Zinc-air Flow Batteries Research Articles

Development of Stable Bifunctional Air Electrodes for Zinc-Air Flow Batteries

Bifunctional air electrodes for the application in zinc-air flow batteries were manufactured in a scalable manufacturing process using precious metal-free oxide catalysts. During repeated charge/discharge cycling at 50 mA cm-2 and with synthetic air supply stable performances over more than 450 h and 200 cycles were achieved. The energy efficiency was 49% at start and 45% after 200 cycles. In addition, the pulse charging method with 150 mA cm-2 pulses was successfully applied on air electrodes.

Development of Stable Bifunctional Air Electrodes for Zinc-Air Flow Batteries

The increasing installation capacities of renewable but fluctuating electricity generators such as wind and solar power systems have raised the need for energy storage with short response times. Out of the many different types of electrochemical energy storage systems, the stationary zinc-air flow battery is promising due to its use of the safe, abundant and inexpensive active storing metal zinc [1]. In this system the zinc is dissolved into the flowing alkaline electrolyte during discharge and can be stored as zincate ion outside the electrochemical cell (see schematic in left figure). It is redeposited during charging, whereby compact zinc morphologies are preferred in order to avoid internal short-circuiting and loss of active material [2]. As in other metal-air batteries, the reactions of the second electrode are the oxygen reduction reaction (ORR) during discharging using oxygen from the air and the oxygen evolution reaction (OER) during charging [1,3]. In practical applications, the recharge capability of the zinc-air cell is dependent on the compact zinc deposition and the mechanical and chemical long-term stability of the air electrode. Furthermore, the low cycling efficiencies of around 50% resulting from the slow ORR/OER reaction kinetics are challenging to overcome and rely on the activity of the chosen catalysts. In air electrodes non-precious metal oxides such as perovskites (e.g. La0.6Sr0.4Co0.2Fe0.8O3, LaNiO3) and spinels (e.g. NiCo2O4) can be utilized, due to their chemical stability in alkaline electrolyte [3,4]. Although many oxide catalysts exhibit bifunctional catalytic activity toward ORR and OER, they are often not equally active toward both reactions. Hence, a combination of two catalysts in one electrode is beneficial, as was investigated in this work. Furthermore, their implementation into a stable and porous electrode structure with balanced gas diffusivity and electrolyte wettability is important in order to obtain a high number of three-phase zones between gas, electrolyte and catalyst. This was achieved by selecting suitable additives such as carbon nanofibers and nickel powder for electrical conductivity and PTFE as hydrophobic binder material [4]. These materials need to be resistant toward the highly oxidative potentials of around 2 V vs. Zn/Zn2+ and the mechanical stress by the vigorous oxygen bubble formation during charging. In addition, nickel foam was found to be an applicable current collector material, which functions at the same time as mechanical backbone of the air electrode. In-house manufactured electrodes were electrochemically characterized in a half-cell set-up in 8 M KOH electrolyte with the addition of 0.5 M ZnO, whereby one air electrode was operated as working electrode and a second air electrode as counter electrode. They were referenced against zinc foil. Discharging was performed at a constant current density of 50 mA cm-2 for 1 h per cycle. Because of the beneficial effects for the deposition of compact zinc layers, charging was conducted with the pulse charging method by applying tripled current densities during a short pulse of 50 ms followed by a pause of 100 ms (24 000 pulses in 1 h). The long-term cycling experiments, as depicted in the right figure, were performed for several hundred hours until the lower cut-off potential of 0.8 V vs. Zn/Zn2+ was reached. Although a decrease of ORR discharge potential of 0.1 V down to 1.0 V was observed within the first 50 hours of cycling, the OER potentials during charging were stable throughout the measurement. All in all, constant long-term performances over the course of more than 200 cycles with maximum charge/discharge potential gaps (ΔV) of 1.03 V were achieved [4]. [1] J. Fu, Z.P. Cano, M.G. Park, A. Yu, M. Fowler, Z. Chen, Electrically Rechargeable Zinc-Air Batteries: Progress, Challenges, and Perspectives, Adv. Mater. (2016). [2] C. Zelger, J. Laumen, A. Laskos, B. Gollas, Rota-Hull Cell Study on Pulse Current Zinc Electrodeposition from Alkaline Electrolytes, Electrochim. Acta. 213 (2016) 208–216. [3] L. Jörissen, Bifunctional oxygen/air electrodes, J. Power Sources. 155 (2006) 23–32. [4] B. Pichler, S. Weinberger, L. Reščec, I. Grimmer, F. Gebetsroither, B. Bitschnau, V. Hacker, Long-term behavior of bifunctional air electrodes with high stability during pulse charging for zinc-air flow batteries (submitted). Figure 1

The Design and Investigation Zinc-Air Flow Battery with Automatic Control System

The zinc-air rechargeable battery are considered as promising candidate for application in electromobility and large-scale stationary energy storage due to its high energy density , inexpensive and safety. However, the traditional battery structure limits the capacity of zinc-air battery due to ZnO generated and slow down the electrochemical reaction after discharge. A zinc-air flow battery with automatic control system is designed and manufactured, in which the flowing KOH electrolyte carries the anode electrode - zinc powder. Experiments investigated that the zinc morphology changes during the charge and discharge.The results show that several factors affect the performance and life of the battery, include the KOH concentration ,viscosity of the fluid，depth of discharge and discharge current. Figure 1

Bifunctional electrode performance for zinc-air flow cells with pulse charging

Bifunctional air electrodes with tuned composition consisting of two precious metal-free oxide catalysts are manufactured for application in rechargeable zinc-air flow batteries and electrochemically tested via long-term pulse charge and discharge cycling experiments at 50mAcm−2 (mean). NiCo2O4 spinel, synthesized via direct impregnation on carbon nanofibers or nickel powder and characterized by energy dispersive X-ray spectroscopy and X-ray diffraction experiments, shows high activity toward oxygen evolution reaction with low charge potentials of < 2.0 V vs. Zn/Zn2+. La0.6Sr0.4Co0.2Fe0.8O3 perovskite exhibits bifunctional activity and outperforms the NiCo2O4 spinel in long-term stability tenfold. By combining the catalysts in one bi-catalyzed bifunctional air electrode, stable performances of more than 1000h and 450 cycles are achieved when supplied with oxygen and over 650h and 300 cycles when supplied with synthetic air. In addition, the pulse charging method, which is beneficial for compact zinc deposition, is successfully tested on air electrodes during long-term operation. The oxygen evolution potentials during pulse, i.e. at tripled charge current density of 150mAcm−2, are only 0.06–0.08V higher compared to constant charging current densities. Scanning electron microscopy confirms that mechanical degradation caused by bubble formation during oxygen evolution results in slowly decreasing discharge potentials.

A sensitivity analysis to determine technical and economic feasibility of energy storage systems implementation: A flow battery case study

An economical and technical feasibility method was developed to determine the best implementation opportunities for a novel energy storage system (ESS). The ESS considered is a Zinc-Air flow battery in which energy storage may be scaled independently of the power output, and it can provide continuous power output of 5 kW during 8 h. Although the application field is vast, we have chosen three applicable scenarios where the new technology can be used: mining deployment, telecommunication tower, and a remote island. All three cases differ in load variability and load size, and we also considered three locations with their specific solar and wind resource. Three different power sources were also considered for this study: Diesel generator (DG), solar photovoltaic (PV), and wind turbine (WT). The best business opportunity for the new technology implementation was found to be in the mining industry. Power delivery from the ESS replaces the operation of DG during low demand periods in the case of variable load, as opposed to constant load, where the DG is permanently running. Fuel consumption reductions up to 75% can be achieved if the ESS is combined with renewable sources. However, the novel system alone represents approximate savings up to 33% in fuel consumption, when added to a conventional power generation system (diesel generator). Furthermore, the presented method aims to identify the main factors that affect the implementation feasibility of the ESS, and to provide a general approach that can be extended to different storage capabilities and fields of application.

Development of an Advanced Zinc-Air Flow Battery

In recent years, zinc-air flow batteries have regained importance as promising energy storage system for mobile and stationary applications. This revived importance is driven by the increased demand of high-performance, efficient, safe and environmentally friendly energy storage solutions to meet the challenges of modern energy supply systems with high amounts of renewable energy. These energy storage systems need to address variable power, capacity and profitability requests. Zinc-air batteries with a specific energy density higher than lithium-ion and low cost, highly available, eco-friendly active materials are suitable to fulfill these requirements. The use of a flow battery type with zinc-particles suspended in alkaline solution (zinc-slurry) in addition with oxygen reduction electrodes developed for the chloralkali process allows the development of high-power zinc-air batteries. This setup also enables the independent scaling of capacity and power. The cooperative research project ZnMobil, supported by the Federal Ministry of Economic Affairs and Energy in Germany, combines the experience of industrial and academic partners (Covestro Deutschland AG; Grillo-Werke AG; VARTA Microbattery GmbH; Accurec Recycling GmbH; Technical University Freiberg, Gottfried Wilhelm Leibniz University Hannover; University of Duisburg-Essen; The fuel cell research center ZBT GmbH) to develop a low-cost zinc-air flow battery with high performance. Here we present the electrochemical performance of the new zinc-air flow battery with respect to different zinc-slurry compositions. The battery system consists of a 100 cm² copper plate as current collector for the zinc-suspension electrode and an oxygen reduction electrode with gas-diffusion layer (supplied by Covestro). The zinc-slurry contains zinc particles (supplied by Grillo) suspended in alkaline solution (30 wt-% KOH) and stabilized with polyacrylic acid. Current voltage curves and depth of discharge were measured as a function of slurry composition (e.g. zinc content, additives) and different flow velocities of the zinc slurry. Corresponding zinc-slurry conductivities were evaluated in a flow-through conductivity measurement setup. Depending on the selected parameters, it is possible to achieve discharge current densities higher than 4 kA/m².

The inhibition of the spongy electrocrystallization of zinc from doped flowing alkaline zincate solutions

Abstract The effects of the presence of additives like lead and tungstate ions in flowing alkaline zincate solutions on suppressing spongy zinc electrogrowth are examined. The results show that the two additives with optimal concentrations in flowing electrolytes can suppress spongy zinc initiation and propagation. And, the two additives can bring about more uniform and compact deposits and, thereby, reduce spongy zinc growth. The influence of lead and tungstate ions on the zinc deposition/dissolution is evaluated by cyclic voltammetry. It also shows that the addition of the two additives is largely a blocking action, and the co-deposition of lead and zinc ions may occur. The performance of the zinc-air flow battery with zinc regeneration electrolysis is determined. It shows that by the addition of 0.6 M Na 2 WO 4 or 10 −4 M to 10 −3 M lead, compact or mixed compact–spongy zinc deposits are created and the favorable charge/discharge performance of the battery is achieved with an energy efficiency of approximately 60%.