SoH Prediction of Thin-Flexible Lithium-Ion Batteries in Dynamic-Folding and Flex-to-Install Applications

The reliability of thin-flexible power sources under stresses of daily motion of dynamic folding, flexing, and flex-to-install are not well understood. Operation in wearable applications requires power sources capable of sustaining static and dynamic stresses of daily motion without significant degradation in the battery capacity while subjected to various depths of charge for several charge-discharge cycles. Lithium-ion batteries (LIBs) present a good combination of specific energy and specific power density as compared to other electrical energy storage technologies. In addition to the high specific energy and power, other advantages of Li-ion batteries are their long calendar-life, high cycle-life, wide availability, high roundtrip efficiency, low maintenance requirements, availability of different chemistries for specific applications, a low self-discharge rate, and high reliability in comparison with other battery chemistries. The power-sources can be folded either longitudinally or transversally in the case of dynamic folding. In this research study, the combined effects of deep and shallow depths of charge, static and dynamic folding load(s), varying fold orientations, and varying C-rates have been characterized for Li-Ion batteries with liquid electrolyte and solid electrolyte and a variety of cathode materials include LCO and NMC. The work builds on the prior work by the authors in which capacity degradation data was presented on non-laminatable LCO batteries. In the current effort, additional hot-laminatable and cold-laminatable batteries have been studied with additional parameters including DCIR, fold-orientation, charge-discharge current, capacity degradation. Thin flexible battery cells were cycled through multiple charge-discharge cycles under simultaneous static or dynamic folding loads. Static-flexure has been enforced for flex-to-install. In addition, the effect of dynamic folding on the power-source capacity degradation along with variation in the fold orientation is investigated with the same bend radius. Output parameters such as battery capacity and its degradation have been analyzed for the battery state assessment. In addition, a new life-prediction model has been developed for life prediction of thin-flexible batteries under dynamic-folding and flex-to-install.