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Sineng Electric launches world’s largest sodium-ion battery storage project
(www.pv-magazine.com)
This is a most excellent place for technology news and articles.
According to a paper published in 2020 here, the specific energy and energy density are in line with what you are saying. But according to the article that Wikipedia cited here, sodium batteries show the opposite.
You're probably right but it looks like there's conflicting info about this currently.
I talked to an energy engineer about it, and I'm pretty sure it's what he said. Would also make sense when China use it like this.