Mg-pillared LiCoO2: Towards Stable Cycling at 4.6 V.

LiCoO2, the first choice cathode material for lithium-ion batteries (LIBs) in 3C products due to its high volumetric energy density, typically only delivers a capacity of ~175 mAh/g although its theoretical specific capacity is as high as 274 mAh/g. The challenge is that cationic/anodic-redox-induced unstable phase transition, oxygen escape, and side reactions with electrolytes always occur when charging LiCoO2 to voltages higher than 4.35 V for delivering a higher capacity, which result in severe capacity fade. Herein, we demonstrate a Mg-pillared LiCoO2 that can be cycled steadily at 4.6 V. Dopant Mg ions, serving as "pillar"in the Li-slab of LiCoO2, prevent slab sliding at highly delithiated state, thereby suppressing unfavorable phase transitions. Moreover, the resulted Li-Mg mixing phase at the surface of Mg-pillared LiCoO2 is beneficial for eliminating the cathode-electrolyte interphase overgrown and phase transformation in the close-to-surface region. Consequently, Mg-pillared LiCoO2 exhibits a high capacity of 204 mAh/g at 0.2 C and a remarkably enhanced capacity retention of 84% at 1.0 C over 100 cycles within the voltage window of 3.0-4.6 V. In sharp contrast, pristine LiCoO2  gives a much lower capacity retention of 14% within the same voltage window.