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

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 Al₂O₃–EPP composites closed pores of the PI separators. Regarding electrochemical performance, the cell cycled with a PI separator that incorporated Al₂O₃–EPP exhibited stable cycling, while the cell cycled with a bare PI separator showed failure. These results indicate that incorporating Al₂O₃–EPP material effectively increases both safety and electrochemical performance. The Al₂O₃–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 Al₂O₃–EPP incorporated PI separator exhibits stable cycling behavior because Al₂O₃–EPP composites effectively prevent internal short circuit in the cell.