Electrochemical characteristic and discharge mechanism of a primary Li/CFx cell

dc-polarization and ac-impedance techniques were used to analyze the discharge characteristic of a primary Li/CFx cell. In most cases, impedance spectrum of a Li/CFx cell shows a suppressed semicircle followed by a sloping straight line. The semicircle is shown to present a cell reaction resistance (Rcr), which reflects an ohmic resistance (mainly, ionic conductivity of the discharge product shell) and a charge-transfer process. It is shown that the overall resistance of a Li/CFx cell is dominated by the CFx cathode, whose resistance is further dominated by the Rcr that is found to be extremely sensitive to the temperature. Therefore, the low temperature performance and rate capability of a Li/CFx cell are mainly determined by the CFx cathode. In addition, based on the discharge curve and open circuit voltage (OCV) recovery of a Li/CFx cell, we proposed a “core-shell” model consisting of a shrinking “CFx core” and a growing “product shell” for the discharge process of CFx cathode. The “product shell” plays an important role in the discharge performance of Li/CFx cells.