Electrochemical characteristics of amorphous silicon thin film electrode with fluoroethylene carbonate additive

• Fluorinated ethylene carbonate (FEC) makes to change SEI characteristics.
• The changed SEI as addition of FEC leads to low resistance of SEI.
• Proper content of FEC leads to enhancement of electrochemical performance.
• The proper content of additive such as FEC is one of the key factors.

The electrochemical and compositional changes of a solid electrolyte interphase (SEI) layer formed on the surface of silicon thin film are investigated in order to determine the effect of the content of fluoroethylene carbonate (FEC) additive in the electrolyte. Comparisons are made with FEC-free electrolyte, in which the major components are (CH2OCO2Li)2 and Li2CO3. The (CH2OCO2Li)2 and Li2CO3 of the SEI layer in the FEC-containing electrolyte decreases, and polycarbonate and LiF increase relatively with the repression of –OCO2Li groups. The additive affects the composition of the SEI layer, which leads to lower resistance. The electrochemical performance regarding cycle retention, coulombic efficiency, rate capability, and discharge capacity in the FEC-containing cell are significantly enhanced compared to that of the FEC-free electrolyte. The observed optimum FEC concentration in the electrolyte is 1.5%, due to the reduced charge transfer and SEI resistance in our experimental range.