Novel bacterial cellulose nanocrystals/polyether block amide microporous membranes as separators for lithium-ion batteries

Bacterial cellulose nanocrystals (BCNCs) were extracted from nata de coco waste and underwent sulphuric acid (H2SO4) hydrolysis for use as a reinforcement giving thermal and dimensional stability to polyether block amide (PEBAX) as a polymer matrix for the fabrication of BCNCs/PEBAX microporous membranes. The H2SO4-hydrolysis of BCNCs yielded rod-like/needle-like BCNCs and negatively charged surfaces, resulting from the generated surface sulfate groups on the bacterial cellulose (BC), which may be competent for numerous applications. The non-solvent induced phase separating (NIPS) and subsequent film casting methods were used to prepare the BCNCs/PEBAX microporous membranes. The obtained films were characterized with regards to their structure in terms of the content of crystalline phases, as well as their ionic transport and performance at elevated temperatures. The presence of the BCNCs fillers resulted in a good thermal and dimensional stability up to 150 °C and correlated with no membrane shrinkage. For NIPS membranes, the formation of a rigid cellulosic network within the matrix was emphasized and attributed to the thermal stabilization at temperatures above the melting temperature. In addition, the wettability, ionic conductivity, and thermal stability were investigated in BCNCs/PEBAX membranes filled with different amounts of BCNCs. Thus, the BCNCs/PEBAX membranes derived via NIPS had a remarkably good ionic conductivity, within the range of 10−2–10−3 S/cm, with up to 56.8% porosity. Such porous membranes are considered as an important and interesting candidate for the replacement of the commercial polyolefin-based microporous separator in lithium-ion batteries due to their superior electrochemical performances and the observed reinforcement effect.