https://news.ycombinator.com/item?id=36585327

Toyota has been putting out PR puff pieces about their "solid-state" (solid-electrolyte) batteries for years, but this story was unique in that it had a quote from Keiji Kaita, who holds some high-level role at Toyota. Anyway, I didn't think much of it, because there was no paper referenced in the Guardian article, which seemed to be the original source.

But while reading about something else, I came across the paper "A near dimensionally invariable high-capacity positive electrode material", published in Nature Materials last December:

https://www.nature.com/articles/s41563-022-01421-z

This paper, reporting a cathode that has very little (much less than normal) change in size or shape when charged and discharged, claims reversible storage with a solid electrolyte. It stands to reason that dimensional stability of the cathode is necessary for interfacing with a solid electrolyte, since if it swells and shrinks, it will probably detach from the electrolyte, and possibly damage it further.

Looking at the affiliations of some of the authors we see a number of contributors from the "Lithium Ion Battery Technology and Evaluation Center (LIBTEC)". A web search about LIBTEC leads to several articles from 2018:

https://www.cnet.com/roadshow/news/toyota-nissan-honda-libte...

which state that Toyota, along with Nissan, Honda and Panasonic (Tesla's major collaborator), have established this consortium to work on solid-electrolyte batteries as of five years ago.

So what does this thing look like? It's a vanadium–titanium cathode, Li8Ti2V4O14. Titanium is common; vanadium technically has a higher crustal abundance than nickel, but it tends to be spread across low-quality deposits, so production is low right now. A review considering the resource outlook for V-based batteries [1] was guardedly optimistic. 750 Wh/kg is great. Vanadium cathodes historically had a problem with high dimensional instability, but it appears that cocrystallization with titanium may have fixed that, and the weird properties of vanadium became an advantage in compensating for Li+ influx/efflux.

The use of a sulfide electrolyte pours doubt on claims of safety, though. It's reasonably likely that if water were to come into contact with the electrolyte, it could release highly toxic hydrogen sulfide gas.

Also, since the battery was developed in collaboration with other major automakers (and funded by the Japanese government), it's somewhat questionable to think it would give Toyota a major advantage in the EV race. But for the Japanese economy, which has been rather slow lately, it could be a boost.

1: https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10....