Anisotropic Li+ ion conductivity in a large single crystal of a Co(iii) coordination complex

Abstract

Large single crystals of a novel lithium cobalt coordination compound, LiCo(NC₅H₃(CO₂)₂)₂(H₂O)_2.125 [LiCo(PDC)₂] were grown via a hydrothermal reaction in high yield. The electrochemical impedance spectroscopy (EIS) data measured on a large single crystal of LiCo(PDC)₂ revealed very interesting anisotropic Li⁺ ion conductivity. The redox potential for Co³⁺/Co⁴⁺ observed at ca. 200 mV in the cyclic voltammogram was consistent with the electric potential where the ionic conductivity occurred. Detailed structural analysis on a series of stoichiometrically equivalent cobalt coordination compounds, ACo(PDC)₂ (A = Na⁺, K⁺, and H₃O⁺), indicated that the presence of ion channels as well as a suitable cation size is critical for the anisotropic ionic conductivity.