Nitrogen and Sulfur Co-Doped Porous Carbon Derived from Thiourea and Calcium Citrate for Lithium-Sulfur Batteries
Round 1
Reviewer 1 Report
Materials studied here is interesting but this reviewer needs more explanation for better understanding from readers. This manuscript cannot be published in this present situation.
How to load sulfur in CaC-S (and CaC/TU-S) is not clearly described. How the structure CaC/TU-S was clarified is not described. Base weight of the specific capacity is not clear. g/S or g/active material? In 2.2., reviewer doesn't understand why LiPF6 should be washed out. No description for LiPF6 containing electrolyte in 2.3. in p.6 l.165, S2P3/2 and S2P1/2is not correct. In fig.6(a), why capacity decreased so much after changing C-rate to 1C? Sulfur loading was 0.7mg/cm2 and it does not seem so much. In fig.6(b), fitting results were shown, but how was this fit carried out ? What equivalent circuit? Merit of materials developed here should be compared with other report quantitatively for insisting the merit of this manuscript.
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Reviewer 2 Report
This paper presented a simple way to prepare a N- and S-doped mesoporous carbon material for lithium-sulfur batteries. The work is interesting, however, a major revision is very necessary before its final publication and some problems need to be clarified. Several points were addressed as follows:
English has to be improved in this paper (including the title). It is quite difficult to follow the entire message in this paper. The authors should pay attention to abbreviations. For example, CaC represents calcium citrate in abstract while it means calcium citrate based carbon later in this paper. In line 174, there is a mistake about CaC (600mAh/g for CaC/TU). In introduction part: in line 37, it is better to specify the type of the commercialized cathodes. There are a large number of cathode materials for various rechargeable systems; in line 39-41, the message is not clear; in line 52, carbon matrix; in line 55, please explain the reason for “no activation process is necessary” and give at least one reference. For synthesis section, please rewrite sentences in line 106-109. The treatment with thiourea could also introduce sulfur between graphene layers in the structure of a carbon. Without further investigation, it is not appropriate to only put sulfur doping in graphene layer as shown in your figure 1 (b). I did not understand the existence of figure 1 (c). For XRD results, please write down the type of radiation used in your experiments and add the reference peak position for Sulfur. Please improve the resolution of your TEM images and they are transmission electron micrographs not transition electron micrographs. For TGA analysis, according to the values in the figure (21% and 28%), I cannot agree with your conclusion in line 148 (66% and 75%). For XPS results, it is necessary to prove the existence of S and N (and indicate their quantities) in CaC/TU without further loading of sulfur. For electrochemical studies, it is necessary to present the electrochemical curves for the first cycle, 10th and 100th and indicate the current for 1C, the columbic efficiency for the first cycle. There is a huge decrease of specific capacity for the 6th I wonder if the current is the same for the whole cycling. Furthermore, the author should compare their results with literature.
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Round 2
Reviewer 1 Report
This manuscript was revised and now much more comprehensive as a paper.
This reviewer has two more subtle questions and this can be published after fixing them.
For question No. 4 in reviewer 1; Authors could not answer why "LiPF6" have to be washed in the original manuscript. This could be suspected as just a small mistake. For XPS (Fig.4(a)); S2p spectra usually are split into S2p1/2 and S2p3/2. Did authors subtract the S2p1/2? And x-axis of XPS is usually opposite.
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Reviewer 2 Report
This version is more comprehensive. In line 24, CaC corresponds to calcium citrate based carbon not to calcium citrate.
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