The low specific capacity and low voltage plateau are significant challenges in the advancement of practical magnesium ion batteries (MIBs). Here, a superior aqueous electrolyte combining with a copper foam interlayer between anode and separator is proposed to address these drawbacks. Notably, with the dynamic redox of copper ions, the weakened solvation of Mg2+ cations in the electrolyte and the enhanced electronic conductivity of anode, which may offer effective capacity-compensation to the 3,4,9,10-perylenetetracarboxylic diimide (PTCDI)-Mg conversion reactions during the long-term cycles. As a result, the unique MIBs using expanded graphite cathode coupled with PTCDI anode demonstrate exceptional performance with an ultra-high capacity (205 mAh g-1 , 243 Wh kg-1 at 5 A g-1 ) as well as excellent cycling stability after 600 cycles and rate capability (138 mAh g-1 , 81 Wh kg-1 at 10 A g-1 ).
Keywords: aqueous electrolytes; capacity-compensation; copper; high energy density; magnesium ion batteries.
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