This study investigates the significance of the mechanics of hybrid particle−polymer separators in the stabilization of lithium metal interfaces by probing these properties in realistic conditions informed by X-ray microcomputed tomography (micro-CT). Elastic properties and viscoelastic behavior of inorganic microparticle-filled poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) films are characterized using a nanoindentation experiment whose displacement simulates the interfacial response seen in operando micro-CT. It is determined that the dominating mechanical behavior in this hybrid separator relevant to lithium metal cell conditions is comprised of viscoelasticity. Consistent with this finding, along with correlations across other physicochemical properties, a mechanism describing the improvement of lithium metal cycling performance according to inorganic filler type and content is proposed.

In electrochemical-mechanical modeling of solid-state batteries, there is a lack of understanding of the mechanical parameters and mode of deformation of lithium metal. Understanding these characteristics is crucial for predicting the propagation of lithium dendrites through the electrolyte — a key element of battery safety. Past theories have assumed linear elastic as well as elastic-plastic deformation of lithium. However, recent experiments show that the primary mode of deformation is creep. This study replicates the temperature dependent mechanical experiments but inside an industrial dry room, where battery cells are manufactured at high volume. Furthermore, this work conducts time dependent studies — also inside the dry room — to gain insight of the large deformation theories of lithium metal. The results confirm the activation energy, which dictates the creep mechanism, is correlated to core diffusion rather than lattice diffusion.

Commercialization of energy-dense lithium metal batteries relies on stable and uniform plating and stripping on the lithium metal anode. In electrochemical-mechanical modeling of solid-state batteries, there is a lack of consideration of specific mechanical properties of battery-grade lithium metal. Defining these characteristics is crucial for understanding how lithium ions plate on the lithium metal anode, how plating and stripping affect deformation of the anode and its interfacing material, and whether dendrites are suppressed. Recent experiments show that the dominant mode of deformation of lithium metal is creep. This study measures the time and temperature dependent mechanics of two thicknesses of commercial lithium anodes inside an industrial dry room, where battery cells are manufactured at high volume. Furthermore, a directional study examines the anisotropic microstructure of 100 µm thick lithium anodes and its effect on bulk creep mechanics. It is shown that these lithium anodes undergo plastic creep as soon as a coin cell is manufactured at a pressure of 0.30 MPa, and achieving thinner lithium foils, a critical goal for solid-state lithium batteries, is correlated to anisotropy in both lithium's microstructure and mechanical properties.

This paper investigates a low-cost testing procedure that measures Poisson’s ratio of thin membranes whose properties may be affected by traditional speckle patterns which are solvent-based. The shear modulus, a key indicator of how materials will fail — especially for thin membranes subjected to interfacial stresses — is a function of Young’s modulus and Poisson’s ratio, which can be determined by tensile testing. The precision of using Digital Image Correlation (DIC) to measure Poisson’s ratio coupled with a solvent-free speckle pattern of fused silica on polyimide film specimen is investigated. DIC processes for thin membranes are currently under development. As such, spraying a conventional speckle pattern may be unfeasible for thin polymer membranes whose properties are a function of solvent content. Experimental factors’ effects, such as vibration and area to which DIC is applied, were also studied in a design of experiments. It was determined that using fused silica as a solvent-free speckle pattern, as opposed to a traditional solvent pattern, does not significantly affect the measurements of Poisson’s Ratio of the polyimide film. Furthermore, it was found that the experimental factors noted above can play a significant role in fused silica-speckled Poisson’s ratio specimen.