Conductivity and interfacial behaviour of bis-1,4-dioxapentyl sulfate (IV) and 1,4,7-trioxaoctyl sulfate (IV) based electrolyte for lithium batteries

Abstract

The electrolytic conductivity and viscosity of lithium perchlorate in bis-1,4-dioxapentyl sulfate (IV) [OS22] and 1,4,7-trioxaoctyl sulfate (IV) [OS32] were determined as a function of salt concentration (0.00005–2 M) and temperature (286–318 K). At 298 K, the highest conductivity (κ=2.77×10−3 Ω−1 cm−1) was achieved for OS22 based solutions containing 1–2 M LiClO4. Formation of electrically neutral ion pairs appeared to be the main reason for a continuous decline in the molar conductivity (Λ) observed in dilute solutions with increasing salt concentration. Additionally, an increase in the dynamic viscosity (η) accounted for a decrease in the mobility of charge carriers with increasing length of the oxaalkyl chain in the podand molecules. The temperature dependence of the conductivity and viscosity was found to be of the Arrhenius type for both systems investigated, while the activation energies, Eκ# and Eη#, varied in parallel with the degree of interionic aggregation. CVs obtained on a polycrystalline Pt electrode indicated the electrochemical stability of OS22 in the potential range between −0.8 V and 4.7 V versus Li+/Li. A linear current density–potential dependence, with the same slope for the anodic and cathodic branches proved the reversibility of lithium electrodeposition and re-dissolution at the Pt/1 M LiClO4+OS22 interface.