Abstract: “We demonstrate for the first time an intermediate temperature (250-350°C) molten hydroxide mediated electrodeposition process to grow ternary lithium manganese oxide chemistries (Li2MnO3, LiMnO2, and LiMn2O4). State-of-the-art synthesis routes for such cathodes for lithium-ion batteries involve prolonged high temperature (over 700°C) processing for long reaction times under high oxygen pressure, followed by slurry casting after mixing with binders and additives. Our electrodeposited oxide cathodes are synthesized with the lowest reported temperature and reaction times, yet still retain the key structural and electrochemical performance observed in the high-temperature bulk synthesized analogs. The binder-and-additive- free, tens of microns thick, greater than 80% dense electrodeposits exhibit near theoretical gravimetric capacities and reversible areal capacities up to 1.5 mAh/cm^2.”
East Central IL ACS Undergraduate Research Conference
Thank you for joining us for the 5th Annual ECI-ACS conference!
Thank you for listening! I’m glad my comments were able to answer your questions.
Very succinct presentation. I had a couple of questions regarding the stability of LMO compared to cobalt and performance of battery over several cycles. However, I see that you have already provided an excellent explanation. Again, great presentation!
Thank you for listening! I’m glad my comments were able to answer your questions.
Excellent presentation, I enjoyed your talk! I have a few questions about your work. In your intro, you say LMO has a higher thermal stability than the cobalt counterpart. At what operational temperature do you see that benefit? Also, you introduced the value of obtaining >25 um thick cathodes. Would you be able to put that into context to describe how this compares to what would be desired? I am interested in learning more about the annealing process you used. Are you able to speak to the optimization process and if there are any potential opportunities to improve the Li2MnO3 content beyond 55%? By SEM, it looks like the two phases of LMO are heterogeneously dispersed. Do you have any thoughts about what a more homogeneous dispersion would do for electrode capacity? What does the battery performance look like on the order of 100s of cycles? (I know fundamentally battery materials development researchers tend to dislike that question but had do ask anyway!) Lastly, I am interested in your thoughts about the value of porosity in developing robust batteries. I know other material systems sometimes prefer highly porous systems so electrodes suffer less damage during rapid charge/discharge. Are you concerned about damage to the cathode material under rapid charge/discharge conditions? Feel free to respond to just a few of the questions since I asked quite a few. Great presentation!
Thanks for listening to my presentation! Great questions, I’ll do my best to answer all of them.
At temperatures above 40 degrees Celsius, degradation can begin to be observed in cobalt-based cathodes, whereas manganese-based systems can operate without degradation up to 50-60 degrees Celsius. This is what makes LMO better for high-temperature battery applications.
On your question about thickness, the thickness of a cathode is directly related to the energy which it can store (i.e. the energy density). Achieving 25 um thick cathodes is important because that is the size of many commercially available cathodes, whereas most of the other reports in literature of direct depositions of LMO are very thin (25 um shows that our synthesis method can produce cathodes that match the thickness and energy density of those which are commercially produced.
The annealing process we use involves placing the as deposited cathode in a tube furnace in air at 550 C for 6 hours. There could potentially be opportunities to shift the phase composition to be richer in Li2MnO3 using higher temperature annealing, but there is a trade-off. The electrical conductivity of Li2MnO3 is several orders of magnitude lower than that of LiMnO2, so having more Li2MnO3 also reduces the power performance and efficiency of a battery. So, although Li2MnO3 has a higher capacity, having a “pure” Li2MnO3 cathode is not exactly desirable. The goal is to produce a composite of Li2MnO3 and LiMnO2 with a composition that optimizes both the capacity and the electronic conductivity.
Your question on the phase dispersion is interesting. A homogeneous dispersion would probably result in a better cycling performance. In the synthesis which I presented, LiMnO2 is electrochemically oxidized from MnO and Li2MnO3 is oxidized from Mn2O3 (MnO and Mn2O3 are the components of Mn3O4). One way to try to homogenize the deposit would be to do a layer-by-layer electrodeposition (i.e. several depositions ~1 um thick) using two molten salt baths (one with MnO, and another with Mn3O4). That would produce multiple layers of LiMnO2 and Li2MnO3 that could be annealed for a homogeneous coating.
Great question on cell cycling, which is an important metric. The cell which I’ve presented on is still running well and showing good performance after about 76 cycles (only 27 cycles were completed and reported on in the slides).
You are absolutely correct that less porous systems can degrade faster through rapid cycling. Porosity plays a more important role in the anode part of the battery, as anode materials (e.g. Si or Sn) expand in volume more than 400% during cycling. Intercalation cathodes like the ones I show here expand ~15-20 % during delithiation, and our structure and interfacial bonding is strong enough to sustain the stress. Even though our cathodes are dense, they have fast Li-ion and electron conducting facets aligned vertically (which can be seen if you zoom into the layered structure shown on the SEM slide). Li ions can easily diffuse through those channels. That is why, even at high current densities we do not see any major degradation of the cathode. We can also confirm this from the texture of the peak (the facet that conducts Li ions faster) at around ~55 degrees in the x-ray diffraction plot for both the as deposited and annealed samples.
Thanks again for watching my presentation! I appreciate your time, and
please let me know if you have any more questions.
Thanks for the responses to all the questions!
Great presentation, brief and to the point!
Thank you for listening!