In this Perspective, we highlight recent progress and challenges related to the integration of lithium metal anodes in solid-state batteries. While prior reports have suggested that solid electrolytes may be impermeable to lithium metal, this hypothesis has been disproven under a variety of electrolyte compositions and cycling conditions. Herein, we describe the mechanistic origins and importance of lithium filament growth and interphase formation in inorganic and organic solid electrolytes. Multimodal techniques that combine real and reciprocal space imaging and modeling will be necessary to fully understand nonequilibrium dynamics at these buried interfaces. Currently, most studies on lithium electrode kinetics at solid electrolyte interfaces are completed in symmetric Li–Li configurations. To fully understand the challenges and opportunities afforded by Li-metal anodes, full-cell experiments are necessary. Finally, the impacts of operating conditions on solid-state batteries are largely unknown with respect to pressure, geometry, and break-in protocols. Given the rapid growth of this community and the diverse portfolio of solid electrolytes, we highlight the need for detailed reporting of experimental conditions and standardization of protocols across the community.

A full morphology ͑FM͒ model has been developed for studying the two-phase characteristics of the gas diffusion medium in a polymer electrolyte fuel cell ͑PEFC͒. The three-dimensional ͑3D͒ fibrous microstructure for the nonwoven gas diffusion layer ͑GDL͒ microstructure has been reconstructed using a stochastic technique for Toray090 and SGL10BA carbon papers. The FM model directly solves for the capillary pressure-saturation relations on the detailed morphology of the reconstructed GDL from drainage simulations. The estimated capillary pressure-saturation curves can be used as valuable inputs to macroscopic two-phase models. Additionally, 3D visualization of the water distribution in the gas diffusion medium suggests that only a small number of pores are occupied by liquid water at breakthrough. Based on a reduced compression model, the two-phase behavior of the GDL under mechanical load is also investigated and the capillary pressure-saturation relations are evaluated for different compression levels.The polymer electrolyte fuel cells ͑PEFCs͒, which convert the chemical energy of hydrogen directly into electrical energy, are considered as the most promising alternative energy-conversion devices in the 21st century for several applications including automotive, stationary and portable power. The electrochemical reaction occurring in the cathode catalyst layer ͑CL͒, referred to as the oxygen reduction reaction combines protons, resulting from hydrogen oxidation in the anode catalyst layer, with oxygen to produce water and waste heat. Although tremendous progress has been made in recent years in enhancing overall performance of the PEFC, one major performance-limiting step is the coverage of the reaction sites in the CLs as well as the blockage of the reactant-transporting networks in the porous gas diffusion layers ͑GDLs͒ due to liquid water, which hinders the oxidant from reaching the active reaction sites in the CLs at high current density operation. The GDL plays a crucial role in the overall water management which requires a delicate balance between reactant transport from the gas channels and water removal from the electrochemically active sites. Mathias et al. 1 provided a comprehensive overview of GDL structure and functions.Several studies have been attempted in recent years to model two-phase behavior and flooding phenomena in polymer electrolyte fuel cells in various degrees of complexities. 2-15 Recent reviews by Wang 16 and Weber and Newman 17 provide comprehensive overview of various two-phase PEFC models and address the water management issue with particular attention to GDL in significant details. However, all of the above-mentioned macroscopic two-phase models are plagued with the scarcity of realistic two-phase correlations, in terms of capillary pressure and relative permeability as functions of water saturation, tailored specifically for actual gas diffusion medium characterized by woven or nonwoven fibrous structures. Due to the lack of reliable two phase correlations, these models often deploy...

Despite progress in solid-state battery engineering, our understanding of the chemo-mechanical phenomena that govern electrochemical behavior and stability at solid-solid interfaces remains limited compared to solid-liquid interfaces. Here, we use operando synchrotron X-ray computed microtomography to investigate the evolution of lithium/solid-state electrolyte interfaces during battery cycling, revealing how the complex interplay between void formation, interphase growth, and volumetric changes determines cell behavior. Void formation during lithium stripping is directly visualized in symmetric cells, and the loss of contact at the interface between lithium and the solid-state electrolyte (Li 10 SnP 2 S 12) is found to be the primary cause of cell failure. Reductive interphase formation within the solid-state electrolyte is simultaneously observed, and image segmentation reveals that the interphase is redox-active upon charge. At the cell level, we postulate that global volume changes and loss of stack pressure occur due to partial molar volume mismatches at either electrode. These results provide new insight into how chemo-mechanical phenomena can impact cell performance, which is necessary to understand for the development of solid-state batteries. File list (2) download file view on ChemRxiv Manuscript Updated.pdf (1.08 MiB) download file view on ChemRxiv Supplementary Information.pdf (1.02 MiB)

We demonstrate the growth of dendritic magnesium deposits with fractal morphologies exhibiting shear moduli in excess of values for polymeric separators upon the galvanostatic electrodeposition of metallic Mg from Grignard reagents in symmetric Mg–Mg cells. Dendritic growth is understood on the basis of the competing influences of reaction rate, electrolyte transport rate, and self-diffusion barrier.

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