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Flexible zinc‐air batteries have received widespread attention due to their high specific energy and eco‐friendly environment. However, the water in the hydrogel is easily lost to the external environment because of the semi‐open structure zinc‐air batteries, leading to performance degradation of the batteries. Here a saline gel of NaCl‐KOH‐PAA (sodium chloride‐potassium hydroxide‐polyacrylic acid) without soaking in the alkaline solution before use is designed, refining the grid structure of the hydrogel and reducing water loss through NaCl doping. Meanwhile, the gel exhibits no significant decrease in ion conductivity before and after NaCl doping and can maintain stability of around 170 and 150 mS cm−1 at room temperature and −20 °C, respectively. The results demonstrate that the lifetime of flexible zinc‐air batteries with NaCl‐doped hydrogel can be extended by nearly 50%. The NaCl doping gel also displays superior flexibility under extreme physical deformation conditions. Moreover, the phenomenon of hydrogel delamination with NaCl doping is observed and the mechanism of gel water retention is uncovered. These findings will pave the way for developing flexible zinc‐air battery. [ABSTRACT FROM AUTHOR]

Flexible Al-air batteries are seen as the next generation of power devices for portable electronics due to the high capacity, low cost and environmental friendliness. However, the anodic parasitic reactions hinder their commercialization. Here, we develop a Zn2+@Agar hydrogel membrane for flexible Al-air battery, whose formed Zn-dominated interphase can inhibit hydrogen evolution and passivation of the Al anode, improving the discharge performance of the battery. The results show that the hydrogen evolution rate of Al anode is as low as 1.65 × 10−2 mg cm−2s−1 when 0.5 M Zn2+ are contained in the membrane, and the passivation layer of Al 2 O 3 is also broken by Zn-dominated interphase. Al-air battery with this membrane has a high capacity of 2592 mAh g−1, specific energy of 2847 mWh g−1 and anode utilization ratio of 86.98% at 10 mA cm−2 at 25 °C, and the battery has a high capacity of 2286 mAh g−1, specific energy of 2084 mWh g−1 and anode utilization ratio of 76.71% at 0 °C. Furthermore, the mechanism of interaction between single chain agar molecule and anode surface is revealed, which greatly promotes the commercial application for flexible Al-air batteries using Zn2+@Agar hydrogel membrane. [Display omitted] • A Zn2+@Agar hydrogel membrane is developed for flexible Al-air battery. • Zn-dominated interphase inhibits the parasitic reactions of Al anode. • The anode utilization ratio of Al-air battery can reach 86.98% at 10 mA cm−2 at 25 °C. • The capacity of Al-air battery is up to 2592 mAh g−1 at 10 mA cm−2 at 25 °C. • Al-air battery with Zn2+@Agar hydrogel membrane has good low-temperature adaptability. [ABSTRACT FROM AUTHOR]

Quasi-solid Al-air batteries with hydrogels are regarded as a promising power source because of their high specific capacity, small-scale bulk, high ionic conductivity and no leakage. However, increasing accumulations of byproducts on the interface between Al anode and solid-state electrolyte block discharging performance and lifespan of the batteries. Here, we firstly present a way of sodium lignosulphonate as a chelating agent for Al-air batteries, forming coordination compounds and decomposing discharging byproducts, where the coordination compounds can make aluminum ions transfer from anodic surface into the interior of hydrogel electrolyte. Compared to Al-air batteries without additive sodium lignosulphonate, the lifespan of the battery with sodium lignosulphonate can be prolonged by 124.6% at a current density of 1 mA cm−2. Additionally, the battery can output high power density of 46.3 mW cm−2 at 56 mA cm−2, and the maximum specific battery capacity of 2161.67 mA h g−1 is achieved at 20 mA cm−2. The use of coordination compounds to decompose and migrate discharging byproducts is not only available for Al-air batteries but for other metal batteries. • The coordination compounds of Al ion and sodium lignosulphonate can be formed. • The accumulated byproduct between Al anode and hydrogel can be transferred. • The lifespan of the batteries was improved using sodium lignosulphonate. [ABSTRACT FROM AUTHOR]