The Study Of All Biomass-based Flexible Supercapcitors

Flexible supercapacitors(FSCs)possess high power density,ultra-long cycle life,extraordinary mechanical flexibility to endure bending,twisting or folding,making them competitive candidates as energy storage devices in the flexible/wearable electronics.Although various carbon materials,conductive polymers,carbon-based composites with metal oxides or conducting polymers are employed to construct three-dimensional porous,fiber-like or paper-like electrodes,the present electrode materials still suffer from inevitable practical problems.For example,metal oxides are non-renewable and exhibit low cost-effect,which limits its wide applications.Even though conductive polymers are easily synthesized,the synthesis of conductive polymers uses toxic monomers and produces needless by-products during the synthesis process,and they exhibit unstable electrochemical performance.In addition,polyvinyl alcohol based gels(such as PVA/H2SO4,PVA/KOH,PVA/H3PO4),as widely used electrolyte for FSCs is corrosive or hardly degradable.Hence,the fabrication of FSCs with aforementioned electrodes and polymer gel electrolyte separator arises environmental concerns,huge resource consumption as well as tremendous electronic garbage after their service lifetime.Thus,developing alternative renewable,earth-abundant,low-cost,biodegradable,environmentally friendly biomass-based FSCs are of great challenges.In this work,the biomass(lignosulfonate)has been introduced as pseudocapacitance materials.We choose the carbon nanotubes and graphene serve as conductive substrate because of its excellent properties.And make cellulose into hydrogel electrolyte separator,combined with lignin based electrode materials,all biomass based flexible supercapacitors were obtained.Their electrochemical and mechanical properties were systematically studied.The main reaserch contents are presented as follows:(1)Ultrasonic dispersion of sodium lignosulfonate(Lig)and single-walled carbon nanotubes(SWCNT)was carried out.Lig/SWCNTHNO3 pressure-sensitive hydrogel is fabricated by one step hydrothermal reaction.The effects of the ratio of Lig and SWCNT,the concentration of SWCNT,the temperature and reaction hours of hydrothermal and the addition of nitric acid on the mechanical and electrochemical properties of the composite hydrogels for Lig/SWCNT system were investigated.The optimum electrochemistry performance gel conditions were obtained by three electrodes:the ratio Lig:SWCNT=4:1,the concentration of SWCNT was 3.5 mg mL-1,the hydrothermal temperature was 180 ?,the reaction hours were 12 h and the 0.01 mol L-1 nitric acid was added to the system.The obtained composite hydrogel has a specific capacitance of 372 F g-1 at 1 A g-1 in the three electrode,and has good pressure sensitive properties through mechanical properties tests.Then the cellulose gel electrolyte separator was obtained by the phase inversion method,the hydrogel electrode and the cellulose gel electrolyte separator were assembled into a flexible supercapacitor,which showed the specific capacitance of 292 F g-1 at the current density of 0.5 A g-1,and the corresponding energy density reached 17.1 Wh kg-1,and showed good flexibility under different angles.Interestingly,when repeated 1000 bending times,can retain the initial 97%of the specific capacitance.(2)High performance flexible thin film electrodes were prepared by mixed of Lig,porous graphene oxide(HGO)and SWCNT through simple filtration and hydrothermal processes.The thin film shows an ultra strong tensile strength of about 25 MPa.The feeding ratio and thickness of the three films were systematically adjusted.Finally,the optimum film forming conditions were obtained by testing the electrochemical and mechanical properties:SWCNT:HGO=1:2,Lig:(SWCNT+HGO)=2:1.And the electrochemical performance test of the film with different thickness under the optimum conditions were carried out.When the mass loading was 16.3 mg cm-2,the area capacitance reached 4260 mF cm-2,and the supercapacitor shows excellent flexibility,which shows outstanding electrochemical stability with 96%areal capacitance retention in 4000 bending cycles for 90°.