Structural and electrochemical studies of Fe-doped Na 3 Mn 2 P 3 O 11 cathode materials for sodium-ion batteries

Due to the limited resources of lithium source and their high price, lithium-ion batteries (LIBs) cannot meet the demands of future large-scale energy storage. Sodium-ion batteries (SIBs) with advantages of the abundant sodium resources and low cost, are one of the most promising alternatives to LIBs. Here, we firstly synthesize a new manganese-based polyanionic compound (Na 3 Mn 2 P 3 O 11 ) through a simple sol-gel method. The resolved crystal structure indicates that single-phase Na 3 Mn 2 P 3 O 11 compound belongs to the orthorhombic structure. When tested as for cathodes, it displays a poor electrochemical performance with a potential window of 1.8–4.3 V (versus Na/Na + ), caused by the Jahn-Teller effect of Mn 3+ generated during charging process. In this context, a series of Fe-doped Na 3 Mn 2-x Fe x P 3 O 11 (0.1 ≤ x ≤ 0.5) are prepared to improve the electrochemical performance. Results indicate that Fe substitution of Mn in Na 2 Mn 2-x Fe x P 3 O 11 structure can not only enhance the electrochemical performance, but also increase conductivity and achieve fast reaction kinetics. Noticeably, when iron-doped amount is 0.4, Na 3 Mn 1.6 Fe 0.4 P 3 O 11 exhibits the best cycling (62.7 mA h g −1 at 0.1 C over 100 cycles) and rate performance (19.7 mA h g −1 at 5 C).