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Comment on New sodium ion battery stores twice the energy and desalinates seawater

finalarbiter@lemmy.dbzer0.com ⁨2⁩ ⁨days⁩ ago

mAh/g (milliamp-hours per gram) is a similar unit, but it’s missing the voltage term. We can do a little dimensional analysis here to translate between them. Power = Current * Voltage, so you’d multiply this (CurrentTime)/(Weight) value by the nominal voltage of the cell to get to (PowerTime)/(Weight). So it is essentially still a measurement of capacity, but in terms of current instead of power.

Phone batteries are often specified in units of Current*Time (e.g. milliamp-hours), but I’m not sure why.

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Wispy2891@lemmy.world ⁨2⁩ ⁨days⁩ ago

I’m not completely sure why

I think it’s marketing

5000 mAh is much a bigger number than 19 Wh and marketing loves huge numbers

Kinda like BMW did with the i3.

In 2013 Tesla was selling a model with a 60 kWh battery so BMW had the genius idea to install a 20 kWh battery BUT refer to it as “60 Ah” battery.

Tesla introduced the 90 kWh battery? BMW responds with a 94 Ah battery (28 kWh)

Newest Tesla has 100 kWh battery now? BMW has 120 Ah battery (38 kWh)

“See? Higher number!”, says the marketing

And in order to have a comparable range number they had to implement heavy weight reduction techniques like using carbon fiber for the body, negating any cost saving from the smaller battery AND giving the owner a total loss after small collisions as it shatters instead of bending

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- timwa@lemmy.snowgoons.ro ⁨2⁩ ⁨days⁩ ago
  That’s an incredibly longwinded way of saying “mahh Tezlur burns three times as much ‘clean coal’ per mile as a commie BMW, yee-haw”.
  
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apftwb@lemmy.world ⁨1⁩ ⁨day⁩ ago

multiply this (Current x Time)/(Weight) value by the nominal voltage of the cell to get to (Power x Time)/(Weight).

This is the part that annoys me. The nominal voltage could vary between different batteries. 200Ah/g means different capacity for a 6v battery verses a 48v battery. I’m guessing battery scientists are using standardized nominal voltages for these tests or are seeing the same Ah/g capacity at different voltages (that I may have simply missed in the paper because I skimmed it and I don’t claim any deeper knowledge on battery research)

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