Ion transport and electrochemical cell performance studies on hot-press-synthesized Ag⁺ion conducting electroactive polymeric membranes: (1 −<i>x</i>)PEO:<i>x</i>[0.7(0.75AgI : 0.25AgCl) : 0.3MI]

Abstract

Investigations on ion transport properties of new Ag+ ion conducting electroactive solid polymer electrolyte (SPE) membranes (1 − x)PEO: x[0.7(0.75AgI : 0.25AgCl): 0.3MI] (M ≡ Rb, K), where x = 0 < x < 50 wt (%), are reported. A novel hot-press/solvent-free dry technique has been used for complexing/dissolving the salts into the PEO polymeric host. The two complexing salts [0.7(0.75AgI : 0.25AgCl): 0.3MI], recently investigated at the present laboratory, are the solid-solution-synthesized quaternary superionic solids in the polycrystalline phase which exhibited Ag+ ion conductivity σ ∼ 10−3 S cm−1 at room temperature. The compositional (x) dependent conductivity (σ) studies identified the composition 70PEO : 30[0.7(0.75AgI : 0.25AgCl) : 0.3MI] as the optimum conducting composition (OCC) SPE films. σ-enhancement of approximately three orders of magnitude could be achieved in both OCC SPEs at room temperature from that of the pure polymeric host: PEO. To explain the σ-increase in OCC SPE films, ionic mobility (μ) has been determined experimentally at room temperature using the d.c. polarization transient ionic current (TIC) technique and, subsequently, the mobile ion concentration (n) has been evaluated from σ and μ data. The ionic transference number (tion) in OCC SPEs has been estimated from the TIC 'current–time' plot and, hence, the ionic drift velocity (vd) has been evaluated. The phase identification and material characterization studies on both OCC SPEs have been done by XRD, SEM and DTA techniques. The temperature dependent studies on the ionic parameters, namely σ, μ, n, tion, vd, provided a deeper insight to understand the ion conduction phenomenon in OCC SPEs along with the information regarding energies involved in different thermally activated processes. Thin film SPE batteries have been fabricated using the two OCCs: 70PEO: 30[0.7(0.75AgI : 0.25AgCl): 0.3RbI]; 70PEO: 30[0.7(0.75AgI : 0.25AgCl): 0.3KI] as electrolytes, sandwiched between the Ag-metal foil anode and the hot-pressed cathode film: (C + I2 + SPE) in 1 : 1 : 1 wt (%). The cell potential discharge performances have been studied at room temperature under varying load conditions.