Amorphous VO<sub>2</sub> : A Pseudocapacitive Platform for High-Rate Symmetric Batteries.
basic_science · Level V
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- Record sourced from PubMed, PMID 34651351.
- Also identified by DOI 10.1002/adma.202103736.
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Abstract
Among the various VO<sub>2</sub> polymorphs, the layered compound, VO<sub>2</sub> (B), has been the most widely investigated lithium-ion battery electrode material. For sodium-ion electrodes, however, an amorphous solid may be more advantageous as a result of the open framework to facilitate ion insertion and the ability to tolerate volumetric changes. Herein, it is shown that the Na<sup>+</sup> insertion properties of amorphous VO<sub>2</sub> (a-VO<sub>2</sub> ) are superior to those of crystalline VO<sub>2</sub> (B). Amorphous VO<sub>2</sub> exhibits a linear voltage characteristic over a 3 V range (4.0 to 1.0 V vs Na/Na<sup>+</sup> ) leading to a reversible capacity as high as 400 mAh g<sup>-1</sup> and rapid redox kinetics, which is attributed to its pseudocapacitive nature. The linear voltage characteristic over 3 V affords the opportunity of fabricating a symmetric Na-ion battery in which the a-VO<sub>2</sub> material serves as both the positive electrode and the negative electrode. Such a symmetric battery offers safer operation in terms of overcharging, overdischarging, polarity reversal, high charge/discharge current abuse, and long-term usage. The results suggest that amorphous transition metal oxides may offer advantageous attributes for rapid, safe, and energy-dense storage.