Two-in-one strategy: Discretely functionalized electrolyte additive for stable lithium metal batteries coupled with Ni-rich cathode

Abstract

Li metal batteries (LMBs) coupled with Ni-rich cathode are regarded as a holy grail to achieve high energy density for the application in electric vehicles. However, the practical applications of LMBs coupled with Ni-rich cathode are limited by the severe Li dendrite growth and structural deterioration of the Ni-rich cathode. Among the various strategies to address these undesirable issues, introducing a dual-functional electrolyte additive is considered as an attractive approach because it can construct beneficial interface on both electrodes with a single agent. Herein, the two-in-one electrolyte additive, calcium tetrafluoroborate (Ca(BF4)2), is proposed for the rational design of interfacial layers on both Li metal anode and Ni-rich cathode. The preferential reduction of Ca2+ formed the Ca-based SEI layer which prevents electrolyte decomposition. In particular, Li-Ca alloy with superior lithiophilicity suppresses the growth of Li dendrite by reducing the nucleation polarization. Concurrently, the preferential oxidation of BF4− in Ca(BF4)2 results in the formation of B-based surface film on the Ni-rich cathode, which protects the Ni-rich cathode from structural deterioration, including micro-crack and dissolution of transition metal ion. As a result of unique characteristics of Ca(BF4)2 as an electrolyte additive, outstanding electrochemical performance can be accomplished in LMBs configured with Ni-rich cathode in carbonate electrolyte.