Hierarchical 3D electrodes for electrochemical energy storage

The discovery and development of electrode materials promise superior energy or power density. However, good performance is typically achieved only in ultrathin electrodes with low mass loadings (<= 1 mg cm(-2)) and is difficult to realize in commercial electrodes with higher mass loadings (>10 mg cm(-2)). To realize the full potential of these electrode materials, new electrode architectures are required that can allow more efficient charge transport beyond the limits of traditional electrodes. In this Review, we summarize the design and synthesis of 3D electrodes to address charge transport limitations in thick electrodes. Specifically, we discuss the role of charge transport in electrochemical systems and focus on the design of 3D porous structures with a continuous conductive network for electron transport and a fully interconnected hierarchical porosity for ion transport. We also discuss the application of 3D porous architectures as conductive scaffolds for various electrode materials to enable composite electrodes with an unprecedented combination of energy and power densities and then conclude with a perspective on future opportunities and challenges.