Peer review of: Spatial quantification of dynamic inter and intra particle crystallographic heterogeneities within li (2020)

Reviewers' comments: 

Reviewer #1 (Remarks to the Author): 

The article is based on solid experimental results consisting of high resolution XRD-CT data. The data 
provide the framework to understand the phase change and degradation mechanisms in LMO cathode 
particles and can be extended to other material systems. In this respect, the manuscript is valuable. 
However, I have some reservations regarding its publication in Nat-Comm as mentioned below. 
1. The logical argumentation which provides the extension of experimental observations to the 
insights and predictive understanding is weak. With such detailed information, it should be possible to 
provide some guideline to build quantifiable prediction model for particle degradation. 
2. The logical flow in the following paragraphs is vague: the one starting at line #119 and the one 
starting at line #200. 
3. In the introduction, there are few misconstrued statements in regards to the literature which are 
factually wrong. For example, in line 47, the referred paper says exactly the opposite as claimed by 
the authors. 

Reviewer #2 (Remarks to the Author): 

NCOMMS-19-33161-T is an interesting manuscript that reports in-situ x-ray diffraction (XRD) 
tomographic study of a LixMn2O4 electrode as it was electrochemically cycled. The cycling procedure 
was purposely paused for the data acquisition to take place because the measurements are rather 
time-consuming. Although this material system is already well investigated and documented, the 
authors nicely utilized the XRD tomography’s sensitivity to the local crystallographic structure to 
visualize the inter and intra particle chemical heterogeneity, which is a broadly observed phenomenon 
and is believed to play an important role in the cathode degradation. In particular, the authors 
captured many particles at once with micrometer spatial resolution, which facilitated in-depth analysis 
of two selected particles, highlighting the coexistence of multiple phases within individual particles. I 
think this manuscript is of interest to researchers working in this field and, therefore, I recommend 
the publication of this paper with specific comments listed below for the authors to address. 

1) The authors highlighted that their data has five dimensions (x, y, z, time, and diffraction). However, 
the majority of the manuscript focused on a single slice, which is understandable as the multi-slice 
data acquisition would take much too long for a study like this. I would recommend the authors to 
take out the buzzword “5D”, which doesn’t add much scientific value here, instead, it could cause 
confusion. 
2) The electrode used in this work was 80 microns thick. One would expect to see a significant 
polarization effect in such a configuration. [see Adv. Energy Mater. 1900674, (2019)]. How did the 
authors choose the z position? Some discussions along this line will be useful. 
3) Maybe I missed this point, how was the reconstruction carried out? Did the authors conduct the 
projection XRD data refining, then use the phase fractions as input for tomographic reconstruction? 
4) The authors nicely captured many particles at once, which could offer an opportunity for statistical 
analysis. For example, is there any particle size dependence? A quick look at Figure 3a suggests that 
smaller particles appear to be red-orange, and the larger particles appear to be pink. I understand 
that the actual available data is over a 2D slice, but couldn’t help to notice this pattern. 
5) Particle 1 is attributed to the Li-rich compound Li1.10Mn1.90O4 . Where is it coming from? It has 
been reported that the resistance for Li diffusion in the Li-rich compound could be quite high at 
charged state [RSC Adv. 2, 8797 (2012); J. Phys. Chem. C 114, 22751, (2010)]. It could result in a 
core-to-surface Li concentration gradient [J. Am. Chem. Soc. 141, 30, 12079-12086 (2019)]. How do 
these reports relate to the observation in this current work? 



Reviewer #3 (Remarks to the Author): 

This is a strong submission. Questions for the authors: 

On line 78 the authors detect crack formation starting from internal pores. Does this support or 
contradict the predictions of Cheng et al, Journal of Materials Research 25:1433 (2010)? 

On line 88, "inter" should probably be "intra." Do the authors have any information about inter-
particle cracks, such as would occur when the binder fails? 

I don't understand the significance of the arrow in Figure 2a. Is it meant to show that a particular 
particle observed in the first image was imaged again in image 1? If so, where is the particle in the 
other images? 

I'm not sure about the description of some of the histograms in Figure 2a as bimodal. It could be that 
the authors are referring to the dip in the center of the histogram. If so, I am not convinced that the 
dip is real and not just noise. 

On line 177 the authors state that the cell was cycled twice. Do they have data for each cycle? Are 
they significantly different? 

In previous work the authors have seen macroscale strains during lithiation. Do they see it here also?