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The mechanical response of Al-substituted LLZO to compressive forces was measured using instrumented indentation testing. Large correlated variations in compressive strength are observed across microscale regions of the solid electrolyte. 

Abstract In situ tensile testing using transmission electron microscopy (TEM) is a powerful technique to probe structure‐property relationships of materials at the atomic scale. In this work, a facile tensile testing platform for in situ characterization of materials inside a transmission electron microscope is demonstrated. The platform consists of: 1) a commercially available, flexible, electron‐transparent substrate (e.g., TEM grid) integrated with a conventional tensile testing holder, and 2) a finite element simulation providing quantification of specimen‐applied strain. The flexible substrate (carbon support film of the TEM grid) mitigates strain concentrations usually found in free‐standing films and enables in situ straining experiments to be performed on materials that cannot undergo localized thinning or focused ion beam lift‐out. The finite element simulation enables direct correlation of holder displacement with sample strain, providing upper and lower bounds of expected strain across the substrate. The tensile testing platform is validated for three disparate material systems: sputtered gold‐palladium, few‐layer transferred tungsten disulfide, and electrodeposited lithium, by measuring lattice strain from experimentally recorded electron diffraction data. The results show good agreement between experiment and simulation, providing confidence in the ability to transfer strain from holder to sample and relate TEM crystal structural observations with material mechanical properties. 

While Li ion batteries are intended to be operated within a mild temperature window, their structural and chemical complexity could lead to unanticipated local electrochemical events that could cause extreme temperature spikes, which, in turn, could trigger more undesired and sophisticated reactions in the system. Visualizing and understanding the response of battery electrode materials to thermal abuse conditions could potentially offer a knowledge basis for the prevention and mitigation of the safety hazards. Here we show a comprehensive investigation of thermally driven chemomechanical interplay in a Li 0.5 Ni 0.6 Mn 0.2 Co 0.2 O 2 (charged NMC622) cathode material. We report that, at the early stage of the thermal abuse, oxygen release and internal Li migration occur concurrently, and are accompanied by mechanical disintegration at the mesoscale. At the later stage, Li protrusions are observed on the secondary particle surface due to the limited lithium solubility in non-layered lattices. The extraction of both oxygen and lithium from the host material at elevated temperature could influence the chemistry and safety at the cell level via rearrangement of the electron and ion diffusion pathways, reduction of the coulombic efficiency, and/or causing an internal short circuit that could provoke a thermal runaway.