Flexible All‐in‐one Quasi‐Solid‐State Batteries Enabled by Low‐water‐content Hydrogel Films

Abstract The high conductivities and good mechanical properties of hydrogel electrolyte films are critical for energy storage devices with high flexibility, fast redox kinetics, and long life. Herein, a low water content (6.63 wt%) hydrogel film is prepared, and a favorable environment is created, with an electrochemical stability window of 2.26 V and a high ionic conductivity of 2.6 mS cm⁻¹. The hydrogel film exhibits good folding ability, low in‐plane swelling, and anti‐freezing abilities. These properties are benefitted by immobilizing free water molecules on the abundant oxygenic groups of polymer fibers in the hydrogel film, offering a unique 3D channel to allow Li⁺ to quickly transport along the polymer network. Therefore, the hydrogel film‐based all‐in‐one flexible cell exhibits stable cycling performance with a retention of 81.8% of the initial capacity after 500 cycles at room temperature and 66.2% of capacity retention at −30 °C. Furthermore, the full cell with high cathode loading (≈21 mg cm⁻²) exhibits a high areal capacity of 2.5 mAh cm⁻² (≈119 mAh g⁻¹). The overall merits of flexible all‐in‐one quasi‐solid‐state batteries demonstrate high potential to be used for power wearable electronics.