Spatially Confined “Edge‐to‐Edge” Strategy for Achieving Compact Na⁺/K⁺ Storage: Constructing Hetero‐Ni/Ni₃S₂ in Densified Carbons

Abstract Transition metal sulfides (TMS) are considered as promising anodes for sodium/potassium ion batteries (SIBs/PIBs), and compositing TMS with conductive nanocarbons is an effective mitigation for improving rate performance and cycling stability. However, such a coupling strategy often decreases the tap density and therefore the volumetric energy of electrode. To achieve fast electron/ion transport and high volumetric capacity simultaneously, herein, a compact nanostructure with hetero Ni‐Ni₃S₂ nanoparticles embedded in a densified S‐doped carbon matrix (Ni‐Ni₃S₂@SC) is constructed via a spatially confined “edge‐to‐edge” strategy. Experimental and theoretical results confirm that the carbon matrix and metallic Ni nanoparticles provide fast electron transport pathways at two scales, while the abundant heterojunctions with strong electric fields promote the ion migration and Na/K adsorption. As an anode in SIBs/PIBs, the Ni‐Ni₃S₂@SC exhibits superior rate capability (289/197 mA h g⁻¹ at 2 A g⁻¹), stable cycling performance (88.1/86.2% capacity retention after 100 cycles), and exceptional volumetric capacity (1048/850 mAh cm⁻³ at 0.05 A g⁻¹). The impressive energy‐power characteristics for Ni‐Ni₃S₂@SC anode are further confirmed in full cell batteries and hybrid capacitors. The reported spatially confined “edge‐to‐edge” strategy might be adapted to the construction of various binary and/or ternary metal sulfide dense electrodes for advanced energy storage devices.