Approaching Theoretical Capacity: 0D/2D Amorphous/Crystalline Bi‐Based Heterostructures Anode for Aqueous Alkaline Rechargeable Batteries

Abstract Although various bismuth (Bi) electrode materials are reported to assemble aqueous alkaline rechargeable batteries (AARBs) owing to desirable potential window and high theoretical capacity, the Bi‐based electrode materials are still confronted with by their “death space” and poor stability. Herein, a zero‐dimensional/two‐dimensional (0D/2D) amorphous/crystalline BiO_x‐Bi heterostructure is successfully synthesized by a one‐step reduction method for achieving nearly theoretical capacity. Under proper NaBHNaBH₄ content, the Bi3³⁺ is reduced to form ultra‐thin 2D metallic bismuth nanoflakes (Bi‐nf), and incompletely reduced amorphous 0D BiO_x nanodots are embedded in Bi‐nf to form the target BiOx/Bi‐nf heterostructure. The embedded 0D nanodots inhibit the aggregation of 2D Bi‐nf, accelerate the mass transport rate with more oxygen vacancies and pores at heterogeneous interface, and the active centers of amorphous nanodots and ultrathin nanoflakes are recognized as completely accessible which is benefit for up to theoretical capacity. Accordingly, the optimized 0D/2D amorphous/crystalline BiO_x‐Bi‐nf heterostructure electrode presents an admirable capacity of 350 mAh g⁻¹ at 1 A g⁻¹ and outstanding capacity retention of 79.9% at 20 A g‐1. Moreover, the assembled BCNP (basic cobalt/nickel phosphate)//BiOx/Bi‐nf battery exhibits exceptional energy density of 191.64 Wh kg‐1 at 1.28 kW kg‐1 power density and durable stability (80% after 14000 cycles).