Combining Multiple-Element Doping of LiCoO₂ and Bilayer Electrolytes for 4.6 V High-Voltage All-Solid-State Lithium Batteries

The halide electrolyte Li₃InCl₆ has been proposed to function as a barrier layer between LiCoO₂ and solid electrolytes Li₆PS₅Cl, aimed at mitigating interfacial issues. Here we reveal that the employment of Li₃InCl₆ as a barrier layer is still ineffective for the LiCoO₂ cathode due to the oxygen redox on the surface and the irreversible phase transition of LiCoO₂ at a high voltage of 4.6 V. To suppress the irreversible phase transition and modulate the oxygen valence on the surface, we have introduced a Ti-Mg-Al doping strategy for LiCoO₂. Remarkably, this doping suppresses the irreversible phase transition, stabilizes the structure of LiCoO₂ under high voltage, and significantly reduces the formation of O^n- (n < 2) on the LiCoO₂ surface. This doping strategy together with a bilayer electrolyte design attains good electrochemical performance in 4.6 V LiCoO₂ all-solid-state batteries, achieving a cycling life of 2200 cycles between 2.5 and 4.6 V with 80% capacity retention.