The Thermodynamic Ceiling on Electrochemical Battery Energy Density: A Full-Mass Recount for Lithium-Ion, Lithium-Sulfur, Sodium-Ion, and Lithium-Oxygen Cells

Full-mass thermodynamic ceilings (Wh/kg, counting both electrodes and oxygen) are computed from Gibbs energies for Li-ion (584), Li-S (2509), Na-ion (316), and Li-O2 (3458), compared with single-electrode advertised figures and best achieved values, decomposing the advertised-vs-achieved gap into bookkeeping (35-73%) and engineering loss.