Health monitoring of mechanically fatigued flexible lithium ion battery by electrochemical impedance spectroscopy

For reliable applications of flexible lithium ion batteries, the states of mechanically fatigued batteries were evaluated by applying electrochemical impedance spectroscopy (EIS). The EIS resistance of the batteries increased with mechanical fatigue, and this tendency was more distinct for the battery in the charged state. The EIS resistance of the fatigued battery was unstable and fluctuated during subsequent storage time after fatigue. Capacity degradation of the fatigued battery was about three times faster than that of the as-received one. By scanning electron microscopic observation of the dissembled electrode materials, root causes of the observed faster degradations were attributed to lithium metal precipitation on the carbon negative electrode as well as collapse of lamellar structures of the polymer separator (i.e., blockage of micro pores for lithium ion movement.)