Peer review of: Metal chloride perovskite thin film based interfacial layer for shielding lithium metal from liquid e (2020)

Editorial Note: Parts of the figures in this Peer Review File are reproduced with permission. Detailed information 
can be found at the end of the Peer Review File. 

Reviewers' comments: 

Reviewer #1 (Remarks to the Author): 

The authors present a simple route to prepare two kinds of metal chloride perovskite thin films as 
solid electrolyte interfacial layers for lithium metal anodes. The perovskite thin films with low energy 
barriers facilitate fast Li+ ion transport, realizing dense deposition of lithium even at high current 
density of 5 mA/cm2. The paper is well organized, but some points should be further clarified. A major 
revision is needed for further consideration. 

1. In many cases, the perovskite shows poor stability. It is shown the Sn XPS peak was broadened
after cycling. Thus, in this study, the stability of perovskite structure in the long cycling should be
further discussed.

2. LTO usually has good cycling stability. However, in Fig.4a, a fast capacity decay was shown for the
LTO battery after 500 cycles, which should be further explained.

3. The authors mentioned a Li-M alloy layer will be formed during a conversion-type electrochemical
reaction, but the element M is not clear initially. More details should be added.

4. The authors mentioned “a gradient thin film consisting of perovskite framework on the top surface
to isolate the liquid electrolyte and Li-M alloy layer”. But according to the EDS mappings, the
perovskite thin film is uniformly distributed along the cross section of the film.

5. The authors mentioned a Li-M alloy layer together with a LiCl layer are formed between the
perovskite thin film and deposited lithium, more evidences are better to be provided.

6. If a Li-M alloy layer mixed with LiCl is formed, how can Li+ ions pass through this alloy layer, and
this should be further explained.

7. The authors mentioned the perovskite thin films allow fast Li+ ion transport throughout its
framework, the Li+ ion conductivities of the MASnCl3 and MAPbCl3 thin films need to be provided.


Reviewer #2 (Remarks to the Author): 

The work by Hongbin Yao et.al fabricated a robust metal chloride perovskite thin film on the Li metal 
anode to isolate Li metal from liquid electrolyte in liquid lithium batteries. Although organic-inorganic 
halide perovskites have been used as anode materials in LIBs in recent reports, this work should be 
the first report about using such metal chloride perovskite as protective layer for Li anode. Taking 
advantages of spontaneous reaction between metal chloride perovskite and Li metal, a SEI layer can 
be in-situ formed on Li metal with fast Li+ transport. As reported in this article, an improved cycling 
stability can be realized by this interfacial strategy. To get this article qualified enough to be published 
on Nature Communications, however, there are still some points need to be addressed. 

My detailed comments on the manuscript are given bellow: 

1. The "solid electrolyte thin film" in the tile is a little bit misleading since there's a big difference
between "solid electrolyte thin film" formed on the surface of Li metal and real "solid electrolyte thin
film" fabricated by solid-state electrolyte. 
 
2. Low energy barrier does not always indicate fast Li+ migration, what is the value of the real Li+ 
conductivity of the metal chloride perovskite? Furthermore, as indicated by the authors, Li+ 
interacalation and conversion reactions happened when metal chloride perovskite contacts with Li 
metal, how would the Li+ conductivity change? 
 
3. Fig S.2a does not reflect the Li+ migration pathway through the lattice of perovskite, please modify 
that. 
 
4. XPS depth profiling need to be further conducted to confirm the valence state of Sn or Pb not on the 
top surface and but also that directly contact with Li. 
 
5. The (100), (200), and (300) diffraction peaks of lithiated perovskite shown in Fig 3c and Fig S9a 
are quite overlapped with that of the sealing bags, please re-consider the assignment of those three 
peaks by testing the XRD pattern of MSC-Li (before and after cycling) covered by films that do not 
show any sharp peaks (such as Kapton film). 
 
6. The Ref. 35 presented higher-angle shift for XRD patterns of the lithiated perovskite electrode, 
which is opposite to the results showed here, please explain that. Another concern is that no other 
species due to the conversion and alloying reactions are reflected in the XRD patterns. 
 
7. Some related references need to be cited, such as: Electrochemical Energy Reviews 1, no. 1 (2018): 
35-53; Electrochemical Energy Reviews 2, no. 1 (2019): 1-28; Angew. Chem. Int. Ed. 2019, DOI: 
10.1002/anie.201909805; Advanced Materials 30.45 (2018): 1804684.