Concentration-Dependent Thermodynamics and Kinetics in Lithium-Metal Battery Electrolytes: Implications for Coulombic Efficiency

Lithium (Li)-metal batteries (LMBs) are promising for high-energy applications but are hindered by dendrite formation and unstable interphases. This study investigated Li plating thermodynamics and kinetics as descriptors governing Coulombic efficiency (CE), focusing on lithium bis(fluorosulfonyl)imide in fluoroethylene carbonate and 1,2-dimethoxyethane electrolytes. First, upshifts in Li+/Li potential (ELi+/Li vs Me10Fc), via low donor number solvents and high salt concentrations, correlated with increased CEs. Second, reaction (ΔSLi+Li) and configurational entropy (SC), obtained via Seebeck coefficient and heat capacity measurements, respectively, did not correlate with CE and formed a minority contribution to Li+/Li reaction free energy, revealing the primarily enthalpic origin of the ELi+/Li correlation. Finally, kinetic analyses to examine the balance of exchange current density (j0) and diffusion (DLi) showing lower DLi/j0 led to higher CE. These CE correlations highlight the combined effects of thermodynamics and kinetics on Li reversibility, informing rational strategies for enhanced performance of LMBs.