Leveraging Water/Ethanol Solvent Ratios to Tailor the Properties of Sodium Carboxymethylcellulose and Ionic Liquid− Solid Polymer Electrolytes for Solid-State Batteries

Due to the growing demand for efficient energy storage systems, solid-state batteries made from solid polymer electrolytes (SPEs) have become a growing research topic. This study proposes a room-temperature SPE based on the sustainable polymer sodium carboxymethyl cellulose (NaCMC), incorporating the ionic liquid (IL) 1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([PMPyr][TFSI]) into the polymer matrix. The focus of our study is to explore how the water-to-ethanol ratios impact the physicochemical and electrochemical properties of the resulting films. In relation to the results obtained, scanning electron microscopy demonstrates that the distribution of IL inside the polymer matrix was altered by solvent ratios. The SPE's thermal stability was assessed by thermogravimetric analysis and differential scanning calorimetry, ensuring that all hybrid materials were suitable for use in battery applications. The IL acted as a plasticizer, and the mechanical tests showed maximum deformation up to 7% in the composite films. Significantly, the SPE processed with 100% water exhibited the highest battery performance with an initial discharge capacity of 71 mAh g−1 and an ionic conductivity of 1.9 × 10−5 S cm−1, demonstrating a lithium transference number of 0.67 and an even discharge capacity of 40 mAh g−1 after 50 cycles at a C/10 rate and room temperature. Overall, this work introduces an SPE based on a sustainable polymer and demonstrates that solvent−IL interactions can be effectively used to tailor the properties of sustainable SPEs, opening the way for high-performance, room-temperature solid-state lithium-ion batteries.