Flexible Osmotic Energy Batteries Enabled by Stacked Bicontinuous‐Network Hydrogels

Reverse dialysis based on hydrogel membranes holds promise for the development of soft electrochemical batteries. However, the energy conversion efficiency is often constrained by excessive swelling, which dilates nanochannels and degrades permselectivity. Here, we present a bicontinuous‐network hydrogel (BCNH) engineered by precisely modulating the hydrophilic and hydrophobic phases to achieve high‐performance osmotic energy conversion. Benefiting from the BCN structure, the hydrophilic ion‐conducting pathways are spatially confined by a percolating hydrophobic matrix, which dramatically suppresses swelling. This structural restraint preserves high permselectivity and enhances mechanical robustness. The resulting BCNH membrane, which simultaneously offers high permselectivity and rapid ionic flux, delivers an outstanding osmotic power density of 21.07 W·m −2 , significantly outperforming conventional homogeneous hydrogels. By integrating cation‐selective and anion‐selective BCNHs into flexible full cells, we achieve a high‐power density of 10.07 W·m −2 , enabling the scalable fabrication of highly flexible battery arrays. Combining integrated high selectivity, ultralow swelling, and robust mechanical properties, the BCNH platform establishes a transformative material foundation for advanced flexible electronics and sustainable energy conversion technologies.