The performance of thin-film Li-ion batteries under flexural deflection

A method is introduced to study the effects of flexural deformation on the electrical performance of thin-film lithium-ion batteries. Flexural deformation of thin films is of interest to engineers for applications that can be effective in conformal spaces in conjunction with multi-functional composite laminates in structural members under mechanical deflections such as thin airfoils used in unmanned aerial vehicles (UAVs). A test fixture was designed and built using rapid prototyping techniques. A baseline reference charge/discharge cycle was initially obtained with the device in its un-flexed state, in order to later contrast the performance of the thin-film battery when subjected to deflections. Progressively larger deflections were introduced to the device starting with its un-deformed state. The cord flexure was applied in increments of 1.3% flex ratio, up to a maximum of 7.9%. At each successive increment, a complete charge/discharge cycle was performed. Up to a flex ratio of 1.3%, no effects of mechanical flexure on battery performance were observed, and the device performed reliably and predictably. Failure occurred at deflections above 1.3% flex ratio.