NOVELTY - An electrolyte comprises: an alkali metal salt; a polar aprotic solvent; and a redox shuttle, where the redox shuttle comprises an aromatic compound comprising at least one aromatic ring and at least one organophosphorus group bonded to the aromatic ring through an oxygen atom. The electrolyte is non-aqueous.    USE - In electrochemical device (claimed), and lithium rechargeable batteries.    ADVANTAGE - The redox shuttle has a redox potential of 4-5 V in the electrolyte; and two, three or four oxygen atoms, thus the redox shuttle is accessed only overcharge potentials; is electrochemically stabile or reversible, and thus the redox shuttle determines how much overcharge protection is provided; and has sufficient solubility in the electrolyte system in order to have an effective amount of the redox shuttle available.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) an electrochemical device comprising a cathode, an anode, and the electrolyte; and    (2) new phosphoric acid 2,5-di-tert-butyl-4-(diethoxy-phosphanyloxy)-phenyl ester ethyl ester; (2,5-di-tert-butyl-4-(diethoxy-phosphorylmethoxy)-phenoxymethyl)-phosphonic acid diethyl ester; phosphoric acid 2,4-di-tert-butyl-6-(diethoxy-phosphoryloxy)-phenyl ester diethyl ester; (2,4-di-tert-butyl-6-(diethoxy-phosphorylmethoxy)-phenoxymethyl)-phosphonic acid diethyl ester; phosphoric acid 2,5-di-tert-butyl-4-(diphenoxy-phosphoryloxy)-phenyl ester diphenyl ester; (2,5-di-tert-butyl-4-(diphenoxy-phosphorylmethoxy)-phenoxymethyl)-phosphonic acid diphenyl ester; phosphoric acid 2,4-di-tert-butyl-6-(diphenoxy-phosphoryloxy)-phenyl ester diphenyl ester; (2,4-di-tert-butyl-6-(diphenoxy-phosphorylmethoxy)-phenoxymethyl)-phosphonic acid diphenyl ester; phosphoric acid 2,5-di-tert-butyl-4-(diethoxy-phosphoryloxy)-3,6-difluoro-phenyl ester ethyl ester; (2,5-di-tert-butyl-4-(ethoxy-hydroxy-phosphorylmethoxy)-3,6-difluoro-phenoxymethyl)-phosphonic acid diethyl ester; phosphoric acid 3,5-di-tert-butyl-2-(diethoxy-phosphoryloxy)-4,6-difluoro-phenyl ester diethyl ester; and (2,4-di-tert-butyl-6-(diethoxy-phosphorylmethoxy)-3,5-difluoro-phenoxymethyl)-phosphonic acid diethyl ester.