Promoting stability and fast-charging capability of LiCoO₂ thin-film battery achieving 500 Wh/kg energy density through MgO co-sputtering

As the earliest commercial cathode material, LiCoO₂ (LCO) offers advantages in high capacity and fast charging. However, only half the energy density is implemented in the current batteries limited by materials instability at high voltages. The mechanisms of the instability of LCO cathodes include irreversible phase transition (>4.3 V), cathode–electrolyte interface formation, oxygen evolution, and cobalt dissolution. To overcome the challenges of existing practical implications, implement applications for LCO cathode of voltage and energy density limitations. The co-sputtering technique incorporating Mg dopants are proposed in this research to provide not only excellent pillar effect to stabilize structure but also faster Li-ion transportation. The best LCO cathode (45 Mg-LCO) with the optimum Mg concentration demonstrates outstanding rate capability (61.7% when comparing 5 C–0.1 C) and cycling stability (47.1% capacity retention over 100 cycles at 1 C as charging to the ultrahigh voltage of 4.7 V), surpassing pristine LCO. Consequently, the energy density leaps forward from 352.8 Wh/kg (LCO cut-off at 4.2 V) to 494.1 Wh/kg (45 Mg-LCO cut-off at 4.7 V). This work provides comprehensive understanding of the working mechanisms behind the doping strategy for LCO electrode materials.