Bismuth: An Epitaxy-like Conversion Mechanism Enabled by Intercalation-Conversion Chemistry for Stable Aqueous...

The exploitation of new anion battery systems based on high-abundance oceanic elements (e.g., F^-, Cl^-, and Br^-) is a strong supplement to the current metal cation (e.g., Li⁺, Na⁺) battery technologies. Bismuth (Bi), the rare anion-specific anode species nearest to practical application for chloride ion storage, is plagued by volume expansion and structure collapse due to limited control of its conversion behavior. Here, we reveal that a unique epitaxy-like conversion mechanism in the monocrystalline Bi nanospheres (R3m group) can drastically inhibit grain pulverization and capacity fading, which is enabled by Cl^- intercalation in their interlayer space. The Bi nanosphere anode can self-evolve and transform into a rigid BiOCl nanosheet-interlaced structure after the initial conversion reaction. With this epitaxy-like conversion mechanism, the Bi anode exhibits a record-high capacity of 249 mAh g^-1 (∼1.2 mAh cm^-2) at 0.25 C and sustains more than 1400 h with 20% capacity loss. Pairing this anode with a Prussian blue cathode, the full battery can deliver an ultrahigh desalination capacity of 127.1 m g_Cl g_Bi^-1. Our study milestones the understanding of conversion-type anode structures, which is an essential step toward the commercialization of aqueous batteries.