Accelerated Life Cycling of Additively Printed Flexible Linear Charging Circuits and its Effect on Evolution of Line Resistance and Charging Current

The rising demand and consumer interest in wearable devices, fitness accessories, foldable smartphones, and biomedical equipment has led to a research impetus in the field of flexible electronics. Apart from the feature of device flexibility, incorporation of flexible electronics in a device also leads to weight and bulk reduction resulting in more sleek and thin devices. Thus, in the past few years, there have been studies focusing on the inclusion of traditional electronics components like resistors, capacitors, LEDs, sensors, etc. on flexible substrates like polyimide. In our previous study, we also demonstrated the lamination of thin-flexible Li-ion batteries, which are an integral component of modern consumer electronics products. However, apart from just the battery, the battery charging circuit is also an important component, which needs to be transferred from the rigid PCB format to the flexible format. This study focuses on printing of a battery charging circuit on a flexible polyimide substrate using electrically conductive ink. Electronically conductive adhesives (ECAs) will be used for component attachment to the circuit. Two distinct electronics printing technologies will be used and compared for this task, namely aerosol jet printing and direct ink write printing. A linear battery charging topology will be used to develop the additively printed charging circuit. After its preparation, the flexible charging circuit will be subjected to accelerated life cycling for 50 charging cycles to study its effect on the line resistance of the circuit and the change in battery charging current. To study the effect of the constant current (CC) charge current of the battery on the degradation in circuit line resistance, circuits with varying sense resistors have been fabricated to provide two different CC charge currents, i.e. 1C and 2C. Finally, the reliability of the additively printed charging circuit will be compared with that of an identical circuit printed on a rigid PCB and subjected to the same accelerated life-cycling test.