Carbothermal treatment for the improved discharge performance of primary Li/CFx battery

Carbothermal treatment was used to improve the discharge rate performance of primary lithium/carbon monofluoride (Li/CF_x with x = 1) batteries. The treatment was carried out by heating a mixture of CF_x and carbon black (CB) just below the decomposition temperature of CF_x under nitrogen for 2 h. In the treatment, poly(vinylidene fluoride-co-hexafluoropropylene) (Kynar) was used as a fluorinated polymer binder to press the CF_x/CB mixture into pellets. It was shown that the content of Kynar significantly affected the discharge performance of the resulting treated-CF_x (T-CF_x). This can be attributed to the catalytic effect of HF formed by the pyrolysis of Kynar on the decomposition of CF_x and on the reaction of CB with the volatile fluorocarbons formed by the decomposition of CF_x. The discharge performance of T-CF_x cathode was also affected by the temperature of carbothermal treatment and by the ratio of CF_x to CB. In this work the best result was obtained from a treatment conducted at 470 °C on a 87CF_x/10CB/3Kynar (by weight) mixture. In the discharge condition of C/5 and 20 °C, the Li/CF_x cell with such-obtained T-CF_x cathode showed about 95 mV higher voltage than the control cell while retaining nearly the same specific capacity. Impedance analyses indicate that the improved discharge performance is mainly attributed to a reduction in the cell reaction resistance (R_cr) that includes an ohmic resistance related to the ionic conductivity of the discharge product shell and a Faradic resistance related to the processes of charge-transfer and Li⁺ ion diffusion in the CF_x reaction zone.