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/CF_x cell. In most cases, impedance spectrum of a Li/CF_x cell shows a suppressed semicircle followed by a sloping straight line. The semicircle is shown to present a cell reaction resistance (R_cr), 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/CF_x cell is dominated by the CF_x cathode, whose resistance is further dominated by the R_cr that is found to be extremely sensitive to the temperature. Therefore, the low temperature performance and rate capability of a Li/CF_x cell are mainly determined by the CF_x cathode. In addition, based on the discharge curve and open circuit voltage (OCV) recovery of a Li/CF_x cell, we proposed a “core-shell” model consisting of a shrinking “CF_x core” and a growing “product shell” for the discharge process of CF_x cathode. The “product shell” plays an important role in the discharge performance of Li/CF_x cells.