Unraveling the LiNbO₃ coating layer on battery performances of lithium argyrodite-based all-solid-state batteries under different cut-off voltages

The coating layer can effectively mitigate the undesirable side effects that occur at the active material/sulfide electrolyte interface in the cathode mixture. Plenty of research has reported the coating layer effect in the typical voltage window, while the influence at different voltage windows is unclear. Herein, the degradation mechanism of the bare and LiNbO₃ coated LiCoO₂ electrodes in all-solid-state batteries when cycled at different cut-off voltages has been systematically investigated. The coated electrodes exhibit superior electrochemical performance than the bare electrodes at different charging/discharging rates when the upper cut-off voltage is 3.6 V, while both electrodes show fast degradation of battery performance at higher cut-off voltages (3.9 and 4.2 V). The electrochemical performances are highly dependent on the interfacial stability between the active material and solid electrolyte in the cathode mixture and the structural instability of LiCoO₂ at different voltage windows. The evolution of interfacial resistances is systematically investigated in combination of in-situ EIS, relaxation time distribution (DRT), TEM, and XPS. Structural changes of bare and coated LiCoO₂ before and after cycled at different cut-off voltages are studied by XRD, TEM, and dQ/dV analysis. The clarification of complex interfaces and phase stability evolution of LiCoO₂ provides a strong theoretical basis for constructing high-performance all-solid-state batteries.