Composition for lithium ion secondary battery separator, two-part composition for lithium ion secondary battery separator, method of producing separator for lithium ion secondary battery, and method of producing lithium ion secondary battery

1. A composition for a lithium ion secondary battery separator comprising:

a first compound including a function-displaying functional group and having a molecular weight of 50,000 or less; and

a liquid medium, wherein

the function-displaying functional group includes at least one type of acidic functional group,

the first compound is at least one compound selected from the group consisting of polyacrylic acid having a molecular weight of 3,000 or more, a copolymer of acrylic acid and a sulfo group-containing monomer having a molecular weight of 3,000 or more, allyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 2-hydroxy-2-allyloxypropane sulfonic acid, styrene sulfonic acid, isoprene sulfonic acid, dodecylbenzenesulfonic acid, dioctyl sulfosuccinic acid, and a salt of either of the preceding compounds, and contained in a proportion of 3 mass % or more and 40 mass % or less, and

the composition for a lithium ion secondary battery separator has a surface tension of not less than 15 mN/m and not more than 30 mN/m.

2. The composition for a lithium ion secondary battery separator according to claim 1 , wherein the liquid medium includes water.

3. The composition for a lithium ion secondary battery separator according to claim 1 , further comprising a second compound that has a molecular weight of 50,000 or less and that is reactive with the first compound, wherein

the first compound and the second compound are contained in a total proportion of 40 mass % or less.

4. The composition for a lithium ion secondary battery separator according to claim 3 , wherein the second compound includes at least one type of basic functional group.

5. The composition for a lithium ion secondary battery separator according to claim 3 , wherein

the second compound is a cross-linker that cross-links molecules of the macromolecular compound.

6. A method of producing a separator for a lithium ion secondary battery comprising:

a step of impregnating a separator substrate comprising a microporous membrane made from a resin with the composition for a lithium ion secondary battery separator according to claim 1 ; and

a step of drying the separator substrate that has been impregnated with the composition for a lithium ion secondary battery separator.

7. The method of producing a separator for a lithium ion secondary battery according to claim 6 , wherein the separator substrate has an air resistance of not less than 10 s/100 cc-air and not more than 1,000 s/100 cc-air.

8. A method of producing a lithium ion secondary battery that includes a positive electrode, a negative electrode, a separator, and an electrolyte solution, comprising a step of producing a separator using the method of producing a separator for a lithium ion secondary battery according to claim 6 .

9. A two-part composition for a lithium ion secondary battery separator comprising:

a first liquid containing a first compound and a first liquid medium; and

a second liquid containing a second compound and a second liquid medium, wherein

the first compound includes a function-displaying functional group and has a molecular weight of 50,000 or less,

the function-displaying functional group includes at least one type of acidic functional group,

the second compound is reactive with the first compound and has a molecular weight of 50,000 or less,

the first compound is at least one compound selected from the group consisting of polyacrylic acid having a molecular weight of 3,000 or more, a copolymer of acrylic acid and a sulfo group-containing monomer having a molecular weight of 3,000 or more, allyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 2-hydroxy-2-allyloxypropane sulfonic acid, styrene sulfonic acid, isoprene sulfonic acid, dodecylbenzenesulfonic acid, dioctyl sulfosuccinic acid, and a salt of either of the preceding compounds,

the first liquid contains the first compound in a proportion of 3 mass % or more and 40 mass % or less and has a surface tension of not less than 15 mN/m and not more than 30 mN/m, and

the second liquid contains the second compound in a proportion of 40 mass % or less and has a surface tension of not less than 15 mN/m and not more than 30 mN/m.

10. The two-part composition for a lithium ion secondary battery separator according to claim 9 , wherein

the second compound includes at least one type of basic functional group.

11. The two-part composition for a lithium ion secondary battery separator according to claim 9 , wherein the first liquid medium and the second liquid medium include water.

12. A method of producing a separator for a lithium ion secondary battery using the two-part composition for a lithium ion secondary battery separator according to claim 9 , comprising:

a first step of impregnating a separator substrate comprising a microporous membrane made from a resin with one of the first liquid and the second liquid;

a second step of drying the separator substrate that has been impregnated with one of the first liquid and the second liquid;

a third step of impregnating the separator substrate that has been dried with the other of the first liquid and the second liquid after the second step; and

a fourth step of drying the separator substrate that has been impregnated with the other of the first liquid and the second liquid.