Particulate polymer for use in binder for lithium-ion secondary battery; adhesive layer; and porous-membrane composition

A particulate polymer for a binder of a lithium ion secondary battery, wherein

• the particulate polymer has a core-shell structure including a core portion and a shell portion partially covering an outer surface of the core portion,
• an average ratio of the outer surface of the core portion that is covered by the shell portion is equal to or higher than 10% and equal to or lower than 99.9%,
• a polymer forming the core portion of the particulate polymer contains a (meth)acrylic acid ester monomer unit and a (meth)acrylonitrile monomer unit,
• a glass transition temperature of the polymer forming the core portion is equal to or higher than 60° C.,
• a polymer forming the shell portion of the particulate polymer contains a styrene unit and/or a styrene derivative unit,
• a ratio of the styrene unit and/or the styrene derivative unit in the polymer forming the shell portion is equal to or higher than 85% by weight,
• a glass transition temperature of the polymer forming the shell portion is equal to or higher than 70° C., and
• ion conductivity of a film of 1 mm in thickness formed by drying an aqueous dispersion of the particulate polymer after being immersed in an electrolytic solution (LiPF6 solution of 1.0 mol/L (solvent:
• a mixture of ethylene carbonate/diethyl carbonate/vinylene carbonate at a volume ratio of 68.5/30/1.5)) at 60° C. for 72 hours is 1×10−5 S/cm to 1×103 S/cm, and tensile strength of the film is 500 N/cm2 to 4000 N/cm2.