Ordered Macroscopic Fiber Assembly From Two-dimensional Tungstate Nanosheets And Their Electrochemical Property

With the vigorous development of wearable electronic devices.flexible fiber-shaped batteries are rapidly rising with their unique one-dimensional struicture and superior flexibility.However.the current research of flexible fiber-shaped batteries often focuses on the flexible display of batteries at the expennse of their electrochemical performance.In order to meet the increasing demand of wearable electronic devices for high-performance fiber-shaped batteries.it is urgent to design and develop fiber-shaped batteries with high flexibility and high electrochemical performance.Recently extensive attentions have been focused on two-dimensional(2D)transition metal oxides that have ultra-thin 2D structures and novel physicochemical properties?which can be used as basic building blocks for the design and manufacture of battery electrode structures.However.because of the low mechanical strength and poor electrical conductivity of 2D transition metal oxides.how to assemble them as high-performance fiber electrodes is still a challenge.In this paper,2D tungstate nanosheets have been selected as the research object.The ordered macroscopic fiber materials of 2D tungstate nanosheets are prepared by the liquid crystal wet spinning,which shows excellent flexibility and electrochemical performance in fiber-shaped lithium ion and sodium ion batteries.Stable monolayer 2D tungstate nanosheet liquid crystal colloids were prepared via the liquid phase exfoliation techology assisted by molecular intercalation,using layered tungstates as precursors.The behavior of nematic phase liquid crystals and the long-range ordered orientation structure of anisotropic 2D tungstate nanosheets in liquid crystals were discovered and confirmed by the orthogonal polarizing microscope,which laid the foundation for the subsequent assembly of ordered macroscopic fibers.Using 2D tungstate nanosheet liquid crystal colloids as spinning solutions,ordered macroscopic fiber materials of 2D tungstate nanosheets were prepared by the wet spinning technology.Through experiments and density functional theoretical calculations(DFT),it is proved that the orderly layered assembly structure and the ionic bond type interlayer bridge based on the electrostatic interaction can effectively improve fiber mechanical properties.The tensile test shows that the tungstate fiber has a tensile strength of up to 198.5 MPa with a fracture toughness of 3.0 MJ m-3 and can be bent and braid arbitrarily without fracture.Tungstate/rGO ordered macroscopic fiber electrode materials were designed and prepared by the wet spinning technology,using 2D tungstate nano sheets and graphene oxide mixed liquid crystals as spinning solutions.The conductive rGO and 2D tungstate nanosheets form orderly layered conformal composite structures in the fiber.which provides good conductive networks and mechanical properties for fiber electrodes.The tensile test shows that the tensile strength of the tungstatei/rGO ordered macroscopic fiber is about 210 MPa.Using the inherent electronegativity of 2D tungstate nanasheets.2D nanofluidic channels for lithium ion and sodium ion transmission were constructed on the basis of orderly layered assembly structures.which can effectively improve the ion transmission capability of fiber electrodes,Moreover,the open three-dimensional interconnection main lattice structure of 2D tungstate nanasheets enables lithium ions and sodium ions to pass quickly in the three-dimensional direction without the restriction of solid-state diffusion?thereby achieving efficient charge storage performance.Therefore.fiber-shaped lithium ion and sodium ion batteries were assembled with tungstate/rGO ordered macroscopic fibers as working electrodes,The electrochemical measurement and charge storage mechanism analysis show that fiber-shaped lithium ion and sodium ion batteries exhibit highly efficient charge storage mechanisms controlled by the capacitance.high reversible capacities(206 mAh g-1 and 178 mAh g-1).excellent rate capability.cycle stability(1000 cycles)and good flexibility(200 bending cycles).Even under the mechanical deformation,fiber-shaped lithium ion and sodium ion batteries can continuously and stably power commercial LED lights.In order to obtain more excellent fiber electrode materials.2D titanium carbide nanosheet(MXene)liquid crystals with metal-like conductivity and high mechanical property were prepared by the liquid phase exfoliation technology.Then.tungstate/MXene ordered macroscopic fibers were designed and prepared by the wet spinning technology.using mixed liquid crystals of 2D tungstate nanosheets and MXene as spinning solutions.MXene provides an excellent conductive network for election transports in the electrochemical process.The open three-dimensional interconnection main lattice structure and the ordered interlayer channel structure of 2D tungstate nanosheets provide an efficient path for the rapid transfer of lithium ions and sodium ions in the electrochemical process.In addition.2D tungstate nanosheets and MXene form stable interlayer bridges through the electrostatic interaction,which effectively improves fiber mechanical properties.The tensile test shows that the tensile str ength of the tungstate/MXene ordered macroscopic fiber is about 220 MPa,exhibiting the excellent mechanical flexibility.Therefore,fiber-shaped lithium ion and sodium ion batteries were assembled with tungstate/MXene ordered macroscopic fibers as working electrodes.The electrochemical measurement and charge storage mechanism analysis show that fiber-shaped lithium ion and sodium ion batteries have a capacitive controlled charge storage mechanism.high electrochemical performance and excellent flexibility.After 1000 bending cycles,its reversible capacity remains above 213.2 mAh g-1 and 195.1 mAh g-1.Even under the dynamic mechanical deformation,it can still continuously and stably power miniature electronic devices,such as digital timers,temperature-humidity meters,and smart wristbands,showing the potential for the wearable application.