Highly safe and stable lithium–metal batteries based on a quasi-solid-state electrolyte

Abstract

Due to impressive thermal stability, outstanding oxidation tolerance, and intensive polarity, succinonitrile (SN) has become an ideal candidate for electrolyte solvent components. However, its inferior compatibility towards lithium metal leads to undesirable side reactions, which will jeopardize the electrode/electrolyte interfaces and hence affect the electrochemical performances of lithium–metal batteries (LMBs). Concentrated electrolytes are able to address these interfacial issues, while the considerable cost of lithium salts will be a technical difficulty for commercialization. In this work, considering the sieve effect of metal–organic frameworks (MOFs) towards electrolyte solvation sheaths with a specific size, a unique quasi-solid-state electrolyte with a MOF skeleton, which is expected to load concentrated SN-based electrolytes inside the MOF channels, was produced. By performing Raman spectrum analysis, it was found that the electrolyte configuration loaded in MOFs exhibits a highly aggregative state with fewer solvent molecules in a Li⁺ solvation sheath than the saturated electrolyte. The well-designed electrolyte displays an extended electrochemical voltage stability window of about 5.4 V (vs. Li/Li⁺), excellent Li-ion transference number (t_Li⁺ ≈ 0.67), qualified ionic conductivity (1.37 × 10⁻⁴ S cm⁻¹ at 25 °C), and outstanding compatibility towards lithium with long-term cycles of over 1600 hours. The LMBs assembled with 4.6 V cut-off NCM-811 cathodes harvest reversibility and stability for over 200 cycles. More inspiringly, the improved safety of the designed electrolyte has been proved by operating a lithium metal pouch-cell under several harsh conditions. The design route of this specific electrolyte may inspire us in realizing the practical commercialization of highly stable and safe LMBs.