Electrolytes and additives for high efficiency lithium cycling

The use of lithium metal in rechargeable batteries continues to be of interest because only lithium metal can provide the very high energy density required in some specialist applications. However, major improvements are required in cycling efficiency, leading to longer cycle life, and in plating morphology to avoid dendrite formation which can lead to cell short-circuiting and safety problems. In this work the lithium plating/stripping efficiency has been measured for a range of electrolyte compositions both with and without additives such as surfactants and complexing agents. This was done with cells in which lithium was plated from a lithium-metal foil counter electrode onto a stainless steel electrode. In other respects, the cells were designed to be similar to complete cells except for the absence of a cathode; the minimum quantity of electrolyte was used and contained within a thin separator and stack pressure was applied. Improvements in cycling efficiency were found for some of the electrolyte compositions particularly those containing certain additives, e.g, perfluoropolyethers and by the use of 1.6 bar stack pressure. The high efficiencies were correlated with constant potential profiles during galvanosatic charge and discharge.