Development, Performance, and Vehicle Applications of High Energy Density Electrochemical Capacitors

Round 1

Reviewer 1 Report

1. This paper is more like a technical report than a research paper. This paper has a very full discussion of supercapacitors. However, in my opinion, it is not suitable to be published as a research article.
2. In SECTION 3.3, “As in HEVs, supercapacitors can replace the power battery.” Please give some more comments in details. How about the energy density of supercapacitors?
3. What are the differences between UC and EDLC? Is SC more suitable for automotive applications? Or EDLC?
4. As a ”*Review* Article”, this manuscript is a well written version. I give a RECOMMENDATION of Minor Revision.

Author Response

Dear Reviewers,

I have reworked the paper and tried to respond to the concerns of the reviewer by including assumptions on engine efficiency and how the energy storage devices were sized,  Also I discussed how the characteristics of the energy storage devices were determined.  I also identified references from NREL that showed that supercaps behaved in vehicles as shown in the simulations.

For Reviewer 1:

Comments:

1. This paper is more like a technical report than a research paper. This paper has a very full discussion of supercapacitors. However, in my opinion, it is not suitable to be published as a research article.
2. In SECTION 3.3, “As in HEVs, supercapacitors can replace the power battery.” Please give some more comments in details. How about the energy density of supercapacitors?
3. What are the differences between UC and EDLC? Is SC more suitable for automotive applications? Or EDLC?
4. As a ”*Review* Article”, this manuscript is a well written version. I give a RECOMMENDATION of Minor Revision.

Author reply:

1. Response: My paper is a review of the present status of supercaps based primarily on new information that I ma presenting in this paper. You do not seem to realize the importance of the large increase in energy density of the Aowei devices.
2. Response: My paper presents very complete data on the energy density of supercaps. In my discussuion of the simulation results I compare the weight and volume of batteries and supercaps in various types of HEVs and show that high energy density supercaps can compete with batteries.
3. Response: I discuss the differences between the hybrid SC and the EDLC carbon/carbon cells in my paper. For automotive applications, I think the high energy density SC are the best fit. That is the focus of the paper.
4. Resperonse: I have made revisions in the paper which I think answer your comments

Reviewer 2 Report

Super capacitor has high specific power, long service life and low temperature resistance, which is more suitable for hybrid vehicle applications. The content described in the article has always been a topic of concern in the field of new energy vehicles.However, the research methods used in this paper are more traditional, and the authenticity of simulation data results is not very high. For example:

1. What is the basis for the selection of vehicle models and their supercapacitors in table 10, and what is the powertrain control strategy of each vehicle model.
2. Fig. 4, FIG. 5 and Fig. 6 show the results in poor form.
3. The lack of real vehicle verification results and the failure to consider the dynamic characteristics of engine fuel cell lead to the unreliability of the only vehicle performance simulation data.
4. Finally, the analysis of the most simulation results is not deep enough to clarify the corresponding relationship between the specific improvement range of vehicle fuel economy and the power consumption characteristics of the studied vehicle.

Author Response

Dear Reviewers,

I have reworked the paper and tried to respond to the concerns of the reviewer by including assumptions on engine efficiency and how the energy storage devices were sized,  Also I discussed how the characteristics of the energy storage devices were determined.  I also identified references from NREL that showed that supercaps behaved in vehicles as shown in the simulations.

For Reviewer 2:

Comments:

Super capacitor has high specific power, long service life and low temperature resistance, which is more suitable for hybrid vehicle applications. The content described in the article has always been a topic of concern in the field of new energy vehicles.However, the research methods used in this paper are more traditional, and the authenticity of simulation data results is not very high. For example:

1. What is the basis for the selection of vehicle models and their supercapacitors in table 10, and what is the powertrain control strategy of each vehicle model.
2. 4, FIG. 5 and Fig. 6 show the results in poor form.
3. The lack of real vehicle verification results and the failure to consider the dynamic characteristics of engine fuel cell lead to the unreliability of the only vehicle performance simulation data.
4. Finally, the analysis of the most simulation results is not deep enough to clarify the corresponding relationship between the specific improvement range of vehicle fuel economy and the power consumption characteristics of the studied

Author reply:

1. Response: The device characteristics in Table 10 are based on testing of the various devices at UC Davis. My testing is very detailed as shown by the data given in the paper for supercaps. The vehicle charateristics (Cd, A, test weight, powertrain powers, etc.)  used in the simulations are apppropriate for each type of vehicle.  I have been making vehicle simulations for many years. The energy storage devices were sized to get a round-trip efficiency of about 90% on the driving cycles simulated.
2. Response: I have removed those tables from the paper as not needed.
3. Response: I do include the changing power demand of the vehicles over the driving cycles and use maps for the engine and electric motors and tables for changes in the resistance of the energy storage devices. I compare my results with available dyno data whwn that is available.  I have added references to NREL studies to show that supercaps function well in vehicle tests.
4. Response: I have made the simulationson appropriate driving cycles for each type of vehicle and compared the fuel economy improvements for each energy storage device for the same round-trip efficiency and power consumption.

Reviewer 3 Report

In this paper, the analysis of electrochemical supercapacitors is discussed, studying the features of the main supercapacitor types by means of literature data and experimental tests. In addition, the use of supercapacitor in vehicle applications is evaluated, analyzing the main performance, achieved by means of numerical modeling through Advisor software.

Generally, the manuscript gathers a great amount of data, concerning the main characteristics of supercapacitors, discussing also the future development of this promising technology. 

Nevertheless, this is a “pro and con”, since several data shown is not commented. Some tables and figures are only cited in the text, not discussed, and Figure 3 is not cited in the text. 

The last section of the manuscript, concerning the vehicle applications, does not seem to be pertinent to the rest of the text. Being a review article, vehicle applications should be better introduced, by means of a deeper state of art analysis, and, then, discussed, showing the simulation results.

In addition, the modeling is not presented; the formalization, implementation, assumptions and validation are not considered.

Therefore, I cannot recommend the manuscript publication in the present form, but minor revisions are requested. 

Author Response

Dear Reviewers,

I have reworked the paper and tried to respond to the concerns of the reviewer by including assumptions on engine efficiency and how the energy storage devices were sized,  Also I discussed how the characteristics of the energy storage devices were determined.  I also identified references from NREL that showed that supercaps behaved in vehicles as shown in the simulations.

For Reviewer 3

Comments:

In this paper, the analysis of electrochemical supercapacitors is discussed, studying the features of the main supercapacitor types by means of literature data and experimental tests. In addition, the use of supercapacitor in vehicle applications is evaluated, analyzing the main performance, achieved by means of numerical modeling through Advisor software.

Generally, the manuscript gathers a great amount of data, concerning the main characteristics of supercapacitors, discussing also the future development of this promising technology.

1. Nevertheless, this is a “pro and con”, since several data shown is not commented. Some tables and figures are only cited in the text, not discussed, and Figure 3 is not cited in the text.
2. The last section of the manuscript, concerning the vehicle applications, does not seem to be pertinent to the rest of the text. Being a review article, vehicle applications should be better introduced, by means of a deeper state of art analysis, and, then, discussed, showing the simulation results.
3. In addition, the modeling is not presented; the formalization, implementation, assumptions and validation are not considered.

Therefore, I cannot recommend the manuscript publication in the present form, but minor revisions are requested.

Author reply:

1. Response: Fig 3 is include, but is after the Aowei device test data. I have discussed the test data when I thought it was needed. I thought the data tables were self explanatory
2. Response: I have removed the detailed tables on summaries of the literature and now the focus is on my test data and the simulation results intended to show the importane of increasing the energy density of the supercaps.
3. Response: the details of the modeling are included in previous papers I have written and I can not incclude them in every paper I write. I reference those previous papers.

Reviewer 4 Report

In my view the part of this paper which can be considered novel is related to the application of EVs. However, this part is not very well presented and has only a minor share compared to other parts which have already been published by the authors in their latest work or by the others. The introduction fails to appropriately describe the novelty of the work. Referencing is not also appropriate. It is needed that the authors elaborate more in referring to the literature. In my view what has been presented is not sufficient for another journal paper since its methodological novelty and strength are missing in the current format.

Author Response

Dear Reviewers,

I have reworked the paper and tried to respond to the concerns of the reviewer by including assumptions on engine efficiency and how the energy storage devices were sized,  Also I discussed how the characteristics of the energy storage devices were determined.  I also identified references from NREL that showed that supercaps behaved in vehicles as shown in the simulations.

For Reviewer 4:

Comments:

In my view the part of this paper which can be considered novel is related to the application of EVs. However, this part is not very well presented and has only a minor share compared to other parts which have already been published by the authors in their latest work or by the others. The introduction fails to appropriately describe the novelty of the work. Referencing is not also appropriate. It is needed that the authors elaborate more in referring to the literature. In my view what has been presented is not sufficient for another journal paper since its methodological novelty and strength are missing in the current format.

Author Response: I have removed the part of the paper that includes the summary tables from my recent paper.  I agree they were needed in this paper.  The present paper focuses on the test data for the new, advanced Skeleton and Aowei supercaps and their application in HEVs and fuel cell vehicles of various types. The simulation results show clearly that increasing energy density of the supercaps makes them much more attractive for automotive applications.  That is the key message of the paper.

Round 2

Reviewer 2 Report

This paper lacks the specific demand analysis of hybrid power system. It only expounds the problems based on the simulation results with poor performance, and can not make an in-depth analysis of the results.

--

1. If we want to compare the fuel economy of the hybrid system, at least the starting and ending power states of the power supply should be consistent, which is not considered in this article.
2. The variation of internal resistance and performance of supercapacitor with temperature is lack of measured results.
3. How is the SOC of the supercapacitor used in this paper calculated.
4. The presentation form of the results of the article is not good, and the simulation interface of advisor should not be used directly.
5. The article lacks a summary of the configuration of the discussed models, such as the parameter configuration of HEV, PHEV and fecv and the weight of the supercapacitor.
6. Most importantly, the article lacks the comparison and summary of the corresponding results. The article should further explore the models suitable for the application of supercapacitors and their reasons.
7. Each vehicle type has its corresponding power consumption characteristics, which should be further analyzed and summarized from the perspective of super capacitor configuration, engine working point and start and stop times during operation.
8. In addition, when pehv enters the HEV stage, its power consumption form should be consistent with that of HEV. From the result curve of the article, the SOC fluctuation of supercapacitor in this stage is different from that of HEV model.
9. What measured data can be used as the basis to show the efficiency statistical results in Table 8 and reflect in the working condition calculation results.

Author Response

Response to reviewer

1. If we want to compare the fuel economy of the hybrid system, at least the starting and ending power states of the power supply should be consistent, which is not considered in this article.

The state of the energy storage units was in the same state at beginning and end because I ran at least 10 cycles of all driving cycles for each case simulated.

2. The variation of internal resistance and performance of supercapacitor with temperature is lack of measured results.

 You are right all my data is for room temperature.  It is common practice to compare the performance of batteries and supercapacitors at room temperature. 

3. How is the SOC of the supercapacitor used in this paper calculated.

The SOC is  1-Qout/Qcapacity = V/Vrated

4. The presentation form of the results of the article is not good, and the simulation interface of advisor should not be used directly.

The Advisor interface was not used to get the fuel economy.  It was calculated from the fuel use given on a separate file

5. The article lacks a summary of the configuration of the discussed models, such as the parameter configuration of HEV, PHEV and fecv and the weight of the supercapacitor.

The weight of all the supercapacitors are given in Table 1. The powertrain configurations were all the standard ones for HEV, PHEV, and FCV.  I assumed the reader would be familiar with those configurations.

6. Most importantly, the article lacks the comparison and summary of the corresponding results. The article should further explore the models suitable for the application of supercapacitors and their reasons.

I do not understand how you can say that.  I have presented the key simulation results in detail in the tables and commented on them in general terms,.  I do not think you realize the importance of my results. People working in the supercap field have waited a long time to see supercaps with energy densities like batteries.  My test data are the first to show that

7. Each vehicle type has its corresponding power consumption characteristics, which should be further analyzed and summarized from the perspective of super capacitor configuration, engine working point and start and stop times during operation.

You are right about that. That is why I simulated 6 vehicle types and 4 different energy storage devices. The same general control strategy was used in all the simulations.  I have never seen the level of detail in a paper like you are looking for

8. In addition, when pehv enters the HEV stage, its power consumption form should be consistent with that of HEV. From the result curve of the article, the SOC fluctuation of supercapacitor in this stage is different from that of HEV model.

What you say is not true.  In the battery depletion mode both the battery and capacitor are providing power.  In the HEV mode only the capacitor is providing power

9. What measured data can be used as the basis to show the efficiency statistical results in Table 8 and reflect in the working condition calculation results.

The efficiency of all the energy storage devices are given a separate advisor file along with the total kJ in and out of the device.