Improvement on the high-rate performance of Mn-doped Na 3 V 2 (PO 4 ) 3 /C as a cathode material for sodium ion batteries

• Published in: RSC advances 2016, Vol.6 (75), p.71581-71588
• Main Authors: Shen, Wei, Li, Hui, Guo, Ziyang, Li, Zhihong, Xu, Qunjie, Liu, Haimei, Wang, Yonggang
• Format: Article
• Language: English
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/C6RA16515J

Mn 2+ doped Na 3 V 2−x Mn x (PO 4 ) 3 /C ( x = 0, 0.015, 0.025 and 0.035) samples were synthesized by a facile sol–gel method and doping effects on the crystal structure and electrical conductivity were investigated by Rietveld refinement of XRD and a RTS-4 linear four-point probe. The results show that moderate doping of Mn 2+ does not alter the structure of Na 3 V 2 (PO 4 ) 3 , and Mn 2+ successfully substituted partial V 3+ sites. Due to the larger ionic radius of Mn 2+ (0.91 Å) as compared to V 3+ (0.64 Å), the lattice volume of Mn 2+ doped Na 3 V 2−x Mn x (PO 4 ) 3 /C noticeably increased, which could significantly accelerate Na + transport in the material. Moreover, moderate Mn doping is in favour of increasing the electronic conductivity of Na 3 V 2−x Mn x (PO 4 ) 3 /C samples. As a result, the Mn 2+ doped Na 3 V 2−x Mn x (PO 4 ) 3 /C samples show obvious improvements on the electrochemical performance in terms of the high-rate performance and cycling stability, particularly for the Na 3 V 1.875 Mn 0.025 (PO 4 ) 3 /C sample. As an example, when the discharging rate is 15C, it can deliver an initial discharge capacity of 86.7 mA h g −1 , and after 100 cycles, 79.4 mA h g −1 can still be achieved.