In Situ Visualization of Structural Evolution and Fissure Breathing in (De)lithiated H₂V₃O₈ Nanorods

Layered H₂V₃O₈ material consisting of V₃O₈ layers features the elastic space for buffering volume change upon repeated ion (de)intercalations. However, its ion transport and phase transformations still remain largely unknown due to lack of direct evidence. Here we employ in situ transmission electron microscopy to revisit this material carefully. Upon lithiation, the localized phase transformation from H₂V₃O₈ to V₂O₃ via an intermediate VO₂ phase was observed, and large structural fissures gradually formed. Unexpectedly, the large fissures were able to self-heal during delithiation with the VO₂ phase as the delithiated product. The fissures could appear and disappear alternately upon subsequent (de)lithiation, in which a stable and reversible phase transformation between V₂O₃ and VO₂ phases was established. These unreported findings are expected to call for renewed attention to this electrode material for a more comprehensive understanding in rechargeable metal-ion batteries.