Conducting Salts Govern Thermal Boundary Conductance across Solid Electrode/Organic Liquid Electrolyte Interfaces in Lithium-Ion Batteries.

Abstract

Thermal boundary resistance at material interfaces poses a major challenge to effective heat dissipation in lithium-ion batteries, particularly at the interface between solid electrodes and organic liquid-based electrolytes. Despite its critical role in thermal management, the nanoscale mechanisms governing interfacial heat transfer in these systems remain poorly understood. Here, we employ all-atom molecular dynamics simulations to investigate heat transport across the interface between lithium cobalt oxide (LCO) electrodes and a liquid electrolyte mixture of ethylene carbonate and ethyl methyl carbonate (3:7 mass ratio) containing either LiPF₆ or LiTFSI salts at concentrations ranging from 0.05 to 2 M. Our results show that thermal boundary conductance is highly sensitive to both the identity of the conducting salt and the degree of lithium-ion adsorption on the LCO surface. While thermal boundary conductance can be as low as 20 MW m^-2 K^-1 at room temperature─comparable to the resistance of a ∼2 μm silicon layer─increased lithium surface coverage enhances vibrational coupling and significantly increases thermal boundary conductance. We also find that larger anions such as TFSI^- enable better interfacial heat transfer than smaller PF₆^- anions, which disrupt vibrational bridging at high lithium densities. Spectral analyses reveal that adsorbed lithium ions facilitate low-frequency vibrational coupling, especially in the LiTFSI system where the contributions from the transverse phonon modes in the solid are crucial. These findings underscore the critical role of salt-specific interfacial structuring and vibrational dynamics in modulating heat transfer, offering key design insights for thermally optimized, high-performance lithium-ion batteries.