Patent ID: 8102152

Claim:
A deterioration detecting method for a rechargeable lithium battery, the rechargeable lithium battery comprising: a positive electrode having a positive active material that absorbs and emits a lithium ion; a negative electrode having a negative active material that contains at least one of elements of silicon and tin; and an electrolyte having lithium-ion conductivity, the electrolyte being provided between the positive electrode and the negative electrode; the deterioration detecting method comprising: detecting a group of a closed-circuit charge cutoff voltage and an open-circuit voltage after charging of the rechargeable lithium battery; calculating an evaluation value based on the detected group of voltages; comparing the evaluation value and a reference value stored in advance to have a comparison result; and estimating a deterioration level of the rechargeable lithium battery based on the comparison result, wherein the evaluation value is an apparent resistance R 1 at completion of charging, the apparent resistance R 1 calculated based on a relational expression of: R 1 =ΔV 1 /I 1 , where ΔV 1 is a difference between the closed-circuit charge cutoff voltage and the open-circuit voltage after charging, and I 1 is a closed circuit charge cutoff current.