7 ms·

It is definitely NOT public info that 2170's are low energy density. Elon even says they are the highest energy density and lowest cost cells. https://electrek

• owenversteeg 10y ago
  It's important to separate 21700s as a whole from Tesla's 21700s. 21700s today don't look too great, and even the best have worse energy density, worse power density, and worse cycle lifetimes than the best 18650s [0]. Tesla's 21700s, on the other hand, are scientifically proven to cure cancer, protect your vehicle from nuclear weapons, and can charge from zero to full in 0.3 seconds using only a potato battery and a paperclip. I kid, of course, but this is why I believe that 21700s will probably be lower energy density: a) current 21700s have a low energy density, b) heat is tricky, and c) Musk wants to make cheap cells, and optimizing the last few Wh/kg to push him over the edge is expensive. I do concede it's certainly possible they'll be over 310 Wh/kg, but I find it unlikely. I think that a very likely outcome is that when the cells are released, we find out that we're both right. For example, if they have a density of over 310 Wh/kg... at 0.1C discharge or something similarly low. But at 1C or 5C or 10C, the energy density falls to around 200 Wh/kg. [0] Sanyo's cells are the current leaders, about 230 Wh/kg. With 18650s the leaders are between 280 and 310 Wh/kg depending on how you measure capacity (cutoff voltage, discharge rate, cooling, etc.)