Additively Printed Flexible Charging Circuits and Effect on Evolution of Line Resistance and Charging Current in Charging Thin Flexible Batteries

Flexible electronics are increasingly finding commercial applications ranging from wearable activity tracking watches, rollable displays, foldable smartphones, and biometrics. There is an acceleration of effort in the research and development of additively printed electronics on flexible substrates. Aside from device flexibility, the usage of flexible electronics leads to weight and bulk miniaturization of the product leading to compact and sleek devices. In our previous works, we have successfully studied the effect of mechanical stresses on flexible batteries and their integration into the flexible format via battery lamination. However, in addition to the battery, the battery charging circuit is a key component that must be transferred from a rigid PCB to a flexible format. This study aims to employ electrically conductive ink to print a linear battery charging circuit on a flexible polyimide substrate using different additive printing technologies, namely, aerosol jet printing and direct ink writing (DIW). In aerosol jet printing, both the ultrasonic (AJU) and pneumatic atomization (AJP) technologies have been used for depositing ink, and their subsequent results have been compared. COTS have to be attached to the circuit using electronically conductive adhesives (ECA). The flexible charging circuit has been compared for the print platforms of aerosol-jet printing and direct-write during charging-discharge cycling of the circuit.