Binder for secondary battery electrode and use thereof
A secondary battery electrode has excellent characteristics. As a binder for a secondary battery electrode, a crosslinked polymer or salt thereof having a carboxyl group is used. The crosslinked polymer or salt includes 30 mass % or more and not more than 100 mass % of a structural unit derived from an ethylenically unsaturated carboxylic acid monomer and a metal ion content of the crosslinked polymer or salt thereof is not more than 100 ppm or less.
1 . A binder for a secondary battery electrode, the binder comprising a crosslinked polymer or salt thereof having a carboxyl group, wherein:
the crosslinked polymer or salt thereof comprises 60 mass % or more and not more than 100 mass % of a structural unit derived from an ethylenically unsaturated carboxylic acid monomer,
a polyvalent metal ion content relative to the total amount of the crosslinked polymer or salt thereof, wherein the crosslinked polymer or salt thereof is in powder form, is not more than 50 ppm, and
a number of metal particles of 10 μm or more and not more than 100 μm in size per 1 g of the crosslinked polymer or salt thereof, wherein the crosslinked polymer or salt thereof is in powder form, is not more than 1.0×10 3 .
2 . The binder according to claim 1 , wherein the crosslinked polymer or salt thereof comprises a structural unit derived from a crosslinkable monomer.
3 . The binder according to claim 1 , wherein a degree of neutralization of the crosslinked polymer is 50 mol % or more and not more than 100 mol %.
4 . A secondary battery electrode mixture layer composition, containing the binder according to claim 1 , together with an active material and water.
5 . A secondary battery electrode provided with an electrode layer containing the binder according to claim 1 on a surface of a collector.
6 . A method for manufacturing the binder according to claim 1 , the method comprising:
preparing a crosslinked polymer or salt thereof; and
removing metal particles from the crosslinked polymer or salt thereof in a powder form and thereby obtaining the binder in which:
the crosslinked polymer comprises 60 mass % or more and not more than 100 mass % of the structural unit derived from an ethylenically unsaturated carboxylic acid monomer,
the polyvalent metal ion content relative to the total amount of the crosslinked polymer or salt thereof, wherein the crosslinked polymer or salt thereof is in powder form, is not more than 50 ppm, and
the number of metal particles of 10 μm or more and not more than 100 μm in size per 1 g of the crosslinked polymer or salt thereof, wherein the crosslinked polymer or salt thereof is in powder form, is not more than 1.0×10 3 .
7 . The method according to claim 6 , wherein the removing includes using magnetic force to remove the metal particles from the crosslinked polymer or salt thereof in powder form.
8 . The method according to claim 7 , wherein the removing includes using a drum-type magnetic separator or an electromagnetic separator to remove the metal particles from the crosslinked polymer or salt thereof in powder form.
9 . The binder according to claim 1 , wherein the ethylenically unsaturated carboxylic acid monomer comprises acrylic acid.
10 . The binder according to claim 1 , wherein the polyvalent metal ion content is a concentration based on the total amount of polyvalent metal ions detected by ICP emission spectrometry on a solution in which the polymer is dissolved by thermal acid decomposition.
11 . The binder according to claim 9 , wherein the polyvalent metal ion content is a concentration based on the total amount of polyvalent metal ions detected by ICP emission spectrometry on a solution in which the polymer is dissolved by thermal acid decomposition.
12 . The secondary battery electrode mixture layer composition according to claim 5 , wherein a viscosity as B-type viscosity at 60 rpm is from 1,000 mPa·s to 3,000 mPa·s.