Mg‐Pillared LiCoO2: Towards Stable Cycling at 4.6 V

Abstract

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.