Ultrasoft all-hydrogel aqueous lithium-ion battery with a coaxial fiber structure

Fiber batteries have been developed as ideal energy storage devices for wearable electronics due to their superior miniaturization, deformability, and flexibility compared with conventional bulk and thin-film batteries. However, currently reported fiber batteries use materials that are intrinsically rigid or have limited flexibility (e.g., metal, carbon materials, and elastomers), which potentially cause physical irritation and internal injury upon close contact with biological tissues. Therefore, it is necessary to design soft materials for ultrasoft fiber batteries that are mechanically matched with biological tissues. Here, ultrasoft coaxial fiber-structured aqueous lithium-ion batteries based on an all-hydrogel design are reported. The all-hydrogel fiber aqueous lithium-ion batteries exhibited a low Young's modulus of 445 kPa, which perfectly matched that of biological tissue. They also showed a high specific discharge capacity of 84.8 mAh·g−1 at a current density of 0.5 A·g−1 and superior performance in terms of cycling behavior and rate capacity. Furthermore, these fiber batteries maintained stable electrochemical performance while undergoing different complex deformations. The present work demonstrates a paradigm for designing ultrasoft fiber batteries and also provides insight into the development of soft wearable electronics. The first ultrasoft aqueous lithium-ion batteries with coaxial fiber structures were fabricated with an all-hydrogel design. The all-hydrogel fiber aqueous Li-ion battery exhibited a high specific discharge capacity of 84.8 mAh·g−1 and superior cycling behavior and rate capacity performance. A low Young's modulus (e.g., 445 kPa) for the battery was achieved by making it entirely from hydrogels, which ensured mechanical compatibility with biological tissues.