Electrochemical One-Step Synthesis of Cu2O with Tunable Oxygen Defects and Their Electrochemical Performance in Li-Ion Batteries
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe paper introduces a novel galvanic oxidation corrosion method for the synthesis of cuprite (Cu₂O) nanocrystals with tunable oxygen vacancies, designed for application as active anode materials in lithium-ion batteries (LIBs). By carefully controlling oxygen vacancies during synthesis, the authors not only enhance the electronic conductivity of Cu₂O but also create additional active sites for lithium ion storage. This approach results in electrodes that exhibit an impressive specific capacity, along with excellent reversibility. Furthermore, the manuscript provides an in‐depth explanation of the Cu₂O formation mechanism during the galvanic oxidation corrosion process, offering insights that could extend to other metal oxide systems.
The study makes several significant contributions. It presents a simple, cost-effective synthesis strategy that overcomes the inherent limitations of traditional Cu₂O anode materials—namely, their poor conductivity and limited cycling stability—by leveraging oxygen vacancy engineering. The work clearly demonstrates that oxygen vacancies improve conductivity and provide extra active sites, leading to markedly improved electrochemical performance. Additionally, by elucidating the formation mechanism of Cu₂O, the paper contributes to a deeper understanding of the relationship between synthesis conditions, microstructural features, and battery performance, paving the way for future advancements in the design of LIB electrodes.
Overall, the manuscript presents innovative ideas and promising experimental results that could significantly advance lithium-ion battery technology. However, the experimental procedures and conditions need to be detailed more thoroughly to ensure reproducibility, and the proposed mechanism linking oxygen vacancies to performance enhancement should be supported by more comprehensive quantitative and qualitative data. Moreover, a more robust comparison with existing literature is needed to better highlight the novelty and advantages of the proposed approach. Addressing these issues will greatly enhance the clarity and impact of the study. Therefore, this manuscript is acceptable after major revision of following comments and questions.
(1) In both the abstract and the main text, the capacity of 1002.3 mAh g⁻¹ is highlighted; however, this value represents the discharge capacity, and the reversible (charge) capacity does not exceed 1000 mAh g⁻¹. As an anode material, the initial discharge capacity is influenced by side reactions such as SEI layer formation, making it inappropriate to emphasize this figure.
(2) In both Cu₂O-3 and Cu₂O-6, there are peaks that cannot be attributed to either Cu₂O or CuO. Could you clarify the origin of these peaks?
(3) In the manuscript, the explanation of the XPS Cu2p is presented first, so it seems logical to place it as Figure 1c, while the O1s spectra, which are explained later, should be assigned to Figure 1d. Additionally, it is necessary to confirm whether energy calibration for the XPS results was performed using C1s. The positions of the deconvoluted peaks for both O1s and Cu2p vary significantly between each sample.
(4) In Figure 4, the sample names have a trailing "v," which needs to be corrected.
(5) A more detailed explanation of the correlation between the oxygen vacancies in the samples and their electrochemical properties is required.
(6) Based on the evaluation of the electrochemical properties, I would like to know which of the three types of samples performs the best.
Author Response
The paper introduces a novel galvanic oxidation corrosion method for the synthesis of cuprite (Cu₂O) nanocrystals with tunable oxygen vacancies, designed for application as active anode materials in lithium-ion batteries (LIBs). By carefully controlling oxygen vacancies during synthesis, the authors not only enhance the electronic conductivity of Cu₂O but also create additional active sites for lithium ion storage. This approach results in electrodes that exhibit an impressive specific capacity, along with excellent reversibility. Furthermore, the manuscript provides an in‐depth explanation of the Cu₂O formation mechanism during the galvanic oxidation corrosion process, offering insights that could extend to other metal oxide systems.
The study makes several significant contributions. It presents a simple, cost-effective synthesis strategy that overcomes the inherent limitations of traditional Cu₂O anode materials—namely, their poor conductivity and limited cycling stability—by leveraging oxygen vacancy engineering. The work clearly demonstrates that oxygen vacancies improve conductivity and provide extra active sites, leading to markedly improved electrochemical performance. Additionally, by elucidating the formation mechanism of Cu₂O, the paper contributes to a deeper understanding of the relationship between synthesis conditions, microstructural features, and battery performance, paving the way for future advancements in the design of LIB electrodes.
Overall, the manuscript presents innovative ideas and promising experimental results that could significantly advance lithium-ion battery technology. However, the experimental procedures and conditions need to be detailed more thoroughly to ensure reproducibility, and the proposed mechanism linking oxygen vacancies to performance enhancement should be supported by more comprehensive quantitative and qualitative data. Moreover, a more robust comparison with existing literature is needed to better highlight the novelty and advantages of the proposed approach. Addressing these issues will greatly enhance the clarity and impact of the study. Therefore, this manuscript is acceptable after major revision of following comments and questions.
(1) In both the abstract and the main text, the capacity of 1002.3 mAh g⁻¹ is highlighted; however, this value represents the discharge capacity, and the reversible (charge) capacity does not exceed 1000 mAh g⁻¹. As an anode material, the initial discharge capacity is influenced by side reactions such as SEI layer formation, making it inappropriate to emphasize this figure.
Answer: We have added the following to the text: The voltage-capacity curves of the three groups of batteries at the 1st, 2nd, and 50th charging and discharging cycles reveal initial discharging capacities of 569.9 mAh/g, 1002.3 mAh/g, and 823.8 mAh/g, respectively. It is noteworthy that the Cu2O-6 group ex-hibits the highest initial charging (826.72 mAh/g) and discharging (1002.3 mAh/g) capaci-ties. The first Coulomb efficiencies are 67.53%, 82.48%, and 75.62% for Cu2O-3, Cu2O-6, and Cu2O-9, respectively.
However, due to the formation of SEI film during the charging and discharging process of the first loop, it results in a lower Coulomb efficiency. We emphasized the initial discharging capacities value.
(2) In both Cu₂O-3 and Cu₂O-6, there are peaks that cannot be attributed to either Cu₂O or CuO. Could you clarify the origin of these peaks?
Answer: We apologize for our negligence. The peaks at 2θ values are 35.504°, 38.735°, 48.66°, and 53.431°, which are attributed to CuO. Which can be found in both Cu₂O-3 and Cu₂O-6.
According to the reviewer’s suggestion, we modified that text. The following is the right. Notably, the distinct diffraction peaks at 2θ values are 35.504°, 38.735°, 48.66°, and 53.431°, which are attributed to CuO [34]. The intensity of CuO peaks increase with in-creasing the applied voltage. It is clearly in the Cu2O-9 sample indicates that, under condi-tions of applied high positive potential, Cu2O may undergo additional oxidation to form CuO.
(3) In the manuscript, the explanation of the XPS Cu2p is presented first, so it seems logical to place it as Figure 1c, while the O1s spectra, which are explained later, should be assigned to Figure 1d. Additionally, it is necessary to confirm whether energy calibration for the XPS results was performed using C1s. The positions of the deconvoluted peaks for both O1s and Cu2p vary significantly between each sample.
Answer: We utilized the C1s peak for calibration. The positions of the deconvoluted peaks for both O1s and Cu2p vary significantly between each sample. We have checked the vary again. The results are consistent with the following references.
[1] Xian Yang, Jun Cheng, Xiao Yang, Yang Xu, Weifu Sun, Junhu Zhou, MOF-derived Cu@Cu2O heterogeneous electrocatalyst with moderate intermediates adsorption for highly selective reduction of CO2 to methanol, Chemical Engineering Journal, 2022 (431), 134171. https://doi.org/10.1016/j.cej.2021.134171.
[2] Jie Chen, Shaohua Shen, Penghui Guo, Meng Wang, Po Wu, Xixi Wang, Liejin Guo, In-situ reduction synthesis of nano-sized Cu2O particles modifying g-C3N4 for enhanced photocatalytic hydrogen production, Applied Catalysis B: Environmental, 2014 (152), 335-341. https://doi.org/10.1016/j.apcatb.2014.01.047.
(4) In Figure 4, the sample names have a trailing "v," which needs to be corrected.
Answer: We apologize for our negligence. The reviewer's comment was correct, we checked it again and corrected it.
(5) A more detailed explanation of the correlation between the oxygen vacancies in the samples and their electrochemical properties is required.
Answer: Based on the reviewers' suggestions, we have added a discussion of the effect of oxygen vacancies on performance.
(6) Abbreviations should be indicated separately - to make the text more transparent.
Answer: We apologize for the difficulties caused by our negligence. We have examined the manuscript to annotate the abbreviated sections.
Answer: Many thanks to the reviewers for their comments, we checked the abbreviations.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript entitle ` Electrochemical one-step synthesis of Cu2O with tunable oxygen defects and their electrochemical performance in Li-Ion batteries` is investigating the potential use of Cu2O as an anode for LiBs. Despite the fact that the manuscript is organized in a systematic way, it has several major and minor flaws, which has pointed out below. Several of them is even questions the motive or relevance of the work. Hence it need a major revision to resolve the issues.
- May give the exact value of theoretical capacity of Cu2O
- Some relevant articles on defect engineering of the LiB such as DOI 10.1088/1361-6528/ac54de, org/10.1002/batt.202200239 shall be added.
- It is true that Cu2O is an earth abundant material. However Cu metal is highly demanding now a days and already known not sufficient for the future needs. In that circumstances, what is the motive to use Cu metal sheet as source for Cu2O. It seems contradictory in the article
- Deconvolution of the bands in figure 1d is not satisfactory. The low binding energy band is broader for the Cu2O-3 that the Cu2O-9 but still claims no deconvolution is possible. How it come? Especially for the Cu2O3, there seems a side lob in the decreasing edge of the band towards the lower binding energy
- Except the (111) in 2d no other markings on 2d, e and f is acceptable since the firings are not present in the visible range. Hence the markings and the associated writing in the text should be removed.
- Though the title and abstract emphasis the use of Cu2O material, the Cu2O-9 with certain percentage of CuO seems to be more reliable from the electrochemical cycling data.
- The current rating of cycling is not provided
- By comparing the capacities though being the same current densities, the capacity fading rate is not matching in the rate and cycling data (comment is only considering the first 10 cycles in rate and cycling for Cu2O-3 and 9)
- In the beginning of the manuscript, it is claimed that this work is attempting to resolve the major draw back of the Cu2O, the capacity fading under cycling. But it seems to be not resolved much. If authors believe it improved, please provide a literature comparison at least in the form of comparative graph.
Author Response
The manuscript entitle ` Electrochemical one-step synthesis of Cu2O with tunable oxygen defects and their electrochemical performance in Li-Ion batteries` is investigating the potential use of Cu2O as an anode for LiBs. Despite the fact that the manuscript is organized in a systematic way, it has several major and minor flaws, which has pointed out below. Several of them is even questions the motive or relevance of the work. Hence it need a major revision to resolve the issues.
(1) May give the exact value of theoretical capacity of Cu2O.
Answer: the exact value of theoretical capacity of Cu2O is 375 mAh/g.
(2) Some relevant articles on defect engineering of the LiB such as DOI 10.1088/1361-6528/ac54de, org/10.1002/batt.202200239 shall be added.
Answer: Based on the reviewers' reasonable suggestions, we have added two corresponding papers.
(3) It is true that Cu2O is an earth abundant material. However Cu metal is highly demanding now a days and already known not sufficient for the future needs. In that circumstances, what is the motive to use Cu metal sheet as source for Cu2O. It seems contradictory in the article.
Answer: Based on the reviewers' comments, we have revised our presentation.
(4) Deconvolution of the bands in figure 1d is not satisfactory. The low binding energy band is broader for the Cu2O-3 that the Cu2O-9 but still claims no deconvolution is possible. How it come? Especially for the Cu2O3, there seems a side lob in the decreasing edge of the band towards the lower binding energy.
Answer: Thanks to the reviewers' questions, we checked our fitting results. It was found that our fitting results were due to the presence of oxygen vacancies. This result is consistent with the following literature.
[1] Xian Yang, Jun Cheng, Xiao Yang, Yang Xu, Weifu Sun, Junhu Zhou, MOF-derived Cu@Cu2O heterogeneous electrocatalyst with moderate intermediates adsorption for highly selective reduction of CO2 to methanol, Chemical Engineering Journal, 2022 (431), 134171. https://doi.org/10.1016/j.cej.2021.134171.
[2] Jie Chen, Shaohua Shen, Penghui Guo, Meng Wang, Po Wu, Xixi Wang, Liejin Guo, In-situ reduction synthesis of nano-sized Cu2O particles modifying g-C3N4 for enhanced photocatalytic hydrogen production, Applied Catalysis B: Environmental, 2014 (152), 335-341. https://doi.org/10.1016/j.apcatb.2014.01.047.
(5) Except the (111) in 2d no other markings on 2d, e and f is acceptable since the firings are not present in the visible range. Hence the markings and the associated writing in the text should be removed.
Answer: According to the suggestion of reviewer’s. we removed the the markings and the associated writing in the text.
(6) Though the title and abstract emphasis the use of Cu2O material, the Cu2O-9 with certain percentage of CuO seems to be more reliable from the electrochemical cycling data.
Answer: We thank the reviewers for their comments. We have made changes accordingly.
(7) The current rating of cycling is not provided.
Answer: We thank the reviewers for their comments. The current rating of cycling is 0.1C.
(8) By comparing the capacities though being the same current densities, the capacity fading rate is not matching in the rate and cycling data (comment is only considering the first 10 cycles in rate and cycling for Cu2O-3 and 9).
Answer: When testing long cycle performance, we always start by activating the version of the battery to bring its energy to a stable value.
(9) In the beginning of the manuscript, it is claimed that this work is attempting to resolve the major draw back of the Cu2O, the capacity fading under cycling. But it seems to be not resolved much. If authors believe it improved, please provide a literature comparison at least in the form of comparative graph.
Answer: We apologize for our expression. We have revised our presentation in the main text. Research on cathode materials for lithium-ion batteries has been conducted for many years. Cuprous oxide is considered a possible cathode material. However, it has problems such as poor electrical conductivity, and we have improved its electrical conductivity and enhanced its lithium embedded capacity by introducing oxygen vacancies.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsCurrent manuscript is acceptable without further correction.
Reviewer 2 Report
Comments and Suggestions for AuthorsManuscript has revised properly against the reviewer comments. It shall be accepted.
