Wetting Interactions Between Porous Carbon Hosts and Liquid Sodium-Potassium Alloys Toward Their Use in Negative Electrodes of Alkali-Metal Batteries

Abstract

Batteries with liquid alkali-metal negative electrodes offer a route to compact, high-performance energy storage. Innovation in alkali-metal management, i.e., controlled storage, release and transport of liquid alkali metal, can enable simpler and cheaper cell designs. Porous carbons have emerged as potential host materials for liquid alkali metals. Here, X-ray computed tomography is used to study the wetting interactions between porous carbon hosts and liquid sodium-potassium alloy (NaK) as a function of carbon host morphology and surface functionalization. While as-received carbon samples show no affinity toward NaK, heat-treated carbon is spontaneously infiltrated with NaK filling almost the entire pore volume. It is explored how forced wetting partially fills pores of NaK-repellant hosts, showing large differences in pore filling based on the average pore size of the host material. In electrochemical discharge experiments, it is shown that both as-received and heat-treated carbon felt enable high areal capacities beyond 40 mAh cm⁻². However, the heat-treated carbon shows ten times lower overpotential. Finally, it is demonstrated how heat-treated carbon felt can enable capillary transport of NaK. In summary, this study elucidates important aspects of the interactions between liquid alkali metals and porous carbon hosts, generating insights into possible applications in liquid alkali-metal batteries.