A Novel Protective Strategy on High‐Voltage LiCoO 2 Cathode for Fast Charging Applications: Li 1.6 Mg 1.6 Sn 2.8 O 8 Double Layer Structure via SnO 2 Surface Modification

Surface corrosion from electrolyte and reconstruction of layer‐structure LiCoO 2 are the most important reasons for capacity decay and charging kinetics limitation. Spinel‐type material forms on the surface of LiCoO 2 after cycling, which is more stable than the layer‐structure. To stabilize the surface and suppress the reconstruction, double layer structure Li 1.6 Mg 1.6 Sn 2.8 O 8 matching LiCoO 2 well is introduced to protect Mg‐doped LiCoO 2 and restrain the structure change. With a simple surface coating of SnO 2 and further high temperature treatment, Mg 2+ in LiCoO 2 and partly Li + are extracted out and reacted with SnO 2 to form double layer Li 1.6 Mg 1.6 Sn 2.8 O 8 . Meanwhile, Co 3+ in pristine LiCoO 2 is partly oxidized and electronic conductivity enhanced after surface modification. The Li 1.6 Mg 1.6 Sn 2.8 O 8 coating efficiently stabilizes the surface structure of LiCoO 2 , with less structure change, less cracks appearing on the surface, and much better cycling performance. In addition, stable surface and higher electronic conductivity of LiCoO 2 lead to better rate performance.