Flexible batteries have attracted great attention due to the growing need of power sources for flexible electronic products. At present, flexible lithium-ion battery dominates the consumer electronic markets, such as flexible displayers and wearable sensors, due to its high power and energy density. However, the limited lithium resourcesslow the sustainable development of batteries. Owing to abundant sodium resources and low cost, sodium-ion batteries have attracted more and more attention. Flexible sodium-ion batteries, which are expected to meet the future market demand, consist of electrode active materials, current collectors, electrolytes, and separators. The electrodes not only require high capa-city and electrical conductivity, but also need good mechanical flexibility to ensure that the flexible battery works properly under various deformations (bending, stretching, folding, etc.). Meanwhile, the flexible electrolytes and separators should maintain a stable interface with the electrodes while maintaining battery safety. However, these key materials are still imperfect which have hindered the development of flexible sodium-ion batteries. In addition, ordinary pouch-type flexible batteries cannot meet the miniaturization and wearability requirement of future electronic devices. Innovative and practical structural design and preparation techniques suitable for mass production are also in urgent need. Here, this review introduces the research efforts with respects to flexible sodium-ion battery, and provides elaborate descriptions about the electrode materials (including anode materials, cathode materials and conductive substrate), electrolytes, battery structure and preparation process. In addition, the existing problems of flexible sodium-ion batteries, such as high cost, poor safety, complicated preparation process and other issues, are critically discussed and analyzed. For further development, lower cost active materials and substrates of flexible sodium-ion batteries, as well as structural innovation are essential to solve the problems of flexible sodium-ion batteries. The combination of advanced materials and novel battery configuration will accelerate the practical application of flexible batteries and promote the prosperity of flexible electronic devices. © 2020, Materials Review Magazine. All right reserved.
