Ultra-flexible and foldable gel polymer lithium–ion batteries enabling scalable production

Flexible lithium–ion batteries are an emerging and promising technology for next-generation flexible devices; however, some potential problems, such as potential safety hazards of organic liquid electrolytes, severe capacity loss caused by poor adhesion between electroactive materials and current collectors, and the unscalable production of flexible current collectors, prevent flexible batteries from being used in practice. This study demonstrates a safety reinforced ultra-flexible and foldable lithium–ion battery using LiCoO2 (LCO) as the cathode, Li4Ti5O12 (LTO) as the anode, a high-quality carbon nanotubes film as a flexible current collector, and a novel porous composite as the gel polymer electrolyte. The flexible battery exhibits superior electrochemical performance compared to other flexible batteries reported, with a capacity retention rate of 93% after 150,000 cycles of mechanical bending. The gravimetric energy density of the flexible electrodes is 1.6 times higher than that of standard electrodes using metal foils as current collectors. More importantly, the flexible battery offers extreme safety performance and performs very well under various severe conditions, such as repeated folding and punching. These results demonstrate the promising potential of flexible batteries for many wearable applications and offer a new platform for the scalable production of flexible and wearable energy storage technologies.