Ni₃S₂–Ni Hybrid Nanospheres with Intra‐Core Void Structure Encapsulated in N‐Doped Carbon Shells for Efficient and Stable K‐ion Storage

Abstract Iron group metals chalcogenides, especially NiS, are promising candidates for K‐ion battery anodes due to their high theoretical specific capacity and abundant reserves. However, the practical application of NiS‐based anodes is hindered by slow electrochemical kinetics and unstable structure. Herein, a novel structure of Ni₃S₂–Ni hybrid nanosphere with intra‐core voids encapsulated by N‐doped carbon shells (Ni₃S₂‐Ni@NC‐AE) is constructed, based on the first electrodeposited NiS nanosphere particles, dopamine coating outer layer, oxygen‐free annealing treatment to form Ni₃S₂‐Ni core and N‐doped carbon shell, and selective etching of the Ni phase to form intra‐core void. The electron/K⁺ transport and K⁺ storage reaction kinetics are enhanced due to shortened diffusion pathways, increased active sites, generation of built‐in electric field, high K⁺ adsorption energies, and large electronic density of states at Fermi energy level, resulting from the multi‐structures synergistic effect of Ni₃S₂‐Ni@NC‐AE. Simultaneously, the volume expansion is alleviated due to the sufficient buffer space and strong chemical bonding provided by intra‐core void and yolk–shell structure. Consequently, the Ni₃S₂‐Ni@NC‐AE exhibits excellent specific capacity (438 mAh g⁻¹ at 0.1 A g⁻¹ up to 150 cycles), outstanding rate performances, and ultra‐stable long‐cycle performance (176.4 mAh g⁻¹ at 1 A g⁻¹ up to 5000 cycles) for K‐ion storage.