Lithium on CH Divacancy Self-Healed Graphane: A First-Principles Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this work, density functional theory (DFT) calculations were conducted to study the energetic stability, structural and electronic properties of Li on graphene with various CH divacancy configurations. The results show that adsorption of Li atom stabilizes the CH divacancy configurations. The charge doping Li^-1-v₁₂ or Li⁺¹-v₁₂ alters the energetic stability, structural properties and electronic characters of Li-v₁₂. The electronic density of states plot for Li^-1-v₁₂ reveals an abundance of electrons and increase in conductivity. Here are comments for this manuscript.

1. In lines 113-114 and 121-122, 6×6 graphane supercell was used to calculate the formation energy and binding energy. However, in line 105, 9×9 supercell of graphane was used for all calculations. Please double check that.
2. In line 43-44, band gaps of graphane were theoretically predicted using different XC functionls. Besides, the band gap of graphane with CH divacancy (v₁₂) was computed in this work (line 234). Are there any experimental results showing the band gap of graphane or graphane with CH divacancy? If yes, please list the experimental results as comparisons.
3. In line 208, the binding energy of Li on pristine graphene is 1.04 eV (ref 31). However, this energy in Table 1 is 1.10 eV (ref 31). Please double check that.
4. In line 18, The Li^-1-v₁₂ enhances the binding force between Li and v₁₂ configuration. However, the binding energy of Li^-1-v₁₂ and Li-v₁₂ is 3.21 eV (line 218) and 3.25 eV (Table 1), respectively. The Li^-1-v₁₂ does not enhance the binding strength according to the conclusion in this manuscript (larger binding energy, stronger binding strength)
5. In Fig 2, the formation energy of Li on divacancies is lower than their corresponding divacancies, therefore, adsorption of Li atom stabilizes the CH divacancy configurations. That makes sense according to the equation of formation energy (equation 1). Same as the equation of binding energy (equation 2), smaller E_b indicates stronger binding strength. However, in this manuscript, the authors claim that larger binding energy indicates stronger binding strength. Can the authors explain this inconsistency?

Author Response

Dear reviewer,

kindly find the attachment.

regards,

Edwin

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript describes a computational study of the interaction of lithium atoms with graphane (hydrogenated graphene) with a focus on its potential application as an electrode material in lithium ion batteries (LIBs). The authors use density-functional theory (DFT) calculations to study the stability of a series of CH divacancies in graphane, the healing processes (structural relaxation) occurring in graphane after the formation of the divacancies, and the influence of the divacancies on the ability of graphane to adsorb lithium atoms. The changes in the electronic structure of the material after vacancy formation, structure relaxation, and lithium adsorption are analyzed in terms of densities of electronic states. The results indicate that one particular vacancy geometry ("v12") exhibits the largest stability. The adsorption of lithium further increases its stability and leads to the appearance of hybrid electronic states in the vicinity of the Fermi energy, with a consequent transition to a metallic regime. This indicates that Li-adsorbed graphane in the presence of v12 divacancies may provide a suitable material for LIB electrodes. 

The work is competent and well carried out. The level of theory used in the DFT calculations (HSE06 approximation) is quite reliable, and this makes this study important as a reference for future work on defective graphane and related systems. The presentation is in general clear and the level of detail is appropriate. The electronic structure analysis is detailed and focussed. In my opinion, the main findings of the work are well supported by the DFT results described. I recommend publication, but I would like the authors to address a few minor suggestions for improvements listed below.

1) The authors used HSE06 for the DFT calculations, which is a very accurate but also quite computationally demanding approach. Why was this high level of theory required for the systems examined in the work? Did the authors make any comparative study of the effects of exchange-correlation approximation on the structural and electronic properties of the systems examined? 

2) The stability of the divacancy structures and of the Li-adsorbed systems was discussed in terms of total energies, formation energies, and binding energies. Is it possible to support further the stability of the structures considered by computing their phonon spectrum and/or by performing ab initio molecular dynamics simulations. 

3) In Table 1, the binding energy should be consistently labeled E_b. For instance, in the table heading it is incorrectly indicated as E_B.

Comments on the Quality of English Language

The paper is readable, but there are several typos and some sentences may need to be improved before publication. Some sentences are imprecise. For instance, at lines 91-92, "which the PBE functional is mixed with the non-local Fock" should be replaced with "which contains a fraction of non-local Hartree-Fock exchange". I recommend the authors to address carefully potential ambiguities in the text while revising the paper. 

Author Response

Dear Reviewer,

kindly find the attached report.

kindest regards,

Edwin

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In the manuscript "Li on a CH divacancy self-healed graphane: A first-principles study" by R. E. Mapasha, S. P. Kgalema, H. Mapingire and E. Igumbor, different CH divacancy configurations in graphane and their effects on Li adsorption are investigated using state-of-the-art ab initio code.

Overall, the study presents valuable insights into the application of graphane as electrode material in Li batteries.

However, I have identified a few points that require clarification and further discussion.

1) The computational details mention the use of a "9x9 supercell of graphane" for all calculations, yet there seems to be a discrepancy. In the same section, it is stated that the formation energy and binding energy are evaluated in the "6x6 graphane supercell," which contradicts the earlier statement. It is unclear whether the formation and binding energies pertain to calculations on the supercells with reconstruction as depicted in figures 2c, d, e, or if they refer to another supercell. Please clarify this inconsistency to ensure the accuracy and reproducibility of the results.

2) The manuscript highlights that the binding energies for Li-v12, Li-v13, and Li-v14 are higher than that of Li on pristine graphene. This observation raises concerns regarding the feasibility of utilizing graphane as an electrode material, as high binding energies can impede the deintercalation process. I recommend discussing the implications of these elevated binding energies on the practical application of graphane and potential strategies to mitigate this issue.

3) The manuscript touches upon the issue of spurious electrostatic interactions among charge replicas in different periodic images for the Li+1 and Li-1 systems. It is crucial to elaborate on how this issue is effectively addressed in the study.

4) In the introduction, the authors report that the work of Watcharinyanon et al. [18] investigated the intercalation of Li ions on graphane by experimental techniques. Unfortunately, the paper of Watcharinyanon with title "Hydrogen intercalation of graphene grown on 6H-SiC(0001)" does not study Li intercalation. Rather, Watcharinyanon et al. cited the paper of Virojanadara at al. [Phys. Rev. B 82, 205402 (2010)] that investigates Li adsorption on graphene.

Comments on the Quality of English Language

Some minor amendments are necessary.

Author Response

Dear reviewer,

kindly find the attached report.

regards,

Edwin

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I am satisfied with the author's response. The quality of the manuscript has been significantly improved after revisions. I therefore recommend that this manuscript be accepted in present form and published in Nanoenergy Advances. 

Author Response

Thanks for accepting our manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have addressed competently and satisfactorily the points I raised in my previous report. I recommend publication of the revised manuscript.

Comments on the Quality of English Language

The English language has been revised and improved. Minor editing/spellchecking may be required in the publication version of the paper.

Author Response

Thanks for accepting our manuscript. We have performed the spellcheck for the entire document.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have satisfactorily improved the manuscript following the reviewer's comments. Therefore, I recommend the present manuscript for publication.

Author Response

Thanks for accepting our manuscript.