Na3V2(PO4)3 (NVP) features a three-dimensional open structure, which allows fast migration of Na+ ions, and thus, NVP is a superior cathode material for sodium ion batteries. However, the application of the NVP cathode is limited by its low electronic conductivity. To overcome this limitation, we developed an NVP nanocomposite cathode by doping carbon with bromine (Br) and nitrogen (N) during the sol–gel assisted hydrothermal reaction. The Br- and N-doping leads to the formation of amorphous carbon (a-C) on the surface of NVP particles. The nanocomposite possesses multilevel structures containing both pores with different sizes and aggregated grains (200–300 nm). Since the doped N provides electrons to the carbon matrix, the electronic conductivity of the nanocomposite is enhanced. Br-Doping leads to the drop of activation energy for V4+/V5+ redox reaction. The nanocomposite cathode exhibits a high reversible capacity of 41 mA h g−1 at 10C. Both the superior rate and cycling performances could be attributed to the synergistic effect of the multilevel structure and amorphous carbon.
Ying Li,Xia Zhong,Xianwen Wu,Mingqi Li,Wei Zhang,Dan Wang
To develop high-performance and low-cost anode materials for sodium ion batteries, novel Bi/C nanosheet microspheres with an open pore structure (labeled as ops-Bi/C nanosheet microspheres), in which nanosheets are assembled from Bi nanospheres and disordered C, are synthesized through facile methods using Bi(NO3)3, glucose and ethylene glycol as raw materials. Benefiting from the synergy of the material's unique microstructure, carbon coating and NaPF6–diglyme electrolyte, the ops-Bi/C nanosheet microspheres exhibit a higher stable reversible capacity (∼400 mA h g−1 at 0.1 A g−1) than the theoretical capacity of Bi metal, excellent rate performance (396, 393, 395, 392 and 381 mA h g−1 at 0.2, 1, 5, 10 and 20 A g−1, respectively) and long cycle life (361 mA h g−1 after 10 000 cycles at 5 A g−1). Moreover, even if the mass loading of the ops-Bi/C nanosheet microspheres exceeds 10 mg cm−2, the electrode still shows a high reversible capacity of 321 mA h g−1 at 0.8 A g−1 with good cycle performance. The sodium ion full cells composed of the ops-Bi/C nanosheet microsphere anode and commercial Na3V2(PO4)3 (NVP) cathode exhibit high energy density (174 W h kg−1(total) at 0.1 A g−1(NVP)) and long cycle performance (600 cycles at 1 A g−1(NVP)).
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