Additive Effects on Li‖CF_xand Li‖CF_x-MnO₂Primary Cells at Low Temperature

Abstract

The effect of additives and electrolyte composition was investigated for Li||CFx and Li||CFx-MnO2 cells operated at low (ca. −40°C) temperature. Electrochemical impedance spectroscopy (EIS) and Tafel measurements indicated that the anode is far more resistive than the cathode at low temperatures. Adding a small amount of fluoroethylene carbonate (FEC) to a propylene carbonate (PC) + 1,2-dimethoxyethane (DME) + tetrahydrofuran (THF) ternary blend was found to have a beneficial effect on the anode of a cell when using 0.5 M LiClO4 as the electrolyte salt. Although the cathode impedance did increase with the addition of FEC, the overall cell impedance dropped dramatically, particularly at −40°C. Capacity at low temperature was not significantly improved with FEC addition, however, indicating that static (i.e. EIS) measurements may not be the best tool to understand the cell under dynamic (discharge) conditions. 15-crown-5 (as an additive) proved to have severe negative effects on specific capacity.