Sodium–oxygen (Na–O2) cells are a promising high energy density storage technology with a theoretical specific energy of 1605 Wh kg–1. However, this technology faces certain challenges in order to achieve both a high practical energy density as well as long-term cycling capability. In this Letter, a superior Coulombic cyclic efficiency, close to 100%, has been demonstrated by the use of a bilayer electrolyte composed of an ionogel and an ionic liquid electrolyte, reported herein for the first time. The presence of the ionogel plays a major role in the prevention of side reactions originating at the anode, providing a promising route to extend cell cycling, whereas the ionic liquid is essential to support high reaction rates at the cathode.

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. NaO 2 and Na 2 O 2 were the major discharge products in cells using PDADMA TFSI and PTFE binders.

Multi-doped carbon nanofibers are used as self-standing air cathodes in Na–O2 batteries. The synergetic effect of multiple heteroatoms greatly enhances oxygen reduction, and diglyme-based hybrid electrolytes remarkably improve cycling performance.