Micro-patterned metal current collectors for high aspect ratio flexible graphene supercapacitors

When graphene thin films are used as high aspect ratio supercapacitor electrodes, their performance can be limited due to graphene's relatively low electrical conductivity, compared with metals. The integration of the graphene film with a metal current collector can overcome this limited conductivity. However, poor adhesion between pristine graphene and metal films adversely affects a supercapacitor's flexibility. In this study, a metal current collector film was patterned on a flexible substrate in the form of a microgrid, via selective laser sintering of silver nanoparticles. The delamination of the graphene film was mitigated by interlocking it with the substrate using laser transmission welding. A specific capacitance of 5.8 mF/cm(2) was obtained at 1.5 mA/cm(2) with PVA-H3PO4 electrolyte, and the capacitance was retained at up to 94% when the electrode length was increased by six times. In addition, a thin gold (Au) layer was electrodeposited to the silver grid to improve its electrochemical stability. As a result, the capacitance change remained below 10% for 10,000 charging/discharging cycles. The electrodeposition of pseudocapacitive manganese dioxide (MnO2) nanoparticles was also performed, further increasing the capacitance to 49.1 mF/cm(2) at 1 mA/cm(2) with 0.5 M Na2SO4 electrolyte.