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Rechargeable zinc–air batteries may become safe, sustainable, low‐cost, and energy‐dense alternatives to Li‐ion batteries for many applications, but problems associated with today's air‐breathing electrodes limit zinc–air performance. To overcome this challenge, researchers have investigated hundreds of air‐breathing electrode variations over the last decade. Unfortunately, the efficacy of these variations remains ambiguous due to nonstandardized cycling protocols that map to areal‐energy values spanning five orders of magnitude. To compete with Li‐ion batteries, researchers should cycle zinc–air cells at 35 mWh cmgeo−2, but only 8, of the 100 publications reviewed here, breach this threshold. Once the community cycles zinc–air cells at the proposed areal energy and better understands failure mechanisms, lab‐scale results will translate to practical advancements. [ABSTRACT FROM AUTHOR]

By applying differential pair distribution function (DPDF) analyses to the energy-storage relevant MnOx/carbon system―but in a 3D architectural rather than powder-composite configuration―we can remove contributions of the carbon nanofoam paper scaffold and quantify the multiphasic oxide speciation as the nanoscale, disordered MnOx grafted to the carbon walls (MnOx@CNF) structurally rearranges in situ from disordered birnessite AMnOx (A = Na+; Li+) to tetragonal Mn3O4 to spinel LiMn2O4. The first reaction step involves topotactic exchange of interlayer Na+ by Li+ in solution followed by thermal treatments to crystal engineer the ∼10 nm-thick 2D layered oxide throughout the macroscale nanofoam paper into a cubic phase. The oxide remains affixed to the walls of the nanofoam throughout the phase transformations. The DPDF fits are improved by retention of one plane of birnessite-like oxide after conversion to spinel. We support the DPDF-derived assignments by X-ray photoelectron spectroscopy and Raman spectroscopy, the latter of which tracks how crystal engineering the oxide affects the disorder of the carbon substrate. We further benchmark MnOx@CNF with nonaqueous electrochemical measurements versus lithium as the oxide converts from X-ray-amorphous birnessite to interlayer-registered LiMnOx to spinel. The lamellar AMnOx displays pseudocapacitive electrochemical behavior, with a doubling of specific capacitance for the interlayer-registered LiMnOx, while the spinel LiMn2O4@CNF displays a faradaic electrochemical response characteristic of Li-ion insertion. Our results highlight the need for holistic understanding when crystal engineering an (atomistic) charge-storing phase within the (architectural) structure of practical electrodes. [ABSTRACT FROM AUTHOR]