Lithium-Aluminum-Phosphate coating enables stable 4.6 V cycling performance of LiCoO2 at room temperature and beyond

Abstract Lithium cobalt oxide (LCO), a promising cathode with high compact density around 4.2 g cm−3, delivers only half of its theoretical capacity (137 mAh g−1) due to its low operation voltage at 4.2 V (vs. Li/Li+) under commercial conditions. To improve its practical capacity, higher cut-off voltages are often adopted, which result in severe structure destruction and cause side reactions with electrolyte. The safety concerns of oxygen release further restrict the application of LCO. Here, we achieve stable cycling of LCO at 4.6 V (vs. Li/Li+) through a surface engineering strategy by using lithium-aluminum-phosphate composite coating materials. This strategy prevents direct contact between cathode and electrolyte, reducing the loss of active materials without hindering the lithium ion migration. After calcination, a doping layer (or solid solution) includes phosphorus and aluminum is formed, which helps maintain the surface structure and stabilize the oxygen atoms around particle surface and shows high ion mobility when operated at 4.6 V (vs. Li/Li+). All these benefits synergistically contribute to the stable cycling of LCO at 4.6 V (vs. Li/Li+) with high capacity retentions of 88.6% (30°C) and 78.6% (45°C), respectively, after 200 cycles.