Mixed ether-based solvents provide a long cycle life with high rate capability to graphite anodes for Na-ion batteries

Energy storage devices using sodium ions have great potential in terms of their low cost, high power, and long life. In particular, there could be a significant cost reduction, because of the abundant resource of sodium. Recently, electro-chemical sodium storage performance has been demonstrated in graphite anodes using ether-based solvents. However, the high power and long life were not compatible in the same ether solution. Here, we demonstrated using mixed ether-based solvents that a long cycle life and high rate capability can coexist in the graphite anodes for sodium-ion batteries. The cycle performance indicated that the discharge capacity retention ratio after 10 000 cycles was more than 90% and the capability of 4 A g(-1)/0.2 A g(-1) (40C/2C) was more than 75%. These results could advance the development of sodium storage devices for practical use.