A review on multi-scale structure engineering of carbon-based electrode materials towards dense energy storage for supercapacitors

Improving the volumetric energy density of supercapacitors is essential for practical applications, which highly relies on the dense storage of ions in carbon-based electrodes. The functional units of carbon-based electrode exhibit multi-scale structural characteristics including macroscopic electrode morphologies, mesoscopic microcrystals and pores, and microscopic defects and dopants in the carbon basal plane. Therefore, the ordered combination of multi-scale structures of carbon electrode is crucial for achieving dense energy storage and high volumetric performance by leveraging the functions of various scale structure. Considering that previous reviews have focused more on the discussion of specific scale structure of carbon electrodes, this review takes a multi-scale perspective in which recent progresses regarding the structure-performance relationship, underlying mechanism and directional design of carbon-based multi-scale structures including carbon morphology, pore structure, carbon basal plane micro-environment and electrode technology on dense energy storage and volumetric property of supercapacitors are systematically discussed. We analyzed in detail the effects of the morphology, pore, and micro-environment of carbon electrode materials on ion dense storage, summarized the specific effects of different scale structures on volumetric property and recent research progress, and proposed the mutual influence and trade-off relationship between various scale structures. In addition, the challenges and outlooks for improving the dense storage and volumetric performance of carbon-based supercapacitors are analyzed, which can provide feasible technical reference and guidance for the design and manufacture of dense carbon-based electrode materials.