Nano‐Confined Electrolyte for Sustainable Sodium‐Ion Batteries

Sodium‐ion batteries (SIBs) are considered as a promising candidate for large‐scale electrochemical energy storage devices due to their low cost, abundant upstream resources, and compatible manufacturing processes with lithium‐ion batteries. However, the highly active free solvent molecules in the liquid electrolyte trigger continuous interfacial side reactions between electrodes and electrolyte, which degrades the cycling performance of SIBs. Herein, a Cu‐based metal‐organic framework (MOF) with a uniform nanoporous channel of 1.1 nm is exploited to confine the electrolyte. Benefiting from the highly‐aggregated solvation configuration, the MOF‐confined electrolyte possesses superior chemical/electrochemical and thermal stability, which guarantees its interface compatibility and flame retardancy. As a result, the batteries with the nano‐confined electrolyte and Na3V2(PO4)3 cathode show an ultra‐long lifetime of 3000 cycles with 93% capacity retention and decent high‐temperature performance (600 cycles with 90% capacity retention). This work presents a viable method for fabricating sustainable SIBs and also provides guidance for solving the side reactions between electrolytes and electrodes in electrochemical energy storage systems. A metal‐organic framework‐confined electrolyte is strategically designed to mitigate the interfacial side reactions and address the safety issues for sodium‐ion batteries (SIBs). Through the simultaneous physical and chemical confinement effect, such electrolyte enables the SIBs to realize excellent cycling and high‐temperature performance.