Oxygen defect engineering and amphipathic molecules intercalation co-boosting fast kinetics and stable structure of S-doped (NH4)2V10O25∙8H2O free-standing cathode for aqueous Zn-ion storage

The exploration of appropriate layered vanadium-based cathode materials (Zn2+-host) is a crucial and important task for the exploitation of high-performance aqueous zinc ion batteries (AZIBs). Unfortunately, these materials suffer from sluggish kinetics of Zn2+ diffusion and the dissolution of vanadium that make them difficult to reach high capacity and long cycle life. Herein, a novel free-standing cathode (denoted as 3D-NPG@S-NVO@CTAB) has been fabricated by hydrothermal growth of sulfur-doped (NH4)2V10O25∙8 H2O (S-NVO) hollow nanoflowers in three-dimensional nitrogen-doped porous graphene (3D-NPG) and subsequent C19H42N+ (CTAB) pre-insertion. Benefitting from the rational design strategy, the oxygen vacancies induced by sulfur doping weaken electrostatic interaction between Zn2+ and cathode, provide more transfer channels and strengthen electronic conductivity. Meanwhile, the simultaneous introduction of S and CTAB into NVO jointly expands interlayer spacing and enhances Zn2+ diffusion kinetics, which suppresses the dissolution of vanadium by reducing water molecule intercalation and maintains the structure integrity with excellent electrochemical performance (525 mAh g−1 at 0.5 A g−1). Even at a high rate of 5 A g−1, the hierarchical cathode (3D-NPG@S-NVO@CTAB) can still deliver a capacity of 356 mAh g−1 with capacity retention rate of 90% after 2000 cycles. Density functional theory (DFT) calculations indicate that S-doping, the introduction oxygen defects and CTAB obviously strengthen carrier concentration, which represents the enhancement of conductivity. This work can provides ideas for the construction of advanced AZIB devices through the inorganic/organic hybridization of vanadium-based electrode materials.