Bifunctional polymer-of-intrinsic-microporosity membrane for flexible Li/Na–H2O2 batteries with hybrid electrolytes

Abstract

Polymeric membranes with high ionic conductivity and solvent molecule blocking capability are attracting considerable attention as separators for new-generation batteries adopting hybrid electrolytes. The performances of the membranes are closely dependent on their microstructures and functional groups. Here, we report the design and fabrication of a carboxyl-functionalized polymer-of-intrinsic-microporosity (PIM) membrane, which has optimal surface properties and microporous channels (∼0.8 nm) to permit cation (Li⁺ or Na⁺) transportation, while preventing solvent molecule penetration. Using a droplet-templating strategy, we create large pores on both surfaces of the PIM-membrane to improve its interfacial contact with electrolytes. The obtained membrane integrates good mechanical strength with high thermal and electrochemical stability, demonstrating a great potential for battery applications as a flexible separator. When intercalated with Li⁺, the membrane (PIM-1-COOLi) exhibits a remarkable Li⁺ conductivity in both aqueous (6.5 × 10⁻³ S cm⁻¹) and organic (7.3 × 10⁻⁴ S cm⁻¹) solutions, as well as a good solvent permeation resistance (19 μmol cm⁻² min⁻¹ at 10 Pa for H₂O). Taking these advantages of the PIM-membrane, we are able to fabricate challenging batteries with hybrid electrolytes, such as Li–H₂O₂ and Na–H₂O₂ batteries (Li/Na anode with organic electrolyte and H₂O₂ cathode with aqueous electrolyte), into a flexible laminated form. The as-fabricated battery shows an excellent discharge performance, comparable to a model battery constructed with the commercial ceramic Li super-ionic conductor, but is more tolerant to mechanical treatment and harsh environment. Our study demonstrates that PIM represents a promising platform for developing flexible secondary batteries with hybrid electrolytes, which are particularly desirable for wearable and portable electronic devices.