Preparation and Electrochemical Properties of Flexible Electrodes for All Solid State Supercapacitors
Author:Guo Gui Zhen
Supervisor:sun you yi
With the popularity of intelligent electronics,people’s requirements on equipment also improved.Portable,wearable and foldable electronic devices with new features have also been commercialized.Due to its high power density,medium energy density,fast charge and discharge,long cycle life and mechanical flexibility,flexible supercapacitor has been regarded as the most promising supply device for various flexible energy storage systems.Furthermore,the key for supercapacitors’development is new flexible electrode material that prepared simplely.Conductive polymers and carbon materials are usually used as the active materials of electrode materials.However,these materials have various defects in using and preparation.For example,carbon materials have lower energy density,and conductive polymers have poorer cycling stability.So,combining conductive polymers with hydrogels is an effective way to improve the electrochemical stability and energy density in supercapacitors.Hydrogels provid an extremely high surface area for conductive polymer and electrolyte,as the 3-D network protect conductive polymer from damage and hold a large amount of electrolyte solution at the same time.At present,most of the preparation methods were tedious or time-consuming,and the prepared hydrogels have poorer mechanical properties,poorer electrochemical stability or serious deformation in the preparation process.This dissertation mainly focuses on the design and preparation of conductive hydrogels,and their applications in flexible supercapacitors.The main research and results are summarized briefly as follows:(1)An electroconductive polyvinyl alcohol(PVA)/polyaniline(PANi)/graphene oxide(GO)hydrogel(denoted as PPGO)with high mechanical strength and electrochemical activity was prepared by freeze-static crosslinking method.The microstructure,mechanical properties and electrochemical properties of hydrogels that prepared by different components were studied.As a resulte,the properties of PPGO conductive hydrogel are obviously better than other hydrogels.The stensile strength of PPGO hydrogel was 3.6 MPa,and the conductivity was 5.6 S/m.At the current density of 0.2 mA/cm~2,the specific capacitance of PPGO hydrogel based supercapacitors reached 2.2 F/cm~2(1573.6 F/g).(2)GO/SA/PANi self-supporting conducting hydrogel(denoted as GOSAP)was prepared by in-situ polymerization of aniline(An)in GO and sodium alginate(SA).The GO layers not only provide effective mechanical support for the hydrogel,but also provide templates for PANi and SA/PANi nanofibers,which prompts the hydrogel structure continuous and uniform,improved the electrical conductivity and mechanical stability greatly.The conductivity of GOSAP hydrogel was 16.8 S/m and the biggest specific capacitance of GOSAP hydrogel based supercapacitor reached 2.3 F/cm~2.(3)A PVA/GO/SA/PANi conductive hydrogel(denoted as PGOSAP)with high flexibility was designed and prepared by introduced PVA in GOSAP conductive hydrogel.Compare to GOSAP conductive hydrogel,this one-step conductive hydrogel has excellent mechanical stretchability.The tensile stress and elongation at break were 3.3 MPa and220%,respectively.As an integrated stretchable electrode material,PGOSAP conductive hydrogel can be used as both electrochemically active material and collector without elastic substrate.At last,PGOSAP conductive hydrogel as electrode combined with PVA hydrogel as electrolyte and diaphragm was designed to integrated flexible supercapacitor.The integrated supercapacitor has higher specific capacitance and better electrochemical stability.This experiment provides a reliable technical support for the construction of flexible integrated supercapacitor and promising to be an energy supply for electronic products.(4)All solid state supercapacitor was assembled by PVA hydrogel as electrolyte(binder)and rGO/CC composite as flexible electrode.Different reducing agents(ascorbic acid,borax and hydrazine hydrate)were used,and the reduction degree of GO was studied by infrared,XRD and Raman.Then the hydrophilicity and flexibility of rGO/CC composites with different reduction degrees were compared.The results showed that the electrochemical properties of rGO/CC were decided by the reduction degree of rGO,and the capacitance and stability of rGO/CC based supercapacitors could increase with the reduction degree.