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7 3 I H I G H L I G H T S 2 0 2 57 2 H I G H L I G H T S 2 0 2 5 I

PRINCIPAL PUBLICATION

Quantifying Heterogeneous Degradation Pathways and Deformation Fields in Solid-State Batteries, J. Hu et al., Adv. Energy Mater. 15, 15 (2025); https:/doi.org/10.1002/aenm.202404231

REFERENCES

[1] P.P. Paul et al., Energy Storage Mater. 45, 969-1001 (2022). [2] J. Janek et al., Nat. Energy 8, 230-240 (2023).

The experiment

Two cylindrical, symmetric battery cells (Li|Li6PS5Cl|Li) were used for this study. One cell was scanned in the pristine, as-assembled state, while the second cell was cycled to failure. X-ray microtomography was used to image the crack network developed in the battery after cycling, while XRD-CT at beamline ID15A generated microscale 3D maps of chemical phases and internal stresses in the cell (Figure 57).

Globally, degradation near the lithium interface was found to be substantially greater than within the bulk of the solid electrolyte, producing elevated stresses of up to an order of magnitude higher than the bulk yield stress of lithium. Locally, cracks (Figure 58a) and corresponding stress hotspots (Figure 58b) were also observed throughout the solid electrolyte volume. An interplay among electrolyte processing, cell fabrication, and electrochemical cell cycling was found to generate significant stress concentrations

around certain cracks, enabling identification of those most influential in driving cell failure (Figure 58c). In the terminal crack responsible for the cell short- circuiting, local stresses far exceeded the lithium yield stress, indicating plastic deformation of lithium into crack regions prior to failure. These mechanical, electrochemical, and chemical degradation pathways – and the resulting stress and strain fields – were quantified using an in situ multimodal approach, which systematically isolated the effects of processing, assembly, and cycling on degradation behaviour.

The resulting 3D stress maps provide a valuable experimental basis for validating and refining computational models of degradation mechanisms and stress mitigation strategies in solid-state batteries and related electrochemical systems. Applying these methods under operando conditions will require a careful optimisation of the cell design, in terms of air exposure, size, chemistry, microstructure, and macroscopic stresses.

Fig. 58: Local degradation features in the battery. a) Cross-sectional microtomography of the region near the lithium metal–solid electrolyte interface reveals a complex network of cracks. b) The corresponding stress field (in MPa) highlights

regions of concentrated stress. c) Phase maps of the solid electrolyte (SE), Li2CO3 (formed upon air exposure), and Li2S (a precursor material used to fabricate the SE) illustrate the spatial distribution of chemical heterogeneities. The terminal

crack, which causes cell short circuiting, exemplified the contribution of multiple degradation pathways arising from cycling (lithium induced cracks), cell assembly (air exposure), or cell fabrication (unreacted precursor). These observations

underscore the complex nature and intricate interplay of chemical, mechanical, and electrochemical degradation mechanisms, emphasising the need for multimodal characterisation approaches.