Ultra-Flexible Li-Ion Batteries using High Mass-Loading Polymer-Rich Thick Electrodes

Flexible batteries have been the research of interest due to various applications of Internet of things (IoT), soft robots and wearable electronics. For the development of advanced electronics, flexible batteries with high energy density and mechanical stability are essential. However, conventional electrodes are limited to achieve both flexibility and high energy density of batteries.<br/>In this work, we developed novel electrode structure to fabricate ultra-flexible Li-ion battery with high energy density. This novel electrode structure was fabricated through reinforcing thermally induced polymer-rich electrode by stainless-steel (SS) fiber current collector. The polymer-rich electrode made through thermally induced phase separation (TIPS) process was suggested for flexible thick electrode. The SS fiber current collector was prepared by a facile method from a bundle. The combination of the polymer-rich electrode and SS fiber current collector enabled structural flexibility and mechanical stability. The electrochemical property and mechanical properties of the battery with the novel electrode were analyzed by comparing with battery of polymer-rich electrode coated on conventional metal foil current collector. The battery with LiNiMnCoO2 thick-film electrodes with SS fiber electrodes showed high rate capability. At 2C rate, the specific capacity of foil electrode is 60 mAh g^-1 and that of the SS fiber electrode is 135 mAhg^-1, which is two times higher. Moreover, up to 12 mAhcm^-2 high areal capacity is attained using about 1 mm thick electrode with SS current collector. Electrochemical performance of high mass-loading pouch-type battery after 2000 bending cycles also showed very high retention of specific capacity. The structural flexibility and mechanical reliability of the novel electrode structure enables to make flexible batteries with high energy density.