High‐Performance Aqueous Rechargeable Li‐Ni Battery Based on Ni(OH)2/NiOOH Redox Couple with High Voltage

New energy storage and conversion systems require large‐scale, cost‐effective, good safety, high reliability, and high energy density. This study demonstrates a low‐cost and safe aqueous rechargeable lithium‐nickel (Li‐Ni) battery with solid state Ni(OH) 2 /NiOOH redox couple as cathode and hybrid electrolytes separated by a Li‐ion‐conductive solid electrolyte layer. The proposed aqueous rechargeable Li‐Ni battery exhibits an approximately open‐circuit potential of 3.5 V, outperforming the theoretic stable window of water 1.23 V, and its energy density can be 912.6 W h kg ‐1 , which is much higher than that of state‐of‐the‐art lithium ion batteries. The use of a solid‐state redox couple as cathode with a metallic lithium anode provides another postlithium chemistry for practical energy storage and conversion.