A Stable Vanadium Redox‐Flow Battery with High Energy Density for Large‐Scale Energy Storage

Abstract

The all-vanadium redox fl ow battery is a promising technology for large-scale renewable and grid energy storage, but is limited by the low energy density and poor stability of the vanadium electrolyte solutions. A new vanadium redox fl ow battery with a signifi cant improvement over the current technology is reported in this paper. This battery uses sulfate-chloride mixed electrolytes, which are capable of dissolving 2.5 M vanadium, representing about a 70% increase in energy capacity over the current sulfate system. More importantly, the new electrolyte remains stable over a wide temperature range of − 5 to 50 ° C, potentially eliminating the need for electrolyte temperature control in practical applications. This development would lead to a signifi cant reduction in the cost of energy storage, thus accelerating its market penetration.

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

“…Figure 8d shows four iterations of charge/discharge profiles of the 20S-26KB catholyte in an intermittent-flow mode at 4 mA cm À 2 , demonstrating catholyte volumetric capacity between 110-155 Ah l À 1 . The power output of the semi-solid sulphur flow cell is comparable to other nonaqueous semi-solid flow cells 13,24 , but significantly lower than aqueous flow cells 3,5,26 . Further improvements on the single-cell stack design, electrical conductivity and interfacial contacts in the flow cathode are expected to improve the power output of the semi-solid sulphur flow system.…”

“…9). In addition, the solid-sulphur flow cathode exhibits similar power capability compared with other nonaqueous semi-solid flow chemistries 13,24 , but significantly lower power output compared with the aqueous all-vanadium flow batteries 3,5,26 . The hybrid configuration used in our study limits the scalability of the negative electrode 17 , which can be improved by replacing the lithium metal with semi-solid negative flow catholytes such as the semi-solid silicon anolyte 27 .…”

“…Figure 9 shows the achieved catholyte volumetric capacity reported in this work (both in 'zero-gap' and '1-mm-gap' cells) in comparison with reported Li-flow-cathode chemistries at various current densities 12,23,24 . The highly concentrated (20 vol% S, 12.9 M [S]) sulphur-impregnated carbon composite catholyte introduced in this work demonstrates substantial improvement in volumetric capacity compared with other aqueous 3,5,26 and nonaqueous 12,23,24 flow chemistries (Fig. 9).…”

“…Achieved catholyte volumetric capacities in this work (half-filled symbols) are compared with various reported work discussed earlier 12,23,24 . Open symbols were calculated from the work of Fan et al 23 , Yang et al 12 and Hamlet et al 24 The dotted green area denotes the range of the catholyte volumetric capacity (2.7-19 Ah l À 1 ) achieved and current density used in the work of Hamlet et al 24 The dotted grey area denotes the state-of-theart performance of all-vanadium flow batteries 26 . Preparation of the S/C composite.…”

“…9) 12,23,24 , but significantly lower than the state-of-the-art aqueous flow-battery chemistries (for example, all-vanadium system 50-500 mA cm À 2 , Fig. 9) 3,5,26 . Substantial decrease in volumetric capacity/efficiency only occurred after the first cycle, which could be attributed to the inefficiency of the lithium anode and/or the loss of polysulphide 44 .…”