A lignocellulose-based neutral hydrogel electrolyte for high-voltage supercapacitors with overlong cyclic stability

A lignocellulose biomass-based membrane (LC-FD) with ultra-high porosity of 95% and high electrolyte uptake of 1100 wt% is prepared by freeze-drying method to fabricate a Li2SO4-based neutral hydrogel electrolyte (LC-FD-Li2SO4). LC-FD-Li2SO4 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 LC-FD-Li2SO4-based SC at 1 A g-1 is 138.4 F g-1, higher than that of liquid electrolyte-based SC. This is due to the ultra-high porosity of LC-FD membrane not only for electrolyte storage provides enough space, and also provides more channels for ion transmission. More importantly, LC-FD-Li2SO4-based SC has the 88% retention after 10,000 cycles at a working voltage of 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. Moreover, 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.