Fiber-shaped aqueous battery: Design, advancements, and perspectives

To meet the demand for energy storage devices with high safety, excellent flexibility, and environmental compatibility in wearable electronic devices, fiber-shaped aqueous batteries (FABs) have become a key research direction in the field of flexible energy storage. This paper systematically reviews the latest research progress of FABs. Firstly, it elaborates on their core working mechanisms, including the intercalation mechanism involving reversible insertion/extraction of charge carriers, the conversion mechanism characterized by changes in the oxidation state and phase of electrode materials and the deposition/dissolution mechanism of metal ions. Subsequently, it summarizes the design principles from three dimensions: electrode fabrication (surface coating, in-situ growth, thermal drawing, solution spinning), device architectures (parallel, twisted, coaxial, crossing), and performance evaluation metrics (energy density, specific capacity, long-term cycling stability, flexibility). Additionally, the paper combs the research breakthroughs of FABs based on Li+/Na+, multivalent ions (Zn2+/Mg2+/Ca2+/Al3+), NH4+, and alkaline systems, and introduces their applications in energy storage-photoelectric response integration, energy storage-sensing integration, and multi-device power supply. Finally, it points out the challenges, such as low utilization efficiency of electrode materials and poor interface stability, and looks forward to the development directions including intelligent materials, manufacturing technologies, and standardization construction, which provides references for the industrialization of FABs and the development of next-generation flexible energy storage technologies.