Lithium-ion cell and method for manufacturing same

The present invention makes it possible to improve the output of a lithium-ion cell, and to prevent the occurrence of short circuiting between the positive and negative electrodes caused by dislodging of the electrode active material. A means for accomplishing the above is a lithium-ion cell having a positive electrode, a negative electrode, and a separator for separating the electrodes, wherein a slit section is formed extending in the longitudinal direction of the separator, the slit section being a groove passing from the front surface to the back surface of the separator. The width of the slit section in the short direction is less than the average diameter of the active material, and the length in the long direction is equal to or greater than the average diameter of the active material.