Vinylidene fluoride copolymer composition and method for producing same, polymer dispersion solution, electrode for nonaqueous electrolyte secondary battery, electrolyte layer for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery
A vinylidene fluoride copolymer composition having stable dispersibility in a dispersion medium over a long period of time, the composition having a melting temperature of 140° C. or lower, a reversing heat flow of the composition has endothermic peaks having an amount of enthalpy of fusion of 2 J/g or more, and an absolute value of a difference between a temperature showing a largest endothermic peak among the endothermic peaks and the melting temperature of the composition is 10° C. or lower. When a dispersion containing butyl butyrate and the vinylidene fluoride copolymer composition (vinylidene fluoride content rate of 10 mass %) is left to stand for 20 hours, a content rate of the vinylidene fluoride copolymer composition in an upper 20 vol % of the dispersion after the dispersion is left to stand is 4.0 mass % or more and 10 mass % or less.
1 . A vinylidene fluoride copolymer composition comprising a vinylidene fluoride copolymer, the vinylidene fluoride copolymer comprising a structural unit derived from vinylidene fluoride and a structural unit derived from a fluorinated alkyl vinyl compound, wherein
the vinylidene fluoride copolymer composition has a melting point of 140° C. or lower;
an average primary particle diameter of particles of the vinylidene fluoride copolymer composition determined by a dynamic light scattering method is 5 μm or less;
when a reversing heat flow of the vinylidene fluoride copolymer composition is measured with a temperature-modulated differential scanning calorimetry, the vinylidene fluoride copolymer composition has endothermic peaks having an amount of enthalpy of fusion (ΔHm) of 2 J/g or more with two or more peak tops;
an absolute value of a difference between a peak top temperature of a largest endothermic peak among the endothermic peaks and the melting point of the vinylidene fluoride copolymer composition is 10° C. or lower; and
after a dispersion comprising butyl butyrate and the vinylidene fluoride copolymer composition and having a content rate of the vinylidene fluoride copolymer composition of 10 mass % is stirred at 25° C. for 30 minutes and left to stand for 20 hours, a content rate of the vinylidene fluoride copolymer composition in an upper 20 vol % of the dispersion is 7.0 mass % or more and 10 mass % or less.
2 . The vinylidene fluoride copolymer composition according to claim 1 , wherein the fluorinated alkyl vinyl compound is hexafluoropropylene.
3 . The vinylidene fluoride copolymer composition according to claim 2 , comprising 15 mass % or more and 70 mass % or less of a structural unit derived from the hexafluoropropylene per 100 mass % of structural units of the vinylidene fluoride copolymer.
4 . The vinylidene fluoride copolymer composition according to claim 1 , further comprising a surfactant.
5 . A polymer dispersion comprising:
the vinylidene fluoride copolymer composition described in claim 1 ; and
a dispersion medium having a relative dielectric constant of 15 or less.
6 . An electrode for a non-aqueous electrolyte secondary battery comprising the vinylidene fluoride copolymer composition described in claim 1 .
7 . An electrolyte layer for a non-aqueous electrolyte secondary battery comprising the vinylidene fluoride copolymer composition described in claim 1 .
8 . A non-aqueous electrolyte secondary battery comprising the vinylidene fluoride copolymer composition described in claim 1 .