Enhanced electrochemical properties of lithium-tin liquid metal battery via the introduction of bismuth cathode material

Abstract The performance of a liquid metal battery can be significantly enhanced by lowering the cell operating temperature through alloying of the cell components. The effect of alloying pure tin metal, a cathode material for liquid metal batteries, on electrochemical properties is investigated by preparing a Li|Sn-Bi (Sn:Bi = 56:44 at%) battery cell. The Li|Sn-Bi cell achieves mean voltages of 0.856 and 0.683 V during charging and discharging, respectively, at 100 mA cm−2, which are 0.039 and 0.067 V higher than those of the Li|Sn cell. The Li|Sn-Bi cell exhibits a high rate capability owing to the low charge-transfer resistance between the liquid electrodes and liquid electrolytes. The charge and discharge capacity losses are 6.5% and 18.6%, respectively, at 1000 mA cm−2 compared with those at 100 mA cm−2. The Li|Sn-Bi cell can be discharged even at 1000 mA cm−2 owing to an increase in the mean discharge voltage by the alloying of tin with bismuth. The Li|Sn-Bi cell also exhibits improved cycle performance, with a capacity retention of 94.2% after 1000 cycles and a capacity decay of 0.0065% per cycle. This is attributed to the lack of formation of intermetallic byproducts between Bi and the stainless steel case and suppression of the side reaction between Sn and stainless steel by bismuth in the Sn-Bi lamellar microstructure. Thus, using a Sn-Bi alloy as the positive material significantly improves battery performance, making the Li|Sn-Bi cell a good candidate for stationary storage applications.