High-Energy and Safe Lithium Metal Batteries Enabled by Interphase Optimization with Synergistic Electrolyte Additives

The combination of lithium metal anodes and high-load Li-rich Mn-based cathodes (LMLO, Li 1. 2 Mn 0. 5 4 Co 0. 1 3 Ni 0. 1 3 O 2 ) empowers lithium metal batteries (LMBs) to reach energy densities above 500 W h kg –1 . However, sluggish kinetics, continuous interfacial reactions, and serious safety concerns impede their practical application. Herein, a flame-retardant carbonate-based electrolyte containing hexafluorocyclotriphosphazene (HFPN), lithium difluoro(oxalato) borate (LiDFOB), and 1-butyl-2,3-dimethylimidazolium nitrate (BDIN) coadditives has been designed to enable 528 W h kg –1 LMBs with enhanced safety performance by synchronously regulating the formation of kinetically enhanced cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI). Specifically, flame-retardant HFPN facilitates the formation of a stable CEI enriched with P-, F-, and N-containing inorganic species, thereby improving the thermal stability and Li + transport kinetics. LiDFOB participates in forming a fast Li + conducting SEI on the lithium metal anode, while the interaction between BDIN and FEC promotes the decomposition of FEC to induce an F-containing organic matter SEI, which achieves a Coulombic efficiency exceeding 95.9% in the Li||Cu cell. As a result, an LMLO||Li full cell with 6.4 mA h cm –2 delivers a capacity of 272 mA h g –1 and 94.7% retention after 50 cycles. This strategy for the interphase regulation and safety enhancement by synergistic additives can practically be extended to other high-energy lithium-ion batteries.