How cell design affects the performance of sodium-antimony-bismuth liquid metal batteries

Low-cost sodium-based liquid metal batteries are attractive candidates for grid-scale stationary energy storage. In this study, the performance of Na//SbBi9 test cells with molten salt electrolyte LiCl–NaCl–KCl (61-3-36 mol%) is evaluated for different cell designs. Cells with a metal foam hosting the negative electrode (5–6 Ah nominal capacity) and cells without foam are investigated. Additionally, the amount of electrolyte and the material used as positive current collector (PCC) are varied. The self-discharge current is only ~0.35 mA/cm2 and depends reasonably on electrode distance and operating temperature. Contact resistances are 10 mΩ in total and thus smaller than the ohmic resistance of the electrolyte. The cell voltage is not affected by cell design, operating temperature, or cell age. Long-term cycling tests show a capacity decrease, which can be attributed to evapo-ration of Na. An additional capacity loss observed in cells with stainless steel PCC can be avoided by using Mo as PCC.