Double function-layers construction strategy promotes the cycling stability of LiCoO2 under high temperature and high voltage

Lithium cobalt oxide (LCO), as a popular commercial material, can release higher capacity by increasing the charging voltage. However, deep delithiation leads to the dissolution of elements and structural disorder. Meanwhile, high-temperature performance is still in urgent need to be improved in practical application. Here, we use LiNO3, NaF and H3BO3 as raw materials to construct the outer LiF-rich layer and the inner B, F gradient doped hierarchical nanostructures through stirring and calcination. The electrochemically stable LiF-rich surface helps to form a favorable cathode electrolyte interphase (CEI) layer to prevent electrolyte penetration. The gradient doping of B and F in the subsurface region increases the stability of the lattice at high temperature and high potential. The unique structure enables treated LCO to demonstrate stable cycling under high voltage (4.6 V) with a capacity retention of 93.2% after 800 cycles and displayed 95.2% retention for 100 cycles under high temperature (45 °C). The postmortem analyses after long cycles prove the strategy of surface modification helps to protect the structure and reduce adverse reactions. This study provides a simple and extendable method for improving the cycling stability of cathodes at high temperature and high voltage.