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

Abstract

Zinc-air batteries (ZABs) using gel polymer electrolytes suffer from low energy efficiency and poor cyclability. This issue is not only associated with the air electrode, as early failure of the battery is often due to the Zn electrode. Here, the cycle life of ZABs using alkaline poly(acrylic acid) (PAA-KOH) as the electrolyte is shown to vary by changing its crosslinking density. For ZABs using hydrogel electrolytes, understanding the failure mechanism and optimization of the hydrogel composition are key to achieving better utilization of the Zn electrode and battery rechargeability. In addition, the effects of crosslinker concentration on rheological properties, sol-gel fraction, ionic conductivity, and water retention ability of the hydrogel are discussed. PAA-KOH gels with lower crosslinking concentrations are weaker, but they have higher conductivity and better water retention, whereas gels with higher crosslinking concentrations affect the diffusion of zincate ions and facilitate passivation of the Zn electrode, resulting in early failure of the battery.[a] T.

Compositional Effects of Gel Polymer Electrolyte and Battery Design for Zinc‐Air Batteries

“…The concentration of KPS was fixed at 1.5 mM, which is consistent with our previous studies. [36,38] Different concentrations of PAA were utilized, i. e., 0.25, 0.5, 1, 1.5 and 2 M, and the KOH concentration was increased accordingly to ensure there was at least 6 M KOH in the PAAÀ KOH network. The samples are denoted as PÀ K1, PÀ K2, PÀ K3, PÀ K4 and PÀ K5, respectively.…”

“…Previously, the authors found similar effects for PAA-based gels with varying concentrations of crosslinker. [38] Although ZnO decreases the conductivity of PAAÀ KOH gels, it can help to reduce water activity and Zn corrosion. [47][48][49] Having zincate ions readily available in the electrolyte can also benefit the charging process.…”

A Review of the Use of GPEs in Zinc-Based Batteries. A Step Closer to Wearable Electronic Gadgets and Smart Textiles

“…Hydrogel networks formed from poly-(acrylic acid) (PAA) have the ability to absorb many times their weight in water and are the basis of a class of materials called super absorbent [271] (PAM is also considered a superabsorbent). The degree of crosslinking in the polymer network structure is critical, as it will endows the hydrogel with specific mechanical strength, swelling ratio, and many other properties [163]. As polymeric host material, PAA is chemically and electrochemically stable under highly alkaline environments.…”

“…The conductivity of PAA-KOH remains stable at high temperatures (360 mScm -1 at 65 • C) because of its high water retention. In battery testing, ZABs with PAA-KOH electrolytes have the potential to outperform batteries with conventional aqueous electrolytes (e.g., 6 M KOH) by reducing interfacial and charge transfer resistance [163]. PAA undergoes a reversible conformational transition (coil-to-globule transition) around pH 5 that is driven by the state of ionization of the carboxylic group.…”

Enhanced Cycling Performance of Rechargeable Zinc–Air Flow Batteries Using Potassium Persulfate as Electrolyte Additive

“…Recently, attempts have been made to modify alkaline electrolytes to enhance the performance of ZABs. Many approaches have been proposed, focusing on the use of inorganic additives, organic solvents (such as surfactants) and polymer gels [ 5 , 17 , 24 , 25 ].…”