Enhanced electrochemical activity of rechargeable carbon fluorides–sodium battery with catalysts

In order to improve the electrochemical performance of Na/CFx cell, fluorinated multi-walled carbon nanotubes (F-MWCNTs) and a new composite consisting of CFx, graphene nanosheets (GNS) and FeF3 (labeled as CGF for short) were employed as cathode materials in rechargeable room-temperature sodium batteries for the first time. The polarizations of Na/F-MWCNTs and Na/CGF cell were found to be 1600 and 800 mV, respectively. These values were much lower than that of Na/CFx cell (2000 mV). MWCNTs formed after the discharge process with intrinsic high surface area, high catalytic activity and “cage” type structure enhance charge reaction activity. Analogically, the combination of GNS and FeF3 with CFx provides more active sites to facilitate the decomposition of NaF during charge process. Moreover, the CGF electrode may have specific channels to avoid the dissolution of fluorine into the electrolyte similarly as the structure function of the F-MWCNTs electrode, leading to much better cycling performance. Overall, our results have demonstrated that the electrochemical performance of Na/CFx cell can be greatly improved by using MWCNTs and FeF3–GNS as catalysts.