Assessment of Flexible Batteries Under Dynamic Folding and Flex-to-Install with Varying C-Rates and Temperatures
Flexible electronics may be subjected to dynamic folding during operation in wearable applications that require the attachment of applique skin-patch or integration of electronics into wearable garments. Operation in wearable applications requires power sources capable of sustaining stresses of daily motion including dynamic folding without significant degradation in the battery capacity under sustained exposure to human body temperature while subjected to various depths of charge-discharge cycles. Asset monitoring using flexible electronics may require the installation of power sources to be flexed-to-install on non-planar surfaces during installation close to the sensor locations. Lithium-ion batteries are a dominant power source for portable electronic devices. Commercial lithium-ion batteries are constructed by connecting individual Li-ion cells in parallel to increase the current or in series to increase the voltage or combined configurations. Multiple battery cells can be integrated into a module, which can be used to form battery packs. Flexible batteries in wearable applications can serve a diverse array of functions including logic, control, memory, and biometric sensing. There are significant technical challenges in meeting the power needs of wearable electronics including maximizing capacity in thinner form-factors, flexibility, and robustness under the operating and usage environment. In this research study, the combined effects of deep-charge, shallow-charge, distinct bending load(s) and operating temperatures have been characterized for Li-Ion batteries. Thin flexible battery cells were cycled through multiple charge-discharge cycles under simultaneous dynamic folding loads plus thermal stresses. Output parameters such as efficiency, power, capacity and charge-discharge time have been analyzed for the battery state assessment. In addition, the battery degradation has been studied at various C-rates. The sensitivity of capacity degradation to a number of charge-discharge parameters is quantified with a regression model.