High Electrochemical Performance of Sodium-Ion Gel Polymer Electrolytes Achieved Through a Sandwich Design Strategy Combining Soft Polymers with a Rigid MOF

Sodium-ion batteries (SIBs) are considered the next-generation candidates for partially substituting for commercial lithium-ion batteries in future energy storage systems because of the abundant sodium/potassium reserves and these batteries' cost-effectiveness and high safety. Gel polymer electrolytes (GPEs) have become a popular research focus due to their advantages in terms of safety and performance in research on quasi-solid-state sodium-ion batteries (QSSIBs). Building on previous studies that incorporated MOF fillers into polymer-based gel electrolytes, we propose a 3D sandwich structure in which MOF materials are first pressed into thin films and then coated and protected by polymer materials. Using this approach, we achieved an ion conductivity of 1.75 x 10-4 S cm-1 at room temperature and an ion transference number of 0.69. Solid-state sodium-ion batteries using this gel film electrolyte exhibited long cycling stability at a 2 C current density, retaining 75.2% of their specific capacity after 500 cycles.