Hf-based UiO-66-type solid electrolytes for all-solid-state lithium batteries

Abstract

Solid electrolytes (SEs) are expected to have a wide potential window, excellent stability, and high safety in electrochemical processes, allowing them to be applied flexibly in all-solid-state batteries (ASSBs). However, SEs suffer from low ionic conductivity and high interfacial impedance, which limits their practical application as key components of electrochemically stable batteries. Hf-based metal–organic frameworks modified by lithium ions (HLMOFs), consisting of functionalised UiO-66 MOFs with excellent electrochemical performances, have been synthesised and processed. The Li/UiO-66-2CO₂Li (Li/HLMOF-4) electrolyte membrane shows excellent electrochemical performance, including high ionic conductivity (2.82 × 10⁻³ S cm⁻¹), high transference number (0.58), and a wide potential window of 1.60–4.65 V at room temperature. The lithium stripping/plating behaviours can be stably cycled under a current density from 0.02 to 0.2 mA cm⁻². The excellent electrochemical performances of the nanostructured Li/HLMOF-4 are attributed to an increase in protons on the carboxyl group in the crystal by post-synthesis modification, which could be exchanged with lithium ions. The fabricated Li‖Li/HLMOF-4‖LiFePO₄ batteries exhibit high charge/discharge capacities. The chemical and structural design of the Hf-based SEs promotes their practical applications in next-generation solid-state batteries.