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).