Facile design of novel nanocellulose-based gel polymer electrolyte for lithium-ion batteries application

Nanocellulose-based gel polymer electrolytes (GPEs) for lithium-ion batteries have attracted great attention due to their biodegradable and renewable precursors, high thermal stability, good mechanical strength and electrolyte wettability. However, their abundant hydroxyl groups lead to the precursor films of GPEs with dense morphology, which severely affect their electrolyte uptake ratio and electrochemical performance. In this work, we aim to pretreat cellulose nanofibrils (CNFs) by acetylation to not only introduce ester groups in the according GPE to improve its electrolyte absorption capacity but also reduce the amount of hydroxyl groups for a stable battery cycle performance. At the optimal degree of substitution (DS) value of 2.37, the generated acetylated CNF (GACNF-3) GPE exhibited the best electrolyte uptake capacity of 301%, ionic conductivity of 2.73 × 10−3 S cm−1, and Li+ ion transference number of 0.65. Due to the high transportation performance of Li+ ions, mechanical strength (tensile strength of 37.66 MPa), and flexibility (elongation of 10.55%), the interfacial resistance of Li/GACNF-3 GPE/Li was 152 Ω, which only increased to 170 Ω after storage for 18 days. In particular, the assembled Li/GPE/LiFePO4 battery demonstrated an initial discharge capacity of 153 mA h g−1 with capacity retention of 88.8% after 100 cycles at 0.2C. The proposed material design would provide a novel perspective for the development of polymer electrolyte for lithium-ion battery.