Research On Flexible Sodium Ion Energy Storage Devices And NO₂ Sensors Based On Electrospinning Nanofibers

With the rapid development of flexible wearable electronic,the flexible nanofibers film prepared by electrospinning has been widely concerned and recognized by the society.One-dimensional nanofiber has numerous advantages,such as uniform diameter,large surface area,and high porosity.Interleaved nanofiber can form the self-supported three-dimensional spatial structure,which is one of the preferred materials for fabrication of the flexible wearable electronic devices.Manganese oxides are promising cathode material candidates with appropriate positive potential windows for low-cost and safe aqueous sodium-ion capacitors（ASICs）.However,their low electrical conductivity issue and the lack of advanced binder-free manganese oxide-based electrodes severely restrict their practical capacitance and application in flexible ASICs.Here,Ni_0.25Mn_0.75O（NMO）nanoparticles uniformly encapsulated in carbon nanofiber films with excellent flexibility are fabricated by electrospinning and subsequent carbonization.The uniformly amorphous carbon layer enhances the conductivity,avoids dissolution and alleviates the volume or stress change of NMO during ion intercalation or mechanical deformation.More importantly,compared with the flexible electrodes prepared by traditional methods,electrospinning materials can be directly used as binder-free electrodes,which can effectively simplify the process and improve the energy density.Finally,a 2.4 V flexible quasi-solid-state ASIC device is integrated,which exhibits a high energy density of 5.95 m Wh cm^-3,a high-power density of 670 m W cm^-3and an outstanding stability of 1000 cycles.This work offers an effective materials engineering strategy for high-performance binder-free NMO-based cathodes and advanced flexible ASICs.Conventional SnS₂shows the long response/recovery times for the detection of NO₂gas at room temperature and can’t even recover completely.In this work,a few（single）layers of SnS₂nanosheets vertically grew on flexible yttria-stabilized zirconia nanofibers（YSZ-NFs）by hydrothermal method,and further integrated the fully-inorganic NO₂sensor.YSZ-NFs not only has large specific surface area,but also can bond well with SnS₂nanosheets.The bionic"branch"and"leaf"structure formed by ion bonding can effectively disperse the stress distribution,which further improves the mechanical flexibility.In addition,SnS₂has favorable electron donor characteristic and suitable adsorption band for NO₂,the surface and edge of layered SnS₂has numerous of active sites,they can effectively contact with the NO₂molecules.At 120℃,the device has excellent repeatability and stability,the sensitivity to 500 ppb NO₂is 3.78,and the response/recovery times is 121/900 s.With the continuous improvement of detection of the NO₂gas and requirements of the flexibly electronic equipment,the development of high-performance and flexible room-temperature NO₂is particularly important.Based on YSZ/SnS₂-NFs,a flexible room-temperature NO₂gas sensor is reasonably integrated for the first time,it is based on YSZ-NFs supported PANI/SnS₂nanosheets（YSZ/PANI/SnS₂-NFs）.Self-supported YSZ-NFs has fine grain size and abundant vacancy bonds on the surface,which has excellent mechanical flexibility.SnS₂nanosheets and YSZ/PANI-NFs form the largely geometric spatial structure not only improves the mechanical flexibility of nanofibers film,but also benefits the transmission and diffusion of NO₂molecules.In addition,the formation of p-n heterojunction increases the active sites of the gas-sensitive materials,and H⁺doped PANI improves the electrical conductivity of SnS₂and promotes electron transfer.At room temperature,the device has excellent gas sensitivity to NO₂,and the response/recovery times for 50ppb NO₂is only 5/15 s.More importantly,the sensor also exhibits excellent reversibility and flexibility,（performance is not significant degradation after 500bending cycles）,which shows great potential for industrial and biomedical applications.It provides certain reference value for the development of flexible room temperature gas sensor.