Electrochemical performances of Al2O3 nanoparticle coated polyimide nonwoven separators by electrospinning

Abstract

owadays, polyolefin(PO) separators have been prevalently used in lithium ion batteries. However, their shortcomings (Low porosity, Thermal shrinkage, Poor electrolyte wettability) have hindered advancement for next-generation lithium ion batteries. To overcome these disadvantages, we introduced polyimide(PI) and electrospinning method to make nonwoven separators. PI serves good electrolyte wettability as well as thermal stability. Nonwoven separators provide high porosity and facilitate ion transport. Although electrospun PI nonwoven separators present high capacity and rate capability compared to conventional PO separators, voltage drop of PI nonwoven separator is faster than that of PO Separator due to their large pore size. Large pore offers pathways between two electrodes for detached active materials to interchange. It causes irreversible capacity loss. Also, fast voltage drop can be considered as higher possibility of short-circuit in case that lithium dendrite forms. The control of pore size was achieved by coating nano-sized Al2O3 powders on PI separators. As a result, nano-sized pores appeared among nano-sized Al2O3 powders. Al2O3 nanoparticle coated electrospun nonwoven PI separators exhibited better electrochemical performance and more stable opencircuit voltage retention compared to PI separators.