Functional Binders Based on Polymeric Ionic Liquids for Sodium Oxygen Batteries Using Ionic Liquid Electrolytes

The polymeric ionic liquid poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (PDADMA TFSI) is herein reported as a functional binder for sodium oxygen (Na-O-2) batteries using ionic liquid electrolytes for the first time. The poly(ionic liquid) PDADMA binder was also shown to enhance the electrocatalytic activity of the electrode through a process that was dependent on the counterion and polycation structure. To prove this concept, two other traditional binders, poly(vinylidene fluoride) (PVDF) and polytetrafluoroethylene (PTFE), were also assessed in this work, and it was shown that the lowest charge overpotential (0.9 V) was attained in the case of PDADMA TFSI. PVDF undergoes dehydrohalogenation in the presence of the nucleophilic superoxide species generated during the oxygen reduction reaction, forming several side products including sodium carbonate and sodium fluoride as previously reported for organic aprotic solvents. NaO2 and Na2O2 were the major discharge products in cells using PDADMA TFSI and PTFE binders.

Automated summary

The polymeric ionic liquid PDADMA TFSI was reported as a functional binder for Na-O-2 batteries with lower charge overpotential, enhancing the electrocatalytic activity of the electrode and resulting in NaO2 and Na2O2 as the major discharge products. PVDF and PTFE were also evaluated as binders, but PDADMA TFSI showed the best performance.