Mechanically Driven Li Dendrite Penetration: A New Perspective on Resolving the “Soft‐Penetrates‐Hard” Paradox

Replacing flammable liquid electrolytes and graphite anodes with solid electrolytes and lithium metal, all-solid-state lithium metal batteries offer a compelling solution for next-generation energy storage [1,2].However, soft lithium dendrites can penetrate hard ceramic electrolytes (such as garnet-type LLZTO), causing short circuits-a "soft-penetrates-hard" paradox that has long puzzled the academic community [3,4].Regarding the mechanism, two main hypotheses exist: "mechanical fracture" and "electron-leakage-induced front nucleation," but direct nanoscale evidence at the dendrite tip has been lacking [5,6].Recently, Zhang et al. [7] employed cryogenic transmission Kikuchi diffraction (cryo-TKD-SEM) and phase-field fracture modeling to demonstrate that the driving force for Li dendrite penetration is not plastic flow but a nearly plasticity-free high hydrostatic stress, overturning traditional understanding and providing a new strategy for dendrite deflection through defect engineering.To lock in direct evidence of the penetration mechanism, the authors designed an in-plane cell geometry (Figure 1A), thinning the LLZTO electrolyte to about 150 μm, thus enabling precise localization of a single straight through-thickness dendrite tip and providing an ideal platform for nanoscale characterization.Based on this design, EBSD analysis (Figure 1B) captured, for the first time, both intergranular and transgranular fracture modes, with a transgranular proportion of about 20%, directly refuting the hypothesis that "Li nucleates only at grain boundaries" and indicating that dendrite penetration is not exclusively along grain boundaries.