Highly ion conductive cross-linked ionogels for all-quasi-solid-state lithium-metal batteries

Highly Li+-ion conductive and stable cross-linked network based flexible ionogels have been prepared using the thermal polymerization of poly(ethylene glycol) diacrylate (PEGDA) in the presence of an ionic liquid electrolyte (ILE) composed of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) ionic liquid and lithium tetrafluoroborate (LiBF4) salt, and their electrochemical behavior and stability have been investigated. The cross-linked polymerization reaction of monomers is confirmed using FTIR spectra. The temperature dependence of the ionic conductivity indicates that the Li–ion transport is coupled with the segmental dynamics of polymer chains. The prepared ionogel [PEGDA:ILE = 20:80(w/wt %)] with a 30 mol. % LiBF4 salt concentration exhibits a high ionic conductivity of ∼12.59 mS cm−1 and a lithium transference number of ∼0.56 at 30 °C. The lithium plating/stripping experiments indicate the formation of a robust and conductive solid electrolyte interface at the lithium electrode surface. The all-quasi-solid-state energy storage device such as a lithium-metal battery fabricated with this ionogel delivers a high discharge specific capacity of 156 mA h g−1 at a current rate of C/20 at 30 °C and achieves 83% capacity retention at the 50th cycle.