Abstract
Ionic conductivity of the polyethylene oxide-LiClO4 (PEOnLiClO4) solid polymer electrolyte (SPE) films with an EO:Li ratio (n) of 10, 12, 15, as well as the hybrid composite solid polymer electrolyte (CSPE) films of PEOnLiClO4 containing 50 wt% of cubic-Li7La3Zr2O12 (LLZO) sub-micron sized particles, have been studied by varying Li-salt content in the films. The complex AC dielectric permittivity and conductivity data obtained from electrical impedance measurements were fitted using a generalized power-law, including the effects of electrode polarization applied at low AC frequencies to obtain various relaxation times. In addition to increased mechanical and thermal robustness, the CSPE films show higher values of ionic conductivity, >10−4 S/cm at room temperature compared to those of SPE films with n = 12 and 15. On the contrary, the ionic conductivity of CSPE with n = 10 decreases by a factor of three compared to the corresponding SPE film due to increased polymer structural reorientation and Li-ion pairing effects. The Vogel–Tammann–Fulcher behavior of the temperature-dependent conductivity data indicates a close correlation between the ionic conductivity and polymer segmental relaxation. The PEO12LiClO4-LLZO film shows the lowest activation energy of ~0.05 eV.
Highlights
Research has shown that the ionic conductivity of solid polymer electrolyte (SPE) films is promoted by coupled motion of Li-ions and polymer segments in amorphous polymer regions [7,8], plasticizers are added to increase the fraction of amorphous regions, but adversely affect the mechanical and thermal stability of SPE films [4,5,6,9]
composite solid polymer electrolyte (CSPE) films with high ionic conductivity (>10−4 S cm−1 ), negligible electronic conductivity, good mechanical stability, and good electrochemical properties are desired for applications [4,5,6]
We have investigated the effect of the Li-salt content (EO:Li ratio n = 10, 12, 15) on the AC conductivity of PEOn LiClO4 —50 wt% cubic LLZO hybrid
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Showed that the addition of sub-micron sized LLZO particles increases the conductivity, reaching a maximum value of 10−5 S cm−1 at 35 ◦ C for PEO films with 52.5 wt%. A study with cubic-LLZO micron-sized particles as a filler in PEO20 LiClO4 (PEO Mw = 105 ) showed a decrease in conductivity of the composite films with the addition of 30–50 vol% of LLZO [16]. In addition to enhanced mechanical and thermal robustness, the CSPE films show higher values of ionic conductivity >10−4 S cm−1 (30 ◦ C) compared to those of SPE films at lower Li-ion concentration (n = 12 and 15). The ionic conductivity of CSPE decreases at a higher Li-ion concentration (n = 10), roughly by a factor of three compared to SPE We associate this observation with structural reorientation of the PEO matrix and. Li-ion aggregation effects in the presence of LLZO particles
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