Not sure what over 250 Wh/kg means. Wikipedia mentions Specific energy 100–265 Wh/kg and Energy density 250–693 Wh/L quoting papers from 2010/1 and 2016/7 [1]. Other sources mention similar numbers (100-265 Wh/kg or 250-670 Wh/L) [2], although the research is ongoing: "Tesla’s new 4680 cells have an energy density of 272-296 Wh/kg and which is considered very high by current standards" [3].

[1] https://en.wikipedia.org/wiki/Lithium-ion_battery

[2] https://www.cei.washington.edu/education/science-of-solar/ba...

[3] https://thedriven.io/2023/04/03/scientists-hail-new-battery-...

Thanks for the sources, as said this shows the article is highly suspect if your "maximum theoretical energy density" figure already is beaten by in-the-market devices.