Study of the Operation of Lead–Acid Battery Electrodes Under Hybrid Battery–Electrolyzer Cycling Profiles

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript demonstrates innovative and practical value in investigating the aging mechanisms of lead-acid battery hybrid systems. The experimental design is generally sound; however, the scientific rigor could be further strengthened through additional data analysis, improved graphical representation, and more comprehensive literature comparison. It is recommended that the manuscript be accepted following minor revisions.
1. Expand the EIS discussion with references to established corrosion models.

2. Include error margins in corrosion rate plots (Fig. 9–10) to demonstrate reproducibility.

3. Strengthen the discussion in the Introduction by explicitly comparing the Battolyzer’s performance and durability against alkaline systems, emphasizing lead’s recyclability and low criticality.

4. The current reference list contains an excessive number of outdated sources. It is recommended to augment the literature with a greater proportion of studies published within the past decade to ensure that the review reflects the most recent advancements and perspectives in the field.

Author Response

Dear Reviewer,

On the behalf of all coauthors, I would like to thank you for the provided critical notes which helped to improve the scientific quality of the present manuscript. Please find below our detailed replay:

1. Expand the EIS discussion with references to established corrosion models.
2. The current reference list contains an excessive number of outdated sources. It is recommended to augment the literature with a greater proportion of studies published within the past decade to ensure that the review reflects the most recent advancements and perspectives in the field.

Authors reply: The bibliographic study carried out by the authors showed significant lack of sources linking quantitatively the positive grid corrosion process inside the battery cells and the battery cell and half-cell impedance spectra. In addition, the vast majority of the recent articles on the corrosion of the lead alloys are based on relatively short-timed corrosion experiments carried out on “bare” electrodes. The latter differ significantly from the Nyquist plots presented in the manuscript as well as in a previous publication of our team cited as reference [26]. The term “bare” electrodes corresponds to electrodes, which are not coated with thick porous PbO2 positive active material.

2. Include error margins in corrosion rate plots (Fig. 9–10) to demonstrate reproducibility.

Authors reply: The error margins in Figure 9 should be in the range of 1 % because the operator error in the estimation of the current collector diameter is about 0.01 mm, no matters that the software of the digital microscope allows a resolution of 0.001 mm. The error margins in Figure 10 should be even smaller, because the current collector samples have weight in the range of 20 – 60 g which is estimated with a precision of +/-0.5 mg. However these low measurement error margins can not be used to demonstrate reproducibility because the corrosion process is not homogeneous, and there are “intrinsic” cell to cell variations related to the manufacturing process. We tried to overcome the above differences by using two independent corrosion rate estimation methods.  

3. Strengthen the discussion in the Introduction by explicitly comparing the Battolyzer’s performance and durability against alkaline systems, emphasizing lead’s recyclability and low criticality.

Authors reply: We cannot apply this recommendation because we cannot find any bibliographic data discussing the performance of the lead-based Battolyzers.

The authors will appreciate, cite and discuss any omitted bibliographic references suggested by the reviewers in the next manuscript-reviewing round.

Reviewer 2 Report

Comments and Suggestions for Authors

The research objective of this paper is to explore the feasibility of lead-acid batteries operating in a hybrid battery-electrolyzer mode, and to clarify their aging process and influencing factors. The study mainly conducts aging tests on lead - acid batteries under different discharge and overcharge conditions, monitors changes in parameters such as energy efficiency, electrochemical kinetics, discharge performance, and electrochemical impedance.  Four cyclic test sequences simulating hybrid operation scenarios are set up. Through a variety of electrochemical testing methods, combined with visual inspection and XRD analysis, data on battery performance and material changes are obtained. Therefore,I suggest it be accepted after the author complements the content,articulates the obscure content,and corrects the format.

 

1. A table appears in the article (Table 1 ), but the specific meanings of the table headers are not provided. For example, abbreviations such as "DOD" and "FC" are not explained either in the table or in the table notes.
2. The research methods are single.Introduce more advanced research methods, such as in-situ characterization techniques (in-situ XRD, in-situ electrochemical impedance spectroscopy, etc.), to observe the structural and performance changes of batteries in real-time during the charging and discharging processes. This can further deepen the understanding of the battery's working mechanism and aging process.
3. When studying the impact of different working conditions on battery performance, there is a lack of comparative research on different battery types or materials, making it impossible to accurately evaluate the advantages and disadvantages of the adopted battery system.
4. There are spelling errors in the article. For example, "couf-off voltage" the correct expression should probably be "cut-off voltage".
5. The way of citing references in the article may need to be further standardized to ensure the accuracy and consistency of the citations.
6. There are problems with the paper's format, and it is not aesthetically pleasing enough.
7. There are relatively few experiments. It is recommended to increase the number of experimental samples, conduct multiple repeated experiments, reduce experimental errors, and improve the credibility of the experimental results. At the same time, a more reasonable control group should be set up.

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

Dear Reviewer,

On the behalf of all coauthors, I would like to thank you for the provided critical notes which helped to improve the scientific quality of the present manuscript. Please find below our detailed replay:

1. A table appears in the article (Table 1), but the specific meanings of the table headers are not provided. For example, abbreviations such as "DOD" and "FC" are not explained either in the table or in the table notes.

Authors reply: The caption of Table 1 has been extended according to the reviewer’s recommendation.

2. The research methods are single. Introduce more advanced research methods, such as in-situ characterization techniques (in-situ XRD, in-situ electrochemical impedance spectroscopy, etc.), to observe the structural and performance changes of batteries in real-time during the charging and discharging processes. This can further deepen the understanding of the battery's working mechanism and aging process.

Authors reply: The application of in-situ XRD is hardly possible in the present case due to the size of the tested cells. The application of in-situ electrochemical impedance spectroscopy could be an object of a next study, considering the unexpected results presented in Figure 6 and 7.

3. When studying the impact of different working conditions on battery performance, there is a lack of comparative research on different battery types or materials, making it impossible to accurately evaluate the advantages and disadvantages of the adopted battery system.

Authors reply: The authors also found that there is a lack of comparative research related to the quantitative study of the anodic corrosion of the positive current collectors of the lead-acid batteries. This fact is one of the reasons to restart the presented corrosion research. The authors will appreciate, cite and discuss any omitted bibliographic references suggested by the reviewers in the next manuscript-reviewing round.

4. There are spelling errors in the article. For example, "couf-off voltage" the correct expression should probably be "cut-off voltage".

Authors reply: The spelling of the manuscript has been revised following the reviewers recommendations.

5. The way of citing references in the article may need to be further standardized to ensure the accuracy and consistency of the citations.

Authors reply: The authors followed the guide for authors instructions listed in the journal website. The list of the references has been re-checked as well.

6. There are problems with the paper's format, and it is not aesthetically pleasing enough.

Authors reply: The authors used the manuscript template provided in the journal website.

7. There are relatively few experiments. It is recommended to increase the number of experimental samples, conduct multiple repeated experiments, reduce experimental errors, and improve the credibility of the experimental results. At the same time, a more reasonable control group should be set up.

Authors reply: The authors cannot accept this comment because the study has been carried out on 24+1 identical battery cells manufactured within the same production batch. 19 of these cells have been tear down analyzed in order to obtain the presented experimental data. For example, the total number of samples prepared for microscopy observations was equal to 76 (19x4).

Reviewer 3 Report

Comments and Suggestions for Authors

This paper studies the operation of flooded lead - acid battery electrodes under hybrid battery - electrolyzer cycling profiles.  Here are some comments:

1. The authorsmentioned the importance of non - critical resources in electrochemistry. But how does your study uniquely advance the research on lead - acid battery - electrolyzer hybrids? What gaps does it fill compared to existing literature?
2. The paper indicates the hybrid system's potential. However, it's unclear what makes it innovative. Is it a new material, cycling method, or something else? Please elaborate on the novelty.
3. Theexperiments used specific cells. How applicable are your findings, like degradation and efficiency, to other lead - acid batteries with different structures or materials?
4. The authors referred to previous work. But a systematic comparison is lacking. Please compare your results on kinetics, discharge, and corrosion with similar studies for a clearer understanding.
5. The quality of the figures need to be improved. Could you add detailed labels, legends, and error bars to improve readability? For example, in some figures, the label is too small. 
6. The authorsemphasize the link between hydrogen production and corrosion. However, the mechanism is unclear. Can you provide more analysis or evidence on how hydrogen affects corrosion in different cell parts?

 

Comments on the Quality of English Language

English can be improved

Author Response

Dear Reviewer,

On the behalf of all coauthors, I would like to thank you for the provided critical notes which helped to improve the scientific quality of the present manuscript. Please find below our detailed replay:

1. The authors mentioned the importance of non - critical resources in electrochemistry. But how does your study uniquely advance the research on lead - acid battery - electrolyzer hybrids? What gaps does it fill compared to existing literature?

Authors reply: According to the results from out bibliographic survey, the battery-electrolyzer hybrid concept is explored only for the case of alkaline systems employing Nickel-based positive electrodes. Our manuscript studies the feasibility of an alternative electrochemistry for the same type of task, based on the lead and the sulfuric acid. The lead is cheaper, recyclable and non-critical resource, while the state of the art high performance electrochemical systems are relying strongly on metals like nickel, platinum, palladium etc… This aspect is addressed briefly in the introduction section of the manuscript.

2. The paper indicates the hybrid system's potential. However, it's unclear what makes it innovative. Is it a new material, cycling method, or something else? Please elaborate on the novelty.

Authors reply: The main novelty of the manuscript is already claimed in its title, because up our knowledge the lead-acid battery electrodes have not been an object of research focused on their use in a hybrid battery electrolyzer cell.

3. The experiments used specific cells. How applicable are your findings, like degradation and efficiency, to other lead - acid batteries with different structures or materials?

Authors reply: This issue is already discussed rapidly in the end of the introduction section explaining why the tubular positive plate technology is selected. On the other hand, the references 9-12 provide a detailed discussion about the impact of the different additives on the corrosion resistance of the lead alloys.

4. The authors referred to previous work. But a systematic comparison is lacking. Please compare your results on kinetics, discharge, and corrosion with similar studies for a clearer understanding.

Authors reply: The systematic comparison is lacking mostly because the lead-acid battery electrodes have not been an object of studies aimed at the their use in a hybrid battery-electrolyzer system employing distinctly different cycling profiles from the state of the art flooded lead-acid batteries.

5. The quality of the figures need to be improved. Could you add detailed labels, legends, and error bars to improve readability? For example, in some figures, the label is too small.

Authors reply: The quality of the figures has been re-checked.

6. The authors emphasize the link between hydrogen production and corrosion. However, the mechanism is unclear. Can you provide more analysis or evidence on how hydrogen affects corrosion in different cell parts?

Authors reply: The link between hydrogen production and corrosion is related to the stoichiometry of the water splitting reaction which produces oxygen at the positive plate. According to the mechanism of the anodic corrosion of the lead and its alloys discussed in references 9-12, part of the produced oxygen oxidizes the metallic lead via semiconductor solid-state mechanism. Up to our knowledge, the correlation between the quantity of water electrolyzed (i.e. the quantity of the applied overcharge) and the corrosion rate is not studied quantitatively at “full-scale” battery level.

The authors will appreciate, cite and discuss any omitted bibliographic references suggested by the reviewers in the next manuscript-reviewing round.

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript presents a well-structured and comprehensive study on the performance of lead-acid batteries operating in hybrid battery-electrolyzer modes. The topic is relevant to the field of energy storage and renewable energy integration, particularly in the context of sustainable battery technologies. The study is methodically designed, incorporating extensive electrochemical analysis and degradation mechanisms under various cycling scenarios. The results contribute significantly to understanding the feasibility of using lead-acid batteries as Battolyzers. However, a few points should be addressed before publication:

1. Introduction – general.

The introduction provides a solid background on lead-acid batteries and their role in energy storage. However, it would benefit from a clearer statement on the novelty of the study. The authors should emphasize how their approach differs from existing research on lead-acid battery-electrolyzer hybrids.

Some discussion on the economic and practical implications of lead-acid Battolyzers compared to other hybrid systems would strengthen the context.

2. Experimental methodology – general.

The methodology is well-detailed, but the rationale behind selecting specific cycling scenarios (MOD1–MOD4) should be clarified. A brief justification for each test protocol’s relevance to real-world applications would enhance understanding.

3. Results

A large portion of results are presented in supplementary material. While this approach is understandable, some critical figures, such as corrosion rate comparisons and impedance trends over time, should be included in the main text to improve accessibility.

The correlation between hydrogen production and battery degradation is well-addressed, but additional discussion on mitigating degradation effects, such as possible modifications to electrode materials or charging strategies, would be beneficial.

Figures related to electrochemical impedance spectroscopy (EIS) and Tafel analysis should include more annotations to guide the reader in understanding the observed trends.

Some sentences are overly long and could be restructured for better readability. For example, the sentence on page 3, line 15, describing the corrosion mechanisms, could be simplified.

There are minor typographical errors throughout the manuscript. A thorough proofreading to correct these would improve the overall quality.

Citations should be reviewed to ensure consistency in formatting and placement within the text.

4. General

The manuscript presents a valuable contribution to battery-electrolyzer hybrid systems. With the suggested revisions, particularly in clarifying methodological justifications, improving data presentation, and expanding the discussion on practical applications, it would be well-suited for publication in Batteries (ISSN 2313-0105).

Author Response

Dear Reviewer,

On the behalf of all coauthors, I would like to thank you for the provided critical notes which helped to improve the scientific quality of the present manuscript. Please find below our detailed replay:

1. The introduction provides a solid background on lead-acid batteries and their role in energy storage. However, it would benefit from a clearer statement on the novelty of the study. The authors should emphasize how their approach differs from existing research on lead-acid battery-electrolyzer hybrids. Some discussion on the economic and practical implications of lead-acid Battolyzers compared to other hybrid systems would strengthen the context.

Authors reply: Up to our knowledge the lead-acid Battolyzer concept has not been discussed in the literature prior to the 

2. The methodology is well-detailed, but the rationale behind selecting specific cycling scenarios (MOD1–MOD4) should be clarified. A brief justification for each test protocol’s relevance to real-world applications would enhance understanding.

Authors reply: The introduction section has been revised accordingly.

3. A large portion of results are presented in supplementary material. While this approach is understandable, some critical figures, such as corrosion rate comparisons and impedance trends over time, should be included in the main text to improve accessibility.

Authors reply: The supplementary materials contain results which do not contain any exceptional novelty. On the other hand the plots in Figure 9 and 10a are directly comparable. We presented the corrosion rate (as a current) only for the case of the weight loss method because it is based on a “global” measurement approach, while the optical data are strictly “local” and the calculation of an average from the three positions (top, middle, bottom) can be misleading. In the present manuscript, the impedance spectroscopy has been used only as part the cells characterization prior to the tear-down analysis. The obtained results suggest that a separate, more detailed impedance study can be an object of our next work.

4. The correlation between hydrogen production and battery degradation is well-addressed, but additional discussion on mitigating degradation effects, such as possible modifications to electrode materials or charging strategies, would be beneficial.

Authors reply: A comment addressing this issue has been added in the end of paragraph 3.7.

5. Figures related to electrochemical impedance spectroscopy (EIS) and Tafel analysis should include more annotations to guide the reader in understanding the observed trends.

Authors reply: The results presented in Figure 2 and Figure 6 are discussed in details in paragraphs 3.2 and 3.4. The legend and the annotations in the plots have been checked.

6. Some sentences are overly long and could be restructured for better readability. For example, the sentence on page 3, line 15, describing the corrosion mechanisms, could be simplified. There are minor typographical errors throughout the manuscript. A thorough proofreading to correct these would improve the overall quality.

Authors reply: The manuscript has been subjected to proofreading according to the reviewers’ recommendation.

7. Citations should be reviewed to ensure consistency in formatting and placement within the text.

Authors reply: The consistency of the citations has been checked following the reviewers’ recommendations.