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COMMUNICATIONS CHEMISTRY | https://doi.org/10.1038/s42004-022-00626-2 ARTICLE Fig. 4 Electrochemical characterization γS-CNFs. a Charge–discharge patterns of γS-CNFs in ether electrolyte (DME: DOL) and carbonate electrolyte (EC: DEC). b Cyclic voltammetry curves of γS-CNFs in ether electrolyte (DME: DOL) and carbonate electrolyte (EC: DEC) at 0.1 mV·s−1. c Cycling stability of γS-CNFs in EC: DEC at a current rate of 0.5 C. d The charge–discharge profiles of γS-CNFs at various cycle numbers. e Differential capacity analysis plot of γS-CNFs displaying a single peak in the charge–discharge cycle. f Nyquist plot of γS-CNFs cathode as a function of voltage during the charge–discharge cycle. The cells were assembled with S loading of 0.5 mg·cm−2 using ~50 wt% sulfur in the cathode and an E/S ratio of 20. the sulfur cathode with and without resting time (Supplementary Fig. 3). Initially, the results demonstrate a small surface charge transfer resistance (~110 ohm) indicating good conductivity of the electrode and efficient interfacial contact which further decreases with resting time (~30 ohm). The electrode demon- strates a reversible electrochemical redox behavior in both elec- trolytes. However, the charge-discharge profiles are drastically different (Fig. 4a). The ether electrolyte charge-discharge profile exhibits a standard two-plateau behavior as reported in most prior literature reports1,6. The first plateau at 2.3 V is attributed to the conversion of sulfur to long-chain polysulfides and the second plateau at 2.1 V represents the conversion of long-chain poly- sulfides to Li2S2 and Li2S (2.1 V). However, the same γS-CNFs cathodes in carbonate electrolytes demonstrate a single plateau at 2.0 V in the first and all consecutive cycles during discharge and 2.2 V in charge profiles suggesting the possibility of a polysulfide digression route to directly form lithium sulfide in carbonate electrolyte. This solid-to-solid conversion possibly also leads to a higher overpotential explaining the lower plateau voltage observed in carbonate electrolytes. The electrochemical behavior is consistent with CV profiles, wherein the cells with ether elec- trolyte show two peaks, while the cells with carbonate electrolyte only show a single peak as shown in Fig. 4b. Figure 4c shows the long-term cycling data for cells made using carbonate electrolyte tested at 0.5 C current rate. The cells exhibit a capacity of 800 mAh·g−1 after the first few cycles with only 0.04 % decay beyond that. The cells still retain a capacity of 658 mAh·g−1 even after 4000 charge-discharge cycles. To the best of our knowledge, this is the highest achieved reversible capacity after 4000 cycles to date. The initial drop in capacity may be attributed to the loss of contact due to volume expansion during cycling which stabilizes as the cycling proceeds. It is well-known in the literature that pure uncoated lithium anodes are unstable and commonly have poor rate capabilities since the high current would dramatically promote the formation of lithium dendrites. Never- theless, to keep the focus of our work on the development of the cathode and its ability to perform with single plateau behavior in carbonate electrolyte, we used excess (thick) lithium, so the anode is not expected to be a limiting factor. Postmortem digital images (Supplementary Fig. 4) after opening the cell show a thick layer of dead porous lithium on the anode. Scraping the top part shows a clear lithium anode. We believe the thick lithium foil used as counter/reference electrode in our cells contributes towards long- term cycling. However, in the future, anode stabilization strategies are required to reduce the thickness of Li, minimize continuous side reactions of Li with electrolyte, and for uniform Li deposition As shown in Fig. 4d, the discharge profile continues to exhibit a single plateau through the entire cycle life of 4000 cycles. The reduction in capacity after cycling is possibly due to the reaction of carbonate electrolytes. It is established from a recent report by Yim et al. that polysulfides (if generated) attack carbonate species via nucleophilic substitution reaction to form irreversible products— thiocarbonate and ethylene glycol—and shut down further electrochemical activity after the first cycle21. Therefore, our data suggest that these γS-CNF-based cells continue to follow a polysulfide digression route through the entire cycling in carbonate electrolyte, which explains not only continued battery operation despite the presence of carbonate species but also our excellent cycle stability of 4000 cycles. For comparison of long-term stability, we have shown cycling data of γS-CNF in ether and carbonate electrolyte with similar sulfur loading and the current rate of 1C (Supplementary Fig. 5). The cathode in ether electrolyte follows a standard route with polysulfides as the intermediate products with two-plateau discharge. Here we see a gradual decline in capacity due to the expected polysulfide shuttling and subsequent loss of active material. To demonstrate the detrimental effects of shuttling COMMUNICATIONS CHEMISTRY | (2022)5:17 | https://doi.org/10.1038/s42004-022-00626-2 | www.nature.com/commschem 5 Content courtesy of Springer Nature, terms of use apply. 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