Lithium-based rechargeable batteries (LbRBs) are essential for applications in vehicles, wearable electronics, and large-scale energy storage due to their high energy density. However, safety concerns associated with flammable organic electrolytes hinder further development. Advancing Li-ion battery technology requires improved conductivity, energy density, and safety, particularly in the development of all-solid-state lithium-ion batteries (ASSLiBs). This work explores carboxymethyl cellulose (CMC)-based solid polymer electrolytes (SPEs) as sustainable alternatives for lithium-ion batteries. The synergistic effects of 1-butyl-3-methyl imidazolium chloride ([BMIm]Cl) ionic liquid, as a plasticizer, and lithium acetate (LiCH3COO) enhance the electrochemical properties of SPE membranes. A wrinkled morphology and optimal ionic transport are achieved at 30 wt.-% [BMIm]Cl, labeled as SPE30-IL30, as evidenced by scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy. SPE30-IL30 exhibit excellent thermal stability up to 508 degrees C, with a crystallinity index (Cr.I) of 43.73 % and stiffness of 48.55x10-3 GPa. At 30 wt.-% [BMIm]Cl, the CMC-based membrane achieves an ionic conductivity of 1.37 x 10-3 S cm-1, a lithium-transference number (tLi+) of 0.96, and an electrochemical stability window of 3.85 V, representing the highest performance among the studied SPEs. Density functional theory (DFT) simulations further reveal that [BMIm]Cl reduces the stabilization energy of LiCH3COO by 14 kcal/mol, strengthening molecular interactions between CMC and Li+ ions. These results highlight the potential of [BMImCl] ionic liquid-plasticized CMC-based SPEs as a sustainable, high-performance electrolytes for next-generation ASSLiBs, aligning with circular economy principles while delivering enhanced electrochemical and physicochemical properties.
