Charge-discharge behavior of tin negative electrode for a sodium secondary battery using intermediate temperature ionic liquid sodium bis(fluorosulfonyl) amide-potassium bis(fluorosulfonyl)amide

The charge-discharge behavior of a Sn negative electrode for use in a sodium secondary battery was investigated in an intermediate temperature ionic liquid, NaFSA-KFSA (x(NaFsA) = 0.56, X-KFSA = 0.44, FSA = bis(fluorosulfonyl)amides), at 363 K. A Na/Sn half-cell was prepared using a Sn-film (10-12 mu m(t)) electrode. The charge-discharge curves at 0.619 mA cm(-2) with cut-off voltages of 0.005 and 1.200 V exhibited three potential plateaus in both the charging (alloying) and discharging (de-alloying) processes, indicating the formation of various alloy phases. Charge and discharge capacities as high as 790 and 729 mA h (g-Sn)(-1), respectively, were obtained for the 1st cycle: however, the capacities decreased rapidly due to volume change during the alloying and de-alloying processes. The best cycleability was achieved when the lower and higher cut-off voltages were set to 0.005 and 0.200 V. respectively. In this case, a reversible capacity of about 300 mA h (g-Sn)(-1) was obtained for the initial 15 cycles. (C) 2012 Elsevier B.V. All rights reserved.