Amorphous aluminum-oxide supercapacitors

¹ New Industry Creation Hatchery Center, Tohoku University - Sendai 980-8579, Japan
² Fracture and Reliability Research Institute, Graduate School of Engineering, Tohoku University Sendai 980-8579, Japan
³ Research and Analytical Center for Giant Molecules, Graduate School of Science, Tohoku University Sendai 980-8578, Japan
⁴ National Institute of Technology, Sendai College - Natori 981-1239, Japan

^(a) fukuhara@niche.tohoku.ac.jp

Received: 27 July 2018
Accepted: 4 September 2018

Abstract

An amorphous aluminium-oxide supercapacitor can store a large amount of electric charge on its blackish, uneven Al₂O_3−x surface, which has a convexity of 21 nm, AlO₆ clusters, and a resistivity of . The electric storage can be elucidated by extremely enhanced electron trapping resulting from both the quantum-size effect and the offset effect of the positive charges at O-vacancy sites. Here, a supercapacitor, characterised by a high surface area of and the formation of large numbers of electric double layers, demonstrates a vertical line in the Nyquist diagram, corresponding to rapidly increased imaginary impedance and phase angle of with decreasing frequency in the Bode diagram using a distributed constant-electric circuit with a parallel assembly of nanometer-sized capacitors on a highly insulating amorphous aluminium surface. The supercapacitor indicates a switching effect for both positive and negative potentials. Thus, we can apply rechargeable dry solid supercapacitors in place of practical Li ions.