| CPC H01M 4/131 (2013.01) [H01M 4/364 (2013.01); H01M 4/366 (2013.01); H01M 4/505 (2013.01); H01M 4/525 (2013.01); H01M 10/0525 (2013.01); H01M 10/0567 (2013.01); H01M 10/0569 (2013.01); H01M 2004/028 (2013.01); H01M 50/46 (2021.01); H01M 2300/0025 (2013.01); H01M 2300/0034 (2013.01)] | 11 Claims |

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1. A lithium secondary battery comprising:
a positive electrode comprising a first lithium-metal oxide comprising secondary particles formed by aggregating primary particles having a particle diameter of less than 2 μm, and a second lithium-metal oxide comprising nickel and at least one or more metals and comprising primary particles having a particle diameter of 2 μm or more, wherein the at least one or more metals comprises manganese, cobalt, or both;
a negative electrode;
a separator interposed between the positive electrode and the negative electrode; and
an electrolyte comprising a lithium salt, a nonaqueous organic solvent, and a compound containing at least one difluorophosphite group and at least one or more olefin groups,
wherein the compound containing at least one difluorophosphite group and at least one or more olefin groups is represented by the following Chemical Formula 4 or Chemical Formula 5:
![]() wherein
R1 to R3 are independently of one another hydrogen, *—(CH2)r—OPF2, C1-C10 alkyl, or C2-C10 alkenyl;
L is C1-C10 alkylene, and the alkylene of L may be further substituted by one or more selected from the group consisting of C1-C10 alkyl, *—(CH2)a—OPF2, and
![]() R′ is hydrogen or —OPF2;
a and b are independently of each other an integer of 0 to 5;
q is an integer of 0 to 5; and
r is an integer of 0 to 5,
![]() wherein
ring D is mono-, bi-, or tri-C6-C20 cycloalkenyl,
wherein the compound containing at least one difluorophosphite group and at least one or more olefin groups is comprised at 0.1 to 5 wt %, based on a total weight of the electrolyte.
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