Stabilizing Surface Lattice Oⁿ⁻ (0 < n < 2) for Long-Term Durability of LiCoO₂

The instability of surface lattice Oⁿ⁻ (0 < n < 2) in charged LiCoO₂ (LCO) limits its long-term cycling stability beyond 4.55 V versus Li/Li⁺. Herein, the spinel and rock-salt (RS) phases are constructed on LCO surface to stabilize lattice Oⁿ⁻, namely S-LCO and R-LCO, respectively. Upon long-term cycling at 4.6 V, the loss of lattice Oⁿ⁻ leads to a progressive deterioration of surface spinel phase, which ultimately transforms into a strong Li⁺-blocking phase. In contrast, for R-LCO, the surface lattice Oⁿ⁻ in the RS phase remains stable in long-term cycles. Theoretical calculations reveal that the migration barriers of lattice Oⁿ⁻ are significantly higher in the RS phase than in the spinel phase. Due to the stabilized surface lattice Oⁿ⁻, the R-LCO||Li cell shows an impressive capacity retention of 78.6% after 1000 cycles at 4.6 V (at 1C rate) and superior floating charge durability at 45 °C. This study highlights the importance of surface structure tailoring in developing advanced LCO cathodes.