The next chapter in the hybrid eutectogel electrolytes

Abstract

Lithium-ion batteries are the energy storage devices of choice not only for portable devices but electric vehicles and grid energy storage as well due to their high gravimetric and volumetric energy density. Their ancestors, the lithium metal batteries offer way higher capacities but suffer severely from safety issues due to the dendrite formation. Solid state electrolytes; e.g. LISICON, garnets, perovskites, etc.; can greatly enhance the safety of lithium-metal batteries but suffer from low ionic conductivity (<10-4 mS/cm). [1] The interfacial resistance between the electrode and the solid electrolyte is another challenge. Hybrid solid state electrolytes can address these issues and allow for an easier implementation into conventional battery technology. The hybrid solid state electrolyte combines the desirable properties of both liquid and solid electrolytes by confining liquid electrolytes within a (meso-)porous solid framework. [2,3] This approach allows to maintain the high ionic conductivity and intimate contact with the electrodes while offering the safety of solid electrolytes. Our group developed the eutectogels in which a deep eutectic electrolyte is confined within a porous silica framework designed via a facile one-pot non-aqeous sol-gel route. This hybrid electrolyte can act as a greener and cheaper alternative to the well-known ionogels. BRON The eutectogels offer a broad electrochemical window, with a beneficial anodic stability limit of up to 4.8 V vs Li + /Li while impedance spectroscopy revealed ionic conductivities of up to 1.46 mS/cm for the optimal composition. LiFePO4 (LFP) demonstrator half-cells were assembled with these hybrid solid state electrolyte membranes and displayed a highly reversible capacity for over 100 cycles. The elaborate electrochemical characterization reveals the promising nature of the newest member of the hybrid solid electrolyte family. Lately, the eutectogel family has been expanded further via two pathways. First, new deep eutectic electrolytes with higher thermal stability have been confined, optimized and fully (electro-)chemically characterized for their potential in electrochemical cells. These new deep eutectic electrolytes improve further on the properties of the aforementioned original eutectogel. Another route is replacing the silica framework with a polymeric cage. This route allows the further simplification of the synthesis while fully harnessing the potential of the confined deep eutectic electrolyte. Both routes will be evaluated for their potential to formulate the design principles for the development of novel eutectogels.