F. By summarizing the fading behaviors of all the samples, the capacity fading shows a linear correlation with the doping elements. The optimized co-doping strategy enables each doping elements to achieve the full potential in the promotion of cyclic stability. The resultant LCO maintains a capacity retention of 81.8% after 500 cycles at 4.6 V of the full battery. Further evidences signify that the capacity fading in the early stage is mainly caused by surficial side reactions and the accompanying structural damage, while the fading in the later stage is due to particle cracking generated by the repeated planar gliding and the anabatic side reaction of the newly exposed surface. Therefore, not only the main factor of structural damage caused by surface side reactions should be considered, but more attention need to be paid on the planar gliding when designing more stable LCO. The tri-sites co-doping strategy, which can better integrate the inhibitory effect of different doping sites on planar gliding, provides a new idea for further improving the cyclic stability of high-voltage LCO.