The development of novel, safe solid electrolyte materials for use in solid state lithium-ion battery technology primarily focuses on improving Li ion conductivity throughout the bulk substrate and at the solid electrode-electrolyte interface. The utilization of novel soft solid electrolytes featuring low affinity channel walls for entrapping ions can improve Li ion mobility, therefore improving ionic conductivity and performance. In this study, cocrystals of adiponitrile (ADN) and LiXF6 salts (X = P, As, Sb) were formed and examined as materials for use as solid-state electrolytes in Li ion batteries. The three different cocrystals that were synthesized all maintained crystal structures, featuring Li ions located in one dimensional ion channels along the crystal lattice. Lithium ion transference numbers, tLi+, calculated from electrochemical impendence spectroscopy measurements from each of the (ADN)2●LiXF6 cocrystals were determined to be tLi+ (X=Sb) &gt; tLi+ (X=As) &gt; tLi+ (X=P). This indicates that as the anionic species becomes more massive, the contribution of Li ions to the overall ionic conductivity increases. Differential scanning calorimetry (DSC) measurements for the (ADN)2●LiXF6 cocrystals indicated no evidence of melting of the cocrystals below the decomposition temperature. However, small melt and crystallization features were identified as indicative of pure ADN. As observed from scanning electron microscopy (SEM) images, these signatures were attributed to liquid-like ADN regions surrounding the co-crystallites. These regions are believed mitigate Li ion transport through the electrode-electrolyte interface, therefore enhancing ionic conductivities.

Synthesis and characterization of adiponitrile (ADN)2●LiXF6 (X = P, As, Sb) cocrystals for solid-state electrolyte Li ion battery applications

ACS Spring 2022

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