(1/n) Last May, I had the chance to present our recent work on solid state electrolytes (Link: https://www.brighttalk.com/webcast/16651/409459). What I didn't have a chance was to answer all questions from the audience -- Follow me and this thread to catch up! https://twitter.com/CellPressNews/status/1260622152543461377

(2/n) The talk mainly focused on the results from these two publications: "Experimental assessment of the practical oxidative stability of lithium thiophosphate solid electrolytes" @ChemMater ( https://pubs.acs.org/doi/pdf/10.1021/acs.chemmater.9b01550)

(3/n) and "How Certain Are the Reported Ionic Conductivities of Thiophosphate-Based Solid Electrolytes? An Interlaboratory Study" @ACSEnergyLett ( https://pubs.acs.org/doi/abs/10.1021/acsenergylett.9b02764)

(3/n) Q: "How can we get XPS characterization for moisture-sensitive materials?" A: Handle the samples with care, but transfer them fast into the chamber. The XPS at our disposal had the possibility of Ar sputtering to remove the first few layers of decomposed material.

Most convenient is having access to a transfer module that prevents exposure of the sample to air at all times.

(4/n) Q: "Using graphite for solid state batteries would result in a reduction of energy densities?" A: This question has many aspects. We should start by establishing that there are two types of energy densities (gravimetric and volumetric).

Since solid electrolytes (SE) are denser than liquid electrolytes (LE), a 1-to-1 replacement of SE for LE will result in a lower gravimetric density. To compensate for this loss, we can think about increasing the overall capacity of the cell.

The capacity can be increased by using high voltage cathodes (>4.0 V vs. Li) or high capacity Li metal anodes. These and other aspects regarding the transition to solid state batteries are very nicely summarized by @ZeierLab and @Janek_Lab_JLU in https://www.nature.com/articles/nenergy2016141

It is well-established in the literature that the thermodynamic stability of thiophosphate-based SEs is limited (see e.g. the work of @YifeiMO who also participated as a speaker in The Future of Batteries Webinar).

And so, our goal for the cyclic voltammetry paper was to determine the electrochemical stability of these materials in practice. We found that these SEs are more stable than what is predicted, but not stable enough to utilize high potential cathodes directly, we need coatings!

Q: "Are the materials (thiophosphate electrolytes) sensible to moisture or not?" A: Yes. The solid-state synthesis of thiophosphate electrolytes requires an Ar glovebox, quartz ampules and electrochemical cell designs that are sealed against air and humidity.

Q: "Are there any materials (thiophosphates) that are commercially available?" A: Also yes, but there are only a few companies that sell these -- NEI Corporation is the first one I can think of (not an endorsement).