A tri-electrode configuration for zinc-air batteries using gel polymer electrolytes

Poly(Vinyl Alcohol)/Poly(Acrylic Acid) Gel Polymer Electrolyte Modified with Multi-Walled Carbon Nanotubes and SiO2 Nanospheres to Increase Rechargeability of Zn-Air Batteries

Zn-air batteries (ZABs) are a promising technology; however, their commercialization is limited by challenges, including those occurring in the electrolyte, and thus, gel polymer electrolytes (GPEs) and hydrogels have emerged as substitutes for traditional aqueous electrolytes. In this work, PVA/PAA membranes were synthesized by the solvent casting method and soaked in 6 M KOH to act as GPEs. The thickness of the membrane was modified (50, 100, and 150 μm), and after determining the best thickness, the membrane was modified with synthesized SiO2 nanospheres and multi-walled carbon nanotubes (CNTs). SEM micrographs revealed that the CNTs displayed lengths of tens of micrometers, having a narrow diameter (95 ± 7 nm). In addition, SEM revealed that the SiO2 nanospheres had homogeneous shapes with sizes of 110 ± 10 nm. Physicochemical experiments revealed that SiO2 incorporation at 5 wt.% increased the water uptake of the PVA/PAA membrane from 465% to 525% and the ionic conductivity to 170 mS cm-1. The further addition of 0.5 wt.% CNTs did not impact the water uptake but it promoted a porous structure, increasing the power density and the stability, showing three-times-higher rechargeability than the ZAB operated with the PVA/PAA GPE.

Improving Cycle Life of Zinc-Air Batteries with Calcium Ion Additive in Electrolyte or Separator

The electrolyte carbonation and the resulting air electrode plugging are the primary factors limiting the cycle life of aqueous alkaline zinc-air batteries (ZABs). In this work, calcium ion (Ca²⁺) additives were introduced into the electrolyte and the separator to resolve the above issues. Galvanostatic charge-discharge cycle tests were carried out to verify the effect of Ca²⁺ on electrolyte carbonation. With the modified electrolyte and separator, the cycle life of ZABs was improved by 22.2% and 24.7%, respectively. Ca²⁺ was introduced into the ZAB system to preferentially react with CO₃^2- rather than K⁺ and then precipitated granular CaCO₃ prior to K₂CO₃, which was deposited on the surface of the Zn anode and air cathode to form a flower-like CaCO₃ layer, thereby prolonging its cycle life.

Strategy of Electrolyte Design: Triethanolamine as a Polydentate Ligand to Improve Solvation of Zinc in Zinc-Air Batteries

The zinc-air batteries (ZABs) are regarded as the most potential energy storage device for the next generation. However, the zinc anode passivation and hydrogen evolution reaction (HER) in alkaline electrolyte situations inhibit the zinc plate working efficiency, which needs to improve zinc solvation and better electrolyte strategy. In this work, we propose a design of new electrolyte by using a polydentate ligand to stabilize the zinc ion divorced from the zinc anode. The formation of the passivation film is suppressed greatly, compared to the traditional electrolyte. The characterization result presents that the quantity of the passivation film is reduced to nearly 33% of pure KOH result. Besides, triethanolamine (TEA) as an anionic surfactant inhibits the HER effect to improve the efficiency of the zinc anode. The discharging and recycling test indicates that the specific capacity of the battery with the effect of TEA is improved to nearly 85 mA h/cm² compared to 0.21 mA h/cm² in 0.5 mol/L KOH, which is 350 times the result of the blank group. The electrochemical analysis results also indicate that zinc anode self-corrosion is palliated. With density function theory, calculation results prove the new complex existence and structure in electrolytes by the data of the molecular orbital (highest occupied molecular orbital-lowest unoccupied molecular orbital). A new theory of multi-dentate ligand inhibiting passivation is elicited and provides a new direction for ZABs' electrolyte design.

Development of electrolytes for rechargeable zinc-air batteries: current progress, challenges, and future outlooks

This review presents the current developments of various electrolyte systems for secondary zinc air batteries (SZABs). The challenges and advancements in aqueous electrolytes (e.g., alkaline, acidic and neutral) and non-aqueous electrolytes (e.g., solid polymer electrolyte, ionic liquids, gel polymer electrolyte, and deep eutectic solvents) development have been reviewed. Moreover, chemical and physical characteristics of electrolytes such as power density, capacity, rate performance, cyclic ability, and safety that play a vital role in recital of the SZABs have been reviewed. Finally, the challenges and limitations that must be investigated and possible future research areas of SZABs electrolytes are discussed.