New sulfone electrolytes for rechargeable lithium batteries.

Sulfones with different length of oligo ethylene glycol segments have been synthesized and tested for use in rechargeable lithium batteries. Relative to the model compound ethylmethyl sulfone (EMS), which has a melting point of 36.5 °C, the new sulfones have low melting points, mostly depressed below room temperature. Their conductivities are lower than that of EMS. The highest ambient temperature conductivity of 10−2.58 S cm−1 was obtained for 0.7 M LiTFSI/MEMS solution (MEMS is methoxyethylmethylsulfone). The sulfones showed wide electrochemical stability windows, in excess of 5.0 V vs. Li/Li+, increasing with decreasing length of the oligoether chains. Unlike their fluorinated analogs, the present sulfones prove incompatible with graphite anode hosts, but a cell with lithium metal anode and manganate cathode performed well, maintaining good coulomb efficiency over 200 cycles.