Interfacial Design and Assembly for Flexible Energy Electrodes with Highly Efficient Energy Harvesting, Conversion, and Storage

Charge transfer between a conductive support and active materials as well as between neighboring active materials is one of the most critical factors in determining the performance of various electrodes in energy harvesting, conversion, and/or storage. Particularly, when preparing energy electrodes using conductive and/or electrochemically active nanoparticles (NPs), the bulky organic materials (i.e., ligand or polymeric binder) covering the NP surface seriously limit the charge transfer within the electrode, thereby restricting the energy storage or conversion efficiency. Furthermore, the flexibility and mechanical stability of the electrode have been considered important evaluation indices for flexible/wearable energy applications. In this regard, considerable research has been directed toward controlling the interfacial structure to enhance the charge transfer efficiency and toward incorporating functional materials into flexible/porous supports. This review describes the central progress in flexible electrodes for energy harvesting, conversion, and storage, along with the challenges in designing high-performance energy electrodes. In particular, layer-by-layer (LbL) assembly is analyzed, which is an ultrathin film fabrication technology that enables fine tuning of the interfacial structure for various electrode materials. It is shown how LbL assembly can be effectively applied to energy electrodes to obtain desired functionalities and improve the charge transfer efficiency of electrodes.