Flexible electrochemical energy storage: The role of composite materials

Flexible electrochemical energy storage (EES) devices such as lithium-ion batteries (LIBs) and supercapacitors (SCs) can be integrated into flexible electronics to provide power for portable and steady operations under continuous mechanical deformation. Ideally, flexible EES devices should simultaneously possess high flexibility, high energy density, and high power density, thus requiring appropriate electrode materials, electrolytes, and advanced structural designs of the electrodes. Generally, composite materials with specific components and unique structures have been widely investigated recently as flexible EES devices because these materials endow the devices with good bending, stretching, and compression capacity and are preferable to single-component materials. Thus, in this review work, we will give a detailed overview of the recent progress in composite electrode materials for flexible electrodes and composite electrolytes suitable for the development of flexible LIBs & SCs. We will special focus on the role of composite materials for applications in flexible EES devices of wearable electronics. We also give a brief introduction of structural designs to achieve flexibility and stretch-ablity in device/system levels. Finally, future perspectives and important research directions are highlighted and discussed.