Preparation And Properties Of Flexible Electrochromic Supercapacitor Based On WO_x/CNT

Flexible electrochromic supercapacitor is a new type of multifunctional energy storage device.It can not only power devices,but also show the energy storage status through different color.At the same time,the energy storage and electrochromic performance can be well maintained during bending process.It has important research and application value in many fields.In this paper,WO_x/CNT composite film based flexible electrochromic electrode is developed by loading highly oriented CNT transparent conductive film on flexible substrate followed by electrochemically depositing of WO_x on CNT.The main contents are as follows:(1)Preparation and characterization of WO_x/CNT composite film.First,the flexible substrate is prepared by spin-coating method.Then,CNT sheets are dry-spun onto the flexible substrate.Finally WO_x is electrochemically deposited on the CNT sheets under constant voltage.The structures of the produced composite film electrode are characterized by SEM,XRD,Raman and XPS.The results shows that the WO_xdeposited on the CNT sheet is particle structure.With the increasing of deposited WO_x,the particles become larger and aggregated.In addition,Raman spectrum shows that WO_x is a hydrated structure.XPS spectrum shows that W⁶⁺and W⁵⁺exist simultaneously in WO_x and W⁶⁺:W⁵⁺is 7:1.(2)Study on the energy storage and electrochromic performances of WO_x/CNT composite film electrode in aqueous electrolyte.The effects of CNT thickness,WO_xdeposition time and areal charge density on the electrochemical energy storage and electrochromic properties of WO_x/CNT composite films are systematically studied.The increasing of CNT thickness can effectively improve the conductivity of the films and increase the deposition amount of WO_x on unit area,and thus can improve the energy storage and electrochromic performance of the composited film.Increasing the WO_xdeposition time in a suitable range can increase the deposition amount on unit area,and thus improve the areal specific capacitance and electrochromic properties of the composite films.However,too long deposition time will lead to the aggregation of WO_x,which is not conducive to the improvement of energy storage and electrochromic properties.The WO_x deposition on unit area can be more accurately controlled by the areal charge density of WO_x deposition.When the thickness of CNT is 200 nm and the deposition time of WO_x is 20 min,the areal specific capacitance of WO_x/CNT composite film can reach 19.93 m F/cm² at 0.1 m A/cm².Assembling into supercapacitor,the areal specific capacitance can reach 3.13 m F/cm² at 0.5 m A/cm².Bending the supercapacitor for 100 times,the capacitance retention can reach 74.12%.(3)Study on the energy storage and electrochromic performances of WO_x/CNT composite film electrode in organic electrolyte.The effects of CNT thickness and WO_xareal charge density on the electrochemical energy storage and electrochromic properties of WO_x/CNT composite films in organic electrolyte are systematically studied.The increasing of CNT sheet thickness can modify the conductivity and rate capability of the composite electrode.The proper increasing of areal charge density of WO_x can improve the areal specific capacitance,but extra WO_x deposition would deduct the performance due to the aggregation.When the thickness of CNT is 60 nm and the areal charge density of WO_x is-0.4 C/cm²,the areal specific capacitance of WO_x/CNT composite film reaches 5.84 m F/cm² at 0.1 m A/cm²,and the rate performance is similar with that of 100 nm composite film electrode.Assembling into supercapacitor,when the potential is 1.8 V,the film is colored and the transmittance can reach 56.95%at 463 nm and 33.89%at 800 nm.Bending the supercapacitor for 100 times,the capacitance retention can reach 80.13%.In summary,the WO_x/CNT composite film electrodes are prepared on flexible substrate.The energy storage and electrochromic performances of the film electrodes in aqueous electrolyte and organic electrolyte are systematically studied.The produced flexible electrochromic electrodes and the developed controllable preparation method can be applied to other flexible electrochromic energy storage devices.