Ionogels for Safer Energy Storage: The Determining Effect of the Interface

Abstract

Ionogels represent a route to biphasic materials, for the use of ionic liquids (ILs) for all-solid devices. Confining ILs within host networks enhances their averaged dynamics, resulting in improved charge transport. Fragility, short relaxation times, low viscosity, and good ionic conductivity, all them appear to be related to the IL / host network interface. The presence of ILs at interface neighborhood leads to the breakdown of aggregated, structured regions that are systematically found in bulk ILs. This “destructuration”,[1] as well as segregative interactions at interface,[2,3] coupled with percolation of the bicontinuous solid/liquid interface,[4] make these materials very competitive among the existing solid electrolytes. Such approach could provide (i) a route to lower locally the viscosity of ILs, and (ii) an easier pathway for diffusion of charged species. Several types of ionogels demonstrate this effect, taking into account of fully inorganic, hybrid, polymeric or organic-inorganic host networks . This “all-solid” approach can be applied to several electrochemical energy storage sources, including lithium batteries (Fig 1)[3,5] and supercapacitors (Fig. 2)[6,7]. Strikingly, high performance were shown on these devices, thanks to interfacial effects of confined ILs, with sometimes heightened properties of the chosen ILs as referred to their bulk properties[3,4,7,8]. Such solid electrolytes are particularly well suited for microdevices that we have been or are being developed (Fig. 3)[6,9]. Herein we will emphasize the results of a systematic study of the effect of size of confinement.