Pyramid-Patterned Germanium Composite Film Anode for Rechargeable Lithium-Ion Batteries Prepared Using a One-Step Physical Method

Round 1

Reviewer 1 Report

figure 2 is confusing especially the arrows does not match with the defined thing. 

 

Raman figures are (fig 8) confusing especially I dont see typical graphite signals D' should come ~2800 but here it is assigned to 1700 cm-1. G band is almost not exist. S/N very bad!

Mass loading missing, Energy density missing, How capacity were calculated missing. Alll electrochemical energy formulation is missing. 

 

fig 11 b: fit and equivalent circuit is missing. 

 

fig11a why 3 cycle? there are 200 cycle in fig10c. 

 

current 1 mA; Impedance: Rct~300 ohm

but high capacity. This is confusing.

 

Author Response

Reviewer(s)' Comments to Author 1:

1. figure 2 is confusing especially the arrows does not match with the defined thing.

Response: figure 2 was modified in the manuscript. (Page 4)

The graphite film was cut to be the disc with 16 mm diameter. The nickel material was first deposited on the graphite film with 10 watts for 5minutes. Then, the Ge material was deposited on the nickel film with 18 watts for 10 minutes. According to the above sequence, a series of experiments were performed. As last, the nickel material was deposited on the upper Ge film with 10 watts for 5 minutes, which covered the whole film. The prepared Ge composite film was used as anode material for LIBs. (page 4, line 14-20)

2. Raman figures are (fig 8) confusing especially I dont see typical graphite signals D' should come ~2800 but here it is assigned to 1700 cm-1. G band is almost not exist. S/N very bad!

Response: Pyramids patterned Ge/nickel film was deposited on the graphite film. The Raman was sensitive to the upper Ge/nickel film of the Ge composite material. The signal of the Ge and Ni was strong in the Raman spectra. The height of the pyramids was not uniform. The bigger pyramids were about on the scale of a few hundred nanometers. Thus, the carbon signal was relatively weaker than that of the Ge/nickel film. In Fig.8c, the carbon peak was observed at 1574.01 cm^-1, which was related to the graphite film. (page 9, line 3-9)

   In the typical Raman spectra of pure graphite, the D peak was at about 1357 cm^-1, the G peak was at about 1577 cm^-1, the D' peak was at about 1620 cm^-1, and the 2D peak was at about 2700 cm^-1.

 

3. Mass loading missing, Energy density missing, How capacity were calculated missing. Alll electrochemical energy formulation is missing.

Response: the diameter of the graphite film collector was 16 millimeters. The average mass loading was 0.37 milligrams, which included Ge film and nickel film in total. The first discharge energy density was 494.5 Wh/kg, the first charge energy density was 686.1 Wh/kg. After 280 cycles, the charge energy density was 350.8 Wh/kg. The Ge composite maintained an average capacity of over 580 mAh g^-1 after 280 cycles.

(page 11, line 2-4, 6-7, 12)

4. fig 11 b: fit and equivalent circuit is missing. fig11a why 3 cycle? there are 200 cycle in fig10c. current 1 mA; Impedance: Rct~300 ohm but high capacity. This is confusing.

Response: In Fig.10c, in order to observe the capacity maintenance rate in the latter discharge-charge cycles, the first, 100th, and 200th voltage-capacity curves were displayed. In the cyclic voltammetry measurement, it usually tested first three cycles to obtain the peaks in discharge-charge process. The voltage range was between 0.01-2.0 V at a sweep rate of 1 mV/s.

The EIS measurement could provide valuable information of half-cell. The equivalent circuit was added in the figure. The equivalent circuit was demonstrated in Fig.11c. The equivalent circuit was demonstrated in Fig.11c. C represented the capacitance. Re represented the electrolyte resistance, Rct represented the charge transfer resistance. Z_w represented the Warburg impedance, R_f represented the resistance of the surface film and contact, and Q represented constant phase angle element. The values of R_ct and R_f were about 330 and 40 ohm, respectively. Because of the nickel layer covered the whole surface of the anode material, which made it difficult for electrolytes to wet electrode material. And the Ge was a semiconductor, which had lower electronic conductivity compared with that of the good conductor. It involved the characteristics of electrolyte and electrode material. The prepared Ge composite material delivered 549 mAh/g after 280 cycles. It improved the cycle life and reversible capacity compared with that of the pure Ge. The average capacity was 588 mAh/g during the whole cycles. (page 12, line )

Author Response File: Author Response.docx

Reviewer 2 Report

In this article, the authors reported a top-down technique of high deposition-rate magnetron sputtering for preparing the germanium (Ge) hybrid film in a single step. The article is well-written and organized. The results obtained by the authors are interesting and genuinely informative, thus, I recommend publishing this paper in Coatings. However, before consideration for publication in the Journal of Coatings, the following minor corrections and additions should be made:

I. Some English grammar and spelling corrections must be done throughout the whole paper. For instance:

— Missing space between 5 and minutes in the phrase "5minutes" in line 118;

— Replace the word "cabon" with "carbon" in line 159;

Below are the full English grammar and spelling corrections for the following sections only: Abstract, Introduction, and Experimental.

Correct this sentence in the Abstract:

— Add "was" in the sentence: "The capacity was kept at 580 mAh g^-1 after 280 cycles."

Correct these sentences in the Introduction:

"It has been utilized in semiconductors, catalysts, optical fibers, and sensors [1-6]". 

"Ge has been also extended to the field of lithium-ion batteries (LIBs) as a result of the rapid advancement of the science and technology [7-13]."

"LIBs, which provide power for electric vehicles, personal computers, and supporting new energy generation, have sparked widespread public concern [14-19]."

"After the de-alloying process, the volume of the Ge-based alloy will shrink."

"The capacity of Ge hybrids was 938.6 mAh g^-1 at 1A g^-1 for 50 cycles."

"The capacity was kept at around 600 mAh g^-1 even when cycled at a current density of 8A/g. "

"The template-asssisted in-situ reduction method was used to create the three-dimensional interconnected porous graphenes [47]."

"The composites’ three dimensional porous graphene improved the materials’ electronic conductivity and reaction kinetics while also providing enough buffer area to minimize volume changes during the cycling and preserved the anode’s structural integrity."

"The flexible graphene framework, which served as an anode for LIBs, was distributed with Ge nanoparticles."

"With the capacity retention of 84.9% after 400 complete cycles, it demonstrated a reversible capacity of 675 mAh g^-1 at a current density of 400 mA g^-1 [48]."

"Dealloying of the GeTiAl ternary alloy in mild conditions made it easy to create a macroporous Ge skeleton that was wrapped by TiO₂ particles [52]."

"TiO₂ particles prevented the Ge skeleton from coming into direct contact with electrolytes by acting as an outer buffer wall for the Ge skeleton."

"The binder and conductive agent that were typically present in traditional Ge-based electrode materials had the potential to boost the stability and the electrical conductivity, but they also decreased the energy density of the whole [54-60]."

"As a result, binder-free Ge-based anode material was promising to elevate the electrochemical performance [19, 31, 61, 62]."

"After 1000 cycles, the binder-free Ge anode had a coulombic efficiency of 99.6% and a reversible capacity of 1300 mAh g^-1 at 1C."

"Additionally, the energy density of the whole electrode increased as a result of the anode material’s decrease of a bind."

"In order to prepare Ge-based composites with novel structures and enhance their electrochemical performance, it is desirable to combine the aforementioned methods."

"The flexible and self-lubricating, good thermal and electrical conductivity of graphite film could also help alleviate stress-strain properties."

"Magnetron sputtering, which was capable of successfully preparing metal and semiconductor film, was used to deposit Ge on the graphite film substrate."

"First, the graphite film substrate was coated with nickel film, and then nickel film was coated with Ge film."

"The morphology of the prepared Ge composite film’s cross-section resembled pyramids."

Correct these sentences in the Experimental Section:

"The graphite film was treated at 3073 K under an argon atmosphere in the graphitization furnace."

"During the experimental process, the working gas was the argon gas with a purity of 99.999% at room temperature."

"The density functional theory (DFT) was applied to simulate the adsorption behavior of Li-ion on the surface of anode materials as implemented in the Vienna ab initio simulation package (VASP). "

"CR 2016-type coin cells were assembled in a glovebox with an Ar atmosphere. "

II. Some additions should be made:

— Please add to the abstract current density at which the initial discharge and charge capacity of the prepared Ge composite film anode was measured. To guide future readers, I also recommend adding the values of current densities in other parts of the article, where electrochemical characteristics of the prepared Ge composite film anode are given.

— Please add to the description of figure 10a (line 290) the current density at which the cycle performance of the Ge composite film was carried out.

— Please add to the description of figure 11 (line 314) a voltage range and a sweep rate at which cyclic voltammetry measurement of the Ge composite film electrode was carried out.

III. Several minor revisions need to be made by the authors to improve this manuscript:

— Where is figure 3c mentioned in line 172? Add this figure or correct the text with its mention.

— The following is stated in different parts of the article:

"The capacity kept at 580 mAh g^-1 after 280 cycles." (Line 22). 

"After 280 cycles, it kept a capacity of over 580 mAh g^-1." (Lines 105-106). 

"Then the Ge composite kept a capacity of over 580 mAh g^-1 after 250 cycles" (Lines 255-256).

I think it's worth replacing the phrase "250 cycles" with "280 cycles" so that readers don't get confused.

Author Response

Reviewer(s)' Comments to Author 2:

1. Some English grammar and spelling corrections must be done throughout the whole paper. For instance:

— Missing space between 5 and minutes in the phrase "5minutes" in line 118;

— Replace the word "cabon" with "carbon" in line 159;

Below are the full English grammar and spelling corrections for the following sections only: Abstract, Introduction, and Experimental.

Correct this sentence in the Abstract:

— Add "was" in the sentence: "The capacity was kept at 580 mAh g^-1 after 280 cycles."

Correct these sentences in the Introduction:

"It has been utilized in semiconductors, catalysts, optical fibers, and sensors [1-6]". 

"Ge has been also extended to the field of lithium-ion batteries (LIBs) as a result of the rapid advancement of the science and technology [7-13]."

"LIBs, which provide power for electric vehicles, personal computers, and supporting new energy generation, have sparked widespread public concern [14-19]."

"After the de-alloying process, the volume of the Ge-based alloy will shrink."

"The capacity of Ge hybrids was 938.6 mAh g^-1 at 1A g^-1 for 50 cycles."

"The capacity was kept at around 600 mAh g^-1 even when cycled at a current density of 8A/g. "

"The template-asssisted in-situ reduction method was used to create the three-dimensional interconnected porous graphenes [47]."

"The composites’ three dimensional porous graphene improved the materials’ electronic conductivity and reaction kinetics while also providing enough buffer area to minimize volume changes during the cycling and preserved the anode’s structural integrity."

"The flexible graphene framework, which served as an anode for LIBs, was distributed with Ge nanoparticles."

"With the capacity retention of 84.9% after 400 complete cycles, it demonstrated a reversible capacity of 675 mAh g^-1 at a current density of 400 mA g^-1 [48]."

"Dealloying of the GeTiAl ternary alloy in mild conditions made it easy to create a macroporous Ge skeleton that was wrapped by TiO₂ particles [52]."

"TiO₂ particles prevented the Ge skeleton from coming into direct contact with electrolytes by acting as an outer buffer wall for the Ge skeleton."

"The binder and conductive agent that were typically present in traditional Ge-based electrode materials had the potential to boost the stability and the electrical conductivity, but they also decreased the energy density of the whole [54-60]."

"As a result, binder-free Ge-based anode material was promising to elevate the electrochemical performance [19, 31, 61, 62]."

"After 1000 cycles, the binder-free Ge anode had a coulombic efficiency of 99.6% and a reversible capacity of 1300 mAh g^-1 at 1C."

"Additionally, the energy density of the whole electrode increased as a result of the anode material’s decrease of a bind."

"In order to prepare Ge-based composites with novel structures and enhance their electrochemical performance, it is desirable to combine the aforementioned methods."

"The flexible and self-lubricating, good thermal and electrical conductivity of graphite film could also help alleviate stress-strain properties."

"Magnetron sputtering, which was capable of successfully preparing metal and semiconductor film, was used to deposit Ge on the graphite film substrate."

"First, the graphite film substrate was coated with nickel film, and then nickel film was coated with Ge film."

"The morphology of the prepared Ge composite film’s cross-section resembled pyramids."

Correct these sentences in the Experimental Section:

"The graphite film was treated at 3073 K under an argon atmosphere in the graphitization furnace."

"During the experimental process, the working gas was the argon gas with a purity of 99.999% at room temperature."

"The density functional theory (DFT) was applied to simulate the adsorption behavior of Li-ion on the surface of anode materials as implemented in the Vienna ab initio simulation package (VASP). "

"CR 2016-type coin cells were assembled in a glovebox with an Ar atmosphere. "

Response: the manuscript has been revised according to the suggestion.

1. II. Some additions should be made:

— Please add to the abstract current density at which the initial discharge and charge capacity of the prepared Ge composite film anode was measured. To guide future readers, I also recommend adding the values of current densities in other parts of the article, where electrochemical characteristics of the prepared Ge composite film anode are given.

— Please add to the description of figure 10a (line 290) the current density at which the cycle performance of the Ge composite film was carried out.

— Please add to the description of figure 11 (line 314) a voltage range and a sweep rate at which cyclic voltammetry measurement of the Ge composite film electrode was carried out.

Response: the current density of the cycle performance has been added in the corresponding parts of manuscript. The voltage range and sweep rate have been added in the cyclic voltammetry performance.

III. Several minor revisions need to be made by the authors to improve this manuscript:

— Where is figure 3c mentioned in line 172? Add this figure or correct the text with its mention.

Response: in the Fig.3, the Fig.3c was embedded in the Fig.3a. It was the surface appearance of the graphite film.

— The following is stated in different parts of the article:

"The capacity kept at 580 mAh g^-1 after 280 cycles." (Line 22). 

"After 280 cycles, it kept a capacity of over 580 mAh g^-1." (Lines 105-106). 

"Then the Ge composite kept a capacity of over 580 mAh g^-1 after 250 cycles" (Lines 255-256).

I think it's worth replacing the phrase "250 cycles" with "280 cycles" so that readers don't get confused.

Response: the above sentences were revised. The "250 cycles" was replaced with "280 cycles" in different parts of the manuscript.

 

Author Response File: Author Response.docx

Reviewer 3 Report

In this paper, Ge is proposed as an anode for lithium batteries. Ge should be compared to Si which is actually used in commercial batteries mixed usually with graphite as a composite. The theoretical capacity of Si is far much than that of Ge ( almost three times more) but both Ge and Si alloys with Li exhibit a drastic increase in volume (almost 300%). Volume variation induced capacity loss during cycling.  In order to address this problem for Ge, a new strategy has been elaborated: a nickel film is sandwiched between a Ge film and the graphite substrate. The designed composite films were prepared by magnetron sputtering. This method is interesting and could be applied to other kind of active materials.

I do not agree with comments relative to cyclic voltammetry. The cathodic peak at 0.53 V is not due to SEI formation but rather to some Ge-Li alloy as it does not desappears on the subsequent cycles. The SEI peak is near 1.2V. The authors have also to explain the origin of the anodic peaks at 0.5 V, 1.1 V and 1.5V. Fig. 11b represent the Nyquist plot of the Ge composite but I recommand to the authors to use the same unots on both axes and so an semi-circle will be seen as a semi-circle. Moreover, no indication of the frequency of interseting points are reported on the figure and this is very importat for determining which transport process is involved. More comments are needed !

As a conclusion I feel that this preparation method is interesting and could be used with cheaper material than germanium. Nevertheless the manuscript needs improvement before publication as indicated in this report. A comparison with thin silicon anodes would be desirable.

Author Response

Reviewer(s)' Comments to Author 3:

In this paper, Ge is proposed as an anode for lithium batteries. Ge should be compared to Si which is actually used in commercial batteries mixed usually with graphite as a composite. The theoretical capacity of Si is far much than that of Ge ( almost three times more) but both Ge and Si alloys with Li exhibit a drastic increase in volume (almost 300%). Volume variation induced capacity loss during cycling.  In order to address this problem for Ge, a new strategy has been elaborated: a nickel film is sandwiched between a Ge film and the graphite substrate. The designed composite films were prepared by magnetron sputtering. This method is interesting and could be applied to other kind of active materials.

I do not agree with comments relative to cyclic voltammetry. The cathodic peak at 0.53 V is not due to SEI formation but rather to some Ge-Li alloy as it does not desappears on the subsequent cycles. The SEI peak is near 1.2V. The authors have also to explain the origin of the anodic peaks at 0.5 V, 1.1 V and 1.5V. Fig. 11b represent the Nyquist plot of the Ge composite but I recommand to the authors to use the same unots on both axes and so an semi-circle will be seen as a semi-circle. Moreover, no indication of the frequency of interseting points are reported on the figure and this is very importat for determining which transport process is involved. More comments are needed !

As a conclusion I feel that this preparation method is interesting and could be used with cheaper material than germanium. Nevertheless the manuscript needs improvement before publication as indicated in this report. A comparison with thin silicon anodes would be desirable.

Response: the CV process was very complicated, which was related to multiple influencing factors. In the manuscript, it was analyzed partial information of CV. The corresponding part was revised as follows: During its cathodic half-cycle, the cathodic peak was clearly observed at potential of 1.2 V as shown in Fig. 11 a. It possibly resulted from the formation of SEI film. In the anodic scan, there were obvious anodic peak appearing at 0.51, 1.11, and 1.5 V. This might be resulted from the structure and component of the anode material. After the first activation cycle, the electrode material was relatively stable. After next two cycles, the peak potential was shifted to 0.49, 1.06, and 1.56 V and overlapped quite well.

   The equivalent circuit was demonstrated in Fig.11c. C represented the capacitance. Re represented the electrolyte resistance, R_ct represented the charge transfer resistance. Z_w represented the Warburg impedance, R_f represented the resistance of the surface film and contact, and Q represented the constant phase angle element. The values of R_ct and R_f were about 330 and 40 ohm, respectively. Because of the nickel layer covered the whole surface of the anode material, which made it difficult for electrolytes to wet electrode material. And the Ge was a semiconductor, which had lower electronic conductivity compared with that of the good conductor. In the prepared Ge composite film, both the graphite film and nickel film had good electrical conductivity, enhancing the electrical conductivity of the entire electrode. As shown in Fig.11d, it had a protruding peak in the high-frequency region, which was related to the first semicircle in the Nyquist plots. In the medium frequency region, it probably resulted from the interfacial charge transfer impedance. The lithium-ion diffusion usually corresponded to the low frequency.

   The silicon film anode material was being prepared, and characterization tests would need to be done later.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Now manuscript can be accepted

Author Response

Respond to editor and reviewers

Dear editor and reviewers,

 

Thank you very much for your email and the comments from the reviewers about our paper. We have revised the manuscript according to the comments. We submit here the revised manuscript and the changes are in blue mark.

 

If you have any question about this paper, please don’t hesitate to let me know. Thanks a lot.

 

Best regards,

Sincerely yours,

Liyong Wang 

 

Reviewer(s)' Comments to Author 1:

Comments and Suggestions for Authors:  Now manuscript can be accepted

Response: Based on the proposed suggestions, we have a deeper understanding of the electrochemical energy storage. Thank you again.

 

Author Response File: Author Response.docx

Reviewer 3 Report

The quality of the presentation has been improved. Almost all referee's recommendation have been taken into account and the english has been corrected. The interest for the reader is increasing. As a minor correction I recommend to re-draw Fig. 11 (b) which will look better (less distorted) if the units on both axes are the same.

Author Response

Respond to editor and reviewers

Dear editor and reviewers,

 

Thank you very much for your email and the comments from the reviewers about our paper. We have revised the manuscript according to the comments. We submit here the revised manuscript and the changes are in blue mark.

 

If you have any question about this paper, please don’t hesitate to let me know. Thanks a lot.

 

Best regards,

Sincerely yours,

Liyong Wang 

 

 

Reviewer(s)' Comments to Author 3:

The quality of the presentation has been improved. Almost all referee's recommendation have been taken into account and the english has been corrected. The interest for the reader is increasing. As a minor correction I recommend to re-draw Fig. 11 (b) which will look better (less distorted) if the units on both axes are the same.

 

Response: in the revised manuscript, Fig. 11 (b) has been redrawn according to the above suggestion. (Page 14, line 7)

Author Response File: Author Response.docx