Poly(acrylic acid)-Based Composite Gel Polymer Electrolytes with High Mechanical Strength and Ionic Conductivity toward Flexible Zinc–Air Batteries with Long Cycling Lifetime

Abstract

The rapid development of portable, flexible, and wearable devices motivates the requirement for flexible zinc–air batteries (FZABs) not only to provide high energy density but also to have sufficient deformability for wearer comfort. The gel polymer electrolyte (GPE) serves as the core part of the FZABs, playing a key function in the battery’s practical output performance such as discharge voltage, energy density, and cycling life. Unfortunately, ascribed to its high water absorption, the GPE regularly shows comparatively poor mechanical strength, which is difficult to offer sufficient physical support between electrodes. Herein, we report an optimized poly(acrylic acid) (PAA)-based composite GPE with the aluminum oxide (Al2O3) filler and apply it for FZAB. The mechanical strength, electrolyte absorption capacity, electrolyte retention ability, and ionic conductivity of the PAA–Al2O3 gel polymers and corresponding GPEs were investigated. The results indicate that the above performances of polymers and corresponding GPEs depend to a considerable extent on the content of the addition of Al2O3 particles. When 20 wt.% Al2O3 is added to the PAA polymer, the obtained PAA–20 wt.% Al2O3 gel polymer exhibits improved mechanical strength. The corresponding PAA–20 wt.% Al2O3 GPE shows a high ionic conductivity of 186 mS cm–1 and pleasurable electrolyte retention capability. This optimized GPE enables the assembled FZAB to display a long cycling lifetime of 384 h, a large power density of 77.7 mW cm–2, and excellent discharge performance. Moreover, the integrated FZAB can power various electronic devices, demonstrating its outstanding practicability and extensibility as a flexible power source.

Flexible Gel Polymer Electrolytes Based on Carboxymethyl Cellulose Blended with Polyvinyl Alcohol or Polyacrylic Acid for Zinc‐Air Batteries

“…For PAA‐based gels, Zhu et al [16] . prepared a PAA‐KOH 6 M gel, reporting 0.288 S cm −1 and ≈10 kJ mol −1 as ionic conductivity and E a , respectively, very close to the present work, while in another work [25] a similar PAA‐KOH 6 M gel achieved 0.127–0.186 S cm −1 , lower than the CMC : PAA (1 : 2) ex‐situ developed in this work. Therefore, the E a achieved are lower than those in other recent works [45,46] and the partial substitution of PAA/PVA with CMC to increase the sustainability seems to not remarkably affect conductivity and E a .…”

“…One of the reasons to replace liquid electrolytes and separators in ZABs is because of the low stability and durability they offer once exposed to air. Liquid electrolytes in technologies open to air, such as ZABs, tend to evaporate causing a decrease in ionic conductivity during operation, [25] consequently, it is important to analyse electrolyte retention over time. To quantify this aspect, CMC:biopolymer (1 : 2) ex‐situ gels have been tested for liquid electrolyte retention for 50 h. CMC : PAA gel only loses 4.08 %, whereas CMC : PVA membranes 17.79 %, after this period of time.…”

“…For PAA, Kwon et al [17] . used a PAA in‐situ 6 M KOH gel achieving a very high 684 mAh g Zn −1 (≈84 % Zn extraction) at 5 mA cm −2 (but a very precious Pt−Ir catalyst was used), while Song et al [25] . used a similar PAA ex‐situ gel soaked in 6 M KOH (and 0.2 M of Zn acetate) in a cell discharged at 2 mA cm −2 achieving approx.…”

“…The final recipes developed in this work are optimized to obtain easy procedures and reproducible results and are reported in the supporting information. Moreover, the state of the art generally reports the use of more than 5 wt % of polymer for developing GPEs, as for example in, [17,24,25] whereas in this study 3-5 wt % of total mass of solid (polymers) was required, representing a further novelty of the developed approach. Thermal and chemical behavior of the blended GPEs are studied, together with physical KOH solution uptake and ionic conductivity.…”

Interface Engineering of Zinc Electrode for Rechargeable Alkaline Zinc‐Based Batteries

“…Among a variety of GPEs, PVA, polyacrylamide (PAM), and PAA-based hydrogels are widely employed homopolymers, which have been explored as the electrolyte component in alkaline zinc-based batteries. And the high ionic conductivities have been achieved by adding electrolyte additives (e.g., SiO 2 , [192] Al 2 O 3 [193] ) and tuning the ionic conductor (e.g., tetraethylammonium hydroxide (TEAOH) [194] ) or polymer host (e.g., designing porous structure). [195] For example, Zhi and coworkers [196] fabricated a dual-network GPE with high stability to tolerate alkaline environment and exhibited a high ionic conductivity of 0.28 S cm −1 , which reaches the same-order magnitude with the value of KOH-based aqueous electrolytes.…”