(735by) Improved Material and Design Considerations of Vanadium Redox Flow Battery for High Power Applications

Vanadium redox flow battery (VRFB) is ideally suited for grid-scale energy storage applications because of its long life, the possibility of long discharge duration, absence of fire hazards, and independent scalability of power and energy. One of the main impediments to its deployment as an energy storage system is its high capital cost, both on a per-kW basis and per-kWh basis. In the present study, we propose measures to address both factors, namely, the power and the energy storage capacity.

In a typical solar PV-driven power delivery system, the charging power of the stack is usually the limiting condition for the design of the stack. Higher power operation will reduce the stack size and cost while reducing the efficiency and energy storage capacity. We show that employing a Bismuth-activated electrode on the negative side (through in-situ deposition of Bi from BiCl₃ added to the electrolyte) can enable up to 50 to 100% higher power operation while maintaining the same energy efficiency. The energy storage capacity is increased by as much as 20% under these conditions, leading to a significant reduction in the volume of the electrolyte, which is a major contributor to the cost of the VRFB.

Bipolar plates made of thick graphite plates add significantly to the cost, weight, and difficulty of fabrication of a VRFB stack. We show that the use of thin expanded graphite or metallic sheets as bipolar plates reduces the weight and prevents electrolyte mixing by seepage. Further, the flow-through mode, as opposed to the flow-past design of the cell, can retain high storage capacity and efficiency while improving the manufacturability of the stack, leading to significant cost savings. Thus, the improved architecture of the VRFB system can deliver high power for longer durations.

Keywords: Energy storage, vanadium redox flow battery, high power operation, high storage capacity