Rechargeable battery with larger curved ends having different radius of curvature

A rechargeable battery comprising:

• an electrode assembly having a positive electrode plate and a negative electrode plate and a separator interposed therebetween, wherein the electrode assembly is wound so as to define a first cross-sectional shape having two curved portions at lateral ends of the electrode assembly and a flat portion interposed between the two curved portions wherein the flat portion has a thickness dimension that is less than the thickness dimension of either of the curved portions wherein the curved portions define a first outermost curved portion located in an outermost portion of a second direction and a second outermost curved portion that interconnects the first outermost curved portion to the flat portion wherein the center points define the center of curvature of the first outermost curved portions and wherein the curvature of the second outermost curved portion is larger than that of the first outermost curved portion and wherein the second outermost curved portion curves inward of the first outermost curved portion towards the less thick flat portion along the larger radius of curvature
• wherein the less thick flat portion extends the entire length of the battery along a direction that is substantially perpendicular to the plane of the cross-sectional shape
• a case having an interior for receiving the electrode assembly, and
• a cap assembly that is positioned on the case
• wherein the less thick flat portion of the electrode assembly is spaced further from the interior walls of the case than the curved portions to accommodate swelling of the flat portion of the electrode assembly during charging of the electrode assembly and wherein the flat portion is compressed together so as to define a continuous mass across the less thick flat portion that is denser than the curved portions across the length of the battery, and
• wherein the thickness dimension of the flat portion and the thickness direction of the curved portions are measured along a first direction that is substantially perpendicular to the flat portion of the electrode assembly,
• wherein the curved portions are spaced along a second direction that is substantially perpendicular to the first direction and wherein the curved portions define center points,
• wherein the flat portion has a length extending along the second direction that is less than the distance between the center points of the curved portions,
• wherein the positive electrode plate and the negative electrode plate includes a positive active material layer and a negative active material layer respectively and wherein the negative active material layer includes a material that has a volume expansion rate of higher than 10% during charging of the electrode assembly wherein the compressed less thick flat portions that define the continuous mass includes positive electrode plates and negative electrode plates.