A Deterioration Diagnosis Method for Li-ion Battery Using a Transient Characteristic and Development of an Automatic Diagnosis Circuit

A deterioration diagnosis method for a Li-ion battery using its transient characteristic is proposed in this paper. The terminal voltage of the battery sharply increases at the beginning of the charging and gradually increases. The terminal voltage suddenly decreases at the end of the charging and decreases toward its internal voltage. The transient characteristic can be explained by the response of the internal impedance of the Li-ion battery. The internal impedance has a close relation to the deterioration of the battery. The proposed method in this paper diagnoses the deterioration using the integration of the difference between the terminal voltage and the internal voltage of the battery after a charging. The integrated voltage depends on both the deterioration and the temperature of the battery. The integrated voltage is corrected for the deterioration estimation of the Li-ion battery. This proposed method is practical because it requires no information except the terminal voltage of the battery and ambience temperature. A diagnosis equipment using a microcomputer has been developed in this paper. The circuit is realized a diagnosis system in low cost because the computational load for the diagnosis is light.