Lithium-ion batteries are short-lived, which is fine for phones but not for grid applications. Liquid metal batteries were born from the practice of electrochemical aluminium smelting (electricity in, aluminium from oxide out), but operating in reverse. Electrons come from the lighter metal on top, where the corresponding ions are travelling downwards through the electrolyte in order to recombine with the electrons at the boundary of the heavier liquid metal at the bottom. For the rest, no mixing takes places and the three layers remain separate. During discharge the top layer gets thinner and bottom layer thicker, during charging this reverses. There is no need for membranes. Degrading of the system is nearly absent. Donald Sadoway c.s. formed a company now called Ambri.
P.S. in a latest development, Sadoway seems to be using a membrane after all, see Nature link below.
[wired.com] – Inside the race to build the battery of tomorrow
[wbur.org] – A Low-Tech Approach To Energy Storage: Molten Metals
[wikipedia.org] – Donald Sadoway
[wikipedia.org] – Molten-salt battery
[news.mit.edu] – A new approach to rechargeable batteries
[greentechmedia.com] – Ambri Still Chasing Its Liquid Metal Battery Dreams
[ambri.com] – Company site
[phys.org] – New battery made of molten metals may offer low-cost, long-lasting storage for the grid. Liquid electrodes solve the problem of degrading solid ones.
[nature.com] – Faradaically selective membrane for liquid metal displacement batteries
[chemistryworld.com] – Solid electrolyte boosts liquid metal battery