Stretchable hydrogel electrolyte films based on moisture Self-absorption for flexible Quasi-solid-state batteries

• The electrolyte film absorbed moisture from the air via the hygroscopic Li salt. • HEF with a lean water content (4.62%) exhibits ionic conductivity of 1.15 mS cm −1 . • HEF with stretchable ratio of > 300% was able to self-heal after a damage. • The OCV of the full cell is stabled after multiple stretching or cutting processes. Flexible rechargeable batteries are urgently needed because of the rapid development of wearable electronics. However, most lithium-ion batteries fail to meet safety and stretchability requirements, which are critical factors to the practical application of such devices. Herein, a freestanding, stretchable, and self-healing polymer film that acts as a hydrogel electrolyte is developed for the preparation of flexible rechargeable batteries. The electrolyte film exhibits a high ionic conductivity of 1.15 mS cm −1 at room temperature with a lean water content (4.62%). It also displays a wide electrochemical stability window of ∼ 2.2 V and a high stretchable ratio of > 300%. A stretchable full battery is then developed using the hydrogel electrolyte film. The full cell exhibits long cyclic stability with 73.2% capacity retention after 1,000 cycles at the current density of 1 A g −1 . Furthermore, the open circuit voltage of the full cell is maintained well when it is stretched by 50%–125% and even after cutting the cell. This study offers a strategy for designing high-performance hydrogel electrolytes, which have potential applications in wearable electronics.