Toward a bottom-up understanding of the impact of high-entropy electrolyte components on the charge storage performance of lithium ion batteries.

High entropy electrolytes show great potential in the design of next generation batteries. Demonstrating how salt components of high entropy electrolytes influence the charge storage performance of batteries is essential in the tuning and design of such advanced electrolytes. This study investigates the transport and interfacial properties for lithium hexafluorophosphate (LiPF₆) in ethylene carbonate and dimethyl carbonate (EC/DMC) solvent with commonly used additives for high entropy electrolytes (LiTFSI, LiDFOB, and LiNO₃). Using a combination of experimental measurements and numerical simulations, transport properties including ionic conductivity, viscosity, transference numbers, and solvation structures of various electrolyte formulations are examined. The results show that the addition of LiTFSI improves ionic conductivity, while LiNO₃ may hinder ion migration due to the formation of aggregated Li-NO₃^- complexes. Both LiNO₃ and LiDFOB may result in an increase in near-surface reaction resistance. The addition of LiNO₃ and LiDFOB leads to an increase in capacity at low current rates but a decline at higher rates due to the coupled effect of additives on transport properties and interfacial properties. This study provides insights into the complex role of additives in optimizing the performance of lithium-ion batteries, particularly in terms of electrolyte conductivity and interfacial properties. This study establishes a general mechanistic design rule, showing that selecting electrolyte additives according to their effects on the solvation structure and aggregation enables predictive tailoring of salt combinations for either high-rate or low-rate lithium-ion battery applications.