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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.

Application‐oriented assembly of two‐dimensional nanosheets with uniform nanochannels is critical for fabricating sophisticated, high‐performance membranes for water treatment. However, fabricating the desired membranes by a simple, fast, and effective method is a challenge as most of the previous methods are based on batch processes rather than a continuous roll‐to‐roll process. Here, a simple Meyer rod‐coating approach to continuously fabricate large‐size and flat MXene membranes at a scale up to 5 m is introduced. This study demonstrated that a high MXene concentration, above 10 mg mL−1, is critical in processability due to the desired viscosity, surface tension, and viscoelastic properties. The as‐made MXene membranes show that shearing and solutal‐Marangoni flow can considerably improve the ordering of the stacked MXene nanoflakes. Thus, the rod‐coated MXene membranes demonstrate a smaller surface roughness and interlayer distance compared to the MXene membranes fabricated by the most commonly vacuum‐assisted filtration. The rod‐costed MXene membranes show superior performance in dye and mono/divalent cation separation. The proposed roll‐to‐roll Meyer rod‐coating method can also be used to fabricate MXene‐based composites, such as MXene/carbon nanotubes and MXene/polymer, using the inks containing high concentration MXene and other desired compositions. This roll‐to‐roll method will promote an industry‐level fabrication and application of MXene‐based membranes.