A Battery Made of Molten Metals

Estimated reading time: 11 minutes

Subsequent investigation led to the liquid metal battery. Like a conventional battery, this one has top and bottom electrodes with an electrolyte between them (see Figure 1 in the slideshow above). During discharging and recharging, positively charged metallic ions travel from one electrode to the other through the electrolyte, and electrons make the same trip through an external circuit. In most batteries, the electrodes — and sometimes the electrolyte — are solid. But in Sadoway’s battery, all three are liquid. The negative electrode — the top layer in the battery — is a low-density liquid metal that readily donates electrons. The positive electrode — the bottom layer — is a high-density liquid metal that’s happy to accept those electrons. And the electrolyte — the middle layer — is a molten salt that transfers charged particles but won’t mix with the materials above or below. Because of the differences in density and the immiscibility of the three materials, they naturally settle into three distinct layers and remain separate as the battery operates.

Benefits of going liquid

This novel approach provides a number of benefits. Because the components are liquid, the transfer of electrical charges and chemical constituents within each component and from one to another is ultrafast, permitting the rapid flow of large currents into and out of the battery. When the battery discharges, the top layer of molten metal gets thinner and the bottom one gets thicker. When it charges, the thicknesses reverse. There are no stresses involved, notes Sadoway. “The entire system is very pliable and just takes the shape of the container.” While solid electrodes are prone to cracking and other forms of mechanical failure over time, liquid electrodes do not degrade with use.

Indeed, every time the battery is charged, ions from the top metal that have been deposited into the bottom layer are returned to the top layer, purifying the electrolyte in the process. All three components are reconstituted. In addition, because the components naturally self-segregate, there’s no need for membranes or separators, which are subject to wear. The liquid battery should perform many charges and discharges without losing capacity or requiring maintenance or service. And the self-segregating nature of the liquid components could facilitate simpler, less-expensive manufacturing compared to conventional batteries.

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