Separator for electricity storage devices, electrode body using same, and electricity storage device
This separator for electricity storage devices comprises a porous base and a thermoplastic polymer layer that is arranged in at least a part of the outermost surface of at least one surface of the porous base, and wherein: a thermoplastic polymer contained in the thermoplastic polymer layer contains a copolymer that has, as a monomer unit, an ethylenically unsaturated monomer (P) having a polyalkylene glycol group; and the thermoplastic polymer layer contains the thermoplastic polymer in an amount of more than 3% by mass but 100% by mass or less if the thermoplastic polymer layer is taken as 100% by mass.
1. A separator for an electricity storage device comprising a porous substrate and a thermoplastic polymer layer disposed on at least one portion of an outermost surface of at least one side of the porous substrate,
wherein a thermoplastic polymer in the thermoplastic polymer layer contains a copolymer with a monomer unit of an ethylenic unsaturated monomer having a polyalkyleneglycol group in which an average number of repeating units for the alkyleneglycol units is 4 or more, and the thermoplastic polymer layer contains the thermoplastic polymer at more than 3 weight % and equal to or less than 100 weight %, based on 100 weight % of the thermoplastic polymer layer,
wherein the thermoplastic polymer is in particulate form, and
wherein a dispersion (σ 2 ) is 0.01 or more and 0.7 or less, as defined by the following formula, using the areas (S i ) of Voronoi polygons obtained by Voronoi tessellation of the thermoplastic polymer layer:
σ
2
=
∑
i
(
S
i
m
-
1
)
2
n
[
Mathematical
Formula
1
]
wherein S i is the measured area of a given Voronoi polygon, m is average of the measured areas of Voronoi polygons, and n is the total number of Voronoi polygons.
2. The separator for an electricity storage device according to claim 1 , wherein the thermoplastic polymer layer is configured to be directly bonded to an electrode.
3. The separator for an electricity storage device according to claim 1 , wherein the substrate comprises at least a polyolefin.
4. The separator for an electricity storage device according to claim 1 , wherein the substrate and the thermoplastic polymer layer are in direct contact.
5. The separator for an electricity storage device according to claim 1 , which comprises the ethylenic unsaturated monomer having a polyalkyleneglycol group at 3 to 50 weight % in terms of the monomer unit in 100 weight % of the thermoplastic polymer composing the thermoplastic polymer layer.
6. The separator for an electricity storage device according to claim 5 , wherein the copolymer has, as monomer units, 2 to 50 weight % of the ethylenic unsaturated monomer having a polyalkyleneglycol group and a monomer without a polyalkyleneglycol group that is copolymerizable with the ethylenic unsaturated monomer having a polyalkyleneglycol group, with respect to 100 weight % of the copolymer.
7. The separator for an electricity storage device according to claim 6 , wherein the monomer without a polyalkyleneglycol group comprises at least one monomer selected from the group consisting of an ethylenic unsaturated monomer with a carboxyl group (b1), an ethylenic unsaturated monomer with an amide group (b2) and an ethylenic unsaturated monomer with a hydroxyl group (b3), at 0.1 to 10 weight % with respect to 100 weight % of the copolymer.
8. The separator for an electricity storage device according to claim 6 , wherein the monomer without a polyalkyleneglycol group comprises a crosslinkable monomer (b4).
9. The separator for an electricity storage device according to claim 6 , wherein the monomer without a polyalkyleneglycol group comprises an ethylenic unsaturated monomer with a cycloalkyl group (A) and a (meth)acrylic acid ester monomer (b5),
the (meth)acrylic acid ester monomer (b5) is a (meth)acrylic acid ester monomer comprising an alkyl group of 4 or more carbon atoms and a (meth)acryloyloxy group, and
the total content ratio of the ethylenic unsaturated monomer with a cycloalkyl group (A) and the (meth)acrylic acid ester monomer (b5) is 50 to 98 weight % based on 100 weight % of the copolymer.
10. The separator for an electricity storage device according to claim 1 , wherein the coating area of the thermoplastic polymer layer is 95% or less.
11. The separator for an electricity storage device according to claim 1 , wherein the value of blocking measured of the thermoplastic polymer layer is 20 N/m or less.
12. An electrode body comprising a positive electrode, the separator for an electricity storage device according to claim 1 , and a negative electrode.
13. An electricity storage device comprising the electrode body according to claim 12 and an electrolytic solution.
14. The electricity storage device according to claim 13 , wherein the thermoplastic polymer layer of the separator is directly bonded to the positive electrode or the negative electrode.
15. The electrode body according to claim 12 , wherein the thermoplastic polymer layer of the separator is directly bonded to the positive electrode or the negative electrode.
16. The separator for an electricity storage device according to claim 1 , wherein the average number of repeating units for the alkyleneglycol units is 100 or less.
17. The separator for an electricity storage device according to claim 1 , wherein the thermoplastic polymer layer contains the thermoplastic polymer at 10 weight % or more and equal to or less than 100 weight %, based on 100 weight % of the thermoplastic polymer layer.
18. The separator for an electricity storage device according to claim 1 , wherein the thermoplastic polymer layer contains the thermoplastic polymer at 20 weight % or more and equal to or less than 100 weight %, based on 100 weight % of the thermoplastic polymer layer.