BINDER, SEPARATOR, AND LITHIUM-ION BATTERY USING SUCH SEPARATOR

1 . A binder comprising a terpolymer formed by copolymerization of a first monomer unit, a second monomer unit, and a third monomer unit; wherein the first monomer is selected from C 1 -C 20 alkyl (meth)acrylate; the second monomer is selected from at least one of acrylonitrile and methacrylonitrile; the third monomer is selected from at least one optionally substituted (meth)acrylamide; and a molar ratio of the first monomer unit, the second monomer unit, and the third monomer unit is 50-58:40-44:2-6.

2 . The binder according to claim 1 , wherein the terpolymer has a structure denoted by the formula (I):

wherein each R 1 is selected from H and methyl and each R 1 may be the same or different as another R 1 ;

R 2 is a C 1 -C 20 alkyl group, a C 3 -C 20 cycloalkyl group, or a C 1 -C 20 hydroxyalkyl group, optionally a C 1 -C 12 alkyl group, a C 3 -C 12 cycloalkyl group, or a C 1 -C 12 hydroxyalkyl group; and R 2 is further optionally a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an n-octyl group, an isooctyl group, a 2-ethylhexyl group, a dodecyl group, or an isobornyl group;

R 3 is H, or a C 1 -C 6 alkyl group monosubstituted by OR 4 , and R 4 is H or a C 1 -C 6 alkyl group; wherein R 4 is further optionally H, a methyl group, an ethyl group, an n-propyl group, or an n-butyl group; and

x, y, and z are each independently an integer selected from 50-2000, optionally an integer selected from 100-500.

3 . The binder according to claim 1 , wherein a weight-average molecular weight Mw of the terpolymer is 40000-150000 g/mol, optionally 60000-120000 g/mol.

4 . The binder according to claim 1 , wherein the C 1 -C 20 alkyl (meth)acrylate is selected from one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.

5 . The binder according to claim 1 , wherein the third monomer is selected from one or more of acrylamide, N-hydroxymethyl acrylamide, and N-butoxymethyl acrylamide.

6 . The binder according to claim 1 , wherein a glass transition temperature Tg of the terpolymer is −20° C. to 40° C., optionally 0° C. to 20° C.

7 . A separator comprising a base layer and a binding layer stacked sequentially;

wherein the binding layer comprises the binder according to claim 1 , thermally expandable microspheres, and ceramic particles.

8 . The separator according to claim 7 , wherein a glass transition temperature of the thermally expandable microspheres is 40-100° C., optionally 60-90° C.

9 . The separator according to claim 8 , wherein a median particle size D v 50 of the thermally expandable microspheres is 0.1 μm-2 μm, optionally 0.3 μm-1.5 μm.

10 . The separator according to claim 7 , wherein the ceramic particles are at least one of alumina, boehmite, silica, and titanium dioxide, with a median particle size D v 50 of 0.5 μm-5 μm, optionally 1 μm-3.5 μm.

11 . The separator according to claim 7 , wherein a mass ratio of the binder, the thermally expandable microspheres, and the ceramic particles is 25-30:10-20:50-65.

12 . A lithium-ion battery, comprising the binder according to claim 1 .

13 . A battery pack, comprising the lithium-ion battery according to claim 12 .

14 . An electric apparatus, comprising the lithium-ion battery according to claim 12 .

15 . A lithium-ion battery, comprising the separator according to claim 7 .

16 . A battery pack, comprising the lithium-ion battery according to claim 15 .

17 . An electric apparatus, comprising the battery according to claim 16 .