Molten Salt-Assisted Catalytic Preparation of MoS2/α-MoO3/Graphene as High-Performance Anode of Li-Ion Battery
Round 1
Reviewer 1 Report
This manuscript reported MoS2/MoO3@graphene being an anode material for Li-ion battery. The in-situ formation mechanism of MoS2 is interesting. There are several points might be helpful for this manuscript:
1) Is there any change on the structure of MoS2 before and after ball-milling?
2) Section 2.6 states that over 400C, it is thermodynamic favorable to form the MoO3 and hexagonal MoS2. But it can’t explain why the more MoS2 was formed at 1200C. Additional data should be provided such as by re-calcinating of 1100C-sample at 1200C for a contain time and characterization their compositions may helpful.
3) besides the calculation temperature, why 20mins was chosen for annealing?
4) how about their durability test of Li-ion battery for a long time test?
Author Response
Reviewer #1:
Comment 1-1: Is there any change on the structure of MoS2 before and after ball-milling?
Response: Thanks to the reviewer for the valuable comment provided. We added the XRD result of the ball milled sample to Fig. 3. From the XRD patterns, the graphite and MoS2 materials do not show any change of crystalline structure after ball milling, while a reduction in the thickness of their flakes can be expected under the influence of the shear forces applied during the ball milling process. This revision can be found in the revised manuscript lines 152-156, and Fig. 3.
Further revision can be found in lines 194-205:
“Further characterization of samples was performed using Raman spectroscopy, and the results are shown in Fig. S4. For C-MoS2, the Raman spectrum shows two major (380 cm−1) and A1g (406 cm−1) activation modes. is due to the in-plane vibration of S and Mo atoms, and A1g is attributed to the relative vibration of S atoms in the out of plane direction. The other two relatively weak peaks observed at 285 and 450 cm−1 belong to E1g and longitudinal acoustic phonon mode in C-MoS2, respectively, as shown in Fig. S4(a). After ball milling process, the E1g peak of C-MoS2 is disappeared, and the A1g-LA (M) peak promoted. However, the structure of C-MoS2 and nature graphite phase has no significant change, as shown in Fig. S4(a). The Raman spectra of the products obtained at various temperatures are shown in Fig. S4(b). As can be seen from Fig. S4(b), in addition to peaks related to graphite and MoS2. There are also peaks related to MoO3 which are marked with red asterisk in the sample heat treated at 1100 °C. Therefore, Raman spectra confirm the formation of MoO3/MoS2@Graphene.”
Fig. S4. Raman spectra of various precursor materials and products obtained at various temperatures.
Comment 2-2: Section 2.6 states that over 400C, it is thermodynamic favorable to form the MoO3 and hexagonal MoS2. But it can’t explain why the more MoS2 was formed at 1200C. Additional data should be provided such as by re-calcinating of 1100C-sample at 1200C for a contain time and characterization their compositions may helpful.
Response: Thank you for this comment. The article was revised accordingly, and the revision can be found in 386-408:
To highlight the role of NaCl in the process, the sample prepared at 1100 °C was washed to remove its NaCl content, and the product (MoO3/MoS2@G-1100) was heated to 1200 °C for 5 min, without the involvement of NaCl. The appearance and X-ray diffraction pattern of the resulting sample are shown in Figs. S9 and 10, respectively, providing evidence that the sample heated at 1200 °C mainly contains molybdenum oxide, without the participation of molten NaCl.In this case, carbon and molybdenum disulfide content of the sample are oxidized during the heat-treatment process to form molybdenum oxide and gas species at high temperature.
It should be mentioned that oxidation in air of graphitic carbon materials typically occurs at temperatures in the range 400-800 °C, depending on their grain size, level of crystallinity and presence of impurities that can catalyze the oxidation process [52,53] leading to the formation of gashouse species and ash. It is known that the oxidation of bulk and few-layer MoS2 flakes does not readily take place at ambient conditions due to the high energy barrier involved [54-57]. However, nonisothermal oxidation of oxidation of MoS2 flakes initiates at temperatures as low as 350 °C with a limited rate, and increases by enhancing the temperature under an apparent activation energy of ≈1 kcal/mol, representing the bulk oxidation event. The oxidation process leads to the increase of molybdenum oxide content (typically MoO3), by increasing the temperature [58,59]. This is in agreement with our observation exhibited in Fig. S10. Based on observations mentioned above, the presence of NaCl provides an essential support toward the formation of MoO3/MoS2@G samples at high temperatures. First, molten NaCl provides an ionic environment to enhance the chemical reactions, while preventing the oxidation of species and supporting the exfoliation of graphite into graphenen nanosheets; the latter is discussed elsewhere [60].
Moreover, Figs. S9 and S10 were added to the article to support the discussion.
Fig. S9. Appearance of MoO3/MoS2@G-1100, the same sample after heating at 1200 ℃ for 5 min.
Fig. S10. XRD patterns of MoO3/MoS2@G-1100 and the sample obtained by heating of MoO3/MoS2@G-1100 at 1200 ℃ for 5 min.
Comment 2-3: besides the calculation temperature, why 20mins was chosen for annealing?
Response: Thank you for this valuable comment. The article was revised to answer this question, and the revision can be found in lines 613-618:
“In this research, we explored the effect of heating at various temperatures on the ball-milled natural graphite/MoS2/NaCl mixture for a short period of 20 min to demonstrate that the process of fabricating MoO3/MoS2@G samples is considerably fast. The influence of heating time on characteristics of the products needs to be explored in future studies.”
Comment 2-4: how about their durability test of Li-ion battery for a long time test?
Response: Thank you for this comment. Fig. S11 shows the cycling performance of MoO3/MoS2@G-1100 at 500 mA g-1. The specific capacity of the electrode after 400 cycles is still maintained at 240 mAh g-1 under such current density.
Reviewer 2 Report
The authors tried to synthesis MoS2/α-MoO3/graphene nanocomposite as an anode for LIB. The authors does not prepared the manuscript carefully, there are a lot of editorial mistakes present in the manuscript mentioned below. Moreover, from the scientific point of view authors has to resolve some concerns. In a nut-shell the manuscript cannot be published in its present form, it needs to be revised.
1. Authors should be careful regarding the editorial aspects. For example in page 3, line number 100-108, the text must be removed.
2. Authors should be careful for reference style. For example the bibliography for reference 7 and 8 are different. This is just example, there are many more mistakes in the bibliography.
3. Figure 2, the indication of (a), (b) …..so on, is missing.
4. Page. 4, line 160, the Table. 3 should be Table.2.
5. Why Table.3 and 4 are same?
6. In the introduction author should describe the technical differences in more details, between their preparation method and pre-existing synthesis method of MoS2/MoO3 nanocomposite. How their methods are more environmental friendly compared to the literature, as the authors used hexane for ball milling?
7. The nanocomposite was heat treated at 900-1200℃, 20 min in air, how did the authors control the carbon to carbon dioxide conversion?
8. Authors should either display the impedance curve of samples heated at 1000 and 1200℃ or compare their diffusion coefficient of lithium for the respective sample.
9. If all the measurements were conducted at room temperature then what is the driving force for high lithium diffusion at the anode? Please discuss the kinetics of lithium diffusion.
Author Response
Reviewer #2
The authors tried to synthesis MoS2/α-MoO3/graphene nanocomposite as an anode for LIB. The authors does not prepared the manuscript carefully, there are a lot of editorial mistakes present in the manuscript mentioned below. Moreover, from the scientific point of view authors has to resolve some concerns. In a nut-shell the manuscript cannot be published in its present form, it needs to be revised.
Comment 2-1: Authors should be careful regarding the editorial aspects. For example in page 3, line number 100-108, the text must be removed.
Response: Thanks to the reviewer for this valuable comment. The article was revised accordingly.
Comment 2-2: Authors should be careful for reference style. For example the bibliography for reference 7 and 8 are different. This is just example, there are many more mistakes in the bibliography.
Response: Thank you for this comment. References have been revised to meet the style of the journal.
Comment 2-3: Figure 2, the indication of (a), (b) …..so on, is missing.
Response: Thank you for this comment. Fig. 2 was modified accordingly.
Comment 2-4: Page. 4, line 160, the Table. 3 should be Table.2.
Response: Thank you for you this comment. This error was corrected accordingly.
Comment 2-5: Why Table.3 and 4 are same?
Response: Thank you for this comment. This was an error with number of Table 4, which was corrected in the revised version. The revised version reads ”Table 4. Electrode kinetic parameters for the MoO3/MoS2@G and C-MoS2 electrodes”
Comment 2-6: In the introduction author should describe the technical differences in more details, between their preparation method and pre-existing synthesis method of MoS2/MoO3 nanocomposite. How their methods are more environmental friendly compared to the literature, as the authors used hexane for ball milling?
Response: Thank you for this comment. The article was revised to cover this comment, as shown in lines 581-593:
“Selected number of methods employed in the literature for the preparation of molybdenum compounds, and their electrochemical performances are compared with those of MoO3/MoS2@G-1100 in Table 5. Methods shown in this table typical use expensive and/or hazardous materials such as (NH4)6Mo7O24∙4H2O [27,28], MoO3 [29], (NH4)2MoO4 [32], and metallic Mo powders [33], in combination with materials such as CH4N2S [27], HNO3 [28], glacial acetic acid [29], HCl [32], and H2O2 [33]. The excessive use of such chemicals limits the large-scale implementation of these methods. In the method reported here, ball milling is applied to incorporate natural graphite and MoS2 in the presence of hexane and NaCl. Both hexane and NaCl can be retrieved from the mixture after ball-milling, and the final washing step, respectively. Nevertheless, the method reported here requires heating at elevated temperatures which might provide some limitations. Utilization of industrial heat waste can be option to enhance the economic features of the method.”
Comment 2-7: The nanocomposite was heat treated at 900-1200℃, 20 min in air, how did the authors control the carbon to carbon dioxide conversion?
Response: Thank you for this comment. The article was revised to cover this point, and the revision can be found in lines 622-627:
“It should be mentioned that at 900-1200 ℃, the interaction between components occurs in molten NaCl, which can effectively reduce the reaction between carbon and oxygen forming CO/CO2 species. According to Figs. S9 and S10, further heating of MoO3/MoS2@G-900 in the absence of NaCl to 1200 °C in air leads to the oxidation of carbon and MoS2 to form CO/CO2 species and MoO3, respectively, highlighting the effect of NaCl.”
Comment 2-8: Authors should either display the impedance curve of samples heated at 1000 and 1200℃ or compare their diffusion coefficient of lithium for the respective sample.
Response: Thank you for this comment. According to your suggestion, we retested the EIS of different materials, and the results were incorporated into Fig. 9 and Table 4.
Comment 2-9: If all the measurements were conducted at room temperature then what is the driving force for high lithium diffusion at the anode? Please discuss the kinetics of lithium diffusion.
Response: Thank you for this comment. The article was revised to accommodate this comment, which can be found in lines 414-417:
“The driving force for the Li-ion insertion/extraction into/out of the electrode during the discharge/charge processes is provided by the negative/positive polarization applied on the electrode, respectively.”
Regarding the second comment, the article was revised to add the kinetics of the Li-ion diffusion. The revision can be found in Fig. 9. We examined the EIS of different materials, and the kinetic parameters of the electrode were determined from the equivalent circuit fitting of Nyquist plots (Fig. 9(a)). The answer can be seen in lines 506-515:
“The kinetic parameters of the electrode were determined from the equivalent circuit fitting of Nyquist plots (Fig. 9(a)), and shown in Table 4. At low values of frequency, the MoO3/MoS2@G-1100 electrode exhibits a high slope (9.77 Ω s-1/2) which demonstrates the relatively high lithium ion diffusion coefficient [67]. The lithium ion diffusion coefficient of MoO3/MoS2@G-900, -1000, -1100, -1200 and C-MoS2 electrodes could be calculated to be 8.7×10-21, 1.8×10-20, 1.2×10-18, 5.3×10-21 and 1.0×10-21, respectively. The larger DLi in the earlier can be related to the shorter diffusion pathways available in the electrode, brought about by the presence of integrated hexagonal MoS2 nanocrystals and graphene nanosheets as shown in Fig. 4.”
Reviewer 3 Report
Journal: Catalysts (ISSN 2073-4344)
Manuscript ID: catalysts-2234979
Type: Article
Title: Molten salt-assisted catalytic preparation of MoS2/α-MoO3/graphene as high-performance anode of Li-ion battery.
Authors: Ali Reza Kamali * , Wenhui Zhu.
[1] Introduction: write the perspective of the present work carefully. And in the end of it erite In this paper ……
[2] Write a head title section: Materials and Methods line 109 and put all like this under this section line 581
[3] Results and Discussion:
[4] What are the new results obtained as compared with literature?
[5] For Fig. 2, … contains graphitic flakes with dimensions typically larger than 20 μm how the author measured the dimensions, do you know the thickness of layers?
[6] Why the author didn’t measure the optical properties and Eg of the material prepared?
References: Please, cite the following recent references
DOI: https://doi.org/10.1088/1742-6596/1795/1/012050
DOI: https://doi.org/10.1088/1742-6596/1795/1/012052
Best Regards
Author Response
Reviewer #3
Comment 3-1: Introduction: write the perspective of the present work carefully. And in the end of it erite In this paper ……
Response: We appreciate the reviewer’s insightful comment. The article was revised to accommodate the comment as can be seen in lines 95-100.:
“In this paper, we reports on the facile preparation of hexagonally-shaped MoS2 nanosheets incorporated with MoO3 nanoribbons and graphene nanosheets (MoO3/MoS2@Graphene) by a simple mechanochemical-molten salt approach using natural graphite and MoS2 minerals, with promising Li-ion storage performance. The mechanism involved in the preparation and the electrochemical performance of the nanostructured materials are investigated.”
Comment 3-2: Write a head title section: Materials and Methods line 109 and put all like this under this section line 581
Response: Thank you for your valuable comment. “4. Materials and Methods” is incorporated in the article as a separate section shown in Page 18. However, a new section title was added to the article as “2.1. Preparation of materials” shown in page 3.
Comment 3-3: What are the new results obtained as compared with literature?
Response: We appreciate the reviewer’s insightful comment. This issue is discussed in lines 588-600:
“Selected number of methods employed in the literature for the preparation of molybdenum compounds, and their electrochemical performances are compared with those of MoO3/MoS2@G-1100 in Table 5. Methods shown in this table typical use expensive and/or hazardous materials such as (NH4)6Mo7O24∙4H2O [27,28], MoO3 [29], (NH4)2MoO4 [32], and metallic Mo powders [33], in combination with materials such as CH4N2S [27], HNO3 [28], glacial acetic acid [29], HCl [32], and H2O2 [33]. The excessive use of such chemicals limits the large-scale implementation of these methods. In the method reported here, ball milling is applied to incorporate natural graphite and MoS2 in the presence of hexane and NaCl. Both hexane and NaCl can be retrieved from the mixture after ball-milling, and the final washing step, respectively. Nevertheless, the method reported here requires heating at elevated temperatures which might provide some limitations. Utilization of industrial heat waste can be option to enhance the economic features of the method.”
Comment 3-5: For Fig. 2, … contains graphitic flakes with dimensions typically larger than 20 μm how the author measured the dimensions, do you know the thickness of layers?
Response: Thank you for your valuable comment. As can be seen from Fig. 2a, the material contains graphitic flakes with lateral dimensions typically larger than 20 μm. The term “lateral dimension” was added to the statement to distinguish it with the thickness. The thickness of flakes was also several micrometers based on microscopy results.
Comment 3-6: Why the author didn’t measure the optical properties and Eg of the material prepared?
Response: Thank you for your valuable comments. According to your suggestions, we have added Raman spectra and measured the energy band gap of various materials. The additions can be seen in lines 196-216:
“Further characterization of samples was performed using Raman spectroscopy, and the results are shown in Fig. S4. For C-MoS2, the Raman spectrum shows two major (380 cm−1) and A1g (406 cm−1) activation modes. is due to the in-plane vibration of S and Mo atoms, and A1g is attributed to the relative vibration of S atoms in the out of plane direction. The other two relatively weak peaks observed at 285 and 450 cm−1 belong to E1g and longitudinal acoustic phonon mode in C-MoS2, respectively, as shown in Fig. S4(a). After ball milling process, the E1g peak of C-MoS2 is disappeared, and the A1g-LA (M) peak promoted. However, the structure of C-MoS2 and nature graphite phase has no significant change, as shown in Fig. S4(a). The Raman spectra of the products obtained at various temperatures are shown in Fig. S4(b). As can be seen from Fig. S4(b), in addition to peaks related to graphite and MoS2. There are also peaks related to MoO3 which are marked with red asterisk in the sample heat treated at 1100 °C. Therefore, Raman spectra confirm the formation of MoO3/MoS2@Graphene.
On the other hand, the band gap energy indicates the energy required for the excitation of an electron to be moved from the valence band up to the conduction band. The Tauc method of evaluating the bad gap using UV Vis spectroscopy was used to measure the values of band gap, as shown in Fig. S5-6 and Table S2. It can be concluded that the values of band gap energy gradually increases with the increase of the content of molybdenum trioxide. The reason behind this variation is based on the fact that MoO3 is an n-type wide band gap (≈ 3 eV) semiconductor [37], so the value of energy band gap in the sample produced in 1100 °C is the largest.”
Comment 3-6: References: Please, cite the following recent references
Response: Thank you for your valuable comments. The suggested references were cited as shown below:
- Enneffatia, M.; Rasheed, M.; Louatia, B.; Guidaraa, K.; Shihab, S.; Barillé, R. Investigation of structural, morphology, optical properties and electrical transport conduction of Li0.25Na0.75CdVO4 compound. J.Phys. Conference Series 2021, 1795, 012050.
- Rasheed, M.; Shihab, S.; Sabah, O.W. An investigation of the Structural, Electrical and Optical Properties of Graphene-Oxide Thin Films Using Different Solvents. J. Phy. Conference Series 2021, 1795, 012052.
Round 2
Reviewer 2 Report
Paper can be accepted in its present form.
