A Deep Eutectic Electrolyte Mimicking a Localized High-Concentration Environment Enables Reversible Aluminum Electrodeposition for High-Performance Aluminum Metal Batteries.

Al is a promising anode for next-generation batteries due to its abundance, high theoretical capacity, and good safety. However, the deployment of Al metal batteries (AMBs) is hindered by the lack of efficient electrolytes capable of enabling highly reversible and uniform Al plating/stripping. Here we develop a relatively economical and low-corrosive AlCl3/tetramethylurea (TMU) deep eutectic electrolyte (DEE) that supports reversible Al electrodeposition with an enhanced (111) orientation tendency. To further reduce viscosity and enhance ionic conductivity, a non-solvating 1,2-difluorobenzene (1,2-dFBn) co-solvent is introduced to construct a localized-high-concentration-electrolyte-like (LHCE-like) DEE. The 1,2-dFBn incorporation selectively modulates the local environment of chloroaluminate species without altering their intrinsic speciation, thereby improving electrolyte fluidity and ion transport. Moreover, 1,2-dFBn promotes the formation of a robust SEI, accompanied by a reduced apparent nucleation overpotential and more uniform Al deposition. Consequently, the optimized electrolyte enables stable Al cycling for over 1,600 h at 1.0 mA cm-2 and 1.0 mAh cm-2 with an ultralow polarization of ∼80 mV. Al||graphite cells deliver 80.6 mAh g-1 after 600 cycles at 500 mA g-1 with nearly 100% Coulombic efficiency. This work provides valuable insights into the rational design of low-cost and high-performance electrolytes for AMBs.