Abstract: For energy storage technologies, secondary batteries have the merits of environmental friendliness, long cyclic life, high energy conversion efficiency and so on, which are considered to be hopeful large-scale energy storage technologies. Among them, rechargeable lithium-ion batteries (LIBs) have been commercialized and occupied an important position as secondary batteries due to their high energy density and long cyclic life. Nevertheless, the uneven distribution of lithium resources and a large number of continuous consumptions result in a price increase for lithium. So, it is very crucial to seek and develop alternative batteries with abundant reserves and low cost. As one of the best substitutes for widely commercialized LIBs, sodium-ion batteries (SIBs) display gorgeous application prospects. However, further improvements in SIB performance are still needed in the aspects of energy/power densities, fast-charging capability and cyclic stability. Electrode materials locate at a central position of SIBs. In addition to electrode materials, electrolytes, conductive agents, binders and separators are imperative for practical SIBs. In this review, the latest progress and challenges of applications of SIBs are reviewed. Firstly, the anode and cathode materials for SIBs are symmetrically summarized from aspects of the design strategies and synthesis, electrochemical active sites, surrounding environments of active sites, reaction mechanisms and characterization methods. Secondly, the influences of electrolytes, conductive agents, binders and separators on the electrochemical performance are elucidated. Finally, the technical challenges are summarized, and the possible future research directions for overcoming the challenges are proposed for developing high performance SIBs for practical applications.

Key words: Sodium-ion batteries, Design strategies and synthesis, Active sites, Reaction mechanism, Characterization methods