Design and characterization of an adaptive polymer electrolyte for lithium metal solid-state battery applications

A major challenge for Li-metal solid-state batteries (LIMSSBs) lies in the mechanical degradation of the solid interface between Li-metal and the solid electrolyte. This work focuses on the synthesis and electrochemomechanical characterization of an adaptive polymer electrolyte (A-PE) that could potentially be applied as an interlayer to stabilize the interfacial contact between the lithium metal anode and the solid electrolyte, mitigating the effects of void formation leading to contact loss. The A-PE operates based on the principle of utilizing the polarization of conducting polymer particles, polypyrrole doped with dodecylbenzenesulfonate (PPy(DBS)), to impart adaptive properties to a polymer electrolyte matrix. The A-PE was synthesized via hot pressing and subsequent UV polymerization resulting in free-standing films with various amounts of PPy(DBS) and ionic conductivities in the range of 0.11-0.16 mS cm⁻¹ at 25 °C. Film characterizations included insoluble fraction, mechanical response under electric field, and Li symmetric cycling with intermittent electrochemical impedance spectroscopy (EIS). The measured mechanical responses of the film were expansion with atomic force microscopy (AFM) and block force response by exciting the film with electric field of variable strength. The results obtained suggest that the addition of PPy(DBS) particles provides adaptive capability in polymer electrolytes at room temperature (20-25 °C), with an expansion response of up to 6% strain with 1 wt% PPy(DBS) at an electric field strength of 0.3 V μm⁻¹. The results indicate that the A-PE shows promise for application as an interlayer in LIMSSBs, with the potential to reduce mechanical degradation at the lithium metal-solid electrolyte interface and enhance durability by expanding to maintain contact with the lithium metal anode.