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Sodium vanadate (Na1+xV3O8 or NVO) has recently attracted significant interest as a potential cathode material for an aqueous Zn ion battery for its unique pillared framework facilitating Zn ion migration. Here, we performed a detailed study on reaction mechanisms of hydrated Na2V6O16·2H2O slabs and nonhydrated Na1.25V3O8 nanorods using transmission electron microscopy. Our initial observation reveals that the thin (30–50 nm) Na2V6O16·2H2O system successfully undergoes discharge with Zn ion insertion into the structure while thick (120–170 nm) Na1.25V3O8 allows Zn ion insertion only at the surface, signifying the importance of both the presence of water and the nanostructure thickness in determining the reaction mechanism of NVO. More in-depth analysis of these two systems revealed the irreversible formation of the stable byproduct phase Zn3Nax(OH2)V2O7 (ZNVO), which likely evolved through a Zn-ion redox reaction, contributing to overall cell performance. Eventually, the entire discharge/charge process ap...

Vanadium dioxides exist as a variety of polymorphs, each with differing structural and electrochemical capabilities. The monoclinic to rutile transition is an interesting system for study as the transition temperature is easily accessible at moderate temperature and corresponds to an increase in electrical conductivity by 2 orders of magnitude. The transition from monoclinic to rutile is characterized structurally herein using synchrotron-based X-ray diffraction and related to lithium-ion electrochemistry using electrochemical impedance spectroscopy and intermittent pulsatile galvanostatic discharge tests. The experimental results indicate a decrease in ohmic resistance for lithium-based cells tested under higher temperatures. Complementary density functional theory calculations described the experimentally measured intercalation voltages and identified a possible Li-induced LixVO2(M) to LixVO2(R) phase transition during the discharging process rationalizing the favorable impact on the function of a lithi...