Iron Gallium Oxide with High-Capacity and Super-Rate Performance as New Anode Materials for Li-Ion Capacitors

Abstract

Thanks to the combination of the advantages of batteries and supercapacitors, battery-supercapacitor hybrid devices (BSHD) with higher power densities than batteries and higher energy densities than supercapacitors have aroused extensive concerns. Through the reasonable design of the capacity and kinetic characteristics of the cathode and anode, BSHD can provide individual advantages such as excellent properties, low cost, and safety. Li-ion BSHD has been widely studied because of lithium’s low potential and small ionic radius. However, the anode with slow electrode process dynamics is a great challenge for developing high-performance Li-ion BSHD. Consequently, it is essential to develop an electrode material with better electrical conductivity and a faster electrochemical reaction process. Here, an inverse spinel oxide iron gallium oxide (FeGa₂O₄, FGO) is designed with Fe²⁺ occupying octahedral sites and Ga³⁺ occupying tetrahedral sites. FGO pure phase was successfully synthesized by controlling the calcination temperature and atmosphere, and the experimental results were verified by X-ray diffraction (XRD). Subsequently, the electrochemical test of the half-cell shows that the capacity is stable at 500 mAh g–¹ after 200 cycles at a current density of 0.1 A g–¹, showing that the electrode has extraordinary cycle stability. Meanwhile, the kinetics of the electrode process of the material was tested by pseudocapacitance calculations, electrochemical impedance spectra (EIS), and the galvanostatic intermittent titration technique (GITT). The results show that the material is suitable for Li-ion BSHD. The assembled Li-ion BSHD exhibits high energy density (up to 107.19 Wh kg–¹), high power density (up to 4126.01 W kg–¹), and long cycle life in a wide working voltage range (0.5–4.0 V). Therefore, this work has carried out a new research direction for Li-ion BSHD’s electrode materials with high performance.