the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Nov 2024
Innovative L-band electron paramagnetic resonance investigation of solid-state pouch cell batteries
Abstract. Usually, the conventional electron paramagnetic resonance (EPR) spectroscopy and imaging use a microwave cavity operating at X-band, i.e. with an excitation frequency of around 9.6 GHz, and remains the most popular mode in the magnetic characterization of lithium batteries to date. We provide here the first low-frequency EPR investigations for monitoring the metallic lithium structures in the solid-state pouch cell batteries. We show that L band, i.e. a microwave frequency of around 1.01 GHz, is an invaluable method to probe in depth the electrode components through a standard pouch cell using aluminum laminated film for packaging without opening the battery. These results offer a new approach for monitoring the nucleation of micrometric and sub-micrometric lithium particles such as dendritic lithium structures which is an important step in the development of reliable solid-state batteries.
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RC1: 'Comment on mr-2024-20', Anonymous Referee #1, 02 Dec 2024
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This paper used a commercial Bruker L-band (ca. 1 GHz) EPR imager to measure a pouch cell lithium ion battery. This image will stimulate extensive applications of L-band EPR to actual batteries and their performance
The paper, however, requires revision to be more comprehensible about the materials used. As written, it would be difficult for anyone to reproduce this work without direct interaction with the lab that did the preparations.
The battery described in this work uses a solid electrolyte and lithium anode. Solid electrolyte LiB are a still developing technology. The majority of LiB in use in personal devices and automotive applications have a liquid electrolyte. There are commercial sources of aluminum encased pouch cells with liquid electrolyte. Could the authors to comment on the feasibility of repeating this experiment with liquid electrolyte LiB? It would have an immediate tie in to the most widely deployed type of pouch cell LiB.
Did they select a lithium anode because they thought sensitivity issues would prevent them from directly observing the cathode material EPR at 1 GHz? Typically, the anode is a graphite-based material. There are stated to be increased safety concerns for the solid lithium anode in terms of thermal runaway.
The authors should add a section discussing the implications of this first experiment. How would they expect the lithium EPR signal to change as a function of ageing in this pouch cell? What do they think they would see with a graphitic anode pouch cell? The EPR audience may not know why these pouch cells are important compared to steel-cased cylindrical cells. For instance, the flexibility in packaging allows pouch cells to be tailored to specific space constraints better than rigid cylindrical cells. The authors don’t need to “take down” cylindrical cells, but they could spend a little time answering the ”so what?” question, which also helps convey the importance of this first measurement.
What is the composition and availability of NMC, SE, the liquid electrolyte, the pouch batter studied, etc. “An argyrodite-type-sulfide electrolyte” is too vague to be useful.
What does it mean that “the different layers were punched”?
It is not evident how “the voltage was then controlled to ensure the pouches were not short circuited.”
Presumably the resonator used was one produced by Bruker. The model/part number should be stated.
What do the authors mean by “can cause serious perturbations of the dielectric”? The context of the statement suggests that they really mean that the conductivity of the metal cell distorts the microwave magnetic and electric field distributions. This is repeated on page 4.
The statement in line 76 that T2 is approximately 10-9 s is inconsistent with the reported results. 10-9 s would correspond to about 65G peak-to-peak derivative spectrum. They report 3 G on the next page. In addition, the paper should provide references for the relaxation times.
The caption of figure 2 should include the microwave B1 at the sample, and the modulation amplitude and frequency used.
The data described in lines 100-105 are not otherwise presented in the paper, and there is no mention of how they were measured. Possibly the information is from a report in the literature and references should be given.
The paper should report and comment on problems encountered in this imaging measurement and solutions developed. The primary value of this paper is to say “yes, you can study these metal pouch batteries with commercial instruments.” It is of value to publish as more than a claim to priority only if it contains proper information to make it reproducible.
The reviewer happens to be aware of other very similar unpublished measurements.
To the editor:
Prior to receiving this paper I was involved in planning similar measurements
Citation: https://doi.org/10.5194/mr-2024-20-RC1
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