Accordion Strain Accommodation Mechanism within the Epitaxially Constrained Electrode

The tremendous benefits of all-solid-state Li-ion batteries will only be reaped if the cycle-induced strain mismatch across the electrode/electrolyte interfaces can be managed at the atomic scale to ensure that structural coherency is maintained over the lifetime of the battery. We have discovered a unique strain accommodation mechanism within an epitaxially constrained high-performance bronze TiO₂ (TiO₂-B) electrode that relieves coherency stresses that arise upon Li insertion. In situ transmission electron microscopy observation reveals the formation of anatase shear bands within the TiO₂-B crystal that play the same role that interface dislocations do to relieve growth stresses. While first-principles calculations indicate that anatase is the favored crystal structure of TiO₂ in the lithiated state, its continued propagation is suppressed by the epitaxial constraints of the substrate. This discovery reveals an accordion-like mechanism relying on an otherwise undesirable structural transformation that can be exploited to manage the cyclic strain mismatch across the electrode/electrolyte interfaces that plague all solid-state batteries