Anions Regulation Engineering Enables a Highly Reversible and Dendrite‐Free Nickel‐Metal Anode with Ultrahigh Capacities

The development of safe and high‐energy metal anodes represents a crucial research direction. Here, the achievement of highly reversible, dendrite‐free transition metal anodes with ultrahigh capacities by regulating aqueous electrolytes is reported. Using nickel (Ni) as a model, theoretical and experimental evidence demonstrating the beneficial role of chloride ions in inhibiting and disrupting the nickel hydroxide passivation layer on the Ni electrode is provided. As a result, Ni anodes with an ultrahigh areal capacity of 1000 mAh cm−2 (volumetric capacity of ≈6000 mAh cm−3), and a Coulombic efficiency of 99.4% on a carbon substrate, surpassing the state‐of‐the‐art metal electrodes by approximately two orders of magnitude, are realized. Furthermore, as a proof‐of‐concept, a series of full cells based on the Ni anode is developed. The designed Ni–MnO2 full battery exhibits a long lifespan of 2000 cycles, while the Ni–PbO2 full battery achieves a high areal capacity of 200 mAh cm−2. The findings of this study are important for enlightening a new arena toward the advancement of dendrite‐free Ni‐metal anodes with ultrahigh capacities and long cycle life for various energy‐storage devices. Nickel as a transition metal has excellent electrochemical properties, which is expected to be one of the attractive metal anodes in aqueous batteries. In this work, nickel‐metal batteries by the design of an anion‐regulation electrolyte achieve reversible nickel plating/stripping with an ultrahigh capacity of 1000 mAh cm−2 and long cycle life of 15 000 times.