Tunnel-structured Na0.66[Mn0.66Ti0.34]O2-xFx (x < 0.1) cathode for high performance sodium-ion batteries

Sodium-ion batteries (SIBs) are attracting significant research attentions for large-scale energy storage applications. Cathode material is the vital part of SIBs to determine the capacity and cycle performance. Here, a series of F-doped Na-0.66[Mn0.66Ti0.34]O2-xFx (x < 0.1) cathodes with tunnel structure are designed and synthesized aiming to enlarge the sodium diffusion paths. The lattice parameters of unit cell are tuned successfully by adjusting F doping amount. Na-0.66[Mn0.66Ti0.34]O1.94F0.06 with the optimized stoichiometry exhibits a reversible capacity of 97 mAh g(-1) and promising cycle performance (85 mAh g(-1) is maintained at 2C after 1000 cycles) with extremely low voltage polarization. More significantly, Na-0.66[Mn0.66Ti0.34]O1.94F0.06 exhibits superior low temperature performance, owing to the much enhanced thermodynamics and kinetics benefited from F doping. This strategy may open new opportunities to design advanced intercalation-type cathode materials for sodium ion batteries, especially for low-temperature applications.