How much energy can each storage technology hold per kilogram, at the most?
research/energy-density
How much energy can each storage technology hold per kilogram, at the most? First-principles ceilings that reproduce five published values within 0.3% (Li-S 2,567, Li-O2 3,458 Wh/kg). No battery couple exceeds 1.65 eV per reactant atom, so light atoms set the winners (Wh/kg = 26,801 × eV/atom ÷ g/mol); flywheels top out near 0.3 eV/atom, heat and pumped hydro far lower. Active material only. First project of track 16.
What it found
Theoretical ceilings from first principles for batteries, hydrogen, flywheels, pumped hydro and heat, reproducing five published values to within 0.3% (lead-acid 170, Zn-air 1,086, Li-S 2,567, Li-O2 3,458 Wh/kg; Al-air 8,100 on Al). No battery couple releases more than 1.65 eV per reactant atom, so the spread comes from atomic mass: Wh/kg = 26,801 × eV per atom / mean g/mol. A carbon-fibre flywheel holds at most 756 Wh/kg (0.34 eV per atom), sand at 500 °C 107 Wh/kg of heat (41% recoverable as electricity) and water lifted 300 m 0.82 Wh/kg. Ceilings for the active material only, with some voltages and material properties assumed.
A figure from its own output
Paper, code and results
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Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.