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

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. 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.