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/CFx with x = 1) batteries. The treatment was carried out by heating a mixture of CFx and carbon black (CB) just below the decomposition temperature of CFx under nitrogen for 2 h. In the treatment, poly(vinylidene fluoride-co-hexafluoropropylene) (Kynar) was used as a fluorinated polymer binder to press the CFx/CB mixture into pellets. It was shown that the content of Kynar significantly affected the discharge performance of the resulting treated-CFx (T-CFx). This can be attributed to the catalytic effect of HF formed by the pyrolysis of Kynar on the decomposition of CFx and on the reaction of CB with the volatile fluorocarbons formed by the decomposition of CFx. The discharge performance of T-CFx cathode was also affected by the temperature of carbothermal treatment and by the ratio of CFx to CB. In this work the best result was obtained from a treatment conducted at 470 °C on a 87CFx/10CB/3Kynar (by weight) mixture. In the discharge condition of C/5 and 20 °C, the Li/CFx cell with such-obtained T-CFx 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 (Rcr) 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 CFx reaction zone.