Poly(acrylonitrile)-based (PAN) electrolytes were prepared by dissolving PAN (0–17 wt.%) in a propylene carbonate–ethylene carbonate mixed solvent (50:50 wt.%) containing LiClO 4 (1 M) at 120–140°C, followed by cooling at −15°C for 16 h. The lithium∣electrolyte interface was observed after electro-reductive deposition of lithium (1 mA cm −2 , 1 h). Although lithium dendrites are formed in liquid electrolytes containing 0–3 wt.% PAN, dendrite formation was suppressed in gel electrolytes containing 5–17 wt.% PAN. Considering this effect together with the bulk resistance and liquefaction temperature of the electrolyte and resistance at the lithium∣electrolyte interface, the optimal PAN concentration was 5–10 wt.%.