Hybrid solid state eutectogel electrolyes in a polymeric cage: towards improved (electro-)chemical properties

Abstract

Hybrid solid state electrolytes combine the desirable properties of both solid and liquid electrolytes by confining the liquid electrolytes within a (meso-)porous solid framework.[1,2] This approach allows to uphold the high ionic conductivity of liquid electrolytes, a typical issue for full solid state electrolytes. Additionally the latter suffer from a deficient/suboptimal/… interface with the electrodes, while hybrid materials offer a more intimate contact. Their liquid precursors can also allow for an facile implementation into conventional battery technology. Hence, the hybrid solid state electrolytes are promising for the transition from liquid to solid state batteries and were first introduced by the group of Guyomard by use of ionic liquid electrolytes to form ionogels.[2] Last year, our group introduced the eutectogels in which a deep eutectic electrolyte (binary mixture of N-methylacetamide and LiTFSI) is confined within a porous silica framework designed via a facile one-pot non-aqueous sol-gel route.[3] The eutectogels offer a broad electrochemical window, good ionic conductivity and good stability in Li/LiFePO4 electrochemical cells. The use of a silica framework obligates the removal of unwanted side-products, e.g. water, formic acid and ethanol, during the formation of the monolith through evaporation. This step is detrimental to the performance of the encapsulated deep eutectic electrolyte and energy-intensive. Therefore, we set out in the search for a framework material that does not produce detrimental side-products to render the heat treatment obsolete. In this presentation, we will show the use of a polymeric cage. This route allows the further simplification of the synthesis while fully harnessing the potential of the confined deep eutectic electrolyte. We will discuss the inherent safety, improved mechanical integrity, and physicochemical properties of these gel membranes. Furthermore, their electrochemical properties will be shown and they will be implemented in hybrid solid state batteries to demonstrate their performance. Acknowledgements B. Joos is a PhD fellow of the Research Foundation-Flanders (FWO Vlaanderen). The authors would like to thank other group members for their assistance.