Stress-Driven Whisker Formation in Lithium Metal Batteries

Abstract

Lithium metal batteries are promising for next-generation high-energy-density batteries, especially when lithium is directly plated on a current collector. However, lithium whiskers can form in the early stages of electroplating. These whiskers lead to low Coulombic efficiency due to isolated lithium formation during stripping. The mechanism of whisker formation is not fully understood, and different mechanisms are proposed in the literature. Herein, we computationally explore a stress-driven extrusion mechanism through cracks in the solid-electrolyte-interphase (SEI), which explains the experimentally observed root growth of lithium whiskers. We model the extrusion as a flow of a power-law Herschel-Bulkley fluid parametrized by the experimental power-law creep behavior of lithium, which results in the typical one-dimensional whisker shape. Consequently, in competition with SEI self-healing, SEI cracking determines the emergence of whiskers, giving a simple rule of thumb to avoid whisker formation in liquid electrolytes.