Abstract
The growing demand of flexible electronic devices is increasing the requirements of their power sources. The effect of bending in thin-film batteries is still not well understood. Here, we successfully developed a high active area flexible all-solid-state battery as a model system that consists of thin-film layers of Li4Ti5O12, LiPON, and Lithium deposited on a novel flexible ceramic substrate. A systematic study on the bending state and performance of the battery is presented. The battery withstands bending radii of at least 14 mm achieving 70% of the theoretical capacity. Here, we reveal that convex bending has a positive effect on battery capacity showing an average increase of 5.5%, whereas concave bending decreases the capacity by 4% in contrast with recent studies. We show that the change in capacity upon bending may well be associated to the Li-ion diffusion kinetic change through the electrode when different external forces are applied. Finally, an encapsulation scheme is presented allowing sufficient bending of the device and operation for at least 500 cycles in air. The results are meant to improve the understanding of the phenomena present in thin-film batteries while undergoing bending rather than showing improvements in battery performance and lifetime.
Highlights
Providing sufficient electrical energy storage is one of the key challenges for the century
An operational thin-film battery stack is developed as a model system on a flexible ceramic substrate using physical vapor deposition (PVD) techniques
The observable change in capacity upon bending state seems to be strongly related to the change in Li-ion diffusion in the thin-film electrode lattice caused by the positive and negative stresses applied, this is according to our first approximations and following the above assumptions
Summary
Providing sufficient electrical energy storage is one of the key challenges for the century. Conventional thin-film batteries are based on brittle or intrinsically inflexible materials These batteries are unable to maintain stable power and energy supply and cycling stability for applications under frequent mechanical stress generated by bending, folding, or twisting [3]. Several effects may appear, such as insufficient flexibility and strength of the electrodes, leakage of the liquid electrolyte, poor adhesion between substrate and active materials, and degradation of the mechanical and electrochemical properties at different deformed states [6]. Another issue is the development of lightweight, thin, flexible, and stable encapsulation materials to protect the battery from external influences [3]. Different thin-film encapsulation approaches are considered and battery performance is evaluated
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