Na3V2(PO4)3-Graphene Nanocomposite As Stable Cathodes for Na-Ion Batteries
Na-ion batteries, because of the high abundance and uniform geographic distribution of Na sources, have been regarded as low cost and high efficiency energy storage devices for stationary applications.1-2 However, it is difficult to find high energy and stable cathode materials for reversible Na ion insertion and extraction because of the large radius of Na ions (~40% larger than Li ions). Recently, layer structured metal oxides and NASICON structured Na3V2(PO4)3 have been demonstrated to be good cathode candidates.1-7 Na0.44MnO2 is known to have excellent cycling stability and can have a theoretical capacity of ~120 mAh/g when it cycles between Na0.22MnO2 and Na0.66MnO2. However, it has to be pre-cycled to 2V in order to fully use the capacity. Na3V2(PO4)3 is at discharge state and has a theoretical capacity of ~117 mAh/g. Yet it suffers from a low conductivity and usually needs large amount of carbon in electrode preparation. In this work, we synthesized Na3V2(PO4)3-graphene nanocomposite and demonstrated its excellent cycling stability and rate performance as cathodes for Na-ion batteries. A capacity of ~102 mAh/g was obtained at 0.5C current density and the capacity retention was ~99% after 600 cycles.
Results and Discussion
The Na3V2(PO4)3-graphene nanocomposite has 10% graphene. It was mixed with conductive carbon (10%) and binder (10%) and casted on an aluminum substrate. Long cycle stability was demonstrated in coin cells with Na metal as the counter electrode. A capacity of ~102 mAh/g was obtained at 0.5C and the capacity retention was ~99% after 600 cycles. We also studied the rate performance. The capacity at 2C rate is ~70 mAh/g.
Fig. 1. Long term cycling stability of the Na3V2(PO4)3-graphene nanocomposite.
The authors would like to acknowledge financial support from the U.S. Department of Energy’s (DOE’s) Office of Electricity Delivery & Energy Reliability (OE) (under Contract No. 57558). We also are grateful for enlightening discussions with Dr. Imre Gyuk of the DOE-OE Grid Storage Program. (A portion of) The research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.
- 1. MD Slater, DH Kim, EJ Lee, and CS Johnson. Adv. Funct. Mater. 23(2013):947.
- 2. HL Pan, Y-S Hu, and LQ Chen. Energy Environ. Sci. 6 (2013): 2338.
- 3. YL. Cao, LF Xiao, W Wang, DW Choi, ZM Nie, JG Yu, LV Saraf, ZG Yang, and J Liu. Adv. Mater. 23 (2011): 3155.
- 4. D Kim, E Lee, M Slater, W Lu, S Rood, and CS Johnson. Electrochem. Commun. 18(2012 ): 66.
- 5. M Sathiya, K Hemalatha, K Ramesha, JM Tarascon, AS Prakash. Chem. Mater. 24(2012):1846.
- 6. ZL Jian, WZ Han, X Lu, HX Yang, YS Hu, J Zhou, ZB Zhou, JQ Li, W Chen, DF Chen, and LQ Chen. Adv. Engery Mater. 3(2013):156.
- 7. K Saravanan, CW Mason, A Rudola, KH Wong, and P Balaya. Adv. Energy Mater. 3(2013): 444.