Because of its high resistivity and subsequent low electroactivity, su
lfur is not normally considered a room-temperature battery cathode. An
elemental sulfur cathode has been made with a measured capacity of ov
er 900 ampere.hours per kilogram, more than 90 percent of the theoreti
cal storage capacity of solid sulfur at room temperature, accessed by
means of a lightweight, highly conductive, aqueous polysulfide interfa
ce through the electrocatalyzed reaction S + H2O + 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- + 3H2O --> 2A
l(OH)3 + 3HS-, giving a cell potential of 1.3 volts. The theoretical s
pecific energy of the aluminum-sulfur battery (based on potassium salt
s) is 910 watt.hours per kilogram with an experimental specific energy
of up to 220 waft.hours per kilogram.