Temperature-Dependence of the Solid-Electrolyte Interphase Overpotential: Part I. Two Parallel Mechanisms, One Phase Transition

TL;DR

This study investigates how the solid-electrolyte interphase (SEI) overpotential varies with temperature across different alkali-metal electrodes, revealing two transport mechanisms and a phase transition affecting ion conduction.

Contribution

It extends the temperature-dependent analysis of SEI overpotential to a broad range and identifies two distinct ion transport mechanisms with a phase transition at a critical temperature.

Findings

Two ion transport mechanisms identified, one active at all temperatures, another above a critical temperature.

A phase transition at T_C switches off the more efficient transport mechanism.

Overpotentials increase rapidly below T_C, limiting low-temperature battery performance.

Abstract

It has been shown recently that the overpotential originating from ionic conduction of alkali-ions through the inner dense solid-electrolyte interphase (SEI) is strongly non-linear. An empirical equation was proposed to merge the measured resistances from both galvanostatic cycling (GS) and electrochemical impedance spectroscopy (EIS) at 25$^{\circ}$C. Here, this analysis is extended to the full temperature range of batteries from -40$^{\circ}$C to +80$^{\circ}$C for Li, Na, K and Rb-metal electrodes in carbonate electrolytes. Two different transport mechanisms are found. The first one conducts alkali-ions at all measured temperatures. The second transport mechanism conducts ions for all seven measured Li-ion electrolytes and one out of four Na-ion electrolytes, however, only above a certain critical temperature $T_C$. At $T_C$ a phase transition is observed switching-off the more efficient transport mechanism and leaving only the general ion conduction mechanism. The associated overpotentials increase rapidly below $T_C$ depending on alkali-ion, salt and solvent and become a limiting factor during galvanostatic operation of all Li-ion electrolytes at low temperature. In general, the current analysis merges the SEI resistances measured by EIS ranging from 26 $\Omega$cm$^2$ for the best Li up to 292 M$\Omega$cm$^2$ for Rb electrodes to its galvanostatic response over seven orders of magnitude. The determined critical temperatures are between 0-25$^{\circ}$C for the tested Li and above 50$^{\circ}$C for Na electrolytes.