Study On Controllable Preparation Of Two-Dimensional Amorphous Niobium Pentoxide And Its Fiber-Based Energy Storage Performance

With the development of technology,wearable electronic devices have become an important part of people’s lives,which has raised higher requirements for energy storage devices.The development of high-capacity,high-stability,and safe flexible energy storage devices is currently a major research direction.Among various energy storage systems,thin and flexible supercapacitors have attracted attention due to their outstanding characteristics such as excellent lifespan,lightweight,and high-power density.It is essential to explore and study advanced electrode materials for improving the electrochemical performance of supercapacitors.Niobium oxide,which has a high capacity and a small intercalation structure change,is considered one of the promising candidate materials for pseudocapacitive anode materials.However,its rate capability and cycling stability are poor due to low electronic conductivity,which severely affects the practical applications.Although the construction of two-dimensional and amorphous structures can effectively improve the electronic and ionic transport of pentoxide niobium,it is still difficult to successfully prepare atomically thick two-dimensional amorphous pentoxide niobium.In this paper,we report a new method for the structure-confined growth of ultra-thin 2D amorphous pentoxide niobium using hexamethylenetetramine as an auxiliary agent.This in-situ grown ultra-thin two-dimensional amorphous structure can not only greatly ensure the efficient migration of electrons and ions but also expose more stable active sites.Its electrochemical testing also confirms that the prepared two-dimensional amorphous niobium pentoxide composite graphene oxide（GO）electrode could exhibite excellent rate capability and remarkable cycling stability.By using traditional wet-spinning technology for spinning,we have made one-dimensional wrapped fiber-based supercapacitor devices,providing a good energy storage solution for smart wearables.The main research work and results are as follows:（1）Formation exploration of two-dimensional amorphous niobium pentoxide composite:The molar concentration ratio of hexamethylenetetramine and Nb ions was identified as the key factor determining the formation by exploring the pH of the precursor mixed solution,the reaction temperature,and the molar concentration ratio of hexamethylenetetramine and Nb ions.Hexamethylenetetramine acts as a ligand to rapidly construct a two-dimensional Nb-hexamethylenetetramine coordination framework with Nb ions as the center,which is then combined with GO as a conductive substrate and electrostatically adsorbed with Nb ions.This strategy of combining hexamethylenetetramine with GO successfully achieved the preparation of ultra-thin two-dimensional amorphous niobium oxide.The characterization of the structure and morphology indicates that the prepared pentoxide is an ultra-thin two-dimensional amorphous structure,effectively solving the problem of the inability to synthesize atomic-layer two-dimensional amorphous structures in traditional solvothermal methods.（2）Study on energy storage performance of two-dimensional amorphous niobium pentoxide composite electrode:Aqueous supercapacitors have advantages such as high safety,environmental friendliness,and low cost.We used 1 M Li₂SO₄ as the electrolyte to perform three-electrode testing on the two-dimensional amorphous niobium pentoxide composite material.At a scan rate of 1 m V s^-1,an ultra-high specific capacitance of 245 F g^-1 was exhibited.When the scan rate was increased to 100 m V s^-1,the capacity retention rate remained as high as 63.2%,showing excellent rate capability.The low voltage drop in constant current charge-discharge testing and low resistance surface electrode in impedance testing have minimal charge transfer resistance.At a current density of 10 A g^-1,after 200,000 cycles,the initial specific capacitance was still maintained at 94.1%,and the morphology and structure characterization after cycling remained basically unchanged,demonstrating incredible stability.The excellent rate capability and cycle stability confirmed that the two-dimensional amorphous niobium pentoxide effectively improved the electron and ion transport issues of niobium pentoxide.（3）Preparation and Performance Study of Two-Dimensional Amorphous Niobium Pentoxide//MXene Fiber Devices:MXenes,a promising cathode material in supercapacitors,were selected as the cathode material in the device.Rheological tests of the two-dimensional amorphous niobium pentoxide composite ink and MXene ink showed that both are non-Newtonian fluids with shear-thinning behavior,suitable for wet spinning.Wet spinning technology was used to prepare coaxial fibers with two-dimensional amorphous niobium pentoxide composite material and Ti₃C₂T_x as the core,and PVA/Li₂SO₄ as the shell.A one-dimensional coiled supercapacitor was obtained by winding the fibers,and electrochemical tests were performed.This device provides a new approach for the design of highly stable flexible electrodes,and has great potential for practical applications in future production.