The impact of operating conditions on component and electrode development for zinc-air flow batteries

Abstract

Rechargeable zinc-air flow batteries are investigated as possible technology for fast responding large-scale electrical energy storage due to the use of inexpensive, non-toxic and abundant materials, and compact system design. The operating ranges for several parameters such as flow rate (2-8 cm s −1 ), concentration of electrolyte (6 or 8 M KOH), charge/discharge current densities (up to 100 mA cm −2 mean), and active or passive air supply as well as their influence on the performance and stability of the electrodes are investigated and compared. Bi-catalyzed bifunctional air electrodes are tested by means of half-cell measurements achieving minimum 200 charge/discharge cycles at 50 mA cm −2 with the longest operation time being 800 h. At this current density, charge/discharge efficiencies are in the range of 50% for all tested air electrodes. End-of-life characterization by means of scanning electron microscopy reveals mechanical degradation of the electrode material. On the negative zinc electrode, zinc deposition morphology on different current collector materials (nickel, brass, and steel) is investigated using Rota-Hull cylinders showing nickel to be the most suitable material. The pulse interrupt current method is thereby successfully applied for compact zinc deposition in a broad current density range without any electrolyte additive. Subsequent scale-up of the rechargeable zinc-air flow battery and unit cell operation is finally performed for proof-of-concept. Graphical AbstractKeywords Zinc-air flow battery · Bifunctional air electrode · Pulse interrupt currents · Compact zinc morphology · Flow operation

Discharge profile of a zinc-air flow battery at various electrolyte flow rates and discharge currents

“…It provides higher flexibility regarding energy and power decoupling 23 , and lower mechanical stress on the electrodes in comparison with other types of batteries, such as LIBs, leading to the fabrication of long-lasting systems 24 . As a result, the scale-up of flow batteries can be achieved in a cost-effective way for stationary large-scale applications 25 . A disadvantage is the reduced energy efficiency due to the required electrolyte movement 24 .…”

“…To prevent dendrite formation during the charging mode of ZAFBs, a trapezoidal structure or a permanent magnet parallel to an anode has been proposed 29 . Pichler et al 25 studied the effects of several parameters including flow rate, electrolyte concentration, and current density on the performance and stability of electrodes.…”

Long‐Term Operation of Perovskite‐Catalyzed Bifunctional Air Electrodes in Rechargeable Zinc‐Air Flow Batteries

“…Bifunctional air electrodes for ORR and OER were manufactured via an easily scalable (4–55 cm 2 ) manufacturing process, employing a La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 perovskite as catalyst in this work. However, the process can be readily adapted for implementation of other catalysts.…”

“…Thus, operation at increased current densities is possible . Obtaining compact zinc morphologies can further be enhanced by applying pulsating currents during charging . Nevertheless, reduced cycle life, either caused by air electrode degradation or by irreversible changes on the zinc electrode, especially in up‐scaled cells, is still a major hindrance for bringing the zinc‐air (flow) battery closer to application.…”

Effects of Crosslinker Concentration in Poly(Acrylic Acid)‐KOH Gel Electrolyte on Performance of Zinc‐Air Batteries

“…Considerable research has been done on bifunctional catalysts for the air electrode to lower the energy barrier for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in order to improve the energy efficiency of ZABs . Other engineering solutions including mechanically rechargeable ZABs and Zn‐air flow batteries, in which the electrolyte is circulated in the cell system, have also been proposed . These solutions may be effective for grid energy storage applications, but they add cost and complexity to the system.…”