High-Energy Aqueous Magnesium Ion Batteries with Capacity-Compensation Evolved from Dynamic Copper Ion Redox

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)).