Abstract: A battery pack including a battery, and a case for housing the battery, the case including: a top surface plate; a bottom surface plate; side surface plates defining the space therebetween; first connecting portions connecting the top surface plate and the side surface plates; and second connecting portions connecting the bottom surface plate and the side surface plates, wherein at least one group of the first connecting portions and the second connecting portions has a thick portion or a thin portion. The thick portion or the thin portion may be: provided entirely across the edge-lines formed by the first connecting portions or by the second connecting portions; provided partially along the edge-line formed thereby; or provided intermittently along the edge-line formed thereby.

Abstract: A wound electrode group includes an electrode stack that is formed by laminating a strip of positive electrode plate, a strip of negative electrode plate, and a pair of separators interposed therebetween. When the electrode stack is wound, a difference L in length between an inner turn and an adjacent outer turn satisfies L=2t?+(W×k), where t is a thickness of the electrode stack, W is a maximum diameter of a cross section of the wound electrode group, and k is a coefficient that is preset in accordance with expansion coefficients of active materials of the positive and negative electrode plates and is within a range from 0.005 to 0.05.

Abstract: A wound electrode group includes an electrode stack that is formed by laminating a strip of positive electrode plate, a strip of negative electrode plate, and a pair of separators interposed therebetween. When the electrode stack is wound, a difference L in length between an inner turn and an adjacent outer turn satisfies L=2t?+(W×k), where t is a thickness of the electrode stack, W is a maximum diameter of a cross section of the wound electrode group, and k is a coefficient that is preset in accordance with expansion coefficients of active materials of the positive and negative electrode plates and is within a range from 0.005 to 0.05.