(300f) Conductive Membrane Coating for High Performance Vanadium Redox Flow Battery Achieved By Air-Controlled Electrospray

With a growing need for the development of safe, large-scale energy storage technologies, redox flow batteries known for their high capacity, energy efficiency and low cost have attracted huge attention. Among all kinds of different flow batteries, Vanadium flow redox batteries (VFRB) are the most promising system. Yet, still, VFRB possess many issues to be solved. One of the most critical issues is the crossover of ions through expensive Nafion membrane. During the charge and discharge process, Vanadium ions, especially the V(II) and V(III) which are relatively smaller in molecular size, will diffuse to the other side due to the concentration gradient, and consequently cause self-discharge and capacity fading. Many scientists have attempted various methods to reduce the crossover effect, but they are either expensive or time-consuming, making these approaches difficult to put into practice.

In our current work, we proposed a facile and cost-effective approach using the air-controlled electrospay process to create a thin and uniform conductive coating of different carbon materials onto the surface of the separator. During the coating process, an electric field is applied to force conductive ink particles to move towards the separator substrate, while high-speed but controlled air flow is added in order to help dry the surface and better control the deposition of conductive carbon on the separator surface. Our electrochemical and single cell testing revealed that depositing a very small amount of conductive carbon (< 0.03 mg/cm²) can drastically change the surface properties of the separator such as the electrical conductivity and permeability, leading to suppressed crossover of vanadium ions, while enhancing the capacity for 28% and energy efficiency for 10% at a current density of 50 mA/cm², demonstrating that a facile conductive carbon coating on cost-effective separators has a potential to replace the costly Nafion separator in flow battery systems.