Redox flow batteries for energy storage

Abstract

The concept of redox flow batteries (RFBs) is explained and their importance in grid level electrical energy storage is highlighted. The benefits of their modular configuration are linked to a flexible service operation, improved safety, recyclability, moderate costs and reduced environmental impact. Types of RFBs are classified and examples of their electrochemistry are provided, for both commercial devices and promising systems under development. Critical design features of electrodes, unit cells, cell stacks and balance of plant are summarised, together with the role of the power conditioner and the battery management system. Benefits and implications of electrolyte flow are considered and operational parameters affecting cell efficiency, performance and scale-up are given. These include cell resistance, reaction environment, mass transfer, shunt currents and pressure drop as well as cross-over through the membranes. Fundamental electrochemical and techno-economical figures of merit are surveyed. Failure mechanisms and durability are discussed. The scope of validated mathematical modelling and simulation in the design process of efficient RFBs is reviewed. The application of RFBs is illustrated at different scales and competition with other devices is briefly explored. Trends in RFB development and application opportunities are followed by further R & D needs