Mesoporous Cellulose Nanocrystal Membranes as Battery Separators for Environmentally Safer Lithium-Ion Batteries

Cellulose emerges as a promising sustainable alternative to traditional polyolefin-based lithium-ion battery (LIB) separators because of its good mechanical properties and inherent hydrophilic character. Therefore, in this work we fabricate high specific surface area mesoporous cellulose nanocrystal (MCNC) membranes with different pore morphology as novel three-dimensional porous separators. N2 adsorption–desorption isotherms and scanning electron microscopy (SEM) analyses reveal that membranes are composed of loosely packed cellulose nanocrystals (CNCs) with specific surface areas up to 172 m2·g–1 and porosities up to 75.3%. The prepared mesoporous separators show low contact angle values when evaluated against conventional electrolyte and ionic liquid, suggesting a pivotal role of the porous 3D structure on the resulting wettability, where mesopores provide efficient paths for Li+ ion migration through the membrane. Furthermore, the membranes show ionic conductivities of 2.7 mS·cm–1, wide electrochemical stability, and good interfacial compatibility with the lithium electrode, delivering a specific capacity of 122 mAh·g–1 and 85 mAh·g–1 at a C/2 and 2C rate, respectively. On the basis of the displayed high discharge capacity, small overpotential, wide electrochemical window, and good cycling stability, the use of ionic liquids (ILs) as suitable electrolytes together with MCNC membranes for the development of environmentally friendly separator-electrolyte systems was also evaluated.