Redox flow stacks with tubular cell design—Feasibility and performance

Redox flow batteries are a reliable option for the storage of energy from renewable resources and the all vanadium cell chemistry features the highest level of commercialization. The storage market demands further cost reductions. A tubular cell design can lower power specific costs by featuring reduced material needs and enabling the use of cost efficient extrusion processes of cell components. The feasibility of tubular all vanadium cells has already been shown in previous studies of the authors. In this study, we report on the progress of a recent cell generation and the integration of single cells into stacks. The performance of the current cell and stack generation has reached the region of planar cells with discharge current densities of i d c h > 300 mA cm -2 at S O C ≈ 0 . 5 and U c e l l = 0 . 8 V as well as maximum power densities of P / A r e a > 300 mW cm -2 with respect to the membrane area and of P / V o l u m e > 750 kW m -3 with respect to the cell body volume. The single cell performance turns out to be reproduceable with negligible losses at stack level in a 5p setup. In this way, the feasibility of tubular stacks is demonstrated. We claim the tubular approach to be transferrable to other cell chemistries. • Feasibility of redox flow stacks with tubular cell design demonstrated. • Improved extrusion production process for tubular cell components. • Performance improvements: in the range of planar cells. • Reproducible cell performances. • Negligible performance losses from cell to stack level.