A sacrificial separator facilitating in situ creation of a durable CEI layer and tailoring lithium dendrites for practical lithium metal batteries

Abstract

A Li metal anode and NCM811 cathode are used to realize practical Li metal batteries (LMBs) with a high energy density. However, during repeated charging-discharging processes, the concurrent occurrence of two adverse effects, i.e., uncontrollable Li dendrite formation and the structural collapse of the Ni-rich cathode, results in severe degradation of the electrochemical performance of LMBs. To tackle these challenges, we propose an interface-targeting separator, which is prepared by anchoring tributyl borate (TBB) onto a polyethylene (PE) separator. The TBB-PE separator can facilitate the robust formation of a cathode-electrolyte interface (CEI) while suppressing the uncontrollable formation and growth of Li dendrites. The TBB-PE separator can tightly hold the anions of the dissociated Li salts, thereby facilitating the transport of Li+ and ultimately suppressing the formation and growth of dendritic Li. Concurrently, the TBB-PE separator forms a robust and uniform boron-rich CEI layer, thereby preventing the occurrence of electrolyte decomposition at the NCM811 cathode. Therefore, these distinctive characteristics of the TBB-PE separator allow enhanced cycling performance in the resulting LMBs assembled with Li metal and NCM811 in a carbonate electrolyte.