Collective Surface Enabling an Ultralong Life of LiCoO2 at High Voltage and Elevated Temperature

Abstract

AbstractRapidly increasing demand for energy density in consumer electronics is eager for developing high‐voltage LiCoO2 (LCO). However, some great challenges such as severe phase transition and surface instability negate the cycle life of LCO operated at high‐voltages (≥4.6 V). Herein, a chemical reconstruction strategy is proposed to form a collective surface of LCO through an interdiffusion reaction of MgHPO4·3H2O (MP) so as to extend the cycle life of high‐voltage LCO. The collective surface renders a three‐layer configuration that demonstrates an amorphous Li3PO4 outmost layer, a spinel‐like layer beneath, and a Mg diffusion layer within LCO bulk. MP with relatively low hardness enables the uniform precoating via mechanical mixing, followed by a sintering process to undergo an interdiffusion reaction. Li3PO4 is an intrinsic electrochemical stabilizer against interfacial side reactions. The spinel‐like compounds build a high‐voltage‐stable surface against irreversible O2 release. In addition, Mg diffuses into the bulk lattice to suppress irreversible phase transition during the deep delithiation of LCO. Therefore, such modified LCO with a collective surface exhibits ultralong life with capacity retention of 82% after 1000 cycles at 1 C within 3.0–4.6 V and stable operating at 4.7 V or elevated temperature (45 °C).