MacFarlane Endowed Distinguished Professor and Director Auburn University, AL, United States
Flexible power sources have received increased attention as a result of the introduction of a number of flexible portable electronics applications. In wearable applications that require the attachment of an appliqué skin patch or the integration of electronics into wearable clothes, flexible electronics may be subjected to static and dynamic folding. While the effect of C-rates and operating temperatures on the reliability of thick lithium-ion batteries has been investigated earlier, the effect of static and dynamic U-flexing on the battery cycle life of thin lithium-ion power sources is not well understood. The combined impacts of deep and shallow depths of charge, static-folding, dynamic-folding, and twisting load(s) have been characterized for thin-flexible Li-Ion batteries under varied fold orientations and varying C-rates in this research work. The lithium-ion batteries investigated have a thickness of less than 1mm. The performance and reliability of cathode chemistries such as NMC and LCO have been investigated. For battery condition assessment, output metrics such as battery capacity and degradation have been examined. Lamination has also been investigated and compared to non-laminated batteries for thin-flexible battery integration. The impact of different lamination process settings on peel strength and charge-discharge cycling degradation has been measured. To explore the combined influence on capacity deterioration, laminated batteries were exposed to static and dynamic fold tests. Finally, a life-prediction model was created to estimate battery capacity decline as a function of cycle number, operating temperature, and depth-of-discharge. Acceleration factors between accelerated test circumstances and use-conditions can be calculated using the model. The model can also be used to calculate the required test levels to ensure dependability in common use-cases.