Design And Performance Investigation On Nanocarbon Based All-solid-state Stretchable Supercapacitors

Due to the increasing demand for wearable and portable applications,various electronic devices are required to be flexible and stretchable.To realize a self-contained stretchable electronic device,it is necessary to integrate a stretchable energy storage component,which could be in the form of batteries,solar cells,supercapacitors,and so on.As an important energy storage device,supercapacitors possess fast charge-discharge rate,high power density,excellent cyclic stability,long cycle life and environmental friendly ability.The specific energy density of supercacitors are several orders of magnitude higher than that of the conventional capacitors.Additionally,the unique charge-discharge mechanism of supercapacitors enable them to store and deliver a large amount of charges in a short time,thus provide much higher power densities than batteries.Under this background,the widely used nanocarbon material-carbon nanotube(CNT)is employed to prepare for new types of all-solid-state supercapacitors.It is believed that the supercapacitors can possess excellent stretchabilities and hold the potential to satisfy the development of mutifountional supercapacitors by desighning unique structures.The carbon nanotube fibers with buckled structures are fabricated through a simple “stretcing-then-releasing” method.The resulted buckled CNT fibers are able to stretched to 40% strain,and their conductivities,performance stabilities during stretching,duribilities,and damage evolutions are studied.Based on the buckled structures,stretchable conductors and supercapacitors are realized.After 10000 stretching-releasing cycles,the resistance of stretchable conductors based on dry spun and aerogel spun CNT fibers show increments of 0.2% and 6%,respectively.The specific capacitances of dry spun and aerogel spun CNT fibers based stretchable supercapacitors change from 4.42 m F/cm~2 and 8.16 m F/cm~2 to 3.60 m F/cm~2 and 9.95 m F/cm~2,respectively.A research on omnidirectionally stretchable high-performance supercapacitors based on the isotropic buckled CNT films is carried out in this part.First,the omnidirectional stretchability of the film is obtained via a continuous and isotropic buckled architecture.The largest stretching strain of the resulted film reaches 200%.Then,an omnidirectionally stretchable supercapacitor is prepared by this buckled CNT film.The resulted supercapacitor forms the baseline for improvement in specifc capacitance and energy density.To this end,polyaniline(PANI),an outstanding pseudocapacitive polymer with high conductivity and specific capacitance,is adopted for conductive wrapping on supercapacitor elec trodes.The isotropic buckled structures combined with the high pseudocapacitance of the PANI deposited composite film results in exceptional capacitive performance.Also,high er omnidirectional stretchability and electrochemical stability of the CNT@PANI based supercapacitor under stretching are comfirmed.A coaxial asymmetric fiber-shaped supercapacitor is designed and fabricated.For achieving freestanding stretchability of the fiber-shaped supercapacitor,a helical structure with uniform helical loops is then realized by overtwisting the core-sheath asymmetric supercapacitor.In this part,Mn O2 nanoflower decorated CNT fiber and CNT/polypyrrole(PPy)composite film are firstly fabricated by electrochemical deposition method.Then CNT@Mn O2 composite fiber is used as the positive electrode and “core”,CNT@PPy composite film is used as the negative electrode and “sheath” and gel electrolyte is used as the electrolyte to fabricate the “core-sheath” supercapacitor fiber.The decoration of CNT fiber and CNT film with Mn O2 and PPy not only improve the capacitive performance of the CNT-based electrode materials,but also enlarge the operating voltage window of the supercapacitor from 0.8 V to 1.5 V.Then,the coaxial supercapacitor fiber is overtwisted to form helical structure to possess freestanding stretchability.The resulted stretchable fiber-shaped supercapacitor exhibits stable capacitive performance with a stretchability of 20% and shows high capacitance,extended operating voltage window,as well as high energy and power densities.