PEI/Super P Cathode Coating: A Pathway to Superior Lithium–Sulfur Battery Performance
, Kyuchul Shin 2, In Woo Cheong 2, Hyunchul Kang 3, Songhun Yoon 3,*, Won-Gwang Lim 4, Jinwoo Lee 4,* and Jin Joo 1,2,*
Round 1
Reviewer 1 Report
The authors describe an efficient method to prolong cycle life of Li-S battery by cheap poly(ethylene imine)/carbon composite layer over cathode active material. This is a significant contribution in the way of potential commercialization of Li-S battery. The manuscript is well written, in clear and correct language, and the results are well supported by experiments. However, I found some flaws which should be corrected before acceptance:
1. The theoretical energy density of Li-sulphur batteries in Abstrac t (2400 Wh/kg) and first paragraph of Introduction (2600 Wh/kg) should be harmonized
2. The data about mass loading of electrodes in both symmetric and three-electrode cells are missing. Further to this, what material (pure S or any composite) is used to calculate current density and specific capacity in Figs 2-4?
3. The diffusion coefficient determined by means of Eq.1 should be called apparent diffusion coefficient, for at least two reasons: 1. The criterium for the use of Eq 1 is pure diffusion control of observed electrode reaction (manifested itself as an independence of peak potential on scan rate, i.e. constant peak-to peak potential difference at each scan rate) which is not fulfilled here. 2. The electrode surface area in Eq 1 is true area which should be determined by specific surface area determination methods. The use of geometric surface area may induce magnitude orders higher result. (See the article: Electrochimica Acta 190 (2016) 1087–1099, and the discussion, Sect. 3.2. in: J. Power Sources 325 (2016) 185-193). This reserve about the exact value of diffusion coefficient should be mentioned in Discussion section
Author Response
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Reviewer 2 Report
Lithium-sulfur batteries offer high energy density, affordability, and environmental benefits but face challenges like capacity fading due to the shuttle effect. This study proposes enhancing lithium-sulfur battery performance by coating the sulfur cathode with a layer of polyethyleneimine (PEI) and Super P conductive carbon. This modification retained 73% of its capacity after 300 cycles and effectively mitigated the shuttle effect by adsorbing lithium polysulfides. The method is cost-effective and suitable for industrial production, making it a promising approach for advancing lithium-sulfur batteries. Thank you for your dedicated effort in writing this paper. It is a valuable contribution to the field. However, the authors requested to address the following aspects to improve the quality of the paper.
1. Please improve the image quality
2. Beyond referencing prior research, what technical justifications underlie the selection of the composite composition sulfur:Super P:PVDF in a 60:30:10 weight ratio, and the application of a 5-μm-thick PEI/Super P coating layer on the electrode surface in the context of enhancing the performance of lithium-sulfur batteries or similar electrochemical systems?.
3. Why did the authors opt for the utilization of larger-sized commercial Super P and sulfur particles, which exhibited a size distribution in the tens of micrometers, when current research predominantly focuses on nanomaterials for cathode design? Are there specific scientific or practical reasons underpinning this choice?
4. Can the assertion of improved performance resulting from the suppression of the shuttling effect be substantiated through comprehensive analytical studies that provide physical evidence of reduced polysulfide migration, enhanced cathode stability, and improved electrochemical behavior in the context of this specific study?
5. It will be clearer if the authors can provide a Schematic illustration of how the shuttling effect is suppressed
6. Why does the PEI/Super P coated layer effectively adsorb lithium polysulfides?
7. The pore structure, porosity, and surface area of the electrode play a key role in the process. However, the authors did not include these aspects.
8. The characterization part will be more strong if you can include XRD, TGA studies.
9. Line 160,161: How this coating improved the contact area and effective LiPS trapping. Any evidence in the study?
10. Line 305: How authors calculated sulfur utilization rates
Author Response
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Reviewer 3 Report
In batteries-2645256 "PEI/Super P Cathode Coating: A Pathway to Superior Lithium-Sulfur Battery Performance", authors report on composite PEI/Super P cathode for Li-S batteries. The paper is well-written, and rigorous electrochemical studies are presented, however, the structure of the carbon-based component and the motivation behind its choice are obscure to me, therefore I recommend a major revision of the manuscript.
Major comments:
1) Parameters of Super P material should be discussed in more detail, as porosity, oxygenation, sp2/sp3 ratio, disordering, and electrical conductivity are crucial parameters of electrode components. Consider providing the structural investigations and/or appropriate references elaborating of Super P structure and properties. In addition, consider discussing the motivation behind the Super P choice as electrode component basing on its features: carbon is widely applicable as Li-S batteries electrode component [10.3390/batteries8060058, 10.3390/batteries9060289], why it is “super P” modification that is essential to enhance the battery performance?
2) Lines 108-109, "Super P was annealed for 3 h at 700 °C in a 5% H2/Ar atmosphere prior to use.": it is also unclear how the structure of the super P is modified in the course of the annealing and other steps of electrode preparation. Do graphitization and disordering take place, is the surface of the material modified, does its porosity change, are these changes desired or not? Appropriate structural investigations should be carried out.
Minor comments:
3) Lines 21-22, "The PEI/Super P-modified electrode retained 73% of its discharge capacity after 300 cycles":
4) Section 2.1, line 102: what allotropic modification of sulfur was used?
5) Line 44, "Ø14": what are the measurement units?
6) The peak at 0.11 V marked in Fig. 2(a) is not discussed in the text. Consider supplementing the manuscript.
7) In Fig. 2(a,d), revise the "SuerP" notation in the legend related to the red line.
8) In Fig. 2(c), consider adjusting the Y scale to make analyzed voltammetries more distinguishable for the readers.
9) Lines 223-225, "This can be attributed to the increase in electrolyte viscosity as sulfur transitions to polysulfides, leading to a significant decrease in Li+ ion diffusion": consider providing appropriate references proving your point.
10) Lines 225-226, "Additionally, the crystallization of Li2S2 also demands more energy, further contributing to this observation": please kindly elaborate what conditions lead to the increase of the energy required for the crystallization.
11) in the discussion of eq.1, the measurement units related to all of the variables should be provided.
Overall English is clear and understandable. Minor comment:
12) Lines 290-291, by "As a result, PEI/Super P-modification not only suppress the shuttle effects but also enhance", did you mean "suppresses ... enhances"?
Author Response
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Reviewer 4 Report
Authors boosted the performance of lithium-sulfur batteries by modifying the sulfur cathode with a coating layer composed of polyethylene-imine (PEI) and Super P conductive carbon. The PEI/Super P coated layer effectively adsorbs lithium polysulfides, suppressing the shuttle effect and acting as an auxiliary electrode to facilitate the electrochemical reactions of sulfur/Li2S. I believe that the use of PEI (Polyetherimide) is of utmost importance for lithium-sulfur batteries. It can serve as a novel coating layer or binder. This manuscript is significant and has the potential to inspire thoughts among researchers and professionals in the field of lithium-sulfur batteries, ultimately contributing to their future commercialization.
Author Response
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Round 2
Reviewer 2 Report
The authors' response is satisfactory, and I appreciate the efforts taken to improve the quality of the manuscript. Thank you
Author Response
We deeply appreciate the reviewer's positive comment.
Reviewer 3 Report
Review 2.
Manuscript ID: batteries-2645256
Title: PEI/Super P Cathode Coating: A Pathway to Superior Lithium-Sulfur Battery Performance
Authors have carried out a rigorous revision of the manuscript and provided detailed response to my questions. However, the presentation of newly-reported studies (Raman spectroscopy and BET) has some room for improvement. In particular,
1) Lines 115-117, what setup was used for BET characterization? What was the p0 value? What adsorbed gas was tested? What temperature was set?
2) What spectrometer was used for Raman studies, what were the excitation wavelength, acqusition time, diffraction grating, excitation power? How were the spectra fitted? What type of the lines was used for the fitting?
3) Figure S1 presented in the Supplementary Materials is hardly readable. Consider increasing the font size and the thickness of the lines.
Author Response
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Round 3
Reviewer 3 Report
Authors have resolved all of the issues related to the Experimental section and methods description. I appreciate their rigoruos response and recommend the manuscript to be published in current form.
