Effect of sodium salts on the cycling performance of tin anode in sodium ion batteries

To determine the effect of electrolyte salts on the cycling properties of tin anodes in sodium ion batteries, sodium/tin cells were prepared using eight electrolytes containing NaCF3SO3, NaBF4, NaClO4, and NaPF6 in ethylene carbonate-dimethyl carbonate (EC-DMC) and EC-DMC/fluoroethylene carbonate (FEC) solvents. The first charge capacity and cycling properties strongly depended on the electrolyte salts. Additionally, an appropriately chosen electrolyte salt in combination with the FEC additive improved the cycling properties of the tin electrode. The tin electrode in the presence of the FEC-containing NaPF6-based electrolyte exhibited the best cycling properties. The first charge capacity and charge capacity after the 45th cycle were 220 and 189 mAh g(-1) (electrode), respectively at a current density of 84.7 mA g(-1) (electrode). The rate performance is also studied using the optimized electrolyte which reveals the ability of the electrode to perform in high current application. At a high current density of 4235 mA g(-1) (electrode), the capacity delivered is 24 mAh g(-1) (electrode). At a current rate of 1694 mA g(-1) (electrode), at the end of 1400th cycle, capacity is about 45 mAh g(-1) (electrode). The results of the study clearly indicate that the electrolyte salts critically affect the electrochemical performance of the tin anode in sodium ion batteries.