• 3D electrodes;
  • ion diffusion and electron transport length;
  • energy storage;
  • template-assisted synthesis;
  • template-free synthesis

Three-dimensional electrodes offer great advantages, such as enhanced ion and electron transport, increased material loading per unit substrate area, and improved mechanical stability upon repeated charge–discharge. The origin of these advantages is discussed and the criteria for ideal 3D electrode structure are outlined. One of the common features of ideal 3D electrodes is the use of a 3D carbon- or metal-based porous framework as the structural backbone and current collector. The synthesis methods of these 3D frameworks and their composites with redox-active materials are summarized, including transition metal oxides and conducting polymers. The structural characteristics and electrochemical performances are also reviewed. Synthesis of composite 3D electrodes is divided into two types — template-assisted and template-free methods — depending on whether a pre-made template is required. The advantages and drawbacks of both strategies are discussed.