Colloquium
Department of Physics, NCU
In situ/operando synchrotron-based X-ray studies on batteries and hybrid capacitors
Prof. Han-Yi Chen (陳翰儀)
Department of Materials Science and Engineering, NTHU
Date 2020.12.01 (Tue)
Place S4-625
Time 14:00-16:00
Abstract
Energy storage technology is the key challenge for power generation and renewable energy sources transporting. Various types of energy storage systems have been developed to store renewable energies. Electrochemical energy storage devices, such as batteries and supercapacitors, have been developed tremendously because of their potential applications such as portable electronics, electro mobility, and large-scale stationary energy storage. Lithium ion batteries (LIBs) which possess high energy density have been widely utilized in portable electronic devices, and they are also a promising energy storage system for electric vehicles recently. Here we synthesized various advanced metal oxides such as polyoxometalates (POMs) and high-entropy oxides (HEOs) and evaluate their electrochemical performance in LIBs. They exhibit different behaviors from the traditional binary or ternary metal oxides. POMs are transition metal oxide clusters which can provide multiple redox reactions during charging/discharging processes. HEOs are a new class of metal oxides which consist of at least five cations in the crystal structure and exhibits high entropy of the system. High capacity (> 1000 mA h g−1) and well cycling stability (without significant capacity fading up to 100 cycles) can be obtained with those metal oxide electrodes. To understand the charge storage mechanism of those advanced metal oxides, several in operando synchrotron X-ray techniques including X-ray diffraction, X-ray absorption spectroscopy, as well as transmission X-ray microscopy were conducted.
Recently, due to the increasing demands of wearable electronic devices, it is requisite to investigate flexible and highly safe energy storage devices. The commonly used energy storage devices such as lithium ion batteries and supercapacitors with organic electrolytes may suffer from explosion and inflammation issues. Therefore, zinc-ion hybrid capacitor (ZICs) with nontoxic and nonflammable aqueous electrolyte have attracted much attention recently. In this study, nanoporous-core-shell-structured multiwalled carbon nanotube@graphene oxide nanoribbons (NP-MWCNT@GONR) with high surface area is utilized as cathode material in aqueous ZICs for the first time. This ZIC device exhibits high energy density of 90 Wh kg−1 at 95 W kg−1 and high power density of 19 kW kg−1 at 31 Wh kg−1. The cycling retention is 86.5% after 200 cycles, but the battery is failed after 200 cycles due to the zinc dendrite formation on anode. To suppress the dendrite formation, freeze-dried gel electrolyte is applied, and the cycle life can be extended to more than 2000 cycles. In situ synchrotron transmission X-ray microscope is performed during the charging and discharging processes, and it demonstrates that the gel electrolyte can restrain the formation of dendrites effectively. Our work reveals that ZICs with NP-MWCNT@GONR cathode and gel electrolyte are highly safe energy storage device for the flexible wearable devices.