Amorphous VO2: A Pseudocapacitive Platform for High‐Rate Symmetric Batteries

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Abstract
Among the various VO2 polymorphs, the layered compound, VO2(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+ insertion properties of amorphous VO2 (a‐VO2) are superior to those of crystalline VO2(B). Amorphous VO2 exhibits a linear voltage characteristic over a 3 V range (4.0 to 1.0 V vs Na/Na+) leading to a reversible capacity as high as 400 mAh g−1 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‐VO2 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.
Funding Information
  • Office of Naval Research (N00014‐19‐1‐2113)
  • Fudan University (JIH2203010, IDH2203008/003)

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