Fabrication, characterization, and electrochemical performance of the HDPE/sepiolite nanocomposite as a novel separator for Li-ion batteries

Separators are one of the most critically important components of lithium-ion batteries to ensure the safe performance of the battery. Commercial polyolefin separators have high thermal shrinkage and low electrolyte uptake, which confines the application of the battery. By using the thermally induced phase separation (TIPS) method, we successfully prepared HDPE/sepiolite nanocomposite separators with high thermal stability and electrolyte wettability. The sepiolite nanofibers are modified with the Vinyltriethoxysilane (VTES) as a coupling agent for better dispersion and interaction in the HDPE matrix. The purpose of fabricating this separator is to decrease the thermal shrinkage and increasing electrolyte uptake of the HDPE separator. The separator electrolyte uptake increased from 86% for pure HDPE separator to 120% for HDPE/sepiolite separator. The thermal shrinkage results indicated that the sample with 3 wt% of sepiolite after remaining for 30 min at 150 °C had only 5% shrinkage compared with 93% of pure HDPE. The results of electrochemical performance showed that the ion conductivity of the separator increased from 0.36・10–3 S・cm–1 for the pure HDPE to 0.9・10–3 S・cm–1 for the nanocomposite separator. The results of cyclability and rate performance showed that the cell assembled with a separator having 3 wt% modified sepiolite has a higher discharge capacity than the cell assembled with a pure HDPE separator