Positive electrode for nonaqeous electrolyte secondary battery and a nonaqueous electrolyte secondary battery

A positive electrode for a nonaqueous electrolyte secondary battery, a folded portion formed at least at one part of the positive electrode in an electrode body, the nonaqueous electrolyte secondary battery having a current density of 3.85 mA/cm2 or more,

• the positive electrode comprising a single first positive electrode composition layer on one side of a positive electrode current collector,
• wherein the single first positive electrode composition layer comprises at least a positive electrode active material, a binder and a conductive assistant,
• wherein a cross-section of the single first positive electrode composition layer has a domain A extending from a central part to a surface side in a thickness direction thereof, and a domain B extending from the central part to the positive electrode current collector thereof, wherein the central part is located with equal distance in the thickness direction from the surface side and the positive electrode current collector,
• wherein the positive electrode has an a/b value of 5 or more, the a/b value being obtained in accordance with a method comprising:
• a step of detecting elements derived from the binder by means of SEM-EDX with respect to the cross-section of the single first positive electrode composition layer;
• a step of selecting a first element included in the binder at a highest quantity among the elements detected, and selecting a second element included in the binder at a second highest quantity among the elements detected;
• a step of drawing a first element mapping of the first element, and drawing a second element mapping of the second element, the first element mapping being drawn in a vision field same as the second element mapping;
• and
• a step of calculating an area where the first element mapping overlaps with the second element mapping;
• wherein the method is carried out on each the domain A and the domain B, a ratio of the area in the domain A is defined as “a,” a ratio of the area in the domain B is defined as “b,” thereby obtaining the a/b value.

A nonaqueous electrolyte secondary battery comprising:

• an electrode body comprising a positive electrode, a negative electrode, a separator;
• and a nonaqueous electrolyte,
• wherein the nonaqueous electrolyte secondary battery has a current density of 3.85 mA/cm2 or more,
• wherein the positive electrode comprises:
• a single first positive electrode composition layer on one side of a positive electrode current collector;
• and a folded portion formed at least at one part of the positive electrode,
• wherein the single first positive electrode composition layer comprises at least a positive electrode active material, a binder and a conductive assistant,
• wherein a cross-section of the single first positive electrode composition layer has a domain A extending from a central part to a surface side in a thickness direction thereof, and a domain B extending from the central part to the positive electrode current collector thereof, wherein the central part is located with equal distance in the thickness direction from the surface side and the positive electrode current collector,
• wherein the positive electrode has an a/b value of 5 or more, the a/b value being obtained in accordance with a method comprising:
• a step of detecting elements derived from the binder by means of SEM-EDX with respect to the cross-section of the single first positive electrode composition layer;
• a step of selecting a first element included in the binder at a highest quantity among the elements detected, and selecting a second element included in the binder at a second highest quantity among the elements detected;
• a step of drawing a first element mapping of the first element, and drawing a second element mapping of the second element, the first element mapping being drawn in a vision field same as the second element mapping;
• and
• a step of calculating an area where the first element mapping overlaps with the second element mapping;
• wherein the method is carried out on each the domain A and the domain B, a ratio of the area in the domain A is defined as “a,” a ratio of the area in the domain B is defined as “b,” thereby obtaining the a/b value.