Secondary battery system and method of estimating an internal state of secondary battery

A secondary battery system comprising:

• a secondary battery having a positive electrode including a positive electrode active substance and a negative electrode including first and second negative electrode active substances;
• and
• a control device configured to estimate an internal state of the secondary battery based on an active substance model of the secondary battery, wherein:
• an amount of change in volume of the first negative electrode active substance with change in charge carrier amount in the first negative electrode active substance is greater than an amount of change in volume of the second negative electrode active substance with change in charge carrier amount in the second negative electrode active substance;
• the control device is configured to, under a condition that the first negative electrode active substance and the second negative electrode active substance are at the same potential, calculate a charge carrier amount in the first negative electrode active substance based on a first active substance model;
• the control device is configured to calculate an amount of change in an open circuit potential of the first negative electrode active substance based on surface stress of the first negative electrode active substance to be determined according to the charge carrier amount in the first negative electrode active substance;
• the control device is configured to calculate an open circuit potential of the negative electrode from the open circuit potential of the first negative electrode active substance and the amount of change in open circuit potential of the first negative electrode active substance in a state in which surface stress is not generated in the first negative electrode active substance;
• the control device is configured to control charging and discharging of the secondary battery according to a result of a control device calculation based on the open circuit potential of the negative electrode;
• the control device is configured to, under a condition that the first negative electrode active substance and the second negative electrode active substance are at the same potential, separately calculate a current flowing in the first negative electrode active substance and a current flowing in the second negative electrode active substance through convergence computation processing such that a predetermined convergence condition is established;
• the control device is configured to calculate a concentration distribution of charge carriers in the first negative electrode active substance and the second negative electrode active substance by solving a diffusion equation under a boundary condition relating to the current flowing in the first negative electrode active substance and the second negative electrode active substance;
• and
• the control device is configured to calculate the charge carrier amount in the first negative electrode active substance and the second negative electrode active substance from the concentration distribution of the charge carriers in the first negative electrode active substance and the second negative electrode active substance.