Three-Dimensional <i>Operando</i> Photoacoustic Microscopy Reveals Hidden Patterns in the Complex Electrochemical Plating Process of Lithium Metal

The electrochemical plating of lithium metal is known to be nonuniform and complex, which can ultimately lead to short circuits and capacity degradation in lithium-metal batteries. These detrimental phenomena are extremely challenging to both predict and manage. Herein, we develop a fast photoacoustic imaging system based on microelectromechanical systems and can thus achieve a high temporal resolution of 0.45 ms per pixel. This system enables operando monitoring of the lithium-plating process under practical current densities, with a lateral resolution of 7.8 μm. We monitor a millimeter-scale region and simultaneously follow the height evolution of lithium metal across 1000 subregions using grid-based tracking. Careful statistical analysis of these growth patterns reveals that the lithium plating begins as a diffusion-controlled process but subsequently diverges into explosive, steady, and diminishing patterns at different locations. This variation likely arises from the spatially dependent lithium-ion diffusivity of the solid-electrolyte interphase formed at the lithium metal–liquid electrolyte interface, which ultimately leads to uneven lithium plating. These findings significantly advance our understanding of lithium-plating dynamics and motivate the development of strategies to mitigate the associated risks in lithium-metal batteries.