Basically all the battery technology research of the last two decades or more has been trying to make them more energy dense and lighter for mobile devices and vehicles. However this doesn't matter very much for stationary backup storage, so there are still a lot of low-hanging fruits for people to develop cheaper and more durable battery storage. In fact most of these systems still use lead-acid batteries, which are quite ineffecient.
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Thing is that even though this is indeed the main focus, as a byproduct of that research we literally have dozens of alternative battery chemistries available with different features.
Indeed, but they need to be also be made available for people to buy and that usually still involves a lot of further product development. Right now it seems more common to just re-purpose automotive lithium-ion batteries for stationary storage, which might be better than lead-acid batteries, but really isn't ideal either.
still involves a lot of further product development
That's what hackerspaces and fablabs are for!
Disclaimer: I am a member of a fablab that explores open hardware automation and solar techs :-) We have talked about producing batteries but have too many items on the todo list for now
Not a physicist or chemist so I wont pretend to know if this is as viable alternative to lithium as its proponents insist, but if it is I'm very excited for this tech.
Google "Iron batteries" if you are interested in building some. This is a tech that is not super efficient in terms of Wh/kg but that is extremely cheap so it can make sense for a static powerwall-style installation. If only we produce it to scale. Exploring the automation of this process has been on my todo list for a while.
On the plus side as well (and kind of the reason why it is so cheap) is that it does not require any "exotic" material or rare earth. From what I heard (did not check personally, I have zero chemistry skills) there is one nasty chemical in the production process but it is reusable and does not need to be discarded.
Just wanted to share a likewise iron powder battery. I have read something of a battery with iron particles being developed in Eindhoven, the Netherlands. But in retrospect after reading the article the powder is used for combustion but the regeneration or derusting is done by electricity from hydrogen or something like that source.