Stable cycling of LiCoO2 at 4.55 V enabled by combined Mg doping and surface coating of NASICON-type electrolyte

Chemical/electrochemical instability of LiCoO2 (LCO) at high voltage limits its deliverable capacity and thereby energy density of the battery, although it has a high theoretical capacity of 274 mAh/g. In this study, stable cycling of LiCoO2 at a voltage as high as 4.55 V can be achieved by simultaneous lattice doping with Mg (LMCO) and surface coating with a NASICON-type Li1.4Al0.4Ti1.6(PO4)3 (LATP) solid-state electrolyte. Uniform coating can be realized by a facile Pechini route combined with solid-phase calcination. The LCO with 4 wt% LATP coating and 2 at% Mg doping (4 wt% LATP/LMCO-0.02) can deliver a high capacity of 204 mAh/g in the voltage range of 3.0–4.55 V (vs. Li/Li+) at 0.4C. After 300 cycles at 0.4C, the 4 wt% LATP/LMCO-0.02 material can maintain 86.2% of its initial capacity, significantly superior to those of undoped and/or uncoated materials. The results show that both doping and coating are critical in inhibiting structural change of LCO and electrolyte decomposition at a deeply charged state of LiCoO2 material.