Rechargeable lithium/sulfur battery with liquid electrolytes containing toluene as additive

The effect of incorporating varying amounts (in the range 2.5–10 vol%) of toluene additive in 1 M LiCF3SO3 in tetra(ethylene glycol) dimethyl ether (TEGDME) liquid electrolyte on the electrochemical performance of Li/S cell at room temperature was studied. Cyclic voltammetry measurements showed the same active voltage range for the electrolytes with and without toluene, consisting of an oxidation peak at 2.5 V and a pair of reduction peaks at 2.35 and 1.9 V. Electrolytes with toluene have higher redox currents resulting from increased ion mobility and ionic conductivity. Toluene addition enhanced initial discharge capacity; a maximum of 750 mAh g−1 (45% of the theoretical specific capacity of sulfur) was obtained with 5% of toluene, which was 1.8 times that of the cell without toluene. The electrolyte with 5% toluene exhibited a stable cycle performance with the highest discharge capacity and charge–discharge efficiency. AC impedance analyses of Li/S cells with the electrolytes showed that toluene addition resulted in a lower initial interfacial resistance and a fast stabilization of electrode/electrolyte interfaces in the cell. Addition of toluene in low amounts is thus an effective means to enhance the electrochemical performance of 1 M LiCF3SO3 in TEGDME electrolyte in Li/S cells at room temperature.