Unveiling the Intrinsic Cycle Reversibility of a LiCoO2 Electrode at 4.8-V Cutoff Voltage through Subtractive Surface Modification for Lithium-Ion Batteries

The thermodynamic instability of the LiCoO 2 layered structure at >0.5Li extraction has been considered an obstacle for the reversible utilization of its near theoretical capacity at high cutoff voltage (>4.6 V vs Li/Li + ) in lithium-ion batteries. Many previous studies have focused on resolving this issue by surface modification of LiCoO 2, which has proven to be effective in suppressing phase transformation. To determine the extent to which surface protection of LiCoO 2 is effective despite its thermodynamic instability and presumably incomplete reversibility involving the O1 phase, here we verify the intrinsic reversibility of bulk LiCoO 2 with extended lithium extraction by ruling out the effect of a surface. Specifically, first, we show that, contrary to conventional belief, electrochemical cycling of LiCoO 2 at a cutoff voltage of 4.8 V (vs Li/Li + ) results in better cycle stabil…