Review Reports

Round 1

Reviewer 1 Report

 

The paper gives an up-to-date review on the study of lithium-ion cathodes by means of the complementary techniques of Compton scattering and positron annihilation spectroscopy. In addition to experimental studies, the results from computational studies of both Compton scattering and positron annihilation in this complex class of materials are presented. The paper is well written und organized, including a general description of each method, specific results of case studies, and a comprehensive overview on literature. In summary, it is a sound review which is interesting to read.

 

The reviewer recommends to consider the following points for minor revision:

Since the redox orbital is a prominent topic of the paper (and even mentioned in the title), its physical meaning should be described in more detail than it is done in the present version (p. 4: „The redox orbital [ 31 ] is a useful concept for describing an electron state ...“)

The combination of Compton scattering and positron annihilation spectroscopy is traditionally well-known in the positron annihilation community for studies of Fermi surfaces and for direct quantitative comparison of momentum distributions obtained from these two complementary methods. A reader of the paper title may therefore at first expect also studies of this kind here. The authors should shortly mention why the combination of these methods was not (respectively, could not) applied for this purpose on this complex class of materials.

In Sect. 5, the term bulk-like state is used. For the general positron community, it would be helpful to describe this state in relation to the usual term free state. In this context, one should also address the issue that positron annihilation spectroscopy is senstive to defect concentration in the range of 10-6 to 10-4, whereas presumably in battery cathodes saturation trapping of positrons prevails. Does the diffusion length of 100 nm (as typical for defect-free crystals), which is scetched in Figure 7, also apply to this complex material class?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The referee’s report of manuscript entitled: “Identifying Redox Orbitals and Defects in Lithium-Ion Cathodes with Compton Scattering and Positron Annihilation Spectroscopies”  by J. Nokelainen et al.

 The manuscript is a review of the experimental results of Compton scattering and positron annihilation on LiBs. The authors present the results obtained by themselves or other authors, published in previous articles. They described both experimental techniques in detail, but such descriptions can be found in many textbooks. It is not clear why they used these techniques that are not actually well suited.  In chapter 6, Conclusions, it is difficult to find solid new conclusions result from their studies.

 I have also other objections.

 Authors should inform readers in the title and abstract that they are reviewing rather than presenting the original research results. Adding 129 citations clearly shows this.

 Figure 1 b. The authors presented the Compton scattering spectrum from Ref. [40]. In this reference no such a spectrum is shown.

Figure 2b was taken from Ref. [40] see Fig. 1 b. This citation was not added.

 Figure 3. The images were taken from Fig. 5 being published in Ref. [37]. This citation was not added.

Figure 4. The images were taken from Fig. 4 published already in Ref. [34] in Fig. 3 This citation was not added.

Figure 5. The plots were taken from Fig. 2 published in Ref. [32]. This citation was not added.

 Figure 6. Presumably the images were taken from Ref. [34] or other. I suppose, because no information about the calculations details.

Figure 7 is misleading, it points out that e⁺ is thermalized entering to the sample. It  is not true.

 They have described the experimental system for Compton scattering in detail, but there is no such information about the positron annihilation setup. In any case, the positron lifetime values presented were taken from the articles by Parz et al. .  

 In the presented form the manuscript is not suitable for publication.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The new version of the manuscript now looks like it is a review of the papers of the authors of the manuscript.