Synthesis of a three-dimensional cross-linked Ni-V2O5 nanomaterial in an ionic liquid for lithium-ion batteries

A three-dimensional cross-linked Ni-V₂O₅ nanomaterial with a particle size of 250-300 nm was successfully prepared in a 1-butyl-3-methylimidazole bromide ionic liquid (IL). The formation of this structure may follow the rule of dissolution-recrystallization and the ionic liquid, as both a dissolution and structure-directing agent, plays an important role in the formation of the material. After calcination of the precursor, the active material (Ni-V₂O₅-IL) was used as an anode for lithium-ion batteries. The designed anode exhibited excellent electrochemical performance with 765 mA h g^-1 at a current density of 0.3 A g^-1 after 300 cycles, which is much higher than that of a NiVO-W material prepared via a hydrothermal method (305 mA h g^-1). These results show the remarkable superiority of this novel electrode material synthesized in an ionic liquid.

Graphene Matrix Sheathed Metal Vanadate Porous Nanospheres for Enhanced Longevity and High-Rate Energy Storage Devices

Rational design of anode materials comprising rich benefits of high capacity, superior rate capability, and exalted lifetime is of considerable significance in the progress of high-performance Li-ion batteries (LIBs) and supercapatteries. Herein, highly porous cobalt vanadate (Co₂VO₄) nanospheres encapsulated with reduced graphene oxide (rGO) nanosheets (rGO@CoV PNSs) were prepared by a facile hydrothermal method and employed as a hybrid composite-based anode material for energy storage devices. The nanocavities and porous features of CoV nanospheres, and the laminated rGO nanosheets over CoV PNSs can significantly surpass the volume changes and enhance the surface electrokinetics, respectively. With benefits of rich redox activity and constructive traits, the rGO@CoV PNSs as an electrode material in LIBs exhibited superior reversible capacity of 780.6 mAh/g after 100 cycles with remarkable rate performance. Moreover, the hybrid composite displayed an excellent reversible capacity of 531.8 mAh/g even after 1000 cycles performed at 1000 mA/g. Utilizing the synergistic features, the rGO@CoV PNSs composite was also explored as a battery-type electrode for supercapatteries. The fabricated supercapattery device with rGO@CoV PNSs and rGO demonstrated good rate performance including superior areal energy (0.048 mWh/cm²) and power (9.96 mW/cm²) densities. Therefore, the graphene sheathed metal vanadates would be an ultrahigh rate electrode candidates for energy storage devices.

Ultrasonic assisted synthesis of Ni3(VO4)2-reduced graphene oxide nanocomposite for potential use in electrochemical energy storage

In the present study, Ni₃(VO₄)₂-reduced graphene oxide (NV/RGO) nanocomposite was synthesized for energy storage purpose. To this end, a mixture containing RGO nanosheets, Ni (CH₃COOH)₂ and Na₃VO₄ mixture was prepared under probe-type ultrasonic irradiation with frequency of 20 KHz and the optimized power of 100 W. The Raman and energy-dispersive X-ray spectroscopies confirmed the presence of RGO nanosheets, nickel and vanadium elements in the NV/RGO, respectively. In addition, field emission-scanning electron microscopy (FESEM) data showed the formation of the NV nanoparticles on the RGO nanosheets. NV/RGO nanocomposite was pasted on nickel foam (NF) and its performance was investigated in energy storage using a three-electrode cell containing 6 M KOH. In cyclic voltammogram of NV/RGO/NF, redox peaks for Ni (II)/Ni (III) with intensities higher than that for NV/NF were observed which confirms the synergistic effect of RGO on the performance of NV. Chronopotentiometry data revealed that the NV/RGO/NF electrode exhibits high capacity of 117.22 mA h g^-1 at 2 A g^-1. Electrochemical impedance spectroscopy also demonstrated an improvement in the electrical conductivity and electrochemical behavior of NV/RGO/NF nanocomposite compared to the RGO/NF and NV/NF. Furthermore, NV/RGO/NF electrode reserved about 88% of its initial capacity after 1000th potential cycle at 50 mV s^-1. Overall, the results of our study suggest that the NV/RGO nanocomposite prepared in the presence of ultrasonic irradiation might be regarded as a suitable active material for energy storage systems.

High Areal Capacity Li-Ion Storage of Binder-Free Metal Vanadate/Carbon Hybrid Anode by Ion-Exchange Reaction

Storing more energy in a limited device area is very challenging but crucial for the applications of flexible and wearable electronics. Metal vanadates have been regarded as a fascinating group of materials in many areas, especially in lithium-ion storage. However, there has not been a versatile strategy to synthesize flexible metal vanadate hybrid nanostructures as binder-free anodes for Li-ion batteries so far. A convenient and versatile synthesis of M_x V_y O_x+2.5y @carbon cloth (M = Mn, Co, Ni, Cu) composites is proposed here based on a two-step hydrothermal route. As-synthesized products demonstrate hierarchical proliferous structure, ranging from nanoparticles (0D), and nanobelts (1D) to a 3D interconnected network. The metal vanadate/carbon hybrid nanostructures exhibit excellent lithium storage capability, with a high areal specific capacity up to 5.9 mAh cm^-2 (which equals to 1676.8 mAh g^-1 ) at a current density of 200 mA g^-1 . Moreover, the nature of good flexibility, mixed valence states, and ultrahigh mass loading density (over 3.5 mg cm^-2 ) all guarantee their great potential in compact energy storage for future wearable devices and other related applications.