NOVELTY - An electrical energy storage device utilizes an electrode reaction of an active material in the reversible oxidation/reduction cycle in anode or cathode. The active material comprises structural element (I).    USE - Electrical energy storage device is used as secondary battery and electrochemical capacitor used in electronic devices including mobile telephones and mobile personal computers.    ADVANTAGE - The electrical energy storage device has high energy density.    DETAILED DESCRIPTION - An electrical energy storage device utilizes an electrode reaction of an active material in the reversible oxidation/reduction cycle in anode or cathode. The active material comprises structural element of formula (I) which is not attached to 1,3,5-triazine ring.    G=group of formula (a-d);    asterisk=valence;    An-=anion of organic or inorganic acid;and    M+=Li+.    INDEPENDENT CLAIMS are included for the following:    (1) manufacture of electrical energy storage device;    (2) use of compound containing structural element of formula (I);    (3) hindered imidazolidinone nitroxide compound of formula (a1 or a2) excluding compounds of formulae (I-V); and    (4) polymer with repeating unit of formula (b1-b5).    G, asterisk=same as defined above;    R1-R4=1-6C alkyl optionally substituted by -COOM+, -COOR6, -CONHR6, -CON(R6)2, -OR6, F, Cl, 1-6C alkyl interrupted by -O-, -NR6- or 5-6C cycloalkyl, 3-6C cycloalkylidene, 7-9C phenylalkyl, -COO-M+, -COOR6, -CONHR6, or -CON(R6)2, R1 and R2 or R3 and R4 or R1 and R2 and R3 and R4 are group of formula (e);    R6=1-6C alkyl optionally substituted by -N3, 2-6C alkenyl, 2-6C alkynyl, glycidyl, 5-6C cycloalkyl, phenyl, 7-9C phenyl alkyl or group of formula (e1);    R5=H, 1-6C alkyl, 2-6C alkenyl, 2-6C alkynyl, glycidyl, 5-6C cycloalkyl, phenyl, 7-9C phenylalkyl, -O-M+, -OR6, -OC(O)R6, -C(O)R6, -COOR6, -CONHR6, -CON(R6)2, 1-6C alkyl interrupted by -O-, -NR6- or by group of formula (f), or 1-6C alkyl substituted by F, Cl, -COO-M+, -COOR6, -CONHR6, -CON(R6)2, OR6, -OC(O)R6, -OC(O)OR6, -OC(O)NHR6, -OC(O)N(R6)2, -NHC(O)R6, -NR6C(O)R6, -NCO, -N3, NHC(O)NHR6, -NR6C(O)N(R6)2, -NHCOOR6, -N(R6)2, -NR6COOR6, -N+(R6)3An-, S+(R6)2An-, P+(R6)3An-;    y=2-4;    E=divalent group of formula (g-n), trivalent group of formula (o or p) or tetravalent group of formula (q);    A1=1-6C alkyl;    n1=0-6;    n2=0-4;    X3=-O-, -NH- or -NR6-;    X4=-OR6, -NH2, -NHR6 or -N(R6)2;    R1-R4=methyl, 3-6C cycloalkylidene, or R1 and R2 or R3 and R4 or R1 and R2 and R3 and R4 are group of formula (e);and    m=2-50000.    when y is 2-4, E is divalent group, trivalent group or tetravalent group, respectively.