Temporal Evolution of Lithium Metal Microstructures During Ultra-High-Capacity Stripping/Plating Cycles

The morphology of deposited lithium (Li) is critical to the stability and reversibility of Li-metal batteries (LMBs). While crystallographic features of Li influence deposition morphology, the orientation of Li crystals during electrodeposition and their temporal evolution under varying kinetic and interphasial conditions remain unclear. This study investigates Li microstructures during electrodeposition at ultra-high capacities (up to 12 mAh cm⁻²) and over repeated cycling, using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The results show that the microstructural evolution of Li depends on the interplay between interphasial properties and deposition kinetics. A layer-by-layer epitaxial Li growth with a coherent lattice orientation is achievable under homogeneous interphase and slow deposition kinetics. However, at higher capacities or extended cycling, deterioration of interphase homogeneity disrupts crystal matching, resulting in island-like deposits with randomly oriented single-crystalline grains. In contrast, an inhomogeneous interphase and faster kinetics lead to whisker-like Li deposits. These results demonstrate that while cohesive interactions between depositing Li crystals can result in isolated single-crystalline grains, maintaining interphase homogeneity and stability is essential to enable coherent lattice matching for layer-by-layer epitaxial growth. This study reveals Li microstructural evolution and offers insights for designing stable interphases and optimizing conditions for durable, high-capacity LMBs.