VS2-based heterojunctions with regulated built-in electric field via ion engineering: Toward superior reaction kinetics and structural stability for aqueous zinc-ion batteries

In aqueous zinc-ion batteries, layered VS 2 cathodes offer high conductivity and multi-electron reactivity but suffer from severe structural degradation and sluggish kinetics. While heterojunction engineering can enhance charge transfer via built-in electric fields, the precise regulation of interfacial electronic structures remains a significant challenge. Herein, we introduce a novel ion-engineering strategy that employs alkaline earth metal ions (Ca 2+ , Sr 2+ ) with distinct ionic radii to effectively modulate VS 2 -based heterojunctions. Experimental characterizations coupled with density functional theory calculations indicate that, relative to VS 2 /CaV 4 O 9 , the VS 2 /SrV 3 O 7 heterostructure exhibits an upshifted V 3d-band center (−0.724 eV), while SrV 3 O 7 possesses a narrower bandgap (2.41 eV), and lower work function (4.27 eV), collectively supporting more favorable interfacial electronic modulation. These electronic modulations induce a robust internal electric field, which effectively promotes interfacial charge transfer. The larger Sr 2+ transforms the morphology from dense stacked layers (VS 2 ) into a 3D nanoflower assembled from ultrathin nanosheets. Consequently, the VS 2 /SrV 3 O 7 cathode delivers an exceptional reversible specific capacity of 455.4 mAh g −1 at 0.5 A g −1 , and an exceptional rate capability of 181.6 mAh g −1 at an ultrahigh current density of 20 A g −1 . Furthermore, it exhibits a dramatically enhanced Zn 2+ diffusion coefficient ranging from 10 −11 to 10 −8  cm 2  s −1 , along with long-term durability, retaining 121.4 mAh g −1 after 10,000 cycles at 15 A g −1 with a highly reversible 3D nanoflower morphological evolution. This work provides deep mechanistic insights into ionic-radius-modulated built-in electric fields, paving a new avenue for rational cathode design.