Connection of Bipolar Plate with Graphite Felt Electrode for Vanadium Flow Battery Using a Powder Thermal Unification Method

Carbon felt electrodes are usually compressed against the bipolar plates in order to decrease the contact resistance, but it leads to high pressure drop and consumption of pumping energy in conventional vanadium redox flow battery stacks. This paper describes the fabrication of an effective way to unify the bipolar plate and graphite felt electrode in order to improve the battery efficiency at lower felt compression pressure. The unification process involves a thermal fusion technique with a component design consisting of bipolar plate, graphite felt electrode and connecting powder. The powder comprises either polyvinylidene difluoride or a mixture of polyvinylidene difluoride and conductive carbon black. The interfacial bonding substance determines the electrical resistance of the resultant fabricated unified assembly. The electrical resistance results prove that the carbon black proportion in the bonding element substantially reduces the electrical resistance. The optimum quantity of carbon black in the powder is found to be 40 wt%. Micro-computed tomography analysis findings indicate that thermally unified assembly interfacial contact electrode porosity is slightly lower than that of an unbonded sample. A two-cell vanadium redox flow battery stack with integrated unified assembly achieves a rather constant energy efficiency of 76% during 100 cycles with 5% electrode compression at a current density of 80 mA cm −2 .