Two more excellent papers

Two more excellent Li-S battery papers from @yuchuan_chien published in as many days!

First: a study of the effect of electrode compression/calendering on electrochemical performance, w/ operando XRD and x-ray CT, published in @Batt_Supercaps.

This study really started as far back as 2015, following already published work showing calendering improved cycle life… which we initially found too but got poor reproducibility over the first couple of years. Eventually, Yu-Chuan found a way to get consistent results. And this looked promising, because we could compress an electrode to ~1/3 of its original thickness without sacrificing much performance, which seemed to have good implications for volumetric energy density, one of Li-S’s (many) weak points. Problem is that a lot of other factors come into play as well, affecting capacity and resistance and we struggled to understand what was actually going on. So even though Yu-Chuan’s PhD started out on this research question, it needed 4 years of method development to answer…

Now with CT, we could quantify porosity and tortuosity in the electrodes, and with the operando XRD + resistance analysis methods developed in recent years, follow how lithium sulfide (Li2S) is formed in the electrodes depending on the degree of compression. (The bad news is that the electrode expands back to close its original thickness after a few cycles, blunting hopes for improved energy density somewhat… perhaps a better binder would help.)

Next, Yu-Chuan’s study on correlating precipitation processes to electrochemical performance through operando small-angle scattering is now published in Chem. Something of a development of the operando XRD methods already developed, the small-angle neutron & x-ray methods let us look at physical particles, and not just the crystalline stuff. This mattered because we found that at quite low currents we started getting an amorphous product forming close to end of discharge.

Correlating this to electrochemical measurements (and taking into account the other studies done over the period of Yu-Chuan’s PhD) we could conclude that depletion of Li ions in the pores of the carbon host is probably limiting the discharge capacity at low rate. And I think these papers, my 17th and 18th on lithium-sulfur I have co-authored, will be the last Li-S papers I am involved in for the forseeable future…