Superionic Bifunctional Polymer Electrolytes for Solid-State Energy Storage and Conversion

Achieving superionic conductivity from solid-state polymer electrolytes is an important task in the development of future energy storage and conversion technologies. Herein, a platform for innovative electrolyte technologies based on a bifunctional polymer, poly(3-hydroxy-4-sulfonated styrene) (PS-3H4S), is presented. By incorporating -OH and -SO₃H functional groups at adjacent positions in the styrene repeating unit, “intra-monomer” hydrogen bonds are formed to effectively weaken the electrostatic interactions of the -SO₃⁻ moieties in the polymer matrix with embedded ions, promoting rich structural and dynamic heterogeneity in the PS-3H4S electrolyte. Upon the incorporation of an ionic liquid, interconnected rod-like ion channels, which allow the decoupling of ion relaxation from polymer relaxation, are formed in the stiff motif of the polymeric domains passivated by interfacial ionic layers. This results in accelerated proton hopping through the glassy polymer matrix, and proton hopping becomes more pronounced at cryogenic temperatures down to −35 °C. The PS-3H4S/ionic liquid composite electrolytes exhibit a high ionic conductivity of 10⁻³ S cm⁻¹ and high storage modulus of ≈100 MPa at 25 °C, and can be successfully applied in soft actuators and lithium-metal batteries.