SECONDARY BATTERY DIAGNOSING APPARATUS AND METHOD

A secondary battery diagnosing apparatus includes a thickness sensor configured to sense a change in thickness of a secondary battery according to a volume change of a negative electrode active material while the secondary battery comprising a negative electrode active material containing silicon or silicon oxide is being charged or discharged; and a processor configured to estimate a capacity ratio, which is a ratio of a capacity provided by the silicon or the silicon oxide to a capacity of the secondary battery provided by the negative electrode active material, using a sensing result of the thickness sensor, and diagnose the state of the secondary battery based on the capacity ratio.