Sodium-Conducting Ionic Liquid Electrolytes: Electrochemical Stability Investigation

Round 1

Reviewer 1 Report

Reviewer’s report

Article number: applsci-1680754

Article type: Full paper

Article title: Sodium­conducting ionic liquid electrolytes: I. Electrochemical stability investigation

Authors: G. Maresca, P. Casu , E. Simonetti , S. Brutti and G.B. Appetecchi

Reviewer’s recommendation: major revisions

 

Review:

The results presented by the authors seems okay but a better interpretation of the voltammety data is desired. Also, if possible author’s may consider doing EIS experiments. It is also suggested that the authors also perform plating experiments and compare the Tafel slope.

 

 

1. Page 1, line 31: “2.71 V vs. H + /H 2 ) of Na with respect to Li.” The sentence seems badly formed

2. Page 4, line 139: When the authors mention minor impurity what they imply. A normal 3 electrode voltammetry should be capable of detecting any. Curiously the hump seems to be absent in CV’s. The authors must put more rigor as well an explanation

3. What is the significance of Table 2 vis-a-vis figure 1

4. Figure 6, did the author’s measured the OCV of a full cell??

 

Author Response

Reviewer #1

The results presented by the authors seems okay but a better interpretation of the voltammetry data is desired. Also, if possible authors may consider doing EIS experiments. It is also suggested that the authors also perform plating experiments and compare the Tafel slope.

Authors’ replies

The authors thank the reviewer for the positive comments. The manuscript was modified according to his/her recommendations. All changes in the text were highlighted in yellow. EIS and plating experiments were object of near-future investigations.

Page 1, line 31: “2.71 V vs. H+/H2) of Na with respect to Li.” The sentence seems badly formed.

Authors’ replies

The sentence was modified according to the reviewer suggestion.

Page 4, line 139: When the authors mention minor impurity what they imply. A normal 3 electrode voltammetry should be capable of detecting any. Curiously the hump seems to be absent in CV’s. The authors must put more rigor as well an explanation

Authors’ replies

The authors thank the reviewer for this point, so the text was modified. Also, the authors agree about the reviewer suggestions. However, the main purpose of the present work is performing an electrochemical investigation on the IL electrolyte formulation for assessing their feasibility both at the cathode and anode side in sodium-ion batteries. Further investigation is actually in progress for better understanding this issue.

What is the significance of Table 2 vis-a-vis figure 1

Authors’ replies

The voltage values reported in Table 2 were determined by the CV measurements reported in Figure 2. The text, however, was modified accordingly. 

Figure 6, did the author’s measured the OCV of a full cell??

Authors’ replies

The manufacturing and validation of HC/NMO full-cells is out of the purpose of the present work and will be object of future paper. However, the OCV value of a full-cell generally ranges from 0.3 to 0.4 V.

 

 

Reviewer 2 Report

The paper “Sodium-conducting ionic liquid electrolytes: I. Electrochemical stability investigation” by G. Maresca, P. Casu, E. Simonetti  , S. Brutti  and G.B. Appetecchi is devoted to timely issue –investigation of lithium-free batteries. For that purpose the authors have performed a number of experiments with various sodium-conducting electrolytes. As a result of experimental tests two types of the electrolytes were recognized as the most prospective. In general the paper is well written and can be published after minor corrections.

There are some comments concerning the paper:

• p.1., line 45: misspelling – combing instead of combining;
• p.5., line 160: Figure 8 instead of Figure 2.
• p.6. Mechanism of electrode degradation in presence of impurities should be explained in more depth.

Author Response

Reviewer #2

The paper “Sodium-conducting ionic liquid electrolytes: I. Electrochemical stability investigation” by G. Maresca, P. Casu, E. Simonetti, S. Brutti  and G.B. Appetecchi is devoted to timely issue – investigation of lithium-free batteries. For that purpose, the authors have performed a number of experiments with various sodium-conducting electrolytes. As a result of experimental tests two types of the electrolytes were recognized as the most prospective. In general, the paper is well written and can be published after minor corrections.

Authors’ replies

The authors thank the reviewer for the positive comments. The manuscript was modified according to his/her recommendations. All changes in the text were highlighted in yellow. 

There are some comments concerning the paper:

p.1., line 45: misspelling – combing instead of combining;

Authors’ replies

The text was modified according to the reviewer suggestion.

p.5., line 160: Figure 8 instead of Figure 2.

Authors’ replies

The text was modified according to the reviewer suggestion.

p.6. Mechanism of electrode degradation in presence of impurities should be explained in more depth.

Authors’ replies

The authors agree with the reviewer. However, the main purpose of the present work is assessing the feasibility of the developed electrolytes at the interface with sodium battery electrodes. A deeper investigation of the contaminant effect on electrolyte degradation mechanism is out of the purpose of this manuscript and will be object of coming-soon studies.

Reviewer 3 Report

This manuscript investigated the electrochemical stability of the synthetized electrolytes by voltammetry measurements with the aim of evaluating their feasibility in Na-ions devices. Both the anodic and cathodic sides were studied. They also investigate the effect of contaminants as water and/or molecular oxygen on the electrochemical robustness of the electrolytes. Preliminary cyclic voltammetry and charge-discharge tests were carried out in Na/hard-carbon and Na/α-NaMnO2 half-cells, and the results show that EMIFSI and N1114FSI electrolytes allows the reversible sodium intercalation without any degradation process charged to the electrolyte. The authors think that it is likely due to a stable SEI layer promoted by the FSI anion. I recommend its publication on Applied science with revision noted below.

 

1: In this manuscript, the authors only use voltammetry measurements to evaluate their feasibility in Na-ions devices. They just simply mention that it is likely due to a stable SEI layer. The authors should give more evidence.  

 

2: The presence of impurities as water and/or oxygen is able to negatively affect the electrochemical performance of the electrolytes. It is Predictable results, and the authors should focus on the effect of the impurities on the properties of anodic and cathodic sides.

   

3: The charge-discharge cycling stability of Na/hard-carbon and Na/α-NaMnO2 half-cells may be better to evaluate the feasibility of the synthetized electrolytes. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I believe that the authors have addressed my queries to my satisfaction,

Reviewer 3 Report

No comments.