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

• Published in: Advanced materials (Weinheim) 2021-12, Vol.33 (49), p.e2103736-n/a
• Main Authors: Chao, Dongliang, DeBlock, Ryan, Lai, Chun‐Han, Wei, Qiulong, Dunn, Bruce, Fan, Hong Jin
• Format: Article
• Language: English
• Subjects: amorphous electrode; Amorphous materials; Charge reversal; Electric potential; Electrode materials; Electrodes; Energy storage; Insertion; Lithium-ion batteries; Materials science; Na‐ion battery; pseudocapacitive behavior; Rechargeable batteries; Sodium; symmetric battery; Transition metal oxides; vanadium dioxide; Vanadium oxides; Voltage
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202103736

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. A wide‐window pseudocapacitive behavior in amorphous VO2 is reported, which allows the construction of a new pseudocapacitive‐mechanism‐enabled symmetric battery to mitigate the slow kinetics and cycling limitations of previous phase‐transition‐mechanism‐based symmetric devices. Attractive safety superiority is illustrated in the new symmetric device, including high tolerance in overcharging, overdischarging, polarity reversal, and large‐current operation.