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

Abstract 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–MnO 2 full battery exhibits a long lifespan of 2000 cycles, while the Ni–PbO 2 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.