Really bad HN title "Same Energy Density at Half the Weight". That is nonsensical; "density" should be elided in the title. The actual goal is to double the energy density so that the battery can provide the same energy at half the weight.
"Simply, the energy density would be doubled. So same energy, same volume base, kind of half [the weight]," Aoyama said.
Could "energy density" not refer to energy-per-volume rather than mass? Then that headline might make sense per this quote from someone at Honda: "Simply, the energy density would be doubled. So same energy, same volume base, kind of half [the weight]"
Although the author himself confuses the matter, suggesting volume is also reduced: "If Honda's solid-state batteries truly do cut weight and size in half without reducing performance, there could be quite a bit more space in the floor of future Honda vehicles."
Fixed. That bogus headline came in through the RSS feed, I did look at the article but I should have taken a third look at the headline. (Looks like management revised the headline again!)
"Simply, the energy density would be doubled. So same energy, same volume base, kind of half [the weight]," Aoyama said.