Iodide addition could make high energy lithium-sulfur batteries commercially viable

A sulfur iodide crystal discovered by US researchers could help solve some of the key problems of next generation lithium batteries. The material is 11 orders of magnitude more electronically conductive than elemental sulfur, drastically reducing the internal resistance of lithium-sulfur batteries. It also has a much lower melting point, which allowed electrode defects from repeated cycling to be healed by gently heating them. This allowed the battery to retain good capacity over 400 charge–discharge cycles.

Many researchers regard lithium-sulfur batteries as a key prospective advance in lithium battery technology because they could have much higher capacities than today’s lithium-ion batteries. These usually use lithium cobalt oxide cathodes: during charging lithium ions intercalate into the structure, reducing the cobalt(IV) to cobalt(III). During discharge, this process is reversed, releasing an electron into the external circuit. Lithium-sulfur cathodes, however, work by electrochemical conversion. ‘Lithium reacts with sulfur to form lithium sulfide – that gives you the energy to form your lithium-ion battery,’ explains computational materials scientist Shyue Ping Ong at the University of California, San Diego. This means more lithium ions can be stored and more electrons released, as well as obviating the need for cobalt, which is plagued by supply-chain concerns.