Transient Polarization and Dendrite Initiation Dynamics in Ceramic Electrolytes

TL;DR

This study uncovers polarization dynamics in ceramic electrolytes related to dendrite initiation, revealing that the critical current density is diffusion-limited and comparable to liquid electrolytes, which advances understanding of failure mechanisms in solid-state batteries.

Contribution

It introduces a novel polarization technique combined with impedance spectroscopy to analyze dendrite initiation in ceramic electrolytes, providing a self-consistent method to determine diffusion-limited current densities.

Findings

Polarization peaks follow the Randles-Sevcik equation indicating diffusion-limited processes.

Critical current density is governed by ion diffusion, similar to liquid electrolytes.

System-specific limiting current density is lower than the critical current density.

Abstract

Solid-state electrolytes, by enabling lithium metal anodes, may significantly increase the energy density of current lithium-ion batteries. However, similar to their liquid counterparts, these hard and stiff electrolytes can still be penetrated by soft Li metal, above a critical current density (CCD). The prevailing method to determine the CCD employs step-wise galvanostatic cycling, which suffers from inconsistent active interfacial areas due to void formations after repeated stripping and plating, leaving large variance in the reported data that preclude precision understandings. Here, we combine a one-way polarization technique with electrochemical impedance spectroscopy to uncover, for the first time, the existence of significant polarization dynamics in ceramic electrolytes. In contrast to the diverging transient current due to metal penetration, the current peaks we observed suggest a diffusion-limited mechanism that follows the classic Randles-Sevcik equation for analyzing the diffusion-limited processes in liquid electrolytes. Our results allow a rigorous self-consistent analysis to reveal that the CCD is a diffusion-limited current density, while the system-specific limiting current density for ceramic electrolytes is still lower than CCD, which suggests that the ion transport mechanism preceding the dendrite penetration in ceramic electrolytes is unifiable with that in liquid electrolytes.