Application Of Lignocellulose Membrane In Aqueous Supercapacitors And Research On Its Performanc

In view of the global development and the increasing demand for the use of environmentally friendly energy storage materials and flexible devices,it is necessary to develop gel polymer electrolytes(GPE)based on natural polymers to prepare supercapacitors(SCs).Aqueous electrolyte is favored in SCs because of its advantages such as easy operation,low cost,safety,high ionic conductivity and high power density.Therefore,this paper uses natural lignocellulose(LC)membrane with rich reserves,low cost,and biodegradability as the matrix to prepare hydrogel electrolyte to improve the electrochemical performance of SCs,and uses commercial separator and liquid electrolyte as control sample for research.According to the different characteristics of alkaline,acidic and neutral three aqueous electrolyte systems,three LC-based membranes were prepared by simple methods such as solution casting and freeze-drying to be suitable for the three aqueous electrolyte systems,and carried out a series of research by means of physical characterization and electrochemical characterization.(1)In the alkaline system,the LC membrane has good thermal stability of 270℃,a porosity of 86.2%,and an electrolyte uptake of 948%.The LC membrane-based alkaline hydrogel electrolyte(LC-GPE)has an ion conductivity of up to 32.6 mS cm-1 at room temperature.The symmetric SC assembled with LC-GPE and activated carbon electrode has a high specific capacitance of 120 F g-1 at 1 A g-1.Even if the current density is increased by 10 times,its capacity loss is only 8.4%,and it has 92.5%capacity retention rate and nearly 100%Coulomb efficiency after 10,000 charge-discharge cycles.In addition,the flat SC composed of LC-GPE and activated carbon electrode is easy to bend to 1800 without cracking,and maintains good electrochemical performance.These results indicate that LC-GPE not only meets the requirements of green/sustainability,but also significantly improves the electrochemical performance of SCs.(2)In the acidic system,LC membrane has excellent mechanical propertie(stress of 10.1 Mpa),ultra-high electrolyte uptake of 1300%,and strong acid resistance.The acidic hydrogel electrolyte(LC-H2SO4)prepared from LC membrane and 1 mol L-1 H2SO4 solution has good ionic conductivity.When the current density increased from 0.5 A g-1 to 5 A g-1,the SC assembled from LC-H2SO4 and activated carbon has only a 10%capacity loss,and after 20,000 long cycles,the capacity retention rate was 115%.The 15%increase in capacity may be attributed to that the hemicellulose dissolved in electrolyte improves the interfacial compatibility,and tis oxygen-containing functional groups provide partial faradic pseudocapacitance.Furthermore,the flat SC assembled with LC-H2SO4 containing a higher concentration of H2SO4 shows better electrochemical performances,and the flat flexible SC assembled with LC-H2SO4 has good bending properties.Therefore,the LC-H2SO4 containing higher H2SO4 concentration(such as 3 mol L-1)can be used to assemble SCs to improve their electrochemical performances,and LC-H2SO4 can be used to prepare flexible SCs such as wearable and flexible.(3)In the neutral system,the LC-based membrane(LC-FD)prepared by the freeze-drying method has an ultra-high porosity of 95%and a high electrolyte uptake of 1100%.The neutral hydrogel electrolyte(LC-FD-Li2SO4)based on the LC-FD membrane has a high degree of gelation,exhibits an ionic conductivity similar to that of the liquid electrolyte,and maintains better electrochemical stability than liquid electrolyte at a high operating voltage of 1.8 V.The specific capacitance of SC based on LC-FD-Li2SO4 at 1 A g-1 is 138.4 F g-1,and its capacity retention rate is still 88%after 10,000 cycles at 1.8 V,much higher than the 53%retention of liquid electrolyte-based SC.This is mainly due to the fact that LC-FD membrane inhibits the activity of water molecules in LC-FD-Li2SO4 through both physical and chemical effects.In addition,LC-FD-Li2SO4-based SC can output a 16.08 Wh Kg-1 maximum energy density.These results indicate that LC-FD-Li2SO4 is a neutral hydrogel electrolyte that is suitable for preparing high-voltage aqueous SCs with high safety performance and environmental friendliness.