Electron Island Effect: Cross‐Layer Embedded Quantum Dot Heterostructures Toward Ultrahigh‐Energy‐Density Alkaline Aqueous Battery

Abstract Alkaline aqueous battery offer exceptional safety and cost advantages for grid‐scale/portable energy storage, yet their commercialization is hindered by cathode materials with limited ion diffusion and sluggish redox kinetics. We report a Co ₉ S ₈ quantum dots (QDs) strong coupled layered double hydroxide (Co ₉ S ₈ ‐QDs/LDH) with abundant hetero‐interface is reported by the electrochemically‐driven in situ etching strategy to unseal their theoretical capacity. The “electron island” effect of Co ₉ S ₈ ‐QDs achieve electrons transferred up to 2.74 e from LDH matrix, which further driven the fast adsorption and electron transfer of OH ⁻ anion. Meanwhile, the abundant hetero‐interface with defect sites can breakthrough the intrinsic 2D diffusion limitation of common LDH and dramatically promote the structural stability with the formation energy 4 time than surface bonding model. Therefore, the optimized electrode material Co ₉ S ₈ ‐QDs/LDH delivers a specific capacity of 14 610 mF cm ⁻² (483.13 mAh g ⁻¹ ) at 2 mA cm ⁻² , and remarkable cycling stability of remaining 95% initial value after 9500 cycles. Furthermore, the as‐fabricated Co ₉ S ₈ ‐QDs/LDH//rGO‐Zn alkaline aqueous battery device shows an ultra‐high energy density of 12.4 mWh cm ⁻² at a power density of 3.3 mW cm ⁻² . The “electron island” effect and interface engineering would unlock the full potential of heterojunction architectures for advanced energy storage applications.