Submicron-thick single anion-conducting polymer electrolytes

Abstract

Non-line-of-sight techniques are well suited for fabrication of thin and conformal solid-state electrolyte (SSE) coatings, especially within three-dimensionally porous electrode architectures. Adapting SSEs to safe and low supply-risk battery chemistries, such as alkaline zinc, requires solid-state anionic transport. We use initiated chemical vapor deposition (iCVD), a non-line-of-sight polymerization method, to generate conformal, pinhole-free poly(4-dimethylaminomethylstyrene), pDMAMS, films on planar substrates. We then vapor-phase react the ∼350 nm thick polymer with 1-bromo-3-chloropropane, an alkylating and cross-linking reagent, to convert pendant tertiary amines in pDMAMS to quaternary ammoniums (pDMAMS⁺) counterbalanced by labile Cl⁻/Br⁻. Solution exchange of Cl⁻/Br⁻ for OH⁻ or HCO₃⁻ yields an anion-conducting SSE compatible with alkaline battery chemistry. The ion conductivity of anion-compensated pDMAMS⁺ films ranges from 10⁻⁸ to 10⁻⁵ S cm⁻¹ and depends on hydration level and anion identity. All three anionic forms of the pDMAMS⁺ SSEs are electrochemically stable and electronically insulating, which in conjunction with their nanoscale thickness and single-ion conductivity render them promising for use in beyond-Li-ion all solid-state energy-storage and conversion devices.