Lithium-Ion and Chloride-Ion Transfer in Chiral and Racemic 3-Hydroxyquinuclidinium Perchlorate: Influence of Defects and a Mixed Plastic Crystal Matrix

Organic ionic plastic crystals (OIPCs) are promising solid electrolytes. To observe the effect of defects and a mixed OIPC matrix on ionic conductivity, lithium-ion transfer and chloride-ion transfer in chiral and racemic (+/+/-)-3-hydroxyquinuclidinium perchlorate plastic crystals were studied. The pure chiral material and racemic mixture and their corresponding doped mixtures showed different thermal behaviors. Powder X-ray diffraction revealed that the cubic crystal structure appeared in both the high-temperature phase of the pure chiral material and the whole temperature range for the racemic system. Solid-state nuclear magnetic resonance spectra indicated the possible ion mobility of the two undoped matrices. The lithium-ion conductivity in the chiral material (above -10 degrees C) and racemic mixture (in the whole temperature region) increased 2.5-3 orders of magnitude, while the chloride-ion conductivity in the chiral material only increased obviously above 50 degrees C. Positron annihilation lifetime spectroscopy demonstrated the dependence of ionic conductivity on defect volumes of the pure chiral material and its doped mixtures, and the defects of the doped mixtures expanded largely. The ionic conductivity and defect volume of the doped mixtures containing lithium ions and chloride ions qualitatively obeyed the Cohen-Turnbull free volume theory.