Stabilizing 4.6 V LiCoO2 via Er and Mg Trace Doping at Li-Site and Co-Site Respectively.

ABSTRACT

Charging LiCoO2 to high voltages yields alluring specific capacities, yet the deleterious phase-transitions lead to significant capacity degradation. Herein, this study demonstrates a novel strategy to stabilize LiCoO2 at 4.6 V by doping with Er and Mg at the Li-site and Co-site, respectively, which is different from the traditional method of doping foreign elements solely at the Co-site. Theoretical calculations and experiments jointly reveal that the inclusion of Mg2+-dopants at the Co-site curbs the hexagonal-monoclinic phase transitions ≈4.2 V. However, this unintentionally compromises the stability of lattice oxygen in LiCoO2, exacerbating the undesired phase transition (O3 to H1-3) above 4.45 V. Fascinatingly, the introduction of Er3+-dopants into Li-sites enhances the stability of lattice oxygen in LiCoO2, effectively mitigating phase transitions above 4.45 V. Therefore, the Er, Mg co-doped LiCoO2 exhibits high stability over 500 cycles when tested in a half-cell with a cut-off voltage of 4.6 V. Furthermore, the Er, Mg-doped LiCoO2//graphite pouch-type full cell demonstrates a high energy density of 310.8 Wh kg-1, preserving 91.3% of its energy over 100 cycles.