Stable structure and fast ion diffusion: N-doped VO2 3D porous nanoflowers for applications in ultrafast rechargeable aqueous zinc-ion batteries.

Aqueous rechargeable zinc-ion batteries (ARZIBs) are promising candidates for fast-charging energy-storage systems. The issues of stronger interactions between Zn2+ and the cathode for ultrafast ARZIBs can be partially addressed by enhancing mass transfer and ion diffusion of the cathode. Herein, via thermal oxidation for the first time, N-doped VO2 porous nanoflowers with short ion diffusion paths and improved electrical conductivity were synthesized as ARZIBs cathode materials. The introduction of nitrogen derived from the vanadium-based-zeolite imidazolyl framework (V-ZIF) contributes to enhanced electrical conductivity and faster ion diffusion, while the thermal oxidation of the VS2 precursor assists the final product in exhibiting a more stable three-dimensional nanoflower structure. In particular, the N-doped VO2 cathode shows excellent cycle stability and superior rate capability with the delivered capacities of 165.02 mAh g-1 and 85 mAh g-1, at 10 A g-1 and 30 A g-1, and the capacity retention of 91.4% after 2200 cycles and 99% after 9000 cycles, respectively. Remarkably, the battery takes less than 10 s to be fully charged at 30 A g-1. Hence, this work provides a new avenue for designing unique nanostructured vanadium oxides and developing electrode materials suitable for ultrafast charging.

Nitrogen-Doped Metallic MoS2 Derived from a Metal-Organic Framework for Aqueous Rechargeable Zinc-Ion Batteries.

Molybdenum disulfide (MoS2) has been extensively studied as a potential storage material for batteries. However, the electrochemical performance of MoS2 is far from ideal, and it exhibits severe activity fading resulting from its low electronic conductivity. The present work synthesizes nitrogen (N)-doped 1T MoS2 nanoflowers made of ultrathin nanosheets via the one-step hydrothermal sulfurization of a molybdenum-based metal-organic framework precursor. The resulting metallic phase shows improved conductivity and hydrophilicity, and characterization demonstrates that N doping effectively expands the interlayer spacing and increases the concentration of sulfur vacancies serving as defects. This material demonstrates high rate performance and good cycling stability when used as the cathode in an aqueous rechargeable zinc-ion battery (ARZIB). Its performance is superior to those of pure 1T MoS2 and 2H MoS2 synthesized with MoO3 as the molybdenum source. Ex situ X-ray photoelectron spectroscopy and X-ray diffraction analyses are performed to explore the reaction mechanism during charging and discharging of the N-doped 1T MoS2. A three-cell series ARZIB system containing this material is used to power five light-emitting diodes to confirm the possible practical applications of this technology.