LAUSR

DOI: 10.1002/admi.201800468 graphite anodes and lithium transition metal oxide cathodes have been commercialized and played indispensable role in our daily life. However, the electrochemical performance of these devices such as energy density, power density, and cycle life as well as safety is far from the satisfying growing demand from our society and new technology.[11] Thus, we have seen an increasing wave of interest in the rational design and synthesis of electrode materials that may offer superior energy density, power density, or long-term endurance and safety.[12–20] Graphene, a 2D single-atomic layer of carbon atoms with conjugated hexagonal lattice, has received enormous attention due to its huge surface area, excellent electrical conductivity, high thermal conductivity, robust mechanical strength, and exceptional electrochemical stability.[20–25] With unique physical and chemical properties, graphene is considered as an ideal electron conductor for electrochemical applications.[26–29] Thus, graphene-based composites have emerged as exciting electrode materials for various electrochemical energy storage devices, including supercapacitor, lithium-/sodium-ion battery, lithium–sulfur battery, and lithium–oxygen battery. However, with extended π electrons and strong π–π interaction, graphene tends to strongly couple with each other to form bulk aggregates, which could greatly reduce accessible surface and prevent the formation of uniform composites that are necessary for optimized electrochemical performance. 3D graphene (3DG) with highly continuous graphene network and hierarchically interconnected porosity can offer highly efficient electron and ion transport pathway, large accessible surface area, and robust mechanical strength to address those above drawbacks.[30–33] Moreover, most of 3DG–based composites could be mechanically pressed into freestanding film and directly used as conductive agent-free and binder-free electrodes, which makes them very promising as lightweight and flexible electrodes. Therefore, integration of electrochemically active components (ECACs) with 3DG to produce high-performance 3DG composite electrode materials has become a significant scientific focus in recent years. So far, 3DG composites with various architectures have been constructed by different strategies and used as electrode materials for various electrochemical energy storage devices.[34,35] The formation of 3DG composites involves the combination of graphene with other functional components and the construction of 3D porous structures. The exact methods can exert a great 3D graphene (3DG) composites have attracted significant interest for electrochemical energy storage applications, including supercapacitor, lithium-/ sodium-ion battery, lithium–sulfur battery, and lithium–oxygen battery. With an interpenetrating network structure of conductive skeleton of graphene and highly continuous porous channels, the 3DG composites can not only ensure efficient electron and ion transport, but also retain structural stability of electrode materials during the electrochemical reactions. Rapidly growing efforts are seen in the design and synthesis of various 3DG composites with novel structures for diverse electrochemical energy storage devices in recent years. To promote deeper understanding and inspire further development of this exciting class of materials, the recent progress on preparation strategies of 3DG composites with applications in electrochemical energy storage is reviewed. A particular emphasis is placed on the detailed physicochemical mechanisms about the synthesis and structural evolution of 3DG composites and their impact on the electrochemical performance. As a conclusion, a brief perspective on future opportunities and challenges is given.