A Co-Axial Microtubular Flow Battery Cell with Ultra-high Volumetric Power Density

Volumetric power density is a key factor determining flow batteries' footprint, capital cost and ability to handle uneven energy resource distributions. While significant progress has been made on flow battery materials and electrochemistry to improve energy density, conventional flow battery assemblies based on planar cell configuration exhibit low packing efficiencies and membrane surface area per volume of the cell, thus resulting in low volumetric power density. Here, we introduce a co-axial microtubular (CAMT) flow battery cell that significantly improves the volumetric power density. This cell design overcomes the intrinsic power limit of planar cell configuration and is suitable for all mainstream flow battery chemistries. Using zinc-iodide chemistry as a demonstration, our CAMT cell shows peak charge and discharge power densities of 1322 W/Lcell and 306.1 W/Lcell compared to average charge and discharge power densities of < 60 W/Lcell and 45 W/Lcell of conventional planar flow battery cells. In addition, the battery can cycle for more than 220 hours, corresponding to > 2,500 cycles at off-peak conditions. Furthermore, we have also demonstrated that the CAMT cell is compatible with zinc-bromide, quinone-bromide, and all-vanadium chemistries. The CAMT flow cell represents a device-level innovation to enhance the volumetric power of flow batteries, and potentially reduce the size and cost of the cells and the entire flow battery. The CAMT design can potentially be applied to other electrochemical systems and lead to a paradigm shift in flow battery fundamental study and commercialization.