Operando ultra-high-resolution X-ray microscopy of lithium anodes with separator interactions

Lithium (Li) metal is an attractive anode material candidate for high-energy-density battery systems that could enable challenging electrification applications, such as flight and heavy-duty vehicles. However, the formation of porous deposits and dendrites during cycling cause capacity loss and internal short-circuit risks. Here, we use high-resolution in-situ/operando Zernike phase contrast X-ray microscopy to directly visualize the lithium electrodeposition process inside a coin cell with a commercial separator. The nucleation and subsequent lithium electrodeposition were imaged by transmission X-ray microscopy (TXM) at 150 nm spatial resolution and <2 min temporal resolution. The resulting lithium deposits were then reconstructed into three-dimensional (3D) volumes by computed tomography (CT), revealing the Li structures above, at, and below the anode/separator interface. Distinct nucleation and deposition mechanisms were observed under varied cell temperatures, charging current density, and electrolyte composition. This work demonstrates the unique strengths of combining TXM and CT imaging techniques: the dynamic evolution of lithium electrodeposition and the comprehensive morphology of the resulting structure were characterized together. Furthermore, our results indicate the importance of in-situ/operando characterization of systems in commercially-relevant configurations in developing practical dendrite mitigation strategies.