Influence of Internal Interfaces on the Structure and Dynamics of IL- Based Electrolytes Confined in a Metal-Organic Framework

J Hessling and L Dick and S Keil and V Alizadeh and MR Hansen and B Kirchner and M Schönhoff, JOURNAL OF PHYSICAL CHEMISTRY B, 129, 6372-6384 (2025).

DOI: 10.1021/acs.jpcb.5c01702

Hybrid solid-state electrolytes, which combine ionic liquids with metal- organic frameworks, offer a promising approach to enhancing the safety and energy density of next-generation batteries. A thorough understanding of the interplay between the solid and liquid phases in hybrid solid-state electrolytes is crucial for optimizing their performance as battery electrolytes. This study investigates how interactions between different ionic liquid-based electrolytes and the metal-organic framework ZIF-8 influence the coordination and dynamics of Li+ in confinement. To this end, we examine five different ionic liquids, varying the chemical nature of the cation. Raman spectroscopy, supported by 2D solid-state NMR and simulations, are used to elucidate Li+ coordination and ion-wall interactions. The impact of these interactions on local Li+ dynamics and charge transport in the ionic liquid-ZIF-8 hybrid system is investigated using 7Li spin relaxation, impedance spectroscopy, and simulations. The results reveal a competitive interaction between Li+ and the ionic liquid cation with the ZIF-8 framework, which can be fine-tuned by modifying the molecular structure of the ionic liquid cation. As a consequence, local Li+ dynamics is enhanced, depending on the ionic liquid cation. The beneficial interactions in the confined system can even make Li+ the fastest diffusing species, in contrast to bulk electrolyte, where Li+ transport is limited by strong Li-anion clusters. Thus, blocking Li+-framework interactions through other competitive interactions might be an effective strategy to enhance Li+ dynamics and increase Li conductivity in a hybrid solid-state electrolyte. Although confinement within the ZIF-8 model system leads to an overall decrease in conductivity, this study provides valuable insights into the design of hybrid electrolytes for next-generation battery applications.

Return to Publications page