Reversible phase transition enabled by binary Ba and Ti-based surface modification for high voltage LiCoO₂ cathode

As a popular commercialized cathode material in lithium-ion batteries, the cycle life, practical reversible capacity, and rate capabilities of LiCoO₂ (LCO) at high voltage are limited owning to structural irreversibility and surface side reactions. Here, we employ a binary Ba and Ti-based hybrid surface treatment on LiCoO₂ (LCO@BT) by facile wet chemical routes. This strategy integrates the advantages of both interface particle doping and surface coating as the layered structure of LCO is stabilized by a binary hybrid surface treatment, and the modified layer promotes the surface Li⁺ diffusivity and protects the LCO cathode from steady corrosion induced by surface side reaction. On the basis of in-situ NMR characterizations, it is found that after the first electrochemical delithiation/lithiation the phase reversibly changes from O3–I-type in LCO@BT and back to O3–I-type L_xCO@BT (0.98 ≤ x＜1) rather than to a two-phase domain of O3–I and O3-II phase in uncoated L_xCO (x＜0.98). The target material is achievable in displaying an initial discharge capacity of 190.5 mAh g⁻¹ and delivers a high capacity retention of 90.29% (172 mAh g⁻¹) at 0.2C after 100 cycles which is superior to most LiCoO₂ cathodes that are operated at high cut-off voltage of 4.5V.