NOVELTY - A pyrrolidinium sulfonate compound is new.    USE - A pyrrolidinium sulfonate compound used as additive in electrolyte compositions, film-forming additives, and electrochemical or electrooptical device, preferably lithium battery (all claimed). Can also be used for double layer capacitors, lithium ion capacitors, solar cells, electrochromic displays, sensors, and/or biosensors.    ADVANTAGE - Lifetime, cycle stability, and high temperature stability of secondary batteries are enhanced.    DETAILED DESCRIPTION - A pyrrolidinium sulfonate compound of formula (I) is new.    X=N or P;    -SO3-=-O-S(O)2-, or -S(O)2-O-;    R1-R3=T provided that greater than or equal to 1 CH2 groups of alkyl, alkenyl, alkynyl, and aralkyl which are not directly bound to X-atom may be replaced by O, 1,2-epoxyethylene, cyclopropylene, or SO3;    T=1-10C alkyl, 2-10C alkenyl, 2-10C alkynyl, 6-12C aryl, and/or 7-24C aralkyl optionally substituted by F, cyclopropyl, 1,2-epoxyethyl, and/or sulfonate;    R1+R2=linked and jointly selected from -(CH2)m- alkylene forming, together with central X-atom, a 5- or 6-membered heterocycle in which greater than or equal to 1 H of -(CH2)m- alkylene may be substituted by F and/or optionally fluorinated 1-10C alkyl, and greater than or equal to 1 CH2 groups of -(CH2)m- alkylene may be replaced by O, S, or NR';    m=4 or 5;    R'=T in which greater than or equal to 1 CH2 groups of alkyl, alkenyl, alkynyl, and aralkyl which are not directly bound to N-atom may be replaced by O, 1,2-epoxyethylene, cyclopropylene, or SO3, greater than or equal to 1 CH2 groups of -(CH2)- alkylene chain which are not directly bound to X-atom or SO3 group may be replaced by O, and 2 adjacent CH2 groups of -(CH2)n- alkylene chain may be replaced by -C=C- double bond or -CC- triple bond;    n=1-8;    R4=1-6C alkyl, 2-20C alkenyl, 2-20C alkynyl, 6-12C aryl, and/or 7-24C aralkyl which may be substituted by F, cyclopropyl, 1,2-epoxyethyl, and/or sulfonate in which greater than or equal to 1 CH2 groups of alkyl, alkenyl, alkynyl, and aralkyl which are not directly bound to SO3 group may be replaced by O, 1,2-epoxyethylene, cyclopropylene, or SO3;    R5=1-20C alkyl, 2-20C alkenyl, 2-20C alkynyl, 6-12C aryl, and/or 7-24C aralkyl in which alkyl, alkenyl, alkynyl, and aralkyl may be substituted by cyclopropyl and/or 1,2-epoxyethyl, and greater than or equal to 1 CH2 groups of alkyl, alkenyl, alkynyl, and aralkyl which are not directly bound to SO3 group may be replaced by O, 1,2-epoxyethylene, cyclopropylene, SO3, and/or NR''; and    R''=1-10C alkyl, 2-10C alkenyl, 2-10C alkynyl, 6-12C aryl, and/or 7-24C aralkyl substituted by 1,2-epoxyethyl, cyclopropyl, and/or sulfonate in which greater than or equal to 1 CH2 group of alkyl, alkenyl, alkynyl, and aralkyl which are not directly bound to N-atom may be replaced by O, 1,2-epoxyethylene, cyclopropylene, or SO3.    An INDEPENDENT CLAIM is included for electrolyte composition comprising greater than or equal to 1 pyrrolidinium sulfonate compound of formula (I).