Recent advances on pre-sodiation in sodium-ion capacitors: A mini review

Rechargeable sodium-based energy storage devices have attracted much attention in recent years due to high abundance and even global distribution of sodium resources. As a new member of the sodium-storage family, sodium-ion capacitors (SICs) are expected to supplement lithium-based energy storage devices because they combine advantages of both sodium-ion batteries and supercapacitors. However, the absence of a sodium source in electrode materials, the formation of a solid electrolyte interface (SEI) during the first cycle and the loss of sodium ions during long-term cycles will have a fatal impact on the performance of a typical SIC. It is currently recognized that the effective approach is to perform the pre-sodiation process. Although the research on pre-lithiation of lithium-ion capacitors (LICs) has been widely reported, the related research in SICs has not received sufficient attention. This work will systematically summarize the pre-sodiation methods of SICs, and further to give some in-depth insights to the future research of SICs towards practical applications.