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 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 concentration, correlated with stable voltage profiles and 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 (jo) and diffusion (DLi+) showed lower DLi+/jo 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.