Aluminum oxide and ethylene bis(diphenylphosphine)‐incorporated poly(imide) separators for lithium‐ion batteries

Abstract Although poly(imide)‐based separators have received great attention as an alternative separator for lithium‐ion batteries, there are serious restrictions because their porous structures enable a great amount of current to leak internally. In this work, we report a one‐step coating process for the structures of poly(imide) (PI)‐based separators that effectively closes their pores. To close the large pores on a PI separator, nanosized aluminum oxide as a coating precursor and the free radical scavenging agent ethylene bis(diphenylphosphine) were co‐incorporated into the PI separator. Screening tests confirmed that ethylene bis(diphenylphosphine) (EPP) can effectively scavenge free radical species via chemical reaction and that incorporating Al 2 O 3 –EPP composites closed pores of the PI separators. Regarding electrochemical performance, the cell cycled with a PI separator that incorporated Al 2 O 3 –EPP exhibited stable cycling, while the cell cycled with a bare PI separator showed failure. These results indicate that incorporating Al 2 O 3 –EPP material effectively increases both safety and electrochemical performance. The Al 2 O 3 –EPP composites are incorporated onto the PI separator via dip‐coating process in order to improve electrochemical properties of PI separator. The cell cycled with the Al 2 O 3 –EPP incorporated PI separator exhibits stable cycling behavior because Al 2 O 3 –EPP composites effectively prevent internal short circuit in the cell.