Ionic Conductivity of K-ion Glassy Solid Electrolytes of KS-PS-KOTf System.

Ternary glassy electrolytes containing KS as a glass modifier and PS as a network former are synthesized by introducing a new type of complex and asymmetric salt, potassium triflate (KOTf), to obtain unprecedented K ion conductivity at ambient temperature. The glasses are synthesized using a conventional quenching technique at a low temperature. In general, alkali ionic glassy electrolytes of ternary systems, specifically for Li and Na ion conductivity, have been studied with the addition of halide salts or oxysalts such as MSO, MSiO, MPO (M = Li or Na), etc. We introduce a distinct and complex salt, potassium triflate (KOTf) with asymmetric anion, to the conventional glass modifier and former to synthesize K-ion-conducting glassy electrolytes. Two series of glassy electrolytes with a ternary system of (0.9-x)KS-xPS-0.1KOTf (x = 0.15, 0.30, 0.45, 0.60, and 0.75) and z(KS-2PS)-yKOTf (y = 0.05, 0.10, 0.15, 0.20, and 0.25) on a straight line of z(KS-2PS) are studied for their K ionic conductivities by using electrochemical impedance spectroscopy (EIS). The composition 0.3KS-0.6PS-0.1KOTf is found to have the highest conductivity among the studied glassy electrolytes at ambient temperature with the value of 1.06 × 10 S cm, which is the highest of all pure K-ion-conducting glasses reported to date. Since the glass transition temperatures of the glasses are near 100 °C, as demonstrated by DSC, temperature-dependent conductivities are studied within the range of 25 to 100 °C to determine the activation energies. A Raman spectroscopic study shows the variation in the structural units PS43-, P2S74-, and P2S64- of the network former for different glassy electrolytes. It seems that there is a role of P2S74- and P2S64- in K-ion conductivity in the glassy electrolytes because the spectroscopic results are compatible with the composition-dependent, room-temperature conductivity trend.