Reliance on lithium batteries to power both personal electronics and emission-free vehicles is significant and growing. It is for this reason that it is essential to optimize both the performance and safety of these devices. The energy density and safety of current lithium batteries can be improved by replacing traditional flammable liquid electrolytes with solid-state electrolytes.¹ Ceramic electrolytes have been shown to be both durable and stable, these materials tend to have poor electrochemical performance when compared to traditional liquid systems.² Ceramic electrolytes can also be difficult to integrate into real devices as they can have significant interfacial resistance with electrodes.³ However, the creation of hybrid electrolytes (generally a combination of polymer and ceramic electrolytes) can improve electrolyte flexibility and decrease electrode interfacial resistance.^4,5 In this work we present a hybrid electrolyte comprised of a lithium-conducting ceramic and a solvate ionic liquid (SIL). A liquid-based hybrid electrolyte was chosen as liquid electrolytes are better able to wet the ceramic compared to polymer electrolytes. As the volume of SIL remains low relative to the quantity of ceramic, the resultant hybrid electrolytes maintain their solidity, taking on the aspect of damp sand as opposed to soft gels but still demonstrate increased ionic conductivity when compared to ceramic-only systems. It is however unclear whether observed improvements in ionic conductivity are attributable to the liquid or an interaction between the electrolytes. Ionic conductivities of the hybrid system (ceramic + SIL), ceramic alone and SIL alone were compared to determine the contributions of the ceramic and the SIL to the ionic conductivity of the hybrid system. In addition, a completely inert powder which has a similar particle distribution as the ceramic was also tested with the SIL to potentially isolate the impact of the SIL on ion transport. Solid-state NMR was used to evaluate potential lithium-lithium interactions in both the ceramic + SIL and inert powder + SIL systems. One-dimensional ⁷Li spectra were acquired to identify lithiated environments. Variable temperature two-dimensional exchange spectroscopy (2D EXSY) was performed to correlate with the temperature range over which ionic conductivity was measured. This technique has been previously used to analyze potential lithium-lithium exchange in ceramic-polymer hybrid electrolytes but as not been extensively used in ceramic-liquid systems.^6,7 Lithium interactions in the hybrid systems, along with conductivity and surface characterization data, will be used to advance the understanding of ion transport in damp sand electrolyte systems.

References

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