Tough hydrogel diodes with tunable interfacial adhesion for safe and durable wearable batteries

Flexible Zn-based batteries with intrinsic safety, non-toxicity and biocompatibility are promising power sources for wearable electronics. To meet practical applications, they need to be durable, robust and stable. However, inevitable self-discharge and interface delamination between electrodes and hydrogel electrolytes often cause serious capacity fading or even failure for flexible Zn-based batteries. Here, inspired from nature, we report hydrogel diodes with strong and tunable interfacial adhesion by attaching oppositely charged hydrogels together. The high adhesion energy is stemmed from strong coulombic interaction and effectively dissipating energy of hydrogel matrix. The adhesion is facilely tuned by narrowing the depletion region in hydrogel diodes. Subsequently we design Hook& Loop-like Cu-Zn batteries by using hydrogel diodes as electrolytes, which are robust, stable and durable and capable for powering wearable electronics. The batteries can eliminate selfdischarge and maintain their capacity by splitted into two half cells during long-term storage and easily reattaching together at working stage. Further, the batteries are ultra-stable during 2000 stretching and bending cycles because of their robust interfacial adhesion. It is believed the hydrogel-electrolyte platforms can be utilized to harness issues including interface contact, stability, durability and safety for flexible power sources.