Vanadium oxides obtained by chimie douce reactions: The influences of transition metal species on crystal structures and electrochemical behaviors in zinc-ion batteries

Preparation of an aqueous zinc ion rGH/V2O5 photorechargeable supercapacitor

A photorechargeable supercapacitor was constructed using vanadium pentoxide (V2O5), reduced graphene oxide hydrogel (rGH), and zinc trifluoromethanesulfonate (Zn(CF3SO3)2) as the photoanode, cathode, and electrolyte, respectively. The phase composition, microstructure, chemical structure, light absorption, and specific surface area of the synthesized products and the electrochemical performance of the rGH/V2O5 supercapacitor were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, UV-Vis spectroscopy, the Brunauer-Emmett-Teller (BET) method, and an electrochemical workstation, respectively. The results show that the device has a specific capacity of 164 F g-1 at 0.5 A g-1 under illumination with 95 mW cm-2 light intensity, which is 20.5% higher than that under normal electrical charging. The supercapacitor has a 75% capacity retention rate and 100% coulombic efficiency, respectively, after 10 000 testing cycles under photoelectric synergistic charging and discharging. The as-constructed rGH/V2O5 photorechargeable supercapacitor exhibits promising application potential in electric vehicles and wearable electronics.

Fullerenol as a nano-molecular sieve additive enables stable zinc metal anodes

Aqueous zinc batteries (AZBs) with the advantages of safety, low cost, and sustainability are promising candidates for large-scale energy storage devices. However, the issues of interface side reactions and dendrite growth at the zinc metal anode (ZMA) significantly harm the cycling lifespan of AZBs. In this study, we designed a nano-molecular sieve additive, fullerenol (C60(OH)n), which possesses a surface rich in hydroxyl groups that can be uniformly dispersed in the aqueous solution, and captures free water in the electrolyte, thereby suppressing the occurrence of interfacial corrosion. Besides, fullerenol can be further reduced to fullerene (C60) on the surface of ZMA, holding a unique self-smoothing effect that can inhibit the growth of dendritic Zn. With the synergistic action of these two effects, the fullerenol-contained electrolyte (FE) enables dendrite-free ZMAs. The Zn-Ti half-cell using FE exhibits stable cycling over 2500 times at 5 mA cm-2 with an average Coulombic efficiency as high as 99.8 %. Additionally, the Zn-NaV3O8 cell using this electrolyte displays a capacity retention rate of 100 % after 1000 cycles at -20 °C. This work provides important insights into the molecular design of multifunctional electrolyte additives.

Hydrophobic Two-Dimensional Layered Superstructure of a Polyoxometalate Cluster as the Cathode Material for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries hold promise for sustainable energy storage, yet challenges in finding high-performance cathode materials persist. Polyoxovanadates (POVs) are emerging as potential candidates due to their structural diversity and robust redox activity. Despite their potential, issues like dissolution in electrolytes, structural degradation, and byproduct accumulation persist. This work introduces a POV-based hydrophobic two-dimensional (2D) layered superstructure that addresses these challenges. The hydrophobic nature minimizes POV dissolution, enhancing structural stability and inhibiting phase transitions during cycling. The 2D arrangement ensures a larger surface area and improved electronic conductivity, resulting in faster kinetics and higher specific capacity. The superstructure demonstrates improved cycle life and an increased operating voltage, marking a significant advancement in POV-based cathode materials for aqueous zinc-ion batteries.

Nitrogen-Vacancy-Rich VN Clusters Embedded in Carbon Matrix for High-Performance Zinc Ion Batteries

Vanadium nitride (VN) is a potential cathode material with high capacity and high energy density for aqueous zinc batteries (AZIBs). However, the slow kinetics resulting from the strong electrostatic interaction of the electrode materials with zinc ions is a major challenge for fast storage. Here, VN clusters with nitrogen-vacancy embedded in carbon (C) (Nv-VN/C-SS-2) are prepared for the first time to improve the slow reaction kinetics. The nitrogen vacancies can effectively accelerate the reaction kinetics, reduce the electrochemical polarization, and improve the performance. The density functional theory (DFT) calculations also prove that the rapid adsorption and desorption of zinc ions on Nv-VN/C-SS-2 can release more electrons to the delocalized electron cloud of the material, thus adding more active sites. The Nv-VN/C-SS-2 exhibits a specific capacity and outstanding cycle life. Meanwhile, the quasi-solid-state battery exhibits a high capacity of 186.5 mAh g-1, ultra-high energy density of 278.9 Wh kg-1, and a high power density of 2375.1 W kg-1 at 2.5 A g-1, showing excellent electrochemical performance. This work provides a meaningful reference value for improving the comprehensive electrochemical performance of VN through interface engineering.

Tungsten-oxygen bond pre-introduced VO2(B) nanoribbons enable fast and stable zinc ion storage ability

The tunnel structure of the bronze phase vanadium dioxide (VO2(B)) can be used as the zinc ion storage active sites. However, the intense charge repulsion of divalent Zn2+ causes a sluggish reaction kinetics in the tunnel VO2(B). Here, a tungsten-oxygen bond pre-introduced (TOBI) approach is proposed to modulate the tunnel structure of VO2(B). The VO2(B) cathodes with TOBI of 0.5 at% to 3.0 at% have been controllably synthesized by a simple hydrothermal method. The results from structural analysis uncover that the pre-introduced W6+ replaces the V4+ in VO2(B) to form WO6 octahedra. Benefiting from the rapid diffusion kinetics, enhanced structural stability and improved conductivity enabled by the TOBI, the optimal VO2(B) nanoribbons with 1.5 at% shows a high reversible capacity of 265 mAh g-1, a high rate-performance of up-to 10 A g-1 and a long cycling stability of 2000 cycles. Moreover, a pseudo-capacitive dominated Zn2+ intercalation/de-intercalation behavior is solidly determined by the electrochemical kinetics testing and structural characterizations. This TOBI method is referential for developing other multivalent ion battery cathodes with outstanding performances.

Defect regulated spinel Mn3O4 obtained by glycerol-assisted method for high-energy-density aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (RAZIBs) show great potential as a competitive candidate for reliable energy storage by virtue of cost-effectiveness, high safety, and environmental friendliness. However, unsatisfactory cycle stability of cathode material impedes the development of high-performance RAZIBs. This study reveals a strategic polyol-mediated process by using glycerol as the solvent for solvothermal reaction. After heat treatment in air, Mn-deficient Mn₃O₄ spinel (D-Mn₃O₄) can be obtained with rich Mn valence states (Mn²⁺/Mn³⁺/Mn⁴⁺), expanded crystal structure, high surface area, and good electrolyte compatability. Compared to well-crystallized Mn₃O₄, the presence of manganese vacancies in D-Mn₃O₄ enables lower charge-transfer resistance (86.0 vs 196.5 Ω), reduced activation energy for ion insertion (30.9 vs 50.4 kJ mol^-1), and boosted solid-state ion diffusivity (9.45 × 10^-12 vs 4.61 × 10^-14 cm² s^-1). Therefore, D-Mn₃O₄ exhibits promising electrochemical performance with high capacity (284 mAh g^-1), high specific energy (388.5 Wh kg^-1) and stable cycle retention (87% after 200 cyclesat 0.3 A g^-1). On the contrary, the well-crystallized Mn₃O₄ sample suffers from severe capacity fading with only 48% capacity retention. Moreover, the specific energies obtained after 200 cycles are 336.1 and 166.0 Wh kg^-1 for D-Mn₃O₄ and Mn₃O₄, respectively. The drastic differences between the electrochemical performance of D-Mn₃O₄ and Mn₃O₄ manifest that the existing manganese vacancies in Mn₃O₄ spinel structure enhance energy storage capability.