New paper from us at ACS Applied Energy Materials (open access). We modeled the localized charging and discharging (i.e. balancing) that happens in a battery after a high current pulse. Great work by Dominick Guida in collaboration with Energizer.
I *wanted* this paper to be about adapting Marcus-type kinetics to MnO2 electrochemistry. But no matter what we tried, adapting a Butler-Volmer expression fit the data better. (AMH=asymmetric Marcus–Hush kinetics.)
We have a new paper out today on polymer-based all-solid-state batteries, focused on the catholyte. We find that when using PVDF, 10% catholyte is a starved condition. But if you replace a little bit of the PVDF with PEO it helps the interface a lot.
We also find that loading up on catholyte has ~some benefits, but also causes the catholyte to agglomerate and hinder transport.
A new paper led by Alyssa Stavola is out today. We study NMC cathodes with an argyrodite sulfide electrolyte. We find *kinetics* are ~13% of the same NMC with a liquid electrolyte, which we attribute to inactive NMC surface area.
We also use micro-XANES and XRF (shown above) to detect reduced Co2+ at the surface of the NMC. The bulk NMC is Co3+. This indicates CoS or Co3S4 at the interface.
We have a new paper out in The Journal of Power Sources, which is a collaboration with Energizer. We use high energy white beam tomography to study the distribution of ZnO in the anodes of cylindrical alkaline batteries. (These are AAA, but we also studied AA sizes.) The finding is that the distribution of ZnO is a strong function of how the battery was discharged. In the image below, batteries (d) and (e) were discharged to the same depth (295 mAh) at the same rate (21 mA).
Continuous discharge (e) matched what you expect from a computational battery model: relatively dense ZnO (pink) found mostly near the separator, around the anode’s circumference. However, if the discharge was pulsed (d), the ZnO had a very low density (blue) and was mostly in large clumps in the anode interior. Since most primary batteries are used in an intermittent or pulsed manner, understanding how this affects where the resistive ZnO is located is important for getting more capacity out of the cells. We found that varying the ZnO density helps reconcile computational models with experimental results.
PhD student Dom Guida came up with a custom segmentation method to analyze these data. All the details are in the paper and the supplemental info. This tomography was special because the resolution was good (a little less than 3 microns) with a quite large field of view, letting us use unaltered AA and AAA cells and record the entire battery diameter.
“Lithiation Gradients and Tortuosity Factors in Thick NMC111-Argyrodite Solid-State Cathodes” Our new work in ACS Energy Letters. Spatial Li gradients change a lot in all-solid-state batteries with NMC loading.
By matching operando synchrotron diffraction data to a computational battery model, we back out the electrode tortuosity factor. In these cells it ranges from 7-25 (much larger than the 2-4 in typical Li-ion cell with liquid electrolyte).