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Polysulfide-based redox flow batteries with long life and low levelized cost enabled by charge-reinforced ion-selective membranes


Polysulfide is one of the most promising aqueous redox chemistries for grid storage owing to its inherent safety, high energy and low cost. However, its poor cycle life resulting from polysulfide cross-over has prohibited its successful commercialization. To exploit low-cost and high-capacity polysulfide flow batteries with industrial-relevant cycling stability, we develop a charge-reinforced ion-selective membrane to retain polysulfide/iodide, restrain membrane swelling and prevent water/OH migration. The polysulfide/polyiodide static cell demonstrates a low capacity decay rate (0.005% per day and 0.0004% per cycle) over 2.9 months (1,200 cycles) at a 100% state of charge. A flow cell containing 4.0 M KI/2.0 M K2S2 demonstrated stable cycling at 17.9 Ah l−1posolyte+negolyte over 3.1 months (500 cycles). Small-angle X-ray scattering and in-situ attenuated total reflectance–Fourier transform infrared/solid-state NMR revealed reduced water cluster size and restrained water movement in the charge-reinforced ion-selective membrane compared to commercial Nafion membrane. Techno-economic analysis shows that the developed polysulfide flow battery promises competitive levelized cost of storage for long-duration energy storage.

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Fig. 1: Different processes in PSIBs with a Nafion and CRIS membrane.
Fig. 2: Permeability and self-discharge.
Fig. 3: Long-term galvanostatic cycling measurements of PSIBs at static mode.
Fig. 4: Electrochemical performance of scale-up PSIBs under continuous flow mode.
Fig. 5: Mechanism of water migration through N117 and CRIS membrane.
Fig. 6: Cost analysis of emerging RFBs.

Data availability

All relevant data are included in the paper and its Supplementary Information. Source data are provided with this paper.


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The work described herein was supported by two grants from the Research Grant Council (RGC) of the Hong Kong Special Administrative Region, China (project no. T23-601/17-R and N_CUHK435/18, received by Y.-C.L.). We thank B. T. W. Lo and the University Research Facility in Chemical and Environmental Analysis (UCEA) from Hong Kong Polytechnic University for assisting with ssNMR measurements, J. Lei for assistance in building up the flow system and W. Wang for assisting with SEM image collection.

Author information




Z.L. and Y.-C.L. conceived the project. Z.L. designed and conducted the experiments and performed the electrochemical and characterization tests. Both authors analysed the data, discussed the results and wrote the manuscript.

Corresponding author

Correspondence to Yi-Chun Lu.

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Peer review information Nature Energy thanks Wei Wang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Information

Supplementary Figs. 1–23, Tables 1–7, Notes 1–7 and ref.

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Source Data Fig. 6

Source data of bar chart in Fig. 6b and pie chart in Fig. 6c.

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Li, Z., Lu, YC. Polysulfide-based redox flow batteries with long life and low levelized cost enabled by charge-reinforced ion-selective membranes. Nat Energy 6, 517–528 (2021).

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