Flexible batteries have attracted more and more attentions as the key component for the flexible electronic devices. Recently, flexible lithium-ion batteries have been developed quickly and applied to roll-up displays, touch screens, wearable sensors and implantable medical devices. In this review, we mainly focus on recent research of flexible lithium-ion batteries, and summarize how to realize flexibility of each component of the lithium-ion batteries, including current collectors,electrode materials and solid electrolytes. In addition, the structural design strategies for the realization of stretchable character are introduced,which can be divided into Wave-Structural Configuration, Interconnect-Island Mesh Configuration, Textile Structural Configuration, Origami Design Configuration and Cable-Type Configuration according to the different structural features. In order to promote the flexibility of the batteries to a large extent, we propose that the flexible materials should combine with novel stretchable structures. At the same time,we make a brief overview on the latest development for other flexible battery systems, such as lithium-sulfur battery, fuel cell and solar cell. Finally, the existing issues of flexible lithium-ion batteries during their development processes, the forecast the prospects and challenges toward the practical applications of flexible lithium-ion batteries in electronic devices are summarized.

Contents
1 Introduction
2 Flexible lithium batteries
2.1 Collector
2.2 Electrode material
2.3 Flexible solid electrolyte
2.4 Design of stretchable structure
3 Other flexible battery systems
3.1 Li-S flexible batteries
3.2 Flexible system of solar cells and fuel cells
4 Prospect of flexible batteries