Improving stability of high voltage LiCoO2 by synergetic surface modification via in situ surface conversion

LiCoO2 is a pivotal cathode material that is widely used in commercial lithium ion batteries, which can further increase energy density by charging to high voltages. However, the practical application of LiCoO2 at voltages higher than 4.6 V is hindered by its structural instability and severe interfacial side reactions at a highly delithiated state. Herein, we improve the high-voltage performance of LiCoO2 through a synergetic surface modification with a high-voltage-stable and ionic conductive integrated layer, which is realized by the surface coating and heat annealing of Li2CoP2O7. It is discovered that nano-sized Li2CoP2O7 reacts with LiCoO2 and residual lithium-containing species on the surface at 650 °C to form spinel Co3O4 and Li3PO4, which accounts for the high-voltage-stability and high lithium-ion conductivity. The Li2CoP2O7-modified LiCoO2 delivers a high capacity of 203.8 mAh g−1 at 0.2C and a high capacity retention of 75.4% after 200 cycles with a cut-off voltage of 3.0–4.6 V. Moreover, the modified LiCoO2 exhibits an excellent rate capability of 186.5 mAh g−1 at 5C rate, showing great potential in the application scenarios requiring high energy density and fast charging.