Development of non-corrosive but highly efficient electrolytes has been long-standing challenges in magnesium rechargeable battery (MRB) research fields. The surface passivation film formed upon undesired reactions of magnesium metal with conventional electrolytes indeed inhibits efficient interfacial electrochemical reactions. In recent years, the new class of electrolyte materials has been reported, and these electrolytes especially incorporating the weakly coordinated anions (WCAs) have overcome some serious problems associated with conventional electrolytes. Among the reported WCA-based electrolytes, certain fluorinated alkoxyborate-based electrolytes, e.g. Mg[B(HFIP)_4]_2/glyme (HFIP = hexafluoroisopropoxy-group), are regarded as promising candidates for practical MRB materialization owing to the excellent electrochemical activity and synthetic accessibility. We herein report several critical issues associated with the use of Mg[B(HFIP)_4]_2/glyme electrolytes in MRBs. The electrolyte containing Mg[B(HFIP)_4]_2 prepared from Mg(BH_4)_2 requires several ten-cycles of pre-activation process. The reductive decomposition of glymes (not [B(HFIP)_4]~-) in the electrolyte solutions takes place upon just contacting the electrolytes with magnesium metal. Non dendritic short-circuit should also be solved for practical application.
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