Sulphur-impregnated flow cathode to enable high-energy-density lithium flow batteries

Redox flow batteries are promising technologies for large-scale electricity storage, but have been suffering from low energy density and low volumetric capacity. Here we report a flow cathode that exploits highly concentrated sulphur-impregnated carbon composite, to achieve a catholyte volumetric capacity 294 Ah l−1 with long cycle life (>100 cycles), high columbic efficiency (>90%, 100 cycles) and high energy efficiency (>80%, 100 cycles). The demonstrated catholyte volumetric capacity is five times higher than the all-vanadium flow batteries (60 Ah l−1) and 3–6 times higher than the demonstrated lithium-polysulphide approaches (50–117 Ah l−1). Pseudo-in situ impedance and microscopy characterizations reveal superior electrochemical and morphological reversibility of the sulphur redox reactions. Our approach of exploiting sulphur-impregnated carbon composite in the flow cathode creates effective interfaces between the insulating sulphur and conductive carbon-percolating network and offers a promising direction to develop high-energy-density flow batteries. Redox flow batteries are a promising technique for large-scale electricity storage, but suffer from low energy density and volumetric capacity. Here, the authors present a lithium redox flow battery with a sulphur-impregnated carbon composite as the catholyte, which leads to substantial performance improvement.