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The design of admirable hydrogel networks is of both practical and fundamental importance for diverse applications of hydrogels. Herein a general strategy of acid‐assisted training is designed to enable multiple improvements of conventional poly (sodium acrylate) networks for hydrogels. Hydrophobic homogeneous crosslinked poly (sodium acrylate) hydrogels are prepared to verify the strategy. The multiple improvements of poly (sodium acrylate) networks are simply achieved by immersing the hydrogel networks into 4 M H2SO4 solutions. The introduced acids would induce transformation of poly (sodium acrylate) into poly (acrylic acid) at hydrogel surface, which constructs dynamic hydrogen bonding interactions to tighten the network. The acid‐containing poly (sodium acrylate) hydrogels newly generate anti‐swelling and self‐healing performance, and show mechanical improvement. The internal poly (sodium acrylate) of the pristine acid‐containing hydrogels is further fully transformed via acid‐infiltration after following cyclic stretch/release training to significantly improve the mechanical performance. The Young's modulus, stress, and toughness of the fully‐trained hydrogels are 187.6 times, 35.6 times, and 5.4 times enhanced, respectively. The polymeric networks retain isotropic in fully‐trained hydrogels to ensure superior stretchability of 8.6. The acid‐assisted training performance of the hydrogels can be reversibly recovered by NaOH neutralization. The acid‐assisted training strategy here is general for poly (sodium acrylate) hydrogels. [ABSTRACT FROM AUTHOR]

[Display omitted] • High-alkali hydrogels are constructed from homogenous crosslinked poly (sodium acrylate). • The polymer network endows soft deformability, robust toughness and high-alkali tolerance. • The high-alkali hydrogels show desirable ion conductivity and freezing resistance for ZABs. • The derived ZABs possess satisfactory power density as flexible energy devices. • The work gives a new strategy to fabricate high-alkali hydrogels tailored for flexible ZAB. Developing hydrogel electrolytes with excellent deformability and desirable conductivity is of paramount importance in improving flexible solid-state aqueous energy devices. Herein high-alkali contained poly (sodium acrylate) hydrogel electrolytes with high conductivities, soft deformability, and considerable freezing resistance are designed and developed for flexible Zn-air batteries. The electrolytes are simply prepared by swelling a high content of 5 M KOH solutions within a homogenous crosslinked poly (sodium acrylate) network. The homogenous crosslinked networks in the electrolytes ensure robust fracture toughness (600 J m−2) during diverse deformation, while the high content of KOH solutions (80 wt%) enable soft feature of low Young's modulus (1.4 kPa), desirable ion conductivity (246 mS cm−1), and anti-freezing performance (<-30 °C) for the electrolytes. Based on these, the derived Zn-air batteries show satisfactory energy density (0.1 W cm−2), multiple flexibility, and wide operating temperatures (−30 °C to r.t.), which are practically applied as flexible energy-consuming devices in different situations. The work here provides a promising approach to develop desirable hydrogel electrolytes for various alkaline energy devices. [ABSTRACT FROM AUTHOR]