Summary
The next generation of IoT, IoMT, and wearable bioelectronics demands the development of a novel form of thin‐film and flexible energy storage devices that offer high energy and power densities, mechanical reliability, and biocompatibility. Hydrogels are a class of materials that can be engineered with a range of desired properties, including stretchability, ionic conductivity, biocompatibility, adhesiveness, and mechanical match with organs, as they can be designed with Young's modulus in the range of the human skin. This review covers different types of hydrogels, including biopolymer hydrogels, carbon‐based hydrogels, and self‐healing hydrogels, and presents their use in the components of supercapacitors and batteries such as electrolyte; electrode, binder, separating membrane, and current collector. We also explain how these hydrogels contribute to improved properties of the energy storage devices and include cases in which the hydrogel is used for several functions in the same device. The contribution of hydrogels in the development of flexible energy storage devices and their impact on electrochemical performance are also discussed.