Thermal-Induced Dopant Precipitation Enabling High-Quality Surface Modification of LiCoO 2 .

Surface modification is an effective approach for overcoming the interfacial degradations to enable high electrochemical performance of battery materials, yet it is still challenging to realize high-quality surface modification with simple processing, low cost, and mass production. Herein, a thermal-induced surface precipitation phenomenon is reported in a Ti-dopped LiCoO 2 , which can realize an ultrathin (≈5 nm) and uniform surface modification by a simple annealing process. It is revealed that surface Li-deficiency enables bulk Ti to precipitate and segregate on the non-(003) surface facets, forming a Ti-enriched disordered layered structure. Such a surface modification layer can not only stabilize the interfacial chemistry but also significantly improve the charge/discharge reaction kinetics, leading to much-improved cycling stability and rate capability. Dopants surface precipitation is a unique outward diffusion process, which differs from the current surface modification techniques and further diversifies these approaches for realizing high-quality surface modification of battery materials.