A concept for future energy storage is depicted in the schematic shown in Fig. 8. In the opinion of the authors, future energy storage systems will be hybrid devices combining the best features of metal-ion batteries and ECs. Such devices are based on hierarchical electrode architectures consisting of interconnected thin scaffolds of an active solid-electrode material containing designed micro/mesopores that provide a large surface area in contact with a liquid or gel electrolyte, enabling fast charge–discharge with minimal strain generation. Electrons should ideally be provided from a conductive scaffold forming the electrode backbone, thus all but eliminating current collectors. Utilization of multi-electron chemistries of both electrolyte and electrode materials will increase the amount of energy stored. The impact of these developments may start with portable electronics but will go well beyond, impacting large-scale EES by facilitating storage of electrical energy from renewable sources such as solar and wind.