Designing a new-type PMMA based gel polymer electrolyte incorporating ionic liquid for lithium oxygen batteries with Ru-based Binder-free cathode

Highlights: • PMMA/IL-GPEs couple with binder-free Ru@NPC cathodes to construct Li–O₂ batteries. • This GPE has good ion conductivity/leakproof property and greatly protects Li anode. • The corresponding Li–O₂ batteries show improved electrochemical performances. Lithium–Oxygen (Li–O₂) batteries have great potential for promising next generation battery, owing to their high theoretical energy density. However, this system still faces many problems such as poor cycling performance and low coulombic efficiency, which mainly stems from the parasitic side reactions on cathode, the decomposition of electrolyte and the corrosion of Li anode. Herein, a novel gel polymer electrolyte (GPE) containing the polymethyl methacrylate (PMMA) with high stability towards the superoxide molecules and ionic liquid (IL) with the non-volatility (PMMA/IL-GPE) is designed by ultra violet (UV) treatment. PMMA/IL-GPE not only possesses the excellent ion conductivity (0.92 mS cm⁻¹), the wide voltage window (not be oxidized until > 4.7 V) and superior leakproof property, but also effectively protects Li anode from O₂-attacking. Moreover, we have further applied electroplating strategy to synthesize the binder-free Ru-coating N, P co-doped cathode (Ru@NPC), which greatly reduce the side reaction of cathode and reduce the charging overpotential. Hence, the Ru@NPC based Li–O₂ batteries using PMMA/IL-GPE show effectively improved discharge capacity (32793.5 mAh g⁻¹). When operated at the limited capacity, this battery can run for over 120 cycles with the low charge overpotential of < 2 V. Moreover, PMMA/IL-GPE-based flexible Li–O₂ batteries also exhibit good performances after different bending conditions.