To flow or not to flow. A perspective on large-scale stationary electrochemical energy storage

Energy storage is experiencing a renaissance as a result of the growing number of vital applications such as internet of things, smart grids, electric vehicles, renewable energy storage, etc. In particular, stationary energy storage must be urgently deployed at a large-scale to support full deployment of renewables and a sustainable grid. Electrochemical energy storage systems (EESS) will be key in this pursuit. Yet, present mature technologies are all sub-optimal. A myriad of new battery chemistries are being developed in research labs, each with specific strengths and drawbacks. EESS technologies such as lithium-ion batteries, lithium-sulfur, metal-air and other post-lithium technologies, but also supercapacitors, hybrid devices and redox flow batteries (RFBs), could benefit from collaborative development between top-down systems engineering and bottom-up material science. Lithium and post-lithium systems have been extensively researched and reviewed. This perspective article examines the energy storage landscape that goes from state-of-the-art flow cells to novel flowing and stationary technologies. While there is a wide scope for improvement of first generation RFBs, a wealth of novel concepts such as ambipolar electrolytes or shuttle cells to semisolid electrodes are also emerging. This could boost the energy density of these flowing systems. In our analysis we also propose other new concepts which could eventually lead to non-flowing large-scale electrochemical energy storage. Schematic comparative diagram of the stages involved in moving from compact solid electrode materials to dilute nanofluids and RFB solutions.