Positive electrode for non-aqueous electrolyte secondary batteries and non-aqueous electrolyte secondary battery
View Patent ↗Disclosed is a positive electrode for non-aqueous electrolyte secondary batteries, the positive electrode including a positive electrode material mixture layer which includes positive electrode active material particles and a binder. A curve representing a correlation between a distance from a current collector in the thickness direction of the positive electrode material mixture layer and an amount of the binder has a first maximum point, a minimum point, and a second maximum point. The minimum point corresponds to a position in a center area of the positive electrode material mixture layer in a thickness direction thereof, and the first and second maximum points correspond to a position nearer the current collector and a position further away from the current collector than the position corresponding to the minimum point, respectively. A ratio W 1 /W 2 of an amount W 1 at the first maximum point to an amount W 2 at the minimum point of the binder per 100 parts by weight of the positive electrode active material particles is greater than 2.
1. A positive electrode for non-aqueous electrolyte secondary batteries, the positive electrode comprising a current collector and a positive electrode material mixture layer formed on a surface of the current collector, wherein:
the positive electrode material mixture layer includes positive electrode active material particles and a binder;
the positive electrode material mixture layer has, in a thickness direction thereof, an area A 1 near the current collector, an area A 2 near a surface of the positive electrode material mixture layer, and a center area A 3 excluding the area A 1 and the area A 2 ,
the area A 1 has a thickness of 0.3T as measured from the current collector, and the area A 2 has a thickness of 0.3T as measured from the surface of the positive electrode material mixture layer, when a thickness of the positive electrode material mixture layer is denoted as T;
when distances from the current collector at a plurality of positions in the thickness direction are plotted against amounts of the binder in the positions to show a plot between the distances and the amounts, the plot has a first maximum point, a minimum point, and a second maximum point;
the minimum point corresponds to a position in the center area A 3 ;
the first maximum point corresponds to a position nearer the current collector than the position corresponding to the minimum point in the positive electrode material mixture layer;
the second maximum point corresponds to a position further away from the current collector than the position corresponding to the minimum point in the positive electrode material mixture layer;
a ratio W 1 /W 2 of an amount W 1 of the binder per 100 parts by weight of the positive electrode active material particles at the first maximum point to an amount W 2 of the binder per 100 parts by weight of the positive electrode active material particles at the minimum point is greater than 2;
the W 1 is 1 to 8 parts by weight;
the W 2 is 0.3 to 1.5 parts by weight;
the positive electrode active material particles include a lithium-containing transition metal oxide;
the positive electrode material mixture layer has an active material density of 3.3 to 4 g/cm 3 ,
the positive electrode material mixture layer has a thickness of 20 to 150 μm; and
the first maximum point corresponds to a position at a distance of 1 to 5 μm from the current collector in the positive electrode material mixture layer in the thickness direction thereof.
2. The positive electrode for non-aqueous electrolyte secondary batteries in accordance with claim 1 , wherein
the binder includes a fluorocarbon resin.
3. The positive electrode for non-aqueous electrolyte secondary batteries in accordance with claim 1 , wherein an amount of the binder per 100 parts by weight of the positive electrode active material particles at a midpoint between the position corresponding to the first maximum point and the current collector is 0.6 W 1 to 0.99 W 1 .
4. The positive electrode for non-aqueous electrolyte secondary batteries in accordance with claim 1 , wherein when a straight line connecting the first maximum point and the minimum point is drawn in the plot, a slope of the straight line is not less than −0.3 part by weight/μm and not more than −0.05 part by weight/μm.
5. The positive electrode for non-aqueous electrolyte secondary batteries in accordance with claim 1 , wherein an amount W 3 of the binder per 100 parts by weight of the positive electrode active material particles at the second maximum point is smaller than the W 1 .
6. A non-aqueous electrolyte secondary battery comprising: the positive electrode of claim 1 ; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, the positive electrode, the negative electrode, and the separator being wound together, forming an electrode group.
7. The positive electrode for non-aqueous electrolyte secondary batteries in accordance with claim 1 , wherein
the W 1 is 1.2 to 7 parts by weight,
the W 2 is 0.5 to 1.2 parts by weight, and
the ratio W 1 /W 2 is 2.1 or more and 10 or less.
8. The positive electrode for non-aqueous electrolyte secondary batteries in accordance with claim 1 , wherein the positive electrode material mixture layer further includes a conductive material, and
an amount of the conductive material is 0.5 to 5 parts by weight per 100 parts by weight of the positive electrode active material particles.
9. The positive electrode for non-aqueous electrolyte secondary batteries in accordance with claim 1 , wherein an amount of the binder contained in the whole positive electrode material mixture layer is 0.9 to 4 parts by weight per 100 parts by weight of the positive electrode active material particles.