New sulfone electrolytes: Part II. Cyclo alkyl group containing sulfones

Three cyclopentyl group-containing sulfones, methylsulfonylcyclopentane (MSCP), methylsulfonylmethylcyclopentane (MSMCP), ethylsulfonylcyclopentane (ESCP), and two cyclo hexyl containing sulfone, ethylsulfonylcyclohexane (ESCH) and ethylsulfonyl-methylcyclohexane (ESMCH), were synthesized and characterized as the solvents for rechargeable lithium batteries. In favorable contrast with the model compound ethyl methyl sulfone (EMS), which has a melting point of 36.5 °C, four of the new sulfones have melting points below room temperature. The conductivities of 1 M lithium salt solutions in these liquids are, however, nearly one order of magnitude lower than for EMS, so they cannot serve where high currents are needed. Their electrochemical windows, however, are high >5.5 v vs. Li+/Li, as for EMS. A Li|graphite cell using these cycloalkyl group-containing sulfones as solvent could be cycled under much higher current densities than one using oligo ether-containing sulfones; however, the capacities dropped quickly with cycling. The Li|LiCr0.015Cr1.985O4 was cycled under the lower current density of 0.15 mA cm−2, and more than 60 mAh/g discharge capacity was maintained after 120 cycles with a coulomb efficiency around 0.86.