| abstract |
The lithium ion secondary battery 100 includes a positive electrode current collector 221 and a porous positive electrode active material layer 223 held in the positive electrode current collector 221. Here, the positive electrode active material layer 223 contains the positive electrode active material particles 610, the conductive material 620, and the binder 630, for example. In such a lithium ion secondary battery 100, the positive electrode active material particles 610 penetrate the corner portions 612 made of lithium transition metal oxide, the hollow portion 614 formed inside the corner portions 612, and the corner portions 612. It has one through hole 616. In this lithium ion secondary battery 100, in the average of the positive electrode active material layer 223, the proportion of the hollow portion 614 in the apparent cross-sectional area of the positive electrode active material particles 610 is 23% or more. Moreover, in the average of the positive electrode active material layer 223, the thickness of each part 612 is 2.2 micrometers or less. |