Reversible Copper Cathode for Nonaqueous Dual‐Ion Batteries

Most reported cathodes of nonaqueous dual‐ion batteries (DIBs) host anions via insertion reactions. It is necessary to explore new cathode chemistry to increase the battery energy density. To date, transition metals have yet to be investigated for nonaqueous DIBs, albeit they may offer high capacity in anodic conversion reactions. Here, we report that bulk copper powder exhibits a high reversible capacity of 762 mAh g−1 at 3.2 V vs. Li+/Li and relatively stable cycling in common organic electrolytes. The operation of the copper electrode is coupled with the transfer of anion charge carriers. An anion exchange membrane separator is employed to prevent Cu2+ from crossing from the catholyte to the anode side. We designed an unbalanced electrolyte with a more concentrated anolyte than a catholyte. This addresses the concentration overpotential ensued during charge and facilitates the high specific capacity and enhanced reversibility. This finding provides a promising direction for high‐energy DIBs. This work reports that copper metal can work as a cathode of dual‐ion batteries in non‐aqueous electrolyte. The reversible conversion between commercial bulk copper metal and copper salt Cu(TFSI)2 demonstrates high capacity, relatively high voltage, and relatively stable cycle life in lithium dual‐ion batteries. This finding may offer a promising direction for enhancing the energy density of dual‐ion batteries.