Secondary battery system and method of estimating stress of active material of secondary battery

A method of estimating a stress generated in an active material of a secondary battery, as a charge carrier is incorporated into and is removed from the active material, comprising:

• calculating an estimated value of the stress from a difference obtained by subtracting a reference charge carrier amount from an amount of the charge carrier contained in the active material, using a linear relationship between the difference and the stress;
• correcting the estimated value to a yield stress of the active material when a magnitude of the estimated value is larger than a magnitude of the yield stress of the active material;
• and
• controlling charging and discharging of the secondary battery in accordance with an estimated State of Charge (SOC) as determined by the estimated stress.

A secondary battery system comprising:

• a secondary battery having an electrode containing an active material into and from which a charge carrier is reversibly incorporated and removed;
• and
• a control unit configured to estimate a stress generated in the active material as the charge carrier is incorporated into or removed from the active material,
• wherein the control unit is configured to calculate an estimated value of the stress from a difference obtained by subtracting a reference charge carrier amount from an amount of the charge carrier contained in the active material, using a first linear relationship between the difference and the stress, correct the estimated value to a yield stress of the active material when the estimated value is larger than tensile stress of the active material at a time of yielding or is smaller than compressive stress of the active material at the time of yielding, and control charging and discharging of the secondary battery in accordance with an estimated State of Charge (SOC) as determined by the estimated stress.