Lithium-functionalized TEMPO-oxidized cellulose nanofiber as a novel binder and its impact on the ionic conductivity performance of lithium-ion batteries

Flexible lithium-ion batteries (LIBs) are receiving widespread attention, and how to obtain the high flexibility, safety, and energy density of LIBs at the same time are one of the main challenges in the field of flexible electronics. The multi-network structure formed by cellulose nanofiber (TOCNF) not only provided sufficient mechanical support and excellent flexibility for the electrode but also promoted uniform distribution of conductive agents and active materials. In this work, we prepared an eco-friendly TOCNF binder from wheat straw, using a method involving 2, 2, 6, 6-tetramethylpiperidinyl-1-oxyl oxidation and high-intensity ultrasonic treatment. Additionally, we enhanced the performance of TOCNF by introducing Li+ through ion exchange, resulting in lithium-functionalized cellulose nanofibers (TOCNF-Li), which were employed as a novel binder for LiFePO4 cathodes. The findings show that, when employing TOCNF-Li binder, batteries were able to obtain an initial discharge capacity of 163 mAh g-1 at 0.1 C rate and maintained 93.2% of the initial reversible capacity after 400 cycles at 2 C rate. Notably, at 5 C rate, the discharge capacity reached 133.7 mAh g-1, with a capacity decay of only 16.1%. TOCNF-Li played a role in increasing Li+ content, opening a new pathway for Li+ transport, consequently enhancing Li+ diffusion efficiency and charge-discharge performance. Overall, TOCNF-Li serves as a novel, environmentally friendly, and efficient binder for flexible LIBs.