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Surface-Functionalized Separator for Stable and Reliable Lithium Metal Batteries: A Review

Nanomaterials 2021, 11(9), 2275; https://doi.org/10.3390/nano11092275

by Patrick Joohyun Kim

Reviewer 1: Anonymous

Reviewer 2: Anonymous

Nanomaterials 2021, 11(9), 2275; https://doi.org/10.3390/nano11092275

Submission received: 31 July 2021 / Revised: 19 August 2021 / Accepted: 25 August 2021 / Published: 1 September 2021

(This article belongs to the Special Issue Low Dimensional Nanostructures for Electrochemical and Optoelectronic Application)

Round 1

Reviewer 1 Report

The review “Surface-Functionalized Separator for Stable and Reliable Lithium Metal Batteries: a review” describes the role of functionalized separator in Li-ions batteries. The article can be considered for publication in Nanomaterials after major revision. Here the comments:

As first the author must consider the commercial aspects: how does functionalization affect the costs? In conclusions and outlook part, the authors should propose new perspectives for industry. What is the most promising commercial trend?
The authors should add a table (or an image) at the end of the paper showing what is (are) the best separator(s) in full battery with a) highest loading, b) highest current densities applied and c)best . Probably the author should consider NMC, LFP and sulfur cathode chemistries. This table (or image) can help to design future research works.
About the use of carbon as interlayer: is it possible a loss of voltage having consequently a lower energy density?
The authors have to add few sentences in the introduction about the evolution of Li-ion batteries and their role in our society: a) Journal of Solid State Electrochemistry 15, 2011, 1623–1630; b) Materials 13 (8), 2020, 1884; c) b) Angew. Chem. Int. Ed. 51, 2012, 5798 – 5800;
About Lithium sulfur batteries some important reports are missing: a) ACS Appl. Mater. Interfaces 11, 2019, 11459–11465; b) Nano Energy 30, 2016, 1–8 c) Journal of Power Sources 427, 2019, 201-206; d) Electrochimica Acta 192, 2016, 346–356 e) The Journal of Physical Chemistry C 122 (2), 2018, 1014-1023; f) ACS Appl. Energy Mater. 2, 2019, 5793–5798
The authors should consider the loss of capacity is due to a slow diffusion of organic compounds inside the electrolyte during cycling and the role played by the separator to address this issue, therefore the following papers related to this subject must be cited: a) ACS Energy Lett. 2018, 3, 12, 2921–2930 b) Scientific Reports 9, 2019, 1213; c) Journal of Materials Chemistry A, 5, 2017, 6532–6537
The authors must consider other articles about flame retardants such as: a) DOI: 10.1126/sciadv.1601978; b) Journal of Power Sources 506, 2021, 230189; c) Journal of Materials Chemistry A, 8, 2020, 14788-14798; d) Journal of Energy Chemistry 64, 2022, 372–384; e) Angewandte Chemie 131, 2019, 7884 –7889
The authors must add a discussion about the influence of electrolyte on battery performance. Some reports must be cited: a) Advanced Materials 32, 2020, 1904205; b) Materials Science and Engineering: R: Reports 134, 2018, 1-21; c) Journal of Electrochemical Society 161, 2014 , A1001
The importance of SEI nature should be discussed more in details: a) Journal of Power Sources 377, 2018, 7–11; b) Electrochimica Acta 51, 2006, 1636–1640 c) Communications Chemistry 2, 2019, Article number: 131; d) ACS Applied Materials Interfaces 12, 2020, 33719–33728

Author Response

Editor and reviewer comments

Reviewer: 1

Recommendation: Major revisions needed as noted.

Overall Assessment: The review “Surface-Functionalized Separator for Stable and Reliable Lithium Metal Batteries: a review” describes the role of functionalized separator in Li-ions batteries. The article can be considered for publication in Nanomaterials after major revision. Here the comments:

Our response: We thank the reviewer for the overall assessment on our manuscript.

Comment 1. As first the author must consider the commercial aspects: how does functionalization affect the costs? In conclusions and outlook part, the authors should propose new perspectives for industry. What is the most promising commercial trend?

Our response: We appreciate the fruitful comment from the reviewer. As reviewer commented, we edit the manuscript in the conclusion and outlook part. Changed parts are highlighted.

Comment 2. The authors should add a table (or an image) at the end of the paper showing what is (are) the best separator(s) in full battery with a) highest loading, b) highest current densities applied and c)best . Probably the author should consider NMC, LFP and sulfur cathode chemistries. This table (or image) can help to design future research works.

Our response: We appreciate the fruitful comment from the reviewer. The main storyline of this paper is to show how the separator coating layer can affect the cyclability and Coulombic efficiency of Li metal anode. Each coating material has different electrochemical properties when it was applied to polyolefin separators. Considering this fact, it is hard to tell which separator is the best. But, the objective of this article is to give an overview of separator coating materials in order for readers to refer to the characteristics of coating materials. In case of the chemistry of Li-S batteries, it is relatively complicated and different from Li|Cu cells and symmetric Li cells. So, we have mainly focused on the Coulombic efficiency of either symmetric Li cells and Li|Cu cells at a certain cycle number for fair comparison. In many cases, loading mass was not provided in the article, since authors want to compare their separator with conventional polyolefin separator. Therefore, we try to compare the cycle data of Li | Cathode full cell, instead. I believe you understand our intention.

Comment 3. About the use of carbon as interlayer: is it possible a loss of voltage having consequently a lower energy density?

Our response: We thank the reviewer’s comment. There are two important roles of the carbon layer on the polyolefin separator when it is applied to Li metal batteries. 1) It reduces the actual local current densities applied to counter electrode. 2) There is a chance that the carbon layer changes the growth orientation of Li dendrite. We put the relevant information in the main text. (NATURE ENERGY 2, 17083 (2017)) According to the article (Advanced Energy Materials 8 (36), 1802665), the full cell (Li vs. LFP) with the graphene-modified separator has shown improved cycle stability due to the above-mentioned effects of the carbon layer. In this regard, it would be okay to mention that the carbon layer does not affect the loss of voltage. Thanks for your fruitful comment.

Comment 4. The authors have to add few sentences in the introduction about the evolution of Li-ion batteries and their role in our society: a) Journal of Solid State Electrochemistry 15, 2011, 1623–1630; b) Materials 13 (8), 2020, 1884; c) b) Angew. Chem. Int. Ed. 51, 2012, 5798 – 5800