Ionic transport kinetics and enhanced energy storage in the electrode/poly(N-vinyl imidazole) interface for micro-supercapacitors

Abstract

The detailed understanding and control of ionic transport pathways in the electrode/electrolyte interface is vital for realizing micro-scale energy storage devices and formulating adequate design principles. A planar device geometry with nanostructured thin solid polymer electrolyte (SPE) and potassium hydroxide (KOH) incorporated poly(N-vinyl imidazole) (PVI) is demonstrated for micro-supercapacitors (MSCs). The adsorption/desorption kinetics of ionic charges in the interfacial regime of ITO/PVI–KOH has been investigated for electrical double layer capacitance (EDLC) characteristics. A single-cell of ITO/PVI–KOH/ITO planar MSC shows the large variation in volumetric capacitance and capacitance retention characteristics when the thickness of PVI–KOH approaches the characteristic nanoscale. Moreover, ITO/PVI–KOH/ITO planar MSC consisting of five series-cells exhibits the maximum operating cell voltage of 5.0 V with maximum volumetric energy and power density of 0.056 mW h cm⁻³ and 6.89 mW cm⁻³, respectively. The electrochemical properties of planar MSC have been systematically studied so as to confirm how the anions and cations are separated at electrode/electrolyte interfaces by means of an electromotive force. Significantly, the hydrated PVI enables charge migration and separation of cations and anions at the electrode/electrolyte interfaces.