As the world transitions away from fossil fuels, energy storage, especially rechargeable batteries, could have a big role to play. Though rechargeable batteries have dramatically changed the energy landscape, their performance metrics still need to be further enhanced to keep pace with the changing consumer preferences along with the increasing demands from the market. For the most part, advances in battery technology rely on the continuing development of materials science, where the development of high-performance electrode materials helps to expand the world of battery innovation by pushing the limits of the performance of existing batteries. This is where vanadium-based compounds (V-compounds) with intriguing properties can ﬁt in; to ﬁll the gap of the current battery technologies.
The history of experimenting with V-compounds (i.e., vanadium oxides, vanadates, vanadium-based NASICON) in various battery systems, ranging from monovalent-ion to multivalent-ion batteries, stretches back decades. They are fascinating materials that display rich redox chemistry arising from multiple valency and coordination geometries. Over the years, researchers have made use of the inherent ability of vanadium that undergoes metamorphosis between diﬀerent coordination polyhedra accompanied by transitions in the oxidation state for reversible intercalation/insertion of more than one guest ions without breaking the structure apart. Such inﬁnitely variable properties endow them with a wide range of electronic and crystallographic structures. The former attribute varies from insulators to metallic conductors while the latter feature gives rise to layered structures or 3D open tunnel frameworks that allow facile movement of a wide range of metal cations and guest species along the gallery. Accompanied by growing stringent requirements for energy storage applications, most V-compounds face diﬃculty in resolving the problems of their own lack of competitiveness mostly due to their intrinsically low ionic/electronic conductivity. The key to producing vanadium-based electrodes with the desired performance characteristics is the ability to fabricate and optimize them consistently to realize certain speciﬁcations through eﬀective engineering strategies for property modulation.
In this Account, we aim to provide a comprehensive article that correlates the fundamental of charge storage mechanism to crystallographic forms and design principles for V-compounds. More importantly, the essential roles played by engineering strategies in the property modulation of V-compounds are pinpointed to further explain the rationale behind their anomalous behavior. Apart from that, we further summarize the key theoretical and experimental results of some representative examples for the tuning of properties. On the other hand, advances in characterization techniques are now suﬃciently mature that they can be relied upon to understand the reaction mechanism of V-compounds by tracing real-time transformation and structural changes at the atomic scale during their working state. The mechanistic insights covered in this Account could be used as a fundamental guidance for several key strategies in electrode materials design in terms of dimension, morphology, composition, and architecture that govern the rate and degree of chemical reaction.
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