No abstract

All-vanadium redox flow batteries (VRBs) are potential energy storage systems for renewable power sources because of their flexible design, deep discharge capacity, quick response time, and long cycle life. To minimize the energy loss due to the shunt current, in a traditional design, a flow field is machined on two electrically insulated frames with a graphite plate in between. A traditional bipolar plate (BP) of a VRB consists of many components, and thus, the assembly process is time consuming. In this study, an integrally molded BP is designed and fabricated to minimize the manufacturing cost. First, the effects of the mold design and injection parameters on frame formability were analyzed by simulation. Second, a new graphite plate design for integral molding was proposed, and finally, two integrally molded BPs were fabricated and compared. Results show that gate position significantly affects air traps and the maximum volume shrinkage occurs at the corners of a BP. The volume shrinkage can be reduced using a large graphite plate embedded within the frame.

An all-vanadium redox flow battery (VRFB) system, with multiple stacks, is typically used for large-scale electrical energy storage applications. In a VRFB system, pumps deliver positive and negative electrolytes, through a piping system, to each stack. Because the electrolytes are electrically conductive, shunt currents can occur within a multicell stack and within the piping system, connecting the stacks due to the voltage differences between cells and between stacks. Shunt currents cause energy loss and are affected by the number of cells in a single stack, the number of stacks, and the piping system dimensions. In this study, we develop a mathematical model, based on Kirchhoff's law, to locate shunt currents in a multistack system. Using this model, we estimate the charge efficiency with various numbers of stacks. The results show that the shunt currents in the central stacks are larger than the currents in other stacks. In addition, the piping system dominates the distribution of the electrolytes, and the shunt currents gradually shift from inside the stack to the piping system.