Deciphering Kinetic Principles of Dual‐Anion Electrolytes for Extreme Fast‐Charging Lithium‐Ion Batteries

ABSTRACT

Tailoring Li ⁺ solvation coordination has been recognized as a strategy to enhance the electrochemical performance of lithium‐ion batteries (LIBs) under extreme fast‐charging (XFC) conditions. Beyond weakening Li ⁺ solvation, increased Li–anion pairing plays a crucial role in the formation of anion‐derived, inorganic‐rich electrode–electrolyte interfaces (EEIs). In this study, we propose an anion‐screening guideline leveraging transport in bulk electrolyte, desolvation energy and interfacial kinetics. We investigated mechanisms governed by dual‐anion electrolytes in both carbonate‐ and ester‐based solvents, aiming to address key challenges such as interfacial instability, lithium plating, and structural degradation. Integrated computational and experimental studies reveal that optimized dual‐anion systems create partially ion‐paired solvation structures and robust anion‐derived EEI on both electrodes, enabling principal merits of improved kinetics under XFC conditions. In LiNi _0.6 Mn _0.2 Co _0.2 || graphite pouch cells, the optimized dual‐anion formulation, PF ₆ ⁻ /TFSI ⁻ , in dimethyl carbonate‐based electrolyte retains over 85% of its original capacity and 94% retention after 500 cycles at 4C, while the ester‐based variant in methyl propionate achieves 94%/83% retention after 500/1000 cycles at 4C. These improvements are attributed to reduced charge‐transfer impedance with enriched inorganic fluorides and sulfates interface. Overall, this work provides a framework for anion regulations and offers a promising pathway to realizing fast‐charging, high‐energy‐density LIBs.