Additive, electrolyte for rechargeable lithium battery and rechargeable lithium battery

An additive represented by Chemical Formula 1 or Chemical Formula 2:

• wherein, in Chemical Formula 1 and Chemical Formula 2,
• R1 to R8 are each independently a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C3 to C10 cycloalkyl group, a substituted or unsubstituted C3 to C10 cycloalkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C3 to C10 cycloalkynyl group, or a substituted or unsubstituted C6 to C20 aryl group,
• R1 to R8 are separately present, or at least one pair of R1 and R2;
• R3 and R4;
• R5 and R6;
• and R7 and R8 are linked to each other to provide a substituted or unsubstituted monocyclic aliphatic heterocycle, a substituted or unsubstituted polycyclic aliphatic heterocycle, a substituted or unsubstituted monocyclic aromatic heterocycle, or a substituted or unsubstituted polycyclic aromatic heterocycle, and
• L1 to L4 are each independently a substituted or unsubstituted C1 to C20 alkylene group.