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−x C x (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 600mAh/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 350mAh/g when x =0.15. Further addition of carbon results in a reduction of reversible capacity to just 135mAh/g when x =0.44, however this alloy retains 99% of its 10th cycle capacity of 117mAh/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.