Al2O3/TiO2 coated separators: Roll-to-roll processing and implications for improved battery safety and performance

Abstract

Heat generation is one of the major concerns with lithium-ion batteries (LIBs) while charging them at higher currents, which could inadvertently impact the rate performance and battery safety. Polymer separator is one of the least thermal conductive components of a LIB. In addition, commercial separators for LIBs are made from polyolefin membranes that tend to shrink and curl at higher temperatures due to lower melting temperature (~130 °C), which increases the risk of internal short circuiting. Developing separators with improved thermal stability and higher electrolyte uptake is essential for enhancing safety as well as performance of LIBs. In this work, thin layer of ceramic coatings (Al 2 O 3 and TiO 2 ) are applied on a propylene membrane to improve thermal stability and electrolyte affinity without compromising rate performance. A slurry with 100% Al 2 O 3 coated on the polypropylene separator exhibited the best improvement in thermal stability (shrinkage of 0.6% vs 6.0% for uncoated membrane) and excellent rate performance with 92% capacity retention at 2C. The Al 2 O 3 coated separator demonstrated excellent electrolyte wettability compared to the uncoated. The cross-plane thermal-conductivity of the ceramic coated separators is analyzed to understand heat transfer behavior. The thermal-conductivity of the separator is improved by ~3.2 times with the Al 2 O 3 coating. • Roll-to-roll ceramic coating on separators for improved safety and performance. • Ceramic (Al 2 O 3 and TiO 2 ) coated separators show excellent electrolyte wettability. • Three times improvement in thermal conductivity with 100% Al 2 O 3 coated separator. • Impedance reveals that Al 2 O 3 coating improves the transport through the membrane. • Self-discharge of the cell improves significantly by ~43% with Al 2 O 3 coating.