Battery system and method for evaluating lithium-ion battery degradation

A battery system, comprising:

• a lithium-ion battery that includes an electrode body, the electrode body including a positive electrode and a negative electrode, each being a planar electrode, being laminated each other, the electrode body being impregnated in an electrolyte solution,
• a current sensor that detects a current charged to and discharged from the lithium-ion battery;
• and
• a processor that evaluates degradation of the lithium-ion battery, using a first score and a second score, the degradation being a phenomenon that an internal resistance of the lithium-ion battery increases with development of unevenness in a lithium-ion concentration distribution within the electrode body, wherein
• the first score is an index for evaluating the unevenness in lithium-ion concentration distribution in a lamination direction in which the positive electrode and the negative electrode are laminated,
• the second score is an index for evaluating the unevenness in lithium-ion concentration distribution in an in-plane direction of the positive electrode and the negative electrode, wherein
• the processor:
• for each computing cycle, calculates a current first score based on a detection value of the current sensor, and calculates a current second score based on an SOC (State Of Charge) of the lithium-ion battery;
• when an absolute value of a second integrated value obtained by integrating the second score is beyond a reference value, evaluates the degradation of the lithium-ion battery based on the current first score, the current second score, and a first integrated value which is obtained by integrating previous first scores beyond a predetermined range;
• and
• when the absolute value is below the reference value, evaluates the degradation of the lithium-ion battery based on the first integrated value.