Binder resin composition for secondary battery electrodes, slurry for secondary battery electrodes, electrode for secondary batteries, and lithium ion secondary battery
A binder resin composition for secondary battery electrodes is described as containing a polymer (A) that has a structural unit represented by general formula (1) and a water-insoluble particulate polymer (B-1) and/or a water-soluble polymer (B-2) where (A), (B-1) and (B-2) are defined as described. A slurry for secondary battery electrodes contains the binder resin composition, an active material and a solvent. An electrode for secondary batteries is provided with a collector and an electrode layer that is arranged on the collector, where the electrode layer contains an active material and the binder resin composition. Alternatively, the electrode layer is obtained by applying the slurry for secondary battery electrodes to the collector, and drying the slurry thereon.
1. A binder resin composition for secondary battery electrodes, comprising a N-vinylformamide polymer (A) having a structural unit represented by the general formula (1):
a water-insoluble particulate polymer (B-1) which is a polymer of fluoride-containing vinyl compounds, and
a water-soluble polymer (B-2) which is selected from the group consisting of polyaniline sulfonic acid, sodium polystyrene sulfonate and lithium polyacrylate,
wherein the polymer (B-2) has an acidic group and/or a salt thereof, and
wherein in the formula (1), R 1 and R 2 are a hydrogen atom.
2. The binder resin composition for secondary battery electrodes according to claim 1 , wherein an average particle diameter of the polymer (B-1) is from 10 to 1000 nm.
3. The binder resin composition for secondary battery electrodes according to claim 1 , wherein a mass ratio of the polymer (A) to the polymer (B-1), (polymer (A))/(polymer (B-1)), is from 5/95 to 95/5.
4. The binder resin composition for secondary battery electrodes according to claim 1 , wherein an electrode layer undergoes no change in evaluating flexibility of an electrode by the flexibility test below:
(Flexibility Test)
the binder resin composition for secondary battery electrodes and water are kneaded;
an active material is added thereto and kneaded, and a conductive auxiliary agent is further added and kneaded in a case that the electrode is positive, and which is then adjusted to a coatable viscosity with water, thereby obtaining a slurry for electrodes;
the amounts compounded are 2 parts by mass of the binder resin composition for secondary battery electrodes and 5 parts by mass of the conductive auxiliary agent based on 100 parts by mass of the active material;
the resulting slurry for electrodes is coated on a current collector and dried, thereby obtaining an electrode where an electrode layer of film thickness from 20 to 200 μm has been formed on the current collector;
the resulting electrode is cut out into 3 cm wide and 5 cm long to obtain a test piece;
a mandrel of 5 mm diameter is contacted to a current collector-facing surface of the resulting test piece and one side of the test piece is fixed by a tape, then the condition of the electrode layer is observed under an environment of a humidity of 10% or less in the state that the test piece is bent and the current collector-facing surface is positioned inside, thereby evaluating the flexibility of the electrode.
5. The binder resin composition for secondary battery electrodes according to claim 1 , wherein the acidic group and/or the salt thereof is at least one selected from the group consisting of carboxyl groups, salts of carboxyl groups, sulfonic acid groups, salts of sulfonic acid groups, phosphoric acid groups and salts of phosphoric acid groups.
6. The binder resin composition for secondary battery electrodes according to claim 1 , wherein a mass ratio of the polymer (A) to the polymer (B-2), (polymer (A))/(polymer (B-2)), is from 5/95 to 99.5/0.5.
7. The binder resin composition for secondary battery electrodes according to claim 1 ,
wherein a ratio (β/α) is at least 5,
wherein α represents a viscosity of 1% by mass of an aqueous solution (a) of the polymer (A), and
wherein β represents a viscosity of an aqueous solution (b), where 10 parts by mass of the polymer (B-2) has been added to the aqueous solution (a) based on 100 parts by mass of the polymer (A) therein.
8. A slurry for secondary battery electrodes, comprising the binder resin composition for secondary battery electrodes according to claim 1 , an active material and a solvent.
9. An electrode for secondary batteries, comprising a current collector and an electrode layer provided on the current collector,
wherein the electrode layer contains an active material and the binder resin composition for secondary battery electrodes according to claim 1 .
10. A lithium ion secondary battery, comprising the electrode for secondary batteries according to claim 9 .
11. An electrode for secondary batteries, comprising a current collector and an electrode layer provided on the current collector,
wherein the electrode layer is obtained by coating and drying the slurry for secondary battery electrodes according to claim 8 on the current collector.
12. A lithium ion secondary battery, comprising the electrode for secondary batteries according to claim 11 .