Controllable fabrication of NiV₂O₆ nanosphere as a high-performance flexible all-solid-state electrode material for supercapacitors

Highlights

• NiV₂O₆ materials with different morphological microstructures were synthesized.

• An interesting structural change according to fixation of NH₄⁺ was observed.

• flexible rGO//N-3 ASCs device exhibit good cycle stability.

Abstract

Flexible high-performance electrochemical capacitors have aroused much attention with their prospect applications in future wearable electronic devices. Herein, a new strategy for fabrication the NiV₂O₆ nanosphere by hydrothermal combined with subsequent room temperature liquid phase synthesis method was investigated. The introduced NH₄⁺ during the preparation is benefit to attain the NiV₂O₆ architectures with high electrical conductivity, large surface area, and exclusive porous networks. When applied as active electrode materials for electrochemical energy storage device, NiV₂O₆ gives rise to superior specific capacity (565.5 C/g at 1 A/g) and cyclic stability (84.6% of initial capacity retention after 3000 cycles). An asymmetric supercapacitor device can reach voltage window of 1.6 V and supply an energy density of 24.3 Wh kg⁻¹ at the power density 800 W kg⁻¹ in an aqueous electrolyte and 7.8 W h kg⁻¹ at the power density of 850 W kg⁻¹ in a solid state gel electrolyte. The cyclic stability of flexible asymmetric supercapacitor has provided 74% capacitance retention over 3000 charge–discharge cycles. Thus, the NiV₂O₆ nanosphere electrode presents a great potential for flexible and transparent energy storage devices.

Introduction

The fast development of portable and wearable microelectronics has increasingly stimulated the urgent demand for flexibility and micro-/nanostructured materials have persuaded a colossal interest due to their structure-dependent properties in various electrochemical energy storage and conversion devices.[1], [2] So the controllable preparation of micro-/nanostructured materials with delicate morphological control has become increasingly fascinating and vital for both fundamental studies and practical applications[3]. Up to now tremendous complex compositions with desired micro-/nanostructures of different morphologies have been synthesized through diverse protocols, including hydrothermal method, electrochemical deposition, chemical vapor deposition method, and electrospinning technique[4], [5], [6], [7], co-precipitation method [8], [9], and microwave-assisted synthesis method [10], [11], [12]. Vanadium oxides, such as VO₂, V₂O₃, V₂O₅, and V₆O₁₃ [13], [14], [15], have been widely studied by researchers due to their high electrochemical activity and low cost in the fields of lithium ion batteries and supercapacitors [16]. Among the various metal oxides, vanadium oxide is considered to be one of the most promising candidates due to its wide potential window, unique layered structure, and a variety of oxidation states (V²⁺, V³⁺, V⁴⁺, and V⁵⁺) which can provide an excellent pseudocapacitance [17]. Superior to single vanadium oxides, metal vanadate provide rich redox reaction kinetics among multiple metal ions owing to the good electrical conductivity of electrons/ions. Therefore, there are synergistic effects and interface effects among multiple metal ions in vanadate.[18], [19] For instance, Liu et al [20] successfully synthesized Ni₃V₂O₈/Co₃V₂O₈ composite material by liquid-phase synthesis method, which showed good electrochemical properties applied as a positive electrode material for supercapacitors. Vanadate composite material such as Co₃O₄-Ni₃(VO₄)₂ nanorods with 3D heterogeneous structure, NiCo₂V₂O₈ hierarchical microspheres, 3D urchin-shaped Ni₃(VO₄)₂ hollow nanospheres, 3D Ni_1-xV_xO₂ hierarchical hollow microsphere and 3D Co₃V₂O₈ porous rose-like structures [21], [22], [23], [24], [25], quasi-cuboidal CoV₂O₆[12] have been also reported as electrode materials for supercapacitors and shown excellent electrochemical performance. Meanwhile, flexible electrochemical devices also play a very important role in our lives. Therefore, it is necessary to synthesize the flexible devices with excellent electrochemical performance.

In this work, NiV₂O₆ with different structures was prepared by hydrothermal combined with subsequent room temperature liquid phase synthesis method. The effect of varying the stoichiometry of ammonium hydroxide on the microstructure and electrochemical performances of NiV₂O₆ has been systematically studied. The result delivered remarkable cyclic stability of the as-prepared NiV₂O₆ at current density of 10 A g⁻¹ and a high specific capacity of 565.5 C g⁻¹ at current density of 1 A g⁻¹ in 2 M KOH electrolyte. The assembled asymmetric supercapacitor (ASC) equipment with an outstanding energy density of 24.3 Wh kg⁻¹ at the power density of 800 W kg⁻¹. And flexible asymmetric supercapacitor (ASC) gives rise to remarkable energy density of 7.8 Wh kg⁻¹ at the power density of 850 W kg⁻¹, together with remarkable cyclic stability with 74% capacitance retention over 3000 charge–discharge cycles. These excellent electrochemical features signify that NiV₂O₆ is a potential electrode material in energy storage materials.