Li Dynamics of Liquid Electrolytes Nanoconfined in Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) are excellent platforms to design hybrid electrolytes for Li batteries with liquid-like transport and stability against lithium dendrites. We report on Li dynamics in quasi-solid electrolytes consisting in Mg-MOF-74 soaked with LiClO-propylene carbonate (PC) and LiClO-ethylene carbonate (EC)/dimethyl carbonate (DMC) solutions by combining studies of ion conductivity, nuclear magnetic resonance (NMR) characterization, and spin relaxometry. We investigate nanoconfinement of liquid inside MOFs to characterize the adsorption/solvation mechanism at the basis of Li migration in these materials. NMR supports that the liquid is nanoconfined in framework micropores, strongly interacting with their walls and that the nature of the solvent affects Li migration in MOFs. Contrary to the "free'' liquid electrolytes, faster ion dynamics and higher Li mobility take place in LiClO-PC electrolytes when nanoconfined in MOFs demonstrating superionic conductor behavior (conductivity σ > 0.1 mS cm, transport number > 0.7). Such properties, including a more stable Li electrodeposition, make MOF-hybrid electrolytes promising for high-power and safer lithium-ion batteries.