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New sodium ion battery stores twice the energy and desalinates seawater (www.sciencedaily.com)
submitted 7 months ago by to c/technology@lemmy.world
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[–] 7 points 7 months ago* (last edited 7 months ago) (3 children)

mAh/g (milliamp-hours per gram) is essentially still a measurement of capacity, but in terms of current instead of power.

We can do a little dimensional analysis here to translate between them. Power = Current x Voltage, so you'd multiply this (Current x Time)/(Weight) value by the nominal voltage of the cell to get to (Power x Time)/(Weight).

Phone batteries are often specified in units of Current*Time (e.g. milliamp-hours), but I'm not completely sure why. I think it has to do with voltages being standardized for certain types of cells, so the only real variable in the battery capacity is the current.

Edit: rearranged some ideas to make more sense

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  • [–] 9 points 7 months ago (1 child)

    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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  • [–] 2 points 7 months 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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