Effect of fibrillated fiber morphology on properties of paper-based separators for lithium-ion battery applications

Abstract The effect of the morphology of Lyocell fibrillated fibers with different beating revolutions on pore structure and electrochemical properties of Lyocell fibrillated fiber paper-based (LF) separators for lithium-ion batteries is investigated. With raising the beating revolutions from 50,000 to 600,000, the number of coarse fibers decreases from 7851 to 743, and the mean fiber diameter decreases from 374 nm to 171 nm. Both the number of coarse fibers and the mean fiber diameter have good correlation with the thickness, pore size and porosity of the LF separators. The risk of battery short circuit is increased, if the mean pore size of separators is larger than the minimum size of cathode particles. Compared to the PE and PI separators, the LF separators deliver excellent cycle performance with different current densities at 30 °C owing to their larger pore size, porosity, and better electrolyte affinity. However, the cycle performance deteriorates at −10 °C due to the severe local lithium plating on the graphite surface caused by a large number of coarse fibers with a diameter ranging from 5 μm to 15 μm as local microscopic defects.