Progress in optimizing the application strategy of SEI membranes for HC sodium ion batteries

With the vigorous promotion of renewable energy and clean energy, the research of sodium-ion batteries (SIBs) in secondary batteries has been fully developed in recent years, in which the hard carbon (HC) material as the anode of SIBs stands out. HC as SIBs have received a lot of attention and postgraduate students because of its green, economic and easy to obtain, but at the same time along with the fatal problem of HC as SIBs is that the first coulombic efficiency is too low, thus affecting its capacity, which leads to a large part of the reason for the lower is the generation of the solid electrolyte interface membrane, referred to as the SEI membrane. Therefore, this paper focuses on the formation mechanism of SEI membrane and its influence and the various methods to improve SEI membrane in recent years with SEI membrane as the core, and discusses the reasons for the insufficient membrane formation of SEI membrane and its corresponding mechanistic explanation. The research done in recent years to break the SEI membrane is further elaborated in terms of the influence of electrolyte system, external factors (temperature, heating rate, precursor treatment, surface functionalization) and external modifications (surface coating, self-assembly technology), which provides effective ideas for better control of SEI membrane formation in the future. Furthermore, a brief overview is provided on the existing obstacles faced by HC as SIBs and the potential future prospects of HC for broader implementation in SIBs.