Studies On Printable And Multifunctional Supercapacitors

Supercapacitors,also known as electrochemical capacitors are currently new energy storage devices.Compared with primary cells represented by alkaline-manganese and silver-zinc batteries,and secondary cells represented by nickel-cadmium,nickel-metal hydride,super-iron and lithium-ion batteries,for the advantages of higher power densities,faster rates of charge-discharge,longer cycle lives and safer operation,supercapacitors have broad application prospects in the fields of electric vehicle,aerospace,information technology,portable and wearable electronic devices,and so on.But,when supercapacitors are used in those applications,there are still some practical problems:The preparation cost of the devices is high,the large-scale productions and industrial applications are difficult;The devices are susceptible to mechanical deformation and damage,which makes their stabilities and life times undesirable;In some fields of practical applications,the mass loadings of the electrode active materials of the devices are too low to meet the requirements of high energy and power;For single function,the devices neither meet the requirements of colorful life nor along with the developments of the times.In allusion to these problems,the studies were set up from the following directions.Firstly,the cheap inkjet and screen printing techniques were explored to fabricate supercapacitors.Secondly,supercapacitors with stretchable and self-healable functions were developed.Thirdly,vertical finger-like asymmetric supercapacitors?VFASCs?integrated with other function?photodetection?were developed.The main research contents and innovations are as follows:1.Highly dispersed silver?Ag?-multiwalled carbon nanotube?MWCNT?and manganese dioxide?MnO₂?-Ag-MWCNT ink were exploited and the best ink concentrations were optimized.Ag-MWCNT conductive patterns and MnO₂-Ag-MWCNT positive electrodes were prepared by inkjet printing technique.Finally,asymmetric supercapacitors were assembled successfully.Tests showed that:After being printed 50times,the sheet resistance of conductive patterns was as low as 300?/sq and the bend stability of them was good;Positive electrode exhibited high volumetric capacitance?30.5F/cm³?and low ESR?8.1??;Assembled asymmetric supercapacitors had high potential window of 1.8 V,the energy density was as high as 1.28 mWh/cm³?power density of 96mW/cm³?,the capacity retention was as high as 96.9%?after charging/discharging for3000 cycles?.2.Carbon?C??MnO₂-MWCNT and molybdenum trioxide?MoO₃?-MWCNT ink with suitable viscosity were exploited.C flexible conductive electrodes,MnO₂-MWCNT positive electrodes and MoO₃-MWCNT negative electrodes were prepared by screen printing technique.Finally,asymmetric supercapacitors were assembled successfully.Tests showed that:The flexible conductive electrode showed good conductivity and bending property;Positive electrode exhibited high volumetric capacitance of 81.7 F/cm³?scan rate of 1 mV/s?and high energy density of 4.81 mWh/cm³?power density of 228.4mW/cm³?;Negative electrode exhibited high volumetric capacitance of 49.5 F/cm³?scan rate of 2 mV/s?and high energy density of 4.89 mWh/cm³?power density of 262.3mW/cm³?;Assembled asymmetric supercapacitors had high potential window of 1.7 V,the energy density was as high as 11.04 mWh/cm³?power density of 614.6 mW/cm³?,the capacity retention was as high as 91.3%?after charging/discharging for 5000 cycles?.3.Intrinsicallystretchablepolypyrrole?PPy?-reducedgrapheneoxide?RGO?-MWCNT fiber springs were exploited.With the protective shell of self-healable polyurethane,the stretchable and self-healable fiber supercapacitors were prepared.The device exhibited excellent stretchable and self-healable properties:Stretched to 100%,the capacity retention was 82.4%;After third self-healing,the capacity retention was 54.2%;After charging/discharging for 3000 cycles,the capacity of self-healed device had only a decay of 16%;The self-healed device could successfully drive perovskite nanowire photodetector without obvious performance degradation.Simultaneously endowing supercapacitors with stretchable and self-healable functions could effectively alleviate outside mechanical deformation and heal the damage,which improved the reliability,stability and life time of the supercapacitors.4.VFASCs with inner integrated photodetecting function were designed and realized.Compared with traditional plane supercapacitors,the VFASCs have the following advantages:Smaller distances between fingerlike electrodes and lower ion-transport resistance;Larger contact areas between electrode materials and electrolytes,so electrode active materials are fully used;Inner integrated photodetecting systems.When the mass loading of electrode materials increased from initial to 5 times,the specific capacitance increased by 44%.This study provides a way of preparing high performance supercapacitor at high mass loading.MoO₃ nanowires with good photodecting performance were used for negative electrodes,so the VFASCs had photodecting function without external connection system,which largely saved the energy&space and simplified the structure of integrated devices.