Ultrafast Zn2+ solvation dynamics unmask a hopping mechanism in eutectic battery electrolytes

Abstract

Understanding and controlling ultrafast Zn²⁺ solvation in deep-eutectic electrolytes is pivotal for advancing safe, high-efficiency Zn batteries yet has remained experimentally unexplored. Two-dimensional IR spectroscopy of tunable Zn(TFSI)₂–acetamide media, with thiocyanate anion (SCN⁻) as a vibrational probe, reveals composition-driven slowing of picosecond solvation dynamics, however, paradoxically, the slowest solvation accompanies the highest conductivity, implying a hopping-like Zn²⁺ migration mechanism. 2DIR measurements provide a direct molecular link between electrolyte composition and macroscopic charge transport, offering a powerful platform for rational design of high-performance Zn-ion batteries.