Electrochemical Energy Storage with a Reversible Nonaqueous Room-Temperature Aluminum-Sulfur Chemistry

A reversible room-temperature aluminum-sulfur (Al-S) battery is demonstrated with a strategically designed cathode structure and an ionic liquid electrolyte. Discharge-charge mechanism of the Al-S battery is proposed based on a sequence of electrochemical, microscopic, and spectroscopic analyses. The electrochemical process of the Al-S battery involves the formation of a series of polysulfides and sulfide. The high-order polysulfides (S-x(2-), x >= 6) are soluble in the ionic liquid electrolyte. Electrochemical transitions between S-6(2-) and the insoluble low-order polysulfides or sulfide (S-x(2-), 1 <= x < 6) are reversible. A single-wall carbon nanotube coating applied to the battery separator helps alleviate the diffusion of the polysulfide species and reduces the polarization behavior of the Al-S batteries.