Strong association dual lithium salts for ether-based electrolyte enable 4.5 V high-voltage lithium metal battery

Abstract

To achieve a battery system with an high energy density, it is crucial to utilize a highly reversible lithium metal anode and a high-voltage cathode. However, conventional electrolytes usually exhibit insufficient thermodynamic stability, leading to aggressive lithium dendrites growth and severe cathode-electrolyte reactions, particularly at high voltage (≥ 4.5 V vs. Li/Li⁺). Herein, we propose a design strategy for a strong association electrolyte (SAE) that reduces Li⁺-solvent coordination number, facilitating the formation of ion pairs or ion clusters, even with conventional lithium salt concentrations (1 M). Lithium salts with high cluster formation constant (K_A), such as lithium difluorophosphate (LiDFP) and lithium nitrate (LiNO₃), create an SAE with anion-dominated solvation structure, which promotes the formation of aggregates (AGGs) solvate species. This unique solvation structure facilitates the formation of a dense, inorgain rich solid electrolyte interphase (SEI) on lithium metal anode. Additionally, the preferential adsorption of anion clusters at the cathode interface constructs a Li⁺-anions enriched double electric layer (EDL), stabilizing the LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) interface. The Li||NCM811 batteries with a 4.5 V high cut-off voltage achieved stable cycling over 1400 cycles with a capacity retention rate of 84 %. Furthermore, 2.5 Ah pouch cells demonstrate superior cycle performance at 4.3 V cut-off voltage and 0.6 A/3 A charge/discharge currents. These findings present a straightforward electrolyte design strategy that contrasts with conventional approaches, which typically rely on increasing salt concentration or introducing complex additives, to promote the practical applications of high energy density lithium metal batteries (LMBs).