Improving Cycling Stability and Rate Capability of High-Voltage LiCoO₂ Through an Integration of Lattice Doping and Nanoscale Coating.

High-voltage LiCoO₂ has attracted much interest owing to the high specific energy density. But the poor cycling performance and inferior rate capacity of LiCoO₂ at a high voltage (≥4.5 V) has restricted the practical applications. Herein, we propose to improve the electrochemical performances of LiCoO₂ at high voltage through a synergy of Al-doping and Li₂TiO₃-coating. In compared to bare LiCoO₂, Al-doped LiCoO₂ and Li₂TiO₃-coated LiCoO₂, the cycle performance, the rate capability and the polarization of Al-doped and Li₂TiO₃-coated LiCoO₂ shows a larger improvement, which can be attributed to the synergic effects of Al-doping and Li₂TiO₃-coating. Firstly, Al doping expands the interlayer spacing which decreases the Li-ion diffusion barrier and enhances the coefficient of Li-ion diffusion. This benefits to the rate capability. Secondly, Al doping enhances the layered structure stability due to the larger Al-O bonding energy (Δ (Al-O) = 512 kJmol) than that of Co-O (Δ (Co-O) = 368 kJmol). Thirdly, the coating layer of Li₂TiO₃ mitigates the surface side reactions and further enhances the cycling performance. Moreover, the coating layer of Li₂TiO₃ as a Li-conductor is also favorable to the Li diffusion and the rate capability. This synergic strategy can also be extended to the modification of other cathode materials.