Study and Property Characterization of LiMn2O4 Synthesized from Octahedral Mn3O4
, Wenhao Hao 1,2, Ju Lu 1,2 and Fanghai Lu 4
Round 1
Reviewer 1 Report
Wang et al. presented the systematic study of Mn3O4 preparation by varying various parameters such as pH regulators, PH, temperature. They also studied the effect of roasting temperature and time during the preparation of LiMn2O4. There are several issues that needs to be addressed before publication:
-Title is too vague, please change it to something else.
-The ammonia concentration of (12%) was used for pH regulator study, where as only 8% was used for pH study. Why 8% was used instead of 12%?
-In line 296-298: authors mentioned the decrease in sulfur content, how was the decrease in sulfur content was calculated or observed?
-The D50 and surface area of the 70C with pH 7 and 80C with pH8 is almost similar but the microstructure based on SEM is different. Why?
-What was the loading of the active material during coin cell fabrication?
-The theoretical capacity of LiMn2O4 material is ~148mAh/g. The electrochemical performance of all materials is well below the theoretical value (<125mAh/g). Is there any other parameters that needs to be tuned to improve the performance?
-How is the performance of final materials compared to other published work?
-Authors have studied the various parameters, sometimes it was hard to follow the results of each. For simplicity, it will be better to have a table that summarizes the results from each section.
-Figure 9: spelling of percent is wrong.
-Please include more recent results and provide citation for those.
Major editing is needed.
Author Response
We sincerely thank the editor and all reviewers for their valuable feedback that we have used to improve the quality of our manuscript. The reviewer comments are laid out below in red text and specific concerns have been numbered. Our response is given in normal font and changes/additions to the manuscript are given in the blue text.
Q1.Title is too vague, please change it to something else.
We sincerely thank the reviewer for careful reading. The title has been changed to “Study and property characterization of LiMn2O4 synthesized from octahedral Mn3O4”
Q2.The ammonia concentration of (12%) was used for pH regulator study, where as only 8% was used for pH study. Why 8% was used instead of 12%?
AnswerQ2：We sincerely thank the reviewer for careful reading. Changes in ammonia concentration cause changes in grain size and uniformity. When the concentration of ammonia decreases, the Mn3O4 grains become larger, the size is uniform, and the voids are reduced. When the ammonia concentration is 12%, many small grains appear. When the ammonia concentration is 8%, the size of Mn3O4 grains is about 280 nm. Ammonia concentration is high, not only Mn2+ and NH3 stable complex formation, excess hydroxide and Mn2+ generate a small amount of Mn(OH)2, Mn2+ and Mn(OH)2 oxidation at the same time improves the degree of supersaturation of Mn3O4, Mn3O4 nucleation rate is fast, so that the Mn3O4 crystallization is more dispersed, the size of the grain is small. Reduce the concentration of ammonia, reduce the generation of ammonia-manganese complex, can slow down the nucleation rate, promote the growth of Mn3O4 grain, so choose 8% ammonia is more appropriate.
Q3.In line 296-298: authors mentioned the decrease in sulfur content, how was the decrease in sulfur content was calculated or observed?
AnswerQ3：We sincerely thank the reviewer for careful reading.We examined the Mn content of Mn3O4 prepared at different reaction pH (Fig. 4 in the manuscript) and found that the Mn content decreased with the increase of reaction pH. Some of the impurities will generate insoluble hydroxides into into impurities, on the other hand, promote the side reaction to generate Mg(NH4)2(SO4)2 and Mn2(OH)2SO4, and the by-products are tightly wrapped into the precipitation, resulting in the increase of sulfur content. The increase in sulfur content can be observed by the amount of white precipitate after filtration.
Q4.The D50 and surface area of the 70C with pH 7 and 80C with pH8 is almost similar but the microstructure based on SEM is different. Why?
D50 is the median particle size of the test, is a lot of small particles agglomerated together to form a large particle, may be related to the mixing speed, temperature and other factors that affect the agglomeration process, so that the same small particles agglomerated to form large particles of different particle size.SEM can only see agglomerates by taking a small magnification electron microscope shot.When the reaction pH is 7, the degree of supersaturation is low, the nucleation rate is low, the number of agglomeration sites is small, the grains attract each other to agglomerate and form large particles. When the reaction pH 8, the solute supersaturation increases, the grains are more dispersed, the particle size is finer, a large number of Mn3O4 nuclei are formed, and the number of agglomeration sites increases, resulting in a large number of agglomerated particles and a small particle size, so the particle size of Mn3O4 is slightly reduced and the specific surface area increases.
Q5.What was the loading of the active material during coin cell fabrication?
AnswerQ5：We sincerely thank the reviewer for careful reading.The active substance was made according to the mass ratio of 8:1:1 for the cathode material (LiMn2O4 burned with Mn3O4 and LiOH), acetylene black, and binder [poly(vinylidene fluoride) dissolved in N-methylpyrrolidone and formulated to a concentration of 0.03 g∙mL-1].
Q6.The theoretical capacity of LiMn2O4 material is ~148mAh/g. The electrochemical performance of all materials is well below the theoretical value (<125mAh/g). Is there any other parameters that needs to be tuned to improve the performance?
AnswerQ6：We sincerely thank the reviewer for careful reading.The MnSO4 used to prepare Mn3O4 in this paper is a high-purity manganese sulfate solution obtained by our lab's patented method of purifying leachate from low-grade manganese rhodochrosite ore, which is filtered and washed to dissolve and precipitate it (the manganese sulfate solution obtained by this method meets the battery-grade requirements).The capacity of LiMn2O4 prepared in this paper, 121mAh∙g-1, is not much different from the theoretical value of 125mAh∙g-1 that you said. On the basis of guaranteeing the capacity, we have realized the efficient solution purification and battery-grade Mn3O4 preparation technology with short flow and low cost, which can not only expand the application channels of rhodochrosite in manganese-based materials, but also contribute to the promotion of the new energy battery industry development of great significance, and at the same time, it is in line with the theme of the journal's sustainable development.
Q6.How is the performance of final materials compared to other published work?
AnswerQ6：We sincerely thank the reviewer for careful reading.The present commercial spinel LiMn2O4 delivers only 90 mAh/g–115 mAh/g, far lower than the theoretical specific capacity.The properties of LiMn2O4 synthesized from octahedral Mn3O4 studied in this paper have superior performance compared to other literature methods. For example, The team prepared LiMn2O4 from spherical Mn3O4 with a capacity of only 117mAh∙g-1（Performance of lithium manganate synthesized from spherical manganese tetraoxide[J]. Battery,2015,45(01):22-25.）.For example,Yang's team co-doped LiMn2O4 with Mg2+ and Ti4+ had a capacity of 124mAh∙g-1, which is almost the same as the LiMn2O4 prepared by our team (121mAh∙g-1) but we are the octahedral LiMn2O4 particles without cationic doping and surface modification showed very good performance（ "Mg2+ and Ti4+ Co–Doped Spinel LiMn2O4 as Lithium‐Ion Battery Cathode." ChemistrySelect 4(2019).）
Q7Figure 9: spelling of percent is wrong.
AnswerQ8：We feel sorry for our carelessness. In our resubmitted manuscript, the typo is revised. Thanks for your correction.
Thanks for your suggestion.We tried our best to improve the manuscript and made some changes to the manuscript. These changes will not influence the content and framework of the paper.
Author Response File: 
Author Response.doc
Reviewer 2 Report
In this paper authors have studied the effects of pH regulator, temperature and reaction pH on some of the physical properties of Mn3O4. They came to the conclusion that optimal condition for synthesis of Mn3O4 is, ammonia water as pH regulator, reaction pH 8, temperature 80C, reaction time 12 hours and oxygen flow 3 L/min. Authors have also used XRD, wet chemical analysis, XPS to identify the composition and impurities within the final product. Subsequently LiMn2O4 is also synthesized with better morphology and it's performance as cathode material is assessed. The study is done in a very systematic way.
Following are the suggestions to make the article better.
Major:
#. The title of the paper is some what not inclusive of the research that has been done. I think, the research is based on the 'Optimal synthesis parameter for LiMn2O4 and it's performance as cathode material'. The preparation of Mn3O4 is just a precursor of that.
#. In figure-9, the particle-size scale is extended from 0.01 to 1000. It might be better to zoom it to the relevant range of particle size.
#. The charge-discharge graph in figure 12(c) is at which cycle? Need to specify this.
#.The specific capacity Vs cycle in figure:12(b) does not becomes stable, rather keeps deteriorating, any comment why it is so?
#. Authors have mentioned about "cell parameter" in section 3.6.1 to explain the table-3. Should it be 'lattice constant'? Similarly in section 3.7.1.
Minor:
1. In the introduction, authors have mentioned that "More and more studies had shown that....". Please cite at least one such article.
2. Similarly cite the reference for 'Jahn-Teller effect' in introduction, 'Scheller Formula' in section 3.5.1 etc.
3. Reference to the figure is missing in section 3.2 line 221. "As shown in Fig, ..."
4. In the conclusion "LiMn2O4 had an Fd-3m spatial structure". Is it "spatial" or 'spinel'?
5. There are multiple typos. E.g., "coud", "wer", "wasn", "consistented", "cycling performance", and many more.
There are multiple typos and wrong grammar. Those needed to be corrected.
Author Response
We sincerely thank the editor and all reviewers for their valuable feedback that we have used to improve the quality of our manuscript. The reviewer comments are laid out below in red text and specific concerns have been numbered. Our response is given in normal font and changes/additions to the manuscript are given in the blue text.
Q1.The title of the paper is some what not inclusive of the research that has been done. I think, the research is based on the 'Optimal synthesis parameter for LiMn2O4 and it's performance as cathode material'. The preparation of Mn3O4 is just a precursor of that.
AnswerQ1：We sincerely thank the reviewer for careful reading. The title has been changed to “Study and property characterization of LiMn2O4 synthesized from octahedral Mn3O4”
Q2. In figure-9, the particle-size scale is extended from 0.01 to 1000. It might be better to zoom it to the relevant range of particle size.
AnswerQ2：We sincerely thank the reviewer for careful reading. I have changed the particle-size scale in the graph to extend from 1 to 50 as per your suggestion.（The figure in the manuscript has also been changed）
Q3.The charge-discharge graph in figure 12(c) is at which cycle? Need to specify this..
AnswerQ3：We sincerely thank the reviewer for careful reading.As you can see Figure 12(c) shows the multiplication properties of the material tested. These are cycles at different multiplication rates (0.2C, 0.5C, 1C, 2C, 5C, 10C, and 0.2C). The performance was observed by cycling ten cycles at each multiplication rate.The larger the magnification, the lower the performance theoretically.
Q4.The specific capacity Vs cycle in figure:12(b) does not becomes stable, rather keeps deteriorating, any comment why it is so?.
AnswerQ4：We sincerely thank the reviewer for careful reading.It can be seen from the lattice constant of LiMn2O4 in Table 3 of the text that the mixture does not react thoroughly enough to form new crystals completely with a short roasting time. While longer roasting time increases the degree of crystal distortion.So except for the optimum 10h the remaining cycle performance will be unstable and decrease faster.Figure (11) can also prove at the same time that at 4h the particles are small, when it reaches 6h,8h,10h, the particles are uniform in size and very compact, octahedral shape, and at 12h some of the products will be deoxygenated leading to the material is not stable, so the cycling performance will be reduced.
The main reasons for the degradation of the cycling performance of lithium-ion batteries are as follows.In the process of charging and discharging, the continuous de-embedding of Li+ leads to changes in the valence state of Mn ions, which transforms their crystal structure from cubic phase to tetragonal phase, hindering the movement of Li+ and decreasing the capacity; secondly, the dissolution of Mn. disproportionation reaction of Mn3+ in LiMn2O4 occurs, generating Mn4+ and Mn2+, and the tetravalent manganese has a strong oxidizing property, oxidizing the positive electrode material, and the divalent manganese is dissolved in the electrolyte, which impedes the Li+ diffusion , leading to a decrease in capacity; third, electrolyte decomposition. Trace water and LiPF6 in the electrolyte generate HF, which erodes the positive and negative electrode materials and reduces their charge and discharge capacity.
Q5.Authors have mentioned about "cell parameter" in section 3.6.1 to explain the table-3. Should it be 'lattice constant'? Similarly in section 3.7.1.
AnswerQ5.We sincerely thank the reviewer for careful reading.I have changed the cell parameter in the text to lattice constant and highlighted it in blue font.
Q6（minor）1. In the introduction, authors have mentioned that "More and more studies had shown that....". Please cite at least one such article.
- Similarly cite the reference for 'Jahn-Teller effect' in introduction, 'Scheller Formula' in section 3.5.1 etc.
- Reference to the figure is missing in section 3.2 line 221. "As shown in Fig, ..."
- In the conclusion "LiMn2O4 had an Fd-3m spatial structure". Is it "spatial" or 'spinel'?
- There are multiple typos. E.g., "coud", "wer", "wasn", "consistented", "cycling performance", and many more.
Answer：We feel sorry for our carelessness. In our resubmitted manuscript, the typo is revised. Thanks for your correction.
Thanks for your suggestion.We tried our best to improve the manuscript and made some changes to the manuscript. These changes will not influence the content and framework of the paper.
Author Response File: Author Response.doc
Reviewer 3 Report
The study presented here provides valuable insights into the synthesis and characterization of Mn3O4 with an octahedral structure and its application in the preparation of LiMn2O4 for electrochemical performance. The research addresses several critical factors that influence the morphology, specific surface area, and properties of these materials. By investigating the effects of pH regulation, temperature, and reaction pH on the structure of Mn3O4, the authors have highlighted the importance of controlling these parameters for achieving desired properties.
The utilization of ammonia water as both a pH regulator and complexing agent, along with the specific reaction conditions (pH 8, 80℃, 12-hour reaction time, and 3L∙min-1 oxygen flow rate) for Mn3O4 synthesis, is noteworthy. These conditions are crucial in obtaining the desired octahedral morphology, which can subsequently enhance the performance of LiMn2O4.
The subsequent preparation of LiMn2O4 from the octahedral Mn3O4 is a significant step forward in this research. The investigation into the effects of calcination time and temperature on the physicochemical and electrochemical properties of LiMn2O4 sheds light on the optimal conditions for achieving good electrochemical performance. The specific parameters for calcination (800℃ for 10 hours) resulting in a well-defined octahedral morphology for LiMn2O4, and the associated electrochemical performance metrics such as the initial discharge specific capacity (121.9mAh∙g-1) and capacity retention rate (93.6% after 100 cycles), demonstrate the effectiveness of the approach.
Overall, this study offers a comprehensive understanding of the synthesis-structure-property relationships of octahedral Mn3O4 and its application in producing high-performance LiMn2O4. The findings contribute to the advancement of materials for electrochemical applications and open up new possibilities for the development of energy storage systems with enhanced electrochemical reversibility and long-term stability. The authors' systematic approach and clear presentation of results make this work a valuable contribution to the field. Therefore, I recommend this paper can be published here.
Author Response
We sincerely thank the reviewer for careful reading. We feel great thanks for your professional review work on our article. As you are concerned, there are several problems that need to be addressed.Thank you again for your positive comments and valuable suggestions to improve the quality of our manuscript.
Round 2
Reviewer 1 Report
The authors have improved the manuscript and can be published in current form.
