Research advances of the electrolytes for rechargeable magnesium ion batteries

Magnesium ion batteries (MIBs) are gaining popularity as lithium ion batteries (LIBs) alternatives due to their non-negligible advantages of high energy density, abundance and low expenditure of Mg, as well as especially non-toxic safety and low risk of dendrite formation in anodes, which enables them to be more easily assembled in electric-power vehicles for the extensive utilization of civilian-military fields. Nevertheless, there are some intrinsic drawbacks including the formation of passivation film of Mg anode-electrolyte interface, narrow electrochemical window and sluggish Mg2+ diffusion kinetic, inevitably existing in the conventional MIBs systems. These factors not only cause the undesirable electronic and ionic conductivity but also disapprove the reversibility of Mg deposition/dissolution process, thus hindering their extended commercial applications. Correspondingly, there are some evidences disclosed that the preferential development of Mg2+ electrolytes is regarded as an effective strategy to response above-mentioned challenges. In this contribution, we systemically summarize several typical strategies to improve the performance of MIBs by analyzing studies related to Mg2+ electrolytes, mainly by enhancing the desolventization of Mg ions in the electrolyte. More specially, we present the challenges, developments and promising strategies adopted for the MIBs electrolytes. This review covers several electrolytes, including MACC, APC, Mg (TFSI)2, HMDS, polymer electrolytes, molten salt electrolytes and boron-based electrolytes. This allows researchers to understand the current issues faced and motivates them to make the most suitable electrolytes for commercial applications. Finally, the development status of electrolytes for MIBs is summarized and the future development trend of electrolyte system for MIBs is prospected.