Improved Energy Storage Performance of Composite Films Based on Linear/Ferroelectric Polarization Characteristics

Round 1

Reviewer 1 Report (Previous Reviewer 1)

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you for your decision and constructive comments on my paper (Manuscript ID: polymers-2930802). We have carefully considered the comments and make some changes in the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report (Previous Reviewer 2)

The authors have considered previous comments of the reviewers and revised the manuscript, correspondingly. The manuscript can be accepted for publication. 

Author Response

Dear Reviewer,

We would like to thank the referee again for taking the time to review our manuscript.

Reviewer 3 Report (Previous Reviewer 3)

Please see attached file.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you for your decision and constructive comments on my paper (Manuscript ID: polymers-2930802). We have carefully considered the comments of Reviewer and make some changes in the revised manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report (Previous Reviewer 3)

The new wording is better, adequate for publishing.

Author Response

Dear Reviewer,

We would like to thank the referee again for taking the time to review our manuscript.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments for author File: Comments.pdf

Author Response

Thank you for your decision and constructive comments on my paper (Manuscript ID: polymers-2816265). We have carefully considered the comments of Reviewer and make some changes in the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

Paper by C. Chen et al. reports the energy storage characteristics of bilayer films of ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) and biaxially oriented polypropylene, which is a linear dielectric. The authors showed that such structures have a very high dielectric breakdown strength and significant polarization, which makes it possible to achieve a high discharge energy density of 10.1 J/cm³ and an energy storage efficiency of 80.9 % at a field of 5.5 MV/cm. The approach proposed by the authors to improve the energy storage characteristics of polymer films sounds promising. The paper is of interest to readers of the Polymers. However, a revision is necessary. The following comments should be considered.

1.       The evaluation of the band gap based on the presented UV-vis data does not appear convincing. How was the wavelength lg estimated? Typically, the band gap is determined using the Tauc plot. In addition, a value of the band gap for P(VDF-TrFE-CFE) films is too small. This material is a good insulator.

2.       Please specify the composition of P(VDF-TrFE-CFE).

3.       The title is misleading. Field distribution is discussed in only three sentences (lines 198-203). The field distribution shown in figure 2f corresponds to the trivial textbook case of a homogeneous electric field in a bilayer with two dielectric permittivities.

4.       In line 187, the authors wrote that “the bilayer film exhibits good dielectric relaxation”. What does it mean? In what sense is relaxation good?

5.       Lines 149-153, the authors wrote “In order to analyze the energy level structure of the thin film, the bandgap widths of the inorganic layer and the polymer films were obtained through Ultraviolet and visible spectrophotometry (UV-Vis) testing, and the lowest and highest energy levels of the inorganic layer and the thin film were measured through Ultraviolet photoelectron spectroscopy (UPS) testing.” According to the paper, both layers are organic polymers. Please, correct.

6.       English needs to be improved. E.g. “polarization intensity” is a misnomer.

1English needs to be improved. E.g. “polarization intensity” is a misnomer.

Author Response

Thank you for your decision and constructive comments on my paper (Manuscript ID: polymers-2816265). We have carefully considered the comments of Reviewer and make some changes in the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper presents a bilayer construction of an apolar (BOPP) and polar (PVTC) layer for improving the energy storage and dielectric performance for applications such as capacitor films. I think there are several points that need clarification, based on the analysis and the related conclusions/statements:

In the introduction, some very general terms are used where some reference is missing. For example, Line 37 (new energy vehicles), Line 39 (compact pulse power devices).

Sections 2.1 & 2.1:

As the multilayer structure is a the heart of this paper, the material properties and preparation is very important:

*What are the nominal thickness of the BOPP films? How where they produced? (sequential or simultaneous stretching? From what kind of base polypropylene resin?

*What are the basic polymer properties of PVTC?

* The thickness of the final BOPP/PVTC multilayer films is mentioned in line 175 as "~15 μm". How exact is that, and how was it measured? In particular given the fabrication method, how homogeneous was the PVTC layer on top of the BOPP films?  This plays a crucial role in all subsequent measurements.

Section 2.3 and Figure 2: At what temperatures did the dielectric measurements take place? (BDS and breakdown strength).

Furthermore, what are the dimensions of the dielectric samples? (area, shape, thickness). 

Page 5, dielectric spectroscopy:

According to the caption of Figure 2, the comparison is done at a frequency of 1 kHz. Why is that frequency selected? It can be seen from Fig2a that there is quite some frequency dependence of the dielectric response.

Figure 1e: I would remove the dashed red line, to be able to better appreciate the inteface by naked eye.

Figure 4c, 4d and related discussion thereafter: The results are compared at different electric fields. For example, the highest value of 10.1 J/cm3 for 67% corresponds to about 550 kV/mm, while all others are measured at lower fields. Thus the comparison is not really straightforward.

References: The geographical distribution is extremely limited. Also there is only one reference from Polymers [30]. Is Polymers really the most suitable journal for this work?

The English language needs a check; some examples:

Line 52: PVDF needs to be spelled out at the first occurrence.

Line 12: The development "proposed"...? Perhaps something like "driven" is better.

Line 19: As the layers are not compounded but rather deposited on each other, it's better to not use the term "compounded".

Line 38: because the energy...

Line 41: polymers

Line 44: good polarization charachteristics

Line 116: PVTC needs to be spelled out at the first occurrence.

Line 134: bought

Author Response

Thank you for your decision and constructive comments on my paper (Manuscript ID: polymers-2816265). We have carefully considered the comments of Reviewer and make some changes in the revised manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Unfortunately, the authors did not give satisfactory answers to the comments of the reviewer. Their response is fairly formal. Therefore, the major revision is still needed.

1.      The evaluation of the band gap is not yet convincing. It appears that the approach used by the authors is error-prone and resulted in a bandgap value that is too low for PVTC. I recommend that the authors analyze the data more carefully, e.g. using the Tauc plot method.

2.      The chemical composition of PVTC, namely the molar ratio of different monomers, was not given. 

3. Please identify the inorganic layer in the sentence “the lowest and highest energy levels of the inorganic layer and the thin film were measured through Ultraviolet photoelectron spectroscopy (UPS) testing” (lines 193-194).

Author Response

Dear Reviewer,

Thank you for your decision and constructive comments on my paper (Manuscript ID: polymers-2816265). We have carefully considered the comments of Reviewer and make some changes in the revised manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

Thanks to the authors for the rigorous responses.

I would highly recommend to transfer to the manuscript key information from the cover letter for example:

* The four BOPP thicknesses.

* The temperature (room temperature) of the dielectric tests.

* The sample size of the dielectric tests. By the way: "In the dielectric test, the sample size is 30mm in length and 30mm in width." --> This is probably the size of the film itself, but I guess the active measuring electrode was disc-shaped, like it is typically the case fot Novocontrol systems? (by the way, small typos here, one space too much in the company name and "Alpha-A" rather than "Alpha-a")

Regarding Comment 2, part 2): "What are the basic polymer properties of PVTC?" --> Here it was rather meant to provide a "signature", such as it molecular weight, polydispersity, MFR...

Most importantly, I feel the discussion around Figure 4 (Comment 6) is not clarified. In the response, the principle of the investigation is explained, however not the way the results are selected and compared. If I would rephrase the original question, it is not the experiment that is challenged, but rather the values which are assigned to each film thickness, because they correspond to different voltages. It would be, for example, as if comparing the performance of two films at different temperatures. This is critical for drawing the conclusions, that's why I am insisting on it.

The manuscript was improved to that respect.

Author Response

Dear Reviewer,

Thank you for your decision and constructive comments on my paper (Manuscript ID: polymers-2816265). We have carefully considered the comments of Reviewer and make some changes in the revised manuscript.

Author Response File: Author Response.docx

Round 3

Reviewer 2 Report

The revision is unsatisfactory.

From the Tauc plots shown, it is clear for me that the band gap of PVTC is between 4 and 5 eV, which is consistent with the insulating nature of this polymer. The author should examine the similar slopes in the Tauc plots for both samples. Therefore, the text should be modified, as well as Figure 3f and the corresponding discussion.

Although the authors mentioned the molar ratio of the monomers in their rebuttal letter, they should also include this important information in the main text.

Author Response

Dear Reviewer,

Thank you for your decision and constructive comments on my paper (Manuscript ID: polymers-2816265). We have carefully considered the comments of Reviewer and make some changes in the revised manuscript.

Author Response File: Author Response.pdf