Metal-organic nanosheet assembly ions sieving membrane for precise lithium ion and anion/solvent separation toward robust lithium metal battery

Abstract

Metal-organic nanosheets (MONs) as a novel material with tunable pore structures and low mass transfer resistance, have emerged as molecular sieves for the separation of gases and liquids. In theory, they can also serve as ion sieves for lithium metal batteries (LMBs), realizing the high-energy and dendritic free LMBs. However, there are rarely relevant reports, because it is difficult to simultaneously balance efficient ion sieving ability, high ion passing rate and high electrochemical stability. Here, we synthesized a stable ultrathin MON [Zn₂(Bim)₄] ([Zn₂(Bim)₄] Nanosheet, HBim = benzimidazolate), which can achieve both efficient lithium ion sieving ability, high lithium ion passing rate and high electrochemical stability at the same time. The separator assembled by this MON exhibits high Li⁺ transfer number of 0.81 due to the accurate lithium ion and anion/solvent separation. The battery containing such separator shows high lithium ionic conductivity of 0.74 mS cm⁻¹ and low activation energy of 0.099 eV, which can be attributed to the nanometer level thickness and the ion sieving effect. What is more, we realized the application of MONs-based ion sieves in LMBs with intercalation cathodes for the first time. And the LiFePO₄∣Li battery with as-assembled separator demonstrates improved Coulombic efficiency (> 99%) and significantly extended cycling life (> 1600 cycles) with 80% capacity retention.