High-performance Mg–organic batteries based on hybrid MgCl2–LiCl/THF electrolytes

Rechargeable magnesium batteries (RMBs) are regarded as one of the promising candidates of next generation of battery technologies, but seriously hampered by the sluggish kinetics of Mg2+-related cathode reactions. A pertinent solution is adding Li salt into the electrolyte to build a hybrid Mg/Li battery (MLB), which combines the high safety of Mg anode and the fast reaction kinetics of Li+ with the cathode material. Herein, we propose a novel, simple, and cheap dual-salt electrolyte for MLBs, namely MgCl2–LiCl/THF, based on the exceptional synergetic effect between MgCl2 and LiCl in THF. The 1.0 M electrolyte demonstrated desired ionic conductivity (1.3 mS cm–1), good compatibility with Mg anode, and adequate oxidation potential (2.2 V vs. Mg) for typical organic cathode materials including poly(anthraquinonyl sulfide) (PAQS), poly(1,4-anthraquinone) (P14AQ), and dilithium salt of poly(2,5-dihydroxy-p-benzoquinonyl sulfide) (Li2PDHBQS). Unlike PAQS and P14AQ adopting MgCl+ as inserted cation, Li2PDHBQS selected Li+ to participate in the reaction. Therefore it demonstrated superior electrochemical performance to most of previously reported inorganic and organic cathode materials for MLBs, including a high reversible capacity (282 mAh g−1), a high rate capability (72% @ 2000 mA g−1), and a high cycling stability (70% @ 500th cycle). The combination of MgCl2–LiCl/THF electrolyte and Li2PDHBQS cathode provides not only a successful example of high-performing and affordable MLBs, but also insights of ionic species in the electrolytes and their interactions with organic cathode materials, which are very significant for the further development of RMBs.