A battery module, comprising: a lithium ion secondary battery which has a negative electrode mixture layer including a silicon-based active material and graphite on a surface of a negative electrode; and a control circuit which controls charge/discharge of the lithium ion secondary battery, wherein the control circuit includes a measurement unit which measures a voltage, a current, and a time (t) of the charge/discharge of the lithium ion secondary battery, an operation unit which calculates a capacity of the lithium ion secondary battery on the basis of the voltage, the current, and the time (t) and calculates a differential value dQ/dV by differentiating the capacity with the 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 the graphite and sets a threshold voltage to a voltage at the peak, 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 the charge/discharge of the lithium ion secondary battery on the basis of the discharge cutoff voltage, characterized in that, the control circuit includes a storage unit in which a maximum value of a capacity difference (ΔQ max) of the capacity at the threshold voltage and the capacity at the discharge cutoff voltage is previously recorded, the operation unit calculates the capacity difference (ΔQ) on the basis of a measurement result of the measurement unit, and the cutoff voltage setting unit sets the discharge cutoff voltage to a voltage lower than the threshold voltage and corresponding to a capacity obtained by subtracting the maximum value (ΔQ max) from the capacity at the threshold voltage, when the calculated capacity difference (ΔQ) is larger than the recorded maximum value (ΔQ max), wherein the maximum value (ΔQ max) is equal to or smaller than 20% of a capacity (Qsi) based on the silicon-based active material. a lithium ion secondary battery which has a negative electrode mixture layer including a silicon-based active material and graphite on a surface of a negative electrode; and a control circuit which controls charge/discharge of the lithium ion secondary battery, wherein the control circuit includes a measurement unit which measures a voltage, a current, and a time (t) of the charge/discharge of the lithium ion secondary battery, an operation unit which calculates a capacity of the lithium ion secondary battery on the basis of the voltage, the current, and the time (t) and calculates a differential value dQ/dV by differentiating the capacity with the 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 the graphite and sets a threshold voltage to a voltage at the peak, 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 the charge/discharge of the lithium ion secondary battery on the basis of the discharge cutoff voltage, characterized in that, the control circuit includes a storage unit in which a maximum value of a capacity difference (ΔQ max) of the capacity at the threshold voltage and the capacity at the discharge cutoff voltage is previously recorded, the operation unit calculates the capacity difference (ΔQ) on the basis of a measurement result of the measurement unit, and the cutoff voltage setting unit sets the discharge cutoff voltage to a voltage lower than the threshold voltage and corresponding to a capacity obtained by subtracting the maximum value (ΔQ max) from the capacity at the threshold voltage, when the calculated capacity difference (ΔQ) is larger than the recorded maximum value (ΔQ max), wherein the maximum value (ΔQ max) is equal to or smaller than 20% of a capacity (Qsi) based on the silicon-based active material.