Stretchable Gas Barrier Films Using Liquid Metal toward a Highly Deformable Battery

Highly deformable batteries that are flexible and stretchable are important for the next-generation wearable devices. Several studies have focused on the stable operation and life span of batteries. On the other hand, there has been less focus on the packaging of highly deformable batteries. In wearable devices, solid-state or pouch lithium-ion batteries (LIBs) packaged in aluminum (Al)-laminated films, which protect against moisture and gas permeation, are used. Stretchable elastomer materials are used as the packaging films of highly deformable batteries; however, they are extremely permeable to gas and moisture. Therefore, a packaging film that provides high deformability along with gas and moisture barrier functionalities is required for the stable operation of highly deformable batteries used in ambient conditions. In this study, a stretchable packaging film with high gas barrier functionality is developed successfully by coating a thin layer of liquid metal onto a gold (Au)-deposited thermoplastic polyurethane film using the layer-by-layer method. The film exhibits excellent oxygen gas impermeability under mechanical strain and extremely low moisture permeability. It shows high impermeability along with high mechanical robustness. Using the proposed stretchable gas barrier film, a highly deformable LIB is assembled, which offers reliable operation in air. The operation of the highly deformable battery is analyzed by powering LEDs under mechanical deformations in ambient conditions. The proposed stretchable packaging film can potentially be used for the development of packaging films in advanced wearable electronic devices.