In recent years, scientists have explored various metals, such as sodium, potassium, zinc, aluminum, and magnesium, for metal-ion batteries to replace lithium from various applications. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Among different metal-ion batteries, rechargeable magnesium-ion batteries (MIBs) are expected to be a potential candidate for large-scale energy storage systems owing to the following excellent intrinsic advantages. 1) Magnesium has a lower electrode potential (-2.37 V versus SHE) than Zn and Al metals. 2) Magnesium is a light metal with a density of 1.74 g cm -3 and is abundantly present in the earth's crust (i.e., approximately 2.1%, which is 10 4 times that of lithium metal). 3) Two electrons can be provided during redox reactions, leading to a higher theoretical volumetric capacity of 3866 mAh cm -3 than that of lithium metal (2046 mAh cm -3 ). 4) A magnesium anode with higher stability than a lithium anode is significantly less susceptible to dendrite formation. Similar to other metal-ion batteries, the core components of MIBs are also anode, cathode and electrolyte. Commonly, the Mg 2+ ions are released from the anode and inserted into the cathode during the discharge process, and the process is reversed during the charging process. However, the electrochemical performance of magnesium is different from that of lithium. The passivation layer formed between magnesium and ordinary electrolyte prevents the diffusion of Mg 2+ ions and limits its reversible deposition from salt-containing aprotic electrolytes such as magnesium perchlorate, magnesium tetrafluoroborate, imide, carbonate, and nitrile. Hence, achieving reversible deposition/dissolution of Mg ions in the electrolyte is very important for MIBs.Because Mg is active in an aqueous solution and easily forms a passivation layer on the surface, researchers have explored different organic systems to realize electrodeposition. [27][28][29] The concept of rechargeable MIBs was first raised in 1990. Gregory et al. constructed Mg//1.0 M N-ethylaniline magnesium chloride, 0.20 M AlCl 3 , THF//Cu batteries, which demonstrated compatibility between Mg organoboranes electrolytes (Mg(BPh 2 Bu 2 ) 2 or Mg(BPhBu 3 ) 2 ) and Mg anodes. [30] Then, in 2000, Aurbach's group reported the first study on electrochemically deposited Mg metal. [31] Subsequently, the same research group prepared a high-voltage (>3 V) all-phenyl complex electrolyte as the product of the reaction between PhMgCl Rechargeable magnesium (Mg)-ion batteries have received growing attention as a next-generation battery system owing to their advantages of sufficient reserves, lower cost, better safety, and higher volumetric energy density than lithium-ion batteries. However, Mg as an anode can be easily passivated during charging/discharging by most common solvents, which are inconducive for magnesium deposition/stripping. Based on this, the development of Mg-ion solid-state electrolytes in the last decades led to the formulization of several concepts beyond prev...
