Transition metal chalcogenides (TMCs) with 3d orbitals have been intensively studied for use as cathodes in magnesium-ion batteries. However, their poor electronic conductivities and sluggish electrochemical kinetics severely restrict their electrochemical performance, preventing wide applicability for these materials. Here, we propose a heterointerface structure of cobalt sulfide (Co₃S₄/CoS₂) hollow nanospheres to enable built-in electric fields generated in heterointerfaces, as verified in density functional theory, finite-element simulations, and ab initio molecular dynamics results. Compared to other TMCs, our cathode exhibited a substantial capacity of 597 mAh g⁻¹ after 120 cycles at 50 mA g⁻¹. When evaluated in a pouch cell, the electrode can sustain 100 deep cycles at 40 mA g⁻¹ with an energy density of 203 Wh kg⁻¹ that displays potential for practical applications. Finally, rational heterostructure engineering of transition-metal-based sulfides provides insights into developing cathodes for high-performance sustainable Mg batteries.