Pattern-Integrated Paper Li-Ion Microbatteries Through Large-Scale Roll-to-Roll Flexographic Printing

The large-scale manufacturing of architecture designable lithium-ion (Li-ion) batteries poses a significant challenge but raises an emerging need for enhancing battery performances and enlarging application scenarios. However, traditional methods of manufacturing Li-ion batteries (LiBs) rely on roll-to-roll (R2R) bar coating, which cannot render the customized pattern or structure for fabricated electrodes and limited electrodes’ application. To get around this bottleneck, we innovatively introduced the well-developed R2R flexographic printing technology to manufacture pattern-integrated Li-ion electrodes. Compared to alternative electronic printing substrates such as metal, plastic, and glass, the inexpensive and biodegradable cellulosic paper with high printability was selected as a printing substrate to improve printing resolution, reduce cost, and protect the environment. Furthermore, the special pores between the cellulosic fibers in the paper were utilized for transferring ions. Therefore, paper can be used both for a separator in LiBs.<br/>In this study, as a novel approach, we integrated large-scale R2R flexographic printing and LiB production to manufacture LiBs with unique patterns, in which flexible and high printable paper was used as both the printing substrate and separator in LiBs. Accordingly, we developed a series of LiFePO4 (LFP) flexographic printable inks and successfully printed them on thin (25 µm) and lightweight (23.4 g/m²) paper with a large-scale R2R flexographic printer. A high-quality and high-resolution flexographic printed pattern was achieved with 35% solid-content LFP at 80 in/min. Moreover, a thin layer of Al₂O₃ was coated to modify the separator. The flexographically printed paper battery exhibited a high-rate performance (97.2% discharge capacity retention at 2 C of that at 0.1 C) and outstanding capacity stability (~100% discharge capacity retention after 1000 cycles at 3 C). The results highlighted the immense potential of integrating flexographic printing with R2R manufacturing architecture for designable LiBs and using flexible, inexpensive, sustainable, and high printable paper as a printing substrate and separator in printed LiBs for the scalable fabrication of flexible batteries with high-resolution patterns to obtain microbatteries for applications in wearable electronics and bioengineering.