Construction And Application Of Fabric-based Wearable Optical Switch And Energy Devices

With rapid development of electronic technology,various types of electronic devices are gradually popularized in people's daily life.The requirements of wearable electronic devices on comfort,portability and real-time monitoring capability match perfectly with the trend of consumer electronics.Flexible electronic devices is now in a rapid development period in both market and fundamental research.An integrated wearable electronic system normally needs several components:sensor,switch,power supply unit,and energy storage device.Thus,it is urgent to develop those electronic elements on flexible substrates separately.Textile is an ideal supporting material for wearable electronic devices because of its good hygroscopicity,air/moisture permeability,mechanical properties,and skin affinity.However,the lack of functionalities,such as conductivity,sensing,and energy storage,greatly limits the application of traditional textiles in wearable electronics.It has become a great challenge in the development of flexible electronics to combine traditional textiles with advanced electronic technology.In view of the above background,three works are conducted in this project to develop flexible optical switch and energy storage devices based on traditional fabrics:1.Screen-printing Bi₂S₃ nanowires on silk fabrics for a flexible optical switchDevelopment of textile-based wearable devices has been one of the hottest research topics over the past few years.However,a fabric-supported optical switch has never been reported.Herein,a pair of interdigital silver electrodes and hydrothermally synthesized Bi₂S₃nanowires were screen-printed on a silk fabric successively to construct a silk fabric-based flexible optical switch.The device shows irradiation power-dependent light-on currents and could response to blue,green as well as red lights.The device possess fast response/recovery time less than 2 ms for pulse incident light.After 120 cycles of distortion or bending,the light-on current remains as high as more than 85%.Bi₂S₃ nanowires films with different patterns could be printed on the top of the devices without significantly affecting their performance.It is also demonstrated that the system could be utilized to trigger the rotation of an electrical fan.This work may provide a facile approach to prepare a silk fabric-based optical switch for wearable electronics.2.A flexible sandwich-structured supercapacitor with PVA/H₃PO₄-soaked cotton fabric as electrolyte,separator and supporting layerIn order to realize the continuous power supply to an integrated wearable system,it is necessary to develop flexible,lightweight and convenient energy storage devices.Herein,a sandwich-structured supercapacitor with a poly?vinyl alcohol?/H₃PO₄-soaked cotton fabric as electrolyte matrix,separator and supporting layer was prepared via screen-printing and transfer-printing.Digital photographs and scanning electron micrographs are recorded to illustrate the preparation process.The device possesses a gravimetric capacitance of 63.7 F·g^-1at a current density of 1 A·g^-1.After 2000 charging/discharging cycles,a capacitance retention of 85%could be achieved.The as-prepared supercapacitor can tolerate 100 times of bending or twisting with the capacitance maintaining at 89.7%and 93.3%of the original level,respectively.By designing the screen-printing mask,a squirrel-patterned supercapacitor was manufactured,showing that the proposed approach could combine both functionality and aesthetics.To demonstrate its feasibility,three in-series connected supercapacitors were produced on a T-shirt to light up a red lamp.This work may provide a facile approach for the preparation of ultraflexible textile-based supercapacitors for potential applications in smart textiles and wearable electronics.3.Flexible Li-ion battery with cotton fabric as separatorLithium ion?Li-ion?battery is usually used to power portable electronic devices.It is highly desirable to develop flexible battery with lightweight and small size to meet the requirements of wearable electronic systems.Inspired by the second work in this project,a cotton fabric is employed to replace the polymer-based separator to build a flexible Li-ion battery.There is no significant difference on cycle characteristics,electrochemical impedance,and charge-discharge curve between the newly structured half-battery and the conventional one,validating the possibility of using cotton fabrics as separators in Li-ion batteries.Subsequently,a Li-ion battery with the structure of lithium foil/cotton fabric/LiFePO₄ was constructed and encapsulated using the thermoplastic packaging technology.Under the current density of 0.2 C,the battery shows an initial discharge specific capacity of 106.5mAh·g^-1.A LED lamp could be lighted up with this device.However,the capacity drops sharply after 12 cycles of charge and discharge.Based on the morphological and crystalline alterations on the electrode materials of a failed battery,it is speculated that immature packing process may lead to poor cycling performance.This work may provide useful information for the development of textile-based lithium ion battery.In this project,novel optical switch,supercapacitor and Li-ion battery with excellent flexibility were constructed by combining conventional textiles with printing techniques.These works may provide new strategies for the fabrication of flexible electronic devices,and may also expand the potentials of traditional fabrics in wearable electronics.