Outside-In Nanostructure Fabricated on LiCoO₂ Surface for High-Voltage Lithium-Ion Batteries

The energy density of batteries with lithium cobalt oxide (LCO) can be maximized by increasing the cut-off voltage to approach the theoretical capacity limit. However, it is not realized in the practical applications due to the restricted cycle life caused by vulnerable cathode surface in deep delithiation state, where severe side reactions, oxygen/cobalt loss and structure degradation often happen. Here, an outside-in oriented nanostructure on LiCoO₂ crystals is fabricated. The outer electrochemically stable LiF and Li₂ CoTi₃ O₈ particles perform as physical barrier to prevent damage of both cathodes and electrolytes, while the inner F doping promote Li ions diffusivity and stabilize the lattice oxygen. With the spinel-like transition layer between them, a solid and complete lithium-ion transport channel generation along the lithium concentration gradient. Under the protection from this structure, the LiCoO₂ withstand the high voltage of 4.6 V and the LCO/graphite pouch full cell with high loading density exhibits 81.52% energy density retention after 135 cycles at 4.5 V.