Adhesive for lithium ion secondary batteries, separator for lithium ion secondary batteries, and lithium ion secondary battery
An adhesive for a lithium ion secondary battery, for bonding members for constituting a lithium ion secondary battery, the adhesive including a particulate polymer, wherein the particulate polymer has a core-shell structure including a core portion and a shell portion that partially covers an outer surface of the core portion, the core portion is formed from a polymer having a swelling degree in an electrolytic solution of 5 times or more and 30 times or less, and the shell portion is formed from a polymer having a swelling degree in an electrolytic solution of more than 1 time and 4 times or less.
1. An adhesive for a lithium ion secondary battery, for bonding members for constituting a lithium ion secondary battery,
the adhesive comprising a particulate polymer, wherein
the particulate polymer has a core-shell structure including a core portion and a shell portion that partially covers an outer surface of the core portion,
the core portion is formed from a polymer having a swelling degree in an electrolytic solution of 5 times or more and 30 times or less,
the shell portion is formed from a polymer having a swelling degree in the electrolytic solution of more than 1 time and 4 times or less,
the amount of the particulate polymer is 50% by weight or more and 99.9% by weight or less with respect to solid content of the adhesive,
each of the swelling degrees represents a ratio (W 1 /W 0 ) of W 1 with respect to W 0 ,
W 0 represents a weight of a 1-cm square piece of a film having a thickness of 0.5 mm that is produced from the polymer of the core portion or the polymer of the shell portion,
W 1 represents a weight of the 1-cm square piece that has been immersed in the electrolytic solution at 60° C. for 72 hours, and
the electrolytic solution consists of a mixed solvent of ethylene carbonate, diethyl carbonate and vinylene carbonate (volume mixing ratio of ethylene carbonate/diethyl carbonate/vinylene carbonate=68.5/30/1.5) and 1 mol/L of LiPF 6 .
2. The adhesive for a lithium ion secondary battery according to claim 1 , wherein
the polymer of the core portion has a glass transition temperature of 0° C. or higher and 150° C. or lower, and
the polymer of the shell portion has a glass transition temperature of 50° C. or higher and 200° C. or lower.
3. The adhesive for a lithium ion secondary battery according to claim 1 , wherein the shell portion includes particles of the polymer having a swelling degree in the electrolytic solution of more than 1 time and 4 times or less.
4. The adhesive for a lithium ion secondary battery according to claim 1 , further comprising non-conductive fibers, wherein
the non-conductive fibers have a fiber diameter of 0.01 μm or more and 1 μm or less.
5. The adhesive for a lithium ion secondary battery according to claim 1 , wherein the adhesive is for bonding a separator and an electrode together.
6. A separator for a lithium ion secondary battery, comprising a separator substrate and an adhesive layer, wherein
the adhesive layer includes a particulate polymer,
the particulate polymer has a core-shell structure including a core portion and a shell portion that partially covers an outer surface of the core portion,
the core portion is formed from a polymer having a swelling degree in an electrolytic solution of 5 times or more and 30 times or less,
the shell portion is formed from a polymer having a swelling degree in the electrolytic solution of more than 1 time and 4 times or less,
the amount of the particulate polymer is 50% by weight or more and 99.9% by weight or less with respect to the adhesive layer,
each of the swelling degrees represents a ratio (W 1 /W 0 ) of W 1 with respect to W 0 ,
W 0 represents a weight of a 1-cm square piece of a film having a thickness of 0.5 mm that is produced from the polymer of the core portion or the polymer of the shell portion,
W 1 represents a weight of the 1-cm square piece that has been immersed in the electrolytic solution at 60° C. for 72 hours, and
the electrolytic solution consists of a mixed solvent of ethylene carbonate, diethyl carbonate and vinylene carbonate (volume mixing ratio of ethylene carbonate/diethyl carbonate/vinylene carbonate=68.5/30/1.5) and 1 mol/L of LiPF 6 .
7. The separator for a lithium ion secondary battery according to claim 6 , further comprising a porous membrane provided on a surface of the separator substrate, wherein
the porous membrane has a surface on which the adhesive layer is provided.
8. The separator for a lithium ion secondary battery according to claim 6 , wherein
the adhesive layer further includes non-conductive fibers, and
the non-conductive fibers have a fiber diameter of 0.01 μm or more and 1 μm or less.
9. A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolytic solution, and a separator, wherein
the separator is the separator for a lithium ion secondary battery according to claim 6 .