Evaluation of health and safety of mechanically fatigued rechargeable lithium polymer batteries for flexible electronics applications

The state-of-health (SOH) and safety of flexible batteries exposed to mechanical fatigue conditions are important issues for the durable and reliable operations of flexible and wearable electronics. In this research, the effects of fatigue deformation of a flexible lithium polymer battery on its capacity fade, SOH, and safety were investigated. Mechanical fatigues under bending, torsion, and complex strain modes at various strains accelerated the SOH degradation of the battery. The electrochemical impedance spectroscopy (EIS) spectra (i.e. Nyquist plots) were analyzed to understand the microdamage occurred to the battery material. The total electrochemical impedance value obtained using EIS tends to be inversely proportional to the SOH value of the fatigued battery. Lithium metal precipitation was observed on the disassembled graphite surface of the fatigued battery, whereas no such hazard existed on the as-received one. The needle-like precipitate resulted in local puncturing of the polymer separator in the fatigued battery.