Fig. 4. Concentration effect of NaFSI-MA electrolytes. Salt concentration in molality (x = 0.5, 1, 2, 3, 4, 8, 11.4). Discharge and charge rates: 0.1C. (a) Charging and discharging profiles of the 2nd cycle; (b) specific discharge capacity vs. concentration; (c) EIS after the 5th cycle; (d) Rohm and Rintvs. concentration; (e) CE (top) and capacity (bottom) vs. cycle number; (f) ICE (left) and average CE (21st–30th) (right) vs. concentration. (g and h) FT-IR profiles of NaFSI-MA with different salt concentrations; (i) C and (j) F atomic percentage of the SEI on the cycled HC anode surface characterized by XPS.
