Fluorine anion doped Na0.44MnO2 with layer-tunnel hybrid structure as advanced cathode for sodium ion batteries

Anion-doping strategy represents one efficient route to adjust the structure of electrode material for advanced reversible batteries. The work herein obtains an optimized F-doping sodium manganese oxide Na0.44MnO1.93F0.07 with a layer-tunnel hybrid structure, and the essential factors such as synthesis temperature and crystal structure which determine the electrochemical behavior for the F-doping cathode materials are systematically explored and investigated. The optimized cathode Na0.44MnO1.93F0.07 prepared at 900 °C for 3 h, among various Na0.44MnO2−xFx samples, delivers an extraordinary discharge capacity of 149 mA h g−1 and 138 mA h g−1 at 0.5 C and 1 C, respectively. In addition, the electrode displays an impressive cycling stability with a superb capacity retention rate of approximately 79% over 400 cycles at 5 C. And thus, it shows enhanced reversible capacity over the tunnel phase Na0.44MnO2. Therefore, this work provides a new avenue for designing and optimizing the advanced cathode materials with superior electrochemical performance for sodium-ion batteries by introducing halogen anions to modify the structure.