A Solid Sulfur Cathode for Aqueous Batteries

Because of its high resistivity and subsequent low electroactivity, sulfur is not normally considered a room-temperature battery cathode. An elemental sulfur cathode has been made with a measured capacity of over 900 ampere⋅hours per kilogram, more than 90 percent of the theoretical storage capacity of solid sulfur at room temperature, accessed by means of a lightweight, highly conductive, aqueous polysulfide interface through the electrocatalyzed reaction S + H 2 O + 2e - → HS - + OH - . This solid sulfur cathode was first used in a battery with an aluminum anode for an overall discharge reaction 2Al + 3S + 3OH - + 3H 2 O → 2Al(OH) 3 + 3HS - , giving a cell potential of 1.3 volts. The theoretical specific energy of the aluminum-sulfur battery (based on potassium salts) is 910 watt⋅hours per kilogram with an experimental specific energy of up to 220 watt⋅hours per kilogram.