Charge–discharge behavior of Sn–Ni alloy film electrodes in an intermediate temperature ionic liquid for the electrolyte of a sodium secondary battery

•Sn–Ni films were prepared by annealing tin-coated nickel foils at 463 K.•Ch.–disch. of the Sn–Ni films was studied in Na[FSA]–K[FSA] ionic liquid at 363 K.•The 0h-annealed film showed a high capacity of 343 mAh (g-Sn)−1 after 100 cycles.•Other (2–25 h) annealed films showed lower capacities and poorer cycleability.•The ch.–disch. behaviors were discussed based on the results of XRD and FE-SEM.

Sn–Ni alloy films were prepared by annealing tin-coated nickel foils at 463 K for 0–25 h, and their charge–discharge characteristics as negative electrodes for sodium secondary batteries were studied in an intermediate temperature ionic liquid Na[FSA]–K[FSA] (FSA = bis(fluorosulfonyl)amide) at 363 K. As a result, a Sn–Ni film without annealing retained a reversible capacity of 343 mAh (g-Sn)−1 after 100 charge–discharge cycles. In contrast, the annealed films had lower capacities and poorer cycleability. Possible mechanisms to understand the cycling performance were identified by X-ray diffraction and field-emission scanning electron microscopy studies.