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.