Binder composition for secondary battery porous membrane, slurry for secondary battery porous membrane, porous membrane for secondary battery, and secondary battery

1. A binder composition for a porous membrane of a secondary battery, comprising a polycarboxylic acid and water, wherein

the polycarboxylic acid includes a carboxylic acid group-containing monomer unit in an amount of 20% by weight or more and 50% by weight or less,

the binder composition for a porous membrane of a secondary battery has a pH of 6.5 or less,

at least part of the polycarboxylic acid is dispersed in the water, and

the polycarboxylic acid has a haze of 60% or more at a pH of 6.5 and a haze of less than 60% at a pH of 8.0, wherein the haze is obtained by measuring scattered light and total transmitted light at an optical path length of 30 mm of an aqueous solution of the polycarboxylic acid having a concentration of 10%.

2. The binder composition for a porous membrane of a secondary battery according to claim 1 , wherein the polycarboxylic acid includes an alkyl (meth)acrylate unit in an amount of 50% by weight or more.

3. The binder composition for a porous membrane of a secondary battery according to claim 2 , wherein

the alkyl (meth)acrylate unit includes an alkyl (meth)acrylate unit (U1) having an alkyl group having 1 to 3 carbon atoms and an alkyl (meth)acrylate unit (U2) having an alkyl group having 4 to 6 carbon atoms, and

the unit (U1) and the unit (U2) in the polycarboxylic acid have a weight ratio U1/U2 of 1.0 to 10.0.

4. The binder composition for a porous membrane of a secondary battery according to claim 1 , wherein the polycarboxylic acid has a glass transition temperature of lower than 30° C.

5. A slurry for a porous membrane of a secondary battery, comprising a non-conductive particle, a polycarboxylic acid, and water, wherein

the polycarboxylic acid includes a carboxylic acid group-containing monomer unit in an amount of 20% by weight or more and 50% by weight or less,

the slurry for a porous membrane of a secondary battery has a pH of more than 7.0, and

the polycarboxylic acid has a haze of 60% or more at a pH of 6.5 and a haze of less than 60% at a pH of 8.0, wherein the haze is obtained by measuring scattered light and total transmitted light at an optical path length of 30 mm of an aqueous solution of the polycarboxylic acid having a concentration of 10%.

6. A porous membrane for a secondary battery, obtained by forming a layer of the slurry for a porous membrane of a secondary battery according to claim 5 and drying the formed layer.

7. A secondary battery comprising the porous membrane for a secondary battery according to claim 6 .

8. The binder composition for a porous membrane of a secondary battery according to claim 2 , wherein the polycarboxylic acid has a glass transition temperature of lower than 30° C.

9. The binder composition for a porous membrane of a secondary battery according to claim 3 , wherein the polycarboxylic acid has a glass transition temperature of lower than 30° C.