Solid-State Hybrid Fibrous Supercapacitors Produced by Dead-End Tube Membrane Ultrafiltration

The development of flexible supercapacitors with high volumetric performance is critically important for portable electronics applications, which are severely volume limited. Here, dead-end tube membrane (DETM) ultrafiltration is used to produce densely compacted carbon-nanotube/graphene fibrous films as solid-state supercapacitor electrodes. DETM is widely used in the water purification industry, but to date its use has not been explored for making supercapacitor electrode materials. Compared with vacuum-assisted filtration, dead-end filtration of the mixture through a porous membrane is carried out under much higher pressure, and thus the solvent can be gotten rid of much faster, with less energy consumption and in an environmentally friendly manner. More importantly, phase separation of the solid constituents in the mixture, due to concentration increase, can be suppressed in DETM. Therefore, highly uniform and densely compacted supercapacitor electrodes can be obtained with very high volumetric energy and power density. The volumetric energy density in this work (≈2.7 mWh cm^-3) is at a higher level than all the all-solid-state fibrous supercapacitors reported to date. This can be attributed to the DETM process used, which produces a densely compacted network structure without compromising the availability of electrochemically active surface area.