Impact of Phase Transformation and Oxidation States on the Charge Storage Mechanism of Tin Oxide-Based Energy Storage Materials

Abstract

Tin oxide (SnO2) is a widely available metal oxide that holds promise for sustainable energy storage. The objective of this study is to investigate the charge storage capabilities of different SnO2 phases obtained under different annealing temperatures. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM) analyses revealed the formation of various phases of SnO2 (Sn3O2(OH)2, Sn0.75O(OH) and SnO2) at different annealing temperatures which directly impacts the charge transport properties of the material. It was found that the electrochemical performance of the samples is inversely correlated with crystallite size, wherein higher performance was obtained with smaller crystallite sizes. Furthermore, cyclic voltammetry (CV) analysis revealed that the samples exhibited a combination of surface capacitive and diffusion-controlled charge storage mechanisms, closely related to the oxidation state of tin and to its state of hydration with the relative contributions varying according to the specific phase of the material. The areal capacitance shows a maximum at 300˚C, when diffusion contribution and capacitive contribution are similar. Overall, the findings from this research provide significant insights into the charge storage mechanism and performance of SnO2 for energy storage applications.

Keywords: SnO2, Tin oxide, supercapacitors, Energy storage materials, Diffusion contribution, Capacitive contribution