Electrochemical energy conversion devices, such as fuel cells and water electrolyzers, offer high power densities and efficiencies, along with quiet, emission-free operation, making them attractive candidates for large-scale applications. Advancing these technologies requires the development of materials including catalysts, membranes, and diffusion media that can deliver the performance and durability metrics necessary for practical deployment. However, the true/relevant active states of materials often exist only under operating conditions of electrochemical devices, making them inaccessible to conventional ex situ characterization techniques. Thus, the characterization of electrochemical devices under operating conditions, namely operando, can offer critical and valuable insights for guiding/informing material development. Synchrotron-based hard X-ray (> 5 keV) techniques are particularly well-suited for operando characterization of electrochemical devices due to their high penetration depth and relatively weak interactions, enabling the probing of various internal components. The various synchrotron X-ray based characterization techniques can provide comprehensive information including chemical (valence) states, coordination environments, and structures across different length scales. The use of these techniques provides unique opportunities to capture active states of materials and track evolving dynamics. In this perspective, we provide an overview of the device-level operando characterization using synchrotron-based X-ray techniques and highlight its potential to inform and accelerate material development towards the large-scale deployment of electrochemical technologies.

Lithium metal is commonly regarded as the "Holy Grail" anode material for high energy density rechargeable batteries. However, the uncontrollable growth of Li dendrites has posed safety concerns and thus greatly hindered its large-scale application. Here we have modified the surface of a commercial anode current collector, Cu foil, with a thin layer of Zn by a facile electroplating method, in order to regulate the Li nucleation and the following growth processes. Because of the formation of a solid solution buffer layer and Li-Zn alloy phases, the Li nucleation overpotential was dramatically reduced, realizing a uniform Li nucleation and a smooth Li plating morphology. As a result, significantly improved long-term cycling performance with a high Coulombic efficiency was achieved by the lithiophilic Zn coated Cu foil as a current collector. Full cells of Li-LiFePO₄ and Li-S using the Li deposited on the Zn modified Cu as the anode, showed increased capacity with low voltage hysteresis and greatly enhanced cycling stability, ascribed to the uniform Li deposition and formation of a stable solid electrolyte interphase (SEI) layer. This work demonstrates the feasibility of employing lithiophilic modified Cu foils as Li metal current collectors for practical applications.