A Comprehensive Review on Supercapacitor Applications and Developments

Round 1

Reviewer 1 Report

Las tecnologías de almacenamiento están teniendo un gran desarrollo en los últimos años, y el almacenamiento con SC no es una excepción, por lo que contar con una fuente que recopile las últimas investigaciones puede resultar de gran utilidad. Pero en relación a este trabajo hay algunos aspectos que en mi opinión deberían mejorarse.

• En un artículo de revisión tan exhaustivo, se agradecería unas tablas donde las referencias con los principales aportes en las diferentes áreas analizadas pudieran verse como un resumen.
• Creo que algunas de las referencias incluidas no están citadas en el texto, por ejemplo, las referencias 46, 97 y 98. Sugiero una revisión en este sentido, en mi opinión es un error importante no citar adecuadamente las referencias.
• I have also observed too high a percentage of references with 10 or more years. Considering that it is a technology in continuous development, in my opinion they should focus on more recent research. If what is intended, as stated in the conclusions, is “inform and inspire the researchers”, perhaps a not so high number of references would be better, but all of them more recent.
• In this sense, for example, “The Toyota company, a 415 hybrid racing car, uses a hybrid drivetrain with SCs” is cited, with a reference from 2013, or “More researchers have explored hybrid electric vehicles (HEV) and supercapacitor / battery combinations ”, with references from 2007 and 2012. And the same happens with references 165 to 170, all prior to 2014 and some from 2008, surely you can cite more recent application examples.
• One of the research areas, in addition to the automotive industry, where SCs are having the most application is in microgrids. The authors mention this fact in section 4 but it seems to me that it is not very prominent and the references cited in this regard are not recent either [68,154,155], some are more than 10 years old.
• Only a table appears where this technology is compared with Lead-acid Battery and Lithium-Ion Battery. However, there are other storage technologies with which the SC could compete, at least in many of the indicated fields of application, it would improve the paper if they were included.
• Por último, cabe señalar que se agradecería que las conclusiones indicaran qué retos todavía tiene que afrontar esta tecnología y, sobre todo, en qué campos queda un largo camino por recorrer para mejorar esta tecnología de almacenamiento. Aunque en el apartado 3 se señalan los inconvenientes de esta tecnología, creo que una mayor aportación de los autores sería positiva e indicaría en cuál de estos aspectos se está haciendo un mayor esfuerzo actualmente.

Author Response

Comments and Suggestions for Authors 1 
Las tecnologías de almacenamiento están teniendo un gran desarrollo en los últimos años, y el almacenamiento con SC no es una excepción, por lo que contar con una fuente que recopile las últimas investigaciones puede resultar de gran utilidad. Pero en relación a este trabajo hay algunos aspectos que en mi opinión deberían mejorarse.
Translated: Storage technologies have been undergoing tremendous development in recent years, and SC storage is no exception, so having a source that compiles the latest research can be very helpful. But concerning this work, there are some aspects that in my opinion should be improved.
Answer: The authors thank the reviewer for their valuable comments. The manuscript was improved in the direction the reviewer comments.
 En un artículo de revisión tan exhaustivo, se agradecería unas tablas donde las referencias con los principales aportes en las diferentes áreas analizadas pudieran verse como un resumen.
Creo que algunas de las referencias incluidas no están citadas en el texto, por ejemplo, las referencias 46, 97 y 98. Sugiero una revisión en este sentido, en mi opinión es un error importante no citar adecuadamente las referencias.
Translated: In such an exhaustive review article, tables would be appreciated where the references with the main contributions in the different areas analysed could be seen as a summary.
Answer:  The summary of the literature part is attached with a table and bibliometric mapping.  
I believe that some of the references included are not cited in the text, for example, references 46, 97 and 98. I suggest a revision in this sense. In my opinion, it is a major mistake not to cite the references correctly.
Answer: They are cited in the introduction part and shown in a different colour. As 45-48 and, and 96-99 which includes 45, 46, 47, 48 and 96, 97, 98, 99. 
I have also observed too high a percentage of references with 10 or more years. Considering that it is a technology in continuous development, in my opinion, they should focus on more recent research. If what is intended, as stated in the conclusions, is "inform and inspire the researchers", perhaps a not so high number of references would be better, but all of them are more recent.
In this sense, for example, “The Toyota company, a hybrid racing car, uses a hybrid drivetrain with SCs” is cited, with a reference from 2013, or “More researchers have explored hybrid electric vehicles (HEV) and supercapacitor/battery combinations", with references from 2007 and 2012. And the same happens with references 165 to 170, all prior to 2014 and some from 2008. Surely you can cite more recent application examples.
Answer: There was given information about historical developments of SC. So there is used some old dated references. Some of them are updated, and there is attached some new references. Also, some of the sentences are revised in the direction of reviewer comments. 
One of the research areas, in addition to the automotive industry, where SCs have the most application is in microgrids. The authors mention this fact in section 4, but it seems that it is not very prominent, and the references cited in this regard are not recent either [68,154,155], some are more than ten years old.
Answer: There is attached some references and application about microgrids. Also, some of the old references are updated. 
Only a table appears where this technology is compared with Lead-acid Batteries and Lithium-Ion Batteries. However, there are other storage technologies with which the SC could compete, at least in many of the indicated fields of application. It would improve the paper if they were included.
Answer: Redox-Flow batteries attached to the table and compared with the other storage technologies. 
Por último, cabe señalar que se agradecería que las conclusiones indicaran qué retos todavía tiene que afrontar esta tecnología y, sobre todo, en qué campos queda un largo camino por recorrer para mejorar esta tecnología de almacenamiento. Aunque en el apartado 3 se señalan los inconvenientes de esta tecnología, creo que una mayor aportación de los autores sería positiva e indicaría en cuál de estos aspectos se está haciendo un mayor esfuerzo actualmente.
Translate: Finally, it should be noted that the conclusions would be appreciated if they indicated what challenges this technology still has to face and, above all, in which fields there is a long way to go to improve this storage technology. Although the drawbacks of this technology are pointed out in section 3, I believe that a greater contribution from the authors would be positive and would indicate in which of these aspects a greater effort is currently being made.
Answer: The conclusion part was revised in the direction of these comments.

Author Response File: Author Response.docx

Reviewer 2 Report

This subject (Supercapacitor) is very interesting, but the writing style of manuscript is not appropriate. There are several phrasing mistakes. Some of sentences are too long.

 

• Some sentences are to be rephrased:

Line 5-6: Researchers have been researching… in recent years.

Line 58-60: The supercapacitor structure is … and a liquid electrolyte.

Line 565: The and history and developments of …paper firstly.

• I suggest authors to rewrite the conclusion. Clear contributions about this manuscript need to be presented

Author Response

Comments and Suggestions for Authors 2

This subject (Supercapacitor) is very interesting, but the writing style of the manuscript is not appropriate. There are several phrasing mistakes. Some of the sentences are too long.

Answer: The writing style of the manuscript, phrasing mistakes were corrected. Some of the long sentences were shortened.

Some sentences are to be rephrased:

Line 5-6: Researchers have been researching… in recent years.

Answer: Researchers have been exploring new materials and techniques to store more significant amounts of energy more efficiently in recent years.

Line 58-60: The supercapacitor structure is … and a liquid electrolyte.

Answer: The structure of the SC differs from a ceramic or electrolytic capacitor. It consists of two solid electrodes polarized by the applied voltage and separated by a membrane separator and a liquid electrolyte [30, 31].

Line 565: The and history and developments of …paper firstly.

Answer: The history and developments of SC were given in the introduction part of this paper firstly.

I suggest the authors rewrite the conclusion. Clear contributions to this manuscript need to be presented.

Answer: The conclusion part is rewritten, and the contribution is presented clearly.

Reviewer 3 Report

In this manuscript, the Supercapacitor (SC) as an alternating or hybrid storage device and their developments have been comprehensively reviewed. The historical results of SC are revealed, as well as the structure, working principle and materials of SC are given detail to be analyzed more effectively. A techno-economic analysis and other applications of SC are summarized. In addition, SC modelling design and module design principles with charge-discharge cycling tests are explored. Other components and the capital cost to produce a compact module for high power density are investigated. So this work may inform and inspire the researchers who will be studying in this area.

I consider the content of this manuscript will definitely meet the reading interests of the readers of the Energies journal. Generally speaking, English writing is very good. However, I suggest the author check the full text for possible grammar errors. I will point out some of them, but cannot cover all of them.

Therefore, I suggest giving a minor revision and the authors need to clarify some issues or supply some more data to enrich the content. 

 

1. Abstract and Introduction

• Line 4, ‘The energy storage methods and increased efficiency have been studied by researchers for many years.’
• The abstract should be a total of about 200 words maximum, and now it is a bit longer (see the rules at https://www.mdpi.com/journal/energies/instructions). In addition, the Keywords are still missing.
• Line 21 to Line 30, the general description is fine, but some more details are ignored during the description.

Firstly, energy storage is not only used for natural events and fossil fuels, but also in the grid system for peak shaving. The electricity sources generated in many forms may also be intermittent, opening spatial and temporal gaps between the availability of the energy and its consumption by end-users [Electrochimica Acta 309 (2019): 311-325]. This issue is also critical for energy storage.

Secondly, ‘However, these conventional storage devices' life is not so long and has some harmful contaminants for nature, and they have some technical drawbacks. So the scientists have been researching big capacity and long life storage devices for many years.’ This description is not clear to most readers. How long can it be called long life? There is no specific value to define in the text. Therefore, it is suggested to compare the lifetime, environmental friendliness, and cost of SC and other primary, secondary batteries (lithium-ion, fuel cell, and redox flow battery). In addition, flow batteries have a long lifetime of 20 years and iron-based systems are harmless [Journal of Power Sources 493 (2021): 229445], which is longer even than SC. The authors may criticize the lower energy density of flow batteries due to lots of aqueous solutions and the low safety of lithium-ion battery/fuel cells. So during the comparisons, advantages and disadvantages between SC and other techniques may also be supplied to give readers the most intuitive impression (Table 1 should be further expanded).

 

• Line 31, ‘The SCs have been proposed by the scientists as an alternating solution for alone and hybrid applications with the other storage devices [12]. Also, as the power source of electric and hybrid vehicles, SCs are increasingly used as interim energy storage for regenerative braking [13].’

 

• Line 55, ‘FDK group corporation [26, 27].’It is not a complete sentence. In addition, Line 60, ‘These electrodes [30, 31].’ has the same issue.

 

• Line 116, ‘Standardised test protocols are required for applications ranging from low to high peak currents [78].’

 

2. Fundamental of Supercapacitor

 

• Line 177, ‘Compared to the distinctions and drawbacks, using them with other storage devices [42].’This sentence is not complete, it should be ‘using them with other devices may lead to ... benefits’.

 

• Line 179, ‘Standard SCs with aqueous electrolytes are rated with 2.1 to 2.3 V voltage, and SCs with organic solvents are rated 2.5 to 2.7 V [40]. For higher application, the voltage is required to connect cells in series.’ And what does ‘higher application’ mean, higher quality, larger-scale, or higher voltage application? So it should be, ‘For higher XX application, it is required to connect SC cells in series’, not ‘the voltage is required...’

 

• Line 250, ‘MnO2 and RuO2 electrode...and exhibit faradaic behaviour... ’

 

• Line 260, ‘Although most of the studies are focused on electrode materials of electrolytes...’

 

3. Modelling and Performance Tests of SC

 

• Line 472, ‘The energy is stored in a static electric field in the conventional capacitors consisting of two electrodes.’

 

• Line 521, ‘and the result is presented in Figure 14 (b) [8, 102] [8, 102]...’

 

4. Conclusions

This part should be named ‘Conclusions and future outlook’ since this is a review article. As the author described in Line 145, ‘the future of SC and new trends are commented at the last parts’. But currently, it is definitely too short for the future trends and outlook, which still needs to be further described.

Author Response

Comments and Suggestions for Authors 3

In this manuscript, the Supercapacitor (SC) as an alternating or hybrid storage device and their developments have been comprehensively reviewed. The historical results of SC are revealed, as well as the structure, working principle and materials of SC are given detail to be analysed more effectively. A techno-economic analysis and other applications of SC are summarized. In addition, SC modelling design and module design principles with charge-discharge cycling tests are explored. Other components and the capital cost to produce a compact module for high power density are investigated. So this work may inform and inspire the researchers who will be studying in this area.

I consider the content of this manuscript will definitely meet the reading interests of the readers of the Energies journal. Generally speaking, English writing is very good. However, I suggest the author check the full text for possible grammar errors. I will point out some of them but cannot cover all of them.

Therefore, I suggest giving a minor revision, and the authors need to clarify some issues or supply some more data to enrich the content.

Abstract and Introduction

Line 4, ‘The energy storage methods and increased efficiency have been studied by researchers for many years.’

Answer: The studying word is corrected as studied.

The abstract should be a total of about 200 words maximum, and now it is a bit longer (see the rules at https://www.mdpi.com/journal/energies/instructions). In addition, the Keywords are still missing.

Answer: The abstract has been shortened to less than 200 words. Also, the keywords are attached.

 Line 21 to Line 30, the general description is fine, but some more details are ignored during the description.

Firstly, energy storage is not only used for natural events and fossil fuels, but also in the grid system for peak shaving. The electricity sources generated in many forms may also be intermittent, opening spatial and temporal gaps between the availability of the energy and its consumption by end-users [Electrochimica Acta 309 (2019): 311-325]. This issue is also critical for energy storage.

Answer: The first paragraph of the introduction is revised to support this idea and attached with the reference. 

Secondly, 'However, these conventional storage devices' life is not so long and has some harmful contaminants for nature, and they have some technical drawbacks. So the scientists have been researching big capacity and long life storage devices for many years.' This description is not clear to most readers. How long can it be called long life? There is no specific value to define in the text. Therefore, it is suggested to compare the lifetime, environmental friendliness, and cost of SC and other primary, secondary batteries (lithium-ion, fuel cell, and redox flow battery). In addition, flow batteries have a long lifetime of 20 years, and iron-based systems are harmless [Journal of Power Sources 493 (2021): 229445], which is longer even than SC. The authors may criticize the lower energy density of flow batteries due to lots of aqueous solutions and the low safety of lithium-ion battery/fuel cells. So during the comparisons, advantages and disadvantages between SC and other techniques may also be supplied to give readers the most intuitive impression (Table 1 should be further expanded).

Answer: The second part of the first paragraph in the introduction is revised to support these ideas and attached the proposed reference. Also, the details of numerical values are given in Table 1.  The redox flow batteries are connected in Table 1 for comparison, and they are mentioned in the text.

Line 31, ‘The SCs have been proposed by the scientists as an alternating solution for alone and hybrid applications with the other storage devices [12]. Also, as the power source of electric and hybrid vehicles, SCs are increasingly used as interim energy storage for regenerative braking [13].’

Line 55, ‘FDK group corporation [26, 27].’It is not a complete sentence. In addition, Line 60, ‘These electrodes [30, 31].’ has the same issue.

Line 116, ‘Standardised test protocols are required for applications ranging from low to high peak currents [78].’

Answer: The typo errors in lines 31, 55, 60, 166 are corrected as mentioned.

Fundamental of Supercapacitor

Line 177, ‘Compared to the distinctions and drawbacks, using them with other storage devices [42].’This sentence is not complete, it should be ‘using them with other devices may lead to ... benefits’.

Line 179, ‘Standard SCs with aqueous electrolytes are rated with 2.1 to 2.3 V voltage, and SCs with organic solvents are rated 2.5 to 2.7 V [40]. For higher application, the voltage is required to connect cells in series.’ And what does ‘higher application’ mean, higher quality, larger-scale, or higher voltage application? So it should be, ‘For higher XX application, it is required to connect SC cells in series’, not ‘the voltage is required...’

Line 250, ‘MnO2 and RuO2 electrode...and exhibit faradaic behaviour... ’

Line 260, ‘Although most of the studies are focused on electrode materials of electrolytes...’

Modelling and Performance Tests of SC

Line 472, ‘The energy is stored in a static electric field in the conventional capacitors consisting of two electrodes.’

Line 521, ‘and the result is presented in Figure 14 (b) [8, 102] [8, 102]...’

Answer: The typo errors in lines 177, 179, 250, 260, 472, 521 are corrected. 

Conclusions

This part should be named ‘Conclusions and future outlook’ since this is a review article. As the author described in Line 145, ‘the future of SC and new trends are commented at the last parts’. But currently, it is definitely too short for the future trends and outlook, which still needs to be further described.

Answer: In general, the title of the conclusion gives the meaning of future work. So we don’t need to change the section title name. The conclusion part expanded for the future trends and outlooks. 

Reviewer 4 Report

Reviewer’s comments

 

Manuscript Number: energies-1438914

Title: A Comprehensive Review on Supercapacitor Applications and Developments

Journal: Energies

 

1. The manuscript reviews the supercapacitors basics, classifications, and developments. The first half of the manuscript (12 pages, Lines 1-428) is very general and listing well-known information about supercapacitors. Now there are so many papers that discussed this basic, thus there is no point of discussing the basics classifications and design again, it is a kind of repetition.
2. In addition, most of the figures are published before in a review paper of the same authors ( E. Şahin, F. Blaabjerg, A. Sangwongwanich. A review on supercapacitor materials and developments. Turk. J. Mater. 5(2) (2020) 10-24). It seems the current manuscript is recycling the published one with some updates. Please refer to the following table which compares similar figures (file is attached).

Current manuscript (energies-1438914)	Published paper (Turk. J. Mater. 5(2) (2020) 10-24)
Fig. 4	Fig. 6
Fig. 3	Fig. 5
Fig. 2	Fig. 3
Fig. 1	Fig. 1

3. Figure 2. Comparison of the energy and power density of storage devices. This is a well-known Ragon plot, thus the citation to the original source is required, even it is redrawn. The same issue is for Fig. 1 and 3.

 

Therefore, the current manuscript can not consider for publication in the current form.

Comments for author File: Comments.pdf

Author Response

Reviewer’s comments 4

The manuscript reviews the supercapacitors basics, classifications, and developments. The first half of the manuscript (12 pages, Lines 1-428) is very general and lists well-known information about supercapacitors. Now there are so many papers that discuss this basic. Thus there is no point of discussing the basics classifications and design again, it is a kind of repetition.

Answer:  I think a comment was made based on a lack of information about the manuscript. It is not possible to find such a comprehensive review of SCs developments and applications.  Only section two gives information's about the fundamental of SCs, but it's not a repetition of knowledge. This part is prepared more tidily and provides all the information necessary for the readers about SCs to understand the following details easily.   

In addition, most of the figures were published before in a review paper of the same authors ( E. Şahin, F. Blaabjerg, A. Sangwongwanich. A review on supercapacitor materials and developments. Turk. J. Mater. 5(2) (2020) 10-24). It seems the current manuscript is recycling the published one with some updates. Please refer to the following table, which compares similar figures (file is attached).

Answer:  The published paper was only about SC materials and developments, but this is paper includes all the matters about SC and their applications. The mentioned figures are similar to the fundamental and materials part of this comprehensive paper. Also, these figures are cited and revised for this new paper. Some of them plotted again. So I'm afraid I have to disagree with the reviewer about this matter thoroughly.   

Figure 2. Comparison of the energy and power density of storage devices. This is a well-known Ragon plot, thus the citation to the original source is required, even it is redrawn. The same issue is for Fig. 1 and 3.

Answer: Thanks for these valuable comments. The original source of Figures 1, 2 and 3 are given.

 Therefore, the current manuscript cannot consider for publication in the current form.

Round 2

Reviewer 1 Report

The comments made in the first review have been sufficiently answered. I have nothing new to add.

Author Response

Thanks for your comments 

Reviewer 2 Report

There is scope to add more information. In the literature, you can find ample amount of work on supercapacitor.

Author Response

Thanks for your comments 

Reviewer 4 Report

Reviewer’s comments

Manuscript Number: energies-1438914-R1

Title: A Comprehensive Review on Supercapacitor Applications and Developments

Journal: Energies

1. The authors failed to address the previous comments. In addition, the current version is still a recycled copy of their previous work. It is meaningless to publish more than 4 Figures in two different papers of the same author!.
2. The manuscript misses the research basics and fundamentals, where the reference given to the well-known Ragone plot which is used for all electrochemistry/energy work for many decades is a very recent study.

Figure 2. Comparison of the energy and power density of storage devices [103]

[103] Liu, Y.; Wu, Q.; Liu, L.; Manasa, P.; Kang, L.; Ran, F. Vanadium nitride for aqueous supercapacitors: A topic review. 853 J. Mater. Chem. A 2020, 8, 8218–8233.

This 2020 review paper is not the original source of the Ragone plot.

The original source could be the following:

Ragone, D. V., Review of Battery Systems for Electrically Powered Vehicles. (1968), DOI: https://doi.org/10.4271/680453

3. In addition, most of the figures are published before in a review paper of the same authors ( E. Şahin, F. Blaabjerg, A. Sangwongwanich. A review on supercapacitor materials and developments. Turk. J. Mater. 5(2) (2020) 10-24). It seems the current manuscript is recycling the published one with some updates.

Author Response

Comment 1. Consider adding the papers below to Bibliography:

Figure 2. Comparison of the energy and power density of storage devices:

Ragone, D. V., Review of Battery Systems for Electrically Powered Vehicles. (1968), DOI: https://doi.org/10.4271/680453

Answer 1: The proposed paper was added to references and used as a reference for Figure 2.

Comment 2. Please make sure that the Figures are different that the ones published below (even though the meaning remains the same:

In addition, most of the figures are published before in a review paper of the same authors ( E. Şahin, F. Blaabjerg, A. Sangwongwanich. A review on supercapacitor materials and developments. Turk. J. Mater. 5(2) (2020) 10-24).

Answer 2: All the figures revised and replotted. There is no any same figure from the mentioned paper now.

Comments 3: Please clearly indicate the contribution of this paper compared to the one mentioned above.

Answer  3: This mentioned above paper is only focused the SC materials and materials developments. This new paper is more comprehensive and includes all applications and developments about SC (Such as; techno economic analyses, applications, modelling and performance tests and more details). If you check two papers you can see it easily. Also there no any similar figure and text now. Also there is no any similarity indexes with the mentioned paper.  I hope this answer clearly indicate the contribution if this paper.