Patent ID: 7452486

Claim:
An aqueous solution for an electrochemical energy storage device which comprises (a) a high purity sulfonic acid with a low concentration of low valent sulfur compounds or higher valent sulfur compounds susceptible to reduction comprising a sum total concentration of dimethyldisulfide (CH 3 SSCH 3 ), dimethylsulfide (CH 3 SCH 3 ), dimethylsulfone (CH 3 SO 2 CH 3 ), trichioromethyl methylsulfone (CH 3 SO 2 CCl 3 ), dichloromethyl methylsulfone (CH 3 SO 2 CHCl 2 ), methyl methanethiosulfonate (CH 3 SO 2 SCH 3 ), and methyl methanesulfonate (CH 3 SO 3 CH 3 ) of less than about 50 mg/l, (b) a metal or metals in an oxidized state capable of being reduced to the zero valent oxidation state, (c) a metal that is in an oxidized state that is incapable of being reduced to its metallic state, and optionally (d) a buffering agent and optionally (e) conductivity salts.