Amorphous aluminum-oxide supercapacitors

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 16.5 Gωcm. 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 ∼ 2,400m² 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 -90° 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 (∼ +66V)and negative (∼ -11V)potentials. Thus, we can apply rechargeable dry solid supercapacitors in place of practical Li ions.