Spectral–Spatial EPR Imaging as a Single-Window Probe for Both Macro-Distribution and Micro-Architecture of Lithium Deposits

An ideal diagnostic for metallic lithium anodes should be noninvasive and can concurrently probe from submicrometer dendrites to millimeter-scale plating distribution due to the multiscale differences in deposit architectures. Here we show that spectral-spatial electron paramagnetic resonance imaging (EPRI) fulfils this need by resolving the Dysonian line shape of Li deposits at every pixel of the electrode plane. The spectral parameters of asymmetry ratio A/B, peak-to-peak line width ΔBpp and double integral (DI) are correlated to microstructure thickness, packing compactness and deposit quantity, respectively, and then mapped onto two-dimensional images to quantitatively characterize the full macro-to-micro landscape of Li deposits. Comparing the conventional and customized electrolytes shows the latter delivers markedly more homogeneous macroscopic distribution, denser deposition and thicker microstructures. By artificially imposing pressure imbalance on the cell, it further reveals that compression dictates packing compactness yet hardly alters microstructure thickness, while dead Li preferentially accumulates in the low-pressure region. This EPRI approach provides statistically robust, multiscale descriptors for studying and designing next-generation Li-metal-based anodes.