(Cu6Sn5)1−xCx active/inactive nanocomposite negative electrodes for Na-ion batteries

The electrochemistry of Sn-Cu-C nanocomposite anode materials in Na-ion cells is described and compared directly to similar compositions from previous work in Li-ion cells. A series of compositions corresponding to (Cu6Sn5)1−xCx (x = 0.15-0.52) was prepared by combinatorial sputtering. This composition range has been shown previously to have good cycling performance in Li-ion cells, having stable capacities near 600 mAh/g for 0.15 < x < 0.45. In contrast, the same composition range was found to have reduced capacity when used in Na-ion cells, having just 350 mAh/g when x = 0.15. Further addition of carbon results in a reduction of reversible capacity to just 135 mAh/g when x = 0.44, however this alloy retains 99% of its 10th cycle capacity of 117 mAh/g after 50 cycles. The potential use and the impact of the addition of carbon to alloy negative electrodes containing Sn for Na-ion batteries are discussed.