Tabless battery

An electrode wound body comprising:

• a positive electrode including:
• a positive electrode foil;
• a positive electrode active material on a portion of the positive electrode foil;
• and
• a positive foil extension extending from the positive electrode foil, wherein the positive electrode active material is not on the positive foil extension;
• a negative electrode including:
• a negative electrode foil;
• a negative electrode active material on a portion of the negative electrode foil;
• and
• a negative foil extension extending from the negative electrode foil, wherein the negative electrode active material is not on the negative foil extension;
• and
• a separator between the positive electrode and the negative electrode;
• wherein
• the positive electrode, the negative electrode, and the separator are wound to define a spiral including a through hole with a central axis extending through the through hole;
• the positive foil extension extends from a first end of the electrode wound body;
• the negative foil extension extends from a second end of the electrode wound body opposite to the first end;
• portions of the positive foil extension include first bends that bend towards the central axis so that the portions of the positive foil extension overlap to define a first surface;
• first bending shapes of the first bends of the positive foil extension are asymmetric with respect to the central axis;
• portions of the negative foil extension include second bends that bend towards the central axis so that the portions of the negative foil extension overlap to define a second surface;
• and
• second bending shapes of the second bends of the negative foil extension are asymmetric with respect to the central axis.