A mechanistic analysis of voltage shape changes in lithium metal anodes explains how dead lithium causes capacity fade and failure.

Solid-state electrolytes (SSEs) have attracted substantial attention for next-generation Li-metal batteries, but Li-filament propagation at high current densities remains a significant challenge. This study probes the coupled electrochemicalmorphological-mechanical evolution of Li-metal-Li 7 La 3 Zr 2 O 12 interfaces. Quantitative analysis of synchronized electrochemistry with operando video microscopy reveals new insights into the nature of Li propagation in SSEs. Several different filament morphologies are identified, demonstrating that a singular mechanism is insufficient to describe the complexity of Li propagation pathways. The dynamic evolution of the structures is characterized, which demonstrates the relationships between current density and propagation velocity, as well as reversibility of plated Li before short-circuit occurs. Under deep discharge, void formation and dewetting are directly observed, which are directly related to evolving overpotentials during stripping. Finally, similar Li penetration behavior is observed in glassy Li 3 PS 4 , demonstrating the relevance of the new insights to SSEs more generally.

The lack of a reliable rechargeable lithium metal (Li-metal) anode is a critical bottleneck for next-generation batteries. The unique mechanical properties of lithium influence the dynamic evolution of Li-metal anodes during cycling. While recent models have aimed at understanding the coupled electrochemical-mechanical behavior of Li-metal anodes, there is a lack of rigorous experimental data on the bulk mechanical properties of Li. This work provides comprehensive mechanical measurements of Li using a combination of digital-image correlation and tensile testing in inert gas environments. The deformation of Li was measured over a wide range of strain rates and temperatures, and it was fitted to a power-law creep model. Strain hardening was only observed at high strain rates and low temperatures, and creep was the dominant deformation mechanism over a wide range of battery-relevant conditions. To contextualize the role of creep on Li-metal anode behavior, examples are discussed for solid-state batteries, "dead" Li, and protective coatings on Li anodes. This work suggests new research directions and can be used to inform future electrochemical-mechanical models of Li-metal anodes.

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Molecular Layer Deposition (MLD) of “lithicone” thin films is demonstrated, which behave as ionically-conductive solid electrolytes for future battery applications.

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Interfacial fracture and delamination of polymer interfaces can play a critical role in a wide range of applications, including fiber-reinforced composites, flexible electronics, and encapsulation layers for photovoltaics. However, owing to the low surface energy of many thermoplastics, adhesion to dissimilar material surfaces remains a critical challenge. In this work, we demonstrate that surface treatments using atomic layer deposition (ALD) on poly­(methyl methacrylate) (PMMA) and fluorinated ethylene propylene (FEP) lead to significant increases in surface energy, without affecting the bulk mechanical response of the thermoplastic. After ALD film growth, the interfacial toughness of the PMMA–epoxy and FEP–epoxy interfaces increased by factors of up to 7 and 60, respectively. These results demonstrate the ability of ALD to engineer the adhesive properties of chemically inert surfaces. However, in the present case, the interfacial toughness was observed to decrease significantly with an increase in humidity. This was attributed to the phenomenon of stress-corrosion cracking associated with the reaction between Al2O3 and water and might have a significant implication for the design of these tailored interfaces.