Phase tuning of P2/O3-type layered oxide cathode for sodium ion batteries via a simple Li/F co-doping route

Element doping is a common and effective method for improving the electrochemical performance of cathode materials, and typically it can be divided into cation ion and anion ion doping. Among the cathode materials of sodium-ion batteries, the important layered oxide cathodes mainly include those of O3 and P2 types, according to the sites of Na ions and the number of oxide layer packings. Hereon, the successful transformation of O3-type cathode NaNi0.45Mn0.4Ti0.1Co0.05O2 (O3-NMTCO) into P2-type cathode of NaNi0.45Mn0.4Ti0.1Co0.05O2-0.08LiF (P2-LNMTCOF) is achieved via a facile Li/F co-doping route. The modified P2-type cathode (P2-LNMTCOF) have main three advantages over the traditional P2-type cathode Na0.7Ni0.45Mn0.4Ti0.1Co0.05O2 (P2-NMTCO): higher Na content, solid solution reaction in high-voltage range, and stronger TM-F bond. As a result, the current P2-LNMTCOF cathode shows the best cycling performance, with the initial capacity of about 160 mA h g−1 and the capacity retention of 61% after 200 cycles. In addition, because of the more stable TM-O (F) octahedron, the voltage drop during cycling has been effectively suppressed. This study provides a new idea and reference for synthesizing high performance P2-type layered oxide cathode materials for sodium-ion batteries.