Charging method for nonaqueous electrolyte secondary cell and charging system for nonaqueous electrolyte secondary cell

A method for charging a nonaqueous electrolyte secondary battery including a negative electrode that contains a carbon material and a Si-containing compound as a negative electrode active material, the method comprising the steps of

• charging a first capacity Q1st at a first constant current value I1st, the first capacity Q1st including a capacity range in which the ratio dQSi/dQ of the amount of change in capacity QSi of the Si-containing compound relative to the amount of change in battery capacity Q is more than or equal to a predetermined threshold value, as a first charging step;
• charging a second capacity at a. second constant current value more than the first constant current value in a second charging step after the first charging step is complete;
• acquiring at least one of the ratio dV/dQ of the amount of change in open-circuit voltage relative to the amount of change in battery capacity Q and dQSi/dQ, as a detection step;
• and
• changing at least one of the timing of switching between the first charging step and the second charging step and the first constant current value I1st on the basis of a change in time of dV/dQ or dQSi/dQ , as a changing step.