Locally Concentrated Deep Eutectic Liquids Electrolytes for Low‐Polarization Aluminum Metal Batteries

Abstract Low‐cost and nontoxic deep eutectic liquid electrolytes (DELEs), such as [AlCl 3 ] 1.3 [Urea] (AU), are promising for rechargeable non‐aqueous aluminum metal batteries (AMBs). However, their high viscosity and sluggish ion transport at room temperature lead to high cell polarization and low specific capacity, limiting their practical application. Herein, non‐solvating 1,2‐difluorobenzene (dFBn) is proposed as a co‐solvent of DELEs using AU as model to construct a locally concentrated deep eutectic liquid electrolyte (LC‐DELE). dFBn effectively improves the fluidity and ion transport without affecting the ionic dynamics in the electrolyte. Moreover, dFBn also modifies the solid electrolyte interphase growing on the aluminum metal anodes and reduces the interfacial resistance. As a result, the lifespan of Al/Al cells is improved from 210 to 2000 h, and the cell polarization is reduced from 0.36 to 0.14 V at 1.0 mA cm −2 . The rate performance of Al‐graphite cells is greatly improved with a polarization reduction of 0.15 and 0.74 V at 0.1 and 1 A g −1 , respectively. The initial discharge capacity of Al‐sulfur cells is improved from 94 to 1640 mAh g −1 . This work provides a feasible solution to the high polarization of AMBs employing DELEs and a new path to high‐performance low‐cost AMBs.