Dependence of lithium metal secondary cell performance on lithium cation solvation state

We investigated the influence of the state of lithium cations in a nonaqueous electrolyte on lithium metal secondary cell performance. We used 1,2-dimethoxyethane (DME) mixed with ethylene carbonate (EC) as a mixed solvent and LiPF6 as a solute. The longest cycle life for a Li/LiMn1.9Co0.1O4 cell was provided by 1.0 mol dm−3 LiPF6 EC-mixed electrolyte containing 20 vol.% of DME. This is the same point at which the state of the lithium cations in the electrolyte changes as detected by 7Li-NMR measurement. With this electrolyte composition, most of the DME selectively solvates the lithium cations. As the amount of non-solvating DME increases in the electrolyte, the cell cycle life becomes shorter.