Separation membrane with sub-nanometer pore size, and lithium ion secondary battery including the same

1 . A lithium ion secondary battery comprising:

a positive electrode mixture layer;

a negative electrode mixture layer; and

a separation membrane between the positive electrode mixture layer and the negative electrode mixture layer,

wherein the positive electrode mixture layer comprises a positive electrode active material, a first lithium salt, and a first solvent,

wherein the negative electrode mixture layer comprises a negative electrode active material, a second lithium salt, and a second solvent that is different in composition from the first solvent,

wherein the positive electrode mixture layer does not contain the second solvent and the negative electrode mixture layer does not contain the first solvent,

wherein the separation membrane comprises pores having an average pore size of 2 Å or greater and less than 20 Å,

wherein each of the first solvent and the second solvent has a molecular size of 20 Å or greater.

2 . The lithium ion secondary battery according to claim 1 , wherein the separation membrane comprises a crosslinked product of polymers each having a group represented by the following formula (1):

wherein R 1 represents an alkylene group having 1 to 6 carbon atoms, and the symbol represents a linking bond.

3 . The lithium ion secondary battery according to claim 1 , wherein the separation membrane comprises a polymerization product of a compound having two or more polymerizable groups, and comprises a lithium ion-conductive compound having at least one group selected from the group consisting of a carbonyl group and a chain ether group,

wherein the polymerization product has a weight average molecular weight of 800 or more, and

wherein the lithium ion-conductive compound has a molecular weight of 150 or less.