Abstract: A battery module includes a lithium ion secondary battery and a control circuit. The control circuit includes a measurement unit which measures voltage, current, and the time of charge/discharge of the lithium ion secondary battery; an operation unit which calculates a capacity based on the voltage, the current, and the time and calculates a differential value dQ/dV by differentiating the capacity with a voltage; a threshold voltage setting unit which specifies a peak of a low capacity side of the differential value dQ/dV generated on the basis of a stage structure of graphite and sets a voltage at the peak to a threshold voltage; a cutoff voltage setting unit which sets a discharge cutoff voltage of the lithium ion secondary battery on the basis of the threshold voltage; and a charge/discharge control unit which controls charge/discharge of the lithium ion secondary battery on the basis of the discharge cutoff voltage.

Abstract: A battery module includes a lithium ion secondary battery and a control circuit. The control circuit includes a measurement unit which measures voltage, current, and the time of charge/discharge of the lithium ion secondary battery; an operation unit which calculates a capacity based on the voltage, the current, and the time and calculates a differential value dQ/dV by differentiating the capacity with a voltage; a threshold voltage setting unit which specifies a peak of a low capacity side of the differential value dQ/dV generated on the basis of a stage structure of graphite and sets a voltage at the peak to a threshold voltage; a cutoff voltage setting unit which sets a discharge cutoff voltage of the lithium ion secondary battery on the basis of the threshold voltage; and a charge/discharge control unit which controls charge/discharge of the lithium ion secondary battery on the basis of the discharge cutoff voltage.

Abstract: An assembled battery is formed by laminating secondary batteries each including a flat wound electrode group formed by winding a laminated body including positive and negative electrodes laminated with separators interposed therebetween and a flat battery container for housing the wound electrode group with a spacer interposed therebetween. The wound electrode group has a flat portion where the laminated body is formed by flat lamination and a curved portion where the laminated body is formed by curved lamination. The spacer has an abutting portion that abuts on a wide surface of the battery container within a range facing the inner side of the both ends of the flat portion and a facing portion that faces the wide surface of the battery container within a range facing the curved portion. The thickness of the facing portion is smaller than the thickness of the abutting portion.