Stabilizing 4.6 V LiCoO2 via Surface-to-Bulk Titanium Modification

Elevating the charging cut-off voltage is an effective strategy to increase the energy density of LiCoO 2 . However, unstable interfacial structures and unfavorable phase transitions in bulk are inevitably triggered during deep de-lithiation at high voltage. Herein, an integrated surface-to-bulk Ti-modification strategy is applied to LiCoO 2 , enabling uniform Li 2 TiO 3 coating on the surface and gradient Ti-doping toward the structural bulk. The resultant Ti-modified LiCoO 2 (T-LCO) electrode can be stably cycled up to 4.6 V, providing a high-rate capability of 137 mAh g −1 at 5C and a long-life stability with 80.5% capacity retention after 400 cycles at 1C, far outperforming the unmodified LiCoO 2 electrode with only 50.7% capacity retention. In situ X-ray diffraction characterization and density functional theory calculation reveal that the synergistic modification of T-LCO enhances Li + diffusion, facilitates the construction of high-quality cathode/electrolyte interphase, reduces the phase transition from O3 to H1-3 and Co3d/O2p band overlap, and restrains layer-to-spinel phase distortion, thus improving structural stability at 4.6 V. This work presents a “two birds one step” strategy to enhance the cycling stability and achievable capacity of high-voltage LiCoO 2 for developing high energy density lithium-ion batteries.