Unravelling stability of current collectors in lithium bis(trifluoromethanesulfonyl)imide salt and polyethylene oxide electrolyte for solid-state lithium batteries

Recent interest in solid-state lithium batteries prevails in the battery community because of their superiority in terms of safety concerns. Many works have been reported for electrodes and electrolytes and their suitability for solid-state polymer electrolytes to adopt in lithium batteries. Herein, for the first time, we report on the electrochemical stabilities of Cu and Al current collectors in a polyethylene oxide (PEO)-based solid-state electrolyte containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. Our work on the electrochemical dynamic- and transient-mode polarization of these electrodes indicates that Cu metal undergoes Cu–O passivation below 3 V. The adhered Cu-F layer on the CuO passive layer may be beneficial to delay undesired reaction such as corrosion. And it is further confirmed that Al metal passivates stably even up to 5 V; namely, the Al surface forms double layers of the outer Al–F and inner Al–O layers. These F- and O-based layers are attributed to the combination of the Al and O from the reductively decomposed PEO and further progress of Al2O3 and HF (H+ + F− →HF), decomposed from the PEO (H+) and TFSI− (F−). Therefore, we verify that successful passivation on Cu and Al metal surfaces facilitates their suitability as current collectors for solid-state polymer lithium batteries.