performance. Metallic lithium has a very high electronegativity while possessing the lowest density among all metals, leading to a theoretically high specific capacity (3861 mA h g -1 ) and thus has been considered to be the best candidate for a rechargeable battery anode. To achieve a high energy value, many efforts have been focused on increasing cathode capacity to couple with the metallic lithium anode, which results in the appearance of various concepts of prototype batteries, such as lithium-oxygen (Li-O 2 ) batteries, [4][5][6][7] lithium sulfur (Li-S) batteries, [8,9] aqueous rechargeable batteries (ARBs). [10][11][12][13] These batteries have demonstrated greater capacity than that of the current LIB. Although Li-O 2 and Li-S batteries have received wide attention due to their high energy density, there still exist some challenges for those batteries. In Li-O 2 batteries, the decomposition of organic electrolyte and corrosion of carbon materials, and the porous cathode blocking, causes capacity fading. [14][15][16][17][18] High internal resistance caused by the formation of polysulfide dissolution will decrease the capacity rapidly for Li-S batteries, [8,19,20] culminating in poor discharge efficiency and rechargeability for Li-O 2 and Li-S batteries. Among other energy storage devices, ARBs have attracted much attention due to their good safety, environmental issues, and low cost. Many types of ARBs have been explored recently, including aqueous alkali-ion batteries, aqueous metal-ion batteries, and aqueous nickel-metal hydride (NiMH) batteries. [11] While the performance of aqueous alkali-ion batteries and metal ion batteries is always restricted by the slow electrode kinetics relating to alkali ion intercalation/deintercalation from its host materials. NiMH batteries have the advantage of fast electrode kinetics reaction based on faradaic reactions, which involves one or multielectron reactions on electrode materials. The NiMH batteries mainly consist of the MH negative electrode, the Ni(OH) 2 positive electrode, and the aqueous alkaline electrolyte. Both cathode and anode materials can deliver a large mass capacity. However, the battery voltage is only 1.32 V due to the limitation of aqueous electrolytes. Therefore, it can only achieve an energy density of 60-100 W h kg -1 . [21] In order to realize high voltage for aqueous batteries, hydrogen evolution reaction at the anode side must be avoided. If the potential of the negative electrode can be lowered below the limitation of the hydrogen evolution reaction, metallic lithium would be used in the extreme case, then battery voltage over 3.0 V can be expected.In the present study, we develop a new type of high voltage, high specific energy density aqueous rechargeable Li-Ni 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 cat...
