Micropores-in-macroporous gel polymer electrolytes for alkali metal batteries†
High-energy-density lithium and sodium batteries have the potential to meet the growing worldwide energy and power demands for all-electric vehicles. However, it is well known that alkali metal anodes impose a major safety issue when flammable organic-liquid electrolytes are used owing to the formation of anode dendrites during charge that can cause an internal short circuit, thermal runaway, and fire. Herein, a macroporous poly(vinylidene-fluoride-co-hexafluoropropylene) (PH) membrane is employed as a flexible three-dimensional macroporous polymer host that can incorporate additional microporous polymers. Introducing hyper-cross-linked microporous polymers within the PH host membrane creates a continuous polymeric network capable of trapping liquid electrolytes and creating a “liquid pathway” across the membrane. Compared to modern separators employed in liquid electrolyte systems, these quasi-solid polymer electrolytes offer superior safety and flexibility without sacrificing the high ionic conductivities of traditionally employed liquid electrolytes. Specifically, we synthesize macroporous PH films with hyper-cross-linked microporous polyfuran or polypyrrole incorporated within the 3D PH structure. These membranes are shown capable of immobilizing a liquid electrolyte within the microporous polymeric matrix that enables a quasi-solid electrolyte with high ionic conductivity, stability, and cycle life when employed in lithium and sodium-metal batteries. Full-cell lithium and sodium-batteries containing these micropores-in-macroporous polymer electrolyte membranes demonstrate rate and interface capabilities comparable to traditional liquid electrolytes, but with significantly improved cycling performance and coulombic efficiencies. Furthermore, these results indicate that the proposed micropores-in-macroporous polymer membranes containing an immobilized-liquid electrolyte can suppress dendrite growth and allow the safe implementation of metallic lithium or sodium anodes.