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Abstract: The electrochemical performances of fluorinated graphite have been improved by coating a uniform carbon layer on commercial CF x (x =1) powder used as cathode material in lithium battery. In comparison with the cell using un-coated CF x as cathode, the cell using carbon coated CF x cathode has a higher energy density and higher power density, particularly at higher discharge current rates (1C above). This is because the conductive carbon coating provides the exterior connectivity between particles for facile electron conduction, resulting in high rate performance. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]