Binary electrolyte based on tetra(ethylene glycol) dimethyl ether and 1,3-dioxolane for lithium–sulfur battery

An electrolyte based on a mixture of tetra(ethylene glycol) dimethyl ether (TEGDME) and 1,3-dioxolane (DOXL) is studied for a use in lithium–sulfur battery. The maximum ionic conductivity is found at the intermediate mixing ratio of TEGDME:DOXL=30:70, because TEGDME readily solvates LiCF3SO3 and DOXL effectively reduces the viscosity of the electrolyte medium. The lithium–sulfur battery based on the binary electrolyte shows two discernable voltage plateaux at around 2.4 and 2.1 V, which correspond to the formation of soluble polysulfides and of solid reduction products, respectively. The UV spectral analysis for TEGDME-based and DOXL-based electrolytes suggests that the shorter polysulfide is favourably formed for DOXL-based electrolyte in the upper voltage plateau at around 2.4 V. The lower voltage plateau at around 2.1 V is highly dependent on the TEGDME:DOXL ratio. The sulfur utilization in the lower voltage plateau region can be correlated with the viscosity of the electrolyte, but with the ionic conductivity. The low polysulfide diffusion for the electrolyte with high viscosity causes significant passivation at the surface of the positive electrode and results in low sulfur utilization.