The morphology of the electrolyte‐filled pore space in lithium‐ion batteries is determined by the solid microstructure formed by μm‐sized active material particles and the smaller‐featured carbon binder domain (CBD). Tomographic reconstructions have largely neglected the CBD, resulting in inadequately defined pore space morphologies at odds with experimental ionic tortuosity values. We present a three‐phase reconstruction of a LiCoO2 composite cathode by focused ion‐beam scanning electron microscopy tomography. Morphological analysis proves that the reconstruction, which combines an unprecedented volume (20 μm minimum edge length) with the hitherto highest resolution (13.9×13.9×20 nm3 voxel size), represents the cathode's pore space morphology. Pore‐scale diffusion simulations show consideration of the resolved CBD as indispensable to reproduce ionic tortuosity values from electrochemical impedance spectroscopy. Our results reveal the CBD as a convoluted network that dominates the pore space morphology and limits Li+ transport through tortuous and constricted diffusion pathways.

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A laser‐based procedure for the preparation of metallic hierarchical porous materials is introduced and exemplified on tin, copper, silicon, titanium, and tungsten surfaces to demonstrate its general applicability. The impact of suitably tuned nanosecond laser pulses triggers a process in which laser‐induced metal ablation and instantaneous recondensation of partially oxidized metals lead to cauliflower‐like superstructures comprising a hybrid micro‐/nanopatterning. Repeated scanning with the intense focused beam over the surface creates microstructures of hierarchically tunable porosity in a layer‐by‐layer design. The 3D morphology of these superstructures is analyzed using tomographic data based on focused ion‐beam scanning electron microscopy to return a fractal dimension of Df = 2.79—practically identical to a natural cauliflower (Df ≈ 2.8), even though the plant is four orders of magnitude larger than the superstructures generated through the laser process. The high Df value signifies a complex morphology that boasts a huge external surface. The introduced concept enables convenient access to a variety of metallic hierarchical porous materials, which are key to performance in environmentally and technologically relevant areas like energy generation, storage, and conversion, as well as sensing and catalysis.

Lithium‐ion battery models often neglect the salt concentration polarization inside the electrolyte‐filled pores of the composite electrodes. However, this concentration polarization causes a significant impedance, in particular in the case of electrolytes with low Li+ transference numbers. Here, we analyze in detail measured and calculated impedance spectra of composite electrodes containing a solvate ionic liquid‐based electrolyte and an ionic liquid‐based electrolyte, respectively, in comparison to a conventional carbonate‐based electrolyte. For calculating spectra, we use a recently published model by Huang and Zhang. We find that the impedance at 10−4 Hz, which is relevant for battery cycling rates around 1 C to 2 C, increases in the order carbonate‐based electrolyte<ionic liquid‐based electrolyte<solvate ionic liquid‐based electrolytes, but exhibits a remarkably weak thickness dependence, when the electrode thickness exceeds 50–100 μm. This suggests that electrodes considerably thicker than the conventional 80 μm can be used in batteries without significantly deteriorating battery power.