The current paradigm in battery technology, which pairs Li<sup>+</sup> ions with a liquid electrolyte, is potentially dangerous: in the event of a short circuit by lithium dendrites, the flammable nature of the liquid electrolyte can result in fire or explosion. A potentially safer alternative to this problem is solid-state electrolytes, which will replace the flammable liquid electrolyte and limit lithium dendrite formation due to mechanical toughness. This project aims to synthesize conductive electrolytes using co-crystalline materials (compounds with unique properties that are composed of a set ratio of salt to solvent) and to characterize the properties of the resulting electrolytes. Lithium-borate salt complexes will be used to synthesize these co-crystal compounds. The primary salt of interest is lithium tetraphenylborate. The lithium cation should have minimal binding to the tetraphenylborate anion, due to its lack of lone pairs and low affinity for the solvating matrix component. Together this is projected to reduce the cation-anion interactions for the lithium cation and improve the conductivity within the crystalline structure. Initial syntheses have suggested that this salt can be incorporated into a crystalline material but produce unstable crystals. Crystallization with other solvents may result in the formation of a stable conductive electrolyte. Previous work from the Zdilla lab has shown that nitrile-based electrolytes are promising candidates, as they exhibit high thermal stability as well as large electrochemical operating windows. Such compounds also show resistance to electrochemical oxidation, which makes them practical for use with high-voltage cathodes. Initial reactions between lithium tetraphenylborate and benzonitrile, as well lithium tetraphenylborate and 1,4-dicyanobenzene have resulted in room temperature stable co-crystals. Further characterized of resulting crystalline materials was performed via FTIR (Fourier Transform Infrared Spectroscopy), NMR (Nuclear Magnetic Spectroscopy), EIS (Electrochemical Impedance Spectroscopy), TGA (Thermal Gravimetric Analysis), DSC (Differential Scanning Calorimetry), and XRD (X-ray Diffraction Spectroscopy).

Synthesis and characterization of nitrile-containing compounds and lithium tetraphenylborate co-crystals for use as electrolytes

ACS Spring Meeting 2021

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