Progress in electrolyte and interface of hard carbon and graphite anode for sodium-ion battery

It is essential to replace lithium-ion batteries (LIBs) from the perspective of the Earth's resources and the sustainable development of mankind. Sodium-ion batteries (SIBs) are important candidates due to their low price and abundant storage capacity. Hard carbon (HC) and graphite have important applications in anode materials of SIBs. In this review, the research progress in electrolyte and interface between HC and graphite anode for SIBs is summarized. The properties and performance of three types of widely used electrolytes (carbonate ester, ether, and ionic liquid) with additives, as well as the formation of solid electrolyte interface (SEI), which are crucial to the reversible capacity and rate capability of HC anodes, are also discussed. In this review, the co-intercalation performance and mechanism of solvation Na⁺ into graphite are summarized. Besides, the faced challenges and existing problems in this field are also succinctly highlighted.