Hydraulic Aspects of Redox Flow Batteries: Flow Fields and Hydraulic Circuits

Abstract

Electrolyte flow is a vital process within redox flow batteries. Firstly, electrolyte flow is critical within the battery stacks to ensure optimal delivery of redox species to the electrodes. The architecture of the bipolar plate/electrode pair has been developed either in rectangular flow-through channels or in interdigitated flow fields, which increase power density while reducing pressure drop. Uniform compression of the porous electrode and adequate contact between the bipolar plate and the porous electrode are important to achieve a low (ohmic) contact resistance. Simulations can be used to optimize the flow field and electrode geometry, minimizing the pumping energy losses and ensuring a sufficient permeability of the compressed porous electrode. Furthermore, a controlled, relatively uniform reaction environment is desirable to minimize resulting effects from secondary and tertiary current distribution. Secondly, electrolyte flow is also of importance within the electrolyte recirculation loop, in which pumps are responsible for the flow from the storage tanks to the stacks (and back) through a piping ancillary system, with the design criteria of low pumping losses and reliable operation. Modeling by computational fluid dynamics has become an important tool for the mechanical design of the balance of plant. Several possible modes of operation, each with its advantages and limitations, are possible. Failure mechanisms related to the presence of conductive fluids can be prevented by adequate choice of materials and controlled operational conditions. Practical aspects, common challenges and trends relative to the hydraulic system of redox flow batteries are described.