Aqueous Batteries Based on Mixed Monovalence Metal Ions: A New Battery Family

As existing battery technologies struggle to meet the requirements for widespread use in the field of large-scale energy storage, new concepts are urgently needed to build batteries with high energy density, low cost, and good safety. Here, we demonstrate two new aqueous batteries based on two monovalence metal ions (Li+/K+ and Na+/K+) as charge-transfer ions, Ni1Zn1HCF/TiP2O7 and Ni1Zn1HCF/NaTi2(PO4)(3). These new batteries are unlike the conventional rocking-chair aqueous metal-ion batteries based on the migration of one type of shuttle ion between cathode and anode. They can deliver specific energy of 46 Whkg(-1) and 53 Whkg(-1) based on the total mass of active materials; this is superior to current aqueous battery systems based on sodium-ion and/or potassium-ion technologies. These two new batteries together with the previously developed Li+/Na+ mixed-ion battery not only constitute a new battery family for energy storage, but also greatly broaden our horizons for battery research.