Cobalt metal enables ultrahigh-efficiency, long-life, and dendrite-free aqueous multivalent batteries†

Abstract

Aqueous multivalent metal batteries represent an attractive option for energy storage. Currently, various metals have been attempted for aqueous battery operation, ranging from divalent metals (zinc, iron, nickel, manganese) to trivalent ones (antimony, indium). However, the fundamental cobalt plating chemistry remains largely neglected and poorly understood, despite its appealing merits in capacity, redox potential, and morphology. Herein, we bridge this knowledge gap by revealing highly reversible Co²⁺/Co plating reaction in a near-neutral 1 M CoCl₂ aqueous electrolyte. Remarkably, cobalt demonstrates exceptional performance, characterized by modest polarization (48 mV), ultrahigh plating efficiency (∼99.9%), long lifespan (4000 hours, 5.5 months), and strong resistance to harsh conditions, including ultrahigh capacities (up to 30 mA h cm⁻²), ultralow currents (down to 0.05 mA cm⁻²), and extended storage periods (24–168 hours). The superb performance primarily stems from its closely packed, spherical, and dendrite-free morphology with a minimal surface area. Moreover, cobalt is fully compatible with various cathode materials, enabling high-energy (240 W h kg⁻¹), high-rate (80 A g⁻¹), and long-cycling (20 000 cycles) batteries. These properties were achieved without delicate optimization of experimental parameters, highlighting the inherent merits of cobalt over other metal candidates. This work unlocks the potential of cobalt for constructing advanced aqueous multivalent batteries.