Hierarchical Engineering for High-Energy-Oriented Sodium-Ion Batteries

Abstract

ConspectusSodium-ion batteries (SIBs) have obtained extensive attention as desirable candidates for smart grids and large-scale energy storage systems (ESSs) because they have the conspicuous advantages of resource abundance and competitive price. However, the biggish radius and heavier molar mass of Na+ and the lower negative redox potential of Na+/Na give rise to low volumetric/gravimetric energy densities, sluggish reaction dynamics, and an inferior life-span. It is therefore crucial to concentrate on the development of tailored electrode materials with robust architectures and expedited Na+ diffusion kinetics so as to take SIB energy systems one step closer to practical applications. Among multitudinous synthetic strategies, hierarchical engineering stands out because of its general applicability for the majority of electrode materials (intercalation/alloying/conversion electrodes) and the competence of structural variability (in macro/nano/atomic level) in response to the unique properties of different materials. The orderly combination of self-assembly, yolk–shell construction, nanotechnology, and precise atomic-level regulation contribute to an improved use of active material, high thermodynamic stability, promoted reaction dynamics, and superior electrochemical performances of hierarchical electrode materials. However, because of the high requirements for precise, controlled synthesis conditions, the poor controllability and reproducibility make it difficult to achieve large-scale preparation and applications. Although hierarchical engineering has been extensively employed in electrode synthesis, on the basis of our knowledge, there are scarcely any overviews relevant to this field. Hence, it is of great importance to review the relative results, provide in-depth insights into hierarchical engineering, and stimulate the further development of this emerging research topic.In this Account, we have summarized our recent research progress in detail to construct high-energy-oriented and high-durability electrodes via a hierarchical engineering methodology. Given the universality of hierarchical engineering for compositional and structural architectures, we have first proposed customized strategies to meet the demand of different materials. The main targets of discussion are flexible regulation methods including hierarchical composite with heterogeneous carbon matrixes, homogeneous materials with hierarchical secondary structures, and precise hierarchical ion doping in lattice structures. Second, we have investigated the correlation of hierarchical engineering on the structural stability and intrinsic activity of the electrodes, while simultaneously highlighting the relevant fundamentals and underlying construction–characteristic relationships behind the performance enhancement. Ultimately, the major challenges and the future perspectives of hierarchically engineered electrodes will be discussed. This Account is expected to offer a more comprehensive and systematic understanding of the modulation approaches and corresponding effectiveness for hierarchical engineering methodology to broaden the roadway for the practical application of SIBs.