Meticulous guard: The role of Al/F doping in improving the electrochemical performance of high-voltage spinel cathode

Spinel LiNi0.5Mn1.5O4, which is considered as one of the most attractive candidates for high energy density battery due to its high voltage platform over 4.7 V, suffers from the side reactions with electrolyte, strong oxidability of Ni4+ and therefore the complicated and frangible Solid Electrolyte Interfaces (SEI) layer that hinders the practical application of LiNi0.5Mn1.5O4. In this work, traditional co-precipitation method is applied and improved by anion and cation doping method to construct superior interface on the surface of LiNi0.5Mn1.5O4 to suppress side reactions especially at high temperature. Detailed properties including structure, morphology and electrochemical performance of pristine sample, single-doped and co-doped samples are probed. Physical characterizations reveal that the co-doped sample with regular octahedron has a moderate grain size and specific surface area between Al and F single doping, and holds the advantages of rate performance and capacity retention causing by Al doping and better stability under high temperature constructing by F. It exhibits the best capacity retention of 92% after 200 cycles under 55 °C, which is higher than that of the pristine sample (87%). Analysis of the electrode after cycling shows that doping reduces the thickness of the electrode interface film and the content of inorganic substances such as LiF to improve the interface characteristics and the high temperature cycling performance. This work has certain significance for the commercial application of LiNi0.5Mn1.5O4.