A multi-functional gel co-polymer bridging liquid electrolyte and solid cathode nanoparticles: An efficient route to Li–O2 batteries with improved performance

Lithium-oxygen (Li–O2) batteries have the highest theoretical energy density amongst all rechargeable batteries and have attracted significant attention. However, large over-potentials originating from sluggish reaction kinetics often lead to low round-trip energy efficiency and short cycle life. We report here a novel multi-functional gel co-polymer that efficiently enhances the discharge and charge performances in Li–O2 batteries by intimately connecting the liquid electrolyte and solid cathode nanoparticles. On one hand, the co-polymer material, poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate-co-methyl methacrylate) (P(TMA-MMA)), functions as a binder during the fabrication of the cathode and forms a gel polymer membrane to retain liquid electrolyte and to increase ionic conductivity. On the other hand, the TMA units, containing N–O radical groups that catalyse Li2O2 formation and decomposition during charge and discharge cycles, are distributed throughout the polymer membrane. This allows more effective formation and decomposition of Li2O2 than surface bound catalytic units. The combination of gelable MMA and catalytic TMA moieties enhances the interface between liquid electrolyte and solid cathode by functioning as a medium both to transport Li+ (enhancing discharge process) and to carry electrons (reducing charge over-potential). Consequently, the optimized P(TMA-MMA) co-polymers provide exceptional electrochemical performance in Li–O2 batteries.