NOVELTY - A secondary battery comprises a positive electrode, a negative electrode and a nonaqueous electrolyte interposed between the electrodes. The negative electrode comprises a titanium-containing oxide as a negative electrode active material. The positive electrode comprises lithium-metal-manganese oxide as a positive electrode active material. The nonaqueous electrolyte comprises a fluorine-containing compound (I), isocyano-containing compound (II), cyclic anhydride (III) or alkyne compound (IV).    USE - Secondary battery is used for forming assembled battery (claimed). Uses include but are not limited to portable apparatus, hybrid motor vehicle, electric vehicle, and domestic electrical storage application.    ADVANTAGE - The secondary battery provides assembled battery having favorable size, capacitance and voltage.    DETAILED DESCRIPTION - A secondary battery comprises a positive electrode, a negative electrode and a nonaqueous electrolyte interposed between the electrodes. The negative electrode comprises a titanium-containing oxide as a negative electrode active material. The positive electrode comprises lithium-metal-manganese oxide of formula: Li1+xM1yM2zMn2-x-y-zO4 as a positive electrode active material. The nonaqueous electrolyte comprises a fluorine-containing compound of formula (I), isocyano-containing compound of formula (II), cyclic anhydride of formula (III) or alkyne compound of formula (IV).    x=0-0.2;    y=0-0.6 (excluding 0);    z=0-0.3;    M1,M2=2-13 group belonging to 3-4 period;    R1=1-6C alkyl;    M=B or P;    R2=H, 1-6C alkyl optionally substituted by halo, 2-6C alkenyl, 6-12C aryl, 1-6C alkyloxy, 2-6C alkenyloxy, 2-6C isocyanato alkyloxy, or 6-12C aryloxy;    X=H, 1-6C alkylene optionally substituted by halo or 2-6C bivalent coupling group containing ether bond(s);    R3,R4=H, halo or 1-6C alkyl optionally substituted by halo;    R5=2-4C alkenyl which has double bond at terminal, or 2-4C alkynyl group which has triple bond at terminal;    R6-R8=1-6C alkyl or H;    n'=1 or 2;    Y'=group chosen from groups of formulae (i)-(iii);and    Z=1-12C alkyl, 1-12C alkenyl or 3-12C alkynyl.    (i) When M is B, n is 3; and (ii) When M is P, n is 5.