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

Rapidly increasing demand for energy density in consumer electronics is eager for developing high-voltage LiCoO 2 (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 MgHPO 4 ·3H 2 O (MP) so as to extend the cycle life of high-voltage LCO. The collective surface renders a three-layer configuration that demonstrates an amorphous Li 3 PO 4 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. Li 3 PO 4 is an intrinsic electrochemical stabilizer against interfacial side reactions. The spinel-like compounds build a high-voltage-stable surface against irreversible O 2 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).