Superbat: battery-like supercapacitor utilized by graphene foam and zinc oxide (ZnO) electrodes induced by structural defects.

Sibel Kasap,Ismet I Kaya,Sergej Repp,Emre Erdem

doi:10.1039/c9na00199a

Abstract

The current work presents a hybrid type of energy storage device composed of both graphene foam and zinc oxide electrodes, which exhibits both the electrochemical performance of a supercapacitor with a relatively higher power density, and a battery with a relatively higher energy density as compared to each individual component as single devices. Te hybrid's improved performance was correlated to the defective structure of the electrodes. To enhance the electrochemical performance of supercapacitors, it is necessary to have a well-defined mass, shape, and surface area of electrode materials. Here, we present an original design of a mounting device that enabled precisely determining all the critical parameters of electrode materials for a particular mass and surface area. With the aid of our original setup, we produced a supercapacitor device that could also act as a battery due to its high energy density values, hence we named it as superbat. In this work, 3D graphene foam was used as the first electrode due to its large surface, while for the second electrode, ZnO nanocrystals were used due its defective structure. Paramagnetic resonance Raman and impedance spectroscopy were performed in order to understand the origin of the performance of the hybrid capacitor in more depth. In particular, we obtained a high specific capacitance value (C = 448 F g−1), which was exceptionally related not only to the quality of the synthesis but also the choice of electrode and electrolyte materials. Moreover, each component used in the construction of the hybrid supercapacitor also played a key role in to achieving high capacitance value. The results demonstrated the remarkable performance and stability of the superbat.

Highlights

Exploring the properties of materials for battery and supercapacitor applications is one of the “dirtiest” kinds of research, because of their hazardous basic components, such as electrodes, electrolytes, and their solvents, separators, and current collectors and the need to go through the thousands of publications in the literature, which present an enormous number of electrochemical performance results
ZnO has paramagnetically active defect centers, namely singly ionized VO, VZn, Zn, and O interstitials. The assembly of such defects or defect complexes consisting of such paramagnetic active centers gives two distinct electron paramagnetic resonance (EPR) centers, as shown in Fig. 4(a) and (b), at g 1⁄4 1.962 and g 1⁄4 2.006 depending on their location inside the ZnO nanocrystal lattice
A special design called superbat was constructed and the role of defect structures in ZnO and graphene foam (GF) were investigated for the improvement of the electrochemical performance

Summary

Introduction

Exploring the properties of materials for battery and supercapacitor applications is one of the “dirtiest” kinds of research, because of their hazardous basic components, such as electrodes, electrolytes, and their solvents, separators, and current collectors and the need to go through the thousands of publications in the literature, which present an enormous number of electrochemical performance results. Electrode materials are o en used in supercapacitors or batteries with little or no investigation of their defect structures, which play a crucial role in their electronic, magnetic, optical, and mechanical behaviors, and in this context, their electrochemical performance.

Results

Conclusion