Rational Synthesis of "Grape-like" Ni2 V2 O7 Microspheres as High-capacity Anodes for Rechargeable Lithium Batteries

Facile Synthesis of a Pyrovanadate Ni2V2O7 Hollow Sphere/Reduced Graphene Oxide Nanocomposite as a Solid-State Hybrid Supercapacitor

Nickel pyrovanadate (NVO) and compositing rGO in different concentrations with NVO are synthesized via the solvothermal process. XRD patterns reveal the formation of crystalline NVO and amorphous rGO in the nanocomposite. The morphology of the material resembles the formation of an NVO hollow nanosphere through a template-free synthesis route with the effect of ethylene glycol. From the CV oxidation and reduction curve, the battery-type faradic reaction is observed. The specific surface area increment via the rGO concentration increment in nanocomposites is due to the partially encapsulated hollow sphere on the 2D active surface area of rGO owing to better specific capacitance and electrochemical stability. In addition, the maximum specific capacitance of 3807 F g-1 at 1 A g-1 for NVO@rGO 20 is obtained via a three-electrode system. The solid-state device shows the specific capacitance retention of ∼70% even after 10,000 cycles for a scan rate of 10 A g-1. The liquid electrolyte device shows the specific capacitance retention of ∼90% from its initial value and the successive charge-discharge process seen over the 10,000 cycles for the scan rate 10 A g-1. The suitable device is identified from this work in terms of high stability, high specific capacitance, and excellent reversibility for electrochemical performance.

Hierarchical Ni3V2O8@N-Doped Carbon Hollow Double-Shell Microspheres for High-Performance Lithium-Ion Storage

Transition metal oxides (TMOs) are highly dense in energy and considered as promising anode materials for a new generation of alkaline ion batteries. However, their electrode structure is disrupted due to significant volume changes during charging and discharging, resulting in the short cycle life of batteries. In this paper, the hierarchical Ni3V2O8@N-doped carbon (Ni3V2O8@NC) hollow double-shell microspheres were prepared and used as electrode materials for lithium-ion batteries (LIBs). The utilization efficiency and ion transfer rate of Ni3V2O8 were improved by the hollow microsphere structure formed through nanoparticle self-assembly. Furthermore, the uniform N-doped carbon layer not only enhanced the structural stability of Ni3V2O8, but also improved the overall electrical conductivity of the composite. The Ni3V2O8@NC electrode has an initial discharge capacity of up to 1167.3 mAh g-1 at a current density of 0.3 A g-1, a reversible capacity of up to 726.5 mAh g-1 after 200 cycles, and still has a capacity of 567.6 mAh g-1 after 500 cycles at a current density of 1 A g-1, indicating that the material has good cycle stability and high-rate capability. This work presents new findings on the design and fabrication of complex porous double-shell nanostructures.

NiCo2V2O8@NC Spheres with Mesoporous Yolk- Bilayer Hierarchical Structure for Enhanced Lithium Storage

Metal vanadates as negative electrode materials for lithium-ion batteries have attracted widespread attention, attributed to their substantial capacity, broad availability, and exceptional safety. In this study, NiCo2V2O8@NC microspheres featuring a yolk-double shell structure were successfully synthesized via ion exchange reactions and surface deposition techniques, employing metal glycerolate as a template. Owing to the bimetallic cobalt-nickel synergistic effect and the N-doped carbon network, this configuration not only optimizes the pore structure but also enhances conductivity, thereby augmenting the stability of the overall structure. The unique yolk-double shell design significantly enhances the utilization of active components and reduces the ion transport distance, thereby achieving high capacity. Thanks to the synergistic effects of this bimetallic and intricate structure, the material demonstrates exceptional capacity and cycle stability in lithium storage. The initial discharge capacity possesses 1522 mAh g-1 at a current density of 0.2 A g-1, with the reversible capacity still maintained at 1197 mAh g-1 after 100 cycles. In addition, at a high current density of 0.5 A g-1, the initial discharge capacity is 1487 mAh g-1, with a reversible capacity of 747 mAh g-1 maintained after 500 cycles. This study offers a perspective and methodology for the design and fabrication of complex porous double shell nanostructures.